Misfire Caused by Distributor Bushing Failure
1996 Chevy Blazer
This case study is on a 1996 Chevrolet Blazer with a 4.3 V6. The complaint on this Blazer was that it had a misfire that was bad enough to make the tach jerk. I drove this SUV for a few miles with no issues. Fuel trims at idle and at cruise were in a fairly normal operating range of -5 to +9. The truck actually ran really good. Idle was as smooth as I would expect. It didn’t miss a beat even while power braking the engine. A P0300 was stored in history codes. The freeze frame did not show any data that was out of normal range. Misfire history showed misfires scattered on all cylinders with the majority on cylinder 3 and the next large chunk on cylinder 4.
1996 4.3 Worn Distributor Bushing
A visual inspection showed that new spark plugs, spark plug wires, ignition cap, and rotor have been installed. Further information from the customer indicated that the truck misfired the worse in drive, not overdrive, at light to normal cruise around 2000 rpm to 2500 rpm. The next test drive indicated that he was right and it was very repeatable. Anything outside that range and the misfire went away. During the misfiring event cylinder 3 was the worse followed by cylinder 4 with a few misfires on the other cylinders. Firing order on this engine is 1-6-5-4-3-2. You can see that #3 is right after #4. During the misfire event, all the data was fairly normal. Even the fuel trims were on the money. The only data pid that was a little off was the cam retard.
Typically on the 4.3 liter engine I see a cam retard around -11 to -12. This engine was at -14 with an occasional drop to -13. I graphed this pid on the Tech 2 during the misfire even and it stayed rock steady at -14. Now most of the time when I have a worn distributor gear or cam sensor that is causing problems, I will also see the cam retard jumping all over the place. Seeing the cam retard hold steady and no DTC P1345 Cam/Crank Correlation code, I wanted to move on but none of the other data gave me any reason too.
1996 Chevy Blazer Worn Distributor Disassembeled
Tech Tip: If your cam retard is off to far you will set trouble code DTC P1345 Crank/Cam Correlation. The 5.7 and other V8 engines have an adjustable distributor. When you move the distributor you do not effect engine timing on this platform but only how far the spark has to jump from distributor rotor to distributor cap cylinder terminal. The 4.3 engine’s distributor is not adjustable and is locked in place. On the V8 engine, you should try to adjust the cam retard as close to 0 as possible. You can watch the scan tool cam retard pid as you move the distributor. The engine has to be above 1000 rpm for the cam retard pid to update and be accurate.
I decided to research these symptoms before I moved on. My research showed that a cam retard outside -12 commonly caused misfire on cylinders 3 and 4. I removed the cap and check the rotor play. There wasn’t much rotational play but there was a lot of back and forth play. With the distributor out and disassembled you could see the wear on the upper seal, top bushing or bearing, and also on the shaft. The distributor gear only had slight wear. With the new distributor lock in place, I checked the cam retard which was steady at -12.
Leave any questions or comments below. Thank you.
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Dustin Palmer
very interesting i keep this one filed in the back.
bodyman36
ok well using a scanner i noted that the timing advace, then under ever so slight tps movement,the advance jumper from 15 to 31 then a neg 61 and back and forth and the misfires were very radid, i have concluded that replacement of the worn dist will be the next step
Travis Dewitz
The timing advance number on your scan tool is not accurate until you rev the engine to about 800-1000 rpm. If it is jumping around that much you may also have a bad crank position sensor. The PCM uses the crank position sensor and cam position sensor (in distributor) to get the cam retard reading.
Rev Bonanza
I’ve had this problem on a newer model 4.3. Problem was caused by worn distributor gear. One side of the gear was worn thin and giving an erroneous cam signal.
steve bates
Ok my tach was also jumping and miss firing. I replaced the distributer, plugs, wires, cap, rotor and speed sensor today on it. The blazer is still miss firing and the tach is still jumping around. Now what do i need to do??. Its a 2001 blazer. What could be causing this problem?
Travis Dewitz
Fuel injectors are a common issue on that model. What is your cylinder compression?
David M
Steve you have had this for awhile, just thought I give you some suggestions.
GM trucks have an odd security system and with it’s computer it will cause odd symptoms with the pass lock and may or may not through DTC I have seen everything from no-start, stall out and back fires and if there is a problem with the BCM it could cause the problem your are having too. Now earlier models have the BCM tied in to the instrument cluster like your tach. Others are in a different place like above the heater control switch.
I would check for lose wire connections around the steering column also at the fuse box. If all checks out go for the BCM “Body Control Module” or the ICM “Ignition Control Module” The ICM directly controls the Tachometer and could also cause misfires.
Andy Steed
Check your timing gear play. Remove dist. cap. Have somebody bar engine back and forth. Rotor and serpentine belt should move together in both directions. If not, pull timing cover and check gear. Mine was toast! I had replaced everything you did. Still misfired. Code P0300 .
Jason
Timing chain
corey
i have the same problem but the miss fire is on the #one cylinder when you changed the worn out distributor did it help the problem go away. mine only miss fires when its cold after it hit temp and 15 minutes its fine any other suggestions?
corey
and i dont have no check engine light on either no codes.. i did see they have replaced the disturbtior with a used one from the junk yard i think i might try a new one and get back to you
Travis Dewitz
Did you check your fuel injector flow for each cylinder? Is the pressure drop equal?
steve bates
My miss fire is on #6. I am going to check compression and fuel pressure this week. I have already did everything for a tune up and it still does it. The car runs great at a idle. The tach starters jumping around at about 2000rpm .
steve bates
I checked fuel pressure today. It was 60psi and about 55 at a idle. The alternator went out last night so i replaced it today. The blazer tach still jumps around and feels like its miss firing. Probley going to take it to a garage next week to see if they can find the problem. Im think fuel injector.
steve bates
All the injetcors read 13ohms.
Travis Dewitz
Resistance isn’t an issue on those injectors. The poppets stick which is why you need to confirm with a flow test.
julio
I did the flow tes and the pressure drop equal
steve bates
How do you do a flow test? Thanks
steve
Im still having problems with blazer.. i done replace the dist,cap, roto button, plugs, wires, fuel filter, computer, speed sensor, crank sensor, cam sensor. The blazer tach is still jerking. and now it is missing when i come to a stop and when going 55mph it feels like its hitting the fuel shut off.. i took it advance auto and the codes kicked out.
mas air flow,
knock sensor.
cam shaft sensor.
crank sensor.
sec air injection.
control ignition off timer.
WHAT CAN I DO? I DONE REPLACED. THE CRANK SENSOR AND CAM SENSOR AND ABUNCH OF OTHER STUFF AND IT STILL KICKS THE CODES OUT? AND WHAT IS CONTROL IGNITION OFF TIMER?
Travis Dewitz
I think you will find your answer in doing these tests. What is your fuel pressure? Fuel volume? Injector pressure drop test? Exhaust back pressure?
David M
After replacing all that and doing some real tests it almost has to be a wiring problem “bad grounds” maybe a bad dash cluster
But then again may I didn’t see a replacement Spider on his list.
Like you said before Travis, the fuel injection systems are known on these GMs Just like coil packs are known on Fords.
steve
I took the blazer to a buddy of mines house and we hook it up to a snapon computer and when was having trouble geting the crank sensor and cam sensor to relearn with the new computer i replaced. We finally got it to relearn and it runs alot better now. But we are now thinking that the new cam sensor is bad. keeps kicking out 0341. I am going to try replace that next. The service engine light comes on and flashes every once inawhile. The tach still jumps but i think its in the gauage itself. Thanks for all your guys help.
dale
have 2000 blazer changed everything including fuel injector and found out it was worn distributor gear and worn shaft gear is 95% worn chevy made the the shaft gear metal to soft and the disrtibutor gear to hard it should have worn out first defective part by gm ,did not do recall just gave notice these 2000 blazers are cheap junk replace all those parts from codes the only way to find its bad is to take off distributor and go in with a camera or lighted scope sell the piece of junk gm is biult to fall aprt at 100,000 miles by foreign honda or toyota i pity the fool who buys late gm
Bart Wallers
Hey dale. Ive owned a fix all shop for years. I wouldnt agree with you about some Honda or Toy? These are ok cars but not at all better quality. Then our chevy ford or even dodge.
Mark
I completely agree my 01 impala and my sisters 01 blazer is complete garbage. It’s almost like everything on them is designed to fail. Cheap Plastic is the main design flaw I think.
Jeremy
I have a 1998 4.3 Blazer with a 106828 miles on it, that has a major misfiring problem. I got it cheep from a family member thinking it would be an easy fix, yeah right Ive replaced the cap, rotor button and plug wires so far. It mainly misses from idle to around 3000 rpm, after hitting 3000 it smooths out and only misses occasionally. The engine has plenty of power even with the misfiring. I’m going to change the plugs today but I have a feeling its not going to help. Any advice would be appreciated.
Travis Dewitz
Testing is really the only right way to figure out the exact problem. Internal engine issue like valves or fuel injectors come to mind. Bad replacement caps are also very common.
Henry Lewis
99 4.3 express with misfiring and bucking problem. Changed distributor, thought problem was gone, It returned. Took connector off distributor expecting it to stop, to my suprise it kept running and missing and surging stopped. Under hood fuse block checked and is corroded on fuse to cam sensor circuit. Problem is non-existent with 3 pin connector removed. Why?
Travis Dewitz
May have a cam to crank correlation issue that is causing a misfire. By eliminating the cam signal, it helps from confusing the PCM possibly.
STEVE CRUSH
I HAVE 2000 GMC SIERRA MISFIRE BELOW 2000 RPM AND CHECKED TIMING CHAIN BY TEARING IT APART IT WAS GOOD CAN`T FIGURE OUT WHATS WRONG
Travis Dewitz
Would need more testing data. Hard to diagnose without more data and some test results. Compression, running compression, fuel injector drop test?
David M
Steve, Like Travis said we need more informationn to help you like what motor to have and what dtc are you getting plus what tests have you done other than timing chain check etc…
Cory
Hey. I got a 2000 s10 with a 4.3. At first it misfired very seldomly. Then one day my light came on and started flashing with a very bad misfire. Got the code checked and it was a random cylinder misfire. Can’t tell which one. Mainly misfires between 1000 – 3000 rpm. Put new plugs in about 300kms ago
Travis Dewitz
A lot more than spark plugs can cause a misfire. If you don’t have the tools to test you may need to bring it to someone who does. Codes only point a direction in which my hands on testing starts.
tony
I have a 2000 Silverado with a 4.3L and started missing. Was light at first, but got really bad to the point of almost no acceleration. I changed the cap, rotor, plugs and wires, still had flashing light. I dropped the exhaust system BEFORE the cats, and the truck ran new! I suggest checking your cat…or cats.
bob
I have fought a p0300 code for the last 2 yrs. After replacing everything and taking my 2001 silverado 4.3 to my local mech. and the local chev. dealer with no answers and mucho dinero later i came across a service bulletin from GM stating that from 96-2002 there has been an ongoing problem with the valves sticking on 4.3, 5.0, and 5.7 vortec engines while towing or going up a grade. There recommendation was to pull the heads and hone the valves .002 of an inch. I ended up bending a push rod. Frustrating as hell when your local chev. dealer is’nt aware of an on going problem. I have seen several other people that were having the same problem with no answers.
Travis Dewitz
The valve issue has had a TSB for a long time. It is a hard problem to verify and is a last resort once you have correctly verified everything else.
fredbently
i just changed a distributor 2001 blazer …driving down the road and it just quit! come to find out the rotor inside the distributor came off…i think it was because the worn bushing on the distributor let the insides wobble enough in side that the rotor hit the cap enough to rattle loose…you’ld a thought it would have given some sort of clue what was going on my advice would be just to get a new one of those first btw IT COMES WITH a camshaft SENSOR i got a remanufactured for 100 bucks. ps if you do just replace a cam sensor DON’T absolutely DON’T break a screw off
Dave
Yeah, all those screws in the 96 and up gm 4.3 distributor’s are tough to work with. The fine thread along with the thread lock make it hard, not to mention the steel aluminum thing going on…
alan eskew
I have a 2001 blazer 4.3 vortec. My distributor was wore out so I replaced it. I now have a p1345 code and it only misfires sometimes. Around 55 and 75. I’ve read a lot on this and after all I’m still not sure where to start
Travis Dewitz
Needs to be timed and positioned correctly with the use of a scanner.
Brock Cline
I thought the 4.3 L distributors were non-adjustable?
Travis Dewitz
Once installed they aren’t but you have to still install it correctly and verify timing with a scan tool.
alan eskew
And I had none of these problems before replacing distributor so I’m nor really leaning toward the cam or crank sensor
alan eskew
Also oil pressuee is fine when first crunk up but then after driving it starts dropping
Dave
Alan, make sure your distributor cap, rotor, coil and coil wire are good, look for fire marks if ok then look at fuel pressure.
These 4.3’s can be tricky sometimes the TPS can act up too…
Remember its all computer controlled and counts on sensor input to set timing and fuel.
alan eskew
Ok well I still had a problem with distributor. Wrong one actually lol. But I still have a question. I have no skip or anything wrong. What is this scan tool and cam retard people talk about. Is it like you might have to do it or you may not have to? And why
Travis Dewitz
That is the only way to time the trucks correctly but most 4.3s the distributor is locked and can’t precisely timed but still needs to be checked to make sure it is within 12.
alan eskew
With it being a non adjustable timing motor how does it time it. Is it basically cheating it? Andif timing is off even a hair the car wouldn’t crank would it?
Travis Dewitz
Timing is computer controlled but you need to have the gear in the correct place. It can start and run with the gear off a tooth many times.
Dave
There are alot of factors that determine timing both ignition and fuel in the 4.3. 96 and later. The computer will set the timing based on all sensor input and starts with the crankshaft positing sensor.
If the timing is off the engine will still crank, act like it wants to start but won’t.
A good scanner will show the ignition timing while the engine is cranking and running.
Keep in mind the with the new computer systems you don’t need a distributor anymore, some engines have coil packs instead.
You can buy a good scanner at the auto parts store for about $200 or online like ebay for a better price, and you almost have to have one if you work on these late model cars and trucks.
I had alot of trouble with my astro 4.3 and turned out to be a passlock antitheft problem, they are very tricky, even the dealer has trouble with then.
Ekelley9548
Having trouble with 2003 4.3. Misfires at idle but goes away at 1,000rpm. Replaced ink spider, cap , rotor , wires ,plugs and camshaft sensor. Comp is equal on all cylinders at 155 psi. Fuel pressure is running at 55psi with no bleed down. Scanner shows misfire is on no.1 and no.2 cylinders only. Rechecked all ignition components several times.
Travis Dewitz
What the running compression? Did you do an injector balance test?
alan eskew
As far as I know everything is fine now. No more skip ir random misfire in diagnostic but I still get code p1345 and my oil pressure keeps dropping. Could my distributor still not bw right?
alan eskew
Is it possible that distributor isn’t sitting quite right and no engaging oil pump
Dave
Alen, as far as the oil pressure, you need a separate gauge to check that, but if your distributor wasn’t into the oil pump you wouldn’t get oil pressure at all and the engine wouldn’t start because the fuel pump circuit checks oil pressure.
I think you know what the P1345 code is; so here is what you need to check for that: The plug connectors and wires on both the Crank and Cam Sensors, the timing position & correlation between the distributor rotor and crankshaft timing plate, should be at TDC or 0 deg., As Trav outlined before the engine will still run one tooth off on the distributor gear.
Here is something else you need to know is the engine will still run with the cam sensor unplugged too, so the sensor could still be bad throwing the code.
Travis Dewitz
The oil pressure to fuel pump circuit is actually the other way around. If your fuel pump relay fails the oil pressure switch can also feed power to your fuel pump.
Dave
Kelley, I don’t know what issues you had before you replaced that stuff but I have seen issues related to the misfire on #1 and #2 low speed or idle. Most of the time it’s related to the coil or coil wire and ignition control module or wires at these locations…
I’d like to see the condition of the spark plugs after running this for about 20 to 50 miles for condition, since you changed them, but check them all not just 1&2 and if all are close to the same “clean no carbon”; then I would rule out a fuel issue.
alan eskew
Any correlation with cam and crank sensors and oil pressure acting up?
Dave
Alan, from what I remember, the oil pressure sending unit is right by the distributor and may have been damaged when the distributor was R&R “removed and replaced”. You more then likely have a bad oil pressure gauge or sending unit to the gauge, you need to put a different oil pressure gauge in line to check the oil pressure; remember to check for bad wires or plug connections too, very common on older cars and small trucks.
alan eskew
I now have 05 chevy 1500. Oil pressure is always like 80. Was told that’s fine?
Dave
That seems to be too high to me,
Like I said before, you need a separate inline gauge to check for faults.
The dash board gauges are rarely actuate…
Much like the temperature gauge reading 212 deg at full running temperature and not boil over; when it should read about 195 deg. is common.
Adam
I have read through all comments about the 4.3 misfiring, jerking, stalling etc… I have a 2001 4.3 1500 Silverado and I have had the same problems, I am just curious if anyone has found a solution to this problem? Seems like a lot of guessing and money spent on parts that aren’t the problem! My problem started with my truck not wanting to start, then once started it was missing @ idle, but once truck came up to operating temp problem went away. After changing plugs problem went away but came back with a vengeance, since I have changed plug wires, cap, rotor, mass air flow sensor, both upstream and down stream O2 sensors(4 total), fuel pump, fuel filter, air filter and have ran several bottles of cleaners through fuel system PROBLEM NOT SOLVED! It is still missing between 1800-2500rpms, but idles and starts great now, not sure if this means anything but I have noticed that when descending down hill it seems to get worse in that 2000-2500rpm range but I can give it gas and get over 2500rpm and missing goes away until I get back to cruising speed (70mph) or 2000-2500rpms. CAN ANYONE HELP!!!!!!!!!!!!
Travis Dewitz
Many things can cause a misfire. New parts are faulty all the time. Did you put in OE AcDelco plugs? Valve float? You say you have been running cleaners? What kind? I only know of three types that actually work well and that still doesn’t guarantee clean injectors and they also do not clean debris and rust.
Dave M
Like Trav said, we need more data; are you getting DTC’s or check engine light?
But with the information you gave us to me it could be the TPS “Throttle Position Sensor” , Ignition Coil or even poor Ignition Wires. GM did have a problem with the EGR valve control and made a firmware upgrade for the computer too.
You need to run more tests and post the data.
alan eskew
Simple solutions. Spend all your money fixing random stuff. Spend your money at a good shop. Or like I did buy something else lol
John
99 blazer with v6, stalling at a stop and firing rite back up, drove it in garage, checked dtc’s, cam sensor code came up, so I pulled out the old, in with the new, also new cap and button, all parts were installed exactly the way they came out, so I go to start it up and the engine binds up, cranks for a second then binds up, strange because all I done was change the sensor and install a new cap and button, sounds like it’s off timing or wired wrong, double and triple checked plug wires , all good, can the distributor go just like that? Help!
Travis Dewitz
The distributor can go in at any location as they are not keyed. You may need to bring #1 up and retime mechanical timing or at least verify the distributor is in correctly. Actual timing must be finished via a scan tool.
Cuppy
2001 4.3 Blazer….
Has a very light miss at around 1-2K RPM but no check engine light. Replaced cap & rotor. New plug wires & spark plugs. New fuel filter. New Battery. Replaced leaking EGR Valve gasket and cleaned egr valve, even checked specs on it from fully closed to fully open. Checked dist. for any wear including gear. Looks new. Motor is at TDC and all marks line up. Replaced all vacuum lines I could see. Replaced a rear o2 sensor that went bad when cat failed due to a torn wire. Fuel pressure @59 psi before starting, and holds at 55psi running. After shutting off, an hour later pressure still holds at 55psi. So I’m assuming spider isn’t leaking… Will be getting a new map sensor seal just to make sure.. Even without the cat the engine still has the light miss. Performed the checks for the ICM as stated.. Used this as a reference:
• http://troubleshootmyvehicle.com/gm/4.3L-5.0L-5.7L/how-to-trobleshoot-a-hard-to-diagnose-misfire-1
•http://easyautodiagnostics.com/gm_icm_dist/distributor_ign_module_1.php
And now I don’t know where to turn before actually taking it in to a shop I don’t trust and that’s gonna throw the same new parts I just put in and still have the problem.
Help please.
Travis Dewitz
Do a running compression test. Sounds like possible valve issue. I would also do a fuel injector pressure drop test.
Lee
P.S…
Oh and cylinder compression are all at 195.
Cuppy
P.S.
Oh and cylinder compressions are all at 195psi…
Travis Dewitz
That’s static compression, you need to check running compression.
Dustin
Has anyone tried oxygen sensors? Stumbles at low end and clears up at higher speed/RPM. Does not sound like ignition or even stopped cats.
Dustin
This is a common problem on mustangs.
Mike
I have a 98 1500 4.3. Stars and runs great under a load but as soon as you let off and cruise it misses terrible. No codes , check engine light nothing showing . It has 130000 on it
Jeremy
I have a 98 gmc jimmy 4.3 vortec with a # 4 cylinder misfire. Checked the distributor. Replaced the d.cap, rotor, plugs, wires, ignition coil, mass air flow all twice and yet it’s still there. Pulled the plenum and checked the injectors. No visible signs of gas leaking and they are spraying. I’m at a crossroad with this. Any suggestions would be greatly appreciated.
Jimmy Man
I have been through this more times than one can count, pull your intake manifold completely off and hook up all of your connections, with manifold off have someone crank the engine, keep a very close eye on the poppets and the spider lines, I would almost bet that you have a clogged poppet valve and/or a leaking high pressure line coming out of the spider
Dave
Jeremy,
Have you check for compression, you could have a valve problem, or a vacuum leak from somewhere on the intake.
What DTC’s are you getting?
Cuppy
How would I perform a running compression test? I have a feeling it’s gonna be an air leak somewhere maybe even at the exhaust manifold but its such a confined space it’s hard to see or feel. Or I have a feeling that I might have an internal gas leak on the spider-injector unit? But I would like to perform some test before tearing the intake off. Im will try to inject smoke with some dry-ice and water and hopefully find a leak somewhere. Any tips? I think I read somewhere to have the valves open or closed so that the fog/smoke can circulate all throughout? Lastly would shooting compresses air into a spark-plug hole be of any help to say find a bad sealing valve? Please advice.
Dave
Cuppy,
If you have a bad valve, your compression will be in most cases less than 100 psi and the only way to do a running compression test is to remove the spark plug on the cylinder you want to check and start the motor but it will shake like hell, I’ve done it before but the results will be the same as running or not, so why start it?
Traci
I have a 2000 blazer Ls v6 4.3 I get a misfire at idle it is cylinder 5. And also if I don’t run my truck every couple days something is draining the battery. I purchased a brand new battery. With my misfire my mechanic showed me come up on his computer but he said it should store it and it’s not it shows up as a misfire and goes away. I have had a new distributor done. Water pump lower manifold gaskets done, head gasket replaced. Fuel pump replaced . Fuel regulator replaced. And something with the file injector replaced when my mechanic did the lower manifold leak. Now he is going crazy because he can’t find what’s causing the misfire or what’s causing the battery drain. He has checked and ran test on my truck. Actually he has had my truck more then me. Any suggestions .
Joe Fazekas
I never in my wildest imaginations would have expected to come across another individual posting the same question about two “likely coincidental” issues. My 2000 Jimmy exhibits these same symptoms, its been draining the battery (2yr old optima yellow top) with nothing left on, and noticed a slight hesitation the last few days till I floored it last night merging onto I80 because of some obviously mentally handicapped motorist couldnt grasp the elementary concept of what merge means. It was then at around 5500rpm that it popped and carried on till i let off the gas and soon after the CEL finally came on after the last few days i was relieved to see it, and flashed under light load rest the way home. Lone code is p0305 cyl 5 miss
Dave
We need more information on the battery draw, like when it started etc. as for the misfire, I would check engine compression and spark plugs if all checks out then look for a possible computer issue like a bad ground around the engine.
Bad ground connections cause alot of problems with the PCM or computer.
Raymond .R.
Having problem with 96 Chevy blazer problem code P0300 ignition or spider or converter. Not sure at this point .oxygen sensors now new Distributer — Rotor- Wires -A.C. Delco Plugs New Ignition Coil- Gass filter Note there’s some sud at Edge of Tail PIPE ? Need Response ASAP Please.
Dave
Hi Ray,
Random misfire code, check the coil wire at the coil, common problem when its wet outside. I found that the coil will ark to ground when it’s wet out. I just use electric tape around the boot of the wire to correct the problem.
Also check the catalytic converter it maybe clogged from all the raw fuel in the exhaust.
David M workman
question. I have a 2003 zr5 s10 with the same problem I have put everthing new and still have the problem what can I do to fix it thanks david
Dave
David, we more information on your situation..
Cuppy
Remove your intake plenum and replace those crappy factory leaky gaskets… 🙂
Zack W. Jr.
I have solved the problem with the 4.3 random missfire under light load at 2000 RPM… The problem is the crank sensor .Pull the crank sensor located at the bottom of lower pully on the timing chain cover by the harmonic ballencer pull out the crank sensor clean it and add a shim . I used a piece of thin cardborde about the thickness of a book of matches i cut three homemade I made three shims each one the same as the thin cardbord out of a book of matches or a cearel box . Sounds crazy but it worked if you have any problems email me zkweis1126@att.net
art westergren
I also had the miss at 2000 rpm to 2500, replaced the fuel filter it was clogged did not fix anything, checked intake no leaks, new plugs same thing new rotor, new battery new battery bolts, no change, but Zack W Jr has the fix, I removed the crank sensor polished the varnish coating off, made a thick cardboard shim, reinstalled it disconnected the4 negative terminal on battery to clear codes reconnected and tested, no miss all power and more like it used to have and drives like a dream thank you Zack!!!!!!
Owen
99 P30 4.3 Engine and transmission rebuilt, everything new except injectors, no codes, starts and runs like new truck all times. starts random ignition failure (watching inline testlight) and gets worse as the engine heats up. noticed that the tach is jumping about at the same time that the test light goes out. I can see the ignition misfire and of course until I can fix this pointless to go beyond that. thanks
Dave
Owen, I would check for vacuum leaks, Coil and Coil wire plus Ignition Control Module (ICM) as that is where the tach wire connects too; since this is a rebuild…
kurt
zack is the man..My 99 S10 with the 4.3..Had a bad miss under load..I replaced cap rotor plugs wires, mainly because they looked bad..then coil ignition modual, and last the spider injector..
I put a piece of card board inbetween the crank sensor..Unit runs fine.
Thanks Zack JR.
Bobby
Yes I have a 2000 S10 V6 4.3 after a long drawn-out process of replacing the ignition the spider injectors and the fuel pump the truck was running fine at first then all the sudden it started not really knocking but a real loud pinging sound and it sounded like it was coming from the top of the engine so the guy took everything back apart and he said there was antifreeze in the number 6 cylinder 2 witch the truck never ran hot I never had a problem with that before never lost coolant or anything I had the intake gaskets and all that replaced a year-and-a-half ago any suggestions as to what that could be and it’s also kind of like backfire and you can hear it in the exhaust so I don’t know
Dave M
Bobby, It sounds like something came lose and fell into the intake and is making the intake valve stick, antifreeze won’t leak into the cylinder from the lower intake gasket see pics. Now if you have antifreeze in the cylinder for sure then the head has to be pulled, in either case. wither the valve is sticking or valve guide is damaged or the head gasket is bad, it will have to be pulled.
Sorry to give you the bad news…
Sorry I can’t upload pics here, but the water ports on the intake are atleast 6 inches away from the port and there are two seal rings, one at each port…
I just did a lower intake on one of these 4.3’s…
Stanley Waggoner
I have a ’96 4.3liter S10 pick-up. It has a new AC/Delco spider injector system, new cap, rotor, new sparks plugs, spark plug wires, new coil, fresh set of intake manifold gaskets and factory rebuilt distributor. Truck ran perfect for 4,000 miles, now I have a P0300 random misfire. The misfire occurs only at 1500 rpm (cold or hot), it idles perfect and at higher rpms. The only odd thing I see with scan tool is the timing is retarded -30 degrees. The timing on the ’96 is non adjustable. How can I advance the timing to see if this will help?
Dave M
Stan, I would look into three things, Fuel pressure, should be about 60 psi, Crankshaft positioning sensor and the Coil wire. I know you said the wires were replaced, but there has been issues with coil and coil wires on gm 4.3L’s as they arch to ground because of the way that ignition timing works advancing by delay in the distributor cap. Think about how it works, there is no mechanical movement for advancing inside of the distributor, the spark has to arch to the post inside of the cap and this puts a strain on the coil wire to hold the voltage without leaking to ground.
I recommend putting one of those plastic looms over the coil wire to make it last longer, it won’t stop it from arching but will buy you more life for the wire…
Brian Coffman
2002 s10 ZR5 idles rough, black smoke when mashing accelerator. Misfire cylinder. 1 and fuel pressure sensor error. New plugs,wires,cap,button,map,and seafoamed it. Still misfire no. 1 and fuel sensor failure.
Dave M
Sounds like It needs a new injection spider and fuel pressure regulator Brian,
You need to run some tests on the fuel pressure and injection bleed down tests; if its blowing black smoke be careful because the catalytic converter will go if it hasn’t already…