my 2001 chevy van w/ 4.3L vortec is reading misfire on cylinder 4.
This code showed up immediately after I had the crank shaft sensor
replaced. I should have done it myself, but I let a local garage do it, and
of coarse they screwed it up. They way over torqued the sensor. I ended
up taking the van to chevy and they shimmed the sensor back into specs.
The van ran fine after that, but the computer has been reading severe misfire ever since ( about 20K miles). The van runs great; gets almost 20 miles per gallon, and the tail pipe emissions are super clean, but I can't get my emissions sticker as long as the check engine light is on. Any Ideas??
my 2001 chevy van w/ 4.3L vortec is reading misfire on cylinder 4.
This code showed up immediately after I had the crank shaft sensor
replaced. I should have done it myself, but I let a local garage do it, and
of coarse they screwed it up. They way over torqued the sensor. I ended
up taking the van to chevy and they shimmed the sensor back into specs.
The van ran fine after that, but the computer has been reading severe misfire ever since ( about 20K miles). The van runs great; gets almost 20 miles per gallon, and the tail pipe emissions are super clean, but I can't get my emissions sticker as long as the check engine light is on. Any Ideas??
Possible bad or gummed up injector poppet. If so use a top engine cleaner or injector cleaner. You may also have to replace the injector. Another possibility is an intake gasket leak. You could do a cooling system pressure check and see if coolant is getting into that cylinder. Hope this helps.
If it is running without a 'miss', to test the spark plug, swap it with one in another cylinder.(see if the code changes)
For your information; The spark plug wire should have no more than 652K ohms resistance. The fuel injector should ohm out between 2.6-2.8 ohms resistance.
In C and K series models, the A/C suction line runs above the distributor, and drips water on it. This will cause corrosion in the distributor, but I don't believe it will effect your application. This is just a thought though.
On some models the cam and crank sensors have to be set in sync. This is done with a "diagnostic scan tool" hooked up, and the engine running. You then have to 'floor' the gas pedal, and then look to see if the cam position sensor is at 0 degrees, plus or minus within 2 degrees of 0. But I don't remember if your model is one effected by this either.
If you do not find any bad ignition parts, and the compression is good. One would wonder if the crank position wheel got damaged(with the #4 cylinder lined up) when the crank sensor was initially installed. One would wonder if this could happen though.
Compression is good. been through several ignition tune ups. no elevated
HC's in the exhaust. Chevy ran a relearn ( or at least they told me they did ).
It runs without misfiring. I've heard the sensor can detect slight misfires that
are undetectable to human senses, but this seems unlikely given that my other
chevy 4.3L does misfire ( needs a spark plugs/tune up ) but the sensors do not
pick it up. ??? This has been an on going code for more than 25,000 miles.
I do hope the reluctor wheel is not damaged. I'll pull the sensor and see if its
marred up, and see if I can get a glimpse of the reluctor.
Thanks everyone
Brian
I doubt the wheel got damaged, as they are pretty heavy units, about 1/4" thick or better. I'd grab a new sensor, and while the old one is out, shine a light up the hole and have a look at the tone ring. You will be able to see if it is damaged. Do you have any codes other than the P0304?
No other codes have ever been stored besides the original crank sensor code,
and then the p0304 after the sensor was replaced. I figured the wheel was stout. I'll try switching the crank sensor from my other 4.3L and see what happens. I also wonder if the sensor is slightly crooked or still out of specs?
As soon as I get a chance i'll post back my findings.
Thanks again!
Brian
The odd part is that it is just 1 cylinder. The sensor works the same for all cylinders. I would take a good hard look at the wheel and have someone throw a scope on it that knows how to determine if all is working well. Also as someone else suggested try swapping the wire coil etc for that cylinder to another one and see if the issue moves. If a non OEM sensor was installed, throw it away and get a factory one.
What was the original issue that they replaced the sensor for.
One other thought, if you can find someone with a 5 gas it is the best way to tell if you are really having misfires or not. The hydrocarbons will be higher than normal
Has any major engine work been done to this van? Also, can you post a picture of the spark plug out of that cylinder?
When was the last time you changed the fuel filter? This may sound 'odd', but if you have a "clogged" injector, like was already posted, it is possible it only effects one cylinder. Every 30K is the recommended change interval.
I keep thinking, maybe you have a bad plug wire, possibly not connected correctly, burned boot, or what ever, but this should be a constant miss fire at idle in gear, as would a clogged injector. Then again, so would a defective spark plug; IE closed up gap, cracked insulator, etc.
The van runs perfect. No elevated hydrocarbons.i have done a basic ignition system tune ups. always the same code. Last time I pulled the plugs,
they all looked fine and consistent, again pointing to a false reading.
I don't know if its an aftermarket sensor, but the sensor is just a magnet. I
can't imagine there would be a quality difference.
I think I'll have some time tonight to investigate some more. i'll post back
thanks
brian
HI Brian,
I have the same symptoms as you had on your 2001 Chevy with the 4.3L V6. I have a code P0304 but do not feel a missfire. Please let me know what ended up fixing yours as I did not read a final post from you. Thanks in advance.
HI Brian,
I have the same symptoms as you had on your 2001 Chevy with the 4.3L V6. I have a code P0304 but do not feel a missfire. Please let me know what ended up fixing yours as I did not read a final post from you. Thanks in advance.
Im still here, and excited to help!
Gary1 is absolutely right. No cheap aftermarket for the ig system.
I did eventually solve the problem, I posted when I got it figured out.
Well I do have advice on this problem. It took two years to figure it out.
My first problem was the crank bearings. The thrust bearing had worn out. This
allowed the crankshaft to slide back and forth. That motion was translated by the sensors into a misfire code. To the computer, the crankshaft appeared to be slowing down during rotation. In reality, it was sliding back and forth.Oh yea, the engine ran just fine the whole time, but I could not get a tag b/c of atlanta's emmissions laws.
No one could figure this out(except me). Different mechanics all had different
"answers" on what the problem was. In fact, chevy with all their fancy diagnostic tools and "skills" determined that the HEADS were bad. The heads were NOT bad-as confirmed by my machine shop! In fact they were in excellent condition.
Check your thrust bearing and crank free play!!
But wait, there's more!
I replaced the engine, fuel injection, accessories, misc, and........the DISTRIBUTOR. All was great, and my van was back on the road. Then.....
All of a sudden the misfire reading came back!!!! Aghhhhh!! I was about to burn my van to ground at that point, But...
The after market distributor I got was a FAULTY DESIGN. Too much free play.
It would spin itself right out of proper timing, causing a misfire reading.
I had to get an ACDELCO distributor.
I also have an s10 pick up that began to read misfire and MAF sensor out of specs. A quick spray with MAF cleaner solved that problem.
So to recap:
1: Check/replace crank thrust bearing.
2: Absolutely use an ac delco distributor
3; Check and clean your MAF sensor.
After all I went through with my van, and truck, I have become a 4.3l vortec
master.
Please let me know when you get it solved. Good luck
Brian
Im still here, and excited to help!
Gary1 is absolutely right. No cheap aftermarket for the ig system.
I did eventually solve the problem, I posted when I got it figured out.
Well I do have advice on this problem. It took two years to figure it out.
My first problem was the crank bearings. The thrust bearing had worn out. This
allowed the crankshaft to slide back and forth. That motion was translated by the sensors into a misfire code. To the computer, the crankshaft appeared to be slowing down during rotation. In reality, it was sliding back and forth.Oh yea, the engine ran just fine the whole time, but I could not get a tag b/c of atlanta's emmissions laws.
No one could figure this out(except me). Different mechanics all had different
"answers" on what the problem was. In fact, chevy with all their fancy diagnostic tools and "skills" determined that the HEADS were bad. The heads were NOT bad-as confirmed by my machine shop! In fact they were in excellent condition.
I can confirm this was without a doubt the problem on my 2001 Blazer 4X4 with Vin W 4.3. No one else on the Internet seems to get this problem with the thrust bearing! Believe it!!
Symptoms: Vehicle did not seem to miss at all at lower RPMs, but had low oil pressure with lifter clacking when fully warmed up. 10psi at idle in drive. I was also setting a false P0304 - would reset code within 2 blocks of driving after clearing code. Induced a miss on each of other cylinders and it was not detected by the PCM (monitored misfire counters for all 6 cyl in Torque app - #4 kept counting a misfire but saw virtually nothing on the other 5). Revving engine over 4000rpm caused severe misfire and a P0300 set. Clacking sound went away with engine in drive (1500rpm park vs. 1500rpm drive).
Physical Diagnosis: I could make the crankshaft clunk by pulling forward on harmonic balancer and then pushing rearward. This should not happen as excessive thrust play in the crankshaft can cause a false misfire code (I found where this is stated in the GM factory service manual but I read it here first). Thrust should be around 0.005" - this would not clunk.
Repairs: Complete engine overhaul. Big-time bearing clearance problems especially with mains. I also replaced torque converter since it was not hooking up before repairs and was a suspect in the thrust bearing failure. You don't want to pull the engine out of a 4x4 Blazer more than once. Used same crank sensor and reluctor and did the Crankshaft Position Relearn using HP Tuners Software.
Analysis: This engine had only 64,000miles. Had lower intake gaskets previously replaced. Also TCC was inop before repairs. I figure the original problem was one of two things:
1. Coolant in oil took out the bearings
2. Inoperative TCC took out the thrust bearing and the rest of the bearings followed.
Only cost me $3000 in parts and machine work on a vehicle that I just bought with the SES light disabled. Wish I would have driven it hot.
But that's all water under the bridge. It's a nice vehicle. Just have too much money in it.
One thing to consider is a misfire needs to be fairly bad before you can feel it. The computer can pickup misfires that you may not feel while driving the vehicle so done assume you don't have one. The sad part is a lot of these "mechanics" try to troubleshoot a problem like this and they don't have the correct equipment. A trained mechanic and a hand held scope and a 5 gas would have help identify Brian's problem and proved there was no real misfire. The test would have taken 10 minutes and identified this as a mechanical issue.
being able to look at the exhaust gas makeup is like a blood test for a doctor when you are sick.
People go to the dealer because they think they are smarter than a non dealer mechanic. The truth is that it is usually just the opposite. If they haven't seen it before or their scan tool doesn't see the problem then you must not have one.
Damn straight. I figured out the problem. None of the people who I PAID were even close. Even the dealer service department got it way wrong.
I would match mechanical wits with them any day; and mechanics isnt my profession.
Yea I had an exhaust gas test. Actually I just took the van into a state emissions station. Their print out is pretty in depth, and I know enough to
"read" this blood test. The exhaust was as clean as could be. Thats when I realized there was no misfire. I provided this info to chevy, but obviously
they didnt consider it info in their diagnostic. To be a great mechanic, one has
to think abstractly, and not just by the book.
It seems like hit or miss.
And man I would like to find a good mechanic here in Atlanta. The search continues.
You may have a faulty reading 0'2 sensor, not bad enough to set a code, but off enough on it's return voltage to lean your engine out enough to set a code.
Do not over look a exhaust manifold exhaust leak either.
Working on car's emission's has gotten tougher here in California. Now it includes diesel truck's. OUCH
Brian,
We have now replaced all main bearings, thrust was good, and replaced distibutor with New AC Delco unit. It made no change. Check engine light flashes when rpm is raised beyond 1500, P0304. I also cleaned the MAF. When the heads were removed the no. 4 piston was much cleaner than all the rest, if that helps.
what year and engine are you working on? Is the engine running well, but setting misfire codes? Or is it running poorly?
your doing a hell of a lot of work.
my van had exactly the same problem. it plagued me for two years.
you may need a correlation relearn performed by chevy, though that never worked for me.
When I first got my fancy $300 AC delco distributor, accidently installed the distributor one tooth off.
the engine ran, but registered misfires -flashing check engine light. i pulled it out and reinstalled, and the misfire code cleared. so check your distributor.
also, the crankshaft sensor is very sensitive. if it is too close or to far from
the reluctor wheel, it wont read correctly. chevy put shims on mine to get
it in specs, ...... but in the end that did not solve the problem. chevy said ïts fixed", and I got about a mile down the road and then the flashing check engine came back! check the crank sensor. make sure its torqued in correctly, and make sure the front engine cover where the sensor is is not damaged.
have you checked your compression? low compression on a cylinder would definitely set a misfire code.
This engine is equiped with a multi pin plug behind the throttle body. The fuel injection system is located under the upper intake plenium, which is not difficult to remove. It has a 'plastic' 'lined' injector system, with a fuel pressure regulator.
The o'ring's on the injection nozzles can fail, and the pressure regulator diaphram will also rupture causing a fuel to leak into the lower intake manifold.
With the upper plenium removed, cycle the ignition key on, and off twice, and look for a fuel leak.
could one look for these leaks using a fuel pressure guage?
without taking the upper intake off. Would this manifest as
low fuel pressure at idle?
I have had several of the csfi engines, and the csfi units have held up
well over many miles and many years. I removed a unit from
my 2001 van with 150K miles. The rubber and the regulator were still
in really good shape. I upgraded to the new direct injection system.
This is a pic of the reluctor that is read by the crank position snesor, except the V6 only has 3 vanes instead of the V8's 4.
Here is a pic of a "knife-edged" distributer gear that can cause missfires when all else checkls out of teh Vorte engines.
Top is the stock CSFI and bottom is the MPFI GM conversion, obviously the V6 versions have 6 spiders legs. 2003+ V6's use the MPFI conversion spiders from the factory/ The MPFI conversion spiders flow the same amount of fuel but they have Multec 2 mini-injectors at the end of the spiders legs, instead of poppet valves that open by fuel pressure on the CSI spiders.
Stock pressure should be 60-66psi, KOEO(Key On ENgine Off) the fuel pressure regulator will bring down the pressure at idle or KOER(Key On Engine Running).
Yea I added the new fuel system when I got the new engine.
I also got a cheap distributor. That distributor had an insane amount of free play built into the design. It spun itself out of time every time I hit the gas.
It was a FAULTY DESIGN. There is no way it would work in any vortec engine.
I took it back and dropped the big bucks on an AC Delco. The van has been running great for a long time now.
The poster has already replaced the dizzy with an ac delco.
Apparently the gear metal is soft and wears rather quickly.
I replaced mine with a $99 reman. It totally did not work.
It had so much free play that it would not stay even close to proper timing.
I have a suspicion that the poster installed the new distributor one tooth off.
So if the stock fuel pressure is running lower than specs, should I suspect
leaking poppet nozzles. I have a 99 s10 with 115K that just started reading
p0304. It has new plugs/wires/rotor/cap, low miles, and is otherwise in great shape. I have not looked into it yet, but should I suspect the 14 year old
poppet nozzles? I already upgraded the csfi on my 2001 express, but like I said before, I never had any issues with the poppet nozzles.
One more question. I kept the csfi unit for parts or to sell. IS IT WORTH SELLING, or should the csfi always be replaced with the direct injection?
I would keep teh CSFI spider for parts. Having done so personally has gotten me out of a jam before. If its good there is no sense swappinmg to the MPFI spider, but GM did start installing them in the 2003 V6's for a reason.
Yes. When they look a bad as the one hogg posted they will cause trouble. I have had them set a p1345 with a gear that worn. They don't like all that lash.,
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