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  #1 (permalink)  
Old 09-16-2008, 06:44 PM
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false misfire reading ?

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??

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Old 09-16-2008, 08:24 PM
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Quote:
Originally Posted by briansansone
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??
Have you had the code cleared? Does it come back if it has been cleared?

Bogie
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Old 09-16-2008, 10:39 PM
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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.
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Old 09-16-2008, 10:54 PM
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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.
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Old 09-17-2008, 07:24 AM
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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
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Old 09-17-2008, 09:07 AM
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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?
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Old 09-17-2008, 09:58 AM
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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
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Old 09-17-2008, 11:19 AM
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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.

Chet
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Old 09-17-2008, 11:22 AM
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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

Chet
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Old 09-17-2008, 01:37 PM
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Another thought.

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.
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Old 09-17-2008, 01:58 PM
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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
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Old 04-19-2013, 09:04 AM
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2001 GMC Safari with P0304 Same problem as you

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.
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Old 04-19-2013, 10:21 AM
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We have found with the 4.3's in Astro vans it is important to use Delco only on the cap,rotor,wires,plugs.When not,weird results happen.
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Old 04-19-2013, 10:25 AM
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Quote:
Originally Posted by ffroese5 View Post
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.

Brian's thread is almost 5 years old. He last logged onto the board in December.
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Old 04-20-2013, 09:05 AM
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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
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