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98 Chevy 5.7 Misfire


gmax1

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My 98 K3500 with 161k was throwing a lot of codes. Replaced all 4 O2 sensors. Then Mass air flow sensor, new AC Delco platinum plugs, new Auto Zone plug wires, New NAPA distributor, tried switching NAPA cap and rotor with new GM brand. Mechanic (Jeff- former Honda, Toy, Subaru dealer mechanic) found cracks in intake manifold gasket and replaced with new upgraded Felpro brand. Still running rough. Jeff unable to find cause.

 

Brought truck to Dick- former GM dealership mechanic. Dick went through all of the diagnostic proceedures Jeff went through. Truck runs okay on start up but within 1-2 minutes starts running rough at idle and gets worse when put into gear. This has been problem from beginning. Number 4 and 8 plugs skipping the worst. All plugs on that side badly sooted up. Other bank of plugs (odd #) looks good. Sometimes misfire carries over to #1 plug. Truck is blowing black smoke and burning excess fuel. Compression in all cylinders is 175 to 185 with one cylinder showing 160.

 

Dick pulled O2 sensor before catalytic on passanger side and engine quieted right down. Says truck has plugged catalytic so new cat and muffler assembly for that side ordered from GM and installed. Ouch! Slight improvement but still running very rough, no power, misfires on 4 and 8, and spark as before advanced by 22 degrees.

 

Pulled NAPA distributer with the new GM cap and rotor button and switched it with a used GM distributor and again used the new GM rotor and cap. No significant change. Replaced central port fuel injector unit with one from a junk yard that supposedly came off a running engine. No significant change. Fuel pressure is 54 or 55 psi.

 

Headed back to junk yard tomorrow to switch used CPFI with another used one they have that is also supposedly off a running engine. If this doesn't work my next step will be to bring truck to GM dealership and have them diagnose it for possibility of installing new GM CPFI as a cure but that's a $500 - $600 fix and currently I have almost $2000 into labor and parts with Dick. Dick thinks the CPFI may be the problem. If it isn't he does't know what to do next as he has tried everything in his bag of tricks and has consulted with other mechanics he knows. We're both frustrated. Nothing anyone has done has resulted in significant improvement.

 

This thing is beating my wallet hard. Any suggestions would be appreciated.

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My 98 K3500 with 161k was throwing a lot of codes. Replaced all 4 O2 sensors. Then Mass air flow sensor, new AC Delco platinum plugs, new Auto Zone plug wires, New NAPA distributor, tried switching NAPA cap and rotor with new GM brand. Mechanic (Jeff- former Honda, Toy, Subaru dealer mechanic) found cracks in intake manifold gasket and replaced with new upgraded Felpro brand. Still running rough. Jeff unable to find cause.

 

Brought truck to Dick- former GM dealership mechanic. Dick went through all of the diagnostic proceedures Jeff went through. Truck runs okay on start up but within 1-2 minutes starts running rough at idle and gets worse when put into gear. This has been problem from beginning. Number 4 and 8 plugs skipping the worst. All plugs on that side badly sooted up. Other bank of plugs (odd #) looks good. Sometimes misfire carries over to #1 plug. Truck is blowing black smoke and burning excess fuel. Compression in all cylinders is 175 to 185 with one cylinder showing 160.

 

Dick pulled O2 sensor before catalytic on passanger side and engine quieted right down. Says truck has plugged catalytic so new cat and muffler assembly for that side ordered from GM and installed. Ouch! Slight improvement but still running very rough, no power, misfires on 4 and 8, and spark as before advanced by 22 degrees.

 

Pulled NAPA distributer with the new GM cap and rotor button and switched it with a used GM distributor and again used the new GM rotor and cap. No significant change. Replaced central port fuel injector unit with one from a junk yard that supposedly came off a running engine. No significant change. Fuel pressure is 54 or 55 psi.

 

Headed back to junk yard tomorrow to switch used CPFI with another used one they have that is also supposedly off a running engine. If this doesn't work my next step will be to bring truck to GM dealership and have them diagnose it for possibility of installing new GM CPFI as a cure but that's a $500 - $600 fix and currently I have almost $2000 into labor and parts with Dick. Dick thinks the CPFI may be the problem. If it isn't he does't know what to do next as he has tried everything in his bag of tricks and has consulted with other mechanics he knows. We're both frustrated. Nothing anyone has done has resulted in significant improvement.

 

This thing is beating my wallet hard. Any suggestions would be appreciated.

 

You never said about anyone checking the EGR valve? Sounds like maybe a piece of carbon is keeping it stuck open a bit, it will run ok on start up and then when idle down run rough and then uses alot of fuel creating black smoke and using lots of fuel. Yes the CPFI on those motors are bad about injectors sticking open and flooding out cyclinders but if you changed the unit and no change you should be good there. But asuming you have good power while driving most likely it wont be the CPFI!! First thing I would chack if it came in my shop would be the EGR it has ALL the right symtoms!

 

Sometimes thinking outside the box always helps and one mechanic is stuck on thinking one thing its hard to find the real problem, we've all been there i hate it. Hopefully this helps you out, let us know!

 

 

Thanks for the reply. Thanks to ZZ327 also. Forgot to mention Dick tried another (good used I think) crank sensor. I also tried a Duralast MAP sensor but that also made no difference so changed back over to my old MAP. Dick removed the EGR valve and cleaned it a little with a knife and reinstalled but this didn't seem to make a difference. Maybe I need to try a new EGR? Can an EGR be cleaned. EGR is not giving any codes.

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The only way you can set a P1345 is

A loose CMP sensor causing a variance in the sensor signal

Excessive free play in the timing chain and gear assembly

Incorrectly installed distributor - 1 tooth off in either advance or retard positions

A loose distributor rotor on the distributor shaft

A loose or missing distributor hold down bolt.

 

With the miles you have on the engine. The only one that fits that you have not done is the timing chain, There are only two ways you can test it.

 

TH FIRST WAY

Pull off the timing cover and messure the chain. (takes to long).

 

THE SECOND WAY

There is a very simple check for a loose timing chain due to a broken tensioner, worn gears, or a stretched chain. Pull the distributor cap and observe the rotor position. Take a breaker bar and a appropriate socket and put it on the crankshaft damper pulley. If you have a degree wheel put it on the damper pulley else you can just chalk mark the timing mark position at the appropriate time.

 

Now - slowly turn the crankshaft pulley in a clockwise direction. Watch the distributor and observe that the rotor is moving. Stop turning. Now - mark the damper pulley position with the chalk or observe the degree wheel. Very carefully turn the crankshaft in the other direction and VERY carefully observe the rotor in the distributor. The instant it begins to move STOP turning and mark the crankshaft position again. Measure the number of degrees of rotation of the crankshaft. If there is a lot of slop in the chain then you will have moved the crankshaft ten or fifteen degrees (or more) before taking the slop out of the chain after the reversal before the camshaft began to turn. Get the picture?? If all is well and there is no slack in the timing chain then you will see about three to five degrees of "reverse motion" before the distributor begins to turn.

 

If you are not sure how many degrees it turned during the procedure there is a simple way to calculate that based on the spacing between the chalk marks. Take a string and wrap it around the crankshaft damper where you made the chalk marks to measure the circumference of the damper. Let's say it was 18 inches. If there is one inch between the chalk marks then divide 1 by 18 and multiply the result by 360 (the number of degrees in a circle). In this case the answer is 20 degrees and it is time to replace the gears!!!

 

Thanks for taking the time to write your nicely detailed reply. I'll print it out and give to the mechanics doing the work. I hope I won't be fighting with this truck for much longer.

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I'm surprised no one has brought this up, but what about a bad knock sensor? My dad's older 454 had one, and it would run EXACTLY as you described, though it was on all cylinders, not just one side as his is TBI. One side being rich would indicate that the knock sensor is detecting knock and trying to compensate for it, but it SHOULD throw a code for that. It might not, though.

 

The knock sensor wont control just one bank like his is doing especaily on a standard disturator system if it was coil on plug setup that might be the case but not his engine, it adjust all cyclinders to adjust ping.

 

 

It might not control SPARK on one bank, but it WOULD control FUEL. It would dump more fuel into one bank and try to run it rich and stop the knock.

 

That said, it sounds like he found part of the problem.

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Final Update and the cure

For those of you who have been following this post and offered much appreciated suggestions her's what finally fixed the problem. Took truck to GM truck dealership ($973 bill). They replaced O2 sensor on right side (passenger side) forward of the catalytic converter. GM tech also said Duralast ignition wires purchased at Auto Zone were not capable of carrying needed spark all the way through to spark plugs. (Junk wires) GM wire set installed. Pricey at $167 a set but they improved misfiring. I had read on the Internet that Vortecs like GM wires best. Another set of OEM plugs at $9.06 each installed.

 

Also GM tech says that NAPA distributor part #9591003 GM 01 10000940

bar code 8 81882 38744 7 is for a 4.3L and not for the 5.7 in my truck! This is the second new and complete NAPA distributor that was installed with the same part numbers with the same same result. GM tech had to oval out bolt hole a lot for hold down shoe so distributor could be turned to adjust spark. I have spoken to NAPA manager about this situation but haven't heard back whether NAPA is having a problem with this particular distributor or part number correlation for 5.7 engines.

 

At this point truck is running well and seems to be getting good mpg but I won't know for awhile what the actual mpg is. After all these repairs I can't afford to fill up the tank!!

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UPDATE: Delivered another used central port fuel injector unit to the 3 mechanics. They said the unusual thing about my problem is that the poor running is all on one bank of cylinders- 2,4,6,8 with 4 and 8 being the worst. They can watch them get worse on their engine analyzer as engine warms up. They have never seen a problem so pronounced concentrated in only one bank with no apparent cause. Nothing they have tried has resulted in any significan improvement. They have also done a leak down test and that was good. They do not think it is an EGR issue as my EGR is located center of both cylinder banks and should distribute evenly to both banks.

 

This is part of the problem a lot of things that could cause a running problem like this would affect cylinders on both banks. For instance if it was a fuel filter or fuel pressure regulator problem it should affect the way all cylinders run.

 

Can't find a used EGR to try. Most recycling yards don't bother with them as they get a lot of bring backs on this part. New EGR is 190.00 so it would be good to be pretty sure that is problem before installing same.

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Thanks for the reply. Thanks to ZZ327 also. Forgot to mention Dick tried another (good used I think) crank sensor. I also tried a Duralast MAP sensor but that also made no difference so changed back over to my old MAP. Dick removed the EGR valve and cleaned it a little with a knife and reinstalled but this didn't seem to make a difference. Maybe I need to try a new EGR? Can an EGR be cleaned? EGR is not giving any codes. Truck runs like on 6 or 7 cylinders going down the road but doesn't stall. Hills are a strain.

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Thanks for the reply. Thanks to ZZ327 also. Forgot to mention Dick tried another (good used I think) crank sensor. I also tried a Duralast MAP sensor but that also made no difference so changed back over to my old MAP. Dick removed the EGR valve and cleaned it a little with a knife and reinstalled but this didn't seem to make a difference. Maybe I need to try a new EGR? Can an EGR be cleaned? EGR is not giving any codes. Truck runs like on 6 or 7 cylinders going down the road but doesn't stall. Hills are a strain.

 

Yes EGR can be cleaned, just look at it and check to see if its seating all the way closed, EGR codes are hard to throw it has to be not working at all. The EGR is a pretty pienny to buy see if someones got one to try.

 

When the upper intake pulled is anything shinny like leaking fuel into the intake somewhere.

 

When in idle how does it do when you give it full throttle a couple of times smooth, real rough, has hard time getting up to it.

 

Also when key on engine off does it hold good fuel pressure or does it bleed off?

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Don't know about leaking fuel, will ask Dick tomorrow. I would hope he would notice if that were so. Heading for bed so I can make run to auto recycler early tomorrow. Leaving by 0700 and it's almost a three hour round trip! Thanks for all your help and if anyone thinks of another angle I'm very interested. I hate to keep throwing parts at this stubborn beast but I don't know what else to do. It's no good to anyone the way it's running at this time.

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My 98 K3500 with 161k was throwing a lot of codes. Replaced all 4 O2 sensors. Then Mass air flow sensor, new AC Delco platinum plugs, new Auto Zone plug wires, New NAPA distributor, tried switching NAPA cap and rotor with new GM brand. Mechanic (Jeff- former Honda, Toy, Subaru dealer mechanic) found cracks in intake manifold gasket and replaced with new upgraded Felpro brand. Still running rough. Jeff unable to find cause.

 

Brought truck to Dick- former GM dealership mechanic. Dick went through all of the diagnostic proceedures Jeff went through. Truck runs okay on start up but within 1-2 minutes starts running rough at idle and gets worse when put into gear. This has been problem from beginning. Number 4 and 8 plugs skipping the worst. All plugs on that side badly sooted up. Other bank of plugs (odd #) looks good. Sometimes misfire carries over to #1 plug. Truck is blowing black smoke and burning excess fuel. Compression in all cylinders is 175 to 185 with one cylinder showing 160.

 

Dick pulled O2 sensor before catalytic on passanger side and engine quieted right down. Says truck has plugged catalytic so new cat and muffler assembly for that side ordered from GM and installed. Ouch! Slight improvement but still running very rough, no power, misfires on 4 and 8, and spark as before advanced by 22 degrees.

 

Pulled NAPA distributer with the new GM cap and rotor button and switched it with a used GM distributor and again used the new GM rotor and cap. No significant change. Replaced central port fuel injector unit with one from a junk yard that supposedly came off a running engine. No significant change. Fuel pressure is 54 or 55 psi.

 

Headed back to junk yard tomorrow to switch used CPFI with another used one they have that is also supposedly off a running engine. If this doesn't work my next step will be to bring truck to GM dealership and have them diagnose it for possibility of installing new GM CPFI as a cure but that's a $500 - $600 fix and currently I have almost $2000 into labor and parts with Dick. Dick thinks the CPFI may be the problem. If it isn't he does't know what to do next as he has tried everything in his bag of tricks and has consulted with other mechanics he knows. We're both frustrated. Nothing anyone has done has resulted in significant improvement.

 

This thing is beating my wallet hard. Any suggestions would be appreciated.

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I'm surprised no one has brought this up, but what about a bad knock sensor? My dad's older 454 had one, and it would run EXACTLY as you described, though it was on all cylinders, not just one side as his is TBI. One side being rich would indicate that the knock sensor is detecting knock and trying to compensate for it, but it SHOULD throw a code for that. It might not, though.

 

The knock sensor wont control just one bank like his is doing especaily on a standard disturator system if it was coil on plug setup that might be the case but not his engine, it adjust all cyclinders to adjust ping.

 

 

It might not control SPARK on one bank, but it WOULD control FUEL. It would dump more fuel into one bank and try to run it rich and stop the knock.

 

That said, it sounds like he found part of the problem.

 

 

Printed out what you said and gave it to Dick the mechanic. Dick says got timing down to 14 degrees but it doen't run well at that setting. Runs best with timing in low 20's. Still loading up on fuel and blowing black and everyone is afraid of damaging the new catalytic converter.

 

He's going to think about what's next over the weekend. Kind of going around in circles right now and were all frustrated. Dick said he doesn't think the new set of Duralast plug wires I put on are faulty as there's plenty of spark. He doesn't think its a bad computer either. Still getting same code on scanner which is a P1345A.

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1998 5.7 vortec missfire solution.

 

Random missfire is a Knock Sensor !

Please read my story !

I own a 1998 Z/71 5.7 K1500

Started off missfireing on a hill or when i pulled my small trailer.

Service engine soon, dash lite came on, went to a shop pluged up to a hand held unit. it said missfire on 3&5, cleared codes & thought its just tune up time. WRONG !

BEFORE THIS I HAD JUST REPLACED THE FUEL PUMP AND FUEL FILTER THE PUMP HAD GONE OUT.143,000

MILES ON IT, NORMAL REPAIR.

OK BACK TO RANDOM MISSFIRE,

REPLACED SPARK PLUGS ,PLUG WIRES,DIST. CAP ,ROTOR,

Driving around the samething {dash lites up service engine soon }

it RANDOM missfires and shakes loosing power. i return to shop we plug up the hand held unit it says random missfire ? so we think its the coil getting weak, replaced the coil same thing random missfire again.

this is over a 2-3 month period i have to drive the truck easy to work and home like driving Miss. Daisy you kinda get the idea.

someone said the intake gasket is Leaking check it , so with the truck at idle i spray starting fluid all around the intake with no changes in RPM.

NEXT Iam about to do a insurance claim, but i love the truck but its driving me and GM mechanics and all others mechanics up the wall at this time iam looking at a whole lot of money spent already and my truck is not fixed, and thinking about standing on a street with a sighn that reads "will work for repaires on my chevy truck "

ok its time to think again , so i'am putting it all together random missfire no power, piston spark knock, so i called O'Reilly auto parts Dalton Ga. and told jeff my sad story he said to change the Knock sensor

for $32.99 it was worth a try.

part # BWD 98012 FOR MY TRUCK.

PLEASE READ ON !! It fixed the problem its never ran so great , Throttle responce is great!

The knock sensor tells the computer to advance or retard the timing,

it cannot adjust the advance without the knock sensor telling it what to do. The Knock sensor is located on the passenger side of the block easy to get to under the truck on jack stands. but it screws into the water jacket of the block between the freeze plugs you must drain all the antifreeze from the engine before replacing it. The truck runs like a brand new one with 160.000 miles on it 0-100 mph is no problem bring on the HEMI'S ! :smokin:

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Will ask Dick if he looked at fuel pressure bleed off when engine is not running. What effect would that have on the engine when it is running? Could it cause my symptoms?

 

Yes if the engine can get pressure but cant get the flow it needs it could becausing no power issues and missing it makes they run funny sometimes each mocar acts differently to the issue.

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