Thought maybe one of you guys have dealt with this before. 99 Chevy Tahoe 5.7 having misfire cylinder six only after driving if you come to a complete stop, put the truck in park no misfire it seems to level out an idle perfectly fine until you start driving things I’ve replaced cap rotor plugs, wires new spider standard motor or Riley‘s product misfire was predominantly on cylinder six with a high misfire account then 2,4,8 would follow with lower misfire accounts. Replace spider ran good for two days then cylinder six misfire happened again same symptoms no check engine light this time when misfire episode is occurring fuel trims on bank two are at -30 new O2 sensors no change fuel pressure test holds 60 psi Keon for over 10 minutes no leak down pulled valve cover off insured all rockers moving. Could this be a bad distributor? What are the chances of replacing a spider and it being the same cylinder, I had on issues with before. I understand parts are finicky in most cases. I would be more comfortable swapping it out if I had a misfire on a different cylinder, but it’s the exact same issue exact same cylinder.
[SOLVED] 99 Chevy Tahoe 5.7 misfire
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Did you replace the SCPI with a new SCPI or did you put in the upgraded MPFI style spider HERE ?
Did you install a new fuel filter at the same time?
What is your compression readings on the engine?
Is it hard starting when the temps are around 25F?
Are you sure you do not have a vacuum leak? Did you remove the lower intake manifold and put new intake gaskets on it? If not it is virtually a guarantee the lower intake gaskets need replaced.
I have found several bad running 5.7s. After changing the intake gaskets and converting to MPFI injectors it is surprising how well they run.
Did you install a new fuel filter at the same time?
What is your compression readings on the engine?
Is it hard starting when the temps are around 25F?
Are you sure you do not have a vacuum leak? Did you remove the lower intake manifold and put new intake gaskets on it? If not it is virtually a guarantee the lower intake gaskets need replaced.
I have found several bad running 5.7s. After changing the intake gaskets and converting to MPFI injectors it is surprising how well they run.
Another good thing to check. I have only seen that once but for sure can happen.
All of these trucks are usually pretty worn out by now. Have to start with the very basics. Valves wear, valve guides wear and valve springs break, along with cylinder wear. These engines were set up very loose from the factory, very common to have piston knock on a cold engine.
I did lower intake gasket back in October. Did the complete set upper and lower gaskets since I was there no issues up until last week distributor is one thing that I really didn’t pay too much attention to when I was in there. The plan is to go home today after work and pull it out and check the gear. I did verify CMP retard stayed at 0°. I have not done a compression test yet. I even adjusted it yesterday to +2 to see if it had any effect no difference.
If you are staying at 0 it should be ok. If i remember right +-2 is within spec. So it ran fine for two days so you know it is capable of running right.
Be sure to check that cap and rotor very well.
Running good for two days then back to running bad kinda leads a guy to looking at electrical. Is the temp sensor reading correct?
Be sure to check that cap and rotor very well.
Running good for two days then back to running bad kinda leads a guy to looking at electrical. Is the temp sensor reading correct?
You know what the temp sensor had me a little worried I replaced it with an AC Delco because the last one was reading 2.14 V which I thought was odd so I replaced it and it’s reading the same 2.14 V when warmed up it does get a little closer to two when fully had operating temperature. I’m OK with replacing the injector assembly again or in this case with this style set up I know you can replace individual injectors now but what I’m having a hard time believing is that I had a failed injector at six replaced it and it just so happens that the faulty injector I got is on six again so that leads me to believe my issue lies elsewhere
It would be odd for the same hole to have a bad new injector for sure.
Odd that it did run fine for two days. It's like you disturbed the wiring and what ever made a connection and worked fine till it did not a few days later.
I know you have looked but check everything again for a vacuum leak very carefully.
-30 STFT is a definite clue. Have you checked the map and maf sensors?
Odd that it did run fine for two days. It's like you disturbed the wiring and what ever made a connection and worked fine till it did not a few days later.
I know you have looked but check everything again for a vacuum leak very carefully.
-30 STFT is a definite clue. Have you checked the map and maf sensors?
I did look at the map in maf sensors. Everything is reading correctly. Everything reads as it should when idling normal and first starting to drive once you’re driving for about five minutes or so it acts up start misfiring and you come to a stop. Misfire is really really bad but if you throw it in park and leave it alone for a little bit, the idle will smooth out misfires are completely gone. I have the scanner connected the whole time so I’m watching the active misfires. Misfire start at cylinder six with a very high count and then two and four will follow with misfire counts under 10 while cylinder six is about 180 misfires.
east302
Full Access Member
Was it doing it before the distributor cap was replaced? Delco caps don’t give me issues, but I’ve had single-cylinder misfires of new parts store brand caps before. A spark tester on plug #6 wouldn’t hurt - see how spark quality compares with the others.
Have you done a coolant pressure test or are you losing coolant? Is the plug dry or does it look the same as the other plugs? Does the oil look good - no chocolate milk?
Have you done a coolant pressure test or are you losing coolant? Is the plug dry or does it look the same as the other plugs? Does the oil look good - no chocolate milk?
Thinking about it that sounds very similar to my 1999 Express van 5.7
Turned out to be a bad ecu. When i took the ecu apart it had a bunch of white crusty stuff in it.
It would start and idle fine but try driving it and it would miss, buck, and die. Restart it and it would idle perfect. Sometimes if i let off the gas it would go back to idling perfect. Try driving rinse repeat.
Turned out to be a bad ecu. When i took the ecu apart it had a bunch of white crusty stuff in it.
It would start and idle fine but try driving it and it would miss, buck, and die. Restart it and it would idle perfect. Sometimes if i let off the gas it would go back to idling perfect. Try driving rinse repeat.
Not losing any coolant, no milky residue or oil discoloration. I did put a spark tester on the spark plug never missed a beat. Spark was pretty strong and I confirmed that by trying to touch it while I was running shocked the hell out of me.
It’s weird I checked connections all plugs throughout the engine bay. Checked all my grounds pulled the plugs off of ECU. No corrosion found it won’t actually turn off it just items really rough until I put it in neutral or park.
Try monitoring as many item as you can fit on screen live data.Wait for misfire and look at which ones are changing. Hopefully you can catch the sensor output change just before missfire to help lead you to the problem.
Recheck vac lines especially at firewall heater connection. A loose or disintegrating line can be intermittant.
Distributor caps are first thing on missfire, and Distributors not unusual. United dist and cap DCR820X only have worked well for me.Rockauto a good source.
Recheck vac lines especially at firewall heater connection. A loose or disintegrating line can be intermittant.
Distributor caps are first thing on missfire, and Distributors not unusual. United dist and cap DCR820X only have worked well for me.Rockauto a good source.
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Carbon build up on valves? Spider injection harness plug terminals clean? Pull valve cover for that side and check for loose rocker or push rod/lifter failure. Compression test that cylinder .
All day of chasing this yesterday with no luck. Performed an injector plus test all injectors firing as they should. Finally wired up a noid light to ground wire for injector 6 noticed as I drove around when the misfire starts the noid is solid checked for chafed wires no luck thought this pointed to a bad injector driver in pcm swapped pcm for another 99 Tahoe no change.
West 1
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I have yet to see where a compression test was performed on this #6 problem. Sometimes start with the basics and the problem shows up. I chased a #4 misfire on a friends 99 Silverado, he had had in 4 shops, spent nearly $7K. It did not help that he took it to another shop each time the previous shop did not fix it. In their defense the problem was hard to find. I had checked his compression, it was good. On test drive it started to misfire, got it home checked compression it was good??? The misfire had stopped before I was able to test. Next test drive it was running perfect till I climbed a long hill and it started misfiring. I took it straight to my garage. Opened the hood pulled that plug and did a leak down test. Leak down because I did not want to crank it over and have it fix itself again. This time the leak down was 40% leak.
Now I pulled the valve cover while the leak down test is still running. I pried up on the 2 #4 valves. The cylinder sealed, leak down changed to 4%. I could tap with a light hammer on the valve and the leak down would jump back to 40%.
It was carbon build up on the valve. I don't remember if it was Intake or exhaust. Sorry, bad memory. I did a valve job on both heads the the truck ran beautiful. Problem was very hard to find but once found it was fixed.
I chased a distributor problem on another 99 Suburban, also a friends, he had a new Summit distributor and it would not hold timing. Pulled it out and inspected it, it had .70 vertical shaft movement causing the timing to jump. I made a shim, reduced the play to .10 and it fixed that one.
Hope this helps.
Now I pulled the valve cover while the leak down test is still running. I pried up on the 2 #4 valves. The cylinder sealed, leak down changed to 4%. I could tap with a light hammer on the valve and the leak down would jump back to 40%.
It was carbon build up on the valve. I don't remember if it was Intake or exhaust. Sorry, bad memory. I did a valve job on both heads the the truck ran beautiful. Problem was very hard to find but once found it was fixed.
I chased a distributor problem on another 99 Suburban, also a friends, he had a new Summit distributor and it would not hold timing. Pulled it out and inspected it, it had .70 vertical shaft movement causing the timing to jump. I made a shim, reduced the play to .10 and it fixed that one.
Hope this helps.
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east302
Full Access Member
Here’s the diagram for a 99 350, the yellow/black should be for the #6 injector. To me, it sounds like it may be grounding out between the injector harness and VCM. Maybe disconnect both ends and check for continuity (one probe to a ground, the other probe to one end of the wire). Jiggle it around, if you have continuity it’s shorting to ground.
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