So i have a 99 tahoe currently I have replaced the CATS, all 02 sensors, spark plugs, wires, cap & rotor and mass air flow sensor.......with that being said I am still getting a random cylinder misfire code and I am unsure as to why? If anyone knows what else could be causing this or atleast point me in the right direction that would be great thanks.
Misfire issues
- Thread starter Joshua363
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First: Welcome to the forum from Oregon.
Second: Did you do a compression test while plugs were out? Should have. Did you do a fuel pressure test? Should have. Check for vacuum leaks. Could also be related to this:
https://www.rockauto.com/en/moreinfo.php?pk=984604&cc=1353721&jsn=935
Third:
We recommend that you put all your rig(s) info in your signature so we all don’t have to guess at year, make, model, engine size, trans, rear axle locker…….etc. While you may have posted pertinent info in your first post, you may forget to do it again and the info is needed by us anyway. Makes it way easier on all members that attempt to help, to have that info right up front. It is also recommended that you take a pic of your RPO codes, on the inside cover of the glove box, and post that image in your signature. All this info will greatly help those that will try to help with a problem.
If there is any other info, like upgrades, mods or recent mechanical/maintenance work done, that would be helpful in any post as well. Too many times a question is asked by the poster and after about 10 responses we find out that the poster has done recent work to attempt to fix the problem or work that was done that SEEMS not related to the problem.
Second: Did you do a compression test while plugs were out? Should have. Did you do a fuel pressure test? Should have. Check for vacuum leaks. Could also be related to this:
https://www.rockauto.com/en/moreinfo.php?pk=984604&cc=1353721&jsn=935
Third:
We recommend that you put all your rig(s) info in your signature so we all don’t have to guess at year, make, model, engine size, trans, rear axle locker…….etc. While you may have posted pertinent info in your first post, you may forget to do it again and the info is needed by us anyway. Makes it way easier on all members that attempt to help, to have that info right up front. It is also recommended that you take a pic of your RPO codes, on the inside cover of the glove box, and post that image in your signature. All this info will greatly help those that will try to help with a problem.
If there is any other info, like upgrades, mods or recent mechanical/maintenance work done, that would be helpful in any post as well. Too many times a question is asked by the poster and after about 10 responses we find out that the poster has done recent work to attempt to fix the problem or work that was done that SEEMS not related to the problem.
What else can you tell us? How are fuel trims? Which misfire codes? How random how soon? Tach dropping out/bouncing? What about CPS? What else replaced?
Pnw vietvet would also want to know if you checked the wiring in Dist when cap off.
Pnw vietvet would also want to know if you checked the wiring in Dist when cap off.
Joseph Garcia
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Welcome to the Forum from NH.
Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.
I hope that you will become a participating member in the Forum's discussions.
You already have one reply, and other folks will chime in, as well.
Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.
I hope that you will become a participating member in the Forum's discussions.
You already have one reply, and other folks will chime in, as well.
If you get this far, this is what you should look for as far as compression. I did not want to just throw a random number out there and this explains it perfectly.
" If a factory value is not available you can estimate it by multiplying your intake pressure by your engine's compression ratio - for example a 2005 Silverado with a 5.3L V8 has a compression ratio of 9.9:1 - if you measure an intake pressure of 17 psi you can expect a cylinder pressure in the 170 psi range."
I do know that a proper functioning 5.7 engine compression test should be at the minimum 150-170. I just wanted you to know how the different compression ratios are reached.
And yes, @exp500 is correct, the pickup coil wiring should be checked under the cap. They can have wiring insulation crack off and have exposed wire and in some cases break but still make contact that can cause misfire.
" If a factory value is not available you can estimate it by multiplying your intake pressure by your engine's compression ratio - for example a 2005 Silverado with a 5.3L V8 has a compression ratio of 9.9:1 - if you measure an intake pressure of 17 psi you can expect a cylinder pressure in the 170 psi range."
I do know that a proper functioning 5.7 engine compression test should be at the minimum 150-170. I just wanted you to know how the different compression ratios are reached.
And yes, @exp500 is correct, the pickup coil wiring should be checked under the cap. They can have wiring insulation crack off and have exposed wire and in some cases break but still make contact that can cause misfire.
On my 04 silverado, I had a bad or malfunctioning lifter causing misfires on one cylinder. So valve train could also be a potential cause. Think I narrowed that down with a compression test. Motor was brand new/ rebuilt as were the lifters.... Good luck.
