runs perfect cold at running temp miss fires badly

[papamac816]

I have a 2005 suburban 1500 4wd automatic trans 5.3 . the truck was hit on the front passenger side.  I replaced body parts . air bags did not deploy. Steering column bearing are loose from impact.. radiator support was pushed back but no damage to electric fans radiator or condenser . it ran good for a month.  now it runs perfect at startup.  when it warms up it misfires terrible. can not be driven.  I have replaced y pipe and cats. all 4 o2 sensors.  plugs,  wires , coils , crank and cam ,oil sensors.  visually checked wiring harness found no damage.  only codes show all misfires when it starts to run poorly.  checked for intake leaks with carb cleaner . it does not have egr. 

[Jsdirt]

Is the code a random misfire P0300, or is it cylinder specific? I'm thinking some coils got smacked harder than they can handle and are breaking down with heat. That would trigger a cylinder specific code rather than a random, unless it was all 4 on that one bank (or more on the other bank). 

 

If that's not the cause, then my money is on a bundle of wires shorting out. I'd want to look at scan data to see what the o2's are doing, MAF, temp sensors. Could be a shorted or open 5v reference. Once warm, the engine uses all those for fueling - when cold, it uses a "program".

[papamac816]

hello,  I believe all the cylinders are misfiring.  I have replaced all the coils wires plugs . when it's running bad it is showing every cylinder code . I have considered a new wiring harness.  but there appears to be no damage to it.  and this morning  my friend tried to move it and it is running poorly cold . I do need to recheck it I may have knocked something loose yesterday.  

[Jsdirt]

Buying a harness isn't the way to go about that. You don't even want to know what that would cost, IF it's even available anymore (my guess would be NO on that one). If there's damage to wiring, you need to find and fix it.

 

Since it's running like crap, start with the basics. What's your fuel pressure? Might be time for a pump or filter if low.

[Supreme Pizza]

Out of curiosity, how much money do you have into replacing all of these parts that did not fix the problem?

 

Checking the codes: Free.

Diagnostic $150.

Throwing parts at it: $3,414.97.

 

If you need to save money, pull the thermostat out and drive it.

 

If you want to spend money, replace the engine, all the computers, and everything else you can find under the hood.