Hi guys, I’m at my breaking point with This car.. So I LS swapped my 72 camaro about 8 years ago and for the first 6 years it ran like a scalded dog. Last year it developed this horrible closed loop miss, it feels and sounds like it’s running on 4 cylinders until you get it above 1500-1800 rpm then it seems to clean right up.

What’s really got me stumped is that it isn’t throwing any codes at all (GM pcm) I pulled all the plugs and they don’t really show anything either….

has anyone run into something like this before?

any help would be greatly appreciated!!

TIA, Scott.

 

I'm guessing since it's a swapped vehicle it's been tuned. I've seen more than once when "tooners" will turn off every DTC.

Do you have a way to datalog it?

 

ever change the o2s ?, they can go bad and cause problems just like you described . have also seen a stuck iac act like that. have also seen bad intake manifold gaskets do some wierd stuff. just some ideas for you.

 

no, I don’t think that’s possible with a factory pcm. But it did run fine for like 6 years.

 

For you to have it running in that car it was tuned at some point, atleast to turn the VATS off.

I'd put a scanner on it, see what's going on.

 

yes the pcm was flashed when I put it in to remove everything that wasn’t needed but I don’t think they did much more than that. And the scanner doesn’t show any codes at all.

 

I have been thinking about changing the 02 sensor I guess that would be the next logical thing g to replace. I have already replaced the IAC motor.

 

I agree with Kjduvallsounds just like a bad O2..... a data log would tell you in 2 seconds...

 

if it ran fine for that long then yeah there is something definitely going on. Do you have HPTuners or anything to datalog it?

 

Not for that set up.. I recently Ls swapped my 69 Chevelle and I’m running Holley Terminator X max on that one.. I can do whatever I want with that set up, but I don’t think I can access the GM pcm.

 

You need to look at your fuel trim and other live data to get the full picture. There is a bunch of different possibilities of what could be going wrong. If you don't have a live data scanner you can get one for pretty cheap. I had one called blue driver. Its just a bluetooth dongle that works with your phone.There are a bunch out there though, take your pick.