Random misfire in closed loop
 

Car is the blue Z28 that was at the Oct meet this weekend.

224/228 cam and longtube headers on a 2001 camaro z28. Its running an off road y pipe with no down stream O2 sensors for after cat, seeing there are none. Newly replaced spark plug wires, spark plugs gapped to .050 and replaced fuel filter. Deleted the air injection system. Car runs fine in open loop holds idle at about 800 rpm and as soon as vehicle gets to operating temp its bucks and misfires and ses light flashes.

Code PO300 is what its reading and replaced the front 02 sensors with brand new gm corvette o2 sensors.

Car has pcm4less tune.

It bucks and misfires real bad at part throttle once this happens. I experienced it after the meet. Mainly between 1500-3000 rpm.

Can he datalog the car when the issue occurs? Does it feel like an ignition miss?

Have to look at the tune, the 02's(have had issues with the 13111's from Bosch) What plugs? Thats a larger gap than I normally run...

Maybe check to make sure the AIR stuff is not leaking and letting air in to throw off the A/F ratio. I have the Diablosport Predator which can monitor the O2 readings to see if they show a strange ratio. I've seen the rough idle on a car with a cracked PCV hose letting air in and throwing off the A/F so check all the hoses and AIR block off plates/gaskets. P0300 is the multiple misfire I think so that could be coils on one whole side or vacuum leak across all cylinders. A scanner might pinpoint 1 or 2 cylinders prior to the P0300.

It bucks pretty bad when it happens. The P0300 code went away with the tuen, and now it just get the 02 sensors code for insufficient switching.

They are Bosch sensors and NGK plugs.

AIR isn't leaking.

I told him to post the data log today.

Did this just happen out of the blue or right after the mods?

Happened after LTs aka 2 weeks ago. ORY, different catback, vette 02s and a new maf were installed the same day. Cam was installed over the summer. No problems until the recent round of installations.

Wait.

Were the headers brand new and coated? Did he replace the O2s after burn-in?

Leading to this as well. I would do the following.

- reinstall old MAF
- reinstall old O2 sensors if they were in good shape
- remove, re-gap and install plugs.

Edit - check the wiring for the O2s for any breaks or w/e. If you buy new O2s, just go with AC Delcos.

Do each of those at a time to isolate the variables.

Here's the log. Will update the post as I hear back about your questions.

New 02s were put in when the headers went in. Headers were brand new stainless, uncoated.

The new headers still have a light protective oily coating sprayed on them to protect them during shipping and storage. When installing new headers it is generally recommended to buy new O2s, but reinstall the old ones to use for a few days or so until the coating is burned off of the new headers. That stuff will kill O2s pretty quick, so that could very well be the issue.

- Justin

Would the coating have burned off truly immediately? This first happened when he went to drive home directly from the install. Regardless he's going to try it.

AFAIK the coating will start to burn off as soon as the headers start to really heat up. Not sure how soon effects will be seen on the O2s.

- Justin

No. The headers do not instantly get up to the temperature where stuff like oil, excess coating, and paint burns off. Usually it's all gone after a few heat cycles.

It may have taken a little bit for the stuff inside to get warm and start heading through the exhaust stream.

Plus, Bosch O2s are known for being dicey in quality and are also much more fragile. AC Delco or Denso only in my opinion.

What type of file is that, Windows XP doesn't identify it to open it.

Thats where I would start...thats just me...

It's an HP Tuners Log file.

- Justin

And what can you view that with?

HP Tuners :lol:

I haven't found anything else.

Nick, can he save it as a .csv file or text file?

Hmm. And He's reusing one Bosch 02 that were on his shorty headers, and ordered one new Denso. :shrug:

See above. I told him.

I asked if he can.

I will try and take a look at the file tonight. Why is he only buying one sensor?

They lost one of the ones that were on the old headers, so he had one left. The bosch that had worked fine before it was taken out. I know :-?

New 02s alone didn't fix it. Still getting insufficient switching on DS 02. Still stuttering in gear even when motor is cold.

What brand headers? The heaters may not be working optimal...

How are the O2 wires? Anything burnt or broken?