This is a new startup in a '95 Camaro. LQ4 SBE, L92's cleaned up, EPS custom cam to marginally pass Md emissions. Takeoff LS3 intake & injectors.

Long time coming but I finally got it together to try a startup. I didn't even have coolant in it yet but just wanted to see if the engine would even turn over. To my surprise it fired up immediately. I only let it run 15 seconds cause I had no coolant in it yet. Grabbed my phone to take that 15 second video....fired it up again. I danced around the garage it sounded SO GOOD and idled smooth as butter. I still couldn't believe it. Knew I had loose ends to tie up. Started again the next day just so my son could hear, and I noticed right away something was different. It started running rough and severe backfire. Shut it off and assumed all the threads I read about not running with open headers were true....days later, coolant in, exhaust on. Fired up again and only getting worse. Bought a used EFI live and tried to log. Car wouldn't even go above 3-400 rpm. Just constant backfire running rough. So, I'm thinking fouled plugs. 1, 3, 5, 7 are probably ok looking. 2 & 4 are black as night. Not wet, just black you can wipe right off. 6 looks better than the odd side and I just didn't take the time to get #8 out. Put 2 new plugs in cyl 2 & 4. Got my laptop set up and logged and fired it up. NO change in the roughness but was able to get rpm around 2000 to keep it from backfiring. Once it went CL the LTFT on bank2 went to 25%. Bank1 at 12%.
Did I cause all this by running with open headers for a 60-90 second total timeframe?
If so, why wouldn't all the plugs looked fouled? And since it pretty much wipes right off am I correct to assume its NOT oil fouled?

Forgot to add the PCM went to EPS also. He tuned on the bench for this combination.

 

Ok. What I'd do is turn off ltft and then after writing the tune, connect with scanner and reset the fuel trims. After you get your exhaust on, you can re enable if you like. That'll at least get you able to diagnose other stuff.

Your O2 sensors are seeing fresh air and don't know that it's from open headers.

 

Thanks for the quick reply sam...I mean darth...
I put the exhaust on before trying this again. It still stumbled and backfired really bad so I changed the plugs. I've been messing with these all afternoon. I'm starting to lean towards 2 & 4 being oily.

Turn off LTFT? I've never flashed the PCM. Probably should save the current one somewhere first I guess

 

saved the config...and see where to disable the LTFT...

 

saved the config...and see where to disable the LTFT...

The car is missing really bad and backfiring even with new plugs and before the LTFT were kicking in. I don't think I ever ran the car long enough to warm up enough to go in to CL. Does the PCM learn that fast while in OL?

 

What PCM are you using? Is injector data correct?

 

0411
It was set up by Geoff at EPS. So I would certainly think so.
They're stock 42(?) from a 5th gen.
I'll see if I can find the data and compare

 

If you need to run with open headers just unplug the O2 sensors.

 

Thanks.
wasn't planning to run open headers, just start it a few times.
I killed the battery messing with it all day.
Still can't find a reason for only 2 plugs being so black.
I did check compression real quick on front 2 cylinders. They were comparable.
Swapped coil & wire also. No change to 1 or 2. Still black on #2 plug.
Put my fuel gauge on, I'm using the corvette filter regulator deal but its 58.
Anyone know where I can monitor battery voltage in EFIlive?

 

Lmfao!!!

To disable them, in the closed loop part of the tune set ltft enable temp really high. You can do the same for the closed loop enable temps and that will stop any fuel trimming

 

Hmm, ok. I found DISABLE LTFT in Fuel>trims>parameters
Is that not the right place?

ALso, just to clarify in my own mind...since I run the engine already, nothing will change in the original "tune" that was put on the PCM from the tuner correct? So by reflashing it, it will be just like the first day I started the car, sans any changes I make like disabling LTFT correct?

 

Ok, assuming you downloaded the tune as a baseline to work from, when you reflash the tune it'll be just like when the tuner first loaded it. If you change the ltft in the tune and write it, it'll run like the tuner set it up but without any ltft.

But yes, you are in the correct place in the tune.

After you flash the tune, in the scanner 2-way controls, zero the fuel trims just to make sure.

 

Sorry to keep on this same point I know you're busy with the new Afcos, but just to make sure I'm clear...
Yes, I did save the tune yesterday.... So after the cars been running and started running bad.
But what you're saying is, the learning it did over this period will all be reset when I reload the tune right?
cause I didn't save it till yesterday.

 

Exactly.

 

My +25 issue was related to pcv being always open.

 

checked pcv again to be sure ... passenger side cover is plugged. Drivers side to TB. small loop hose from LS6 cover to intake. Should be good.

fresh plugs, disabled LTFT, reset fuel trims in the DVT.
No change to the way it runs. Missing bad and severe pop out the exhaust. Only ran about 20 seconds before it died. Very hard to restart.

Couple things...

Since the engine fired originally and ran smooth for a couple minutes does that rule out me needing to perform a case relearn? This PCM has never run this engine.

Since it didn't run long I can't really see a difference in what the plugs look like, but the past ones with cylinder 2 & 4 being black, could I have those 2 injectors sticking flooding those plugs?

And lastly, it looks like I have a MAF problem too. I just noticed on this scan there's no reading g/s from the MAF.
edit:looked at that again and it does slightly move, maybe 4 g/s during this run. The previous scans at about 2100rpm , its at 37g/s.

 

Mind posting the tune?

 

Absolutely will...soon as I figure out how

 

Damn, it's efilive. I have the HPTuners...

Try this. Go to the first cell in you maf curve and set it to 15 g/sec. Then, unplug the maf and write the tune. If the maf is only reading 4 g/sec, it could be screwing with you or you have a severe vacuum leak. Either way, going to SD will at least get it running so you can diagnose.

Edit - for only running 20 seconds, if it was flooding plugs would be wet

 

yeah that's what I'm thinking too. I need to find a way to keep it running and check that coils are all firing. Maybe my timing light has long enough leads to clamp on each and sit in the seat at the same time lol..

I think it was only reading the 4g/s because it was barely running. Other scans did show movement there.

Generally speaking, what causes any engine to pop so severe out the exhaust...bad A/F mixture, bad gas, timing?