My dad and I have been trying to fix his car for a year now, on and off. It started when he was driving home from a car show on a really hot summer day. The car started missing and he had to keep the RPMs up to keep it running. It eventually flooded and stalled. Around that same time, my dad's car started backfiring/popping as he backed off the gas after accelerating.

At some point in time early in the troubleshooting, we discovered that if the MAF was unplugged that the car wouldn't run at all - that struck us odd because I know my 1994 Camaro, cammed with an open loop tune, will run without the MAF plugged in. His wouldn't even start with the MAF unplugged. So we thought something might have been awry with the PCM.

We ended up having our tuner reflash the PCM and drove the 30-something miles home. It popped the whole way home, but we were told one of the O2s looked laggy and we might have an exhaust leak.

We replaced the one O2, that didn't fix it. We couldn't find any signs of an exhaust leak; all of the header bolts are tight. We tried swapping MAFs and ICMs to no luck. We pulled a few of the easier-to-access spark plugs and they were nice toast colored, not showing signs of lean or rich combustion.

We started datalogging using DataMaster and TunerPro RT and noticed split BLMs pointing to an issue with the right bank. We couldn't find any true source for it, so again we started wondering if something was wrong with the PCM. I read Gregrob's tutorial on using TunerPro RT and WinFlash and was able to download my dad's tune to my computer and look at it in TunerPro - it looked all weird - like the injector flow rate being 730+ lbs per hour and a cylinder volume of 0. The fuel per cylinder table (can't remember the right name) had cylinder 7 at 0.07.

I found a stock tune online, turned off the EGR/EVAP/AIR/etc and uploaded it back to the PCM. Immediately the popping was gone but after running for about 30 minutes we were able to capture in the datalog the same incident a year ago when his car started acting up and stalled. We watched as the short term fuel trims climbed steadily up (lean condition) and the injector BPW climbed from 3 to 8, flooding the car and causing it to stall. It was at this time we finally succumbed that it was probably the optispark.

This past weekend we changed the optispark and the blaster coil (my dad didn't believe me when I told him it was important to get it out of the way and he broke the coil plug off with his ratchet). Fired the car up and it sounded good, no popping. Once the car got to operating temperature it went into closed loop but the short term fuel trims immediately started climbing (lean condition). This time, though, the injectors stayed steady at 3.5BPW. The car didn't flood, it reached 194 INTs and triggered lean o2 codes and kicked back to open loop, recovering before stalling.

We're completely stumped. Later tonight I can upload TunerPro datalogs (XDL format) for people to review.

What we've replaced or swapped:
MAF
ICM
Blaster Coil
IAT
PCM
Tune
Both heated O2 sensors

What we have ruled out:
MAP sensor - MAP readings in comparison to BAR look OK in the datalog
TPS sensor - looks OK in datalog

What we haven't tested/checked:
Spark plugs
Fuel Pump


Aside from plugs and fuel pump, does anyone have any other ideas of what we could check? My dad's headers have a lot of surface rust, is it possible that the rust ate through the headers to make enough pin-sized holes to cause such a lean condition on BOTH banks? We've examined the headers and don't see any holes.

 

Have you checked the fuel pressure regulator?

 

Also, I thought Satan's Camaro was a 72 lol.

 

Haven't yet, but I'll add it to the list for tomorrow. To be honest prior to swapping the optispark this past weekend we never would have thought it was a fuel related issue aside from too much of it killing the engine. We actually had to change the oil after we replaced the optispark because we could smell gas in the oil - sure enough when we drained the oil there was more than 6 quarts of fluid that came out.

Anyway - now with the current conditions it's definitely something for us to check. Tomorrow when we get a fuel pressure tester from a buddy I'll check the regulator as well.

 

All you have to do for the fpr is to pull the vacuum line off it. It's a very thin line that goes from the passenger side of the intake to the fpr at the back. Pull it off and check for fuel coming out of it or a fuel smell. Either of those is an indicator of a bad fpr.

 

Yeah I know - the car is at my dad's house so I'm at his mercy on whether or not he's willing to check it - it's his own car, but he's been kind of disgusted with all the problems. I already left him a message to call me since it's so easy to check, but I haven't heard back from him. I'd love for it to be that. At this point it seems like it has to be something simple that we've overlooked -- I was so happy yesterday when I saw in the datalog that the IAT was reading 85* when it was only 50* out. We rushed to the parts store to buy a new IAT thinking that HAD to be the problem only to plug in the new IAT and get the same damn reading - didn't realize the air being sucked into a car on jack stands in a garage could be that much warmer compared to ambient temps.

 

check fuel pump.. mine was doing this awhile ago... had to have it floor board just to drive 55 and it was back fire like crazy once i took my foot off gas it would just die
replace your fuel pump also might have faulty injectors too might as well replace those as well

 

Bummer - called my dad again and he pulled the FPR vacuum line out. Granted the car has been sitting for a day so he said it wasn't wet with gas, but my dad took it to my mom to smell it and she doesn't smell any gas at all.

Tomorrow's tasks are fuel pressure tester and also to take starter fluid and spray it around the engine bay to see if we can spot any leaks that could be sucking in unmetered air.

 

Power is sent directly to the fuel injectors. The PCM grounds the other side of the injector as it needs.

When I had my '94, I had an intermittent ground in the harness from one injector to the PCM. This will dump fuel.

There's a way to test the injectors with a GM Tech 2. You'll also need a fuel pressure gauge. Through the tech tool, you can cycle the fuel pump on. Watch the gauge, confirm the pressure is correct and holds. Then you can do a test on each injector, one at a time. After each one, cycle the pump back on. Each injector should reduce the pressure by about the same amount.

http://www.ntxtools.com/network-tool.../OTC-3628.html

 

Thank god - only 3500! There's no way we can do that. We'll be checking the fuel pressure tomorrow.

I also forgot to mention we had the fuel injectors themselves all flow tested and calibrated because we originally thought the popping/backfiring was a leaky injector.

 

OK cool, you had them tested.

I had included the link so you could see the tool. Most better shops have it, you just gotta get them to do all the tests.

That's actually a good price, they go for over four grand.

Good luck with the fix! Every LT1 car has a little Satin in it.

 

For anyone with TunerPro that's interested in looking at the datalog:
http://www.meissenation.com/datamast...riginalPCM.xdl

 

Hmmm, I just caught this. Testing the injectors outside the car does not confirm the wiring harnesses.

 

Yes I realize that. Tomorrow we'll have a fuel pressure tester at our disposal so we'll check that and my dad was wanting to replace the fuel filter regardless of the results of the test. We'll also have starter fluid to spray around to see if there's any leaks letting unmetered air in.

If neither of those tests yield any results, we'll find a shop with a tech2 that can help us. Someone on my forum mentioned that if you hold a screwdriver against the injector you can hear it "clicking" as it fires. I don't know if that'd really work since it'd be clicking so fast, but is that worth a shot in lieu of the tech2? Just trying to stick to tests we can do in our garage at this point since it's up on jackstands for easy access to the under carriage.

 

How are all the plugs for the opti including the one into the unit itself? Any weirdness, corrosion, burned pins, etc?

 

A bad ECT in the waterpump will cause the car to run rich and backfire/be barely driveable if it is bad enough.

 

Here's the guide for testing the ECT in an LT1.

http://shbox.com/1/4th_gen_tech2.html#ect

 

Thanks for all the responses guys - I really appreciate it! All the ideas help us narrow in on what it can or can't be. It can't be the ECT because we're watching the data log and the temperature signal the ECT is sending to the PCM shows up in the data logs - it's in line with the gauge cluster's temp gauge. Plus we replaced the waterpump unit as a whole when we replaced the optispark as a maintenance precaution.

The wires going into the opti looked good as far as I could tell - the wire going from the optispark to the blaster coil is brand new.

 

Well we know the problem is when it's in closed loop. That means IAT, MAF, or O2s. I'd check the wiring from the IAT to the PCM, judging on the computer reading 83* when it's 50* outside.

Also, couldn't you just spray starter fluid on the headers to see if they're sucking in air like w/ other exhaust leaks?

 

Yes, we call it the Optispark