I've been having a snow ball effect of electrical issues as of late on my '96 LT-1. Started with the driver's door switch and hatch switch not working. Then the Oil Pressure gauge went loopy. Now the O2 heating element randomly doesn't work and the EGR keeps throwing a code as well. The latest two issues though are what makes me wonder about the ECU. The Instant gas milage calculations are way off, but I don't seem to be going threw gas that much more. The instant MPG is only showing 12-13 when it's normally 16-21 for my drive home. And I've also had trouble connecting my phone to the OBDII port, but I figured it was just my phone. I do need to try to connect it to my wife's car to see if I have any issues.

I've checked the ground on the bellhousing that almost all of these issues seem to have in common. It was dirty, but secure. So I unbolted it, cleaned it up, and tightened back down. Nothing.

I found a Delphi Reman Unit via RockAuto for a good price, but then I have to have it reprogrammed. Gotta find someone to do that...if it is indeed the ECU. The car does have a funky idle, but runs great at partial and wide-open throttle. Even did great at the last autocross.

Wow, when it rains it pours!

It sure sounds like an ECM/ECU. You're right on with checking the ground like you did. I'm not too familiar with the OBDII cars, but before you drop the dough on a new unit, have you tried disconnecting the negative battery cable for a while to reset the ECU? Leave it off for a few minutes, and maybe even try turning the ignition switch on and off a few times while the battery is disconnected, just to make sure there isn't any residual voltage still lurking somewhere. If there's at least SOME change when you restart the car after having the battery disconnected, that would likely narrow things down a bit closer to being the ECU.

"The car does have a funky idle but runs great at partial and wide-open throttle."

Man, if I had a dime for every time I've heard that from an LT1 owner. I'm beginning to think that's normal for all LT1s, mine included.

Ron

Thanks. I did disconnect the entire ECM from the car for a few hours over the weekend. Went ahead and disconnected the battery. Did notice the negative cable is a tad loose like its slightly stripped out on the side post. It's about due to be replaced anyway (right at three years old which my typical life span of a battery here in FL). Might look into a nice dry cell battery and go from there. Man, I wish that could cause all this madness!

Where in FL?

Do you store the car in a garage for long periods of time?

I would check the harness... this also sounds like a rodent attack. All it takes are the right few wires gnawed on and you are so screwed.

Clearwater/Tampa Bay Area. The car is outside all the time, no garage. Have been curious about that too. Sadly when my dad had the car, the engine harness had to be replaced due to rodents.

hm... lightning striking twice...

I would check those areas... and, if they replaced the harness, check where they did the fix... a bad connection and this becomes a problem.

I'm pretty sure they replaced the entire harness as it was the section behind the motor that was destroyed (had to be towed to the dealership and was still under warranty, so it's been well over 10 years). I inspected it as best I could when I checked the ground on the bellhousing, and I didn't notice anything obviously chewed up or loose. Looked like it was still nicely wrapped in the factory tape. I'll be getting under the car again this weekend and looking around. The car did sit a lot from August to Late December last year when I was chasing down an Opti issue.

check the O2 harness wires, make sure they didn't rest against the header or exhaust in some way.

Yep, checked that off the list already too. Bank 1 sensor 1 was reading weird before it all went haywire, so I replaced it with a new delphi unit, so I know it's good. Bank 2 looked good last time I checked when I did an oil change a few weeks ago. The CCM is in the same ground as a lot of these components so it's on the list of crap I may have to replace too. Damn I hate electronics.

The CCM would have no effect on engine operation, past starting the car.

Did you check the downstream O2s? 1996 has all 4.

Yep, back two are reading fine, and everything is tucked away nicely.

hm... ok...

thinking...

The code reader... that makes me think... perhaps you are right. The ECU has a set of UARTs (chips - Universal Asynchronous Receive Transmit). These manage communications. If they are failing, that might have an effect.

Yeah, I need to check it on my wife's car. I still think its the phone, but you never know. The obdII app has certainly never acted like this before. Hmm, I should try hooking up my hypertech power programmer and see if resetting back to factory does anything, or if it has problems connecting.

that would be a good test. Anything to see if it behaves differently.

Will be hooking that up tonight to check as I want to be able to drive the car to work tomorrow for Drive your Vette to work day!

Quote:

Friday the 28th is "Drive your Vette to work" day?! I had no clue.

And of course, I work from home on Fridays.

I drive mine every day...

Yep, closest friday to June 30th, the official Birthday of the Corvette.

Powerprogrammer connected just fine. Went ahead and reset the computer to factory specs...just in case things really go haywire. Will drive it tomorrow and see if it did anything. You never know, but I'm not expecting miracles.

One thing I did remember, the exhaust shop managed to cut a few wires on the trans harness, but it's been over three years. I'll check that this weekend to see if something is loose. The 4L60E seems to be running just fine though.

Keep us posted!!!

Running like hell today. Crossing my fingers I find a loose wire in the trans harness this weekend. Sure would make my day to find something obvious. This damn car has way too much crap intertwined within its self. May have to sell it and just get a suburban. I love the car, but really getting tired of always working on it.

Checked codes today. Bank 2 sensor 1 and 2 codes. So I ordered up three new o2 sensors as it looks like they are all going out at once. Also ordered up a new EGR purge valve from rock auto while I was at it. Previously, the ses light was for the EGR purge valve and bank 1 sensor 1 o2. So far, just looks like crappy timing. Going to pick up a diehard battery today. $45 off their platinum batteries today and found a $5 coupon! Hope to get the sensor in on Wednesday and install on Thursday and Friday. Just in time for my next autocross on Sunday!

I sure hope that fixes it... if not, you are in for a new ECM, I am afraid, or else there is something really wrong with the harness.

Question, does the poor running start after driving a bit or is it instant?

It's intermittent. Ran great on the way home. Figured I'd start with what the codes are calling for, and I know the bank 2 sensors haven't Ben replaced in quite some time. So I'm sure they are due anyway.

Got a Die Hard Platinum battery installed yesterday. Now just waiting on the O2 sensors and a couple of EGR pieces before taking the time to fire her up. PKE sure was working better afterwards though.

So far, fix the older, potential issues. Need to be done anyway, good move.

Replaced the EGR valves on top of the intake (not the big one) and all four O2 sensors. Ran great for a few miles, then all of a sudden started missing at low RPM. Seems to run fine at higher RPMs. The SES light that an O2 Sensor is out. Haven't gotten to see which one(s) yet. I do know I plugged them all in though.

Still having major issues connecting my OBDII reader though. It does get power for sure, but the app isn't working. Worked fine on my wife's hyundai, but the power-programmer seemed to read just fine when I set it back to stock (just in case the ECU just up and fails on me). Going to try it on my new truck and see if it takes a while.

So just incase I got some water remover gas treatment. Haven't driven it since saturday evening, but I seriously doubt that's the problem. I'm still pretty sure it's in the electrical system somewhere.

Might be getting to the end of my rope with this car. God I don't want to sell it...mainly because I know I'm only going to get peanuts for it. Much less for how much I love driving it, when it works.

This line: "Replaced the EGR valves on top of the intake (not the big one)"

What are you referring to? There is only one EGR valve, and it's on the back of the intake... large black thing.

PCV? That's Positive Crankcase Ventilation. That sucks in the nasty gasses within the engine block and burns them off. But there is only one...

Can you put a vacuum tester on the EGR?

Ah, it was the EGR Vacuum Solenoid and the EGR Solenoid Valve. Had to look them up on rockauto.com to remember what they were called. Those codes haven't come back...yet.

Haven't had time to mess with her lately. Going to crawl under the car tonight to check out a few connections. After replacing all the O2 sensors, I got a SES light again with one of the sensors throwing a code. Of course I don't remember which one and my code reader isn't working on GM cars for some reason. Awesome. Going to give the car a shakedown at an endurocross (multi-lap autocross) on saturday. Might be our last hurrah as I'm considering getting rid of this torn in my side of a car. Will be sad to see her go, but would be nice to keep some money in the pocket. Going to lose my ass in the Van Steel suspension I just put on the car. Damn it!

Car ran great today, until I finished my first run (4 lap autocross, about 3.5 minutes total) and my car was at a VERY unusually hot 240degrees. She normally runs about 210 in the summer at an autocross. Turned the A/C on and still no fans. Fuses and relays all check out ok. And since the 96 fans are controlled by the ECU....

Mis-routed - not properly secured - spark plug wires grounding out, will emit EMI - same as a nuke. So says FSM.

Solid-state electronics don't like that. Makes for a bad day.

Well, i'm an idiot. Could have sworn the fuse was ok, but the fan and O2 sensor fuses were blown. Been pouring raining, so haven't had a chance to replace them and see if they blow again yet. Once the fans are running again, she'll go to my electrical guru and have him check out the oil pressure gauge and door switch ground. Then we'll see how she goes! I think she's telling me to get her a garage. LOL