I just got his car a week or two ago and it's already giving me some problems. It's a slightly modded 95 Z28 (OBD1) M6 First things first....at cold start it idles low and doesn't fun very smooth. I usually let it sit for about 3 or 4 minutes before leaving the lot. Within 2 miles of driving I'm already at or a little over 175 as far as the change says.
After getting warmed up....I get some spark knock when completely in gear and under 2k when I put any throttle more than 1/8. I can usually keep it from happening if I slip the clutch till it's higher in the RPMs. This happens in every gear....anytime i'm totally in gear and under 2k.
I have a intermitent Service Engine light. Can't really nail down what makes it go on and off. Sometimes it'll be on the whole time i'm in the car, and sometimes it'll come on for 5 and stay off for 5 and back and forth. Lately I've also noticed the low coolant light come on and off. Mostly is on when the engine is cold, but will come on then off while hot too. Today I checked the coolant while hot, and found the radiator full (overflowing when trying to take cap off) and the overflow was full as well. I only checked the overflow with the dipstick, so as long as they are accurate my coolant is fine.

Mods are as follows....
K&N CAI
borla catback
Cam...not for sure which one, but I was able to talk to the mechanic who did the job and he claims it's a comp cam and is the highest one without computer tuning. Not sure about that though, cause I'm starting to think it might need tuned because of the cam. The guy I bought it from says it's had problems like this ever since the engine got rebuilt and cam put in.
Forged pistons...not sure brand and compression ratio, but I assume stock compression since it was built for nitrous

That's all I know about....

What do you guys think?
Ryan

 

Make sure you bleed it very very good. I use my elec water pump to bleed my system. I bled it for about 10 minutes after I notice no more coming out. I drove it the next day, and it was low on coolant, I had to adout about a 6 to 8 ounces of coolant more. That might cause a low level if there is an air bubble flowing past the sensor.

Z

 

A nice flush/bleed was the first thing i was going to do, and thanks for the input.

My major concern though is the spark knock...i should add too that the car doesn't feel as fast as it should be, like it's retarding the timing all the way through the powerband. I'll have a scanner on it this weekend and hopefully find the problem, but was hoping to get some suspect issues that are common amoung LT1's.

Ryan

 

Yeah, low coolant won't cause low power. I don't know if you have access to a laptop, you could try downloading datamaster. That scanner works very well. Other then trying the usual tuneup issues, sorry I can't help more. False knock might be a culprit as to why it seems like its pulling timing. Thats not very uncommon. Goodluck

Z

 

There is very definate, very audible spark knock when "totally in gear and under 2000 RPMs". My buddy is big into his turbo car and has stand alone fuel...he's got a great ear for spark knock. He thinks he hears a little spark knock when I'm WOT and up in the RPMs (4-5k+). I can't hear it up there, but I didn't notice it at first.
The time it's most audible is if I let the skip shift activate....and then give it ANY type of throttle after getting it in gear.

Ryan

 

I'll still need a cable to use those free scanmaster software...I'll be using a Tech 2 on it this weekend, so we'll see what happens.

Ryan

 

Yeah dude it has happenned to me more then a few times, it is more than likely a burnt plug wire or a fouled plug. If like you say, accelerating from a lower gear than normal and it vibrates and then cleans up after you get some rpms. I'd guess around 2500-3000 rpms, you can't hardly notice the miss.

A similar past situation that has happenned to me, I changed plugs and wires, and still had the same problem. I was stubborn to beleive that it was something else. Well a friend talked me into changing out plugs/wires again, and it worked. I can't explain why or how, but it worked the second time. I'm not saying it could happen to you, but I wouldn't rule it out. Opti's are expensive, so I'd try that before changing the opti spark. I'd try new coil also before that too.

GL:

Z

 

Well, I would get the car scanned. At least at the local auto parts store to see what the SES is tripping for. Also, put some high octane gas in it and see if it still knocks. No octane booster, unleaded race gas. Get a scanner on that thing and drive it, sounds as if the PCM is pulling timing due to knock, but not enough. Also, your Knock sensor may be bad.

 

Yeah definately put some 93 or so octane fuel in there, it can't hurt anything. I have actually felt mine retard the timing, because the car bogs down momentarily, you can sure tell it. When the gas prices went up here recently it was like $2.49 for 93, so I thought I'd try some 89.....and that's when I felt the timing retarded. I'm going back to Premium!

 

Definitely check the plugs and wires first.. A scanner will only help if the car is throwing codes.

 

Today I got my 1LE intake elbow in the mail. The owner had told me there was a vaccume leak....so i ordered this one. It's a brand new piece with a new intake air temp sensor. After putting it on and driving it about 4-5 miles the SES went off and stayed off. I stopped completly....went from a stop and let the skip shift put me into 4th. Normally this make major spark knock cause of wrong gear/low RPM, but this time it didn't knock. So the rest of the way down the street I tore into it....got it up to 5k in each gear. The SES light came back on, and the spark knock came back in low RPM. The rest of the day I tested my theory. Everytime the SES light IS on it will knock...when the light is NOT on it won't knock.
I'm thinking some sensor is bad, or I have some type of vacume leak. I also think the air temp sensor was bad, but wasn't the only problem.

ryan

 

Ok, got the Tech 2 on it today and it's throwin four codes....

0013 Bank 1 HO2S Circuit

0032 EGR system

0034 MAP sensor Circut Low

High Res. Pulse Circut

Then i checked the data section and found this relating to the problems....

Bank 1 O2 reads 350-400 at idle....while
Bank 2 O2 reads 800-900 at ilde

Two readings for the MAP sensor
11 KPa
0.02-0.04 volts

My first guess is that I need a Bank 1 O2 sensor and a MAP sensor...the EGR can kiss my *** cause it's coming off anyway. The last one i'm not sure about though. Anyone know what that means?

Ryan

 

High res. pulse is the optispark.

Replace the MAP sensor, its right on top of the intake.

Maybe need an o2 sensor.

Or maybe the PCM has issues, thats alot of unrelated codes at once.

 

does this code mean i need to replace the opti?

 

Sorry for the late reply. If you haven't fixed your problem yet, and still have access to a scanner, make sure you reset the computer and see if the same codes are popping. I just scanned mine last weekend and had 5 codes popping. I reset the computer, and rescanned and only had one code pop up. I had already fixxed the other problems referring to the other previous codes, but they were still saved in the computer.

Z