Well, I'm stumped. Please help me!
 

Hi guys,

I usually post over on CF, but I'm having an issue with my vette that I just can't seem to figure out. This is lengthy, but bear with me.

A couple of months ago, the car started not wanting to run when cold. It would die, buck, stall, hunt, etc. at idle. Once the car warmed up, it was much better, but not perfect. You'll get a couple of rare pops from the exhaust also. I discovered I had two leaky injectors, replaced them, no change.

I've thrown many new parts at it. Coolant temp. sensor, esc module, o2, injectors (needed those), IAC (needed that too). The engine in the car is only 2 years old. When it was first put together and tuned by tpis, the car ran flawlessly, so I can rule out the tune being the problem.

During base idle adjustment one day, I noticed that the car idled perfect with the electronic spark timing (est) wire disconnected. That leads me to believe there is no vacuum leak, fuel problem, internal problem, etc. Must have to do with timing. Took it to the mechanic, had him check timing. He said it was way advanced, set it to 10 btdc. No change.

Most recent discorvery: I had developed a knocking sound from the rear of the engine. Turns out one of the flywheel to T/C bolts had backed out. Maybe the knock sensor was picking up this knock and retarding timing? Put bolt back in (no damage to flywheel :) ) No change!

I'm left to three things as far as I'm concerned.

A. Harmonic balancer has slipped and timing isn't being set properly.
B. Bad ground in the esc circuit.
C. Something in the distributor is whack.

Its at another mechanics now, he's putting on some new valve covers and he's going to check the valve adjustment while in there. Don't think that'll change anything. He's also going to check timing, check vacuum, check the balancer, etc. Hopefully he finds something.

Not getting any check engine light, unless I run the car with the wire disconnected. The ecm appears to be functioning correctly though, it will throw a code for any sensor I unplug.

I'm getting a diacom setup for my laptop this week, maybe that'll show me something, not sure what could be causing that though.

This problem is :crazy: Any ideas? Anyone!

Here's my mod list to the car: tpis miniram III, gmpp fast burn heads, tpis solid roller cam, headers, forged 383 bottom end, 30lb bosch III injectors, custom 3" dual exhaust, gutted MAF, holley 58mm TB, air pump delete, and some drivetrain mods.

Help me please! :help:

Re: Well, I'm stumped. Please help me!
 

have you tried unplugging you maf sensor and see how it runs ....i had kinda the same problem no codes ..car ran like crap ..even hooked it up to one of those snap on scanners and it showed nothing wrong ...unplugged the maf sensor and ran perfect ....bought a new one and have had no problems since

Re: Well, I'm stumped. Please help me!
 

Yes I have. I think I've unplugged almost everything at least once to see what effect it had on the car. Unplugging the maf made it run terrible. The only thing that works is the timing wire, and then it runs very steady. Has some flat spots when trying to accelerate with the wire disconnected, but thats because the computer can't advance timing. It also runs very rich, wire plugged in or not.

Everything on the car is dead on, just need the spark to come at the right time.

You guys may see a thread titled "Miniram, fast burns, 383, solid roller, and more for sale!" if I can't get this thing straightened out.

Re: Well, I'm stumped. Please help me!
 

I also had the same symptoms as you were describing, ended up being a bad mass air flow sensor. It also threw no check engine light, but ran like crap. I replaced it, descreened it, and it was perfect. No issues at all

Re: Well, I'm stumped. Please help me!
 

It idled good with the est wire disconnected, but not with it connected too? My issue seems to point to the knock sensor, esc module, ecm, prom, distributor, or something else that controls timing.

I used to get a code 34 (maf low voltage), but it seemed to disappear over time. The other day, I got a code 33 (maf high voltage). Thats a thought. My maf has been descreened and gutted, but maybe the sensor has went. Although, unplugging the MAF makes the car run even worse, so I doubt thats were the problem lies.

Re: Well, I'm stumped. Please help me!
 

all good points. I definately look into the base timing. you need to verify what the ecm is seeing by getting a laptop and tunerpro rt or some other scanner and connecting to the ecm thru the aldl data port.

also solid rollers are typically louder than hydraulics and the knock sensor could be hearing that and pulling timing on and off, causing the car to hunt idle and stumble/stall. But if it ran fine awhile ago then its gotta be somethign else.

Could be a MAF problem but i'm not sure. I'd try timing first and then look to the MAF. I dont think its a ignition problem but you never know so thats one more thing to check.

Re: Well, I'm stumped. Please help me!
 

I remember a thread where someone was having a similar problem to yours, another member mentioned a ground wire somewhere close to or in the distributor, same scenario where he was throwing parts at it, and sure enogh cleaned and regrounded it and walha. check the esc ground.

Re: Well, I'm stumped. Please help me!
 

If you gutted your maf by cutting the cooling fins out ,you probably cooked the electronics in the maf.

Re: Well, I'm stumped. Please help me!
 

i was a little aggressive when i ported my MAF (removed heat sinks)and had issue similar to this, i ended up replacing it with another maf equally hogged out but retained the heat sinks car ran great. thing is CF has probably already told you to ck MAF. i would follow the flow chart in a chiltons or shop manual and check both those codes, i had a bad wire in MAF harness which was throwing both those codes, traced it back to about 2 ft section of bad wire in harness. my advice would be to grab the following : a manual, a test light, a volt meter, a friends stock MAF, a flash light, a schematic, some amstel light, and a weekend. when you figure it out reward your car with a proper flogging.

Re: Well, I'm stumped. Please help me!
 

Well, I already tested the maf the best I could with a voltmeter. It also runs badly when unplugged. The MAF has been gutted for 2 years, problem started 3 months ago.

A bad ground in the esc circuit really gets me thinking. I believe the timing is retarding, but unplugging the esc or knock sensor with the est plugged in gives me the same bad results.

The next two things I have planned are to check for balancer slippage and confirm timing with wire off and wire on (although all this has been done already). After that, I'm plugging in my new diacom setup to see what I'm getting from all the sensors, maybe I've just got something completely off. (like the knock sensor!)

I've got to check the wiring to the cts. Symptoms match cts all too well. Yet, I'm pretty sure the issue is a timing issue, nothing else.

Thanks for the help so far! I'm open to trying anything to fix this, or its getting parted out! :goodidea:

Any interest in some parts? :D

Re: Well, I'm stumped. Please help me!
 

Little update for y'alls.

The problem is now a cold start only problem, after warm, the car is running way smoother than it was before. Today, I tried to crank it up, it fired up, sputtered, died. Unplugged the MAF, fired and ran perfect, hmm...

Tomorrow, when it is completly cooled off, I will try starting with the maf unplugged again. If it runs good, looks like a new Mass air flow will be ordered. I did read that gutting the housing makes the sensor life shorter, but I need the airflow, so I think I'll just get a new sensor and slap it in my housing.

I'll let you guys know how it goes tomorrow.