Okay, I've replaced plugs, wires, and HEI distributor cap. I'm beginning to think that ignition isn't the problem, but everything about the way the car is acting points in that direction.

The problem is either time, or heat related. The car seems to run great for about two to three minutes after startup, or until it hits around 180 degrees. Then it immediately stumbles...hard. It will randomly fire about every second or so (but not like clockwork) until it finally dies completely out a few seconds later. This symptom comes on instantly. A moment ago I cranked the car and spun around the block. I was getting full power until about 3/4 the way around the block then boooomp............booomp............... ...booomp........ dead. I'll let it sit for 20 minutes then I'll be able to crank it and pull it back into the driveway.

When I replaced the distributor cap/coil (Hypertech Street-Strip unit) the metal tab on top of the rotor had a huge hole worn in the center and seemed practically destroyed. It seemed obvious that this was my problem! I suppose not.

The only thing of the entire ignition that I haven't replaced is the MSD-6AL unit. Is there any way that a bad MSD would cause the car to completely die cold like this? Shouldn't the car run regardless even without the amps from the MSD since it has a new cap/rotor/coil unit in place now?

I can't imagine this being fuel since the car goes from full power to dead cold with no bog at all. I don't want to buy (and wait for) a new MSD unit if the one I have isn't malfunctioning. Car's been down for two weeks now so any advice at this point would be priceless! Thanks,

Rome

 

A timing light will tell if it's an ignition problem.

But it sounds a lot like my bad MAF problem. Try to substitute the MAF from another Vette or a 3rd Gen F-body.

 

That's kind of a trick, because my car was not equipped with a MAF sensor when I bought it :/ I'm really not sure how it compensates for the fact that there is no MAF tube. I'm curious, how exactly would the MAF have caused the symptoms I described?

 

Hmm, no MAF; does it have a MAP then?

When my MAF died the engine would start but soon as it went closed loop is would surge and die out, without throwing a MAF code.

 

I've searched my Helms manual exhaustively and can't find any info on the MAP sensor. Throw me a bone on where I can find it (on the manifold no doubt) and I'll see if its still operable.

Is there any chance a faulty MSD-6AL unit could cause these symptoms?

I played hell replacing electronic ignition modules on my previous car. Symptoms were vaguely similar. I'm going to try replacing the module on the distributor tomorrow to see if it clears up the problem.

Did I mention that my car had a mild case of its current symptoms back in Spring? After the car sat for a while it cleared up. All I did back then was shake the hell out of the harness where it runs underneath the throttle body (not sure if that's what cleared it up or not). The moments when this trouble has reared its head have been very intermitent making it hard to narrow down the source of the problem. The fact that the rotor in my distributor was quiteleads me to believe it's not just a harness problem. These damn gremlins finally have me dead parked, and I'm starting to believe this is going to take alot of time & money to solve. :mad

 

Just replaced the ignition module and the car cranked and ran like a top!......up until it reached 180 degrees where it stumbled, crapped out, and shut down as usual. :rolleyes:

This has got to be an electronic problem judging from the way the symptoms come on so immediately. The car goes runs perfectly from startup, then just seems to "short out" and die around 180 degrees. Any chance that fuel flow or maybe the injectors could be affected in a way that would cause a shutdown to come on like this?

Last time I had it to the shop (for idling problem diagnosis) the technician was unable to get a diagnostic reading via the serial port. The car came with a laptop programmable CALMAP computer installed under the passenger's seat which is a nifty item, but I have no idea to what degree it replaces the stock ECM. I'm thinking that this system surely can't be bypassing the stock ECM completely, to the point where the diagnostic port wouldn't work at all. The guy could have been mistaken I suppose since it took him all of 30 seconds to conclude that he was getting no readings from the port and to move on. His findings are the reason I've yet to buy a diagnostic computer to check for codes.

Limbo-ville here in Louisiana. Any tips to further me along towards a possible remedy would be super. Thanks :)

Rome

 

Rome-

Yeah, since the MSD takes complete control over the ignition signal, if it freaks out then the car doesn't run. Try unplugging the unit and running without it.

 

I had similair problems with my 90, once up to temp it would hunt and stall as i slowed down at juctions the run fine for a bit and then just die on me until it cooled down. also the egr valve would open and cause it to run rough once warn etc etc etc. It turned out to be the ECM after i had changed all the wires,plugs,cap and rota etc cost me $90 for an exchange and its ran fine ever since. It got worse over time and was intermitent so you could never pin it down.

its worth checking if you can borrow someone elses

:cheers:

 

Ran the car without the MSD and got the same problem so I placed an order for a new ECM. I feel fairly confident that the ECM is the culprit now. At least I know the car's ignition system as I've practically replaced the entire setup :) The only electronic factor left unprobed is the Electronic Control Module AFAIK which prett much makes it a shoe-in as the source of the problem.

BTW, can anyone tell me whether the internal ignition module in the distributor is bypassed when the MSD is used? Just curious if I replaced a part that isn't even active in the system. Thanks for the help!

Rome

 

maybe a shot in the dark, but if it were me, i would change the fuel filter and maybe the pump! can you hear the pump whine when you first turn the key as it primes the lines? if so, i would replace the fuel filter, if NOT, then the pump might be the culprit....my guess is the ECM is NOT the problem, as i thought the same thing on mine, $80 later, that didn't fix it, and ECMs are exchange, so i couldn't sneak it back for a refund! :crazy:

 

Would it be possible to use a fuel pressure gauge to determine if the pump or filter is the culprit? If the fuel is being delivered properly then constant pressure should exist before and after the problem occurs, correct?

The only reason I don't think its the fuel system is that the car runs STRONG right up until it dies, and it always dies at the very moment it reaches proper operating temperature (180 - 190 degrees). Up until that very moment I have no problem breaking the tires loose, and there's no 'bogging' as I might expect if the fuel flow was restricted.

Since the fuel pump is in the very back well away from any heat source, I can't imagine how it could tie in to the manner in which the symptoms come on. The fuel pump is a high flow unit installed by the previous owners 20K miles ago. The problem will come on the exact same way whether I'm hanging corners or sitting in the driveway.

I'm going to AutoZone for a fuel pressure gauge right now to eliminate the possibility of fuel starvation.