After a refuel one day the vette died about 30sec after start up at the pump... ever since then its had a number of problems ranging from dieing on the road and stumbling at stop signs to now being hard to start and having a rough idle, but not dieing anymore, lol. I first thought it could have been bad gas since it happened at the pump so I put an octane booster in to no effect, water remover didnt help either; it would back fire sometimes on acceleration at first but hasnt done that in a while.

It's a 94 LT1 automatic with an MSD ignition, the check engine light comes on sometimes but I dont know what codes it might be sending, it does sometimes start right up and if it does there's no engine lights on. and it's had a couple tanks of fuel ran through it since this all started (daily driver).

It's also quite cold right now (20's-30's °F) in case maybe there's a cold start or something that could be failing

 

well I just got through with starting problems and it landed up being my ICM that was bad but your problems sound like an opti. Guys will chime in pretty fast and help you with some things you can check to see if its certain parts. But I would check your fuel pressure and see if you have spark first at your coil, then if you do go to your spark plug wires and check there. make sure you check fuses. Its hard because it could be 100 things but you will figure it out

 

Thanks Guzz

All i have atm is a multimeter but it gets spark and addiquate fuel press, most of the time, cause once it starts (it does start) it runs fine except for being cold (other thread) and a rough idle (also intermitend).... apparontly only randomly does it die on the road and such. I'll double check all the wires that I can cause it seems to me like something may be moving around.

 

loose battery cables, fuses ect. It was soo hard to find out what was wrong with my car because there is soo much to check and find out. Hope to hear what happends and you find it out cheap...

 

I'm also getting horid fuel milage (13 or so all the time)....

I'll get the codes posted shortly.

 

Do a fuel pressure check

 

Working on acquiring a fuel pressure tester

and codes are:

C12
H36
H42
H62

*sigh*

 

The 36 is a high resolution opti code---42 is ign. cont. shorted or grounded---62 is oil temp signal voltage low--indicating high temperature. The "H" prefix would mean history codes ie not current.
Since the problem is intermitant---IMO you'll need a good scanner to catch it when problem occurs--some here are big into the "paper clip method" for pulling codes-I own multiple scanners and that's what I use.

Making a guess from your description--I'd GUESS bad opti --but first I'd check wire terminals at connector to the opti--once again IMO you're better off removing this harness checking for corroded terminals and using your ohm meter to check each wire --look closely at it--checking for breaks and rubbed spots.(this is a short section of harness that plugs into the opti and into the main harness above the right valve cover and they're known to give problems) The 42 code COULD be ICM but that wouldn't explain the 36 opti code---the ICM can be tested at some parts stores BUT---if engine will start it will likely test good---most ICM failures are heat related and even if it has FAILED at the moment-- it will cool off and test ok. Check very-very closely the harness/connector to the ICM also for rubbed/grounded or broken spots. I see you mentioned MSD ign. so I'll assume you mean opti ?? Once again the code 36-- USUALLY means opti failure.


BTW--- your codes wouldn't be related to fuel fill up---at first glance your problem sounded like water in the gas---if you clear the codes --do they come back ??

 

Hi Twister

The vehicle has never over heated since I've had it and the oil temp has always been on the low side, in my opinion.

The MSD ignition is a small red box immediatly forward of the RH valve cover... which sounds like the opti spark location :P It's got a small bundle of de-loomed wires going to it with what looks like a coolant line sitting on top of it....
looks kinda like this
http://www.summitracing.com/parts/MSD-8226/?rtype=10

You think it could have been pure coincidence that it happend immediatly after refuel? I tend to think it's something electrical as well. I'll know if it's fuel related as soon as I get that pressure tester.

Unfortuanatly the ''clear'' button on the ol' paperclip quit working a while back and I'm un able to clear the codes (to my knowledge). I'd rly like a paperclip with the ''monitor'' function right about now too Was going after the older GM OBD1 scanners on ebay and such but they kept jumping up to over $100!!... might as well get a new autoxray or something.

 

The "location" you're speaking of is where the stock ign.coil and ICM would be. The opti distributor is behind/beneath the water pump and above the crank pulley/balancer. The plug wires connect to it.


PS My bad i just opened the link that IS the ign. coil.

 

Oh ok, rgr that

 

DTC #36: Distributor Ignition System High Pulse

What exactly would a ''high pulse'' be in the ignition? Too much juice? wrong wave pattern?? lolz

DTC #42: Ignition Control Circuit Shorted

and my ignition shorted somewhere?!?

btw, thanks guys! keep it up!

 

Static fuel psi @ ~47 and psi running was 39... flow check good too.

Service ASR light comes on now too, still no current codes.

 

Did fuel pressure stay up with engine off?

 

lolz.....

 

Yes it did SFC 97

 

Well you've ruled out fuel issue. Now go to spark. I'm no help with the LT engines but if I see this open I'll bump it up till you get it resolved.

 

TWISTER has made many valid points. Some of the running problems does sound like an opti. But most opti problems are poor running, stumbling , bucking when hot on acceleration, and possible poor idle. The ICM can cause a no start or cause the engine just to stop in its tracks. But with your MSD ignition if defective could cause similar problems. It's hard for me to take a firm stand on the non standard ignition parts (MSD) and giving advice.

I’m not really sure what the MSD had eliminated, but if you had a ICM and a standard ignition system, I would say to replace the ICM only because it's easy and not too costly. As said, you can't get an accurate operational check over temperature from a parts store.

There is no cold start valves or circuits. When starting the engine, the PCM adjusts the pulse width (makes it longer) to the injectors to give added fuel.

Since you can't clear the codes using the buttons, you can remove the battery cable for 30 seconds. This will clear the codes in module 1 and 4. Module 4 is the PCM and the one you are most interested in. The codes in module 9, the brake computer (EBTCM) cannot be cleared by removing the battery cable. It has to be done with the use of the buttons (on board), scanner or tech1,2 device.

If you feel like you got bad gas or debris in the tank, pulling the fuel pump and sending unit out is a straight forward and relatively easy thing to do (providing you have the right tools) . Check for junk in the tank with a good flashlight (without dropping it in). Also look at the sock on the bottom of the pump for any crud buildup.

Code 36 hi-pulse although affects timing (crank position), is non-essential for actual running and probably not a good indicator of your problem. Check if it returns.

Code 42 relates the ICM. If you had a hard short the engine would not run. I have seen these codes pop up all the time with a running engine. So I would just keep it in the back of my mind and would not put too much emphases on it for now but treat it as a possible indicator.

 

Ok, I'll just keep changing/testing things and post if I get any leeway.

The problem has slowly changed from it's initial debut... The engine req an extended turnover to start (~4 seconds key time) and occasionally a rough idle, and the cooling fans run all the time too but I've made a separate thread for that; although, once in a blue moon, the car will start normally and the fans will stay off so I'm sure they're connected to this issue somehow.

Thanks everyone

 

The cooling fans are controlled by the PCM which is driven by the temp sensor in the water pump and A/C when on, will turn on the primary fan. It has some signs of the limp-home mode of operation although can't remember what actually triggers that operation.

If it was an earlier model like 93 and earlier which uses a ECM, I would think it might be going bad. But the 94 uses a PCM which is a much better unit and does not have all the problems the ECMs have. But definitely not impossible it could be the problem. I would check the connections to it and any other connectors that might have a corrosion build up.

Might also consider to check the drive pulses to the injectors using the node lamp.