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94 vette running rough
Thread Starter
Cruising
Joined: Jun 2005
Posts: 11
Likes: 0
94 vette running rough
OK I have a 1994 vette convertible with the LT1 engine. approx 72000 miles. I bought it last memorial day and it ran great. Awesome gas mileage. If stalled once when it was drizzling out. Took forever to start it back up. Ran fine for a few weeks afterwards. Now it only runs good when its cold. Once it warms up it runs rough. If it stalls I can only start it once it cools down. I ohm'ed the fuel injectors and they were all the same. Opti? Ignition coil? Ignition module? Any ideas? Help 
also where does everyone like to get their parts from? Its mostly all Oreilly's here in my town and they arent too bright.
Oh yea, I have an autoxray scanner 6000 and there are no codes.
thanks!
Justin
also where does everyone like to get their parts from? Its mostly all Oreilly's here in my town and they arent too bright.
Oh yea, I have an autoxray scanner 6000 and there are no codes.
thanks!
Justin
Last edited by SuperCharged78Vette; Apr 12, 2010 at 05:39 PM.
Le Mans Master
Joined: Mar 2001
Posts: 7,999
Likes: 14
From: Life is just one big track event. Everything before and after is prep and warm-up and cool-down laps
Cruise-In III Veteran
Cruise-In IV Veteran
St. Jude Donor '12
Start with the simple stuff first:
What codes are you getting?
check fuel pressure while running
pull the plugs and see what they look like
Capture data while its running and see if you may have a "lazy" O2 sensor
If the coil and ICM are original try changing the ICM - don't forget thermal paste between the ICM and heat sink!
Good luck!
What codes are you getting?
check fuel pressure while running
pull the plugs and see what they look like
Capture data while its running and see if you may have a "lazy" O2 sensor
If the coil and ICM are original try changing the ICM - don't forget thermal paste between the ICM and heat sink!
Good luck!
Le Mans Master
Joined: Jan 2006
Posts: 5,621
Likes: 206
From: Orlando FL
IMHO - Suggestions
Forget the codes, they only monitor as few things and that is not going to get you to home base. You have a intermittent (temperature) problem that will take some troubleshooting and possibly some substitution.
There are lots of items that may cause you symptoms. I would get the easy ones out of the way like fuel pressure check and FPR leakage. Check for the coil wire for possible arking where it goes thru the water pump, might try a mister also.
Injectors are much better than the earlier vetts and although can go bad, the 94 injectors and PCMs hold up very well. Check TPS for smooth operation as well as connectors and pins on ICM and opti.
An engine running rough, bucking and coughing can be an opti. However generally they cause poor running but usually do not kill the engine completely with a no re-start.
The ICM will definitely cause heat related problems with no start, engine dying or just plain no run condition.
I would not jump on the opti yet, but I just might try the ICM if I was going to replace a part because it is so quick and easy to replace. Even if it is not bad, it is a nice part to have for a spare.
There are lots of items that may cause you symptoms. I would get the easy ones out of the way like fuel pressure check and FPR leakage. Check for the coil wire for possible arking where it goes thru the water pump, might try a mister also.
Injectors are much better than the earlier vetts and although can go bad, the 94 injectors and PCMs hold up very well. Check TPS for smooth operation as well as connectors and pins on ICM and opti.
An engine running rough, bucking and coughing can be an opti. However generally they cause poor running but usually do not kill the engine completely with a no re-start.
The ICM will definitely cause heat related problems with no start, engine dying or just plain no run condition.
I would not jump on the opti yet, but I just might try the ICM if I was going to replace a part because it is so quick and easy to replace. Even if it is not bad, it is a nice part to have for a spare.
Thread Starter
Cruising
Joined: Jun 2005
Posts: 11
Likes: 0
ok so far we did: new msd coil, test icm at parts store, ohm'ed fuel injectors, checked fuel pressure, checked codes with my autoxray 6000....none, shook my fist at the car a few times while swearing.... today we rerouted the icm wires farther away from everything and it seems to run good so far. gonna go for a cruise tonight to see how she really runs. the only other thing today thats different is that its 75 outside finally maybe tomorrow when its back down to 50 out she will run rough. hopefully not! 
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Racer
Joined: Mar 2006
Posts: 251
Likes: 1
From: New Mexico
ok so far we did: new msd coil, test icm at parts store, ohm'ed fuel injectors, checked fuel pressure, checked codes with my autoxray 6000....none, shook my fist at the car a few times while swearing.... today we rerouted the icm wires farther away from everything and it seems to run good so far. gonna go for a cruise tonight to see how she really runs. the only other thing today thats different is that its 75 outside finally maybe tomorrow when its back down to 50 out she will run rough. hopefully not!
If it did, give me the details!
Racer
Joined: Mar 2006
Posts: 251
Likes: 1
From: New Mexico
Hey SuperCharged
Have you ever watched the coolant readout temperature gauge to find out where your roughness begins? Mine starts at the exact same place. Early 160's by the time that I am in the higher 160's I'm toast!
Have you ever watched the coolant readout temperature gauge to find out where your roughness begins? Mine starts at the exact same place. Early 160's by the time that I am in the higher 160's I'm toast!
Le Mans Master
Joined: Jan 2006
Posts: 5,621
Likes: 206
From: Orlando FL
A part store test of the ICM might find a dead non working ICM. But if the ICM is working at all, it will probably check good. They do not test it under operating conditions with heat applied to it.
I was just wondering if it gets hot when they test it. If it does not, then I would probably figure there is a light load on it if it is not generating any heat. I have never had one tested myself but might just try just to see what they are doing.
I was just wondering if it gets hot when they test it. If it does not, then I would probably figure there is a light load on it if it is not generating any heat. I have never had one tested myself but might just try just to see what they are doing.
