94 LT1 Engine Dying Issue
Thread Starter
Burning Brakes
Joined: Mar 2001
Posts: 1,228
Likes: 17
From: Mansfield Texas
94 LT1 Engine Dying Issue
Ok I have an issue with the engine dying on my 94 LT1, has newer Opti, plugs, wires, coil, ignition module, fuel pressure regulator, maf and throttle position sensors, fuel pump etc.. when it dies it will often restart after 10-15 key cycles and I held the rpm's up at 2500 and it would drop a few hundred after 10 seconds or so and then drop to zero and die. Also died after starting and just idling.
I thought perhaps I had a week battery as it is 4 years old and I had it tested and it showed to have short in it so I replaced it and after driving it again today it did the same thing after 30 minutes of driving. Finally got it restarted and babied it home 20 miles and then after parking in the garage was able to get it to repeat the same problem. I even filled the gas tank as it was at 1/8 tank and thought perhaps it was a fuel pickup issue. If I had to guess the darn opti is crapping out again what do you guys think?
Just ran the codes with the paper clip method and came back C12 and H23. From what I understand C12 is normal operation and H23 is Intake Air Temperature (IAT) Sensor Circuit (Signal Voltage High).
I thought perhaps I had a week battery as it is 4 years old and I had it tested and it showed to have short in it so I replaced it and after driving it again today it did the same thing after 30 minutes of driving. Finally got it restarted and babied it home 20 miles and then after parking in the garage was able to get it to repeat the same problem. I even filled the gas tank as it was at 1/8 tank and thought perhaps it was a fuel pickup issue. If I had to guess the darn opti is crapping out again what do you guys think?
Just ran the codes with the paper clip method and came back C12 and H23. From what I understand C12 is normal operation and H23 is Intake Air Temperature (IAT) Sensor Circuit (Signal Voltage High).
Last edited by wheeljo2; Jan 14, 2017 at 06:32 AM.
Le Mans Master
Joined: Jan 2006
Posts: 5,621
Likes: 206
From: Orlando FL
You need to get some real data so you can go to the area of the problem. If it dies on the driveway that makes it easier. You need to have a fuel pressure gauge taped to the windshield so you can monitor the pressure.
Have you ever check for spark when it happens. Offhand it does not sound like spark however it should be checked on principal.
Did you look in the fuel tank to see if there was any excess dirt or anything that looked like water?
Did you replace all these parts trying to cure this problem? If you did, then it's unlikely those parts are the problem. Sounds like you have tools but you need some test equipment also which is always money well spent.
Don’t believe that code would cause the symptoms that you have. That may be a separate issue but I would clear the codes as well. I don't think you're going to find this problem with a code.
Have you ever check for spark when it happens. Offhand it does not sound like spark however it should be checked on principal.
Did you look in the fuel tank to see if there was any excess dirt or anything that looked like water?
Did you replace all these parts trying to cure this problem? If you did, then it's unlikely those parts are the problem. Sounds like you have tools but you need some test equipment also which is always money well spent.
Don’t believe that code would cause the symptoms that you have. That may be a separate issue but I would clear the codes as well. I don't think you're going to find this problem with a code.
Thread Starter
Burning Brakes
Joined: Mar 2001
Posts: 1,228
Likes: 17
From: Mansfield Texas
I will check the fuel pressure first been running great last few thousand miles parts replaced just normal maintenance or upgrades. How are you supposed to see inside the gas tank? _
Race Director
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Race Director
Joined: Oct 2011
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From: Dallas Texas
2025 C4 of the Year Finalist - Modified
I would still diagnose the code h23. Do you have a real time scanner? On a cold engine, does the scanner show -22 fahrenheit, or colder for the IAT? Also, you can ohm the sensor. At 50 fahrenheit, it should be ohming at 5,670. 86 at 2238, 104 at 1459. FSM has a big chart for that.
Thread Starter
Burning Brakes
Joined: Mar 2001
Posts: 1,228
Likes: 17
From: Mansfield Texas
Looks like my initial inclination was correct a faulty opti spark I pulled it off and it had oil splashed on the bottom from the crankshaft hub seal which is original with 85k miles had replaced the other two seals for the timing cover last time for the distributor and water pump. Any moisture or oil will kill an opti in no time. I plan to pull the opti cover to confirm my suspicion before I put it all back together.
Last edited by wheeljo2; Jan 16, 2017 at 02:48 AM.
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From: Austin TX
Cruising
Joined: Oct 2016
Posts: 11
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From: Lake Stevens Washington
Hook a fuel pressure gauge up and see what you have for pressure. I had the same exact problem as you...troubleshot EVERYTHING!! Changed fuel pump, fuel pump strainer, coil, IAT, ICM, plugs, wires, opti unit...you name it. Everytime I drove it..same thing. Would die...not start, waited between 5mins to an hour...it started right up..rough idled for a few seconds and then ran great. Hooked up a pressure gauge and watched the fuel pressure drop when the engine was warm to hot...started looking at the fuel injectors, I tested them with an ohm meter..they were perfect...long story short, $9.73 later, replaced the O-rings on the injectors and WHOOLA...problem solved. Fuel pressure holding at 38psi no matter what temp the engine is and runs perfect. Don't rule out those O-rings.....
Thread Starter
Burning Brakes
Joined: Mar 2001
Posts: 1,228
Likes: 17
From: Mansfield Texas
Great advice on the fuel injector o-rings being a potential fuel pressure problem. So far so good on my repair with a new opti and crankshaft seal oil was seeping onto my opti and causing it is misfire.