94 LT1 help
Thread Starter
Cruising
Joined: Oct 2013
Posts: 11
Likes: 0
94 LT1 help
I have a 94 base 6sp
it just shuts off and won't restart
Dies like you shut it off
Spray a little starting fluid while it won't start and it fires up, once fluid is burned it dies again.
New parts installed
Opti
I'm
it just shuts off and won't restart
Dies like you shut it off
Spray a little starting fluid while it won't start and it fires up, once fluid is burned it dies again.
New parts installed
Opti
I'm
Plugs/wires
Fuel pump relay filter and strainer
Map sensor
Air filter
Oil and filter
Fuel pressure regulator
Any advice or help would be appreciated.
Fuel pump relay filter and strainer
Map sensor
Air filter
Oil and filter
Fuel pressure regulator
Any advice or help would be appreciated.
Le Mans Master
Joined: Jan 2006
Posts: 5,621
Likes: 206
From: Orlando FL
If it cranks and starts, or just cranks and does not start it is not VATS. VATS will not cause an engine to stop for any reason at all.
"I'm"……….I guess you actually mean ICM.
It could be a bad fuel pump and poor fuel pressure.
Possible ICM problem temperature related but probably not if it starts with starting fluid.
What you need here is actual data. Measuring fuel pressure would be good too and that requires a pressure gauge. Checking for good spark would be good to know also.
FYI
If you have a aftermarket ICM they are not as good as the GM ones. Regardless, just cause it's new doesn't matter, anything could be defective.
Don’t be guessing, get some real data to start with rather than thro parts at it and work in the dark.
"I'm"……….I guess you actually mean ICM.
It could be a bad fuel pump and poor fuel pressure.
Possible ICM problem temperature related but probably not if it starts with starting fluid.
What you need here is actual data. Measuring fuel pressure would be good too and that requires a pressure gauge. Checking for good spark would be good to know also.
FYI
If you have a aftermarket ICM they are not as good as the GM ones. Regardless, just cause it's new doesn't matter, anything could be defective.
Don’t be guessing, get some real data to start with rather than thro parts at it and work in the dark.
Le Mans Master
Joined: Aug 2015
Posts: 6,091
Likes: 1,972
From: St. Charles MO
If it cranks and starts, or just cranks and does not start it is not VATS. VATS will not cause an engine to stop for any reason at all.
"I'm"……….I guess you actually mean ICM.
It could be a bad fuel pump and poor fuel pressure.
Possible ICM problem temperature related but probably not if it starts with starting fluid.
What you need here is actual data. Measuring fuel pressure would be good too and that requires a pressure gauge. Checking for good spark would be good to know also.
FYI
If you have a aftermarket ICM they are not as good as the GM ones. Regardless, just cause it's new doesn't matter, anything could be defective.
Don’t be guessing, get some real data to start with rather than thro parts at it and work in the dark.
"I'm"……….I guess you actually mean ICM.
It could be a bad fuel pump and poor fuel pressure.
Possible ICM problem temperature related but probably not if it starts with starting fluid.
What you need here is actual data. Measuring fuel pressure would be good too and that requires a pressure gauge. Checking for good spark would be good to know also.
FYI
If you have a aftermarket ICM they are not as good as the GM ones. Regardless, just cause it's new doesn't matter, anything could be defective.
Don’t be guessing, get some real data to start with rather than thro parts at it and work in the dark.
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
X4. The diagnostic path seems pretty clear. 
Race Director
Joined: Oct 2012
Posts: 17,329
Likes: 6,509
From: Melbourne, FL
If it cranks and starts, or just cranks and does not start it is not VATS. VATS will not cause an engine to stop for any reason at all.
"I'm"……….I guess you actually mean ICM.
It could be a bad fuel pump and poor fuel pressure.
Possible ICM problem temperature related but probably not if it starts with starting fluid.
What you need here is actual data. Measuring fuel pressure would be good too and that requires a pressure gauge. Checking for good spark would be good to know also.
FYI
If you have a aftermarket ICM they are not as good as the GM ones. Regardless, just cause it's new doesn't matter, anything could be defective.
Don’t be guessing, get some real data to start with rather than thro parts at it and work in the dark.
"I'm"……….I guess you actually mean ICM.
It could be a bad fuel pump and poor fuel pressure.
Possible ICM problem temperature related but probably not if it starts with starting fluid.
What you need here is actual data. Measuring fuel pressure would be good too and that requires a pressure gauge. Checking for good spark would be good to know also.
FYI
If you have a aftermarket ICM they are not as good as the GM ones. Regardless, just cause it's new doesn't matter, anything could be defective.
Don’t be guessing, get some real data to start with rather than thro parts at it and work in the dark.
I chased intermittent no start issues for years, replaced the whole fuel and ignition system, and finally realized the issue was the ecm portion of vats.
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
This is NOT correct. If the starter kill portion of vats is disabled (commonly done), the second stage that keeps the injectors from firing CAN AND WILL still keep it from starting. The car will crank endlessly, sometimes nearly start (even on starter fluid) but notbrun because Injectors are not turned on.
I chased intermittent no start issues for years, replaced the whole fuel and ignition system, and finally realized the issue was the ecm portion of vats.
I chased intermittent no start issues for years, replaced the whole fuel and ignition system, and finally realized the issue was the ecm portion of vats.
But the car won't start when VATS is intervening and the start enable relay has been jumped. The OP said: "it just shuts off and won't restartDies like you shut it off"
TO me, that implies that it started and ran normally for a period of time...which VATS wouldn't allow. But...it's not totally clear either. OP could provide a little more detail, helping us to help him.
Last edited by Tom400CFI; Apr 19, 2018 at 05:44 PM.
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Le Mans Master
Joined: Jan 2006
Posts: 5,621
Likes: 206
From: Orlando FL
This is NOT correct. If the starter kill portion of vats is disabled (commonly done), the second stage that keeps the injectors from firing CAN AND WILL still keep it from starting. The car will crank endlessly, sometimes nearly start (even on starter fluid) but notbrun because Injectors are not turned on.
I chased intermittent no start issues for years, replaced the whole fuel and ignition system, and finally realized the issue was the ecm portion of vats.
I chased intermittent no start issues for years, replaced the whole fuel and ignition system, and finally realized the issue was the ecm portion of vats.
This is the basic operating parameters of VATS for people who need an basic understanding of how things work. There are always ands, ifs and buts and exceptions to the rule. Other things can always go wrong that don’t conform to the norm. But if you explain every left field diversion to a person who might have a limited knowledge of system, electronics , mechanics, signal flow and digital systems it would get so complicated the actual focus on learning and presenting a concept could be lost.
Aside from that, most PCMs don’t have the screwy problems you described that ECMs have.
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
How are you coming to that conclusion with no test data to indicate anything like that...and the OP said this:
If the opti don't work...car don't start on ether or any fuel. 
Race Director
Joined: Oct 2012
Posts: 17,329
Likes: 6,509
From: Melbourne, FL
It doesn't sound like an opti to me. To really know, we need more info. Does it run, you key it off, and it IMMEDIATELY will not restart? Does it take 5 minutes? Does it cut out while running and not restart? If it doesn't start and you wait 15 minutes, does that make a difference?
When it won' restart, does it crank or does it just not even crank? Engines require 3 main things, air, gas, spark. Air is easy to get. Spark is relatively easy to test for, as is fuel. Finding WHY you'e not getting one is the trick, but you need to know what you'e looking for first.
When it won' restart, does it crank or does it just not even crank? Engines require 3 main things, air, gas, spark. Air is easy to get. Spark is relatively easy to test for, as is fuel. Finding WHY you'e not getting one is the trick, but you need to know what you'e looking for first.
Thread Starter
Cruising
Joined: Oct 2013
Posts: 11
Likes: 0
Security light seems to be fine. Blinks when it should. New I'm coil tests fine. But it wouldn't fire with starting fluid if those were out. I thought maybe oil pressure sensor since it ties into the fuel pump?
Le Mans Master
Joined: Aug 2015
Posts: 6,091
Likes: 1,972
From: St. Charles MO
The ICM can certainly work properly cold and fail when it gets hot (and they do get hot quickly). But I agree, if the car will run on starting then I don't see how it could be the ICM or any other ignition-related issue. Get it into failure mode and then check fuel pressure, and put a noid light on one of the injectors to ensure it's getting a signal to cycle when you crank it.
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
Check fuel pressure when the symptom occurs.Oil pressure switch is a redundant back up power supply to the fuel pump...so if that failed it wouldn't affect anything if the fuel pump relay still works.
Last edited by Tom400CFI; Apr 20, 2018 at 09:54 AM.
Race Director
Joined: Oct 2012
Posts: 17,329
Likes: 6,509
From: Melbourne, FL
Does the car still die after the starting fluid burns off?
What happens if you try to start it with the pedal to tje floor (flooded engine mode)?
If you unplug the Icm does it react or sound any different?
What happens if you try to start it with the pedal to tje floor (flooded engine mode)?
If you unplug the Icm does it react or sound any different?
Le Mans Master
Joined: Sep 2013
Posts: 6,192
Likes: 750
From: near the thumb in the mitten
Carry what I call a no start kit : Noid light, spark tester, fuel pressure gauge, and DVOM.
VATS is only in play at start up. It is the only time key is read is when cylinder is turned to "start". When it quits install fuel pressure gauge and noid light see what is not right. If injector wont blink. You will need to check opti although it should set code if it fails. There should be 12v on term C yellow wire and term D black ?pink wire is ground on pcm side of opti harness. On opti side terminal D should not have continuity to ground.
VATS is only in play at start up. It is the only time key is read is when cylinder is turned to "start". When it quits install fuel pressure gauge and noid light see what is not right. If injector wont blink. You will need to check opti although it should set code if it fails. There should be 12v on term C yellow wire and term D black ?pink wire is ground on pcm side of opti harness. On opti side terminal D should not have continuity to ground.
Thread Starter
Cruising
Joined: Oct 2013
Posts: 11
Likes: 0
Car dies after starting fluid burns off. I will try the other tests this morning. Problem is sometimes it can go 100 miles or sometimes 100 feet before it happens. Ignition control module is new. Tried three different ones.
Thank you all and I will update this afternoon on progress
Thank you all and I will update this afternoon on progress