94 LT1 help
Burning Brakes
Joined: Nov 2017
Posts: 1,060
Likes: 80
From: Fort Mill, SC
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.
Im curious, what kind of fuel pressure guage do you carry that could be quickly used in the field. Is there a port on the c4?
Burning Brakes
Joined: Nov 2017
Posts: 1,060
Likes: 80
From: Fort Mill, SC
Le Mans Master
Joined: Feb 2000
Posts: 9,060
Likes: 214
From: Epping NH
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Le Mans Master
Joined: Sep 2013
Posts: 6,192
Likes: 750
From: near the thumb in the mitten
You need FSM. I don't have 94 manuals. On a 93 which maybe similar fp1 and fp2 are powered by fuel pump relay and oil pressure switch. The bulk head connector c100 from fuel pump fuse in under hood fuse block to fuel pump relay. C237 in a multiple wire connector on right side of dash. It carries 12v from oil switch to fp1. It also has part of the fuel pump relay ground circuits. You might look at the connectors for loose, corroded, or overheated terminals. Also connectors not fully seated. When the engine stalls the feeds the oil pressure feed will stop, however it should be present when engine is cranking immediately after stall. Cold engine can take longer to charge oil circuits then close switch. Clicking relay sounds like poor connection condition. You should also make sure the ground connections are clean and tight.
Pro
Joined: Dec 2004
Posts: 597
Likes: 24
Search Natrlone93 in the search function. You will find my thread from last December titled Another Non Start Issue Thread. As you will read mine was crazy intermittent non start issues. Would always start on starter fluid though. Always had good spark and good fuel pressure at scrader valve. Mechanic checked injectors and multiple other things. Was the ECM. When it was cold and wouldn't start, tapping on it would make it start most of the time. When it was hot and wouldn't start, icing the ECM with ice pack would make it start every time. Sent it for rebuild and haven't had a single non start situation since. Simple to check with ice pack when it wont start hot.
Last edited by Natrlone93; Jul 20, 2018 at 10:43 AM.
Le Mans Master
Joined: Sep 2013
Posts: 6,192
Likes: 750
From: near the thumb in the mitten
Maybe. The ECM makes the engine run and turns on the fuel pump relay. The fuel pump oil switch requires engine to create oil pressure to power fuse. IMO Diagnosis will require a helper and needs to be done when car quits.
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
Last edited by Tom400CFI; Jul 20, 2018 at 01:06 PM.
Pro
Joined: Dec 2004
Posts: 597
Likes: 24
NIce work on the diagram research. So the way mine was explained to me the solder joints get old and when heated from the engine can separate causing any untold number of conditions. When they cool they come back together. Mine was crazy the things it was doing. So a simple icing of the ECM when it's hot and dies or wont restart may off some clue. Just a suggestion. I had done and had done a lot of diagnosing before the shop tested mine with ice and then I retested it several times myself and it worked every time so I spent the 166 dollars and it worked.
