LS1LT1 Forum banner

1 - 6 of 6 Posts

·
Registered
Joined
·
4 Posts
Discussion Starter #1
Hello all , im a newbie here but have been messing with cars a long time and I have a problem that has myself and a few techs scratching our heads , I put a 1992 LT1 from a vet into a 71 chevelle . Had stand alone harness made up , new stock front harness , new optispark , new icm , new ignition coil , new battery , repaired (?) ecm , then went a bought another from a running car only to have same problem . Removed cleaned and bench tested injectors all check out also have 12v to injector with key on , also tested injectors with noid light , now get this car will run on ether I have spent many hrs staring at this beast and many hrs searching the forums any help is greatly appreciated.
 

·
Global Moderator
Joined
·
13,107 Posts
Welcome to the forum.

I hope the engine harness you made up has the aldl port. You need to check for codes. The 4 ignition biggies don't light the check engine light. All 3 of these codes will disable fuel injector ground from ecm.

Since you have a lt1 engine with optispark, you need to buy a $70 PC based oscilloscope. It is the only 100% way of testing the low & high resolution pulses sent from opti to ecm.

If you bought a cheap China made opti, parts store opti, or anything other than a GM, Delco, Delphi, or MSD opti, you could have a bad opti right out of the box.

You need wiring diagrams. We don't have vette diagrams but BBB Industries- Premium Alternators, Starters, Power Steering Products and Turbochargers | BBB Industries- Premium Alternators, Starters, Brake Calipers, Power Steering, Turbochargers does.
Get them and study ignition wiring. If you can find a used 92 vette service manual, even better.

Did you disable the vats security part of the 92 vette ecm. If no, the security system also locks out the fuel injectors, if problem occurs. The PC oscilloscope will test for 30 hertz fuel enable signal that ecm gets from theft deterrent module ( TDM ). I'm betting you probably didn't install the tdm from 92 vette
 

·
Registered
Joined
·
4 Posts
Discussion Starter #3
Yes I sent out prom to have what needed to be done and the harness was professionally built , my next step is to replace the map sensor and map sensor . From what I read they have something to do with fuel distribution , Ill figure it out sooner or later but I appreciate the advise .
 

·
Global Moderator
Joined
·
13,107 Posts
Before you spend $$$ on parts you probably don't need, you should put the car on an obd 1 scanner that does real time sensor data. I'm not completely up on 92 vette sensors, but I believe 92 was a speed density car that didn't use a maf sensor & used the map, coolant temp, & charge temp sensors to compute fuel charge to engine.

Even with engine not running you can read those 3 sensors. Coolant & charge temp will give readings with key on engine not cranking or running. The map reading with key on will be around 5 volts. But if you crank engine, vacuum will be produced and voltage of map will drop. If it remains 5 volts, then replace map.

Also read the codes, if any, that ecm has stored.
 

·
Registered
Joined
·
4 Posts
Discussion Starter #5
I did get OBD code 42 I think which said injector problem but after sending back ECM I have OBD code 12 which means no codes present I think . Another person told me about adapter to read the oscilloscope runs , Also I have a sensor ( maybe not maf ) on the air intake tube that is one of the sensors that's needed by the ecm .
 

·
Global Moderator
Joined
·
13,107 Posts
The sensor in the intake tubing is the one I called the charge temp sensor. It probably has a different official name. But it's 1 of the 3 sensors you should check the readings of, as outlined in my last post.

If your scanner only reads codes, our member GaryDoug wrote a PC based scan program called "scan9495" It was written for 93-95 f-bodies. But it has a good chance of working with 92-95 vette ecm & pcm. Best way would be to PM GaryDoug and ask him. He's more active on the site in the following link. And be more likely to get a response to your questions. www.firebirdnation.com

Let me know if your interested in the program. If you are, I'll give you links to program and cable to connect car's aldl to usb port of PC based computer. If you want scan9495, you will also need Microsoft dot net framework version v4 or newer. It will be found on same page as scan9495.
 
1 - 6 of 6 Posts
Top