greenzee28

I have a 94 z28 that i just purchased in December so i am new to this motor but have been snooping on various forums since then. It is an automatic lt1 with obd1 and around 240k miles. I am having a problem with it randomly stalling on me and sometimes it will start right back up and sometimes it wont. Never has a problem on cold start. Being that it is intermittent i am having problems diagnosing the problem. The first thing i checked was fuel pressure and it was just over 40 psi at the rail with key on engine off and the same during crank no start. Next i checked for spark by pulling a wire off a plug and had no spark there. To check if it was the distributor i checked at the coil and no spark there. I had the icm tested at 2 different places and it tested good multiple times in a row to make sure it got warm. The coil had good resistance as well. So next i will be doing the shoebox tests on the opti. Just wanted to throw out a few observations and get some opinions. When i have a crank no start the tach doesnt move and im wondering why. Is there anything else i could have over looked?

greenzee28

O yea and prior to stalling i start getting a miss or hesitation then the check engine light comes on. I have had the codes pulled but not right after it dies being it is obd1. The only codes were for the coolant temp sensor which i replaced after and O2 sensor.

Injuneer

Whatever turns on the SES light will stay in the PCM as a stored code, for quite a while, before it eventually self-clears.

I'd be interested in a current scan, looking for DTC 16. That does not turn on the SES light. But when it is active, it shuts down the fuel system and the ignition. That's for the low resolution pulse signal from the cam position sensor in the Opti, and the PCM needs that info to time the sequential injectors and time the spark.

The fuel pump will normally prime to ~40psi for a couple seconds, then shut down. The check valve in the pump should hold that pressure while the engine starts. But the fact you have pressure does not mean the pump is actually operating.

greenzee28

I have no way to scan it being that it is obd1 but the one time i did have it scanned was right after a no start.

greenzee28

The codes that came up were 15 13 and 12

Injuneer

There is no "12" for a 94. The "handshake" 12 was discontinued after 1993.

http://shbox.com/1/Dtcs.htm

There are several free software downloads that allow you to scan the 94/95 codes. There are older AutoXray OBD-1 scanners that work. There is the ScanMaster LT1.

This is the absolute best software available:

https://www.camaroz28.com/forums/com...95-lt1-874306/

You indicate the tach doesn't move. The tach is driven off the PCM, based on input from the cam position sensor in the Opti.

greenzee28

You were right the fuel pump was only priming. I checked for injector pulse and got nothing so i just went ahead and replaced the distributer. So far so good. Ses light hasnt come on and its running smooth. Does anyone on the forums sell the obd1 cables or am i better off making one?

Injuneer

Get one of the cables recommended by GaryDoug... ALDLCable or Red Devil River.

He has found the Chinese component required to make your own cable to be very unreliable, and inconsistent in design, components and wiring.