LS1 runs on after key is switched off

[jraddington]

Howdy folks, newcomer to HP Tuners here. I have installed a 2002 F-body LS1 into my 74 Corvette. Motor is in good running condition, I have used HP Tuners to remove VATS and disable EGR ( not required in '74 ). No other changes have been made. The engine runs great, trouble is it continues to run for about ten seconds after the key is shut off... The engine slows, stumbles, and then dies.

Here's the fun part... I disconnected the alternator and the problem persisted. So I turned off the key, and it started to stumble. I pulled the positive battery cable and it shut off immediately, as it should...

This tells me the problem is electrical, and that something in the motor or ECM is getting power when it shouldn't.

Any suggestions on where to start??? Any help is much appreciated.

- Josh

[bpm]

are your radiator fans running full time?

[gold98Z28]

what kind of wiring harness is in the car? does it have the stock fuse block and dash wiring? older cars were not wired to handle the electrical load of the newer cars. i would start by checking the ignition switch it self.

[EC_Tune]

Sounds like the fuel pump is shutting down but the PCM isn't.

[jraddington]

EC Tune, I agree with your statement... I know that the fuel pump is shutting off with the key, and it appears that the motor runs until there is not enough fuel pressure left to run it.

Gold98Z28, the engine wiring harness and computer are stock 2002 Camaro SS and I have added a "stand-alone adapter kit" from PCM America. It has fused power and relays to control the fuel pump, fans, and coils.

I have replaced every electrical wire in the Corvette with a brand-new painless harness. The wires are the high end "TXL" high temp coating, etc. I made all connections either by soldering or by using weatherpack connectors. I have checked and verified that the ignition switch functions as it should.

bpm, I have not plugged in my fans as of yet. I will do so today and see what I get. They are relay controlled from the PCM America box I have. If they are always on or if they never come on, I would suspect a problem with my wiring or with the PCM America box itself.

Thank you all, and any more suggestions would be greatly appreciated.

- Josh

[jraddington]

Just a quick update, I have verified proper function of the ignition switch. When I cut the key off, I lose the 12VDC voltage on my coil power wire coming out of the fuse box. The fans do not run all the time. I did not run the motor up to temperature to test if they would come on, but they were not on when testing this morning.

I am concerned about the switched ignition wires for the engine harness. I have five pink wires that I understand all need switched 12VDC. One is the IGN power for the PCM. The other four are IGN power for the coils and fuel injectors. The PCM America box instructions have all five of these wires connected to the same switched feed wire. When I cut the key off, I still have 12VDC on all five of these wires ( until the engine dies because fuel has been cut off ).

[Final GTS]

Most automotive harnesses will incorporate an "ASD" or Auto Shutdown Relay. This relay, supplied ground by the PCM, supplies power to the fuel injectors and all other engine systems. When the key is turned off or engine stalls, the ASD relay is turned off, and all injectors, coils, and engine control relays (including fuel pump) lose their 12V+ as well.

Sounds to me like this relay was wired around... hence your issue. something may be backfeeding the coils keeping them alive somehow.

[jraddington]

I am starting to believe that the problem lies within the adapter box I purchased from PCM America. It contains fuses and four relays that are supposed to do exactly what you mentioned; shut the power down when the motor is off.

I have contacted PCM America by email, no response yet. In the meantime, I am working on bypassing it so I can see for sure if that is what is causing my problem.

- Josh

[EC_Tune]

Might just simply be a relay crapped out. Check between terminals 85 & 86 (relay coil terminals) and between 30 (battery power) and 87 (Ignition)

[jraddington]

I have isolated the problem to the PCM America box... Either wiring is bad or the relay is bad. I bypassed the box and I can turn the car off normally. Thanks for the help, folks. - Josh