Having problems with my GMPP LS480/4L70E connect and cruise. Most threads say ground problems are the major cause. My instructions for the harness say that there are three ground connections. I laid the entire harness out in my house prior to installation. I could only find two obvious ground connections. These drop down from the right and left side of the engine and connect to each head at the rear of the engine. I took a picture of the entire harness in my house and there is no third ground eyelet. Can someone tell me where this third ground should be so I might be able to find a black wire in the harness?Otherwise, what additional grounding should I do?

 

I see what you mean...

https://www.chevrolet.com/content/da...d-17-tooth.pdf

However, if you look at the pinouts in the document, there are only 2 grounds listed (the ones going to the heads. There is a ground reference in the 12 cavity bulkhead connector, but generally that is not used.

Can you elaborate more on the kinds of problems that you are having? Is the engine itself properly grounded to the battery?

Andrew

 

Thanks for the quick response. The battery is in the trunk but is directly grounded to the engine block in front of the starter with a large welding cable. The positive cable runs to the starter using a remote solenoid. An 8 gauge positive wire runs directly to the ECM horizontal lug. The battery is also grounded to both the front and rear subframe. I ran the starter quite a bit without the ECM connected and without spark plugs to prime the oil pump. Turns over just fine. After connecting the ECM and turning the key on, the fuel pump ran a few seconds and I registered 60 PSI on a gauge attached to the fuel rail. When I tried starting the engine it seemed the ECM shut down. I was showing a large voltage drop going to the ECM ignition wire, so I ran a new wire from the interior fuse panel to that wire. I also attached a light to the fuel wire from the Fuse/Relay box. The light would come on and then immediately go off. Now it doesn't even turn on the fuel pump for priming. I'm in process of going over all my connections to make sure they are clean but since everything is new, I'll be surprised if that fixes my problem. Any advise would be appreciated.

 

Battery to chassis.
Battery to engine.
Engine to chassis.
In the case of a body-on-frame vehicle, tie both the engine and the battery to the body and the frame.

You mentioned the battery being in the trunk. How long of a run is it to the starter? How thick of a cable did you use for the main positive and ground cables?
Are you sure that your ignition switch is in good working order?

 

Sounds like you have the ECM power wire connected to a source that is only ON when the key is in the RUN position and not in START. The ECM needs to see power when the ignition switch is in RUN and in START. So when you put the key in RUN, the ECM sees power and primes the pump and as soon as you hit START with the ignition key, the ECM shuts off. So the engine is cranking, but the ECM is shut off, and when you stop cranking the ECM comes back on.

I don't know what car you're working with, but on older cars I generally take the old coil wire and have that trigger a relay, which in turn powers the ECM. The coil wire is hot both in RUN and START.

Andrew

 

Thanks for the help, I'll check all of those suggestions above out. The car is a 1968 Camaro, with a standard key switch, red, brown, orange, and purple. The battery and starter connections are the same as was on the 350 with an MSD box that I pulled out of the car. The ignition switch is new Delco. I'll advise the gauge and length tonight but they are HEAVY cables.

 

Going from the trunk, you could get away with 0 AWG, but I would recommend 2/0 AWG. If the battery was in the engine bay, then your typical 2 AWG welding cable would be sufficient.

I would also second to make sure that you have everything connected to the correct power sources, being 12V constant, 12V switched, and 12V start.

 

You ran enough cables that I don't think your issue is grounds. Time to start tracing power wires like suggested above.

Try jumpering the ECM power right to a power source and see if that works.

 

My electrical system is as follows:Optima trunk mounted battery. Negative terminal has a 1/0 12 foot long cable that is attached to the engine block in front of the starter. Also an additional 2 gauge cable attached to the rear subframe. There is another 2 gauge cable from the attachment to the engine block to the front subframe and radiator support. There is a ground strap from the left head to the firewall and through to a junction block where all the dash components are grounded.The positive terminal has a short 1 gauge cable direct to the rear mounted starter solenoid. The other side of the solenoid has a 1/0 gauge 12 foot long cable attached directly to the starter. There is also an 8 gauge wire attached to this terminal that runs directly to the horizontal terminal on the fuse/relay center. A 6 gauge wire also is attached to this terminal that runs to the alternator.The dash fuse panel is fed from one of the 50 Amp vertical posts on the fuse/relay center through a 10 gauge wire. Also attached to this is a 12 gauge wire to the A/C circuit breaker.I isolated the ignition switch from the starter to test it. Off reading was zero, In the on position the ignition wire to the harness showed 12.74 volts. Turning it to the start position gave the same reading. Turning it back showed no dead spots.I disconnected the battery to see if that would reset anything in the fuse/relay center. When I reconnected it the check engine light seems to be dimly blinking with the ignition switch in the off position. Turning the switch to the on position gives a steady red light. I’ve read that this is normal and the light should go off when the engine starts, which hasn’t happened yet. Also my Dakota Digital dash shows check engine with the key on as it is connected to the MIL wire. There is a noise in the engine compartment like a relay engaging when the key is turned to the on position. I will try to determine the source of this sound when my grandson is here this weekend to help me.

I have a FIXD app and OBD connector but it apparently has to have the engine running to read codes.My current weekend plan is to check all voltages when trying to start the engine, cleaning all battery and ground connections and retightening, detaching and reattaching all sensor connections, and adding a ground strap from each head to the engine block. Let me know if there are other checks I can make or things to do.

Thanks again for the help to date!!