Good deal. I add several extra grounds. I sometimes add a ground to the pump, directly from the battery.

 

Now it's running like a champ. Took a drive this evening and it has more power than it ever has had. Seems like that little ground wire to the pump was the main issue.

 

I like to do the battery bolt mod. I use a stainless 1 1/4" Allen screw. It makes it easy to add grounds.

I add some 10 ga ground wires. One to the battery box bolt - it replaces the screw in the fender that I have had problems with over the years.

one to the frame by the starter

one to the stud on the back of the intake by the firewall with all the other grounds - I have seen this stud lose continuity to the block.

one to the ground on the heater blower motor. This is a short ground to the dash mount bolt just inches away.

That one helps feed the computer.

One to the PMD heat sink - some say it's not needed and others have said it's a good idea.

Cheap and easy problem preventers.

 

After the grief that ground caused I think I will be adding a few more fresh grounds to both trucks.

 

Lets hope thats all it was.
If not, see my lengthy comments here >Rough Start After Oil Change

 

It was looking good, drove to the city and put about 60 miles on no problems and lots of power. ran the best it has ever run....until this morning. After a 10 mile drive it died. Towed it to my daughters, and added a new ground wire to the big pump along with the ground that was already there. It started and ran fine for 10 miles, than it died again, Tugged and twisted wires and it ran for a couple miles, then died again several times. Switched PMD extension harnss and made it home , another 10 miles. This is driving me nuts.

 

I had to change the ignition switches on all of my vehicles except the 89 and 94's.

It caused similar problems.

I do not know how to do the diagnostics on the switch. When I ran out of ideas on diagnostics for the wiring I would just throw that part at the vehicle. So far it worked every time I did it.

I have also taken to throwing an engine wiring harness at the vehicles. A couple I had to. And I am working at doing the rest as preventive maintenance.

 

good grief, it never ends.
I put a new PMD and extension harness on , fresh from the post office.Started it up, ran it in the yard for half an hour, all is good. Go for a test drive 5 miles down the road and all is good there and back until I pull in the yard. It died again. hit the key, starts right up, park it and it dies.
Under the hood checking wires and anything I can get my hands on to no avail. Can't make it stall by pulling and twisting wires. It sounds perfest and idles for an hour while I try to find a bad connection.
Off I go for another test drive, and the dam thing dies as I slow down to turn a corner. It starts instantly and dies again 3 more times.
Finaly it decides to stay running and I make it home.

This is going to drive me crazy.

 

Yes it will.

Makes me crazy reading about it. I've been there before.

Have you swapped the ignition switch yet?

I have had to swap ignition switches on all my GMT400's except the 1994's and the 1989. Usually around 200,000 miles. When I pulled them apart the contacts were burnt looking.

After the first couple. I just did it as preventive maintenance if I could not figure out a problem - every time I swapped them it cured my issue.

But I do not know how to properly diagnose the ignition switch.

I am also taking to replacing the engine harnesses on these. Mine are getting old and brittle. I have had to repair a connector on just about every one of them.

Now I am starting to replace them as preventive maintenance.

 

Well I added a fresh large ground wire from the battery to the grounding stud at the rear of the engine, and cleaned the handful of ground terminals there. Also added a new wire to the PMD coolers, and the body. Took it for a 20 mile drive, and all seemed fine. Got home and let it idle for 45 min with no issues. It seems to be working, but I need to do more country driving before I risk the city.