Diesel Place banner

1 - 10 of 10 Posts

·
Registered
Joined
·
290 Posts
Discussion Starter #1 (Edited)
1993 K3500 6.5TD. The truck sat for a while before I bought it, ~1yr.

Sometimes when I try to start it in the morning, the GP light won't come on and the GP's wont lite off. Sometimes if I bump the engine over with the starter, they will then turn on. Other times I have to pop the hood and poke the connector to the GP controller from the harness. That sounds like a bad connection, but when I stop pushing on the connector, the GP's stay on for the correct amount of time.

So I lived with that for a little while, and now I went to start the truck the other day and the batteries were dead. I didn't leave anything on, it was random. I jumped it with two cars and got it running, it was showing just a hair over 14V while going down the road, so it should have been charging the batteries. The truck started fine after that, until I let it sit for a few days. Then it was a bit of a labored start, but it did catch on its own. That was this morning.

And now a new symptom from today. While going down the road, the GP light illuminated several times for a second or two at a time. I don't want to drive it until I can figure this out, so that I don't mushroom a GP in the head. They are the Duratherm GP's I think.

It also fired the GP's the other day, on start-up, after driving for 30 minutes and letting it sit for 5 or so. The coolant temp was still close to 210 when I started it... so I thought that was wierd...

Could this be a bad controller? Any other ideas?
 

·
Registered
1995 GMC Suburban
Joined
·
17,832 Posts
Probably bad controller. The contact in there can wear out, there is a picture here of TD tearing apart a GP controller/relay.
 

·
Premium Member
Joined
·
17,906 Posts
When I lost a rectifier diode in my '82 6.2 (with a 10SI alternator), the glow plugs would cycle while driving. (There are 6 rectifier diodes in there and one failed open on me). It would still charge the battery. Changed the bad part in the alternator, and the problem went away.
 

·
Registered
1995 GMC Suburban
Joined
·
17,832 Posts
I did not see the alt issue, do you have the tach going haywire? If so, that is the sign of bad alt.

It may just be weak. My bad alt last me around 6 months before it went completely out.

You can see if you can figure out what Heymccall suggested.
 

·
Registered
Joined
·
5,553 Posts
I was thinking power hiccup too. How does the wiring in this truck look in general?
 

·
Registered
Joined
·
290 Posts
Discussion Starter #6
There was a good bit of corrosion on this truck, so it could be wiring related.

How do I check the rectifier diode? That would seem to tie the hard-start problem in with the glow plugs firing while driving problem. It would still leave the problem where they don't want to fire when I first start it, it seems.

Thanks for the tips!
 

·
Registered
Joined
·
5,553 Posts
I have never seen a good explanation of exactly how the controller works but when it first sees power on one of the pins in the small connector it is supposed to cycle the plugs unless something (a temp sensor on the pre 96 or the ECU on post?) tells it not to. So I am thinking that its possible that its getting intermittent signal and that is why it sometimes comes on when it should not and not when it should? Just a theory. I dont have any detailed info on a 93 otherwise I would try to give you the pin outs to maybe investigate that side of things.
 

·
Registered
1995 GMC Suburban
Joined
·
17,832 Posts
You need to clean all the electrical corrosion and change the cable/connector as necessary first.

There is a recent thread on this about the importance of ground.
 

·
Registered
Joined
·
290 Posts
Discussion Starter #9
The corrosion on the wiring isn't bad, after checking it out. It was all pretty low (the corrosion) probably from being a plow truck for 2 years, and pretty much limited to the heavy metals like the frame/suspension.

Just wanted to update this thread, I think I figured out the problem *knock on wood*.

I took the GP controller out Saturday night and took it apart. It turns out that all 4 pins were a bit loose at their soldered connections to the PCB. The solder had cracked and was probably providing a good bit of resistance. I re-soldered the connections and now the GP light comes on when it should, and stays off when it should. Or at least it has the 4-5 times I've driven it since the fix.
 

·
Registered
Joined
·
5,553 Posts
That would fit my theory that it was loosing the connection it thought you were just turning on the key and was running a normal starting cycle.

Good to know that they can be taken apart and possibly repaired.
 
1 - 10 of 10 Posts
Top