Electrical Issue

[HeisenBob]

Hey Fellas,

I’m having an issue with the volt gauge and electrical system. My batteries are fully charged and I went into town this evening to top off with diesel before the impending snow storm of the century hits Oklahoma. So the truck was warmed up. I noticed a clicking noise under the dash and the volt meter gauge goes from slightly in the yellow to in the green when the clicking noise cycles on/off. Happens every 5 seconds or so. The lights also go slightly dim and the heater fan slightly slows down.

Couple of things I’ve done recently - new glow plugs, new coolant sensor, rebuilt gen 1, replaced heater/blower switch, and I’ve cleaned as many connections/grounds as I could reach under the dash and under the hood. Oh, also completed the dog head mod and replaced the glow plug relay under the hood.

It’s cold as shit outside (16 degrees) so I’m not sure if that matters but I wanted to mention it. Any suggestions/thoughts as to what’s going on?

 

[Tow4]

Sounds like the glow plugs are cycling. When I start mine it does that for a short period of time immediately after the engine starts. It's not more than about a minute. The cold may make a difference, but it shouldn't do it continuously.

 

[HeisenBob]

Sounds like the glow plugs are cycling. When I start mine it does that for a short period of time immediately after the engine starts. It's not more than about a minute. The cold may make a difference, but it shouldn't do it continuously.

Thanks. I thought that the clicking was coming from the glow plug card but I wasn’t sure. Tomorrow I’ll put a piece of cardboard in front of the grill and see if that helps warm it up and stop the cycling.

 

[royalflush55]

What brand of glow plugs and temp switch on rear driver side temp sender and glow plug relay did you use? You have changed a lot of parts at once making it a little harder to diagnose. I suspect one of the new parts is defective or not the right one or a wire is in the wrong place or moving them around you have found a short.

I would check all the wiring and make sure it is wired right. The glow plugs will not last long if they are cycling all the time. If the old parts were working right before you could change them back out one at a time to find the problem. Good luck!

 

[Sharecropper]

I suspect the issue is your new glow plug sensor. That sensor, and that sensor alone, controls when the glow plugs come on and when they go off. When the engine reaches a certain operating temperature, the sensor causes the glow plug circuit to shut down. They are currently cycling off and on because that’s what they do when they are “on”. Either you have the wrong sensor, or your new sensor is not wired correctly, or if it IS wired correctly there is a short in one of the wires. To make sure you have the correct sensor, find the diagram in the -34P technical manual ( downloadable from this site ) which shows the sensor and then extract the GM part number from the next page. Cross-reference this part number with the part number of your new sensor to determine correctness of part.
Hope this helps.

 

[HeisenBob]

What brand of glow plugs and temp switch on rear driver side temp sender and glow plug relay did you use? You have changed a lot of parts at once making it a little harder to diagnose. I suspect one of the new parts is defective or not the right one or a wire is in the wrong place or moving them around you have found a short.

I would check all the wiring and make sure it is wired right. The glow plugs will not last long if they are cycling all the time. If the old parts were working right before you could change them back out one at a time to find the problem. Good luck!

Thanks. When I said recently, I meant within the last 10 months for the total list.

Two months ago I rebuilt Gen 1 due to the romantic glow and I also had the intermittent clicking noise with volt meter abnormalities. Yesterday I changed plugs to AC Delco 13gs, it had another set of AC Delcos in it but they were only 10.5v but I’m not certain on the part numbers. Yesterday I also changed the coolant sensor on the rear driver side of the block. I searched the forums for the correct part and found it at OReilly’s. Only one they had in stock was a MasterPro 2-8296.

 

[HeisenBob]

I suspect the issue is your new glow plug sensor. That sensor, and that sensor alone, controls when the glow plugs come on and when they go off. When the engine reaches a certain operating temperature, the sensor causes the glow plug circuit to shut down. They are currently cycling off and on because that’s what they do when they are “on”. Either you have the wrong sensor, or your new sensor is not wired correctly, or if it IS wired correctly there is a short in one of the wires. To make sure you have the correct sensor, find the diagram in the -34P technical manual ( downloadable from this site ) which shows the sensor and then extract the GM part number from the next page. Cross-reference this part number with the part number of your new sensor to determine correctness of part.
Hope this helps.

Yes that helps me greatly! Thanks I’ll dig in and see what I can find.

 

[HeisenBob]

I suspect the issue is your new glow plug sensor. That sensor, and that sensor alone, controls when the glow plugs come on and when they go off. When the engine reaches a certain operating temperature, the sensor causes the glow plug circuit to shut down. They are currently cycling off and on because that’s what they do when they are “on”. Either you have the wrong sensor, or your new sensor is not wired correctly, or if it IS wired correctly there is a short in one of the wires. To make sure you have the correct sensor, find the diagram in the -34P technical manual ( downloadable from this site ) which shows the sensor and then extract the GM part number from the next page. Cross-reference this part number with the part number of your new sensor to determine correctness of part.
Hope this helps.

Looks like the sensor I bought is the correct part. Is there a chance my GP is not functioning properly?

 

[royalflush55]

Thanks. When I said recently, I meant within the last 10 months for the total list.

Two months ago I rebuilt Gen 1 due to the romantic glow and I also had the intermittent clicking noise with volt meter abnormalities. Yesterday I changed plugs to AC Delco 13gs, it had another set of AC Delcos in it but they were only 10.5v but I’m not certain on the part numbers. Yesterday I also changed the coolant sensor on the rear driver side of the block. I searched the forums for the correct part and found it at OReilly’s. Only one they had in stock was a MasterPro 2-8296.

Since both coolant sensors are clicking either they are both bad or I suspect you have a problem with the plug to the sensor or the wiring itself. Do the sensors have resistance on a volt meter when cold?

 

[HeisenBob]

Since both coolant sensors are clicking either they are both bad or I suspect you have a problem with the plug to the sensor or the wiring itself. Do the sensors have resistance on a volt meter when cold?

I just checked resistance on the one I pulled out. Showed 9000+ in my garage. It’s 5 degrees outside but probably a little warmer in the garage. I brought the sensor inside to test warmed up and see what it reads. It’s definitely working. I tested it under hot water and cold water and it goes up and down like it should.

I haven’t traced wiring from the plug back to the GP board yet.

 

[HeisenBob]

Update: I went to town about an hour ago and it took a few times cycling the GPs to fire up. But I let her sit for about 20-30 min to warm up and I blocked off the grill with cardboard. When I came outside to leave, the the GP card was no longer cycling and off I went. After a few minutes on the road it started cycling again and then stopped after about 10 min on the interstate. I arrived at my destination and it started cycling again within a few minutes of idling. Then I was on the road again and it stopped after about 5-10 minutes.

 

[royalflush55]

If you disconnect the plug from the sensor does the wait light come on and stay on. Sounds like a loose wire or connection somewhere .

 

[Sharecropper]

If you disconnect the plug from the sensor does the wait light come on and stay on. Sounds like a loose wire or connection somewhere .

Yeah it sounds to me like something is going on with that sensor. There are 2 wires coming out of the sensor, so I would suggest tracing those down to make sure there are no issues there. Do you still have your old sensor? Was it working before it was removed? If so, I would reinstall it to see if it resolves the issue.

 

[royalflush55]

Yeah it sounds to me like something is going on with that sensor. There are 2 wires coming out of the sensor, so I would suggest tracing those down to make sure there are no issues there. Do you still have your old sensor? Was it working before it was removed? If so, I would reinstall it to see if it resolves the issue.

He said old sensor was clicking off and on too.

 

[HeisenBob]

He said old sensor was clicking off and on too.

Yeah the old one did it as well. I’ll have to try and trace the wires from the sensor the the card. The two wires have electrical tape so could be an issue with the connection somewhere. I’ll check and report back.

 

[royalflush55]

Sounds like you are getting close to the problem.

 

[HeisenBob]

I haven’t had a chance to tear in the wiring but the past two days have been warmer and the cycling has been going away after the truck is good and warmed up. Could it be that the thermostat is too low and I need a hotter one?