No start; GP + GPC issue?

[riotwarrior]

Make sure 8 GP are same...not sure why you are stuck on six...but make sure all 8 are same for best results.

IIRC 6.9 had 6v gp but could be wrong...do your gp have a flat male spade connector or do they have a round bullet tip on them?

If the 6.9 gp controller is in the head and failing, as others said it can fail on thus frying gp.

Either go full manual control or update gp system to the newer 7.3 style which IMHO works very well.

Please anser folks and we will endeavor to assist.

Btw read stickies and tech articles

 

[bbjordan]

screwed in the head controller

You got that right!

 

[OLDBULL8]

CAUTION

If in fact he does have the screwed in controller, there is an internal resistor that cuts the voltage to 6 or 8 VDC, the ZD1 GP's are a 6 volt GP. Any changes done, like to a manual or an updated controller, the GP's should be changed to the ZD9 GP's which are 12 volt GP's. Then the harness connectors have to be changed from spade to the round pin connectors.

 

[riotwarrior]

CAUTION

If in fact he does have the screwed in controller, there is an internal resistor that cuts the voltage to 6 or 8 VDC, the ZD1 GP's are a 6 volt GP. Any changes done, like to a manual or an updated controller, the GP's should be changed to the ZD9 GP's which are 12 volt GP's. Then the harness connectors have to be changed from spade to the round pin connectors.

Yes and he said he is getting 12v...so determining what parts and such he is using is critical.
12 v to ZD1 6v plugs is not a good thing.

Hence dont do anything until answer us

 

[bbjordan]

CAUTION

If in fact he does have the screwed in controller, there is an internal resistor that cuts the voltage to 6 or 8 VDC, the ZD1 GP's are a 6 volt GP.

False! The GPs get 12 volts directly from the GP relay. The resistor(s) in the controller for the sensing system to see how hot the GPs are.

If going manual, do not glow for more than 8 seconds!

 

[School_Bus]

False! The GPs get 12 volts directly from the GP relay. The resistor(s) in the controller for the sensing system to see how hot the GPs are.

If going manual, do not glow for more than 8 seconds!

According to my research this is correct. Even if you read the wiring schematic the GP's get 12v from the relay, not the controller. The controller just determines when to turn on the relay. I've read the manual relay bypass upgrade threads on here so I know not to let them run longer than 8 seconds.

Let's say it is supposed to be 6v. Then why would all the GP's be getting exactly12v? That's not how relays fail.

Furthermore, the diagnoses of the controller being bad sounds correct. Since GP's only fail prematurely due to being energized for extended periods of time. That's the only thing that could fail brand new GP's after two drives around town. Since the controller fails on.

Lastly, after the suggestions of the controller being bad I remembered the last time driving the truck the GP indicator light lit up for over a minute while driving. I read in the manual that the GPC will light the GP's sometimes during normal driving for short periods of time 2 minutes after start up. But this was way after the 2 min warm up and it stayed lit for a long time. I thought nothing of it at the time but now I think that was when the GPC cooked the GP's.

 

[icanfixall]

So far you can't describe what type of controller you have. Know this.. If you have the solid sate controller and are using the ZD1 glow plugs with the spade connectors you will burn them out. If you are still running the controller that screws into the head to see the coolant temp that might have failed because you posted the dash light came on well after the engine warmed up and stayed on for bout 1 minute. Those screwin controllers have been an issues for many years on the early 6.9 engines. Mel at Conestoga Diesel has a much better solis state screwing controller too. He tested this on his personal engine for many miles and is now selling the controller thru his business. Honestly I would remove the power from the glow plugs and use a VERY SHORT mist of staring fluid. A 1 or 2 second shot directly into the air intake before the filter will cause this engine to come awake and run fine. There is no limit on how many cold engine starts either. When used correctly starter fluid will not harm your engine. Some like to think it makes an engine addicted to it and wont start unless it gets a fix. Well that right there is BS...

 

[bbjordan]

Theory and practice

The GPs get 12 volts directly from the GP relay.

That's in theory. When I glow my plugs, the voltage meter drops to 8-9 volts!

 

[OLDBULL8]

CAUTION

If in fact he does have the screwed in controller, there is an internal resistor that cuts the voltage to 6 or 8 VDC, the ZD1 GP's are a 6 volt GP. Any changes done, like to a manual or an updated controller, the GP's should be changed to the ZD9 GP's which are 12 volt GP's. Then the harness connectors have to be changed from spade to the round pin connectors.

False! The GPs get 12 volts directly from the GP relay. The resistor(s) in the controller for the sensing system to see how hot the GPs are.

If going manual, do not glow for more than 8 seconds!

@bbjordan
IF IN FACT YOU DID READ WHAT I SAID ABOVE. THEN YOU WOULD UNDERSTAND WHAT I'M TALKING ABOUT.

SINCE THE OP CAN'T OR WON'T SAY WHAT MODEL OF CONTROLLER HE HAS, THAT'S WHY I SAID WHAT IT WILL DO TO THE ZD1 GLOW PLUGS WITH A LATE MODEL ELECTRONIC CONTROLLER. I EVEN POSTED A PIC AND ASKED IF THAT IS THE KIND OF CONTROLLER HE HAS.

IF OP DON'T GIVE THE INFORMATION BACK FROM WHAT HAS BEEN ASKED, THEN I WILL TO THE BEST OF MY KNOWLEDGE, TELL THEM IN THIS CASE, WHAT WOULD HAPPEN IF IN FACT HE DOES HAVE THE SCREWED IN CONTROLLER.

OVER AND OUT 10 - 4?

 

[madpogue]

It's a 1986 truck. Unless it has been modified, it has the first-generation controller.

To the OP - the photo you posted is of the starter relay. The GP relay should be on the horizontal surface of the inner fender well on the passenger side. It will look similar.

 

[Agnem]

He does not have an 7.3L glow plug system. They did not have them on 6.9's until 1987. He has the old style screw in controller and fender relay. You have 3 options.

1) - Replace all 8 glow plugs, and the glow plug controller.
2) - Replace all 8 glow plugs and implement a manual switch.
3) - Replace all 8 glow plugs with ZD-9's and get a glow plug harness and controller off of a 7.3 in a junk yard.

Most 6.9 guys will opt for choice #2. It's the simple quick fix. However, most who opt for a manual push button system, will end up using more glow plugs than those who have a properly working controller.

New flash... all our glow plugs, be it 6.9 or 7.3 are technically 6 volt. The system is designed to use them, so that they heat extra fast. They draw a ton of current because of this, and this is why they will burn out so easily.

Don't discount cranking RPM when having problems with hard starts. You always need 150 RPM minimum.

 

[bbjordan]

@bbjordan
IF IN FACT YOU DID READ WHAT I SAID ABOVE. THEN YOU WOULD UNDERSTAND WHAT I'M TALKING ABOUT.

SINCE THE OP CAN'T OR WON'T SAY WHAT MODEL OF CONTROLLER HE HAS, THAT'S WHY I SAID WHAT IT WILL DO TO THE ZD1 GLOW PLUGS WITH A LATE MODEL ELECTRONIC CONTROLLER. I EVEN POSTED A PIC AND ASKED IF THAT IS THE KIND OF CONTROLLER HE HAS.

IF OP DON'T GIVE THE INFORMATION BACK FROM WHAT HAS BEEN ASKED, THEN I WILL TO THE BEST OF MY KNOWLEDGE, TELL THEM IN THIS CASE, WHAT WOULD HAPPEN IF IN FACT HE DOES HAVE THE SCREWED IN CONTROLLER.

OVER AND OUT 10 - 4?

I hear you loud and clear @OLDBULL8. It sounds like you might want to file a hurt feelings report.

Not looking for trouble...it finds me all too often as it is.
I understand what you are getting at. The only point I am contesting is the "internal resistor that cuts the voltage to 6 or 8 VDC" bit.

If I have offended you, I apologize. That was not my intent. I highly respect your contributions to this site.
I believe we all want what is best for the OP.

Peace out.

 

[OLDBULL8]

Amen.

 

[bbjordan]

83-86 glow plug circuit

I found this in my Haynes Diesel Engine Repair Manual. It explains how the '83-'86 glow plug system works.

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