GP Relay Befuddling issue

[rorykillam]

1992 Ford F250 NA 7.3L IDI
Hello folks this is my first post here so please bear with me. I'm going to try to keep this as concise as possible while still giving you all the information.
About 3 months ago now I found a crack in one of the fuel injector lines after an 800 mile or so trip, I had already been planning on replacing the GPs as I did not know how old they were. Replaced all the fuel injector lines (they were original lol) and replaced the GPs. The old ones were autolites but thankfully the truck has spent most of its life in the desert on the west coast so they were not swollen. Replaced them with Ultrapowers or something off rockauto (I know, I know foolish but I have learned since to only use ZD-9s). It took a lot of cranking with the fuel lines cracked to get her started, and since then she's been starting hard (at first it took 15 seconds of cranking 3-5 times with 3 minute intervals in-between, now it takes one try of 8-12 seconds after doing everything listed below). Sometime between then and now the wait to start light no longer illuminates for longer than a split second after I turn the key (sorry its warm here so It never stayed on long to begin with, I do remember it used to stay on for 3-6 seconds without clicking though) I have done the following:

Replaced all the rubber fuel lines with clear fuel resistant/high-heat rated line. Fuel is not draining and there are no visible/audible leaks or air bubbles in the lines. Fuel filter stays full and has less than 1000 miles on it.
Replaced starter (it was quite old and burnt out)
Replaced batteries (they were over 5 yrs old lol)
Replaced fender starter solenoid(at some point it fried and I had to jump it)
Replaced fusible links to GP relay
Checked maxi fuse K it (replaced it and nothing changed)
Replaced GP wiring harness with one from a reputable diesel parts website
Replaced GPs with motorcraft Beru ZD-9s
Checked WTS light bulb it's not blown
Checked every ground I could think of or find
Ohms Checked GPs, grounds, harnesses.
Checked voltage, 12.5v at fender starter solenoid, 12.5v at GP relay hot terminal and GP relay ignition terminal.
Replaced relay and controller twice, each one had the same voltage and each just begin to click when turn key to run. Intermittent voltage reading of 2-7v on glowplug side of controller with key in run, same reading at glowplugs while controller is cycling.

Any advice would be greatly appreciated I am really at a complete loss. Electrical is not my Forte by any means either haha. Does the engine temperature switch play any role in the GP controllers job? All my reading says no but I'm pretty sure my switch is bad ,going to replace that at first light tomorrow just because I am fairly certain it is shot or the terminals are corroded.


Short and sweet of it: replaced nearly every component in the glow plug system and the controller still seems to think the GPs are hot when they are not, can't find resistance anywhere either.

Also I am aware I could just wire a manual GP switch however at this point my pride won't let me give up haha

Thanks in advance, sorry for the long read.

 

[rorykillam]

Also just so yall don't think I was just throwing parts at it every part I have replaced tested bad, was the original 30 yr old part or in the case of wires looked really beat up. Except the GP controller which I admit I just replaced out of the fear I didn't test it properly or got a false reading. I have spent 70+ hours in the past three weeks diagnosing, testing, reading and watching trying to figure this out and I am officially at a loss.

 

[Austin86250]

First make sure you have the hardline dampers on that’s the only time they crack is when they are absent

I’m not too much help when it comes to stock glow plugs because every time I have issues I put a manual glow plug switch on as it’s the easiest route there’s alot of write ups on how to do so

Even though they are brand new motor crafts i recommend you ohm them out .2-.8 is what you want
I got a set of 8 beru glow plugs and 6/8 of them where bad

I had a similar problem due to a bad connections and ground so make sure they are all clean as-well as make sure your wiring isn’t all corroded on the inside

 

[rorykillam]

I ohmed them out and the beru plugs are good, I will clean the GP threads out a bit better tomorrow and see if that helps. I haven't cleaned the threads in the block where the plugs ground through, any suggestions on a good way of doing that? I don't want a bunch of solvent leaking into the pre combustion chamber.
I was thinking about running a longer ground somewhere but I've already cleaned the stock controller ground and grounded it in two different places on the block with no new results, so I'm not sure if that will help sadly.

 

[Old Goat]

I agree make sure you have the vibration dampers on the Hard Lines to keep them from cracking.
You said you found a crack on one of the lines. Did you replace it?

If not, Iam wondering if that is the problem, the fuel is draining back. It`s sucking air making a hard start after sitting for a while.

I usually just blow the crud from around the GP`s before removing them with air, then use Anti-Seiz on the thread`s of the new one`s.

Why not trying to by pass the Controller and go manual to see it will start.
I have an 86, so not sure how you do the newer style.

keep your old Controller, it may not be bad. If the relay goes bad on one of them. You can change the Relay. order one for a 86, same thing. Parts house will want to sell you one for a 93 if you tell them your year.

Its something simple....you do have fuel in the tanks?


Goat

 

[Austin86250]

Why not trying to by pass the Controller and go manual to see it will start.
I have an 86, so not sure how you do the newer style.

Same process just need to put the white wire on the output for the light

 

[MadMac]

It took a lot of cranking with the fuel lines cracked to get her started, and since then she's been starting hard (at first it took 15 seconds of cranking 3-5 times with 3 minute intervals in-between, now it takes one try of 8-12 seconds after doing everything listed below).

So, I've done nearly everything you have above on my '85 rescue, which is simpler - and additionally replaced the battery hot&cold harnesses with 4-0 copper. You should not need to do that - but it may explain why at 12.4 your voltage looks low. Still it sounds like two separate issues.

First - the GP on light flickering off immediately sounds like a short. We all hate those and the work it takes to track them down. I hope someone here can help you with a wiring map, and potentially the diagnosis manual. A fuse which does not fail is what comes to mind. Gawd lets hope its not a frayed wire.

Second - The length of time to start it - sounds like an air intrusion / vacuum issue. I'd start with the block heater overnight - and put a room heater under the block overnight (if its not outside). If your starting times go down significantly, then its not likely to to be a vacuum issue. if they stay the same... then you have a fuel/air problem. I chased electical/GP issues for a very, very long time only to end up finding my base problem was a water separator can leaking both. Which does not address the GP light flicker issue.

FWIW, after everything I did and then replacing the can with a marine unit, my start times after 3 GP cycles are ~1 second, even when it rarely freezes here in Northern California. I'm not a great wrench by any means, just my reaction.

 

[rorykillam]

So, I've done nearly everything you have above on my '85 rescue, which is simpler - and additionally replaced the battery hot&cold harnesses with 4-0 copper. You should not need to do that - but it may explain why at 12.4 your voltage looks low. Still it sounds like two separate issues.

First - the GP on light flickering off immediately sounds like a short. We all hate those and the work it takes to track them down. I hope someone here can help you with a wiring map, and potentially the diagnosis manual. A fuse which does not fail is what comes to mind. Gawd lets hope its not a frayed wire.

Second - The length of time to start it - sounds like an air intrusion / vacuum issue. I'd start with the block heater overnight - and put a room heater under the block overnight (if its not outside). If your starting times go down significantly, then its not likely to to be a vacuum issue. if they stay the same... then you have a fuel/air problem. I chased electical/GP issues for a very, very long time only to end up finding my base problem was a water separator can leaking both. Which does not address the GP light flicker issue.

FWIW, after everything I did and then replacing the can with a marine unit, my start times after 3 GP cycles are ~1 second, even when it rarely freezes here in Northern California. I'm not a great wrench by any means, just my reaction.

Yes I replaced all the hard injector lines when I found the one cracked, also replaced all the return lines, injector o rings, hose clamps and plastic covers. I have the vibration dampeners on thanks for the tip! I wasn't going to put them on because I thought they looked kind of useless but I'm glad I did.

I have both tanks 3/4 full, I know my tank selector switch is good and both my fuel tank pickups are good because I've run each tank down to below 1/4 before switching to the other tank and I haven't had any issues there.

I'm afraid it is a short, I'll have to keep following wires I guess. I've checked all the wires from the starter to the controller and from the controller to the GPs. I just haven't checked them from the ignition to the MAXI K fuze to the controller.

I attached the two wiring diagrams I've been working off of through all this.

Thanks for all the advice, sadly at the moment I can't hook up the block Heater unless I buy 500 feet of extension cords haha. I'll probably move the truck this weekend and try that just to confirm it is the glowplugs.

 

[IDIBRONCO]

If not, Iam wondering if that is the problem, the fuel is draining back. It`s sucking air making a hard start after sitting for a while.

The length of time to start it - sounds like an air intrusion / vacuum issue.

I agree that this sounds like two separate issues. Even though it would be fuel drain back and not air intrusion, I don't think it's either one. There was no mention of the engine starting, running for a few seconds, and then dying. If it was fuel drain back, the engine would start quickly and then die, requiring a long time of cranking with the starter. Then it would probably run rough for a few seconds after starting until the air got worked out of the fuel system. I think that maybe the timing's slow. Rorykillam, try advancing the injector pump timing a little bit and see how it starts. If it starts better, you are on the track to fix one issue. If not, you didn't hurt anything and the timing can be put back to where it was before.

 

[franklin2]

Don't get off track. Like was mentioned in the previous post, it does not sound like air intrusion. It's obvious what problem is causing the long cranking, the glowplugs are not heating up. These engines fire on heat, no heat means no go. The light in the dash coming on very briefly is a sign the glowplugs are not glowing.

Double check again all your heavy wiring to the controller. Originally they had two heavy yellow wires feeding the controller, if you have this type there is a plastic plug near the pass side valve cover that has these and some smaller wires also. This plug likes to melt around the two heavy yellow wires. You can cut these yellow wires out of this plug and wire them around the plug with another type of plug, or just bolt them together with crimp ring connectors. I have heard some of the later trucks also used one large single wire to feed the controller. If yours is like this, make sure it's in good shape.

The controller brain monitors the current flowing through the controller to the plugs. If there is one bad plug, it will short cycle since there is less current flowing through the controller. Less current is why it "thinks" the glowplugs are hot. Reasons for less current are;

One or more bad glowplugs.

Poor connections at the glowplugs

Poor connections anywhere else in the high current wiring like the area I mentioned in the 2nd paragraph with the wiring plug, and any other heavy wire connections like at the controller.

Wrong or faulty glowplug types can also cause short cycling if they are drawing less current than they should.

 

[rorykillam]

Thank you for the all the help. This is frustrating because I know what should cause the problem but still can't seem to fix it. To make sure everyone understands my situation I'll add a few things for clarification:
It takes about 15 seconds of cranking for the truck to fire. After starting and immediately shutting down and restarting it takes about 3-5 seconds. Once at operating temperature and shut off the truck will fire in less than a second for around an hour until it cools down.
I've found if I let the GP controller cycle through the "afterglow" clicking 3-5 times it reduces the cranking while cold to about 8 seconds or less.
Brand new ZD-9 GPs
Brand new GP relay and controller
Brand new GP wiring harness with connectors.
All the fuel return lines I replaced with clear line and hold fuel overnight with no airbubbles.
The truck runs and drives beautifully once started and has never stalled on me.

I have heard some of the later trucks also used one large single wire to feed the controller. If yours is like this, make sure it's in good shape.

Yes my truck has a single large red power wire from the starter solenoid on the passenger fender. I've heard they switched to this style wire in 91 or 92.
All the wires on my truck have the heat shielding over them, I pulled it off the power wire and inspected it but It didn't seem to be damaged.
I get constant 12-13VDC at the hot terminal on the GP solenoid, the controller just isn't pushing that to the GPs for some reason.
I might end up wiring a manual GP button however for the time being I want to keep this truck as original as possible, and I hate running into problems I can't fix lol.

 

[rorykillam]

I am going to double check some of the wiring tomorrow morning, I'll report back if I find anything suspiscious.
Part of the reason I'd like to figure this out is to be able to help anyone else that might have this issue. I don't mind throwing new parts on this truck but I know not everyone likes doing that willy nilly.

Rorykillam, try advancing the injector pump timing a little bit and see how it starts. If it starts better, you are on the track to fix one issue. If not, you didn't hurt anything and the timing can be put back to where it was before.

I do want to do this, the truck has the original pump on it with almost 200k miles so I think it could use a timing adjustment. I was a little worried the pump might be weak however the truck drives great and has great power, even with 1000lbs+ of stuff in the bed going up steep inclines the acceleration is relatively good. So I'm a little hesitant to suspect the pump.

 

[Old Goat]

Do you have a Block heater? Does it work?
Plug it in over night, or at least 4 hours. it should start right off w/o GP`s.

If it does, there is your problem.

When they are cold, they need heat to start.
I think you already know this...

200K miles on your pump, as they wear, the timing drifts off.
Makes since what rorykillam mentioned.

They say these pumps are good for 150K miles or???





Goat

 

[MadMac]

Brand new ZD-9 GPs
Brand new GP relay and controller
Brand new GP wiring harness with connectors.

I hate to say this, and its remote - but you can’t always trust that a new electronic part actually works…

I might end up wiring a manual GP button however for the time being I want to keep this truck as original as possible

So, don’t make it permanent. A remote starter button transformed my ability to test. You can do something similar with a manual GP setup. My manual GP conversion gave me so much more information about what was actually going on.

After everything was working - I reverted my manual back to stock b/c so many family members borrowed my now running rescue… explaining that GP sequence can be difficult, and their ability to remember it even more difficult. When ever I have a GP issue now - I simply bypass back to the manual switch.

 

[rorykillam]

Do you have a Block heater? Does it work?
Plug it in over night, or at least 4 hours. it should start right off w/o GP`s.

If it does, there is your problem.

When they are cold, they need heat to start.
I think you already know this...

200K miles on your pump, as they wear, the timing drifts off.
Makes since what rorykillam mentioned.

They say these pumps are good for 150K miles or???





Goat

I do have a block heater, not sure if works, sadly where I live at the moment it's nearly impossible to hook it up to an outlet. I am thinking about bringing it to a friend's house to leave overnight though.
I might try to advance the timing today, I am a little hesitant because I am not super familiar with timing or tuning.
I have heard these pumps are good for 150k miles but I've also heard they should be replaced at 80k. I've also heard some people swear that if you take care of them they'll last upwards of 200-300k miles so I don't really know what to believe haha.

I hate to say this, and its remote - but you can’t always trust that a new electronic part actually works…

So, don’t make it permanent. A remote starter button transformed my ability to test. You can do something similar with a manual GP setup. My manual GP conversion gave me so much more information about what was actually going on.

After everything was working - I reverted my manual back to stock b/c so many family members borrowed my now running rescue… explaining that GP sequence can be difficult, and their ability to remember it even more difficult. When ever I have a GP issue now - I simply bypass back to the manual switch.

Tracking on that, I don't trust new parts, especially electronic ones. But I replaced the GP controller and relay twice so unless I have absolutely terrible luck I think one of them should have worked lol. I also tested all the zd-9s before I installed them.
I am probably going to wire a manual switch today, thanks for the advice!

I was just going back over some of the wiring right now, pretty sure the power wire that runs from the battery to the starter relay and then to the GP relay is good. Tested it for continuity and resistance and visually inspected the entire wire. Ohmed out at almost zero (With battery disconnected of course).

However I believe I may have discovered something, the 14ga (I think) red and green wire that runs from the ignition to the MAXI K fuze then to the GP relay has a resistance reading of 2.2 Ohms. Not sure if this is the entire problem but it definitely could be contributing.
The problem is that it runs through the main engine electrical connector.
I'd like to replace the whole connector at some point because it's in somewhat rough shape and its a bit cruddy. However i haven't been able to find this specific connector anywhere online, I'm going to take another look right now but any advice would be appreciated. Also not sure how to replace a single wire in a connector like this but I'm going to give it a try this afternoon after i run to the hardware store.

Actually I just realized if I really got excited about It I could just cut that connector out completely and splice all the wires couldn't I? The connector is just there for convenience if I'm not mistaken.

Can't express enough how much I appreciate your guys advice and patience with me!