Interesting GPR Problem - PowerStrokeNation : Ford Powerstroke Diesel Forum
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post #1 of 14 (permalink) Old 10-27-2009, 02:39 AM Thread Starter
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Interesting GPR Problem

Ok 96 F250 7.3L
Stock as a rock.

Terrible cold starts. Key on, the gpr clicks to life. After start up, my GPR clicks like a clock rhythmatically every second or so. A nice audible click that can be felt if you put your hand on the actual relay. I measured voltage, And it fluctuates on both post from 12-14 each click. I replaced the relay and had the same issue.

any ideas? IDM/PCM sending some funky signals?
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post #2 of 14 (permalink) Old 10-27-2009, 02:57 AM
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Re: Interesting GPR Problem

Our old idi truck does the same thing, but starts fine?? Good-luck! Reuben

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post #3 of 14 (permalink) Old 10-27-2009, 03:16 AM
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Re: Interesting GPR Problem

i let my glow plugs go through the full cycle and right when they shut off i turn the key and she fires right up,you must have some bad glow not sure if that would cuase the irregular cycling after start up.

96 f250, ZF5,160cc,
300k miles

96 f350 plow truck
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post #4 of 14 (permalink) Old 10-27-2009, 03:26 AM
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Re: Interesting GPR Problem

the old idi trucks were suppose to do that on off clicking by desighn, They used a 6volt glow plug that was having 12 volts applied to them so if they did this for more then about 5 seconds they would fry the glowplugs. Thats why you would have so many glow plug failures on the older truck the relays would stick on and fry em all. The 94.5+ have 12 volt glow plugs that why they stay on for 30-60 seconds all the time. You definatly have a controler or relay problem id start disecting wireing back to the pcm or try swapping pcms


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post #5 of 14 (permalink) Old 10-27-2009, 05:25 AM Thread Starter
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Re: Interesting GPR Problem

Where is the GPR controller?

I wouldnt care about the problem but unlike your obs, it doesnt fire up perfectly every time. Tons of white smoke and long crank....GPR is doing its general function, just erratic voltage spikes, clicking.
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post #6 of 14 (permalink) Old 10-27-2009, 05:47 AM
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Re: Interesting GPR Problem

Hmm, could the alternator be putting out fluctuating voltage? Try lighting it off, wait for the PCM to cycle off the glow plugs (2 minutes-ish?), and check the battery voltage then.

Edit: 'Course, that wouldn't explain the white smoke at start-up. That, AFAIK, is a pre-start GP issue of some sort. Have you checked the voltage drop at the GP relay pre-start? One thing you might try - unplug all but one valve cover connection, pull the #22 fuse, turn the key to RUN, then go back under the hood and push in the #22 fuse and immediately check the voltage drop at the relay. This will be with just two GPs connected. Then pull the relay (plugging / unplugging the relay is just a simpler way of testing, rather than running back into the cab to turn the key), disconnect that one VC connector, and connect another one. Test again. Do this with all four, each just one connector connected at a time. If you see a major difference in the voltage drop with one of them, that narrows down a possible bad GP, or bad wiring to it.

Have you ohm-ed out the GPs at the valve cover connectors?
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post #7 of 14 (permalink) Old 10-27-2009, 08:32 PM Thread Starter
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Re: Interesting GPR Problem

I checked ohms today and found the entire passenger bank is dead and one gp on the driver side registered at .9.... wierd though, I contacted the injector pins and didnt get a reading?

Truck runs great after it finally gets going...but im thinking i have a few bad UVCH and gps....
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post #8 of 14 (permalink) Old 10-29-2009, 01:40 AM
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Re: Interesting GPR Problem

Smell the oil cap . . . If there is a slight burn't plastic smell the UVC harnesses and maybe even the gasket itself where the connectors pass through are toasted . . . You need to ohm the GP's by themselves , without connectors or harnesses for a more interpretive reading . . .

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post #9 of 14 (permalink) Old 10-29-2009, 03:11 AM
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Re: Interesting GPR Problem

The PCM is actually the GPR controller. Power goes from fuse #22 to one post of the GPR's solenoid coil (that wire is always energized). The other post of the coil is wired directly to the PCM. When it's cold, the PCM grounds the coil wire, which makes the GPR come on.

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post #10 of 14 (permalink) Old 10-29-2009, 03:17 AM
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Re: Interesting GPR Problem

Both my 97s will cycle the glow plugs. They will pull in at idle and hold for 30-60 sec, but if you apply throttle they begin to cycle, per the ammeter. I am thinking about wiring in to the circuit to make that stop. Dimming / brightening headlights drive me nuts.

Replace the GPR anyway, use a Napa GPR-109. little different mounting but a good relay, and only about 18 bucks. I replace them once a year now, need it or not.

Good set of GPs pull about 100 amps initially, then settle to 60-70....
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