2000 f550 7.3l no start when cold (long)

nunan · November 9, 2012

Had a friend of a friend drop off a 2000 f550 7.3 for a hard/no start when cold. but it starts right up when it is plugged in. truck is a landscaping truck, and you can tell it was not taken care of in the slightest. on the way down here, it actually stalled out, and had to get towed the rest of the way. I finally got power back, so I was able to figure out why it died (CMP allowed it to start and it had a code for it) and got it running.

Prior to it running, it had a list of codes. I replaced the IPR, due to hi ICP cranking pressures (like 5k psi)ICP sensor was replaced as well. Glow plug relay was replaced because it was cracked. Now it starts and runs, poorly but i think thats because the PCM is reading -40 degrees...which is obviously wrong. So i need to replace the sensor on that. Now my question is, does the ECM switch power or ground to the GPR? I checked continuity on all the wires to the glow plug and intake heater from the bulkhead connector (engine side) to the relays. Right now I'm getting power to both sides of the relay for both of them, so I'm not sure if i'm getting a short to power, or if the glow plug control module or IDM (if thats even involved) is bad. anyone got an idea what to check?

mrbudge · November 9, 2012

PCM ground both relays to energize them. If I have one of these that won't start cold I take my little pocket screwdriver and short across the high current terminals on the glow plug relay (the short one), count 30 steamboats, and fire her up. Those relays are so crappy, even the ones with the gold base, that I would recommend changing them every fall.

Aaron · November 10, 2012

^^. What he said.

nunan · November 12, 2012

the pcm is sending a power signal. goes to ground with key off, then kicks to power, so both have terminals have power going to them. i checked the harness from the bulkhead and everything had continuity. from what I can tell its a short to power, but wasnt sure.

now this truck is beat to crap. like not worth the money putting into it. should i just offer to install a heavy duty push switch to energize the two coils so he can just energize the relays for 10-15 seconds, or 30 seconds whatever the time may be? i dont think its worth the x amount of hours of diag time going through the harness just to find out its an IDM or GPCM and have it not be worth replacing those items.

Bruce Amacker · November 12, 2012

No, don't put a push button on it, that's a bullshit repair that makes you a hack. I'm thinking the PCM supplies control power to the relay from PCM pin 71, 97 (and through the 42 way connector pin 24) and control ground for the relay on PCM pin 101 (and through the 42 way connector pin 13).

With the truck cold (or the EOT disconnected, IIRC, which is on the rear face of the HP reservoir right above the HP pump) pull both small control wires off of the GPR and connect a test light between them. Turn the key on, the light should illuminate for 5-10 seconds or more as the GPR is commanded on. Maybe you have a bad or misboxed GPR, but checking the basic circuit will prove it out.

IIRC, disconnecting the EOT forces the GPR on for its max time when you cycle the key on. If "it" (EOT, I assume) is reading -40F maybe someone already disconnected the EOT, you might want to fix that since it will piss off the PCM pretty badly.

Good Luck!

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nunan · November 12, 2012

the -40 was the ECT,

i dont have access to the oasis or anything, so I'm just tracing wires at this point. I will try putting a test light in between them. The wait to start light does come on. It was giving power before I replaced the relay on top of the engine. I will try disconnecting the EOT to maximize the amount of time the glow plugs stay on.

I agree its a bullshit repair, but its a beat to shit truck. looks like someone went over the engine bay with an oil spray gun, and half the shit was either loose or just broken (cac tubes, air cleaner clips, injector connectors etc) i dont know why almost all landscapers do not see the value in quality repairs of their vehicles, but it seems like every side job i get is the same MO. I will give it a shot tonight when I get home and see if that rememdies the problem.

Jim Warman · November 17, 2012

If you have 12 volts at both of the small terminals on the relay, it means that the module isn't grounding the circuit to turn the relay on. It is at this point that you desperately need to grasp the operation of these circuits.

If the PCM is reading -40 when it isn't -40... what can I fucking say?

You mention that landscapers are continually looking for hack type repairs. If people would stop doing "hack type repairs" - the demand for them would drop off.

Seeing as you are moonlighting this job.... I could offer a lot of advice- none of it complimentary.

This trade has a lot of problems... most of them self-inflicted. I have little patience for .... I'm going to stop there.

nunan · November 20, 2012

No I agree Jim. turns out the hack mechanic was a mechanic i worked with at chevy, hah.

I wrote a quote for him to fix the whole truck, because i also found out it had bottom end damage as well (dusted turbo, pulled glowplugs on 1&8 and saw scoring in the cylinder).

When he saw the quote, I explained to him what was happening and why it happened, and he was better off either selling the truck while he can, or investing in it for the long haul. Had him pay me for the parts and labor i put into it, and he drove it away (at least better than when it came in)

I did find out the wires for the ECT were rubbed through. explained the -40. I did not find a break in the wires for the GP or IH, so I am guessing it was the module that was messed up, but I do not know. I didnt really want to work on it, between Sandy and power outages, it pushed me into my schedule I set up for my kitchen remodel. so off she went. Thanks for the help gentleman. Hopefully the next one will be when I have more time