[AllAboutJeeps]

Hi All, I am stumped and could use the help of the 7.3L gods! (2001 X, 7.3L, 242k)

I have been living with a cold start issue for a couple of years, and getting by b/c the X hadn't been my daily driver. Well, that has changed this year and so now I am trying to get the cold start issue licked. Now before you tune me, this isn't your average Cold Start Issue. So bear with me...

It is an X, so it has the GPCM instead of the GPR. I have verified it is alive and functioning, along with the glow plugs. I verified the GP were working by checking their resistance, and measuring the voltage across each of them while the GPCM is active, and even verified the current flow through the GPs. Everything in the GP system seems good to go.

In the winter I switch to Rotella 10w-30 to aid with starting.

I have new batteries and even run have the issue while on a big charger on the 100amp boost setting.

So the symptoms. When cold, on the initial start up, turn the key, let the glow plugs do their thing, crank the engine and it cranks away like she wants to go. Right when it sounds like it is going to kick (about 2 seconds) and roar to life, the sound changes and it just cranks and cranks and cranks. Never starts. Let off the key, crank again, nothing, just cranks and cranks. Now the interesting part. Cycle the key off, go back to the run position, let the GPs do their thing, crank it and sometimes it will kick and take off. Repeat the key off, back on crank cycle, maybe 4-5 times at most and she will start. It is so weird.

My latest theory is that while cranking, something changes and it stops getting fuel. Like a module is going off-line and has to have the key cycled to cut power, reboot and come back to life. I am trying to think of a good way to test the theory, but can't recall the inner working of the injector drive system on these engines. If I recall, their is a FORD ECM that is in charge of the timing of the injectors. It communicates with the injector driver module (which I believe is a navistar design if I recall). The IDM then does the voltage boost and control (according to the FORD module) that fires the HEUI injectors in these engines.

So, my problem is I don't know how to test the theory. If anyone has a schematic showing all that stuff, I am sure I could come up with a way. I know the IDM is ~110V so you have to be careful.

Any thoughts on my theory and/or how to check for it?

Is there any other system that might change suddenly that would keep it from firing? (I thought about the HP Oil pressure falling, but I the timing of the drop out seems so consistent. I also didn't know if the HPOP would drop so low that no fuel would make it into the engine.

Thanks!

 

[1999f-250superduty]

How long are you letting the glow plugs run before you try starting it? The glow plugs are on for up to two minutes. And have you checked battery voltage while cranking if it drops below 9 volts the pcm stops firing the injectors.

 

[klhansen]

I truly doubt it's an electronics issue, and probably not a fuel delivery issue either.

I would suspect first the starter. Do you know that you're getting a cranking speed of 100 RPM minimum? A weak starter could easily cause what you're experiencing.

I would also check your fuel pressure just to be sure that you're getting adequate flow and pressure. You should get a minimum of 45-50 psi.

Your best approach would be to get it on a scan tool that can monitor parameters while cranking.
You should get the following:
Battery voltage of 8V minimum
ICP of 500 psi minimum
Injector Pulse Width of 1-6 milliseconds
IPR duty cycle of 14% before cranking and less than 35% while cranking

1999f-250superduty was posting as I was typing. What he says about low voltage is true. A dragging starter can cause that. Check all your battery connections.

 

[AllAboutJeeps]

Great tips guys, I will start checking those things, need to try and run down a good diagnostic tool.

As to the glow plugs, have tried all sorts of combinations up to and including cycling the key off and back on repeatedly to get them nice and warm (the problem has been around for a couple of years).

Good call on the 9 volts. I have checked it with the minimum voltage capture mode on my meter, but thinking about it now, I was measuring that voltage at the batteries, I need to find a location closer to the PCM to account for any voltage drops.

Do you know if the IDM has a similar operating voltage drop out? Also, isn’t it powered through a dedicated relay circuit (which could make it easier to measure the voltage to it. If I recall, it location can be tricky to get to.)

Lots for me to check. Plenty of cold temps ahead to play with. It is a pain to troubleshoot as once it fires up, you have to let it cold soak a while to get it to do it again.

 

[AllAboutJeeps]

Interesting on the starter. It sure ‘sounds‘ like it is cranking along great, but I realize that isn’t a good check. Are there any easy ways to check the cranking speed without a good diagnostic tool?

 

[DENNY]

I usually just cheat and make Kevin come over and listen to it. I even pulled my starter and had it tested by as good by the NAPA store. When I finally put in a new starter it was night and day difference in cranking speed. Once you hear a good one, the slow one is easy to spot just by the sound. One of the Gods has spoken I would listen closely. DENNY

 

[AllAboutJeeps]

I usually just cheat and make Kevin come over and listen to it. I even pulled my starter and had it tested by as good by the NAPA store. When I finally put in a new starter it was night and day difference in cranking speed. Once you hear a good one, the slow one is easy to spot just by the sound. One of the Gods has spoken I would listen closely. DENNY

Alright. What is the best starter on the market for the 7.3? (I have stopped trusting auto parts store brands!)

 

[bugman]

Alright. What is the best starter on the market for the 7.3? (I have stopped trusting auto parts store brands!)

A genuine Denso or what I am looking at Powermaster.

 

[klhansen]

I would recommend AutoEnginuity for the diagnostic tool. It will measure all those parameters, including voltage at the PCM. Others use ForScan, which is a free download, but you need to buy an adapter to plug into the DTC connector. (The IDM is dependent on the PCM to turn it on, so you only need to measure it once.)
Before you replace the starter, clean up your battery posts nice and shiny and check the cables for corrosion nearby the clamps. When cranking, you should see NO voltage drop between the battery post and the clamp. You can check that with a multimeter.
If you have a local starter/alternator rebuild shop, they likely will be able to supply you with a better starter than the typical auto parts store one.
Bugman's recommendation is a good one too. When he says genuine Denso, he means GENUINE. There are knock offs out there that aren't worth what they charge.