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Discussion Starter #1
1996 F250 7.3 Cranks, No Start
Truck sat for roughly a year before I bought it. It was "running" when parked. (Yeah, I know... why'd I buy a non running truck? Same engine as my 95. It's worth more than the price I paid in spare parts if I can't fix it.)

RPMs 200+ don't remember the exact number.
3k+ psi oil
No fuel pressure tester. (I will be testing soon... ish.)
Per previous owner, new icp and ipr before truck was parked.
I installed new OEM cam sensor.
Haven't tested the batteries or starter, but I don't suspect either as a problem, as the truck spins over better/faster than my 95 F350.

Truck fails injector buzz test. (KOEO injector electrical self test) code P1668.
Key on engine off on demand self-test pulls no faults/codes.

The PCM was removed from the 96 F250 and installed for testing in the 95 F350, which ran.
The IDM was removed from the 96 F250 and installed for testing in the 95 F350, which ran.

Fuses checked. Relays swapped around. Diode swapped with 95 f350.

I am assuming at this point that there is a wiring issue somewhere. Are there common areas to check? I know the valve cover harness is a failure point, but would it cause a comms error between the two modules?

Replace engine bay harness? Open to any thoughts or suggestions. Hoping there's a more in depth no start flow chart or something for the P1668.

I would really rather get this thing back on the road than to use it for spare parts.
 

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When you run the buzz test, do the injectors buzz and then you get the p1668, or is there no buzz at all? I would recommend you get a subscription to alldatadiy for the truck as they have great flow charts for all the error codes. I am attaching the one for my 03, but I suspect it will be close for yours - maybe a few pinout differences.
 

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My thanks for that RT!
No buzz at all. I tried the same scanner on my f350 to make sure I wasn't running the test incorrectly, and it passed without issue.

I'll follow this rabbit hole for awhile and report back what I find... if anything.
 

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Here are the tests for P1668 for 1996. Cheers!
 

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Discussion Starter #5
So, time for an update. First, thanks Patrick!

Found my fuel pressure tester and it's at 30+ psi.
Previous IDM and PCM swaps were done one at a time. Tonight, I pulled both out of the F250 and installed both into the F350. The F350 started and ran. I did not put the F350 IDM or PCM into the F250.

Testing per the P1668 diagnostics revealed no issues... though 1 test I need to recheck.
I found a pdf with a wiring schematic that's given me some thoughts on other wires to check.
 

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Check your oil level, better to change it, if it is low it won't allow a start. If you have white smoke from the exhaust while cranking, it's the Glow Plug Relay. Not sure if you fixed it but sometimes the simple stuff is the cause.
 

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Check your oil level, better to change it, if it is low it won't allow a start. If you have white smoke from the exhaust while cranking, it's the Glow Plug Relay. Not sure if you fixed it but sometimes the simple stuff is the cause.
First thing I checked was the oil level and then the HPOP pressure... I learned the hard way with my 95 F350 that she won't run low on oil...;) No smoke either... I have been looking intently at the wiring diagrams though. Hoping something will pop out at me.

I haven't fixed it yet. Mostly because I haven't been out to it for the last week.
 

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Well, just remember these powerplants aren't computerized like my 6.0 and later engines. Think tractor engine. Compression, fuel, and heat are all that needs to have to run. You are missing one of those. The greatest thing is the simplicity. Start with those 3 things and work backward. It will run on 4 cylinders but not start. I think something much less complicated than wiring or the like. Check each injector, glow plug, and cylinder pressure. It is in there. Oh, and battery and starter speed/torque can interrupt the start sequence.
They great thing is you have another running Powerstroke sitting next to her. Might help to reset this and start from the beginning. I guarantee it is something simple. Not easy, but basic. I've fought this battle and it is frustrating!
 

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Well, just remember these powerplants aren't computerized like my 6.0 and later engines. Think tractor engine. Compression, fuel, and heat are all that needs to have to run. You are missing one of those. The greatest thing is the simplicity. Start with those 3 things and work backward. It will run on 4 cylinders but not start. I think something much less complicated than wiring or the like. Check each injector, glow plug, and cylinder pressure. It is in there. Oh, and battery and starter speed/torque can interrupt the start sequence.
They great thing is you have another running Powerstroke sitting next to her. Might help to reset this and start from the beginning. I guarantee it is something simple. Not easy, but basic. I've fought this battle and it is frustrating!
These engines have been completely controled by a computer since 94.5.
 

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Where is that button? Oh, THERE it is!

To the OP:
Some of the wiring strung back & forth across the top of the engine is for starting it. But not ALL...
 

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RT

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#2 11 d ago
"When you run the buzz test, do the injectors buzz and then you get the p1668, or is there no buzz at all? "

JadeMattican

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Discussion Starter • #3 11 d ago
"My thanks for that RT!
No buzz at all. I tried the same scanner on my f350 to make sure I wasn't running the test incorrectly, and it passed without issue."


Ok, read it, Patrick... He was asked if he had a code P1688 and buzz OR no buzz at all... He responds no buzz. No mention of a code.
Comprehension?? You fricking internet wizards are amazing... Go work on the engine before you start passing judgement.. morons...
Truck fails injector buzz test. (KOEO injector electrical self test) code P1668.

Replace engine bay harness? Open to any thoughts or suggestions. Hoping there's a more in depth no start flow chart or something for the P1668.
Miss anything? Right in the first post. Carry on.
 

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To the OP, try performing the tests in the attachment. Cheers!
 

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Discussion Starter #13
Wow... just wow... this blew up spectacularly. Thank you everybody for trying to assist.

It is my current opinion that the injectors aren't firing due to a communication issue between the pcm and idm. Though I am open to other ideas as to why the injectors aren't firing. (3000+ psi hpop at the passenger side head while cranking, oil level is spot on, swapped the batteries from the f350 just to test with known good batteries)

It is my understanding that the pcm instructs the idm to fire the injectors based on the signal recieved from the cam sensor. As I understand it, the idm determines the duration that the injectors are fired. Though I could be mistaken.
 

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Do you know anyone around you that has a 94-2003 Powerstroke that you could swap IDM with, and then try starting?

My head hurts trying to read through a bunch of those post from yesterday.


Never mind I saw where you swapped it out
 

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I didn't see it mentioned earlier, but is the WTS light coming on as normal? With the key in RUN, is there a 5V reference voltage at any of the sensors that use it (Brown wire w/White Stripe on CPS, BARO, EBP, MAP, ICP, TPS)? Do all the pins on the IDM and PCM connectors look OK and seated correctly? Cheers!
 

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Discussion Starter #16
I didn't see it mentioned earlier, but is the WTS light coming on as normal? With the key in RUN, is there a 5V reference voltage at any of the sensors that use it (Brown wire w/White Stripe on CPS, BARO, EBP, MAP, ICP, TPS)? Do all the pins on the IDM and PCM connectors look OK and seated correctly? Cheers!
There was an earlier issue with the wts light. I didn't think to mention it because I managed to resolve that issue. When I first got the truck, the wts light sometimes wouldn't come on, and when it did, it would just flicker rapidly. I fixed the issue simply by removing and replacing the relays... as in I swapped them around. They all work, i just think it was a poor connection and may be my problem with the rest of my no start...

I haven't check for the 5v ref yet. I assume that it's there as I'm getting rpm and icp readings on my scanner. Will check to verify though.
 

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My head hurts trying to read through a bunch of those post from yesterday.
You and me both!

Bear in mind I tried the broken truck's idm and pcm in the running truck (which still started and ran), but I did not go the other way...
 

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