High IPR/ICP PSI @ Idle / intermittent

Hayapower · February 24, 2006

Hey Guys...

Got this late 94-(95) 7.3 DI.. It starts cold with no probs. and runs 'smooth'. After about 45-60+ seconds depending on ambient, it will send the Injection/High Oil pressure from 750/800PSI to 1400-1500+.. ICP almost doubles as well.. Duty is running 14% at start up, and will peg to 22+ with an immediate CEL.. Doesn't store any DTC's.. Not terribly suprised there with the early calibration/s.. It will run/remain this way until the key is cycled on/off with a restart..Then, it'll run OK again for about 15-20 seconds 'maybe' on a warmed engine with a repeat of the over PSI condition.. The repeat is each and everytime..This isn't a gradual transition in pressure like a restriction would/might cause, but more like a 'light switch' with an instant/hard application of HPO.. Being that duty cycle is PCM/ground low controlled, I'd think it was caused by a dieing PCM.. But I'm not sold at this point.. Being that this is "SO"' predictable pushes me in that direction.. I haven't gone too far with this at this point, but thought I'd toss my hat in the ring before I go searching for 'possibilites'..This is one of our service trucks and down time is of essence...

Anyone run into this situation before?? Any help would be great...

Thanks much.....Rob..

Keith Browning · February 24, 2006

What are your RPM's doing when this happens?

Hayapower · February 24, 2006

Hey Keith..

Well it grunts some from the extra drag but maintains a good 750 or so.. The only thing that changes is IP/IPR,IPC/V..I do also notice a drop out in PW to .42 for a split second at a time.. Only when at high pressure though..

But I did 'discover' that this high pressure situation is 'directly' tied to the glows.. Don't know why I didn't think of it before.. Hence the time 'on' for good running!! As soon as the glows go out.. Boom, high pressure.. Disconnected the relay and still the same..

Gotta be a grounding prob. in the PCM..

gasgasman · February 24, 2006

I would look at the ICP sensor. Possible short.

Hayapower · February 25, 2006

Thanks gasgasman...

ICP is new.. My first thought.. Didn't see any connection/chaff issues either.. ICP is text book at all throttle angles 'until' the glows go out.. Each and every time the duty/volt/pressures 'settle' at the same high points, or very close too, on an idle after the glows go out.. Odd thing is, that with the oil temp sensor unplugged it just plain runs bad all the time even though the glows are on..

I'll get back on this one later next week and hopefully have a fix to post..

Rob........

Hayapower · March 15, 2006

Well, finally got this one back in for another look, and a fix..

The thing that through me on this one, was the fact that this truck ran 'absolutely fine’ as long as the glows were ON.. Forced, or otherwise.. Cold or warmed.. At first I thought that ANY time the glow relay was closed that the engine would run fine, and that the HPO numbers would stay within idle spec that way altough a smidge high.. What I found was that if you removed the glow load at the relay while ‘running’, that the HP PSI/Duty would instantly jump to almost double of what the idle specs. should be even though the relay was still closed.. My first thought was a possible PCM grounding issue, but it ran too good.. After ruling out any IPR/ICP/PCM wire/ohm issues, I resorted to a love tap on the outside of the IPR during a run time.. Then, while pulling the glow solenoid grounding wire or load, it would now run for a good 5-10 seconds ‘maybe’ without the glows powered up before a return to the high pressure condition.. Hook the load back on, and after about the same time of 5-10 seconds run time, fine again.. The IPR ohmed out to 10., but was replaced with a new unit and the truck ran fine all the time, glows or not.. What ‘seemed’ to be happening was that the IPR would short on battery voltage, and would then work OK when the glows were pulling the extra amp load dropping voltage until the relay went open and the problem would return..

It also had a few inj. low side codes appear that weren't there in the first test 1,5, that passed for buzz and balance, and ohmed within spec.. Checked all the connectors for tension/condition, both topside and under cover.. All good.. Codes would repeat and the IDM was swapped for a known good unit.. Now a system function pass throughout, and the low codes transferred to the donor system.. Not sure how the IDM would/could play in a fault for IPR, but once the IPR was replaced, it ran fine.. I ran a final code check (worried by now) test/function and got a P0476 that wasn’t there during the previous tests.. New EBP and all is well..

After it was all buttoned up and getting ready to be moved out of the shop late in the day, the batteries went dead!! The ‘reasonably’ new glow relay was stuck closed killing the batteries that ‘were’ fully charged.. Then,, it also decided to drop a little anti freeze out of the almost new (Ford) water pump just before leaving.... …

New pump.. and leave it did........