Interesting Problem

Hotrodtractor · Jun 3, 2012

So this afternoon I've been troubleshooting a 7.3 and I need some opinions.

Its a little slow to turn over - about 130-150 RPMs - that could be a starter issue, but I think its mostly unrelated to the rest.

Sometimes - it just doesn't build ICP pressure turning over - it only gets up to 350-400psi - but other times it cranks the ICP right up through the roof and starts right up.

When it starts right up - it will sit there and purr like a kitten at idle - then for no reason it loses like 400 RPMs - sometimes it catches itself, sometimes it doesn't. When it does start - the ICP goes right to 3600psi the RPMs go up to say 1500 or so - then it comes back down to idle.

My initial thoughts on the cranking ICP problem is of course the IPR sticking - I personally haven't had a ton of issues with them doing that - but it seem logical given the symptoms. What I can't truly account for is the sudden loss of RPMs at idle - the only thing that I can come up with is it ALSO has a CPS issue that is starting to rear its head - the CPS is literally 2 weeks old, grey, and honestly probably has 20 miles on it at best.... not unheard of to have a bad CPS out of the box - but I'm looking for other ideas and opinions to help diagnose this thing fast.

Thanks,
Jason

pontiacross · Jun 3, 2012

I have had a ipr stick and do that sort of thing before but very rare like you said. could it be loosing rpm due to icp falling off or is the icp still up when it dose that?

what dose it do if you unhook the icp sensor?

as for the cps I have had to replace the connector to the cps several time because it was making bad contact. usually some one would replace the sensor and it would make good connection for a few weeks because of the clean contacts on the sensor, but then it would start messing up again. replaced the connector and it took care of the problem

Hotrodtractor · Jun 3, 2012

AE says the ICP stays rock steady when its running - but then the RPMs drop - I never saw it drop the ICP though. I really kind of wish that I had my mechanical gauge on the truck. I never got it to start with the ICP sensor unhooked - and I never had a chance to unhook it while the truck was running as I was trying to check as many things as possible because it seemed like I would only get a couple of minutes of run time at best today.

It was really irritating - this hard start low ICP stuff came up at a truck pull two weeks ago - I attributed it to a dying alternator that we changed out at the truck pull and it seemed OK. I went out there to change tunes today - put new tunes on the truck - it started right up - tested it to make sure the issues we were tweaking for were gone - everything was fine - and then BAM - truck dies - back to low ICP hard start - start/run/die crap.... I seldom go to work on a truck and have it running when I get there and not when I leave....

Hotrodtractor · Jun 3, 2012

AE says the ICP stays rock steady when its running - but then the RPMs drop - I never saw it drop the ICP though. I really kind of wish that I had my mechanical gauge on the truck. I never got it to start with the ICP sensor unhooked - and I never had a chance to unhook it while the truck was running as I was trying to check as many things as possible because it seemed like I would only get a couple of minutes of run time at best today.

It was really irritating - this hard start low ICP stuff came up at a truck pull two weeks ago - I attributed it to a dying alternator that we changed out at the truck pull and it seemed OK. I went out there to change tunes today - put new tunes on the truck - it started right up - tested it to make sure the issues we were tweaking for were gone - everything was fine - and then BAM - truck dies - back to low ICP hard start - start/run/die crap.... I seldom go to work on a truck and have it running when I get there and not when I leave....

On EDIT: I also when back to the old tunes just to make sure something wasn't goody with the new ones - no dice - same thing.

lincolnlocker · Jun 3, 2012

sounds like what mine did when i had a bad icp sensor and after my ipr took a chit. did sorta the same thing when my batteries took a chit and after my alternator took a chit... only time it ever died was when the ipr was bad..

OSCS · Jun 3, 2012

IPR.. mine did the exact same thing when i swapped injectors and hpop, ran fine for like 2 days and then BAM same problems you had.. changed the icp with no luck but as soon as i changed the IPR it ran perfect.

Dieselboy. · Jun 4, 2012

Jason, whats the oil pressure look like (LPOP)

Possibly a failing LPOP not supplying the HPOP ?

907DAVE · Jun 4, 2012

Is the truck an automatic?

davey99ps · Jun 4, 2012

I know I had similar problems when I somehow had debris in my oil after a thousand miles an I must of cleaned my ipr 5 or 6 times. Changed the oil an all was well again

Hotrodtractor · Jun 4, 2012

907DAVE said:
Is the truck an automatic?

Interesting - yes it is an automatic - but there is a PCS running the transmission.

lincolnlocker · Jun 4, 2012

When it starts how long will it run for?

Hotrodtractor · Jun 4, 2012

lincolnlocker said:
When it starts how long will it run for?

It varies - sometimes it will shut off immediately, sometimes a minute or two, and it sat and idled for a little while this morning when I talked to the owner.

lincolnlocker · Jun 4, 2012

i see. just thought maybe the lpop was possibly losing prime... is there an actual lpo gauge on the truck... not the stock one.

Hotrodtractor · Jun 4, 2012

lincolnlocker said:
i see. just thought maybe the lpop was possibly losing prime... is there an actual lpo gauge on the truck... not the stock one.

There isn't one - and I don't really think that is the issue because when it does run and isn't quirky - it makes GREAT ICP pressure - it just seems to have this issue at idle. I'll take a pressure gauge out there with me and double check it though just to make sure.

lincolnlocker · Jun 4, 2012

when you started it this morning and it idled for a while, was that the first start of the day?

Hotrodtractor · Jun 4, 2012

lincolnlocker said:
when you started it this morning and it idled for a while, was that the first start of the day?

I wasn't there - but I would say yes. Yes - I think its a heat related IPR issue - it gets hot - it goes wonky.

lincolnlocker · Jun 4, 2012

fresh oil? or throw some 50w in it and see what it does.

so it runs and idles with cold oil and the icp is steady... after it warms up is when it goes wacky does the icp go crazy with it or does it just say F U and die?

Hotrodtractor · Jun 4, 2012

lincolnlocker said:
fresh oil? or throw some 50w in it and see what it does.

so it runs and idles with cold oil and the icp is steady... after it warms up is when it goes wacky does the icp go crazy with it or does it just say F U and die?

It just flat dies. It has a random RPM drop - but according to AE the ICP remains steady - I didn't have my mechanical gauge there to confirm. Its not the ICP sensor - already tried unplugging that to see if it made a difference - it was just noticeably the default values when I did that.

It always seems to start cold - once hot it seems hit and miss to build enough ICP to fire.

It is already running straight 50w racing oil in it - but planning on changing it with the IPR.

lincolnlocker · Jun 4, 2012

chang oil first and see... then the ipr.. i would like to know what it is out of the two if those cure it without changing both at the same time.

kyle43335 · Jun 4, 2012

Hotrodtractor said:
I wasn't there - but I would say yes. Yes - I think its a heat related IPR issue - it gets hot - it goes wonky.

i ran into that as well.

ive also had a truck run weird when,and only when it rained.

turned out the female cavities were loose in the cps plugs.

i used a awl,to squeeze them tight for a good solid connection. straightened the truck right out.