Mystery stall - Ford Powerstroke Diesel Forum
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post #1 of 11 Old 08-18-2019, 08:55 PM Thread Starter
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Mystery stall

So I am new to diesels but fair with a wrench. I've got a real hum dinger for me being a gasser and all.
1997 7.3 4x4 f250hd xlt obs 200k on it.

The truck surges at idle 400ish to 650ish it will stall occasionally on its own and if any extra load at idle is applied it will almost always stall. If you give it gas it evens out and runs. I am not sure if it's making power as the tranny is going and for all I know it's in 2nd gear, but its real sluggish to get going either way but at 2000rpms it seems good for what I think is stock equipment.

Now this truck was a headache for the previous guy who never had it run good and who was not a do it yourself and had shops do the work for him. He had a after aftermarket intake put in, the tanks replaced, new 4inch straight exhaust installed, pedestal delete, new turbo, all new sensors, new vacuum pump. Injector o rings replaced and injectors professionally tested new under valve cover harnesses. He started to install aftermarket gauges and has a 7 position ts performance tuner on it.

The injection shop said maybe hpop, I don't have the tester for that yet but the forscan tells me hpop is ok.

I think for what ever reason the pcm is starving the engine.
I thought pcm because I put in a 12v hot to the ipr and this resolves the issue and the truck sounds normal. High idle also does the trick. So I feel like the mechanicals are all good.
I've swapped the pcm with two known good ones as well as the idm no change. The only indication I have on the scanner is maybe maps one is 105 one is 2-3 and one is 0 at idle.

Also electronic backpressure control both the psi and volts constantly jump from min to near max. 30 times a minute at least at park or drive I am guessing the solenoids are shot but I pulled the connector on the passenger side and still jumps I replaced the position sensor on the transmission as well. No change.

Any ideas? My guess is the pcm is commanding something that's causing it based on a bad something else. But I've got no idea what either of those things are.
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post #2 of 11 Old 08-20-2019, 01:45 AM
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First off remove the tuner completely. Eliminate that from the equation.

If you supplied 12V to the IPR then it's most likely shot. It's a solenoid that only receives somewhere around 5V max.

To really know what's happening we need to see IPR % at idle and HPOP pressure. Should be able to get those #'s with a good scanner.

Check the ICP connector for oil. Has CPS been changed?
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post #3 of 11 Old 08-20-2019, 09:47 AM Thread Starter
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Thank you for the help, going in order.

Ive run it with and without for testing no change other than High idle seems to mask the problem and it seems to stall more frequently in power tunes, I don't keep it plugged in.

On the IPR I will probably replace it anyways and keep this one as a spare if it doesn't fix it but FYI I think the 12v isn't a problem dieseltechron (youtubber) who I believe is a ford diesel tech suggests it as part of a diagnostic process to eliminate the PCM aspect, he said this defaults the IPR to 60%. What worries me is that when running at idle with the bypass in place to keep the truck running I pick up 12v on the connector hot side with a multimeter. I think ill run those wires back as far as I can go but it doesn't fluctuate its a constant 12V but I cant monitor at anything other than idle right now. Ill find a way to get a read during a road test if I cant trace out a short. Could it be that it receives a constant 7v and has 5v variable control circuit doesn't really make sense but I don't know what I don't know? This sounds like a problem but considering that its running at a loop at idle instead of low or high and no issues at partial to WOT I am not sure this is the fix I am looking for but ill see about fixing it anyways. I intend to restore the truck completely.

Readings are with the bypass in place otherwise no readings are steady. IPR duty cycle% is steady reading at approx 13% to a max of 34.77% at WOT. I could not find a HPOP reading in forscan there is an injector control pressure reading that has a steady range from 725 to 2465 idle to wot. I think the key reading is the IPR voltage at WOT varies from 3.2 to 4 volts while IPR duty cycle% is stable at 34.77% it does the same thing at idle with 13% IPR dutycycle.

ICP sensor and CPS sensor were changed ICP is free of oil. Connectors are original. I am thinking about replacing the CPS again anyways as most of the parts the PO used were aftermarket. I've heard anything other than ford oem is prone to issues.

Does the truck have a pressure reading for HPOP? Would the scanner get confused with a 96 vs 97 code profile, I don't know but wasn't 97 the year they changed body styles as well as PCMs?
Are the fuel lines supposed to be so damn hot?
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post #4 of 11 Old 08-20-2019, 09:53 AM
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IPR will get battery voltage, but it will be "pulsed" (not steady) based on being turned off and on (frequently and fast duty cycle %) by the PCM as needed to control HP oil pressure. It may get fried by applying a steady B+ to it, but if the duration was short enough it could be OK. Cheers!
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post #5 of 11 Old 08-20-2019, 01:36 PM
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Lets step back for a moment to get a better understanding of how this works.....

The ICP reads High Pressure Oil from the HPOP. Based off this pressure it tells the IPR what % to open/close at.

IPR is a % of HPOP demand and if the HPOP can't keep up then you will get a high IPR % and a weak HPOP pressure(ICP pressure).

So with that very basically explained, if you put 12V to the IPR you can fry it.

If IPR % is around 13% at idle and HPOP is at 725 then you are looking good at idle. BUT if it dies once you touch the throttle then it sounds like your IPR is crapping out.

IPR = Injector Pressure Regulator
ICP = Injector Control Pressure
HPOP = High Pressure Oil Pump
CPS = Cam Position Sensor
PCM = Power Control Module (aka Powertrain)
IDM = Injector Drive Module
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post #6 of 11 Old 08-20-2019, 02:22 PM
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Don't forget to replace the IPR harness end. Most of the time the little section of wire/connector is so soaked with oil/heat even a good IPR will give you false negatives. I would start with IPR Harness/IPR and see where the truck sits.

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post #7 of 11 Old 08-20-2019, 07:13 PM
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The IPR% is a "duty cycle" meaning the percentage of available time the IPR is operating (battery voltage applied) to close off the drain path (and thus raising HP oil pressure in the rails. The PCM will provide the ground to apply voltage to the IPR. Maximum commanded IPR% is 54% for 94-97, so in that case slightly over half the time the IPR is getting the voltage. Cheers!
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post #8 of 11 Old 08-20-2019, 08:27 PM Thread Starter
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Thank you for the replies. I appreciate the feedback.

Something I forgot to mention since its been 104 down here and the truck is already warm when I go to start it in the afternoons. Is when the truck is cold it doesn't surge first 1 to 2 minutes and it progressively develops as the truck warms up. A cold start with the bypass doesn't have the surging. But I haven't seen it do this in a couple weeks.


I don't have a steady idle on the pcm at any throttle position the truck runs fine just not at idle it won't stall if you have it on any throttle. With the bypass it runs fine at idle and any throttle position.

Isn't the hpop supposed to build to 5000psi?
I got a good fuel pressure tester in today its sitting at 55psi so I guess I don't have to worry about that. Also that Schrader valve is shot. I am ordering the hpop adapter and the guide I read said at least a 5000psi gauge. Also the transmission temp sensor has a short don't ask me why that showed up during the contribution test.
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post #9 of 11 Old 08-20-2019, 08:49 PM
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The term ya'all are looking for is PWM, pulse width modulated -- in this case the IPR valve is just that -- as explained previously the valve is fed 12 volts by the PCM and the return path(ground) uses a switched ground to vary the "on time" of the valve -- kinda like turning a light switch on/off at different speeds and making a brighter or dimmer light

Rather than adding B+ to the IPR, use instead a ground(most you will do is pop a fuse) -- when measuring the voltage in the connector(disconnected), you should see 12 volts and zero -- with the connector in circuit, you would measure 12 volts and some measure of less than 12 volts(IPR coil feeds thru) -- depending on the quality of the meter and the frequency(PWM) of the ground leg -- this is really scope territory to measure properly

The IPR valve can have straight 12 volts applied, but only for a short time <30 seconds

I would not recommend adding 12 volts to the IPR harness connector, unless you are sure of the polarity -- 12 volts without a fuse on the PCM ground could be a disaster for the PCM

"Are the fuel lines supposed to be so damn hot? "
Where are you seeing this?

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post #10 of 11 Old 08-21-2019, 03:23 AM Thread Starter
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The fuel lines in and out of the bowl. Like I said I was a gasser I feel like it's too hot but I know the thing has a fuel heater some aspects of the engine are completely new to me. I think a southern Texas truck could do without.

Last edited by ApexPredator; 08-21-2019 at 03:27 AM.
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