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Old 11-15-2012, 03:44 PM
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Exclamation Loping idle at start & slow throttle response

Hi all,

New here, but been reading a lot (both here and elsewhere) and a new diesel owner.

Vehicle:
1996 Automatic F250 XL with 7.3 PSD 170k+ miles, AFE Big Boost intake, everything else stock.

Symptoms:
Rough loping idle at start only, regardless of engine temperature. Once throttle depressed approximately 1/2 inch, to bring RPM up to 1000 RPM, then slowly released completely, idle stabilises.

Accompanied by very slow throttle response which is especially bad when cold (for my purposes throttle response being the rate of acceleration with the throttle fully depressed).

As soon as RPM above 1500, one can feel turbo boost commence and throttle response improves. Runs smoothly at higher RPM.

When revving up and abruptly releasing throttle, the engine would falter and drop below 500 RPM, at times dying out.

Had water in fuel light illuminate intermittently (on right hand turns) a couple of times, whilst burning through both tanks, drained fuel bowl a couple of times when that happened, problem has not presented itself again.

Transmission shift points are kinda all over the place, sometimes shifts smoothly (usually the lower gears) then abruptly for higher gears, sometimes not shifting to OD by 3000 RPM requiring me to throttle down somewhat, then it shifts.

Assuming shifting issue to be unrelated to engine running issue at the moment. Not addressing until engine resolved.

Corrective actions taken: (I attempted to accomplish the cheapest alternatives first)
- Changed engine oil (Delo 400) and filter (that's a lot of oil!)
- Changed fuel filter (in water separator housing); quite dirty.
- Replaced Exhaust Back Pressure (EBP) pipe & sensor; both totally blocked with fouling
* IAW Welcome to guzzle's Exhaust Backpressure Sensor Cleaning Maintenance Web Page)
* purchased at DFUSER Diesel Performance Products Exhaust High Performance Part Diesel Intake Diesel Power Chips
- Previous owner replaced Camshaft Position Sensor (CPS), then I changed it again, with blue international version, just to be sure.
* IAW TikiWiki : P0344 Camshaft Position Sensor Circuit Intermittent
* purchased at Improved Blue CPS for 7.3L Ford Powerstroke Diesel
- Engine Control Module (ECM) was replaced by previous owner in an attempt to address this problem.
- Previous owner replaced mechanical fuel pump.
- I connected an OBD2 analyzer; no fault codes stored statically and no problems found on running tests.

Outcome:
No noticeable improvement.

Clutching at straws now (well, I have been since I started, but hey!), I will be pulling the Fuel Pressure Regulator (FPR) screen.
* IAW FPR Screen cleaning writeup - Ford Truck Enthusiasts Forums
Other than that, i am kinda at a loss. I did read elsewhere that the turbo veins may be stuck open??
* Low Power Until About 1500 RPM - PowerStrokeNation : Ford Powerstroke Diesel Forum
Any advice or suggestions would be greatly appreciated at this point.

Thanks
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  #2  
Old 11-16-2012, 08:15 AM
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Quote:
Originally Posted by thinkB4uh8 View Post
Hi all,

New here, but been reading a lot (both here and elsewhere) and a new diesel owner.

Vehicle:
1996 Automatic F250 XL with 7.3 PSD 170k+ miles, AFE Big Boost intake, everything else stock.

Symptoms:
Rough loping idle at start only, regardless of engine temperature. Once throttle depressed approximately 1/2 inch, to bring RPM up to 1000 RPM, then slowly released completely, idle stabilises.

Accompanied by very slow throttle response which is especially bad when cold (for my purposes throttle response being the rate of acceleration with the throttle fully depressed).

Can you post a vid? These first Gen Power Strokes aren't as bottom end friendly as the newer trucks They LOVE to play above 2000RPMs. On each head at the valve cover there are two (each) injector/glow plug connectors. Remove each connector and inspect the insides for oil (should be clean and dry) and burned pins (should be bright and shiny).

As soon as RPM above 1500, one can feel turbo boost commence and throttle response improves. Runs smoothly at higher RPM.

Normal for a stock turbo. With the stock turbine housing you are not going to see good usable boost till about 1600RPMs but more like 1800RPMs. Again look at the VC harness like stated above.

When revving up and abruptly releasing throttle, the engine would falter and drop below 500 RPM, at times dying out.

HHmmmm...Possible weak HPOP (high pressure oil pump), IPR, ICP, or shorted wiring harness.

Had water in fuel light illuminate intermittently (on right hand turns) a couple of times, whilst burning through both tanks, drained fuel bowl a couple of times when that happened, problem has not presented itself again.

Sounds like you got a handle on this. With winter on us (I don't know where you live) look into a winterizing fuel additive (like Diesel Kleen [white bottle] from Power Service at your local parts store). Diesel turns to jelly when it gets cold enough. The truck can't inject jelly. Winterizing additives keep the gelling at bay.

Transmission shift points are kinda all over the place, sometimes shifts smoothly (usually the lower gears) then abruptly for higher gears, sometimes not shifting to OD by 3000 RPM requiring me to throttle down somewhat, then it shifts.

PCM controlled. Like you said, get a handle on the engine issues and the tranny may smooth out. Also, when was the last tranny fluid swap? Look to see if the fluid is bright red and absolutely clean. Does the speedo needle jump around as you accelerate?

Assuming shifting issue to be unrelated to engine running issue at the moment. Not addressing until engine resolved.

Corrective actions taken: (I attempted to accomplish the cheapest alternatives first)
- Changed engine oil (Delo 400) and filter (that's a lot of oil!)
- Changed fuel filter (in water separator housing); quite dirty.
- Replaced Exhaust Back Pressure (EBP) pipe & sensor; both totally blocked with fouling
* IAW Welcome to guzzle's Exhaust Backpressure Sensor Cleaning Maintenance Web Page)
* purchased at DFUSER Diesel Performance Products Exhaust High Performance Part Diesel Intake Diesel Power Chips
- Previous owner replaced Camshaft Position Sensor (CPS), then I changed it again, with blue international version, just to be sure.
* IAW TikiWiki : P0344 Camshaft Position Sensor Circuit Intermittent
* purchased at Improved Blue CPS for 7.3L Ford Powerstroke Diesel
- Engine Control Module (ECM) was replaced by previous owner in an attempt to address this problem.
- Previous owner replaced mechanical fuel pump.
- I connected an OBD2 analyzer; no fault codes stored statically and no problems found on running tests.

Outcome:
No noticeable improvement.

Clutching at straws now (well, I have been since I started, but hey!), I will be pulling the Fuel Pressure Regulator (FPR) screen.
* IAW FPR Screen cleaning writeup - Ford Truck Enthusiasts Forums
Other than that, i am kinda at a loss. I did read elsewhere that the turbo veins may be stuck open??
* Low Power Until About 1500 RPM - PowerStrokeNation : Ford Powerstroke Diesel Forum
Any advice or suggestions would be greatly appreciated at this point.

Thanks
Please see above.

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  #3  
Old 11-16-2012, 02:01 PM
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BigFuel,

Thanks for your expeditious response.

Attached couple clips in zip archive;
One shows the slow throttle response on pull away, sometimes its even slower. This is with max throttle.
The other shows the lope at start, as soon as I depress the throttle somewhat, it corrects itself.

I will check injector/glow plug connectors shortly, as per your suggestion.

With regards to IPR or ICP, wouldn't I get some kind of error indication on code reader if one of my electrical sensors were failing/failed?

Those videos may shed some light, you hear the engine noise quite clearly too, I know diesels can be loud and make a "tappet sound" predominantly caused by the detonation that's occurring (as opposed to combustion in a petrol engine), but this one is particularly loud. Actually diminishes when it gets warmer.

I currently reside in Hawaii, so cold weather is not really a concern

Cheers
Attached Files
File Type: zip vids.zip (4.89 MB, 91 views)
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Old 11-16-2012, 02:14 PM
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Do a compression test, I had a problem like that and it was a bad valve!!! Any "O's" coming out the exhaust?
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Old 11-16-2012, 02:35 PM
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WOW, that is a cranky b1tch. Sounds like a Caterpillar on cold start. Any smoke on cold start? What color? The ICP reports to the PCM what the HP oil galleys have in them for pressure. The IPR restricts the unused oil from the galleys back into the HPOP sump. Its' signal is translated into percent restricted. 2% is awesome, 50% is bad HPOP. The higher the number the more work your HPOP needs to perform BUT the PCM normally doesn't set a code it way late in the game. Now, the common issue with these engines is leaks in the engine valley. Either oil or diesel but diesel eats wiring harness isolation causing wiring issues that report bad signals to the PCM.

Your engine noise, either your glow plug system is shot, fuel pump is pressurizing to less then 45psi, or your HPOP is pressurizing to less then 500psi. With a volt meter (not a test light) ground the black lead and use the red lead to touch one side of the glow plug relay's big lugs. 12.6v ?ok, touch the other side big lug. Still 12.6v? Get a cheap dail tire gauge and get the truck running. On the back of the fuel bowl there is a Schrader Valve (like a tire valve) push it on and report the high/low (it's going to bounce a lot) pressure in the bowl. Throw away the gauge.

And again when you get the chance pull and inspect those VC harness connectors.

Last edited by BigFuel; 11-16-2012 at 03:43 PM.
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Old 11-16-2012, 03:32 PM
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LOL, my neighbours are getting pissed with my Caterpillar start in the mornings. Feels like I'm starting an old tractor.

@ BigFuel

This thing doesn't smoke, no matter what I do, how much throttle, what the condition, there is no smoke at all. With high throttle, as she shifts down, I can smell a surge of burnt diesel while driving, but never see any smoke.

Just checked the harness, aside from some minor oil contamination, that I cleaned, it looks nice and shiny, also no smell of burnt wires. No change to run though. Looks like the harness had been messed with previously though, some retaining clips broken off - no effect though, manually pushed em in all the way while running, same same.

I suppose Ill go get myself a cheap pressure gauge and check fuel pressure at the pressure regulator Schraeder. I assume the 45 PSI or more should be at stable idle? what should it be at higher RPMs? If that's good, is there a way to check HPOP output pressure without getting a blast of highly pressurized oil in the eyeball?

I assume the dealer told the previous owner that it was the mechanical fuel pump, resulting in him changing it out.

I'm getting approximately 12.6V on my glow plug relay; indication as specified - from one side only, relay seems to be operational.

@ Evanla_33

It might be stuck valve, but without smoke indications I feel as though its probably a fuel issue. Ill see about checking that though, right now any lead is better than none and if it doesn't involve me replacing parts as part of the troubleshooting process, I'm happy.

Thanks for all the tips thus far.

Cheers
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  #7  
Old 11-16-2012, 03:38 PM
Hee Hee, he's doing it...
 

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Just post turbo on the exhaust (before it goes down under the truck the the Exhaust Back Prssure Valve (EBPV) Those things do stick closed and cause some of your issues BUT there is usually a loud "WOOSH"'ing noise to go with it. The truck needs 45+ on the fuel pressure but ideally it needs to hang at 65psi at idle, cruse, WOT. The glow plug relay should show the 12v on both sides if you cycle the key.

The EBPV:

-Put your hand on the turbo (when cool)
-move it to the left to the little outlet from the turbo but before the exhaust down pipe
-move your hand to the underside of that outlet
-there will be a actuator rod and a butterfly valve arm
-pull straight down to release the rod from the arm and see if the butterfly arm rotates smoothly

Last edited by BigFuel; 11-16-2012 at 03:44 PM.
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Old 11-16-2012, 04:32 PM
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The EBP valve seems to be free and clear.

Also when I performed the running OBD2 check, the thing does it's own diagnostic, changing RPMs, etc. At one point I think it closes or restricts the EBPV because it sounds like there is a sudden restriction for a while, ran it twice, same thing. Suspect its checking the EBP sensor and function.

It runs the test in it's entirety and comes back with no problems detected.

Will get to that fuel pressure check when I get some time.

Cheers
Pete

Last edited by thinkB4uh8; 11-16-2012 at 04:37 PM.
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Old 06-02-2013, 07:18 PM
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Was this problem ever resolved. I am having similar problems.
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Old 06-25-2013, 08:15 PM
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I would like to know the same. Lol
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