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99 & up 7.3L Power Stroke Engine and Drivetrain Discussion of the 99 & up 7.3L Power Stroke diesel engine and drivetrain in the 1999-Up Super Duty trucks and Excursions. No gas engine discussion allowed except on transmissions and drivetrain that pertain to all models. Please confine discussion of topics in this forum to those items that are specific to the 7.3L Power Stroke engine.

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Old 10-26-2006, 02:54 PM   #1 (permalink)
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Rough idle, barely runs at low RPMs.

I have recently aquired a 2001 7.3 E450 (only 11k) miles. I ran into a problem with a clogged filter 'cause the weather changed abruptly when using diesel-veggie oil fuel blend. I have some experience doing this, but I didn't finish the installation of the fuel heaters on this particular vehicle. Anyway, my girlfriend needed a ride and she was livid when we got stuck on the highway. She's been stuck on the highway with me before - once 100 miles from home. Anyway, I had no spares on hand and it was too late to purchase another one. In an attempt to keep her happy, I did something pretty stupid. I poked a couple of holes in the filter to allow some fuel to flow. This was just supposed to be a quick fix to get us home, but a leak from the filter housing gasket sprayed diesel/veg-oil blend all over the engine compartment - wiring harness, etc. Had to fix that, and in the mean time, she got pissed and took the subway home...wouldn't let me in when I finally got there.

The next day I got 5 gallons of "diesel" that a friend had lying around, and although it looked and felt like diesel when I rubbed it between my fingers, I later detected the smell of gasoline.

After one more day I cleaned the injector to valve-cover gasket wiring harness with silicone spray, filter housing with brake parts cleaner, installed a new filter and filled the housing with SeaFoam. It helped, but not very much. I also installed a pre-pump filter, that will be heated for later use with veggie-oil, and filled the tank with 55 gallons of fresh diesel fuel with 16oz of DieselKleen. Now the engine idle cycles from about 515 to 850 RPMs. I assume this is from the Powertrain Control Module trying to compensate. Upon acceleration (driving) when it FINALLY reaches about 1300 RPMs, the engine smooths out quit a bit. Then, after coming to a stop-light it often stalls.

I'd really like to get some ideas about what other folks think the problem may be. My guess is either moisture in the main wiring harness connector (above the filter), or I screwed up the injectors. Am I on track, here? The scan tools from Autozone don't seem to be able to tell me anything. Please help.
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Old 10-26-2006, 04:13 PM   #2 (permalink)
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Re: Rough idle, barely runs at low RPMs.

How old is your engine oil? An idle lope like that could be caused by worn out oil. Another possiblity is a sticky IPR.

Then again, you may need to remove your injectors and have them gone thru if crud got thru the filter and into them. The fact that it's running kind of indicates that your injectors may be OK, though.

You'll need to go to a shop with a PSD capable scan tool.

A more understanding gf would be good, too. [img]/ubbthreads/images/graemlins/crazy.gif[/img]
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Old 10-26-2006, 04:19 PM   #3 (permalink)
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Re: Rough idle, barely runs at low RPMs.

if you don't have a SES (service engine soon) light then I'd say, with 99% certainty, that all electronic connections/harnesses are OK.

...which leaves mechanical issues from running poor/questionable fuel through the system & injectors.

Even a small dose of gasolone into the injectors will score & gall the parts...plunger & barrel assemblies to be exact...rendering them 'cores'.

Now, on the other hand, if you DO have a SES light, and the AutoZone 'codereader' (hardly a diagnsostic scantool for these trucks) was unable to register any faults...then there's hope that the injectors ARE OK...and it is simply a wiring harness issue...

If you don't have the SES light...then you'll need to have some (real) diagnostic tests performed...some requiring a 'real' scantool.

Something you can check on your own, would be fuel pressure. Get a mechanical gauge installed in the rear of the drivers side head...(take off the air inlet to turbo) look for a square headed plug (9/32")...remove that plug, and install an 1/8" pipe fitting into the head with a liquid filled 0-100psi gauge on the other ned of the hose...

fuel press at idle should be aroud 55-65psi...more importantly is the fuel pressure under load...if the pressure drops below 35-40psi at wideopen (while driving, not in parl or neutral) then start with a new filter (yes, another one)...

if fuel pressure is still low, replace the electric fuel pump on the frame rail...(O'Reilly auto parts # E2236)

If fuel pressure comes up, but the truck still runs like crap...then take it to a mechanic that can run a couple of critical tests.

The first test is the Injector Buzz test (key on, engine off) this test will determine if all connections to and from the engine computer and the injectors are good.

The second test is the Cylinder Contribution Test (CCT)...key on, engine running at operating temperature...this test will turn off (and on) each injector, electrically, and "measure" each injectors contribution to total engine power...if your test passes the previous test (the Injector Buzz Test) but fails the CCT test, then 99.9% the problem will be a problem internal to the injector...and the CCT test will flag any injectors not contributing as much as the others.

good luck (and quit pouring junk into your fuel system)

take care~

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Old 10-26-2006, 09:44 PM   #4 (permalink)
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Re: Rough idle, barely runs at low RPMs.

a more understanding gf? what is a gf?
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Old 10-26-2006, 10:00 PM   #5 (permalink)
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Re: Rough idle, barely runs at low RPMs.

gf=girl friend [img]/ubbthreads/images/graemlins/biggrin.gif[/img]
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Old 10-26-2006, 10:00 PM   #6 (permalink)
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Re: Rough idle, barely runs at low RPMs.

The Service Engine Soon light does NOT illuminate. I'll have to come up with some money to get someone with a decent scan-tool to look into it. Perhaps I'll buy one of those PC-scan-tools. Does anyone know some inexepensive ones that work well for the PSD?
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Old 10-26-2006, 10:19 PM   #7 (permalink)
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Re: Rough idle, barely runs at low RPMs.

I'm not sure of the age of the oil, but I know it ran absolutely wonderfully, prior to the filter getting clogged. After thinking about the replies thus far, I'm leaning towards the injectors. I will get someone to do a more comprehensive test first, though. I've even considered doing some temporary work for the local Ford dealership, in exchange for the use of some of their tools.
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Old 10-28-2006, 12:47 PM   #8 (permalink)
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Re: Rough idle, barely runs at low RPMs.

golfer: with regard to fuel pressure. I did hook up a pressure gauge. I wish I'd used your idea of opening the plug in the cylinder head. Instead, I'd already cut the fuel suppy line (near the filter housing) and installed a "t-connector" with rubber hoses (fuel-injection rated) and clamps. Pain in the butt, however it will serve as a nice way to replace the fuel supply line with a custom heated one, later.

Anyway the fuel pressure was reading around 110psi. I cut about 3 milimeters off of the fuel pressure regulator spring where the return fuel exits the filter housing. I re-assembled everything, and found the pressure to be right at about 55psi. I have to get a better gauge, though, as mine reads 7psi even when disconnected. Under load and above 1300 rpms, the engine runs pretty well, though. I'll probably install an aftermarket FPR, and "t-connect" both cylinder head plugs to it, allowing return fuel to flow out of the heads - like they did in the 97s - 98.5s.

Thank you all for your responses, and if you think of anything else, please clue me in.

Thanks again.
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Old 10-28-2006, 04:51 PM   #9 (permalink)
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Re: Rough idle, barely runs at low RPMs.

Holy moley! 110psi, LOL?!? [img]/ubbthreads/images/graemlins/laugh.gif[/img] Not that that's bad (other than for the pump)...just unnecessary...65-75psi is fine.

Since it sounds like your going to install a "real" regulated return fuel system, inplace of the stock super duty factory junk...then you can cap off that factory return line/regulator and set the pressure back up to 70 or so with your "new" regulator (when the time comes)...

I'd suggest that you move on to having the buzz & Cyl Contribution Tests performed...

if it turns out you need an injector or 2...I'm inclined to recommend that you flush your fuel system...from the tank to the heads and back...it's a nasty job, but if you've scored your current injectors, and new ones go in with the same ol' "questionable" fuel...then...well...you can imagine the rest.

take care~

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Old 10-28-2006, 05:13 PM   #10 (permalink)
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Re: Rough idle, barely runs at low RPMs.

[ QUOTE ]
Holy moley! 110psi, LOL?!? [img]/ubbthreads/images/graemlins/laugh.gif[/img] Not that that's bad (other than for the pump)...just unnecessary...65-75psi is fine.

[/ QUOTE ]

Dave,

Since ktraglin punched a hole in his fuel filter, maybe the cause of the high FP is junk clogging the inlet of the regulator. I've seen some posts where guys had rough running trucks, and they would smooth out when they opened the fuel drain valve.

I don't have any direct experience with this, but it could be a possibility. Maybe an experiment with my return regulated system is in order to see what happens when I jack the pressure up to the max. [img]/ubbthreads/images/graemlins/shrug.gif[/img]

kttaglin,

Have you managed to get it running better yet? Checking out the fuel pressure regulator might be a good idea. Pull the return line off, and then the regulator housing and clean the parts out. Also check that the port from the filter bowl to the regulator is clear.
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Old 10-28-2006, 07:53 PM   #11 (permalink)
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Re: Rough idle, barely runs at low RPMs.

dont they say kevin that excessive fuel pressure will pop the injector o-rings?
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Old 10-28-2006, 08:00 PM   #12 (permalink)
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Re: Rough idle, barely runs at low RPMs.

[ QUOTE ]
dont they say kevin that excessive fuel pressure will pop the injector o-rings?

[/ QUOTE ]

Not sure about that. O-rings are usually pretty stout, and the external injector o-rings stand up to HP oil pressure (much higher than fuel pressure) on the other side. Maybe Dave (golfer) could weigh in on any affect on internal o-rings.
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Old 10-29-2006, 06:55 AM   #13 (permalink)
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Re: Rough idle, barely runs at low RPMs.

Well I think we need some more information. [img]/ubbthreads/images/graemlins/shrug.gif[/img]

-When it's running bad, is it smoking?
-Has the sound of the engine changed? maybe to more of a "clacking" sound?
-Once the 1300rpm mark is hit and the engine runs great again, does it matter if the truck is traveling over 40 or under 30? Can you press the accelerator and have the same response as you use to?
-When you start the truck, is it hard to start and once it does barely faster than the starter was turning it and then you think its going to die while it chokes and heevs up to idle?

Sounds to me like you have a leak in the fuel line and are sucking air. Don't ask me how I know [img]/ubbthreads/images/graemlins/phoney.gif[/img]. You may click on my sig link for how I've butchered my fuel system [img]/ubbthreads/images/graemlins/biggrin.gif[/img] [img]/ubbthreads/images/graemlins/biggrin.gif[/img] These truck will run (after started) with out a fuel pump! Sooo if you have an obstruction, the engine is going to attempt to "draw" fuel and depending on the durability/design of your fuel taps or filter cap gasket or fuel/water drain O-rings, allow air in when you think it would be blowing fuel [img]/ubbthreads/images/graemlins/eek.gif[/img]

One more thing, unless your added hose (even though it's fuel injector rated) is Viton, you'll be kickin your self in the keyster for installing a component that is contraindicated for Veggi Oil/Bio-Diesel [img]/ubbthreads/images/graemlins/phoney.gif[/img] To allow an alternate inlet of fuel into the filter housing you could have also just opened the #4 ORB plug seen here in the upper left quadrant of the fuel filter housing. (You looking at the REAR of the filter housing)
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Old 10-29-2006, 08:33 AM   #14 (permalink)
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Re: Rough idle, barely runs at low RPMs.

Word of advice unrelated to the GF. After years of marriage and 80% of our friends now divorced. If either partner is that impatient the marriage will likely not last. Do you think the pioneers who walked across this country treated each other that way? You stated you took risks and did things you likely would not have to “attempt to keep her happy”. Also the fact that you were locked out when you finally got home was another indication… Word of advise from someone with 25 years of marriage. You need a partner who answers the “sickness & health, richer/ poorer, good times and bad”, etc. sincerely. You don’t need a slave but a friend who has your back. IF you learn anything from this forum this will be of the most value over the next 50 years. Just my $.02.
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Old 10-29-2006, 09:01 AM   #15 (permalink)
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Re: Rough idle, barely runs at low RPMs.

[ QUOTE ]
Word of advice unrelated to the GF. After years of marriage and 80% of our friends now divorced. If either partner is that impatient the marriage will likely not last. Do you think the pioneers who walked across this country treated each other that way? You stated you took risks and did things you likely would not have to “attempt to keep her happy”. Also the fact that you were locked out when you finally got home was another indication… Word of advise from someone with 25 years of marriage. You need a partner who answers the “sickness & health, richer/ poorer, good times and bad”, etc. sincerely. You don’t need a slave but a friend who has your back. IF you learn anything from this forum this will be of the most value over the next 50 years. Just my $.02.

[/ QUOTE ]

Agree 100% !!! I had bad running engine as you described. I put gas in mine too. Would barely run & had to restart a few times to limp home. I syphoned out as much as I could. Refill tank with 10 gal of diesel & one quart of Diesel-kleen. Cycled key about 7 times and waited for pump to stop each time(about 20-30 seconds) Then try & start. Ran very, very poorly for about 2-3 minutes then slowly cleared up. Then ran it about a good 20 minutes to get real hot. Everything seems ok now. I hope yours is just fuel related & can fix with filter & good fuel. Good luck & keep us informed of out come .
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