Very rough idle, runs better at higher rpm, help! - PowerStrokeNation : Ford Powerstroke Diesel Forum
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post #1 of 18 (permalink) Old 07-28-2017, 02:06 AM Thread Starter
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Very rough idle, runs better at higher rpm, help!

I've got a very rough running 7.3, 97OBS. It runs like it's missing on 4 cylinders when idling, particularly hot. If it's cold, it runs better when idling, and after it warms, it gets worse. I have an obd dongle, and loaded the pid's for the psd. my ICP reads around 550-600, and the IPR reads about 12-14%. I think that is within spec, and it kind of stopped me in my tracks as i thought some o-rings were bad and was getting ready to replace them all.

I did just complete e-fuel conversion. No change other than no more fuel leaks.

Found some online tech info that suggested checking for flywheel balance if m/t, mine is. Also, suggested a compression check, which i don't really have a way to do so at this point, particularly if the engine shows signs of bad air filter. I did buy the truck in Texas and the moron who had it before had a K/N filter on it, and the turbo blades are chewed up. Would a worn cylinder really cause this much of a bad idle? It seems to run much better at higher rpms. Running down the road smooth, i get like 18 mpg, with a crew dually and 4.10's. I can't believe the mpg would be so good with worn cylinders.

Recent maintenance: New glow plugs, battery cables, UVCH on one side, (obvious bad burned wire) and all circuits ohmed out good when done. Glow relay, efuel. Haven't dug into sensors much yet. The buzz test had them all buzzing about the same. I was going to do all injector o-rings and ipr orings next. then the readings i finally got look ok, so i don't know i want to pull all the injectors yet.

Any wisdom here PSN gurus?

Thanks

1997 F350 CCLB Dually XLT
1986 Bronco 6.9 Turbo XLT
Powertrain engineer by trade have worked for three OEM's.

Last edited by 86turbodsl; 07-28-2017 at 02:12 AM. Reason: typo
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post #2 of 18 (permalink) Old 07-28-2017, 02:19 AM
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Re: Very rough idle, runs better at higher rpm, help!

Any codes produced by the buzz test?
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post #3 of 18 (permalink) Old 07-28-2017, 03:30 AM Thread Starter
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Re: Very rough idle, runs better at higher rpm, help!

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Any codes produced by the buzz test?
Nope. I just ran the buzz test again, and they all sound identical.

I also thought i should mention that it's idling at about 550 rpm. I do think this is low. What is normal?

1997 F350 CCLB Dually XLT
1986 Bronco 6.9 Turbo XLT
Powertrain engineer by trade have worked for three OEM's.
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post #4 of 18 (permalink) Old 07-28-2017, 04:06 AM
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Re: Very rough idle, runs better at higher rpm, help!

I'm having the EXACT same problem, except mine had a CEL and threw code p0261 from the buzz test. Interested to see where yours goes.


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post #5 of 18 (permalink) Old 07-28-2017, 02:23 PM Thread Starter
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Re: Very rough idle, runs better at higher rpm, help!

Additional info:

Oil consumption is low. IE, at 3000 miles, it wasn't really down much if any on the dipstick. Before i changed oil, when it was cold, it would run decent for a bit and then warmed up and idled worse. AFTER the oil change, it idled pretty much bad from cold start. Oil is 15w-40 dino.

That's what made me think marginal injector o rings.

What are acceptable ICP/IPR values at idle?

The truck does have a TS chip. Can bad tunes make it idle lower? What's a normal idle speed?

1997 F350 CCLB Dually XLT
1986 Bronco 6.9 Turbo XLT
Powertrain engineer by trade have worked for three OEM's.
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post #6 of 18 (permalink) Old 07-28-2017, 03:27 PM
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Re: Very rough idle, runs better at higher rpm, help!

That's usually a sign of a misfire or dead cylinder. It smooths out because there is less time between the powerstrokes so a missed one won't be felt as much.

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post #7 of 18 (permalink) Old 07-28-2017, 03:50 PM Thread Starter
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Re: Very rough idle, runs better at higher rpm, help!

Ok, since the fact that it runs ok cold on old oil, where the viscosity is high, and not warmed up when it thins out, sort of points again to a bad o-ring on one of the injectors does it not? Can a single bad injector still keep the icp/ipr numbers in the good range, or does a bad injector skew the numbers a lot? i'm new to diagnosing 7.3 heui's. Just not enough experience to know what i'm looking at yet.

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1997 F350 CCLB Dually XLT
1986 Bronco 6.9 Turbo XLT
Powertrain engineer by trade have worked for three OEM's.
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post #8 of 18 (permalink) Old 07-28-2017, 05:26 PM
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Re: Very rough idle, runs better at higher rpm, help!

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Originally Posted by 86turbodsl View Post
Ok, since the fact that it runs ok cold on old oil, where the viscosity is high, and not warmed up when it thins out, sort of points again to a bad o-ring on one of the injectors does it not? Can a single bad injector still keep the icp/ipr numbers in the good range, or does a bad injector skew the numbers a lot? i'm new to diagnosing 7.3 heui's. Just not enough experience to know what i'm looking at yet.

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Is your eot[engine oil temperature] sensor reading properly?Try running it without the chip. If no change do a compression check. If that's good put new o-rings on the injectors as long as the valve covers are off.
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post #9 of 18 (permalink) Old 07-28-2017, 06:03 PM
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Re: Very rough idle, runs better at higher rpm, help!

Icp is good. Ipr is a touch high.

I would pull the valve covers and start it. Watch the oil squirters on the injectors. If one is not squirting or it's weak it could be a bad injector. While to valve covers are off I would unplug one injector at a time and see if it changes anything. If you unplug one and nothing happen. You have an issue with that cylinder.

But also to consider. With no codes it could fuel problem but you did just do efuel. So what is your fuel pressure at.

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post #10 of 18 (permalink) Old 07-28-2017, 06:06 PM Thread Starter
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Re: Very rough idle, runs better at higher rpm, help!

I set my fuel pressure at 65psi. I will do a cold start tonight when i get home and see if i can get more accurate numbers. Pulling valve covers is a more invasive task for the moment.

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1997 F350 CCLB Dually XLT
1986 Bronco 6.9 Turbo XLT
Powertrain engineer by trade have worked for three OEM's.
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