Idles fine, misses under throttle - Ford Powerstroke Diesel Forum
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  #1  
Old 06-14-2013, 11:30 AM
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Idles fine, misses under throttle

First off, a couple weeks ago the truck initially dropped a cylinder or 2 or however many for a few seconds. truck was warm but had been sitting for maybe 30min so not hot. This happened about 1/4mi up the road and seemed like it was when I let off the go pedal. let it idle for a few seconds and it straightened itself out. Got another 1/4 mile or so and same exact thing. turned around and headed home. During each of these the CEL came on and went off as soon as it cleared up

I later did some testing to see what did what. I replaced the CPS, no change. Unplugging either of the passenger side UVCH plugs reproduces the symptoms but without the CEL and when I rev it to reproduce, the symptoms don't get any worse. The driver side plugs do the same thing but when I rev it to reproduce the symptoms, it fires on even fewer cylinders and eventually dies.

I can reliably reproduce symptoms by revving it to a bit over 1000 RPM and letting off. Haven't tried any higher. If I don't rev it quite as high it will do it but won't do it as long it seems like. It varies in how long it continues running rough. IT will idle all day long no problem.

I replaced the passenger side valve cover gasket and the two harnesses under the VC and symptoms persist.

Last week I bought AE to figure this out and here are my results.

Ok so ae is hooked up. Initial codes were as follows:
P1280 icp sensor circuit low
P0113 intake air temp circuit high input
P0470 exhaust pressure sensor

KOEO produced:
P0113
P0475

KOER:
P0476 exhaust pressure control valve range/performance

CCT produced no codes until i started unplugging uvch connectors.
With the cyl 1&3 connector unplugged i got:
P0263 cyl1 contribution/balance fault
P0269 cyl3
P0275 cyl5

With the 5&7 connector unplugged:
P0275 cyl5
P0281 cyl7

With 2&4 unplugged the truck shut off during the test.

With 6&8 unplugged, no codes for some reason. Wanted to shut off it seemed like.

It doesn't seem like it's storing the code that triggers the CEL when symptoms are present unless I'm just not doing something right.

I'm at a loss here guys, any help is very much appreciated!
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Old 06-14-2013, 12:32 PM
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Have you checked fuel pressure under load?
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Old 06-14-2013, 02:07 PM
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Quote:
Originally Posted by STROKED_NY_023 View Post
Have you checked fuel pressure under load?
I didn't really pay attention to fuel pressure while driving but when it does it in neutral the fuel pressure doesn't do anything weird. Stays right at about 70psi

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Old 06-14-2013, 04:27 PM
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Fuel pressure under load can be very different, but it doesn't sound lime that's your issue... Did you inspect all uvch harness really well for bare wires?

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Old 06-14-2013, 04:45 PM
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Go into AE and do a KOEO buzz test. That will tell you if you have a weak/disconnected injector.

With AE hooked up, take the truck for a drive, data log TPS, ICP, IPR %, and EBP.

Look at the results once you are parked. Make sure the ICP seems to follow the driving habit (ICP climbs immediately when throttle mashed then taper off.) Watch the EBP to see if it "sort of" mimics what you'd see your boost gauge do.
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Old 06-14-2013, 05:27 PM
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Quote:
Originally Posted by alberta 7.3 View Post
Go into AE and do a KOEO buzz test. That will tell you if you have a weak/disconnected injector.

With AE hooked up, take the truck for a drive, data log TPS, ICP, IPR %, and EBP.

Look at the results once you are parked. Make sure the ICP seems to follow the driving habit (ICP climbs immediately when throttle mashed then taper off.) Watch the EBP to see if it "sort of" mimics what you'd see your boost gauge do.
Did the buzz test multiple times, never any codes. I think that's because it's not constant. Is there a way to measure pike change in inertia by cylinder?

I'll do the data log and see what that turns up.

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Old 06-14-2013, 05:29 PM
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Quote:
Originally Posted by STROKED_NY_023 View Post
Fuel pressure under load can be very different, but it doesn't sound lime that's your issue... Did you inspect all uvch harness really well for bare wires?

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I didn't check the drivers side at all, replaced the passenger side gasket and two harnesses. Didn't bother checking the drivers side because it seems like the problem is on the passenger side.

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Old 06-14-2013, 06:02 PM
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I'm not sure if a buzz test will create a DTC. The big thing is to listen to see if they all sound off with the same strength.
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Old 06-14-2013, 09:01 PM
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From what i can tell they all sound about the same.

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Old 06-15-2013, 06:20 AM
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Have you checked all the easy stuff??? IPR can cause these symptoms as well.

Check this vid here for an easy cleaning rebuild to rule it out...

IPR Rebuild - 7.3L Powerstroke - YouTube

Here is the rebuild kit...

#14-007 IPR Re-Seal kit 94-03 7.3L Diesel
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