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Gang -

Over the course of the last month, the Service Engine Soon (SES) light has come on a handful of times in my F250. It's an "Early" 1999, stock, except for a homemade intake and a straight exhaust.

When the light comes on, the truck runs rough; it'll drive, but it feels like it's running unevenly. Shortly after it does it, the truck starts to run correctly again, and the SES light goes back off.

When this first started, it happened in parking lots, just after starting it and trying to move away from a standstill, so just off idle. Tonight, for the first time, it did it while I was driving down the road.

The Actron OBD code scanner that Whitney kindly lent me says there's nothing wrong. I've even managed to scan it, while the truck was running and the light was on, and still, it came back with a "PASS."

When the light is off, it runs fine, makes good boost, good power, and sounds totally normal. I have yet to find a predictable method with which to reproduce the problem.

CPS has been replaced under recall. It's got fresh oil in it, and I changed the fuel filter about 1000 miles ago.

I've dug around in The Diesel Stop, and found about eleventy different things that it could be. One poster mentioned the notion of an OBD scan tool that is somehow "diesel aware." I didn't know there was such a thing.

Any ideas?

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Karl S.
2014 Baby, 2014 House, 2013 Ford Focus ST, 2013 BMW 328i, 1994 Mercedes E320
(Insert passive aggressive signature line here)

can't really speak regarding a 7.3 but i can tell you i had a similar issue with my 6.0. i only have a cat with straight pipe from there and i installed an AFE high flow intake.

the 6.0s are very sensitive to intake changes Karl. and coupled with the straight exhaust, i did not have enough recirculated air in the system. sorry for the lousy explanation but i can't remember the exact sensor that is not getting proper airflow.

it seems counter-intuitive that a diesel would need backpressure but my model Ford apparently does.

i re-installed the OEM intake and no issues since.

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BenchWarmer Motorsports

another one of those damn LeMons heads

just another Chump

we are an Autocross Club Dammit............

Thanks Steve - I may try putting it back to stock this week. The intake has been on there for at least 6 months, though, and the straight exhaust for about 2 months.

The current leading candidate is this weirdo wiring harness thing that runs *under the valve cover* to the injectors. The way these motors work under the covers is sort of like witchcraft to me...

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Karl S.
2014 Baby, 2014 House, 2013 Ford Focus ST, 2013 BMW 328i, 1994 Mercedes E320
(Insert passive aggressive signature line here)

by any chance are you noticing a large plume of black smoke with the loss of power?

the way it was explained to me was the MAF was unable to properly read airflow because it was too fast in and too fast out. so some sensor was dumping fuel into the injectors randomly.

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BenchWarmer Motorsports

another one of those damn LeMons heads

just another Chump

we are an Autocross Club Dammit............

probably not the case, but also consider that you could have been right on the line of acting up and not. With all this wet weather we have had this week, and all the super moist air, your engine could be putting a few droplets more moisture into the chambers.

as always, I hide behind my default banner of "i am not a machanic and take no responsibility for broken parts based on my advise"

hope you figure it out.

Boost leak?

I would expect most service shops these days would have a scantool that can read the ford specific codes.

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In need of car.

check engine light at start-up...... air / fuel and/or water/fuel issue IMO.

so yes any number of hose connections could be loose.

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BenchWarmer Motorsports

another one of those damn LeMons heads

just another Chump

we are an Autocross Club Dammit............

Check Engine Light doesn't stay on at vehicle startup. It only comes on for seconds at a time, then once the truck clears its throat and runs properly, the light goes back off.



I didn't notice. I was too busy fishing the code scanner out from between the seats to look in the mirror.

Jason - doesn't feel or sounds like a boost leak to me. When it does it, it sounds like it's down at least one cylinder. I would have also imagined that a boost leak would be there all the time, rather than intermittently, but perhaps not. I defer to you on that.

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Karl S.
2014 Baby, 2014 House, 2013 Ford Focus ST, 2013 BMW 328i, 1994 Mercedes E320
(Insert passive aggressive signature line here)

I'm pretty sure that if a CEL is coming on at all then there ARE codes you can retrieve with the proper tool. But normal OBDII scantools probably aren't going to do it...


--Donnie

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My Blog

A larger boost leak would cause a real rich condition and make the vehicle stumble like you hit a rev limiter of sorts. They can appear at certain boost levels but work fine at other levels. A small leak can seem intermittent due to heat and the amount of pressure that you're making at any given time. Of course, a small leak probably wouldn't cause the issues you're having, at least not on a gasoline powered vehicle. A large leak is relatively easy to find, just pressurize the intake system with the engine off.

Do you still have the factory airbox? Is this the first cold weather that the vehicle has seen with the DIY airbox?

I also agree with Donnie. I know you probably are avoiding the Ford Dealership due to cost, so try calling some shops and see who has a Ford Specific Scan Tool. There is a Hickok NGS and models from OTC and Snap-on that should be able to give you more detail over what that Actron is reporting.

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In need of car.

The 7.3L motors with electronic injection control have wiring that is part of the valve cover gaskets. An ex Ford mechanic I work with says that this harness tend to break wires that pass through the gasket and this wil cause all kinds of drivability issues and intermittent conditions. I would have it checked out by a pro because this is not a cheap part.

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George Bright Member # 141
One of the youngest of the old farts.
Yes I voted against you joining the club.

Jason - I've got the factory airbox, and I suppose I can try putting it back on. I took it off, mainly, because the access lid for the air filter had a broken mounting tab on it (which is common), so I took it out of there to make sure I had a properly seated air filter.

I'll also try and get it over to Conover Motorsports tomorrow - they should have the appropriate diagnostic tools. One of their other guys is also a certified Ford diesel guy, so that'll help too.

George - that harness that runs under the valve cover is currently the number one candidate. Pending me taking the truck out to Conover, I'm going to try and pick up replacements at an International dealer. They're considerably cheaper there.

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Karl S.
2014 Baby, 2014 House, 2013 Ford Focus ST, 2013 BMW 328i, 1994 Mercedes E320
(Insert passive aggressive signature line here)

obviously karl has jinxed me, my psd excursion threw a SES light as i was leaving for vir this afternoon. doesn't seem to run any differently though, but a stop/start cycle hasn't cleared it. is there any way to display the basic trouble code without a reader?

Jason - I don't remember, does yours have an electronic odometer? If it does, there's probably a way to at least read the codes. I'm pretty sure my 01 Excursion had a mechanical odometer, though.

Anyway, let me know on the odometer question. I don't have the how-to in front of me, but IIRC, you hold down the trip reset button while the key is in the off position. Then, turn it to On. The button will then cycle through a bunch of pages, which you should be able to find on ford-trucks.com. I did it on an Escape, so those pages are unlikely to be the same.

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Karl S.
2014 Baby, 2014 House, 2013 Ford Focus ST, 2013 BMW 328i, 1994 Mercedes E320
(Insert passive aggressive signature line here)

actually the SES light was gone this morning. maybe it just needed a long drive. but thanks!

and yeah, it's a mechanical odometer. you know, the kind you can roll back easily.