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Discussion Starter · #1 ·
Long story short, about 6 months ago, my truck would run real rough and come to find out one of the electrical plugs on the injector wiring harness was bad, so we replaced and it ran like a champ.

Well over the weekend, it started running real rough again, but this time it would die it was so bad. I finally got it to crank and so long as I kept the RPMs way up it wouldn't die. After about 2-3 minutes of running rough with the RPMs increased, it cleared up and began running fine, so I drove it straight over to the mechanic's shop. Well it was Saturday and he was closed, so it sat there until yesterday afternoon when his technician finally got a chance to look it over and he says there is nothing wrong with the truck. He scanned the computer for any codes that may have been stored, but there were none (even though the check engine light did come on apparently turning the key off will clear the code if the problem doesn't persist), he then ran an electrical test on the entire electrical system and found nothing (I assumed it was the same issue as before).

I'm supposed to be headed to Rockport to due some fishing this weekend and I certainly won't let this keep me from going, but now I've got to find another truck to use as I can't trust taking this one 3 hours from the house knowing it may act up again.

Any suggestions on what else can be done to try and diagnose the problem?

Thanks
 

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Take a spare CPS with you it will sometimes start acting up like that sometimes die and not start then start up etc. one bolt holds in at front of motor on the timing cover, not sure if this is it but when it will not crank look at your tach if your tach does not move while trying to start it is more then likly your CPS (Cam Position Sensor) I hope the spelling teachers don't get me I was in a hurry.
 

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Discussion Starter · #4 ·
There is no problem with it cranking...its keeping it running that seems to be the problem. It honestly sounds like the truck is not running on all 8 cylindars and that's causing it to die. I'm no mechanic, but its just a hunch.
 

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Another voter for the CPS. I had weird and intermittent problems and this finally fixed it. Mine would be running along fine this all of a sudden run like you described I have a manual, I would turn it off and on let out the clutch and it would start and run good again. Got worse and worse replaced the CPS and it fixed it, probably what you have going on.
 

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this is going to sound stupid but check your oil level or if you got time change it it has to have plenty of clean oil to operate. Drain your fuel cannister, could be water in it (yellow handle) does your truck have a chip in it sometimes the contacts on the chip will cause this, could be alge in the fuel I just giving things to look at first, you need to put a code reader on it. CPS would be my first thing to change, you can get one for around $30 check with the dealership 1st.
 

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I agree. The CPS caused my 7.3 to run rough and sometime die. Replaced the CPS and the truck started running like a champ. From what I understand once the CPS starts to fail it will cause strange issues like this, but once it does fail, it will leave you stranded unless you have a spare.
 

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wfishtx said:
There is no problem with it cranking...its keeping it running that seems to be the problem. It honestly sounds like the truck is not running on all 8 cylindars and that's causing it to die. I'm no mechanic, but its just a hunch.
The crank position sensor is referring to the crankshaft position sensor. It's necessary for the truck to run proper.

Like the others have said, it's starts with an intermittant problem, then it dies and leaves you on the side of the road waiting for a tow truck.

Have your mechanic replace for piece of mind. It's not too much and shouldn't take too long to replace.
 

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Bad injector/wiring harness or the cps. Had both fail on my 7.3. The bad injector was a horrible engine miss. When the cps failed, it wouldn't stay running.
 

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Dumb question, but have you checked your oil level. If it gets low the IPC signal will be low(below 500PSI) it will not run right or at all. If it is full it is probably another harness or connector. I've never seen one with a bad cam sensor that would run rough & then straighten out, they will just quit & maybe not restart
 

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Discussion Starter · #11 ·
Thanks for the info all. I think I'm going to borrow my dad's truck for the trip to Rockport this weekend and probably talk to my mechanic about the CPS and see what his thoughts are in regards to that being the problem. Thirty bucks doesn't seem to bad for piece of mind.

Thanks again
 

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I don't think you will find a CPS for thirty dollars. Expect to pay around 100.00 for it. Also, as weird as it may seem, check to make sure your gas cap is on tight. You might have air in the system.

LW
 

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7.3 mysteries

Sorry to hear about your problem, I feel you pain. I'm an owner of a '95 PSD and have learned allot about the engine by replacing/having replaced almost everything other than a short block over the last three years. Thanks to having a brother-in-law that is a Ford service manager, the diagnostic and assistance has always been available.

One of my most recent episodes involved a very similar problem to yours. Occasionally the engine would have a miss to it while driving, usually at lower rpms and it eventually would happen a higher rpms which caused the engine to shut off. The computer diagnostic was performed and nothing other than problems we knew that have existed already were found.

My ace BIL had me check a few things and finally we found the problem, the valve covers were full of diesel. By removing the injector wiring harness plugs one at a time from the exterior of the covers diesels leaked out from all of them. Once the valve covers were removed it was noticable that some of the harness wires had insulation rubbed off and were shorting out, sending bad signals to the controller. The wires were cleaned up and to save some money and to keep from replacing the costly harness assembly, they were taped individually with black electrical tape. He also replaced a fuel ratio sensor (I think that was the description) to be on the safe side.

While I was having these intermittent problems for sometime, my fuel mileage decreased drastically from 16-18 down to 9-11 mpg.

Good luck, hope your fix is not too costly- Curtiss
 

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Discussion Starter · #15 ·
Well, I spoke with my mechanic and although he did consider the Cam Sensor as a possible problem, he said that 99% of vehicles that have Cam Sensors go out do not typically run rough prior to shutting off. He described it to me as more like someone turning the key off with no notice and then not being able to restart it. He also said that if the Cam Sensor was the problem, then the computer would have stored a "hard" code, which didn't happen as there were no codes stored.

I think I'm to the point of just having to drive it around (close to home) until the problem becomes more persistant and therefore easier to target.

I'll keep everyone posted.

Thanks again for everyone's help and suggestions.
 

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My dad's did the same thing on his 7.3 and it was the cam position sensor.
 

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That's strange it didn't throw any codes if the light came on. Fuel pump running when you go key on, ignition off? I've never had one fail, but my mechanic claims the 7.3Ls will run at higher rpms with a failed pump cause they pull so much vacuum, but it'll idle like cr*p.

Craig
 

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My 7.4 (which I just reluctantly traded in for a '08 6.4) used to do that and it was a problem with algae in the fuel or injector clog...... May be a long shot, but I cleared it up (about 5 times) with adding a full can of SEAFOAM to a 1/4-1/2 tank of fuel (4-12 gallons). It was the only problem I ever had with that old 7.3 and SEAFOAM always cleared it up.
 

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I assume he is using a good scanner, and pulling all the codes running key on engine off and cylinder contribution tests? Another thing to check is your main harness plug there it runs over the valve cover. Alot of times it rubs and grounds out there. Throwing a ligt and not pulling it up sounds like its somehting stored in the Injector Driver Module. Bet its the harness or something in the IDM. If its still running, does not sound like CPS. When its runnign rough try getting uder the hood, and wiggle your harness.

Id get him to check the Injector pressure while runnig, and th IPR valve. Rule out oil supply or stuck injectors.


Good Luck
 

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Discussion Starter · #20 ·
Mechanic said it probably threw a "variable" code as oppossed to a "hard" code, which means the instant you turn the key off the "variable" code disappears. I'm hoping it happens again and I can keep it running, so I can immediately take it to him and have the computer scanned with the light still on. According to him this is the only way to read a "variable" code.

I'll be traveling on business next week, so I think I may just leave it with him on Monday and have him do some trial and error testing and see if he can find the root of the problem.

Thanks again everyone for your help and suggestions. I'll let you know the final outcome.

hoosierplugger said:
That's strange it didn't throw any codes if the light came on. Fuel pump running when you go key on, ignition off? I've never had one fail, but my mechanic claims the 7.3Ls will run at higher rpms with a failed pump cause they pull so much vacuum, but it'll idle like cr*p.

Craig
 
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