Missing, low power, Idles rough, Check engine light on.

[SickRick]

Check engine light came on last night and at exactly the same moment truck started running and lost most of its power. This lasted a few seconds and then ran normally for a few minutes.

Problem began to repeat itself. I shut the truck off and it restarted fine, I was able to rev the engine in nuetral and proceed for a few miles. Then it happened again. Everytime the check engine light instantly corosponded to the poor running. When it did this I was only able to achieve 50 mph after a couple of miles.

If I restart the truck there is no check engine light for 1-2 seconds and the engine runs great. after a couple seconds the engine light comes on and the engine instantly starts running rough.

Oil is new.

I would suspect fuel by the way it runs, but it idles/runs perfectly until the check engine light comes on.

I am very mechanical and have all tools for most repairs.

I am going to have the codes pulled at local dealer if needed, just hoping this is an easy fix and that won't be needed.

This is my first post on here so please take it easy on me if this problem is common knowledge.

Thanks for your help.

Rick Snell
Elk River, Minnesota

[SCUFFY828]

if the check engine light is on its probably not fuel, im not sure what truck or engine this is , but if its a 7.3 sounds like short harness under the valve cover is loose

[SickRick]

A refferal to a good diesel shop in my area would also be appreciated.

[SickRick]

Originally Posted by SCUFFY828

if the check engine light is on its probably not fuel, im not sure what truck or engine this is , but if its a 7.3 sounds like short harness under the valve cover is loose

Opps its a 1995 4x2 f350 dually with a 7.3 di engine and auto trans.

I will start checking that immediatly.

[SCUFFY828]

sounds like its possible to have a melted short harness then , pop the connectors off at the valve covers and see if any of them look melted , there are 2 connectors on each side going into the valve cover

[SickRick]

I started the truck and let it warm up for a couple minutes.

I then took my infrared temp gun and took temp readings on the exhaust manifolds.

Passenger side quickly warmed up to over 200 degrees, Drivers side even after the engine was running was aunder 60 degrees.

Obviously we are looking at the driver side as being the culprit.

Here is my new question:

Does the harness in the front of that valve cover handle the front two cylinders and the rear handle the rear two?

If so is it normal for them (harness connections) to fail as a pair? or is there some other thing involved?

I will begin pulling the cover.

[SickRick]

Took the decrative cover off the top of the engine and started the truck.
Same as before running rough etc.

Began to wiggle the wiring harness connections and engine started running perfectly.

It did this as soon as I touched the wire on a sensor coming out of the back an aluminum manifold like thing that is mounted on top of what I would guess to be the timing cover. It is the thing with 5 vertical bolts. This sensor has 2 wires.

Truck is now running fine, no check engine light.

Any ideas?

[SickRick]

After some internet serching I found the sensor wires I wiggled when the engine started running properly were from the engine oil temp sensor.

I am now guessing that the engine running properly and wiggling of the wires was coincedence?

[SCUFFY828]

the eot sensor isnt the problem, the short harness is gonna be the problem, you wiggled and got better connection, need to disconnect them and look for melted wiring , the glow plugs are the culprit of the melted wiring , high resistance in the glow plugs cause heat in the wiring and melt the connections , therefore open circuit to injectors

[SickRick]

Thanks Scuffy.

I got busy today and couldn't finish working on it but I will let you know what I find in the valve cover.

Is the proper fix to replace the harness? Where should I get a new one?