Intermittent rough idle, loss of power and severe shaking
 

Hello all,

I need some help with a 99 7.3L / auto trans/ 189k miles. It is not my truck but I have been asked to "take a look at it" :)

Here is a short history of the problem.

A couple weeks ago it started running VERY rough. The engine was missing and shaking so bad that the person driving it thought it was going to fly apart. At an idle the truck would run a little rough but when they drove down the road it would shake, surge and lose power so bad that it would hardly move.

They had the CPS changed and it ran good for a few miles but it started having the same problem again. They changed the CPS a 2nd time and had the fuel filer replaced before they gave it to me to "take a look at". I drove the truck 3 or 4 times for a total of 35 or so miles with no problem until today.

Today I started the truck and right away noticed that it idled a little rough. I drove about 5 miles and it started shaking so bad that I didn't think I would make it back to the house. The CEL came on just for a second or so. I stopped at a local auto parts store but they were unable to get any codes for me. When I left the auto parts store the truck ran great with no problems. I drove 15 miles with no problems at all. This afternoon I took the truck out again and after a few miles it started to run a little rough. I shut the truck off, restarted it and the problem was gone again. I checked the CPS wire and connector as well as the fuel filter and they seem fine. I drove at least 60 more miles this afternoon with no more problems. I stopped and started the truck half a dozen times and have not been able to get it to act up again. :-huh

I would guess that its an electrical problem/short/sensor since it seems to come and go but the way it loses power and shakes it seems like its starved for fuel. I have also noticed the smell of raw fuel from the truck.

Any help would be greatly appreciated.

Ps. Driving this truck around sure makes me miss my old 7.3L Maybe someday I will have one again

take a close look at the big wire harness that goes under the valve covers.
those are the uvch's that typically get a worn spot on the underside where they rub... and ground out. those carry the signal for your injectors... if that signal grounds out... the symptoms you are describing occur.

i'd bet thats whats going on.

xtof

Sounds like a UVCH issue to me. Look at this thread for some info and pictures. https://www.ford-trucks.com/forums/8...ck-shakes.html

UVCH is my bet. Ohm out the pins to see what's up with the plugs.

Thanks for the help guys!!!

Chris - The link was just what I needed. Thank You

As soon as I get a chance I will ohm out the pins and report back with what I find.

Update:

Since I last posted I found out that this engine had been recently pulled out to replace the oil pan. The guy that did the oil pan did such a poor job that the pan gasket fell into the bottom of the oil pan when he re-installed the pan. This guy apparently didn't even notice that the gasket was not in place. The truck was then taken to a shop and the mechanics there were able to lower the pan enough to retrieve the gasket and install it correctly.

Because of the bad work done by the 1st "mechanic" I started looking around the engine and found several problems that I was able to repair. I repaired 5 pinched and skinned wires as well as 1 broken wire in the harness that goes across the engine just under the hood. I also found 3 of the 4 battery connections were corroded/loose. The medium size copper stud on the starter solenoid had been stripped which left the connection loose and unreliable. I was able to chase the threads and install a lock nut to hold the starter wire in place. I found that one of the ground straps had been frayed and the radiator reservoir wasn't installed properly.:-X15

I have a feeling that more things will show up in the future or upon closer inspection of the engine.

The truck hasn't been driven much since I repaired the electrical problems so I don't know whether or not the problem has been resolved.

I finally got a chance to ohm the valve cover plugs yesterday. The injectors all tested around 3.6 ohms. There was 1 glow plug on the passenger side and 2 on the drivers side that failed.

Any thoughts?
Does the failed glow plug test mean that I need to remove the covers and check the plugs and harnesses or dose is simply mean that there are 3 bad glow plugs?
Is it possible the electrical problems that I found were the cause of the rough idle, shaking and loss of power?

Thanks in advance for your help

Pull the valve cover and check all electrical. I would change all glow plugs and any wiring you find to be bad. Old wiring gets brittle and should be replaced, even before problems start. Good luck and I hope you found your problems.

Chet

I finally got the UVCH's and glow plugs changed.

The pass side UVCH plug was slightly disconnected. Both harness plugs and wires looked to be in good shape. Since the repair the truck hasn't has the power loss and shaking it did before but I have noticed an occasional slight miss at an idle.

Thanks for all the help guys.

What would you suggest that I check next to fix the occasional slight miss?