Loses a cylinder every once in a while - Diesel Forum

dieselnewb · 01-23-2013, 04:28 PM

Hello,
I'm new to the world of diesels and picked up a 1996 7.3l for a fairly cheap price. It looks to me like the privious owner(s) did not take too good of care of the truck. I figured I would take it in and try to clean it up some and save it from the abuse it was taking. The truck has 218,XXX miles on it now and some blow by so the motor is a bit tired but she runs great most of the time.

Every once in a while, I will be driving along and hit a bump. All of a sudden I believe one cylinder stops firing. The truck starts running rough and vibrates the whole truck and I lose power. It will stay like this for a few minutes until I hit another good bump then it will go back to normal. Sometimes it goes back to normal on its own as well. And one time I figured the motor went and I was on my way home. I floored it because I figured, if the motors shot, it's shot. After I floored it, the motor ran as it had before I lost the cylinder.

I have no idea where to start. Almost sounds like an electrical connection due to the fact that I lose a cylinder sometimes when I hit a bump. I was thinking it could be an injector? I'm just hoping it's not a valve sticking or something along those lines because it's my daily driver and I don't want to have to take the motor apart.

Thanks for any input!

preith · 01-25-2013, 05:49 PM

it's probably a UVC (under valve cover) harness, they're notorious for cutting out like that. It's probably in your best interest to replace all 4 (2 each side) if they're not the bailing wire clip style.

dieselnewb · 01-27-2013, 11:14 PM

Sounds like a project for the spring when it's warmer! Could it possibly be as simple as a loose or dirty plug? Or is it the harness the majority of the time? Any idea on how much the harnesses go for?

preith · 02-01-2013, 05:45 PM

Quote:

Originally Posted by dieselnewb

Sounds like a project for the spring when it's warmer! Could it possibly be as simple as a loose or dirty plug? Or is it the harness the majority of the time? Any idea on how much the harnesses go for?

Ultimately the problem is a loose or dirty plug, it has to do with the securing of said plug on the injector solenoids. The old ones have weak plastic clips on the ends whereas the newer have a stronger metal clip over the top. The harnesses go for about $36 each, riffraff is one of the preferred vendors I use:

Riffraff Diesel: Ford Under Valve Cover Harness 94.5-97

As far as replacement, the valve covers come off in short order, and the harness themselves are pretty easy to replace. With that said I'd hate for you to replace them only to find out that's NOT the issue, but on the other hand it is a good preventative maintenance anyway.