Hi there,

I am new to being registered on these boards but I read and refer to them all the time and know them to be a wealth of knowledge!

We've had many Fords over the years but the one that has me posting today is our 99 F350 7.3L truck. We've only had it about six months and it's running pretty well. We use it to pull a heavy load-steel horse trailer and several horses, nearly every weekend in the mountains. It's an automatic transmission (which may not have been the best choice but here it is).

I usually drive it without the trailer on-my husband usually drives when it's loaded.

On the way home from the last loaded trip the "Service Engine Soon" light came on when we started the truck. After a few miles it went off and we made the mental note to get it checked. Yesterday I went to drive to town and it started up just fine, as usual, and the SES light came on. When I got up to about 45 MPH on the road the truck shifted up a gear and immediately started shuddering. I slowed, it dropped a gear, and stopped shuddering. Turned around to take it back home as I didn't have an appt with a mechanic that day and it did the same thing again when I got up to speed. I dropped the speed again and brought it the rest of the way home in low gear.

Obviously it really needs to go to the mechanic but I wanted to pick your brains first.

Points-we notice this truck doesn't seem as strong as our 96 F250 7.3-we attributed that to the automatic transmission. If we're loaded and heading up a hill it slows much more than the F250, if we STOP loaded on a hill the truck just about doesn't go-you can floor the fuel pedal and it will roar and just barely move. Again, we attributed it to the automatic but now I'm wondering...

Also-my husband just loves to put it in a lower gear to go down a hill. We live down a fairly steep mile long hill and he always downshifts it (to save the brakes)(we do have trailer brakes also) and it just feels like it's really pulling to me. I don't like putting all that weight and stopping power on the downshift-I'm more of a "use the brakes" driver. Husband assures me that I am wrong. lol but I thought I'd mention it here since I've been fussing about the transmission holding that trailer back and now weirdness with the transmission.

In the reading I've done here this morning it seems that the SES light really means "go to your mechanic and put the truck on the machine?" Or is there any way to narrow down but the problem might be before dealing with the mechanic?

Any ideas? Thanks everyone!

 

You'll probably have better luck with this in the 7.3 forum.

What you describe sounds like a bad injector, not a tranny problem. 45 is about when you hit 4th gear TC locked and at a low RPM. At that point you feel any slight miss in the engine as a vibration.

 

Thanks for the heads up, I copied the post over there.

What you say makes sense... is there something we could do now to see if it can be a DIY fix?

 

Welcome to FTE.

Your engine is running on 7 cylinders. Retrieving the stored codes is the next step here. If your mechanic is familiar with these engines, he/she will have the proper code reader (diesels take a certain kind of reader to pull the codes...). You could have a wiring issue or a problem with one of your injectors. A buzz test might also help the diagnosis process.

Don't throw any parts at the problem until you have pulled the codes and confirmed the wiring is good. Post back with the codes and we can decide what to do next.

If you absolutely have no way of retrieving the codes, then you can still trouble shoot but the process is more involved.

 

dang-I don't know to be glad it's not a tranny thing or concerned about an injector thing!

I'll get it in to the mechanic and get the code ASAP.

 

In my case it was a fairly simple fix. I had the exact same symptoms and it turned out to be a loose armature plate. I might have just been able to tighten up the screw but I had a rebuilt injector on order so I just swapped it out and it completely solved my problem.

A bad injector solenoid might do the same thing, or a chaffed wire on the 42 pin harness at the driver's side, etc.

It's also possible that you just have a loose connector on the harness under the valve cover. If so, that only costs 25 cents to fix plus your time.

Are you comfortable removing the valve covers to check the simple stuff before taking it to the mechanic?

 

I'll get my husband on here tonight to read through and hopefully he can check it or ask any questions he might have.

It's been on some washerboard roads so it's certainly possible that something has just worked its way loose.

We bought it from a reputable dealership and they would have gone through it pretty well before selling it to us just a couple thousand miles ago so I'm hoping it's not major medical!

I appreciate the help and input!

 

Ok sounds good. Here are some good threads to read:
50 cent mod. Fairly common issue. It's simply a loose connector under the valve cover. Usually an easy fix.
https://www.ford-trucks.com/forums/8...ml#post6900483


If it turns out that you do have a bad injector, here is a link to a thread that discusses injector R&R.
https://www.ford-trucks.com/forums/1...l#post10438805

You guys can read this and see if you feel comfortable tackling it yourself. If not, then at least you will be armed with knowledge so you can communicate with your mechanic to have the issue repaired.


Keep in mind that I gave you links to 2 ends of the spectrum as far as solutions go. There a few other things to check before jumping to conclusions and ordering injectors...so don't order any parts just yet.

 

Thanks a ton! I really appreciate the info and your time-we will tackle it tonight and I will let you know what we come up with!

 

Moved to the 1999 - 2003 7.3L Power Stroke Diesel forum.