The Diesel Stop banner

Towing - OD light flashes and other issues

6141 Views 9 Replies 6 Participants Last post by  z.alvco
So I have had my 1994 F350 7.3 IDI for about a month now, and to say the least, at this point, I am pretty disappointed. I sold my F150 with a 5.8 last weekend, so I am stuck with it for now. I have already replaced the power steering pump and hose, oil cooler rings, and flushed the cooling system and changed the oil/filter.

Took it out camping this weekend and pulled my trailer with it. This is a 3500 lb. or so trailer, 24 foot. I bought this truck because I thought it could pull anything, and am hoping to get a boat at some point.

As I was heading up a pass - not a huge pass mind you - the truck was an absolute dog. Pulled it great leaving town, but getting up the pass, it was dropping to 40 mph and didn't seem like it wanted to downshift to push harder. Awful. Then at some point I noticed the overdrive "off" light on the shifter flashing. Figured that might be a problem.

Once we got to the camping spot, I drove it around town without the camper, and eventually, the light stopped flashing. Hooked the camper up to tow it home today, light came back on. So basically the light flashes just when towing. I've read some other threads on this light, getting codes, etc., but is it going to not have a code if I just go to the parts store and there is no light flashing? Why would it do this only when towing? There are no other lights on - i.e. ABS or anything like that.

I haven't checked my mpg yet either, but a full rear tank went down to almost 1/4 left, and I only went 125 miles. That does not seem good at all, and one reason I got this truck was hoping to improve my mileage from the 8 I got in the F150.

I must say, I was more hopeful for this truck, but so far, it seems like it is just going to be an endless project.

E40D transmission, 3.55 gears.

Any thoughts on this? Just get a code reader and hope the light comes on? Will the tranny issue help with the mpg?

And the real question - should I just go back to gas? I don't want to, but man, so far this has not been a great experience. This truck seemed to pull fine in the flats, but most trucks will pull ok in the flat areas.

Thanks in advance.
See less See more
1 - 3 of 10 Posts
Are you turbo'd or N/A ? With 3:55 rear end your gonna need to downshift manualy to keep the RPM's up on a grade. I haul 9K of trailer and I normaly have to cancel O/D long before I get into the hill and I have 4:10 rear end.

Try keeping the RPM's up at about 2800-3200 when your going up the hill. I will come off the "go" pedal just long enough to take the strain out of the drivetrain and then move the shifter. E4OD and 3:55 gears are great for the flat road.

As for the O/D light flashing: The Tranny computer has detected a problem and you need to retrieve the code(s). You need a FORD OBD I code reader or an analog OHM meter and this link:

Don't give up your diesel rig..I had a gasser (460) that drank fuel @ 7.5 MPG with the trailer.
Your F150 might have had the same tranny but I suspect the rear end gears were different. the 7.3 IDI peaks HP @ about 3200 RPM If I remember right. a non turbo'd 7.3 only has 180 HP and your 5.8 gasser probably had more..My '86 F250 with it's tweaker 460 was putting just about 500 HP to the rear. It would yank the same trailer in sig up any pass at 40 MPH or better, just had to fill it back up at the top of the hill.
My truck in sig will yank the trailer up the same hill but it has to lumber up at speeds as slow as 25 MPH.

Driving a diesel powered truck with a trailer is a different world after gassers. If your not turbo'd I would consider saving up for one..It will suprise you how much it adds!!

a FORD OBD I code reader will read all the codes. It is possible that your tranny may have had an issue causing low mileage, but I suspect more that your driving style on the hills had more to do with it. Did you find yourself just getting into the go pedal and waiting for the tranny to downshift? Diesel engines and specialy the non turbo's ones don't do well with this style.
See less See more
So at the end of the day, can I ask - what is it you love about your IDI?
Mainly the fact that I know it will start and pull my trailer every time I need it to. and I DID go from 7.5 MPG (gasser) to 10.3 MPG with the trailer.

If so, why does the 7.3 turbo IDI only rate at 190 HP
Because Ford saw fit to restrict the turbo on the IDI since the Powerstroke was due out the same year. I was able to get the parts that allowed me to get like 240 HP and close to 400 Lb/Ft of torque. comparable to the first generation PSD's.

You didn't say what rear end gears were in your 150. Like I said before 3:55 gears are good for mileage.
1 - 3 of 10 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.