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Towing - OD light flashes and other issues

6144 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.
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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.

Thanks for the response. Just out of curiosity, why do I need to downshift for the hills? My f150 had the same transmission (pretty sure about that - 1997 F150), and I never downshifted that thing going up hills. The biggest hills I go up, it may have dropped to ~ 50ish, but never down to 40. Is it just because of the torque of the diesel motor?

Will the OBD1 reader read all of the transmission codes as well as check engine light codes? Or should I do the transmission codes just with the analog/ohm meter?

Any chance the tranny issue killed my gas mileage?
My truck is a non-turbo 7.3. So it has less HP than my 5.4 and is going to lumber up hills at 25 pulling a load? Can you remind me why I made this switch over again, and why it is a good idea? Really. I love my crew cab, and I love my long bed - I wanted to have more room in the cab for the kids, and I wanted to have the long bed to take both ATV's side by side in the bed, but it sounds like a lot less power and pull than the gasser. Not sure this was such a great idea.

So I ran some searches on turbos. It sounds like Banks, Hypermax, and ATS are the way to go. On a Banks site, it was saying you could add up to 82 HP and pull some 50% faster uphill. Are numbers like that accurate? If so, why does the 7.3 turbo IDI only rate at 190 HP - 5 above the non-turbo? I don't think I would spend the money to get 5 more HP.

I know I sound kind of down on this truck right now, and I really want to make it work out for the best, but man, so far it has been nothing but working on it and spending money, hoping for the best, but then feeling like it has no guts as I try to climb the hill. And that was only with an ultralite trailer that's less than 4,000 lbs. Put a boat back there and I feel like I'm going to be driving backwards down the hill.

So at the end of the day, can I ask - what is it you love about your IDI?
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