Hi. I have a 1988 Ford F-250 Regular Cab Light Duty 4 wheel drive truck with the 302, Mazda 5-speed transmission and semi-floating rear end. I have had the truck in storage for approximately 5 years. The body and interior on this truck are immaculate. I lost compression on the #8 cylinder is why I stored the truck. I do not want to fix the engine in this truck due to not wanting the computer etc. I do not want to sell the truck due to the condition of the rest of the truck. What I would like to do is convert this truck to a 7.3 diesel with the ZF 5-speed. I have a wrecked 1989 F-250 Heavy Duty supercab donor truck. From this truck, I should be able to use all of the running gear which includes the engine, trans, transfer case, front axle assembly and rear axle assembly. What I don`t know is if the frame for this truck (light duty 3/4 ton regular cab) is the same as the frame for the heavy duty 3/4 ton regular cab? If is not, will the light duty frame hold up to the additional weight of the 7.3? I also don`t know if the wiring harness under the dash is the same for the gas and diesel? Do they all have the same harness with the gas engine using only certain plugs and the diesels using other plugs in the same harness or will I have to change the complete underdash wiring harness? Has anyone done this swap before or does anyone have any useful info for me that could save me some time and headache before I begin? Thanks, Robert

 

I don't know much about this, but I am running some stuff through my mind, and I am thinking the diesel has some stuff involved in pre-heating the engine, like glow plugs doesn't it? If so, it probably has a light in the dash and could it possibly have a different ignition switch to accomodate this? Also the ignition switch would not turn on the ignition, since a diesel doesn't have one. So there might be a lot of difference.

What you could do, is find a website like www.partsamerica.com or www.autozone.com, or www.napaonline.com, and plug in both of the trucks you have. Try finding some important stuff you can think of that they hopefully carry, like the ignition switch, the radiator, or anything you are curious about being the same. Compare part numbers, and if they are different, you know you may have problems. You might try the headlight switch to see if they are the same.


I was just reading your post again, and you might have to take your supercab driveshaft, and have it shortened to fit the regular cab wheelbase. The heavier driveline may have bigger u-joints. Does one of them have leaf springs, and the other coil springs in the front?

 

They are both leaf spring trucks. Everything off of the donor truck should work except for the rear driveshaft. I have a place nearby that builds driveshafts and I will probably have them shorten it and balance it. Good point with the ignition switch etc. The main concern I have is with frame strength and wiring. I do have all of these parts in the donor truck except for a heavy duty 3/4 ton regular cab frame. I know I will have to swap the under hood wiring harness and I will more than likely have to swap the in cab harness as well. I was just hoping someone may have already pulled this off and could save me a few headaches and cussing sessions swapping out the harness. As far as all of the glow plug lights and H2O in fuel etc., I plan on swapping the guage cluster etc. out of the donor truck. I could also swap out the steering column as both the trucks have tilt and are loaded to the hilt. Thanks for the input. I`m sure glad I stumbled upon this site today. Loads of info on here. Have a good Thanksgiving.

 

Well, looks like you have everything covered. If you have both trucks there, you could measure the frames. Measure the height and width of the rail, and try to get hold of some calipers or micrometers, so you can measure the thickness of the rail. Also, you may have already done this, but post your frame question in the correct year forum above, and maybe somebody knows something up there.

 

I am in the process of the same gas to diesel conversion. The truck is a 1989 F-250 "Heavy Duty" 4WD. The original engine was a 351/5.8L gas job. Found a 7.3L IDI and a ZF s42-5 trans. The wiring for the diesel is very different than the gas job. The diesel with a manual trans does not have the EEC (computer). The fuel system is different in that the gas has low pressure pumps in each tank and the deisel only has the fuel sender ( gauge level indicator) so there is a big difference as to how the fuel selector valve is wired. Additionally as mentioned by others the fuel/water and glow plug sensor light on the dash that tells you "ok to start" is different. The diesels with a manual trans also had a tach which operates off a sensor on the timing gears up front. There are a litany of issues you will be confronted with such as adding a leaf spring on each side in the front. The gas engine weighs 600 pounds and the 7.3 diesel is 900 pounds. The front radiator support is also very different in that the gas radiator is a different square shape than the diesel. Nevertheless, you have a donor vehicle so you can hopefully pick everything you need from the donor but just make sure the wiring under dash, engine, fuel system and engine compartment are in good shape from the diesel. If you have any questions contact me directly.

 

By some now some 15 years later I am sure the OP either did the swap or moved on.

 

Well good things take time.