6.9 to 7.3 idi swap

[diesel dad 96]

Have a 1985 f250 6.9 automatic 140000 miles runs greats serviced at all intervals since day 1. Rusted to pieces.And a 1988 f250 automatic 276000 runs like crap stalls, smokes, doesn't start unless it wants to. Trannsmission slips when warm & wont go ito reverse.Body in excellent Condition. How hard would it be to put the 6.9 engine and trans into the 1988.Visuals look like an even swap, heard that I would have to change the injector plugs. Any other problems that I might incure. Also how to I pull up old threads about this subject. I'm sure that this has been tryed before.Both are idi engines.Thanks for the help.

[Powerstrokedogg]

it is a simple swap everything is the same except the glow plugs(i think thats what you mean when you said "injector plugs")

being a 88-85 swap the transmissions are the same, both C6 so the flywheel is the same

[mattinthebox]

Well my truck which is an 87 has undergone the swap you intend to take on.

The swap on my truck was done before I bought it but from what I've done on it I've noticed at least two possible differences.

The first difference is the type of glow plug controller.
This shouldn't be a problem if your handy with wiring... the 6.9l used a different glow plug controller but the wiring will work just fine if you know what goes where.
This is a solid state glow plug controller for 7.3L


The other area of concern is the fuel system...
If you search the forum you will see my posts concerning this matter...
The problem on my application is that the previous owner kept the 6.9L fuel filter/water separator.
I think mainly because of the high cost on the 7.3L filters, but getting back to the issue... the injector return lines on a 6.9L are smaller than the lines on a 7.3L.

In the picture below, the 69120 cap is for the 6.9L and the 73120 cap is for the 7.3L


Everything in the injector return line kit was good except for the rubber hose that connects to the fitting which comes off the fuel filter header.
The 7.3L hose was 1/4 and the barbed fitting was 3/16 so I needed to modify this fitting.

This fitting connects the return lines from the injectors and the hard line that goes directly in the front of the injector pump.

My quick but reliable fix was to grind off the 3/16 nipple on the elbow and tap in a 1/8 Male Pipe Thread X 1/4 barbed fitting.
This looked to be my only option because the fitting I'm talking about is not available in the combo I needed.


I was a little confused at first but I got all the help I needed here to overcome the problem...

I can't think of anything other than those two obstacles...

If you need any other pictures or wiring diagrams don't hesitate to ask...

Good luck...
Matt