7.5L to 6.9L IDI swap

[MechRick]

First post- I've recently purchased a 6.9L IDI with the intent of swapping it into my gas F250. This will be my first diesel, assuming I got a good one, but I've got quite a bit of experience working on them (and Cummins too), as I was a line mechanic for 30-odd years.

I plan on reusing the big block ZF5 (after drilling), and would love to be able to use the 12" 460 clutch as well (new). The engine will go on a run stand. I want to run it and allow the cooling system to pressurize before I tear it down to reseal and clean.

The 1987 engine came with the core support from the same truck, I'll have to buy a radiator.

What's the simplest way to rework the gas fuel system to work with diesel? I can run one tank to start, but eventually want both tanks to function.

Will I need new front coil springs for the heavier diesel?

-Thank you

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[Big Bart]

Rick I had a 95 F-150 gasser and now a 88 idi. I have never done a gas to diesel swap so no expert here.

The IDI does not use a fuel pump in the tank. Just a suction line and a return line. So you will have to make sure there is no fuel pump in the tanks blocking the suction line and that it does have a return line. (As I recall the EFI also had a return line but I am not 100% sure.) Also the IDI uses a mechanical lift pump to feed the fuel filter on the passenger side of the engine. So you need to route the feed line to it.

The IDI I believe uses the same tank selector and wiring. So I do not think you have to do anything there. But someone who has done this should weigh in shortly. Be sure to get all the gas out of the tank and lines as thinning your diesel with gas would be problematic.

You will use your current starter soleniod to energize the starter soleniod on your idi starter. Yes you will use a soleniod to another soleniod. Sounds odd but how Ford did it.

You also will need to wire for your glow plug controller but suggest you start a different thread to pose best way to do that.

Not sure about the exhaust so will let others weigh in.

Not sure about the front springs either.

 

[franklin2]

The 460 uses a return system. But it does have in tank fuel pumps that need to be taken out and a hard line plumbed in to take their place.

If the 460 was carbed (you didn't list the years you were working with) the valve will be the same. If the 460 is EFI, the selector valve is different and won't work. The EFI valve has no wires to it, it is switched by the pressure from the fuel pumps.

Also depending on what years you are messing with, your core support may not be a bolt in. The diesel core support must be from the same year spread. In other words, there is a diesel 86-dwn support, a 87-92? support, and a 93-up support. The different headlight buckets and frontends won't bolt up to a wrong year support.

 

[MechRick]

The gasser is an '88.

So the selector valve from the EFI system won't work. I'm not too fond of the electric switch valves, I've replaced a few on carbed trucks.

I'll probably plumb in the front tank to get it running. Thought about running the fuel line from the rear tank to the filler neck of the front tank, on a toggle switch.

 

[franklin2]

Later on you could put the 38 gallon rear tank in place if you don't mind moving the spare tire to a different location.

Your core support should work. Good thing you got it, they can be hard to find.

 

[MechRick]

Tell me more about these 38 gallon tanks!

I'm cobbling together a run stand from my scrap pile. I was going to buy 2" x 2" 12 gauge square tubing to build it, but about had a heart attack with the quote from the steel yard. Steel is ridiculous at the moment.

Should be done in a couple of weekends...

 

[Philip1]

Tell me more about these 38 gallon tanks!

I'm cobbling together a run stand from my scrap pile. I was going to buy 2" x 2" 12 gauge square tubing to build it, but about had a heart attack with the quote from the steel yard. Steel is ridiculous at the moment.

Should be done in a couple of weekends...

"38 Gallon Rear Tank Conversion Kit for 1983-1997 Ford Diesels – Classic Diesel Designs" https://classicdieseldesigns.com/co...products/38-gallon-bronco-tank-conversion-kit

 

[Old Goat]

With Classic Diesel`s tank, he says the Sump must be installed. That means you have to drill a 3" hole in the bottom to install it. Wonder why the sump must be installed?

I bought the f26E 38 Gallon tank and installed it in my 86 F250. Put in a new sending unit. Added a length of tubing with compression fittings for the suction tube, and cut the Float Arm, and welded on a length of wire. Think I extended it about 5.5".
Been working just fine for the past couple years.
It is the Spectra f26E tank made in Canada. Seems to be a shortage right now according to the various sellers.

Charlie

 

[franklin2]

With Classic Diesel`s tank, he says the Sump must be installed. That means you have to drill a 3" hole in the bottom to install it. Wonder why the sump must be installed?

I bought the f26E 38 Gallon tank and installed it in my 86 F250. Put in a new sending unit. Added a length of tubing with compression fittings for the suction tube, and cut the Float Arm, and welded on a length of wire. Think I extended it about 5.5".
Been working just fine for the past couple years.
It is the Spectra f26E tank made in Canada. Seems to be a shortage right now according to the various sellers.

Charlie

I think that guy is setting his tank up differently. If you read in the description, he says it's "gravity fed". I think he is pulling fuel from the bottom for some reason, instead of pulling fuel from the sending unit. You also can see he mentions it's easy to drain (fitting on the bottom of the tank) and that is uses all the fuel out of the tank. When you use the factory sending unit setup, there is always about 3 gallons left in the tank.

 

[Philip1]

You can either use the sump kit or use the factory pick up lines in the top of the tank. You will have to modify the pickup tubes to be longer along with the arm for the fuel sending unit so it will read correctly. Wes at classicdieseldesigns at least used to sell (I don't know if he still does) the modified sending units

 

[MechRick]

I'm pretty close to a running 6.9L. It's mounted to the run stand, wired, plumbed and ready to go. Injector return lines are leaking, and #2 cap is weeping fuel, but I'm hoping it will start and run. I had to wire in the glow plug controller, it wouldn't even hit without them. I juiced the cold start advance solenoid with a power probe, stuck a block of wood in the throttle and cranked it.

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It hit and ran up to 1500 RPM or so, then shut down and wouldn't restart. I'll try it later today after the battery recharges...

 

[The_Josh_Bear]

Probably the fuel filter was half full of air from the leaks. Pull it off before you start it next and make sure it's topped up, then it should go fine.

Cool test stand!

 

[MechRick]

I think you are right, it probably had an air pocket. I've gotten air in the IP on these engines before when changing fuel filters, before I know the trick of filling them with ATF. Had one I had to crack a few injector lines to purge.

Moving right along...

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[MechRick]

After running on the engine stand, I pulled the heads on this engine intending to replace head gaskets. Measured a few cylinders, had a few that were right at .005" above the rest of the bore right where the top piston ring changes direction. Pulled a piston, removed the top ring, stuck it in the bore and the end gap measures .060". Max taper appears to be .003". Guess I'll go ahead and do an overbore with new pistons while it's apart.

The main reason I chose a 6.9 over a 7.3 was to minimize the chance of cavitation. In light of this, the least overbore needed seems prudent, but .020" over pistons are way more expensive than .030" over.

Should I be worried? Is there a way to pull core plugs and view the cylinder liners for cavitation? I do have a borescope if needed.

-Seems a 4.030" bore should be less risky than the 4.1-something bore of the 7.3, but I don't want to destroy a block, or lose longevity.

-Has anyone checked the Speed Pro or Silvolite piston weights to see if they match stockers? I've had good luck in the past with Speed PRO's, but have no experience with them on IDI's.

 

[SuperDave]

I've never had problems going 0.30 on a 6.9, hell I think the 6.9 in my bronco is 0.40 over and it does ok. I'm not a big time engine builder and I won't pretend to be, but I've built a few idi's over the years. As far as a 7.3 my machinist won't bore them because of possible cavitation issues, if they need bored then they get sleeved but he leaves a good little bit of metal for support at the bottom of the bore so the sleeve doesn't drop into the crank like it does on a lot of reman idi's.