New to IDI's, 7.3 questions

[RLDSL]

The impression that I've gotten from working on the IDI in my 89 is that it isn't the most refined or well engineered engine, rather it was something slapped together and dropped in to meet a demand for a diesel pickup.

First impressions can be deceiving. I maintained a fleet of buses that had these engines in them when they first came out, and about the only difference between those and what got dropped into the Ford pickups is the injection pump ( bus pumps are governed at about 2700 rpms and set for max fuel mileage and torque, which they accomplished with flying colours. The things got excellent city fuel mileage and in the mountains they would have to pull over and wait for the cummins powered units when they were having to convoy groups up to camps ) and , the oil pan( the bus and dump truck engines got a front sump pan )and the oil cooler headers are slightly different shape( oil pan and cooler header shape were due to clearance issues ). but that's about it.

It was in no way something that was slapped together to meet a demand for a diesel pickup engine. rather, they took a proven commercial mid range diesel and put it in the pickups with minimal adaptations.
I just wish Ford would have used the Clark 5 speed trannys that those buses and a lot of dumps and box beds used to have instead of these zf5 trannys. The Clarks gearing shift points match the engine better. and the reverse is much better.

 

[IHDiesel445]

Don't write off that IDI for towing heavy loads until you try it out first. When I was a mechanic, I used my truck regularly to pull some pretty substantial loads. Most commonly a Bame equipment trailer loaded with a mini excavator or large skidsteer. Total (trailer) weight was usually around 13-14k. I never had a situation where I was wishing for more power. As you correctly pointed out however, these IDIs DO love to rev. On a long steep grade I would usually be in 4th gear at 3000-3500rpms (55-60mph speed limit) and the engine was quite happy there. Other than that my driving took me on mostly mountainous back roads with lots of accelerating and decelerating (twisty and steep). That's where it really shined. Mileage was about 12mpg loaded, 16mpg around town (empty), and 20mpg highway (empty).

In addition to mine, we also had a '93 rollback with an IDI that also gave excellent service. If the IDI turns out to not be enough motor, then by all means, swap in a CTD, but don't give up on the IH until you've really worked it for a while. It might surprise you.

Just my 2 cents. Hope it helps.

 

[VanBoy]

The 7.3L IDI and it's predecessor the 6.9 IDI are medium duty truck engines as people stated. I actually ran across an IH truck from the early/mid 1980's that had the 6.9L and it was a '2 ton' truck.

I suppose the origin of V8 diesels (in my opinion) comes from the American fascination of V8 gas engines. People think that if it's a inline engine, it's not as good as a V.

Look at the old Cat 3208 (NA and Turbo) and it's predecessor. For what they were at the time (pre 1980 diesels), they did the job. They chugged up the hill nice and slow, had 225HP, but reved up to 2700RPM. Most diesels back then were NA, at least smaller engines. Inline diesels tended to be "turbo". Heck, even the 906 (or is it 908) Cummins V8 diesels eventually got phased out of on the road trucks for the NT series I6's. The weight to power ratio is very different from a V8 vs I6 engine. Most I6's have a better power to weight ratio. An old 3208 NA will chug around and last for ever if pushing about 32-36,000 pounds. You put a Turbo on it and try to fast and hard, a buddy said they tend to go about 250,000 only (and he was a Cat shop supervisor).

As a departed buddy said to me once, "You drive a truck, not a race car." Well, that may have been true back then, pre 1980's. But a lot of the engines back then were made for med. duty use with a LONG life span (high millage) and that is what people who bought 6.9 and 7.3 IDI's wanted in a medium duty truck. Times changed and people wanted to go faster w/ their diesels. The 6.9 was designed back in the late 70s and the 7.3 was just a "bigger" 6.9L. The turbo of the late 80's early 90's helped the 7.3 move forward- as putting a turbo on a NA diesel was 'the in thing' for the 70's on (in my opinion).

Some here have stuffed a DT466 into a F350. I don't know when the DT466 I6 came out, but if it was around during the same time as the 6.9L, there must have been a reason why it wasn't put in. Like I said, maybe it was he American 'perception' of a V8 being better then an inline engine.

 

[averagef250]

I towed 7500 pounds behind the truck yesterday. It was pretty pathetic. I'm not new to heavy towing, I've made 500 mile trips over the cascades with a highboy and trailer at 35K. I don't need nor want a racecar to tow with, just something with reasonable power to maintain safe speed up grades and get a load moving comfortably. My 3.9 powered '71 has been over 18,500 where this IDI truck was yesterday many times. The 3.9 handles it much better and at 500 RPM less.

There could be more wrong with this engine than I'm aware, but it feels by my seat of pants dyno to have maybe 300 lb/ft at 2200 if I'm being generous. I wouldn't be joking at all if I said this truck doesn't need 5th gear with any weight at all behind it.

The hardest part for me to still get ahold of is the RPM's this thing needs to move down the road. The engine sounds good at 2000-2200. It sounds terrible above 2500. I'm used to towing with Ford big blocks and Cummins engines and I love the sound of a well built truck FE at half throttle and 2500 pulling a very heavy load up a grade, the Cummins also sounds great when it's working, even up around 3000. The IDI sounds like it's going to come apart.

On the plus side, the thing does have excellent compression for downgrades, the truck's brakes work unbelievably well with a load and the engine doesn't seam to care about what fuel it runs. I've got 50/50 WMO/diesel in one tank right now and it runs the same either tank.

 

[RLDSL]

There could be more wrong with this engine than I'm aware, but it feels by my seat of pants dyno to have maybe 300 lb/ft at 2200 if I'm being generous. I wouldn't be joking at all if I said this truck doesn't need 5th gear with any weight at all behind it.

The hardest part for me to still get ahold of is the RPM's this thing needs to move down the road. The engine sounds good at 2000-2200. It sounds terrible above 2500. I'm used to towing with Ford big blocks and Cummins engines and I love the sound of a well built truck FE at half throttle and 2500 pulling a very heavy load up a grade, the Cummins also sounds great when it's working, even up around 3000. The IDI sounds like it's going to come apart.

On the plus side, the thing does have excellent compression for downgrades, the truck's brakes work unbelievably well with a load and the engine doesn't seam to care about what fuel it runs. I've got 50/50 WMO/diesel in one tank right now and it runs the same either tank.

Problem is that you're lugging the thing. If you try to drive it like a cummins it's not going to treat you very nice. When pulling heavy on a hill, you won't have anything to work with till you get well over 2500 rpms. The thing is built to be driven up around the governer. get that sucker up there around 3200-3300 and youll finally find out where the power is, and it will run cooler too. If you don't have a turbo, forget about towing in 5th with a load on , it'll just make you eat fuel . drop a gear and keep the rpms up. If you have a turbo and cant hold 5th on the flats, your timing is retarded or you have other problems. I can pull my 10k 5er on the flats all day long at 70

 

[averagef250]

I'm not lugging it. I'm at defuel 95% of the time.

I'm sure if this was a pickup it would be much faster, but this is still sad for 11K pounds. The engine is pretty much maxed out at the trucks empty weight.

In a way I'm saying don't tell me I need to get used to going slower or this engine will move the truck fine. It doesn't. I mean seriously a 400+ cube diesel with a close ratio 5 speed, 4.10's and 31" tires moving 18,500 pounds down the road up maybe a 1% grade should not be wound to the nuts in second gear and fall on it's face and slow down when shifted into 3rd at full throttle. It won't maintain speed at the smallest grade increase.

My 3.9 truck is not fast. It's a realistic 400 lb/ft at 1700 and maybe 200HP, probably 180. It's very easy to drive and will run 3500 RPM if I need it to. Regardless of the load, if the engine will rap a gear to defuel it will hold that speed or accelerate when upshifted, it just makes far less power past 2500 than it does from 1600-2000. And it has a much wider gear spacing with 4.10's and 35"s with the same tranny ratios as the 7.3 truck.

The 7.3 truck just doesn't feel right. I would love to drive a similiar truck that an owner claimed was running great and made decent power or a pickup with a 7.3 that was towing a trailer that put it around the same weight as this truck.

 

[averagef250]

I bought a wrecked 91.5 Cummins dodge 250 4x4 with 200K for a grand today.

After I sell the axles and tranny/case the engine should be free. I'll mill up an adapter plate and drop it in with a powerstroke intercooler, HX35 and some screw turns.

I will never own another IDI truck.

 

[VanBoy]

Sorry to hear that your first experience w/ an IDI will be your last.

Good luck w/ your project.

Oh, by the way, I mentioned before buddy who build a 3208 cat and put it into a pick up (not sure if it's this thread). Any how, he said it had about 225HP NA and he built an adapter and put a 'built' turbo 400 behind it with an early model GV OD (70's era). Last I knew, it was running around this area when he was forced to sell it when he fell on to hard times. He never had any issues w/ the Turbo 400....

 

[Exekiel69]

I'm not lugging it. I'm at defuel 95% of the time.

I'm sure if this was a pickup it would be much faster, but this is still sad for 11K pounds. The engine is pretty much maxed out at the trucks empty weight.

In a way I'm saying don't tell me I need to get used to going slower or this engine will move the truck fine. It doesn't. I mean seriously a 400+ cube diesel with a close ratio 5 speed, 4.10's and 31" tires moving 18,500 pounds down the road up maybe a 1% grade should not be wound to the nuts in second gear and fall on it's face and slow down when shifted into 3rd at full throttle. It won't maintain speed at the smallest grade increase.

My 3.9 truck is not fast. It's a realistic 400 lb/ft at 1700 and maybe 200HP, probably 180. It's very easy to drive and will run 3500 RPM if I need it to. Regardless of the load, if the engine will rap a gear to defuel it will hold that speed or accelerate when upshifted, it just makes far less power past 2500 than it does from 1600-2000. And it has a much wider gear spacing with 4.10's and 35"s with the same tranny ratios as the 7.3 truck.

The 7.3 truck just doesn't feel right. I would love to drive a similiar truck that an owner claimed was running great and made decent power or a pickup with a 7.3 that was towing a trailer that put it around the same weight as this truck.

I agree with You the C does have much more power and if You want You can rev it up high not like many think that it only has a power band of 2200rpm, it can go well past 3200rpm and id gives better fuel mileage than the IDI too.
Now for what I read something must be wrong with that IDI You have in that truck, could be something simple bad lift pump, fuel filter, timing but I know this trucks will pull 10k all day long with plenty of power bc I have done it several times and yes it is not like a C but it doesn't fall on its face either. I'm not trying to start an argument, I just think there must be something going on with that new IDI You acquired and unfortunately it leads You to think they are worthless.

On another note, if You ever have a chance and post any photos You have of Your 4bt conversion I'd love to see them.

 

[averagef250]

The IDI I have may have head injector/pump issues that I'm not thrilled about the idea of investing time/money to figure out. The more I drive it, the clearer it becomes that the engine probably isn't in the best of shape. It really rattles above 2500, it is not running smooth and has a mild miss somewhere. It is also a little erratic in how it behaves. Sometimes it has decent power when I throttle down on it, 90% of the time it doesn't.

I've changed the oil, filter, fuel filter, cranked the pump timing, backed off the timing retard arm and disabled the cold start advance. The truck already had true dual 2.5" exhaust The largest gain has been in the engines sound, it sounds much better than it used to, but the power gains were marginal once I really drove and worked it. The engine does not smoke, even when running on considerable amounts of WMO, but it consumes about a quart every 200 miles and more the higher RPM's I run it at.

I'm familiar with C motors, I really like the power they make and they've always treated me very well. I have a shop full of Cummins parts and pieces so instead of fill my shop with even more crap in the way of spare IDI parts and pieces converting the IDI truck over makes way more sense to me.

I have to get this shell of a didge hauled off then the IDI comes out and the part I enjoy starts.

 

[res0wc18]

Dustin,

Didn't realize you were on the board! Welcome.

The idis are no power houses but when taken care of and have less then 500k miles they are ok. The lack of a turbo kills them though with a load.

I put an ats kit on one of my older idis and it was not even funny the difference it made.

Those little cummins you have when built will eat one all day though. The main reason most of use run them because they are so cheap to buy and maintain its like its all government surplus! Plus i ran mine off of Waste motor oil, so that was a benefit.

 

[typ4]

els tended to be "turbo". Heck, even the 906 (or is it 908) Cummins V8 diesels eventually got phased out of on the road trucks for the NT series I6's.


That would be the V903 or VT903. Good screamer engine.

 

[VanBoy]

I was soooo tempted to pickup a 5.9L Cummins a few weeks ago. And it was a Cummins 'Cummins' engine.... not in a Dodge. I think it went for $1800 or so. Would have come w/ an Allison tranny..... and the whole school bus too. Was being sold by the Washington State Surplus. There were two of them.... a 92 & 93 so not computerized yet.

Didn't need another project... plus would have to dispose of a bus body after ward too.

 

[averagef250]

With scrap at $100+ a ton that wouldn't be a bad option. Those old allisons are worthless though. The SAE3 adapter is worth a few bucks on ebay, but the tranny itself is best sold for scrap.

 

[typ4]

I was soooo tempted to pickup a 5.9L Cummins a few weeks ago. And it was a Cummins 'Cummins' engine.... not in a Dodge. I think it went for $1800 or so. Would have come w/ an Allison tranny..... and the whole school bus too. Was being sold by the Washington State Surplus. There were two of them.... a 92 & 93 so not computerized yet.

Didn't need another project... plus would have to dispose of a bus body after ward too.

Shoulda grabbed that one IIRC they are 230 HP with a P pump. I would put one of those allisons in in a minute, 5 speed at least ,not a 4, they dont break unless you are very ******* them.