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7.3 IDI Educate me

OK i tried this on another forum and quickly got swarmed by "CUM.mans" fans that wouldnt sthu about them.... so guess ill try this again here....

Ive been trying to research these. But been spinning my wheels in the mud so to speak. Most the threads i find on them people are just talking about issues with the glow plugs or glow plug relays. Or not being able to get them started and seems to be an issue dealing with glow plugs of some shape or forum.
Just trying to find out more about the 7.3 IDIs and their "known" issues to look out for. Ive always heard these things were pretty much non-killable. Slow but non-killable. And that they were all mechanically driven. But outside of that i dont know a thing about them.
had one guy that actually tried to help with the edjucation before the C humpers showed up... he said the valve cover gaskets had tendency to leak and oil cooler (the oil cooler i knew about), the CDR valve apparently prone to failure (which i had to look that up because id never heard of a CDR valve.. looks like its similar to the ICP valves... ) and something called air intrusion getting in that has something to do with the return lines and fuel filters...

i know they came with dual mass flywheels, everyone talks about converting them to single mass when doing new clutches for cheaper than replacing both with original.. but not finding originals on either... so what else is missing here...


Staff member
I will dig into this later. There are a lot of positives and negatives as with any but the darn things can be quite reliable and comparatively lower cost to keep running typically. They definitely won't win races without a ton of work, but will pull pretty much anything you want. I scaled my 6.9 in hauling scrap at 24,500 before. Not bad for a naturally aspirated version. A tad overweight on many counts..
The one im looking at is a 92 7.3 idi with the zf. Partly wanting to know what to look for, partly to help others, and partly just to know more about them. Always heard they were hard to kill and could pull the gates off heck. But slow.

One thing ive heard many times a out the 7.3's was their injector harnesses had a tendency to short out and that they were part of the valve cover gaskets. Is this true for the IDI's as well?? Or was that a later/newer design thing.


Staff member
Ok, so now I can spend a little time on getting into this a bit more. The 7.3 IDI has the updated glow plug controller and was typically what the previous systems generally updated to. They did not go into the valve covers, the glow plugs are accessible from the intake manifold. They are a bit touchy in that many had a habit of swelling and then would not be removable and would often break off and if not removed from the cylinder would likely cause damage. This is why you will find most IDI owners swear by the Motorcraft Beru glow plugs as they rarely swell when they burn out.

The injection system on these motors are completely mechanical. The full set of injectors can typically be had for less than the the cost of just 1 power stroke injector. The injection pump is a Roosamaster which is essentially the same pump GM used on their 6.2/6.5 motors as well as back to the 5.7. Obviously there will be differences so don't let that be an issue. IH also used the Roosamaster on many diesel tractors like the 856 my dad has. These systems are very reliable and have some tuning capabilities but you have to spin a wrench, not plug in a computer.

The lugging power these motors have comes from the high compression they have. I forget the actual number, but it is around 21-24:1 compression. As such, it is easy to over boost these motors with a turbo so care is needed if playing with a turbo. Factory boost was not particularly high but effective. The 93 -94 motors were the only factory issued years with a turbo. Rumor has it that they actually detuned the motors just a bit in 94 as they didn't want it to overshadow the performance of the 94.5 DI Powerstroke motors. I obviously can't validate it, but the claim has been made many times.

So now for the common issues - first is the block killer - cavitation. If you don't keep up with the antifreeze or use a quality antifreeze with the proper sca levels, the vibration of the motor actually can cause the cylinder walls to actually erode away to the point pinholes will form in the cylinder walls and allow coolant to leak into the crankcase. Generally heavy equipment antifreeze is sufficient. The 7.3 has a larger bore then the 6.9 which then showed itself as an issue with the cavitation problem.

The CDR valve, essentially the pcv valve of these motors, require some maintenance in the form of cleaning the crud out or they can hang open and allow oil to getinto the intake. The motor will still run fine, but will show oil smoke in the exhaust. It is as simple as removing and soaking it in some form of degreaser solvent, flush and reinstall. Some have taken them off and installed road draft tubes which are essentially just a hose that relocates the vapor vent to under the truck.

The dual mass flywheel is named such as it actually has two main parts - one part bolts to the crankshaft, the other has the pressure plate bolted to it and then instead of springs in the pressure plate, the springs are inside the flywheel. When these wear out, the whole flywheel must be replaced, not a low cost part. The reason for this mechanism is to absorb the vibration from the power pulses of the motor and keep it from getting to the transmission where it can cause it to make a rattling sound. A lower cost option is to replace it with a single mass flywheel kit which is simply a traditional flywheel and clutch type. It can allow the rattle in the transmission and many claim that the engine seems to have better torque. I installed one in a friend's dad's 94 turbo 5 speed and he said right away it really amped up its response. Typically the rattle is only present at idle.

The return lines on these motors are a combination of plastic caps, o-rings, and rubber lines/spring clamps. Not too hard to imagine that this can develop leaks. It not only seeps fuel out, but also allows air in which can cause trouble with the injection pump. When sitting, the fuel will siphon out and a short fire/no start condition results. The injection pump then run out of fuel and causes what is known as air intrusion. In order to clear it, the injection lines must be loosened, crank the engine until the air clears and fuel fill the lines again. Why this is a thing - the injectors are hydraulically opened. The same as air in the brake system makes the operation oif the brakes less, the same happens in the injection system. If there isn't enough pressure, the injectors don't open.

As to the oil cooler. I so far have been lucky in that I have never dealt with it on my 6.9. While they do on occasion fail, they actually are generally pretty reliable. Regarding the cuma prts, I had to change the oil cooler out on the 91 motor I swapped in the place of a 460. They have a bit less spectacular track record... They also have the killer dowel pin issue, where one of the lineup dowels on the timing cover like to walk out and get into the timing gears.

I am sure there is more to tell, but I am blanking at the moment on more to state.
Nice info there. Appreciate it.