Hi, My 1994.5 F350 7.3 power stroke had begun smoking for the first 5 minutes after starting so i performed a compression test as first step to diagnose. It has always started right up but after I put it back together it won't start.

I followed the steps for the compression test described in my 1994 7.3L DI Turbo Diesel manual supplement, page 03-01D-14, including disconnecting the injector driver module (IDM). Actually, the manual says to disconnect the IDM "relay", but I have no idea what that might be, if not the IDM itself. Can someone clue me in?

Anyway, the compression was fine, between 395 and 420, except i couldn't test the #1 cylinder because the top of the glow plug sheared off.

But then it wouldn't start so i checked all the fuses, topped off the battery, tried again, no luck. The "Wait to start" light comes on then off, so it seems the IDM must be properly connected. Anyone have an idea what I might have done while running the compression test that would prevent starting? I assume the fuel is not getting to the cylinders. How should I diagnose this problem?

I really appreciate any help you might offer.

 

When cranking does the dash oil pressure gauge register anything? If not thinking maybe with all that cranking the HPOP reservoir might of drained down a bit. It should be about 1/2 inch from the top.

 

I did not realize that cranking without the injectors actuating would draw down the reservoir. I'll take a look. Thanks!

 

Cranking should NOT drain the HPO reservoir. It should FILL the reservoir at least as fast as the HPOP would use the oil.

The relays, including the IDM relay, are in the underhood fuse box. The underside of the cover provides a guide. IIRC, they're also listed in the owner's manual. Of course, the RIGHT way to crank the engine without firing the injectors is to leave the key OUT and use a remote start switch on the starter relay.

As for the no-start, the WTS light only tells you that the PCM is active; it indicates nothing about the IDM. Does the tach move when you crank the engine attempting to start it? Do you get any smoke from the tailpipe?

Did you disturb any of the wiring around the fuel bowl in order to get the valve covers off? One of the connectors goes to the IPR; would be worth an inspection. Did you disconnect any of the UVCH connectors when you removed the valve covers?

 

some more things to look at, is there any smoke coming out of the exhaust? does the tachometer move when cranking? how is your fluid levels? how old are the fluids?

im watching tv while writing this so i didnt see that madpogue posted that

 

Hi, Okay, the service manual DID say to use an auxiliary starter switch, so I will look into that for next time. But they also said to disconnect the IDM relay (and I now know what that is thanks). What's the problem with cranking with the key on (assuming the IDM relay is disconnected)?

Would cranking with the IDM itself disconnected, instead of the relay, do any damage?

Yes I did disconnect some UVCH connectors but I double checked all the connections when I was done including the wiring around the fuel bowl.

I'll check the tach and the tailpipe tomorrow morning in daylight. Thanks, I appreciate your input. I really want to get to know this engine well - it's a new one for me.

Anders.

 

Re check the connection at the IDM... I had this problem one time after doing some work to the engine. Disconnect it.. look into the plug. make sure none of the pins are bent over and that there is no corrosion