7.3 idi trouble shooting

[Thurmondator]

I have a 91 F350. Its an old Uhaul truck. I bought it to haul my race car. At 55mph I'm turning 2600-2700 rpm's. If I keep it at 55 the engine dosen't over heat. But if I'm on the highway and get it above 55 for an extended period of time my gauge pegs and the warning light comes on.
Also this thing is a severe pooch. On going up a grade it bogs down so bad. It feels like it has a miss at idle and smooths out a little when it gets higher into the rpm's.
The truck is a 3-speed automatic with 4.10 gears.
I would love to keep this in the truck but I don't know how to trouble shoot it.
What do you do for a tune-up?
How do you tell if it has a miss and which cyl. is it?
Any help would be appreciated.

Thanks. Paul

 

[Andylad13]

im not a big help in the cooling troubleshooting, currently when i pull a trailer in the summer time mine overheats in no time. but i can tell you how to pin point a dead cylinder if thats the case. loosen the injectors one by one, there should be a noise, like a knock if its missing. when you get to the one where the knock goes away, thats the problem one.

tune up wise, i would say oil change and check the condition of the oil. if its real sooty, try cleaners in the crank case. check and ohm your glow plugs, replace your air filter if its crappy. run some fuel injector cleaner through it too. i use lucas upper cylinder.

remember, with a c-6 trans shes definatly going to wind up on the highway, but on the other hand, she should pull like a damn rapped ape! some people here will put on an aftermarket OD unit for added driveability. if its not pulling, you might have multiple dead holes, or bad compression from siezed rings. depending on the severity of the ring situation, some cleaners can treat that too.

 

[69dieselfreak]

you could have a plugged up radiator hows the fan clutch
get an egt gauge expecilly if you are going to be pulling your race car

 

[Mr_Roboto]

First thing, never buy a used rental truck. They only sell those things once they know the needed repairs are more than the truck is worth including rental income.

The truck not running right will create more heat that can cause or exasterbate a cooling problem.

 

[h2odrx]

Welcome To OB!

Check the cooling system flow? May need a new thermo stat? Don't trust stock gauges get some mechanical ones then report back....

 

[seawalkersee]

Naw...Like the gassers, I think it needs to have the timing checked. When you retard the timing, it causes the power to drop and, I believe it causes the engine to overheat.

SWS

 

[Thurmondator]

Thanks everybody. I know buying a used Uhaul is a gamble. But its what the pocket book allows. I didn't know you could set the timing like you can on a gas engine. I have a Haynes manual, I will check that out. Thanks for the info on checking for a dead cyl. When I get to working on it I will report back.

The Thurmondator

 

[DeepRoots]

not exactly like a gasser.

for instance setting it while the engine is running is a pretty bad idea.
look up timing via search here at OB.

 

[Full Monte]

On the over heating, you may have air in the system, trapped so it can't get out. The last time I had this, I removed the temp sensor in the back of the block to "burp" out the air. There may be a better way to do it. There is no way a diesel will run hot like yours unless there is something really wrong. They tend to run cold, if anything. Check the radiator and thermostat too.

On the missing problem, you can get the truck running and then unscrew the injector line nuts one at a time. If the injector is working well, it should miss when loosened. If no change, the injector may be bad.

 

[funnyman06]

My truck was running warm before i swapped the water pump, thermo and changed out the coolant. now it runs just below the middle of the gauge, before it could creep around the higher side.

 

[Thurmondator]

I'm thinking more and more about putting a 351M in it that I have setting in a 79 F250. Anybody interested in a 7.3 and auto tranny?

The Thurmondator

 

[Agnem]

So you would swap motors because you can work on gassers, but not diesels? Why buy it in the first place? Here is what you need to do...

Send the radiator to a shop, get it cleaned, rodded and checked out.

Replace the injection pump, injectors, and have it timed by somebody who knows how and has the tools to do it.

Replace the fan clutch.

Change all the fluids.

A nicety would be to check the compression. If you have some low numbers, maybe you can try AutoRx in it. Don't have any experience with that, but hear great things about it.

That truck, when properly maintained, withstood the decades of abuse dished out by countless people who ran the snot out of it, probably over loaded it, and if it has been overheated often and for long periods of time, you could have some serious issues with it. They usually won't over heat if maintained properly.

 

[69dieselfreak]

ok i hate working on gassers but i can do it
if you can work on gassers you can work on diesels
same basic principals apply
ok