General IDI Questions

[brandonlear]

First off, let me just say that I'm a newb when it comes to diesels. I have a 1991 F250 turbo 7.3. I just have a few questions.

1) My valve cover gaskets need replaced, but I've noticed a small bit of oil underneath, would this be because of the leaking valve covers or another problem?

2) When I slow down/stop and the truck begins to idle, the oil pressure gauge will drop as if the truck was turned off, and them return to normal in 1-2 seconds. Is this something to be concerned about or do the IDI's indeed rely on oil volume and not pressure?

3) I put 30 gallons of fuel in the truck on Friday when I bought it, and I've probably driven less than 100 miles, and I have less than 1/8th of a tank left. The majority was highway driving as well. How can I help fuel mileage?

4) On the dash next to the lights and wipers, there is a "Fuel Switch", if I leave it where it was when I purchased the truck the fuel gauge shows normal, if I turn it "off" so to speak, the fuel gauge drops straight to empty. What is this?

5) On the right side of the steering wheel, there is a black switch and when you turn it on, a red light comes on. Is this for the block heater or something else?

6) This is a contradiction, but in addition to the better MPG I mentioned above, I'd like it to smoke a bit more. It does NOT smoke AT ALL, and I want it to smoke just enough that people will know I'm driving a diesel.

For now, this is all I can think of. If I think of more, I will add them to the list as they come to mind. If you guys have any advice to help the longevity of the motor/transmission, and other parts, please let me know. I'd like for this truck to last forever, but if fuel mileage doesn't improve, I may have to get rid of it. Thanks in advance for your help!

 

[direwulf23]

Is this an automatic? If so, the button to the right of the steering wheel on these models would/should be to turn overdrive off/on. When lit O/D would be off.
The fuel switch should be to select which fuel tank you're running on, if you have two fuel tanks. If this is the case, I'd guess your other tank is empty, this the fuel gauge dropping off.

1994 Ford F250 Superduty, 2wd, 7.3L IDI, NA, E4OD

 

[brandonlear]

Is this an automatic? If so, the button to the right of the steering wheel on these models would/should be to turn overdrive off/on. When lit O/D would be off.
The fuel switch should be to select which fuel tank you're running on, if you have two fuel tanks. If this is the case, I'd guess your other tank is empty, this the fuel gauge dropping off.

1994 Ford F250 Superduty, 2wd, 7.3L IDI, NA, E4OD

The switch is between overdrive and the steering wheel. Also, I had fuel in both tanks so it's odd that it would drop like that when I switched it.

 

[direwulf23]

Then, possibly, the fuel sensor in that tank doesn't work? There at a lot more knowledgeable people on here than me. I'm like a level one above a newb lol

1994 Ford F250 Superduty, 2wd, 7.3L IDI, NA, E4OD

 

[79jasper]

Get a pic of the switch. Could be a aftermarket overdrive unit.

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[madpogue]

2) The IDI doesn't depend, for its operation, on oil at all. You might be thinking of the direct injected version of the engine, the PSD, aka HEUI engine. But like any engine, it does depend on oil pressure for its lubrication. The "gauge" is just an idiot light with a needle. It moves somewhere around the middle when there's "enough" oil pressure (something like 7-8 PSI). If it drops at idle, one of two things is the case. Either there really isn't sufficient oil pressure at idle, or the sender/switch is not working right. You could connect a real oil pressure gauge and take it for a test drive. Or the first thing to try, since it's reasonably cheap, is to replace the sender and see what it does to the gauge.

3) When you say "1/8 of a tank", which tank? Did you fill both tanks? The gauge is notoriously inaccurate (like most vehicles), but with either tank, if you filled it, you probably burned 12-15 gallons to get the gauge down to 1/8. You really can't measure the fuel economy with the gauge, though. You have to fill up, reset the trip odometer, run it down (either or both tanks), refill, then divide the distance driven by the volume of fuel needed to refill.

4) Not sure what you mean by "off" for the fuel switch. When it's set to "Front" it's on the front tank. When it's set to "Rear" it's on the rear tank. If the gauge is dropping to empty on one of the tanks, and you have fuel in that tank, the float for that tank has probably failed.

5) The block heater isn't part of the truck's electrical system. That switch is something aftermarket, by definition. You could check the owner's manual to confirm.

6) People will know it's a diesel the moment you start it up. Smoke is equivalent to a running problem. People seeing smoke won't think it's a diesel, they'll think something's wrong. Just put a "Real Trucks Don't Have Spark Plugs" sticker on it, if you want to remove all doubt.

 

[direwulf23]

As loud as these engines are, it would be hard not to know! Lol
That's what I think whenever I see a diesel smoking. Black smoke I would think it's not burning enough of the fuel being fed to the engine, wasting fuel. Mine doesn't smoke at all, and I'm really glad for that

1994 Ford F250 Superduty, 2wd, 7.3L IDI, NA, E4OD

 

[icanfixall]

Welcome to the forum. nobody is going to tell you how to make more smoke. More smoke will heat up the engine and blowby will increase. then that black soot ruins the oil fast. As for the dash oil pressure gauge. Its just an indicator telling you there is pressure of 7 lbs to run the engine. nothing more. If you want to actually read the oil pressure please install a aftermarket pressure gauge. So far we have no idea what size fuel tanks you might have. If they are stock the front is 19.7 and the rear is 17.2 gallons. Our tanks fill slowly most of the time too. As for one level indicator not showing a level. That sender must be broke. If its the front tank its an easy removel. you don't have to drop the tanks to fix it. the rear is a much bigger job. You either remove the bed ... cut a hole in the bed or drop the mt tank. Don't try dropping a tank with fuel in it. It will unbalance easily and cause more trouble than you know. Lot needs to be removed and lines needs to be cut loose to get it out so hope thats not your issue.s

 

[TahoeTom]

The switch may be a manual glow plug switch installed by PO. Is it the " wait to start light" that turns on with the switch?

 

[vandy7.3]

As far as the valve cover gaskets go, if they are leaking they're cheap to buy and not very hard to replace. Driver side is as simple as removing the bolts, passenger side you have to take the fuel filter bracket and all that out of the way to get to a couple of the valve cover bolts. But as far as the oil leak goes, just grab a flash light and lay under the truck and follow the oil leak up until you find where is coming from

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