Well I have the truck on the road now after chasing a air intrusion problem and upgrading to an electric fuel pump. So I take it for a test drive and the shifting seems off. I pull the TCM and see evidence if trans fluid in the vacuum line. I replace the TCM shifting is still not quite right. So question #1 can you adjust when the TCM shifts? well after I replace the TCM I go to start the truck......no start, cranks good but no start. I start to think I have another air intrusion issue when it hits me, I pulled the vacuum tube off the TCM, There's not enough vacuum build up....OK so some cranking later truck fires up no problem....whew I really need this truck tomorrow. so I now have a truck that is running and shifting ok. The next step is to start making the truck more improved, like getting the tach to work again....It stopped working during all the air intrusion crap. so question #2 how do I troubleshoot the tach? I beleive it has to do with the sending unit in the front of the engine.....does anyone know how to work on that or do I hve to replace it? Thanks guys I will update as things progress.

 

You can try wiggling the wires around a bit, but pretty much just have to replace it

 

I figured the wires would be the only thing I could mess with.....Bummer.

A little more about my diesel. 1987 F250 w/ 6.9L NA super-cab long-bed upgraded with an electric fuel pump(2 weeks ago) and bypassed fuel/water separator(PO did that), fuel tank switching valve(1 week ago), and fuel return to filter head(1 week ago). new injectors and return lines about 1 yr ago.
C6 trans with a black stripe TCM replaced TCM today.

Any ideas on how to adjust the TCM to change when it shifts?

 

if i tis an adjustable modulator, there is a screw in the vacuum hose nipple. you need a very small thin screwdriver to adjust it.
you can also set shift points by adjusting the VRV on the injector pump.
the VRV can make it shift sooner, or later at full throttle.

 

Thanks Tom, if I turn thr screw in the nipple for the TCM to the right will that help it to shift sooner? and which way to I adjust the VRV to shift sooner ? Sorry I am new to a lot of this.

 

it has been 15 years since i messed with the modulator.
the vrv has a touchy adjustment procedure to get it set properly, but i have found that moving the vacuum hoses towards the firewall lets it shift a bit sooner, rolling the VRV up or towards the radiator will make it shift later.

 

adjusted the modulator still shifting a little late. I will try the VRV possibly on Monday. I found I have a fuel leak so I need to fix it or them......looks like the fuel return line from the injectors to the tank. well at least that is one, I need to check everything though. The truck is drinking fuel. Well back to finding leaks......

 

OK I am not finding a lot of leaks but I used about 14 gal of diesel in about 80 miles! and I lost a quart of oil......That's less than 6 miles a gallon not including the oil. WTF is the electric fuel pump sucking that much fuel? I was getting 15-17 MPH before I changed things.........Please help and let me know what I can do.......ugh.

 

Do you have dual tanks and are you sure it isn't pumping fuel somehow, either directly or through the fuel return system, into the other tank? It's possible.

 

Yes I have dual tanks so I guess it is possible but I can't switch tanks due to a bad tank selector valve. I ran a fuel line for the supply straight from the tank to the pump. I guess I should do the same for the return......I hope this works. I am thinking of going back to the mechanical fuel pump....I need to get decent MPH, this is my daily driver. Thanks for the input I will be updating as soon as I can road test it.

 

From which tank are you drawing the supply? Unless you are certain that the selector valve is set to that same tank, you wil be returning fuel to the other tank. In that case, it will of course eventually overflow. This is a conventional return fuel system (whether electric or mechanical), so any work on the supply must also be done on the return, unless you want a nice surprise spill.

 

I am drawing from the front tank which is the only one that was working before I started my adventure. I will be bypassing the return soon. Thanks for all the info.

 

OK I got fed up trying to find leaks so I decided to try switching back to a mechanical fuel pump. I removed the Electric fuel pump checked all connections and tested the truck on a short drive(about 20 miles). Fuel usage went down, needle did not move off of full all the way. Yesterday at that same distance it was down 1/8 of a tank.......The e pump I had must have had too high of a flow rate. The trans seems to shift a little better not as hard, not sure if that is related or not just telling you what I am experiencing. So hopefully I will not be going through fuel as fast. So I guess I down graded the fuel pump but my truck seems to like it better. Let me know your thoughts. This is a huge learning experience for me. Thanks for all your help I will update as I make more changes or as I find new issues.....This truly is an adventure, and you are welcome to come along......

 

The capacity of the pump only determines how much fuel is made available to the engine. It has no impact on how much is consumed. Either that pump was leaking, or one of its lines was, or it was letting air in or something. Or, by switching back, you got it to return the unused fuel to the correct tank, which is the only way you can get any kind of meaningful fuel economy estimate. In any event, if it's working, I'd stick with it.

 

Well I took the truck out for a 100 mile road test, I had a lot of errands to run, and I am up to 10 MPH which is much better.....I still have a leak though. When I drive I can smell raw diesel I am wondering if the return line is leaking at the back of the engine.....Is this a common place for fuel leaks? Has anyone had this problem and are there common places I should check first? WFS has been bypassed already o rings and return lines have been done.....She drives but I would like to have her running better......also can adjusting the TCM help with late/hard shifting? Any help is appreciated...Thanks