Engine/Transmission (1994 - 1998) Mileage problem post 2

[dbartos]

Well, I’ve had my fill of some of the local repair shops and their expensive (worthless) expertise. So I’ve decided to dig in and try to get to the bottom of my poor fuel mileage problem myself. I looked the other day in the back of the owners manual and I found a log where the previous owners had recorded their oil changes and maintenance and found it interesting that at 22,770 miles they wrote the following: “had 2 front rotors put on under fact. Warranty. They started trying to find out why fuel mileage low. ” What could there be about this truck that would have been causing low mileage even back then? It currently has 155,000 miles and gets about 13. 5 on the highway. I’ve been reading a lot Here and on some of the other forums and as a result here are some of the things I intend to check. #1. I want to make sure the wastegate actuactor is working corectly and is not stuck open. #2. I also want to check to see that the fuel return line is not pluged or broken. #3 I want to make sure I’m not loosing boost in the intercooler or anywhere between the turbo and the intake.

If anyone here can think of anything else that I might check I would welcome you’re advise. I’m not much of a mechanic, but I think I can do some of the simple stuff. I’m already convinced that you guys know more about these trucks than the repair shops and I’m glad I found this web site. Thanks you guys!

 

[Todd T]

4:10 rear end gears??? those would explain alot.



have you had the timing checked lately (or ever) that could cause it.

 

[chrleb1]

If you would like to check for boost leaks, an easy way is to go to your local hardware store and by about 4 inched of 4 in hose. Then find a PVC plug that will fit into it (i think a 3 1/2 in plug). Then take that plug and put a air hose fitting in it. The tap that you would use would be a 1/4 pipe tap. When that is done, put the hose (with the plug and and fitting in place) on the turbo inlet. Clamp down the both sides of the hose (turbo and plug). Next, hook up an air compressor (only have about 20 psi in the tank) to the fitting and turn on the air very slowly. This will let you find leaks in your system. Of course all of this would be done with nothing running.

Also a problem with gas mileage sometimes is the timing. There have been motors that have come from cummins with retarded timing. By increasing your timing to say 15. 5 or 16, you can increase your mileage.

 

[Deezul1]

Auto or 5spd? Dually+auto+4:10s = stacked deck against good mileage. Should be better than 13. 5 though. put a boost gauge on it and check boost levels. Any pressure gauge will work for temporary checking like an air gauge for a compressor or whatever. The timing will play a big part in mileage and if they have been chasing a problem since way back when the I would suggest doing that first but make sure that who ever does it can set it to whatever spec you chose or they will just push in the timing pins and say yea thats good and take your money. Go for 15. 5 or so, thats a good all around number for most uses.

Good Luck

John

 

[dbartos]

OK, so whats the best way to check to see if timing is off? And if it is off, how do you change it. Looking at the haynes book I have it looks like you would have to take either the cam or the crankshaft gears loose and turn them. Is this corect?

 

[Deezul1]

You have to remove the gear on the P pump, by removing the oil fill tube from the front cover you can access the gear bolts. The gear is on a tapered shaft that has to be VEEERRY clean when reassembled to keep timing from slipping. There are several ways to do this correctly as far determining where the timing is set at and the way a lot of them are done is called "spill port" timing. I had mine done by Piers and Co and they used a different way of setting it and I was not there when they did it so cant describe it but Al was very positive that the setting was accurate. It takes some specialty tools to set it so depending on your ability as to whether you get the tools or have a competent shop do it. I have most every common tool you can think of but elected to have it done as I didnt want it slipping when I was far from home. There are several very good shops in the "Midwest" to choose from, cant tell you who with no info on where you are.

 

[Missouri Mule]

An easy thing to rule out is odometer some or the speedometers/odometers were off. Taller tires will also decrease mileage figures. Take it out on highway see if odometers keeps up with mileage markers or route you know the exact mileage.



Auto trans could be dropping it is if not performing correctly.