I just bought a 1991 F-250, non turbo and I am getting about 14.5-15 mpg. The truck is a regular cab 4x4, automatic with 3.55 gears. I have not hauled anything with it yet, and it has a brand new injection pump, injectors, glow plug controller and return line. The truck only has 136K on it and runs/drives great. I was hoping to get much better than this out of it, which is part of the reason I traded in my straight six. I am considering a Banks Stinger kit to help a little on power and economy, but if there is something wrong with the truck I need to fix it first before upgrading. Anyone have an Airgate? I have heard they help reduce drag on the highway. I am a little disappointed with the mileage, so any help would be greatly appreciated. Thanks.

 

I would say that is about right. I would check and see the calibration settings at the injection place you had it rebuilt. Look for black smoke under accelaration. If you cna see a little wisp of smoke that is fine, but if it is pouring black smoke then the pump is set to rich.

Also a diesel will not get better mileage just fopr use as a daily driver. For example a 4.9L will get about 12-15 around town with no load, once fully loaded it will get about 5-8mpg. A diesel will get about 15 around town empty and once fully loaded it will get about 10-12. A diesel still is more econmical for pulling loads being that it produces more torque that a gasser.

I only get about 10-11 aound town with a 6.9L with 4:10's and about 15-18 on the highway. So I'd say your close.





1986 F-250 6.9 diesel,4x4,XLT Lariat,Ex Cab, 8'bed,etc...

 

Thanks for the prompt reply, maybe there is nothing wrong and I'm just looking for trouble. (Wouldn't be the first time.) I was hoping for a little better economy, but what I'm getting now beats the heck out of a big block gasser. I guess I will try to upgrade with the Banks kit and maybe a turbo eventually, I've heard that they improve mileage as well as power. Any other performance upgrade recommendations would be appreciated. Thanks again for the help.

 

Propane Induction will really help out in power and economy. Propane acts as a catalyst to diesel.



1986 F-250 6.9 diesel,4x4,XLT Lariat,Ex Cab, 8'bed,etc...

 

You don't necessarily need to see black smoke to be wasting fuel. I recently picked up a '91 F-250 with 117,000 miles exactly like yours except a 4x2. Although it didn't smoke at all, it only got about 13 MPG and I wasn't happy about it. I took it to a diesel shop and told them to set the injector pump for minimal performance and maximum economy since I don't do much towing. I also started using Stanadyne Performance Formula fuel additive. I now average 19-20 MPG regardless of city or highway - that's with the E4OD automatic. My fuel savings more than pays for the additive, and it seems to have the same performance it did before. The rig is now my second-best friend.

 

That sound like what I need to do. How difficult is tuning the pump, and do you notice a bid loss of power from the economy setting? Also, where do you get the additive? Maybe the Banks Stinger would make up for any loss of power from de-tuning the pump. I don't want to drive a dog, but if I could get 17-18 out of her I would be very satisfied. Thanks for all your help and suggestions.

 

I am told that adjusting the fuel rate screw is easy, but I don't have any experience with it and it's not covered in any of my manuals. The shop agreed to do it free since they rebuilt the pump two weeks before. The great people who use this board will probably post detailed procedures for you before the week is over; if not, post a new message asking for help. I expected a performance loss from the fuel rate change but didn't see one - maybe because of the additive.

 

Thank you very much for your help. I will head to the dealer tomorrow and see if they can adjust that pump, since they installed the new one. I found the procedure in my Haynes manual, but it lists at least three speciality tools from Ford that are required and says that unless you have access to them, take it somewhere. Apparently they are rather pricy and not of much use to the home mechanic. Hopefully they will adjust it and my gas mileage problems will be a thing of the past. It will never be as good as my Buell Thunderbolt, but it can be better than any other truck I have ever owned. Thanks again for your guidance and assistance.

 

Are you referring to the Haynes Diesel Techbook #10330? There is an excellent cutaway view of the injection pump on page 3-21, and step-by-step dynamic timing procedure, but nothing on adjusting the actual fuel rate. It might be the "metering valve" shown on page 3-21, but I'm not sure. It's a ticklish adjustment - any more than 1/4-turn between road tests can foul things up and cause hard cold starts. If you decide to play with it yourself and get good results, I'd appreciate some feedback.

 

That is the book I have, and the metering valve is what I was thinking about. Unfortunately you are right, there is no process given for adjusting fuel flow. I found a diesel mechanic here who works for $35 an hour and said that the pump timing looks to be off. He told me that he has to take it off and reset it properly on the timing gear and that should fix the problem. He seems to know his stuff pretty well, and for that price I'm willing to let him work on it for a few hours. Will let you know how it turns out. Keep your fingers crossed...

 

14MPG? 15MPG?!? WOW! I used to own(and still do untill I sale it) a '94 F-350 withthe 7.3L IDIT. About the best I averaged was high 13s on mostly high-way driving. I think I have a 4.10, and the previous owner said the fuel pump had ben sped up. However, I almost never saw smoke. I think the Turbo that on the IDITs are of an ATS design?

Logan

 

It does sound like your pump was turned up, although the 4.10 rear end gobbles up plenty of fuel. It took me 3 months and at least 30 test drives to find a "freeway rig" in good enough shape to buy. With the 3.55 rear end, 2WD, and 235-85R16's, I'm turning 1950 RPM at 70 MPH. Probably the heaviest load I'll ever be able to carry is a cab-over camper, but she puts money in the bank every day.

 

The mechanic adjusted the pump timing, said it was off about two degrees. The truck starts a lot easier now, but gas mileage remains abysmal. Just took a trip to Ft. Benning, about 550 miles round trip and got 15 mpg (unloaded the whole time). Half the trip was at 60mph and the other half at 75 or so, cruise control the whole time. I asked the guy who timed it about mixture adjustment, but he told me that it was preset and couldn't be adjusted. This confuses me a little, since the diagram in the manual clearly shows an adjustment screw. I guess this means a trip back to the dealer, but I'm getting tired of this. The mechanic also suggested that the lift pump might not be up to spec, but I can't imagine how that could be. It runs well and that should have nothing to do with bad gas mileage. I am reaching the end of my rope here. Any other sugestions?

 

Your mechanic may have been confused by the word "mixture" which is a carburetor term. Since there is no mixture in any injection pump, it can't be adjusted. The fuel RATE certainly can be adjusted though, and many of the guys on this site know how to do it, I'm just not one of them. I've sent e-mails to some of my diesel gurus asking for the procedure; also some of the FTE guys are likely to reply to this thread within a few days. If not, I will post a new message asking for it. The lift pump has no effect on mileage that I know of, so I don't know what your mechanic is thinking.

 

Sorry, you are right. The screw in question adjusts the rate of fuel flow. I have been restoring a 1977 F-150 for my dad and have carburators on the brain. I guess this is the last thing to look at since everything else has been done, so if this doesn't cure the problem I will just say the hell with it and start saving for a turbo. Looking forward to hearing what the experts have to say, and I will inquire locally here as well. If it is too complicated then I will leave it to the pros, but I would like to tackle it myself. Thanks again for your help with this little headache.