another poor milage thread

[chrisangelski]

Hello everyone,
I recently acquired a 1997 6.5turbo 1500series automatic transmission quad cab with new 265/75/16 michelins all seasons from my uncle who is in too bad of shape to get in and out of her anymore. I am a complete newby to deisel engines, and a novice with gas engines but am eager and willing to learn. I have 2 young children and my wife is not working, so I need minimal dealership/mechanics labor. I know that my uncle serviced this truck regularally and I have all the service records for the past 2 years.
My uncle told me that the truck in the past got 18.5mpg and recently it gotten worse. I have filled it up twice now and I am on average 11.2mpg(11, 11.4) mix of city/hwy. The truck does smoke pretty bad when shifting, but seems to perform pretty good(I am very light on the pedal)but she does seem to have a VERY light studder when driving with my foot steady on the pedal(feels like I need to give more fuel) . The only thing that has coded is an air intake leak, which I am not completly sure is fixed as of yet. One last thing to add is my uncle had the oil changed at jiffy lube, and if I have time today I am changeing the oil to Rotella T 15-40, and the air filter is clean and new.
So to my question: Where could a guy start on changeing things to improve milage. Fuel filter and an oil change is top priority, but is there anything else that comes to your minds. ANY help would be very greatly appreciated.
P.S I live in Ontario Canada, and I do understand a little about winter fuel.

[trbankii]

Simple things would be the fuel filter and air filter - then diagnostics from there.

[convert2diesel]

Diesels and Canada...isn't it grand. Agree with the above plus also check where you are buying your fuel. If it is a low volume station, its very possible you are still buying mid January fuel. That means it can be as high as 50% kerosine. This would account for the mileage.

You didn't mention if this was a 4X4 or 2WD nor if your mileage was in US gallons or Imperial. Big difference.

Would also suggest, before you dig into it in earnest, that you give the truck a double dose of Stanadyne Fuel additive (preferred) or you can get Power Service at your local Canadian Tire Store. I do know the specs for ULSD is supposed to include a lubricant but the stuff up here, especially in the winter, is dryer than pop corn flatulations. Adding the fuel treatment makes a big difference especially in the older engines.

Hope this helps

Bill

[JohnC]

And, make sure the fuel lift pump is working properly.

[chrisangelski]

thanks for the replies gentlemen. My truck is a 4x4 and it gets 11.2mp/us gallon. I changed the oil today and took her for a ride. I drove her a little harder this time and she smokes alot! On another note, when I give her more gas and rev her, she pings a little sounding like the pistons, definetly getting too much fuel. I think its time to take her to a friend for a diagnosis. The truck runs good, sounds great at idle, but smokes when i rev her. My friend is gone on a trip this week, so I will post any updates after that. Any more suggestions is still appreciated.

[chrisangelski]

Update:
Got the dtc codes and there are 2 of them: P0101(Mass air flow sensor) P0400(EGR flow valve). Do you believe these codes would give me a 50% decrease in milage and make excessive black smoke from the exhaust? Does anyone know if the Mass Air Flow sensor the same from a 6.5L to a 4.3L? A new refurb is $350.

[JohnC]

Fix the EGR valve first and the mass air flow may fix itself.

[DaveBr]

What color is the smoke? White or black?

White is unburnt fuel. Could be injectors are peeing instead of spraying.

Check to see if your turbo is making boost.

Change fuel filter & check lift pump as already suggested.

Check cat to see if it is plugged.

[Artworks]

check your turbo and make shure that waste gate is moving free. Also check solenoids & vacumn at these solenoids as they control waste gate & egr. My truck gets from frome a low of 13 to 18mpg in on winter fuel depending on idleing and if I have to use 4X4.

[chrisangelski]

I had oil on my mass air flow sensor, either oil is escaping from valve covers through the baffles in the ---- (not sure of the name of it) or my turbo is leaking. I cleaned all the oil out and I will drive it today and see if any more oil appears. I noticed that most of my constant black smoke is when I'm driving steady above 80km/hr. I will definetly check into the wastegate actuater, and inspect for any vacuum leaks.I am still only getting 12 mpusgallon, seems like a loss of power and black smoke. Any more suggestions is GREATLY appreciated!

[bobt]

What about a bad vacuum pump? My son's '98 had power problems and lots of black smoke and his vacuum pump was bad. Replacement fixed the problem.
Bob

[6.5TDTahoe]

I highly recommend The 6.2/6.5"Troubleshooting & repair guide" from the DieselPage web site. May be the only manual you need. Another DP publication,"Removal & Replacement guide" will be very good to speed any repairs needed! Check them out there on the web site. Some of the best money spent IMO.

[DaveBr]

Plug a vacuum gauge into the pump and tell us how much vacuum you have.