6.5L Poor Gas Mileage

[macman]

I have had a gas mileage issue ever since I bought my 94 pick up. When I don't haul any thing around I get around 12.5 mpg or 21L/100km. The vehicle has 300,000 km on it and it does not smoke nor does it have an issue starting up. It has been in the shop a number of times and this is what has been done.

Injectors, glow plugs, PMD module, Eprom, ugraded the cross coolant manifold, new temp sensors and have had a number of scans.

The computer produces no codes at all. The mechanics feel that their is no issue with a worn out block nor is their one with the Injector pump. The feul pump timming does need to be recalibrated but they say even though they could do that that it would not affect the mileage I am experiencing.

Its hard to describe the situation although I have not had a compression test done, Nor have I had a new injector pump installed, nor a pump calibration.

Any advice or avenues to go down.

[Bornready6.5]

Where is your timing at right now?


Also, have you looked into other areas such as transmission lockup, condition, etc.?

Do you have a brake caliper hanging or rear brakes mis adjusted?

Exhaust restrictions? Wastegate, turbine.

And the obvious....tire size, tire pressure, tool boxes or general wieght.

Course, w/ 410's.....it may not get much better.

[moondoggie]

Good Day!

You might want to look at my post in What's your fuel mileage with a load? (Click in colored text) Look at the pre-Gear Vendors numbers; this is for my 95 pickup, which is otherwise identical to yours. IMHO 12.5 mpg with this truck means something is MASSIVELY wrong. I'd make real sure you're doing the math right. I'd get a compression check too, although I think you'd have been experiencing real bad hard-starting issues long before things got bad enough for mpg to drop this much.

At that odo reading, maybe your timing chain is worn real bad. How crisp does it sound? Does it rattle some when it's idling warm, or does it sound almost like a gasser? I think if the timing was really retarded due to timing chain wear, it'd be pretty mild sounding - advancing timing seems to crisp 'em up some.

Blessings!

[Warren96]

It sounds like you have a very good mechanic.If there are no codes being set.I would have to vote on those 4.10s being the biggest contributor to lower mileage, with a worn timing chain running a close second.Do you tow anything with those 4.10s?

[moondoggie]

Good Day!

"I would have to vote on those 4.10s being the biggest contributor to lower mileage..." I mean no disrespect, but I disagree. Lower, certainly, but not THIS much lower. My 95 pickup, in the above link, has 4.10 gears - look at my mpg B4 adding the Gear Vendors for a pretty direct comparision to macman's truck. B4 adding the Gear Vendors, I was getting ~ 18 mpg averaged over a whole year, with the Gear Vendors I get ~ 20 mpg. Before I installed the Gear Vendors, I had tires that were 8% oversize, so my effective ratio was 3.80; about the same time I installed the Gear Vendors, I switched to 4% oversize tires, giving an effective ratio of 3.08. That change increased my mpg ~ 2 mpg.

Is your truck DRW (dual rear wheels)? I don't know if they even put DRW on 3/4 ton trucks so the question may not apply, but I know the DRW guys have always had a hard time with mpg.

Blessings!

(signature in previous post)

[Warren96]

I apoligize if I stepped on anyones toes, but macmans request was for an avenue to go down.I enjoy reading your posts on this topic because they are very informative.Just my 2 cents.

[moondoggie]

Good Day!

Nothing to apologize for. We just have a different take on macman's problem. We all have to sort what sometimes is conflicting information from the really good DP folks. You've done what we all try to do here - help each other keep our stuff running.

I had hoped some of our more well-informed folks would chime in. I really know pretty close to nothing about these trucks - most of what I write is simply parroting what I've read on the Page over the years.

Blessings!

(signature in previous post)

[DmaxMaverick]

How many km's at the time you bought it? Do you have a service record?

If the injectors are original, a new/rebuilt set will have a profound effect on performance and mileage. The timing chain will contribute to mileage loss to some degree, but usually not much. Remember, the IP will track the valve timing, and only the valve/IP will offset from the piston timing.

What is your normal operating temp, and which thermostat(s) are installed? If too cool, your mileage will suffer, considerably. 195

[DennisG01]

Just my 2 cents - I had mileage issues and replaced my coolant temp sender and immediately got almost 20% better mileage.

[Mark Rinker]

Dennis - where is this sender located? If memory serves me, there are two - one for the ECM and one for the gauge, correct?

[DennisG01]

Yes, you are correct. The one I replaced is the one in the themostat crossover.

[offrdk5]

Just to be a pain:

I get terrible GAS mileage with my engines...mine seem to run great on Diesel!!

[macman]

Sorry I missed a few points on what had been done so far.

-Two coolant sensors have been replace, one for the cluster module the other is for the computer I think.
-Brake calipers and rear drum brakes are free.
-Transmission locks up when it should.
-The truck currently runs with no load but that doesn't seem to change the diesel consumption.
-The Mill rate I can't remeber what the shop said it was but they felt it was ok.
-The engine does run at arount 185f.

The thing I found out with the 94's is that that year they made two styles of injector pumps, one heavey duty the other light duty. Apparently they operate the same but that also means the EPROM has to match. Witch I am running a check to see if they match up.

What is the optimal/minimum feul pump pressure suppose to be?. I herd its at 4 psi. I think mine is at 2.5 but again I was told its ok.

I think at this point I will do a compression test. But what are the pressures I should be getting?

And yes as bad as I am with math I am geeting 12.5 mpg or 21liters per 100km.

Help!!!!!!!

[DennisG01]

Just another thought: How long have you had this truck? The reason I ask is that if you had bought it recently (and you're in a colder climate) your experience would be limited to winter diesel, which will drop your mileage.