It seems the best I can get is about 15 MPG, much less if I'm towing or hauling.

My truck is essentially stock, with no pump mods.

There is a kink in my exhaust at the point at which it goes up and over the rear axle, but it is not severe. I'm sure this is at least part of the problem, but I wonder how much....??

Any other things that folks out there might be able to think of that might be causing this problem?

From what I've read, it sounds like a bigger exhaust and new injectors are two mods that might improve fuel mileage as well as deliver modest power increases. Is this correct? Anything else?

Thanks,
CR

 

I'd go this way:
1. Unkink the exhaust
2. Change the turbo hot side from 18cm2 to 16cm2
3. Tweak the pump
4. Bump the pump timing up 1/8"
5. Shotgun the intake air box

After that, things get more expensive. You might be surprised at what a stiff torque converter can do to put the power to the road (in conjunction with a turned-up valve body in the xmission).

DBF

 

I get just under 17 mpg mixed city/hwy with my W250, but I've got 33x12.50 tires that don't help things. I can get around 19-20 if I stick to the highway and stay off the loud pedal. Your right foot can make a huge difference!

 

1. what are your numbers like?
2. how are your EGT's?
3. what is your max boost?
4. how many miles on the truck?

 

The kinked exhaust might be a significant factor, but poor mileage is often associated with timing. I would make sure the exhaust is clear, check your fuel pressure to the injector pump (fuel starvation can cause retarded timing) to make sure your lift pump and filter are okay, and then try advancing the timing using the "I moved her about an 1/8th inch at the marks with a ratchet strap" approach.

That all said, are you sure your tranny is not slipping, etc.?

You should probably see about 3 lbs of boost and pre-turbo egt's around 8-900 running on the flat at seventy in your truck I would guess. My truck with a manual and 12cm housing runs around 5-6 psi and 6-700 degrees at 70+. Before the dump insert I was getting between 19 and 21 on the highway at 70, got up to 23 if I drove 55-60 on two-lane long distance.

 

22.9 best tank average so far timing advance gave me almost 2 mpg

 

My EGT's float between 700 and 1000, usually, sometimes more if I'm towing up a hill or whatever.

Max boost is about 15, 16 sometimes.

240,000 miles.

I guess I need to unkink the exhaust one of these days. What I'd really like to do is go up to 4" all around, but that sounds expensive. Has anyone ever done it themselves with individual weld-together segments?

And a general question on the 4" exhaust upgrade: Where do you transition from the stock size to the bigger stuff?

How does one advance the pump timing 1/8"? From what I can gather from reading various posts, you loosen the 2(?) bolts securing the pump, put a ratchet strap somewhere safe on the pump, with the other end somewhere over on the passenger side of the engine or the bodywork, and tighten the strap until the index mark on the pump moves approximately 1/8" from the corresponding mark on the gear case, then re-tighten everything. (so you're turning the pump clockwise when viewed from the rear of the pump, or from the driver's seat?) Did I get it right? Can I do this before I perform any other pump mods?

My airbox already had a few 1/2" holes drilled into it when I got the truck... I suppose that's what you mean by "shotgunning" the airbox, DBF ..??

 

on the exhaust pipe they all come with the kink. I took the kink out of mine and did not notice any difference in preformance or mpg.

 

Well if I understand your signature right it looks like your hauling around a lot of weight all the time. Is that correct? At least a lot more than a completely stock truck. That will make a huge difference. Also someone suggested getting a 16cm exhaust housing, however a 93 has a 18cm and you really won't see much of a difference going that route, however if your not planning on getting POD injectors than I would suggest getting a 12cm wastegated housing. I probably picked up 1.5 to 2mpg in town with this setup. Also someone suggested the TC and trans I would suggest looking into this also. In stock form especially high mileage you can loose a lot a lot of power through these slush boxes!!

 

Robox,

I have pretty much the same setup as you, less the crane, and I get around 14mpg pretty consistently.

I'm actually quite happy with 14mpg, considering what I'd be getting with a gasser.

chaikwa.

 

Your mileage is a factor here too.....
Look after the "air in/air out" like mentioned. Next I'd run a good healthy double dose of injector cleaner thru it. Double up on a full tank of fuel then repeat....after that change over to a cetane improver
At this point your pump and injectors are getting tired...it's normal to see mileage like you have...over time the injectors will start to stick a bit, they'll also start to open early and so forth as they age....kinda like people...

Timing is not hard to do, just do some reading and poking around on the site, look for pictures and you'll have 'er done in no time.
There are 3 nuts on the front of the pump (flange to gear housing) and one small bolt down below/back side of the pump. This thing is at the bottom, back from the pump itself. It fits into a bracket and at first glance appears to be unconnected but it is...you need to twist your head down and look under all the throttle bracketry just back from were all the lines come out of the pump, you'll see it. The bolt actually faces toward the firewall and it's a 10mm.

bob....

 

take a look in my pics i did the ratchet strap thing and what bushy said is the right number of bolts to do timing

 

Yeah, AND???

Did your mileage change? More power?

Tell us! If it worked, I'LL do it!

chaikwa.

 

I have 1/8" timing bump, and yes, more power and better MPG.

Like the NIKE commercial.... just do it.

 

Now my truck was advanced already by the PO. I retarded it back close to stock last weekend and picked up noticable low end power and 2lbs boost. I don't know if mine was advanced to far or what. It was extremely loud under the hood before I set it back. It is still more agressive sounding at idle than my dads 90 though. Maybe my pump was already advanced more from the factory and the 1/8" was to much?

Cant do any comparos on milleage from before/after since I am filling it out of the fuel barrel at home over the winter. (buy up a stockpile at the end of summer to avoid high winter prices)