Hi everyone. As a newbie I have a question concerning my fuel mileage. I have a 99' 2500 4X2 5.9 24v basically stock. The only mods are a K&N in the factory box, 3" glasspack instead of factory muffler, and a Holley Blue FP pusher with the factory lp removed and it is mounted back by the tank on the frame rail. I did have an issue with the occasional dead petal when cold or sometimes around 60-65 but have performed the APPS voltage adjustment and that seems to have cleared that up. Anyway my question is shouldn't I get better than 11.81 mpg around town. I rarely have my foot in it and just can't figure what might be the issue. The truck produces no smoke that is discernable except for a little on cold start. Today I am going to clean the MAP and IAS sensors and check that the wastegate is operational properly. After that what would all of you smart folks tell me to try. We do not have alot of money and I have basically traded my Chevy Silverado 5.7 gas for this 189,000 mile Dodge diesel work truck (she has no frills other than A/C, is/was a fleet truck). Tranny supposedly rebuilt 10k ago. Also would anyone have a used chip they would sell me cheap. I cannot afford these $300.00+ tuners at this time to try to see if that helps. Thanks in advance, John in Jackson, MS

 

I was getting about 16 MPG before I did 2 things... First, I installed a BHAF air filter and second, I took the truck on a 700 mile round-trip to the coast. I got 19 MPG on the road down and 20 coming back. I think your truck needs a good long run on the highway. Mine runs much better now. Oh Yeh. I also use 12 OZ Power Service at every fill-up. You might go to a 4" exhaust system too.

 

Wow. OK I will try that. I did not get at the IAS/MAP/Wastegate thing I mentioned today. I do need to drive about 100 mile round trip in the morning so I will recheck it.

Did the 4" make that big a difference? I figured the removal of the stock strangulator (muffler) would be a big diff just by that.

Thanks for the reply..John

 

This truck should be knocking on the door of 20 mpg with a 2wd according to your info. It's easy to kill the mpg with just town driving . These truck go about 7000-7500 pounds and even just brisk acceleration from every stop light can kill the mpg. One good solid blast from a stop light to 70 mph will knock me off the 20 mpg list. Even more so with the Smarty.

You don't say anything about the codes. I would get the codes scanned and see what's going on. If you have already had "dead pedal" I'd guess the IP is getting weak. Most guys will agree that poor MPG is a symptom of a weak VP. Since you are new to the diesel world, you may not have noticed a lack of performance which also is a symptom. I surely would start saving for an IP on a '99. Mine lasted 165k and dropped dead without warning. A fact of life on second gens 24 valves. You already have the pump relocated and assuming you have 12-15psi idling and 9 or better at WOT it's good. It's what may have happened prior tothis that would be of concern. What prompted the fuel system changes???

Cleaning the MAP and IAS are a good idea. I assume you have a fuel press gage with the relocated LP. How's the psi?

The glass packed muffler sends a little concern. These trucks run just fine without a muffler at all. Any kind of muffler needs to be a diesel type and very low restriction. A car muffler might not do the job.

You should air up the tires to around 75 front and something comfortable like around 60-65 rear. If they aren't there already. And depending onthe tires. I can get 2 mpg better by adjusting tire pressure.

Some of the auto guys can help out with the trans. Sometimes misadjustment or converter problems can cause poor mpg.

Ckeck the brakes. Dragging brakes can kill mpg but you usually will at least smell them.

Intercooler boots can be leaking so boost will be low.

Just some things to check out.

start that IP savings account today. I throw about $4-5 a fill in my IP envelope just for such emergencies.

 

Thanks for the great info Bentwings. I will check into the tings mentioned and will start that IP trust fund for the VP44.

When I bought the truck it had sat (was started from time to time) for a year because of the pedal issue. The owner said it had started after the transmission had been replaced. He said take it to the dealer and have them flash the ECM and it will clear it up. I took him at his word. I still need to talk with him concerning what has been done to it and when.

When I started reading on this forum (before I joined) I learned about the VP44 and the LP's going bad frequently and consequently I replaced the fuel filter and when I hit the key it did not bleed (did it 5-6 times). OK bad lift pump. I decided that the Holley was the best economical replacement for the little Carter and thanks to the DTR I learned to relocate it to the tank area. I have all 3/8 line from the banjo's back and am going to replace the banjo's with better fittings soon. The truck ran better with the new pump, takes no time at all to bleed a new filter.

Apps adjust also prompted by the forum and the pedal thing.

I also did the "Hold down the odometer button and key on off on off on" thing and it ran better still.

The K&N was done in response to a very dirty FRAM I found in it and for the $20. difference in price it was worth it. A BHAF is in it's future, diesel mechanic at work warned of light oil and dirt getting passed it. To quote him "A K&N will flow small boulders".

Thank the guy upstairs I started out as a mechanic!