MPG question. My truck is '99 3500 4x4 extended cab, 148K miles, 4:10 gears, automatic (rebuilt about 10K miles ago), has BHAF, 4 inch all the way, no muffer, 4-inch down pipe, 3-piece exhaust manifold, no electronic power adders. Also has a soft tonnue bed cover. Well maintained vehicle.

It's my daily driver -- just to and from work about 28 miles round trip. Probably average at 30 -35 mph. I don't haul anything heavy and I take it easy on the gas. If I'm on the highway I drive between 60 -65 mph. I know I'm slow.

Having said all of the above, I'm getting 14 MPG hand calculated.

Is that about average for my rig? I'm just concern since I expected a little higher MPG since I have the BHAF and a straight exhaust and I'm easy on the gas pedal.

Please advice. Thank you.

 

we have one that was getting 15 when the VP went out . installed a blue chip spec.X pump now we get 17 . I just installed a 2000 engine in a guys 99 5sd with Gear venders ,before he burned up the 99 53 block he was only getting 14 .with the new engine and RV275 he now gets 19 mpg but that trucks a stick .you should be able to get a few more MPGs out of it try cleaning your intake air temp and MAP sensors

 

Sounds about right. I have 3:55 gears on my 99 and average 15+ combination city/hwy/hwy up steep mtns OD off. I want beter MPG thats fur-sure.

Mine is bone stock.

 

That sounds pretty low especially when you're only running 30-35mph. Is this start and stop traffic? Have you checked your codes? Could be a number of things but start with the codes and go from there.

As long as the rpms are kept below 2100, you should be getting good mileage.

 

Yes that's stop and go traffic.

Being a '99 truck, I can't do the key process to get the codes. Do I just hook up the scanner and get the codes even if the engine light is not on?

 

Its worth a try. Autozone will read them for free but they can only see some of the codes. In order to see all, you have to have one that reads dodge codes (can't think of them right now). Do you have gauges? You can diagnose a lot just by seeing what your engine is doing.

I've always been under the impression that a 4.10 got better in stop & go because it is easier to get the truck moving..

 

I have no extra gauges on my truck. I'll try to get it scanned for codes at Autozone. I'm hoping this isn't a sign of my VP44 or lift pump going bad? Is it?

 

My truck gets its best mileage at around 62 mph in 6th gear. 35 mph for me is 2000 rpm in 3rd or bogging it in 4th so I don't see that great of mileage at a lower speed.

Your mods aren't really going to affect mileage. A larger exhaust gives lower egt's, A bigger air cleaner just has more surface area to pull from and should last longer.

Mileage gains are found in properly aired tires, lower profile stance, less weight, aerodynamic effects, fueling adjustments, gearing/OD, etc.

14 around town isn't bad for a 3 ton 4x4 with 6 tires on the ground.
Poorer mileage can be a sign of a going south vp. But I think that's about right.

You also may be into the winter blend fuel.

Just my .02

 

I was getting approx 13.6 mpg with the type of driving your talking. Then I in stalled a Adrenaline and the milage jumped 3mpg. I think any timing box would have done the same. I was certainly surprised and happy with that increase.

I think low intake air temps cause the ecm to pull alot injection timing during the warm up of the engine. Good Mileage for the Cummins is hard to get for short trips.

 

x2. Plus, 4:10's may make it a little easier to get over 3 tons moving, but all that starting and stopping means getting over 3 tons moving again and again. Your mileage sounds fair to me, considering your conditions.

 

The sad part of all this is there is absolutely no excuse for this power plant/application to not achieve 25-30 mpg.

Don't get me wrong, I love the Cummins. It's the mpg that's crap.

imho, Taz

 

Do you really consider 1500 rpm 'bogging' at that low of speed? At that speed, I'm usually in 5th, or 4th if its my 5 spd.

 

Thank you all for all the response. I feel a little better knowing my mileage is not too out of wack. But again it should get better MPG's. I'll check some things out like some of you folks had suggested and hopefully I'll get some benefit out of it.

 

Not really bogging, just at the low end of where I was told the rpm's should be to not prematurely wear my clutch disc. Do you think its a high enough rpm for good clutch life?

 

You're not gonna wear a clutch out unless you are slipping it. When I pulled my 5 spd out of this truck for the 6 spd swap, the clutch looked great. 70k km on it, I routinely let it go down to an idle in any gear but OD.