2nd Gen Non-Engine/Transmission '97 3500 Extremely Poor Mileage

[Max Wedge]

Thanks for all the helpful input from you guys who posted with positive advise. I will not even respond to the name calling from

willyslover



GPS showed mph to be off about 4 mph @ 65 mph--this was factored in when doing the mileage math. If I would have posted every variable in the original question it would have been so long nobody would have read it.



Maybe his overflow valve is shot so the fuel pressure is too low to make any power



Is this located on top of the fuel tank?



One more thing, seems the truck won't RPM more than 2500 no matter what--is that normal for a 12 valve?



Thanks again guys, much appreciated. Its nice to know that MOST guys will still answer a question without criticism.



Max

 

[ToolManTimTaylor]

Originally posted by Joe G.

Tim,



I did not post that as a flame at all.

It wasn't you It was the reference to a horses Darier.

gist of my post I was in agreence as our posts matched



I-6DZL, You are there However Whilst towing at 55-65 mph that motor is a chuggin along with that combo to begin with ... however I suspect underlying issues that are hurting his performance and quite possibly may be an easy fix I. E Clogged cat.

 

[Joe G.]

Max,



The overflow valve is on the side of the injection pump. It controls fuel pressure available to the injection pump.



The point I was trying to make with my list of what may be wrong is that some trouble shooting is going to be necessary to find the problem.

 

[Cooker]

I think I would like to disagree about this particular truck being the worst possible combo for mileage. I think if he had 4. 10's his MPG's would be a little worse but not much. 65-70 with a 31" tire and 3. 54 gears is about 1900 RPM's as already mentioned. I think this is about perfect. I don't think 7,000 is in excess of what this setup should tow reasonably.



As already noted, a #5 in this truck with no gauges and towing is asking for trouble.



Here are a few things that come to mind, some of which have been mentioned:

Is the TCC slipping while towing?

Fuel pressure may be low?

Timing may be off?

Boost leak?

He needs to open up the exhaust.



What is his empty MPG's?

 

[Joe G.]

Cooker,



I agree completely. I think I said "almost" the worst. A lot of things could cause this problem.



It's time to get the test gauges and tools out and start trying to find what is wrong. AFC could be sticking or low boost isn't moving it. Dirty pre-filter maybe.



Just a note to the 24 valvers. The 12 valve engine does better at 1900 than 2400 for MPG for towing. Some 12 valve engines will start to defuel at 2500. Mine would not defuel until 2800 when it was stock.

 

[Cooker]

Originally posted by Joe G.

Cooker,

I agree completely. I think I said "almost" the worst.

Sorry Joe. The first time I quick read though this thread I got the impression that it was reading to say the 4. 10 gears would have been better or that this setup was not optimal for towing 7,000 lbs. Maybe I was reading too fast

 

[I-6DZL]

Any updates on performance or MPG?

For some reason me still thinks the cat got too fat over winter and clogged up the exhaust..... Plz keep us posted



I-6DZL

 

[moparguy]

Looks like I'm late to the dance, but, I'm fairly sure a 97 does not have a cat, the resonator would look catlike, but likely isn't the problem.



Have your bud hold the pedel to the floor while setting still, if it white smokes and runs rough at high rpm, the timing is off.



On my truck, speed is the main factor that affects mpg.



Good luck, RJR

 

[SEmerson]

With a #5 and no gauges maybe he is in need of pistons

 

[Joe G.]

I would think that if it needs pistons he would have reported that it runs ratty. As far as I can tell from the posts it runs ok, just drinks fuel and power is low.

 

[Max Wedge]

Hey guys--He took Cat & muffler off--easier that way 3" to 3", now it makes 2800 rpm VS 2500 rpm before. We will be inspecting the prefilter and going for another test pull on I-77 this weekend. I will keep you all up-to-date.



Just to Reiterate, he is not having a problem with power/performance, as much as he is with the thing drinking fuel like a drunk monkey. There is no white smoke under full hard load, heck the thing runs as good as my '00 w/the EZ box.



Many Thanks again to those who are honestly have something to contribute.





Max

 

[SteveMiller]

Here's my . 02 if it will help.



I have a 97 and

1. they do have a cat (at least when they left the factory) No resonator that didn't happen until the 24v.



2. check the fuel shut off solenoid and boot. Mine was in bad shape and the solenoid was opening but not all the way as the link was broke and the internal spring was keeping it pushed out too far. This is a cylinder looking thing behind the fuel pump with a linkage going down.



3. I was also having problems with the overflow valve on the pump. It was weak and I had low fuel pressure because of that.



Just some things to check.

 

[Joe Mc]

Not sure about the 12 valvers but, if they have an intake air temp sensor it could be dirty. Cleaned mine some time back and it seemed to help. My $0. 02.

 

[Max Wedge]

My Mistake on the plate size!! It's a#8 , not a #5

Well, here is an update:



Took Cat & Muffler off, towed back to National Trail Raceway Sunday--torque converter slipping badly now So that could part of it, but still can't get full throttle, as after 3/4 throttle engine seems to nose over without making any more power and RPM's go down??



So now we will tearing into the transmission.



Max

 

[Extreme1]

Put in a good torque converter, that was one of the biggest improvements I made on my truck.



The 3. 54 ratio with an automatic and a weak running engine is not a nice truck to tow a heavy parachute with. Yes, the trailer shape has a huge effect over 50 mph.



With that stock (or poor running) combo, the engine can't even rev high enough to get the truck up to interstate speed on steep on ramps. It can't rev high enough to upshift.



The exhaust helped, that's good. For the trans repair/upgrade, see the vendors here. I recommend Goerend Brothers but there are others that he may feel more comfortable with. Call the ones he's considering and ask questions. DO put a different torque converter in it. DON"T expect to get something good for real cheap (ebay junk).



After the trans is fixed, if it still isn't running strong enough, it's time for a few guages to be able to monitor what's going on. As mentioned above, it could be a boost leak, weak overflow valve, out of adjustment throttle linkage (not opening the lever all the way), a sticking shut down solenoid or (maybe, that trailer is a huge air restriction at 70 mph) weak compression.



With a trailer that large and at that speed, he's probably going to get 10-12 mpg tops. These square edged trailers pull much harder than 5th wheels.



I hope that this helps AND didn't offend anyone.

 

[Joe G.]

I don't think anything associated with the transmission is going to cause the engine to fall on it's face at full throttle. I think there is a real need to check fuel pressure. It sounds like it is starving at full throttle.

 

[Max Wedge]

Extreme1--Excellent Post, thanks for explantions. 10-12 mpg is a realistic number that was expected when purchased. Man I am lost with these 12 valver's



On my truck just Call Power Edge, throw $$$$ at it, plug in another box, and walla'--its fixed



Max