Power fade

[SAronson]

I was out on the freeway this past weekend trying to keep up with traffic, and noticed I could'nt go much faster than 70mph and the boost was'nt comming up to it's normal 16lbs. At lower speeds it seems that the boost comes up to @ 16lbs. The power seems to be down, and I was wondering if it could be the lift pump. I'm fairly new to this rig, but I have already done the following:

fuel filter, fuel conditioner, air filter, oil & filter, adjusted the valves, *****AND the only fuel leak I had was at the top of the fuel tank... ... the top cover gasket was leaking so I tightened it.



Otherwise, the truck starts first crank, idles smooth, and has no other apparent problems. If it is the lift pump..... where can I get it at an affordable price?

 

[MFalkinham]

Hi,



You should get your signature set up so we can look at the details on your truck. In this case, knowing the mileage on the odometer and the gear ratio would be helpful.



My truck has 4. 10 gears, and still has good power up to 80mph. Of course, the engine rpm's are high at that speed, but that won't hurt the Cummins, just the fuel economy.



If you truck is high mileage, it might very well be the lift pump. Some have said that the VE pump and injectors also start getting tired around 150k-200k or so, depending on bombing level, fuel quality, and just plain luck in general.



- Mike

 

[dpuckett]

Ditto what he said, esp the signature. If you have 4. 10s and stock fuelling, 78mph may be your top end, then 70-72mph power fade is about right.



ALso, check to see you are getting full travel of your throttle shaft on the pump. Have someone floor the pedal (preferrably with the engine OFF), and see if the throttle ass'y bumps the high idle screw on the end of the travel. If there is some gap there, you may be cutting yourself short as far as RPM vs governor cutoff. If that is the case, you will need to adjust the pedal under the dash, either lift up on the pedal, or do it like I do with baling wire on the end of the cable, between the end of the cable (inner part) and the accelerator pedal rod. PM me if the mud is still too thick.



Daniel

 

[SAronson]

updated

OK, I updated my sig, but it is'nt showing up yet?????



Anyway, it's a '91 W250/ auto/ 3. 07's/ 33" tires/ Banks intercooler and exhaust/ 150K miles, and I've turned the fuel screw in 1 turn and the AFC is at the max setting.



During the episode of power fade on the freeway, it took a lot more than normal throttle to keep the boost up. This is why I suspect it was not getting fuel.



Any thoughts?

 

[MMiller]

The easiest to check is the fuel filter, if you think a fueling problem. Its possible to get bad diesel, and start to clog the filter. Will start and run fine, but not move enough fuel under load. With the conditioner, and driving it, you might have shook up some crap on the bottom of the tank and got it in the fuel filter.



Lift pump is a possibility, I replaced mine about 175,000 or so. Had bad fuel, then poor performance, no smoke. Changed the fuel filter and didn't get power back. I got mine from cummins, can't remember how much. I prefer cummins parts on the engine. After replaceing the lp then it ran right again. Cummins guy said if I got bad enough fuel it could have finished off the lp.



I think Daniel can tell you how to check fuel pressure. I cannot even tell you the spec.



Michael

 

[BushWakr - RIP]

You didn't mention whether you had any extra smoke or temp variations... .

Since you are describing you power as "going away" you might want to check the I. C. and all the boots/clamps.

If you start loosing boost you won't get full AFC travel and that means less fueling.



just a thought...



pb...

 

[phillips5]

Make sure you have complete throutle travel when things where the pump throtle travel gets less and less over time. That defueling before rated speed. Is that a 727 direct drive auto or a 518 overdrive auto. If it is overdrive and you run out of go power at 70 it must be more than throtle travel problem.