Engine/Transmission (1994 - 1998) Low HP & Fuel Mileage -- Any Ideas?

[Mike129]

Hi, all.



I have had my '98 for a bit over a year. I love it. Mostly. I have always thought it was down on power & MPG but could never prove it. I just did the emissions test and have the following results (numbers at the rear wheels, of course):



Speed Power Torque Opacity %

----- ----- ----- --------

60. 2 ... ... 140..... 1304... ..... 15

50. 4 ... ... 149..... 1658... ... ... . 5

40. 1... ... . 138..... 1934... ... ... . 3



For fuel mileage I get <12 mpg city and usually <14 mpg hwy.



Both the HP and mpg numbers seem low to me as does the opacity at 40 & 50 mph, but I don't really have much to compare with.



I live in Colorado Springs at ~6000 ft. , and I don't understand the impact that has on HP with a turbo. The vehicle is a '98 w/70K miles, 12-valve, 4x4, auto with a 3. 55 axle ratio.



What I have already done:

- changed the overflow valve

- had the waste gate actuator replaced

- reset the injector pump timing

- replaced all of the filters (including fuel)

- cleaned the fuel pre-heater screen

- replaced the transmission (it was slipping a bit)



Most of the above that cost any real $$ was covered by the extended warranty I bought with the truck (which is lucky b/c I never buy those things, but I had a feeling this time). I do not want to BOMB until the warranty runs out in 2 years.



Any ideas?



Thanks!

--Mike

 

[PUMPERDUDE]

It might be worth checking your fuel pressure going to the injector pump. Not often these lift pumps quit,but they do Sounds like you've got most everything else covered.

 

[Joseph Donnelly]

Does it idle a bit rough? If so, injectors or a plunger/barrel in the injection pump could be bad. Your mileage is low, but not unknown. . . others have suffered similarly if something is not right. Your altitude is also a factor in poorer mileage and higher egt.

 

[Howard Durand]

The mileage I get with my 94 seems rather dismal too. I don't have access to an emissions test but Joe mentioned rough idle.

Mine has always idled a little rough up to about 1400 rpm then smooths out.

I replaced the 160 injectors with 215's that I bought from Piers but the rough idle did not change.

How do you determine if one of the pump plunger/barrels is bad and can it be easily corrected?

 

[Mike129]

PUMPERDUDE: Thanks, I'll check the lift pump. Any chance it could also be the fuel pump?



Joesph: It idles just fine, so I think the injectors are okay.



Anyone know if the opacity numbers are low? They seem low to me, but I don't really know. If they are, that would lead support to it being some sort of fuel delivery issue, yes?



Thanks for the replies!

--Mike

 

[Joseph Donnelly]

The opacity numbers are in line with my expectations, maybe the star wheel has been loosened because the one number is high.

 

[bmoeller]

Have the valves ever been adjusted?



I checked mine shortly after buying my truck at 139k. They were up to . 015 th's out of adjustment, probably never been done before.



It has always idled a little rough, going to check the nozzles out next, but it did help smooth it about quite a bit but not all.



First thing I noticed right away was that when I got the truck, you couldn't hardly hear the turbo unlesss you laid into it, after, it was much louder. Didn't really seem low on power but it did seem to have a little more power after.

 

[PUMPERDUDE]

Hey Mike. By checking the fuel pressure going to the injector pump ,you'll know if your lift pump(fuel pump,same thing) is putting out. It can also tell you if you have a plugged filter or bad overflow valve. Good luck with it.

 

[Mike129]

Thanks, guys.



Yes, the valves have been adjusted and all of the filters replaced . . and the o-flo valve. I'll check the pump pressure.



--Mike

 

[wcjp]

Lose the cat