Cummins turns dieselaholic

[R.E. Miller]

Well, I put a post here a while ago about a new injection pump, but I really need to know what to check to determine what is shot. My milage has just taken a dive without more smoke, and no leaks... . no the parking brake is not on either

My truck has 165,000 miles, and everything is original so I guess anything is possiable.



Could this be the lift pump? If so yippy!



Should I yank the injectors and have them pop tested?



Could there be some restriction in my return line that could cause this? Yikes.



Or injection pump



The MPG when from highway unloaded 23, and loaded 25-50% 14-17MPG to barely 11-16 all the time



Thanks,

Looks like I need to fax Santa soon.

 

[Lil' Dog]

I'd hedge a guess at a combo of the injectors and the timing being a little retarded. But I am far from an expert. Just the degradation of the mileage seems to point to the injector IMHO. With the timing being a little behind probably wasn't a problem until the injectors start to wear.



Another thought was you haven't really layed out the time line of the mileage drop. 1 week, a couple of years??... ya know. .



J-eh

 

[R.E. Miller]

Lil' Dog,

The fuel mileage has dropped in the last five months, and I have changed the filters regularly.



The retarded timing is because of the mileage and wear to the pump and injectors? Just a question eventhough it makes sense to me, I had to ask.

Thanks,

Russell





Oh yeah, your sig says "tweaked" pump. Did you follow the instructions on Dave Fritz's page? I have been reading the pump page and have finaly come to terms with what is going on with the adjustments. Did you turn the AFC diaphram? Or did you just do the normal adjust the smoke screw and turn the full power adjustment up?

Thanks for the info

 

[Lil' Dog]

Firstly, that is a pretty short time frame for mileage drop, that is perplexing. I haven't checked this trucks timing, but after 180,000 Km in my 89, the timing was out by 5° from wear of all the components. As the injectors wear and the gears wear, the pump wears, the pressure to crack the injector is produced later in "real time" and the timing delays. But that was over 5 years, not 5 months. I would still have those things checked.



Secondly, my pump tweeks are a trade secret!!!LOL.....

Naaa. Basically since my 89 was BOMBed, I had to tweek this one too. I have turned the fuel pressure (power) screw up 2 full turns (removed screw and popped off the collar since it was already bottomed out). Removed the fuel delivery pin and measured full taper advance and re-installed for full advance. Then backed the aneroid (smoke) screw out about 1/2 turn to reduce the off-line smoke. Turned the star wheel in about 1/4 turn, and just recently, like yesterday at noon, shaved about . 020" off of the nylon washer stop on the fuel delivery pin. There, Now its tweeked. It went from a leiserly rise to 15 psi at 2500Rpm to a quicker rise to 15 psi at 1500 Rpm and up to 20 - 21 psi at 2500 Rpm. There is alot more smoke that I would like but, hey, about another $1000 of injectors and a housing would cure that .



Whew... . I hope that helps.



J-eh

 

[R.E. Miller]

He he he

That was what I thought, top secret pump tinkering I need gauges first, and a fuel system check-up. By the way, how many miles do you get out of a tank, I got 325-350+ miles on a tank, now I only see 305

Thanks for the info!

Russell

 

[Lil' Dog]

Yipe..

Well converting over from Klicks to miles. I usually get around 750 to 825KM between fills. Thats from brimmed to the 1/8 mark as the LOW FUEL light really bothers me... LOL... . Typically 80 to 90 litres or 21 to 23 US gallons.



So thats around 470-515 miles, depending on how much idling, city traffic and the infamaous heavy right foot...



J-eh

 

[R.E. Miller]

Great

Good to hear I think, yipe is right I did a search here to see what others have gone through, and saw a thing that said some one here had the pin that rubs up against the excentric thing in the AFC housing stick and that was causing a loss in fuel mileage, guess it's time to dissect this thing...

 

[Power Wagon]

Re: Great

Originally posted by R. E. Miller

Good to hear I think, yipe is right I did a search here to see what others have gone through, and saw a thing that said some one here had the pin that rubs up against the excentric thing in the AFC housing stick and that was causing a loss in fuel mileage, guess it's time to dissect this thing...

Your AFC should have little effect on fuel economy. The ONLY thing it does is vary max fuel with boost. If you're not blasting a lotta smoke out when you bump the pedal, I'd look elsewhere.



What I would suggest, is that you have a combination of things. One, if you have an automatic, your torque convertor could be worse than death warmed over.



two: Set your valve clearances. Even small changes in those seems to have noticeable effects on milage, but no perceptible change in running.



three: Your pump could be tired. at 165K miles, it is possible that your injection pump's internal supply pump is weak, meaning the advance kicks in too late, and the economy suffers when running at highway speeds. Sometimes all you gotta do is have it tweaked back into spec and it runs like a champ, without spending a pile of dough. However, at that milage, you could need some linkage parts and perhaps even a throttle bushing or seal.



four: look for restriction in fuel flow in... this has the same effect as a weak injection pump.



five: is your fuel supplier doing something stupid to you? Try another brand for a tank or two.



If your truck does not smoke when cold, runs smooth, etc, I'd not be extremely concerned about injectors. Of course, it's a good excuse to put some in. I would at that milage. And since the performance ones cost no more than the stock... hey, who needs stock???