Help!! C15 twin turbo MPG...

I agree with getting the over head done. It's time. Checking for leaks in the air to air is also important, these engines will not respond without good boost. I agree with Jas, do not make modifcations until you know what is causing your current problem or you will mask the original problem. As some of you know from watching my problem, loss of oil pressure in the intake valve actuator (IVA) will cause a drop in boost and mileage. Have an IVA cutout run when you have the oevrhead done.

 

I have a couple cd's worth of trim files I would share with you.I have also tried to play with trim files without much luck,but I am very interested in what you are saying.

 

You don’t need a lot of trim files but they all help….. Especially with the Series 4 ECM as you need 6 Different trim files which is not a problem as each injector is different and in most cases will need a different trim anyways. Once you test doz’s of them you will find that you can mark them and note the % of lift or reduction so when you have an injector that is down simply pick the one that will give you the % lift you need and then test it. At first you seem to be trying trim after trim but once you get a handle on it you can usually trim within thee codes.

 

But do you need the injectors in your test bench to be able to trim them?The reason I couldn't change trim files was because of the confirmation codes.

 

The best way to trim them is on the test bench.... but once you know the trims you can tell by which trim is used as to the injectors actual flow as its used to lift it or drop the flow so after a while you can tell. Doesn't happen overnight I can assure you....

 

Update on my troublesome 625, the truck came in for a service on sunday, with the muffler mod done (haven't had time for the primary filters stuff yet) fuel economy average between services is now 1.72km/litre, thats a jump of 0.11km/litre, ie an extra 110 meters travelled for every litre of fuel burnt... almost cant believe it!!

 

Hey Jas...Is that actual tank mileage or ecm trip mileage? I ask this because when you change fuel numbers, you need to recalibrate fuel correction factor with an average tank mileage to make the trip in the ecm correct. Also, what speed is that 625 average, 4.11 with 24.5 or 22.5 rubber? Whats his rpm at cruise speed?

 

he will be on 22.5 rubber. 24.5 i have never seen used out here.

 

I haven't changed the fuel correction, At this point I have no reason to thinks it very far out, Am going to check this though, getting acurate records from a driver can be difficult due to the crap we have to go through with axle weights in Aus.( cant always fill up full everytime, have to top off the tanks after going though a weigh bridge, etc. due the truck being over weight on the front axle with full tanks....#### T908, but they do look cool though! )
Whoops, read my notes wrong, it actually has 3.9 diffs not 4.11s, it has 11R22.5 tyres. actually think its geared to high, it runs what we call the coast road between Sydney and Brisbane which is up hill in both directions so to speak.
Average load factor before mufflers was 62%, now is 58%, not sure about the speed.

 

Any time you change fuel numbers, fuel trip mileage can be out an easy 10%. The engine is making more power due to increased fuel flow, the ecm does know what is actual fuel flow. The ecm thinks it it flowing at proper spec. My race ecm thinks its getting 25 miles per gallon.