Air In Fuel Effects?

[LorenS]

I have read the Caterpillar, University of (Indiana?) and Air Dog, etc. documents about entrained air in diesel fuel affecting power and retarding injection events.
Does anyone know if that significantly affects MPG and EGT in our trucks, specifically?  It sure seems like my EGT is higher than most (700-800F), my MPG is around 17.5-18 (hand calc) even at 65 MPH in average weather/wind conditions running empty.  When I give the fuel a super dose of PDS gray stuff to increase cetane in an effort to advance the ignition, everything improves - but PDS gray isn't free, even if it isn't expensive.  I ran Rotella T6 almost 10k miles and had an oil analysis done to check for fuel dilution, coolant, etc.  It came back with a good bill of health, including TBN.

Before I found this site I had purchased a FASS DRP pump and relocation kit which I have not yet installed, so am still running Carter on the block.  I have clean fuel filter, pressure usually in the 8-12 PSI range measured at the VP44 (Vulcan big line from filter to IP), but does drop to around 6 PSI on long grades when I baby it to stay in overdrive (automatic) - with EGT climbing to 1100F .  Should I really be looking at putting in an expensive Air Dog, and sell the FASS?  The fuel lines from the tank to pump are stock, truck has 300k miles.  Should I upsize those and change all gaskets, etc., on the suction side ensure I'm not sucking in air?  I do not know the health of the in-tank screen or if it's still there.  Symptoms are the same regardless of fuel tank level.

Any advice appreciated, even to forget about it because it's normal.

[wil440]

I have the same fuel lift pump or transfer pump whichever you want to call it, I fitted a Caterpillar fuel filter head and filter off of a C9 as PO just didn't use one, luckily It didn't do too many miles like this, I then fitted a mechanical fuel pressure gauge and saw maybe 5psi pulling hard in lockup 3rd or OD and to be fair I had noticed a hiccup sometimes when pulling so I took another look at the lines and PO had used a pre pump filter similar to a cheapo gas filter that fitted the stock lines, it was tiny, I fitted a Caterpillar prefilter, same fitment idea but bigger, I did have to use a larger line from the stock steel line as I just couldn't get the original rubber one over the cat prefilter, my FP now doesn't drop below 15psi and at idle is 20psi and I still have to relocate FP and do bigger lines and DS

I would say your FP is too low and fit the relocation kit and bigger lines sooner rather than later, I would say that anything that retards injection timing is going to increase EGT's as it then doesn't fully burn in the cylinder but carries on in the exhaust manifold

 

I would sort the fuel pressure first then see whats going on

[LorenS]

I have also purchased a similar spin-on prefilter that uses Donaldson filter to protect the FASS I bought, much preferring a big spin-on to the tiny in-line filter they supplied (and said needed to be changed every 5k miles!)  Maybe someday before I break down on the side of the road my wife and kids will "let" me complete this work.

When you say you have the same pump, are you on the stock Carter, or did you mean the FASS?  If your Carter is putting out 20 PSI, that's amazing to me!

[wil440]

mines an inline filter but much bigger than the supplied small thing.

I'd say complete the fuel system work or you WILL be stranded and out of pocket for a good chunk, just take a read on this forum for "VP's died"  then if the rest isn't right take a look at "ECU died", "PCM died" there is the most posts or questions on this whole gen2 forum....... and yes I may be a tad cautious as I'm well over 3k miles from a good source of parts

You say you get 6psi babying it to stay in od, check pressure nailed pulling a grade in od locked and I'll say it's going to be nothing

 

I really baby mine at 15 to 20

 

my pump is a drp fass, if I change it it will be an   assasin for sure

Edited October 24, 2019 by wil440

[LorenS]

If I go WOT in OD, it'll downshift about every time. Engine RPM comes up and fuel pressure goes up. I've never even seen it drop to 5 PSI.  I'm hoping next Thursday or Friday I can take a day to address the matter.

[Evan]

Only ever ran a factor filter but do run a fuel system with 150 pump and all big line to injection pump. It's done well for 12is  years  now and all on the same injection pump. I run 20psi at idle and rarely ever drop below 18 maybe 16 loaded standing on it pulling a grade loaded. Loaded on the freeway running 80 it's still about 18 could be towing 8k or 16k doesnt matter on thr flats its 18psi

 

Yes I run 80 loaded and 70 empty;) no sence in running for mpg numbers when towing, towing I like the revs 1800-2000 but keep it under 2200. Unless I'm pulling grades then I'll see 2200 in 3rd to try to manage temps.

I would not run a pump at only 5psi ever it's at zero or well below when pulling and injection pumps pulling 90% of the fuel doing all the work