loss of MPGs after valve adjustment???

[LB72004]

I know this is not necessarily an EFI Live or tuning question but i thought that with your guys smarts on how these engines work you would be able to help me out.

ok, so here it is, a few months back i replaced my injectors (The infamous LB7s). while i was in there i decided to adjust the valve lash, based on some other forums recommendations as it would help quiet down the engine and make it smoother running. well it did, but i now it seems that i get worse mileage. (i know, internet mechanics:bash:)

the valve was already close to stock (.012~.013) and seemed fine but i was curious how much quieter the engine would run with them tightened up. well i adjusted them down to .010 as this was the max recommended and said to make the smoothest, quietest engine.

anyways, after installing the new injectors and making the valve adjustment the engine runs great. balance rates all below 1, spools great (maybe too well. will explain later). the only issue is that it seems that my MPGs took a dump. i used to get between 430 to 450 miles to a tank taking the same rout to & from work every day for almost every fill up for over a year. now for the last few month since the adjustment i have a hard time breaking 320 miles to a tank. that is a drop from about 16~17 MPGs down to about 12 MPGs. highway MPGs are also not much better

my theory is that the exhaust valve is now opening up earlier and letting the exhaust gases out sooner. this would lessen the amount of time the combustion pressure would be able to work on the piston. this seems to be backed up by the fact that i can now hear the turbo running, small amount of turbo whistle, all of the time ever so slightly when cruising around 60-65. i never was able to hear it before unless i pressed the accelerator down more, supplying it with more fuel to speed up. it also seems to spool faster then before and smoke a little bit more too. all while seeming to make slightly less HP on my butt dyno.

things i have done to try and remedy it:
-raise timing in the cruise area. probably went dangerously high on the test as i slowly worked my way up to about 9 degrees at 20 mm3 and 2200 rpm (about 500 pw at 115 Mpa). didn't seem to help much so returned it to the previously good values.
-raised and lowered fuel Mpa. got as high as cruising around at 150 Mpa. now running at 65 Mpa. thought that i might be able to get the fuel to finish burning by the time the valve has opened up.
-currently playing with pilot injection. running with the events closer together right now. not impressed yet but still too early to tell.

any ideas guys? do you think the valves are too tight? should i dig back into it and readjust the valves or just wait until the injectors go bad again. almost 100 miles less per a tank could add up to quite a large number $$$ by that time.:bawl:

my next step will be logging boost during steady cruise to see if it is higher then my logs before the change

anyways, i am open to suggestions to tuning ideas that may get me by until i can restore the valves to stock.

thanks for any help and sorry for the long read

Jason

PS: this may make a good discussion on valve lash and MPGs. why some engine get good mileage while other don't, etc.

[rcr1978]

This is interesting but I would suspect injectors and fuel quality before the .003" you tightened up valve lash. Did you do something else to the truck around the same time, tires, intake anything else?

Edit- just saw your sig any of that stuff on or removed before/after the injectors/valve lash?

Also thinking about the valve lash maybe its a tad to tight on the exhaust side, everyone uses feeler gauges differently. It could be possible the exhaust valves could be held slightly of there seat when at full temp causing lost exhaust energy. Not saying for sure but a thought, .001-.002 could be enough to loose compression and lost energy from combustion.

[LB72004]

thanks for the reply

the only thing i did was, while the last set of injectors where on there way out, i installed the second CP3 to help hold rail pressure until i could get new injectors. i haven't increased the PW any from before. do you think two CP3s require that much energy to turn?

in my reading it seams that the valve lash will increase as the engine warms up, but this is from the same source of my valve lash adjustment. if it was leaking past the exhaust valve would hot starts be hard as it would make it more difficult to build up the pressure in the cylinder or is this offset by the extra heat already in there???

most of the fuel i have gotten from the same place but several times i filled up at other stations. the fuel filter is a rancor double coalescing type with less then 5000 miles on it.

several others on the duramax forums seem to be running .011 just fine but few have tried .010. i wonder if i was to go the other way .013~.014 i could get 25 MPG on the highway:mrgreen:

[anarchydiesel]

I definitely would suspect the injectors before the valve adjustment in regards to your drop in mileage.

[LB72004]

But this is with new injectors. :bawl:

[THEFERMANATOR]

But this is with new injectors. :bawl:

New doesn't always meen good. Are tehse stock injectors or oversized? If your running 2 CP3's with stock injectors, I would think you would have alot of parasitic draw on teh engine that isn't needed. If it is oversized injectors now, were the old ones oversized as well. MANY variables here to consider, but I wouldn't think the valve lash would hurt it.

[LB72004]

Stock injectors before and after. I guess I could put the stock belt on and see if there is any change.

[LB72004]

Removed the 2nd CP3 and put the stock belt back on. Now I just need to run some fuel through it and see what kind of figures I get.

if this ends up being the cause I am going to look into attaching an ac compressor clutch or similar to the fuel pump and activate it with a boost switch or something. That way it won't be running all of the time. But turns on when I want it to.

[THEFERMANATOR]

If your running stock sticks, then a stock CP3 should be able to keep up with it just fine to most any sane amount of pulsewidth provided your injectors are in good shape and on the tight side(very low return rates).

[minytrker]

I installed new injectors on my LB7 dually and adjusted my valves earlier this year also. My valves were all really loose. I went from 18-20mpg to 15-16mpg now. I talked to several diesel shops and they said thats normal and the mileage should go up with 15-20,000 miles. It really sucks losing mileage BUT the truck runs so much smoother and quieter now.

[LB72004]

they said thats normal and the mileage should go up with 15-20,000 miles

so is this how long it takes for the valve lash to loosen up till its closer to stock? this could take me several years:bawl:

[LB72004]

quick question, does anyone know how much energy/HP it takes to run a CP3? i know it will be different at low pressure and higher pressure but i was just wandering if anyone had any idea

[LB72004]

i ended up having to fill up before the light came on but i was only at about 280 miles and about an 1/8th tank left. this would have gotten me roughly 300~320 miles. doesn't look good.:bawl: i was really hopping it was the 2nd CP3. whats next?

guess i should log boost and MAF G/S, compare them to an earlier log before the valve adjustment and see of there is any differences. if cruising boost is higher then MPG will suffer, Right?

[LB72004]

i logged boost and MAF G/s today. boost PSI was at 18.7 running at a steady 70 MPH. this is the same as a log that i did before the valve adjustment. the one thing that did stand out was the MAF Grams/s

before adjustment 111 to 113 running 70 MPH
after valve adjustment 162 to 165 at 70 MPH

looks like the engine is moving more air. about 46% more!

[DirtyMax03]

Did your EGTs go up? I guess it is possible that something got messed up during your lash adjustment and that you are now hanging the exhaust valves slightly open on 1 or more cylinders all of the time. Lash gets tighter as the engine warms up. In a perfect world, the lash setting is specified so that when everything is warm and thermally grows that there is 0 lash. Engine engineers error on the conservative side and specify the lash slightly higher than this 'thermal growth of the valve' effect to ensure that the thermal growth is never so great that the lash goes 'negative' which means the valve is being held open all of the time.

If you have this condition, I would remedy it quickly and would not run it full throttle because the valve relies on coming in contact with the valve guide to transfer the heat out of the valve head. IF it is hung open at high power levels, the valve head and stem will overheat which will torch the valve or cause the valve to stick in the guide and smack the piston. Either way, running with an exhaust valve stuck open is NOT something that you want to do.

Unless you are VERY confident that you set the lash properly, I would double check it.... even though I know it is a huge PIA. Merchant Auto has a nice cheat sheet for setting valve lash.

[minytrker]

I lost some mileage but my truck is the quietest lb7 I have seen. Also my oil now is WAY cleaner. I change it every 5,000 miles, it used to black like tar and I had to add 1qt per 5,000 miles. Now my oil is just lightly tanish almost like new oil. I also don't have to add qt anymore.

[LB72004]

i wont rule out the possibility of the valve not closing all of the way or that i messed up the adjustment but i am pretty sure that i did it right (other then setting them all a little on the tight side). i did you the procedure from Merchant. adjusted the lash and checked three times just to make sure i didn't mess it up.

as to the EGT, i dont have a gauge for this. i need to have an excuse to upgrade to a larger turbo but i cant replace a perfectly good one. and if i run it hot then i could upgrade it sooner:devil_2:. no, i should get a prob for this. i dont think i am running it particularly "hot", if i remember right it maxes out at something like 2200pw, 35cad, 180mpa at 4800rpm. (what HP would you guess this is?) i have the pulse width set to where it runs strong but doesn't smoke much at WOT.

i thought i read somewhere that the valve lash actually loosened up has the engine got warmer. it had to something to do with the engine expanding more then the valves, alloy?, and so the lash was set so it was a bit on the tight side when cold and "corrects" it's self when it warmed up. this may be backwards but thats what i read. dont know if i could find it again but i will look.

so if the exhaust valve was not closing all of the way would this make hot starts a problem as you'll be loosing compression while cranking?

i have debated taring all of the junk off and getting into it again to adjust the valves back to stock. does it seem like it would be beneficial to keep the intake valves tight and the exhaust loose? help fill the cylinders with as much air as possible and then have the combustion work as long as possible before the exhaust valve opens? or play it safe and put them all at .012?

minytrke, my truck is also much quieter too. but at this point i think i would rather take the better MPGs with the increase in noise. i dont know if it has changed my oil cleanliness any. i dont have to add any oil between changes and i typically push it to 10K or one a year. how long did it take for yours to clear up?

thanks Jason

[DirtyMax03]

On the Duramax engine, especially after the initial break in, you are correct the lash tends to open up. This is because the valvetrain (cam, rollers, rockers) wears more than the valves (heads and seats). Whether the lash opens up or gets tighter is engine architecture dependent. I work with large Cummins engines and we tend to have more valve wear than valvetrain wear and the lash closes up over many, many hours.

But your symptoms sound like you are holding an exhaust valve open. This would cause a poor hot start due to lack of compression on that cylinder. I would set the lash to spec. You aren't going to gain much by varying from the spec. And you may run into problems.
Higher lash causes increased wear and lower than designed max lift.

2200 PW is probably around 400-425ish RWHP, maybe more if you are maintaining 180 MPa. I assume you meant 3800 rpm instead of 4800 :). On a side note, the LB7 rail pressure sensor maxes out at 180 MPa and once it is exceeded the fuel pressure regulator on the CP3 goes wide open if you are commanding 180+ MPa and it thinks you are only making 180 MPa. Setting it at 180 MPa max commanded is probably OK, but don't command 190 MPa with a stock rail sensor. Commanding 175 MPa or 178 MPa might be safest to stay within the range of the stock rail pressure sensor. I work with a guy from Bosch and got this info from him.

[LB72004]

interesting

i believe for the Duramax the valve lash will get larger with time and wear. i was reading a thread a few months ago, Dieselplace???, where people who had adjusted their valve lash while changing out bad injectors, almost all where more then stock and a few at stock. i dont think any reported lash getting tighter when they measured it before the adjustment.

my engine starts up quick hot or cold. i have even gotten it to start just fine when it was turning over slowly from running the batteries down on accessory. it is obviously too tight but i don't think the valve is staying open. balance rates are all good too with low numbers around 1.

i have no problem maintaining 180 MPa (with dual CP3s). with the one CP3 it drops some but i dont think it was much. my rev limiter is maxed out and i have fuel up to 4800 rpm. it has no problem revving up but i rarely let it get that high. at 3800 RPM and 100 mm3 timing is 28, at 4800 it is 32.

i have my rail sensor rescaled up by continuing the graph up linearly from where it tapers off. this in theory allows it to read up to 200 MPa but is it likely not accurate up that high. at WOT i command 190 MPa to make sure the regulator is 100 % open. from the logs the pumps max out at close to 180 MPa. are you saying that the sensor can be damaged from presser over 180?

i ran a Diablo predator at the "120 HP" setting before i got my EFI Live and that thing felt week compared to my current EFI Live tunes. off the top of my head i was thinking 450ish RWHP but your numbers likely more accurate

thanks Jason

[LB72004]

filled up yesterday

349.8 miles
22.75 gal
15.37 MPG

looking better:D

[LB72004]

Update,

the last few fill ups where all around 320~350 Miles to a tank, dont remember the number of gallons, but it was no better then before. one trip was almost all highway miles and it was almost 430 miles. that sucks. it used to get right at 600 miles to a tank on highway only.

then, what are the odds, one of the injectors shorted out. so i ended up having to tear into it and replace #5. i decided that while i was in there i might as well adjust the valve lash back to stock.

now we wait and see if there is any improvement.

[hecatti]

Hi! Any update on this?

[LB72004]

i am only about a hundred miles into my first tank after the adjustment. i will post any updates here

[LB72004]

First tank after valve adjustment.

404.6 miles, 24.282 gal - 16.66 mpg

only about 30 miles total highway, rest are all stop and go/city

best tank so far since the initial adjustment. 16ish mpgs is where I used to be at in town so it is looking promising.

[LB72004]

449.1 miles, 25.273 gal - 17.769 MPGs :cucumber:

of curse this was with about 180 miles highway, rest with stop and go and back country roads. i am liking it so far. a few more like this and i am convinced that valve adjustment plays a big roll in MPGs

[LB72004]

PS this is with the 2nd CP3 back on

[minytrker]

449.1 miles, 25.273 gal - 17.769 MPGs :cucumber:

of curse this was with about 180 miles highway, rest with stop and go and back country roads. i am liking it so far. a few more like this and i am convinced that valve adjustment plays a big roll in MPGs

Thats about where my highway mileage is up to now after 6-7,000 miles on the injectors. Im still getting 14-16mpg around town though. Its slowly getting better, but I still like the way trucks runs and how quite it is compared to before. Also quit burning oil and its only tan now at 5,000 miles when I change it vs black after few hundred miles.

[minytrker]

PS this is with the 2nd CP3 back on

How do you like it? Im been debating buying one.

[andrewjamesbond1]

This is awesome to hear! Good data with known constants and variables!

[LB72004]

How do you like it? Im been debating buying one.

i like it, of course mine is home brew with an Ebay CP3. i built the bracket and assembled the lines myself so i put no more then about $350 into it. the primary CP3 was getting weak. when i started having trouble with my injectors and i couldn't build enough pressure to start the engine i decided to put the extra pump to use. i was then able to start it and drive it for a couple of weeks till i got new injectors. after the injectors where put in i decided to keep it on.

when i removed it for this MPG test i found that the throttle response seemed a bit slower, i think i got used to the "have pressure when you need it" ability and my weak CP3 couldn't satisfy me anymore.

unless you are planing on having larger injectors and a turbo upgrade, along with some internal work if you turn it up, you wont see much of any gain. if you can maintain 21+K PSI at WOT it would not even bother. the problem is more along the lines of keeping yourself in check and not turning up the pulse width too much and destroying your engine.

i only run 2200 PW and command 190 Mpa (makes around 180 Mpa) at WOT.

one aspect that i do love is the ability to start the engine even if i run the batteries down and it is turning over real slow. its ability to build pressure is amazing.

overall i think it was well worth it at $350 i spent to put it together