loss of MPGs after valve adjustment???

[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

[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. 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. 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