RollsCoal

I bought the tools to check the timing of the injection pump on my 95 cummins 12 valve. I found top dead center using the method where you compress the valve spring and allow the valve to rest on the top of the piston. I marked tdc on the damper, and double checked it about 6 more times. So I KNOW I had the correct TDC.

The amount of lift shown on my dial indicator at the #1 delivery valve location corresponded to 18 degrees timing!

How could this be? The truck was all factory, considering I bought it off an old lady who pulled a tag along horse trailer.

I did notice the oil filler tube had broken threads where it may have been removed at some time.

Do you think the pump timing could have slipped sometime during the life of the truck, and she took it to have it repaired and they incorrectly set the pump to 18 degrees?

I set the pump back to a more appropriate setting (16.5), and now it runs excellent. It seems to have more low end grunt than before.

How come I did not blow the head gasket at 18 degrees, if that is supposedly so bad for it? Just got lucky??

G1625S

Welcome to the site! Someone had to have been in there and set it wrong previously. 18* is not super high, and the truck would likely go for years with moderate fueling and driving style. Fill out your signature so we can see all your mods. That will make it easier for people to give advice. I need to get to my timing. It's stock/slipped. Maybe 10-11*, lol!
greg

RollsCoal

OK Thanks. I filled out my signature. It does seem to accelerate faster in the low end, which would correspond to the change in timing I made from 18 degrees to 16.5. I hope my fuel mileage will improve. I normally get about 18 mpg.

cumminsdriver635

18* is maybe a touch high for a street truck with a stock gasket, but it should last a while like that. You will be fine at 16.5* though. Mine is at 16* and has been for around 3 years with no problems at 40psi.

Eric

infidel

More than likely the timing was never set right from the factory, few are.
18 is actually a good number for the '94-'95 pumps.
I wouldn't mess with it.

RollsCoal

Why is 18 deg timing good for 94 - 95 pumps? It seems like 18 deg would be best suited for high rpm trucks, up to 4k + rpm.

It is too late now, I set it to 16.5 deg. The concensus I got from reading many different opinions online was to set the truck somewhere around 15.5 - 16.5, so I went with 16.5, bc I plan to upgrade to 4k gsk and 60 lb vs in the future.

If factory is 12.5 deg, and alot of folks agree that around 16 deg is a good number, then why would 18 degrees be better?

I just want to get a better understanding on this, so please enlighten me if you will. My truck seems to have better acceleration around 2k - 2700 rpm, (the range it is in most) than it did before.

cumminsdriver635

The smaller 160 and 175hp P-Pumps like some extra timing. The injection isnt as agressive as the 180 and 215hp trucks because the pump cam is different, so the extra timing helps to make up for the differences in the cams in the pumps. I plan to go 19 or 20* with mine when i stud the head. 18* is still more likely to blow your head gasket though.

Eric

kawi600

What timing is typically run on the 215 pumps? I have mine set to 19 right now.

infidel

The 215s seem to like it best 15.5 - 16.5.

1workinman

There is two different cpl numbers for a 95. I have run 18 for several years gives fair mileage. A lot better than stock timing.

RollsCoal

Well I filled up and set the odometer on zero after setting the timing to 16.5, from 18. I ran that tank out, and filled back up, calculated my mpg at 18.6.

I was running the truck pretty hard too. About 30% city, 70% highway, accelerating rather hard. That is not bad for a 4wd truck with 35's. I normally got in the 17's for mpg with the timing set at 18*. Normally around 17.5 -17.7 mpg or so.

Time will tell, but my first fill up shows an increase in mpg from switching my timing from 18* to 16.5*. Does this seem plausible? I know going from 12.5 to 16.5 will improve MPG, but should going from 18* to 16.5* improve mpg, like I think I am seeing? Too much advanced timing would decrease mpg due to negative work associated with the rising piston fighting cylinder pressure. The question is: Is 18* too much advancement for best fuel economy in my 95?

Johnny0874

I can't say for sure... never played with mine (don't even know what it's set to)... but from an engineering standpoint, there is usually a "sweet spot" that lies somewhere in the middle of the range depending on what all is going on with your engine. Yes, it is harder for the rising piston to compress a more viscous mix (ie more fuel) but if it is already spinning at a certain RPM then the sheer brute force of the inertia from the rotating assembly (these things are heavy for a reason) will compensate and probably overcome that issue. I'd imagine you'd only notice the difference under heavy loads at low RPM's (like towing a horse trailer from a stanstill up a steep hill). If your doing a lot of highway driving then you'll probably not see this condition too frequently.

I'd be interested in seeing where you guys are getting your recomended settings from... is there a formula out there or is it just the bubba-network passing along tribal knowledge? I'd like to think there was a way of calculating the best cam plate and timing set up for each style of pump and how much fuel your rig actually needs. Right now mine is still set to the factory timing (unless the previous owner changed it)... and I'd like to try and get a few extra MPG's out of my truck. If I can get it to produce a few more ponies to boot... well, sign me up. =^))

Any suggestions on where to look???
Johnny

Just4Smoke

I am looking for someone in the MN area that could spend a few hours and help me set my timing... or set my timing for me and I'll pay them. Any recommendations? Either way I need to know what I want it set at. Its a 95 12v and up until now I was thinking 16 degrees. After reading this post though it sounds like with the 160 pump I should consider setting the timing at 16.5 or even 17. Is this correct?

infidel

Many years of trial and error...

John Faughn

Farkum , where about's are you in MN.
I had to replace my 160 pump just recently , found a 180 pump from the classifieds here .
Set the time to about 16 , having better trans shifting now , than with the old pump , need to do more , because my millage is still around 17-19 .