What is the Normal cylinder pressure of a 94 CTD motor? When I had my motor checked at Cummins it was 280 all across. Cummins said 350 would be normal range. Cummins said my truck runs strong except for the Injection Pump issue ( rough idle)

When the head was off the cylinder hatching looked excelllent. But injection shop is telling me I should be in the 375 and up range for cylinder pressure?

My truck runs excellent. With the timing bumped up the truck lost a lot of the dark smoke and runs great. Once the injection pump comes back I expect it to run even better. Any suggestion on why I would have low cylinder pressure but truck runs great???

Dave

 

While i don't have a direct answer for your question, I will say that when doing a compression test , the tech is usually/should be looking at the difference between cylinders , not for the actual number , IIRC the general rule of thumb is the highest pressure should not be more than 20% off of the lowest pressure.

This is even more important in your case , since you had a miss of some sort at idle, 5 of the cylinders could have made 400 psi , but if one was low , 200 psi , that would definetly give you a miss.

Since all of yours were apparently fairly even , that ruled out the engine being a source of this miss.

 

JKM that is what I am thinking. Truck runs to good to worry about the cylinder pressure not being close to a new engine. All cylinders are dead even at 280. And again, truck screams once I get past 1300 rpms
....

The injection shop had to replace the aneroid (sp) because of the first shop screwing in lag screws into the afc housing. They also found that the pump to be a little out of calibration on 2 cylinders. Shop had to send the pump out to their main shop in California to have it run on the bench. Tomorrow they will bench test to check flow and dv issues. I am really hoping for a dv gasket. They said if comes back with a dv broken they will replace all dv's not just the ones that are broke. But they said dv's are $100 a pop. $600.00 seems steep. I thought I saw on this site where I can get bigger dv's for $280-$300? Any thoughts....

Thanks....

Dave

 

Yeah , you can DEFINETLY get some DV's cheaper than that.

I just checked a couple different vendors online , and 191's are around 250$

 

I will post back tomorrow after I find out what the injection shop says. I am really hoping is just a DV gasket. But if it is the DV's I will be purchasing them from some one else.

Dave

 

West Coast
The last compression test I did on mine the pressure where 375-380 psi. Like JKM said the fact that they are even is good and I wouldn't be too concerned about that. I suspect their gauge is messed up or someone misread or wrote the numbers down wrong.

 

JD730 I had our local Cummins shop to the compression test. I hope they mis read the gauge. I was just looking at Cummins invoice again and it said at cylinders where at 280. Cummins also did a blow by test which it states the gauge did not move at all during the blow by test.

When I had the head off for head gasket replacment I was able to look at the hatching marks and cylinder walls. Everything looked in excellent shape.

Is there anything with a new Head Gasket install that would cause low cylinder pressure evenly across the holes??

And how much more smoke would I get if I bump up to 190 DV's from my stock DV's. After I bumped up the timing the truck smoked much less and I was very happy with how it seemed to be running much cleaner.

Thanks....

Dave

 

There's nothing I can think of that would or could cause that. I highly suspect user error or a typo on your invoice.

On a different note, I put together a gas engine a few years ago for tractor pulling, shaved the head, high compression pistons, ported, etc... IIRC it had around 250psi of compression when cranking, could have been 150psi I can't remember now. I need to start keeping a notebook of all this stuff.

 

I just got back from the Cummins shop. They said the numbers are correct. But they see a lot of "low number" cylinder compression test but the motors make tons of power.

Also the injection shop called. All cylinders needed to be phased (calibrated) and had bad DV gaskets. So I am hoping this now solves my bad idle issues.....

 

West coast, There gauge could be causing the low numbers.

I recently did a compression test on my racecar with 2 different gauges. My gauge showed cranking psi to be 240. The other gauge I used showed 200 psi. But all the cylinders were dead even.

With the numbers being the same across the entire engine, you should be good for many more miles. Espiecally with your results on the leakdown test.

 

Ya Kemble my truck runs to good to worry about numbers... ha ha... I will report back after the Injection Pump go back in on Monday....

Dave