Compression testing M929A2 8.3 Cummins

Anybody done a compression test on Cummins 6cta8.3? Ive got a dump truck that is hard to start and puts out tons of white smoke while cranking. I thought it was just losing prime but thats not it. The smoke does not smell sweet. Its a bit acrid and diesel smelling. When the truck finally starts to light off I have to keep the starter going a bit before it has enough rpm to sustain itself. This engine shows about 1800 hours on tach. Once it first starts it has a slight miss until warming up. Has ok power. Oil is fine and there is no evidence anywhere of a blown head gasket. Im thinking it could just be tired so thats why Im considering the compression test route.

Sounds like low fuel pressure. You should have 25-35 at the inlet of the injection pump.

I Put a new lift pump on it and a new return fuel check valve but have not checked the fuel pressure. Is the best way to check it to install a T in the fuel line for a pressure gauge?

You can do that or drill and tap the inlet fitting at the injection pump for 1/8 pipe and install a fitting there. When it runs, take the oil filler off. If it tries to blow off when you get to the last of the threads there is an internal issue. If it just has small puffs of smoke, you should be gtg.

Could be sucking air on the tank lines. Have you replaced them?

Cummins does not not specify compression data, or even leak down data. They only assess engine health via crankcase blow-by measurement. I did buy an adapter to do compression and leak on my 8.3, but have not used them yet.

Sure they do, copied from QSOL

014-012 Engine Compression

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Last Modified: 03-Sep-2002

Leak down testing is good for spark fired but as far as I know there is no leak down for compression fired engines

Interesting, thanks. We could not find such information when working on an ISX and was told Cummins does not publish such info. What is the source of this info (what is a QSOL)?

That is correct. No compression testing in anything above the midrange engines. I don't even recall if it is done on any B,C or L series beyond 1998 with the exception of some off road engines, for Cummins anywho.

QSOL,
https://qsol2.cummins.com/info/index.html

Thanks for the info.

Thanks for all the great info. I did the test with the oil filler cap and there really is no blow by. So ill keep looking for a leak in the fuel supply.

Ordered a Torks banjo bolt with built in snubber and a schrader valve from dieselORings.com. Plan to get a tester that will plug into the schrader valve. I already installed an adjustable return fuel check valve from Torks but since it was set at 25psi for a P7100 pump not sure what pressure it produces on the MW pump. When using the hand primer I can hear fuel squeezing past it with just two strokes so I think it is at a pretty low setting.

Will produce the same pressure on either pump. Your OFV sounds correct, not low.

Ill have the pressure gauge set up next week and see what I'm getting.

Got the new banjo bolt with snubber and schrader valve installed. I used a fuel pressure gauge set from Harbor Freight. Its meant for gasoline vehicles so it may not survive long but it only cost $16. Anyway the pressure at idle is 22.5 psi and at 1800rpm it is 30psi. So I think this is correct and the lift pump is performing properly. I tried adjusting the return fuel check valve and ended up with it at the max pressure setting but it did not increase the pressure from its original setting.