Engine/Transmission (1994 - 1998) compression test how to ?

[SFrey]

what is the proper way to do a compression test on a 96 CTD ?



thanks, scot

 

[HBrunton]

1. Remove all injectors

2. Install adapter

3. crank engine over with starter until guage stops climbing

4. Record results

5. repeat 5 more times

 

[SFrey]

may sound stupid but is there a way to keep fuel from coming out of injector lines ?



thanks, scot

 

[REFLOYD]

disconnect the fuel shutoff solenoid.

 

[Vaughn MacKenzie]

3. crank engine over with starter until guage stops climbing

I was told a more accurate way to do this is to record the number of the 2rd or 3rd compression stroke (pick which you want and stick with it for all cylinders). This is because a cylinder with less than perfect sealing will still pump up pretty well.



When I did a check on my '96 with 360k on the clock one cylinder only came up to about 120 on the first hit, whereas all the others shot up to 180-200psi. However the slow one topped out at 500, the others at 520psi. It took about 4-5 compressions to peak out, but about 6-7 for the weak one to top out.



Vaughn

 

[HBrunton]

compression test

Vaughn, you are correct, this is one of the reasons that Cummins does not give any compression specs, Cummins likes to judge engine health by blowby specs, boost psi, oil psi, etc...

Another thing to consider... putting oil in the cylinder to do a "wet" test, alot of times the oil squirted in will just go into the combustion bowl of the piston. not a good idea anyways because it has the possibility to ignite, possibly ruining guage or causing injury.

I like to use a infra-red temp gun to check each cylinders exhaust temp individually.

Technically, the valves should be adjusted prior to doing a compression test on any engine.

I one time had a 8. 3 "C" series that I was troubleshooting and I ended up having to put compressed air into each cylinder individually through the removed injectors to determine which cylinder was worn.

 

[Vaughn MacKenzie]

I one time had a 8. 3 "C" series that I was troubleshooting and I ended up having to put compressed air into each cylinder individually through the removed injectors to determine which cylinder was worn.

That sounds like a great trick and to me would be more of a difinitive test than a standard compression check. I would assume you do it with the piston of each cylinder at TDC so it won't move (or use a barring tool to make sure it stays there). I suppose you wouldn't need to use more than about 50-100 psi to get a good idea how well sealed things are.

 

[HBrunton]

yes, at TDC with compressed air, this is where the cylinder will have the most of its wear.

 

[Vaughn MacKenzie]

I wonder if it can be done as a leakdown test, with a gauge and then measure how fast it leaks down after disconnecting the air? I suppose it wouldn't be too hard to build a setup to do this.

 

[MAleksandrowicz]

similar to a pressure tester for an intercooler. use a t with a gauge on one end and a valve with a quick disconnect compressor fitting on the other end. open the valve until the desired psi is reached on the gauge and then see how fast it drops.