Proper way to check compression?

[csnider]

I searched the forum but Alls I can come up with is "I think" or "I've heard" but I haven't came accross a instructive thread on checking compression (yet). . I have a Snap On 6bt VE tune up kit with the guage and adapter but I've never done compression checks on a Diesel. . Anyone Know how?. I've been chasing down a rough running engine here and before I pull the pump, i want to make sure my compression is good/equal. . All temps at the exhaust ports are as close as can be . Injectors have been bench tested,new lift pump but maybe I have a soft engine? Thanks for any help ...

Chuck

 

[JFaughn]

1st shut down the fuel , on a warm eng / does not need to be hot / but
should be about 70*F , starter/batteries should be in as new condition , needs to turn over fast / as new .
Pull injectors , screw in tester , turn over eng at least 2-3 time & should not need to go more that 4-6 , watch gauge , at least 70% of compression should be there in the 1st full stroke [ not in the middle of the 4 stroke cycle ]
, write down results at each cylinder , all cyl. should be within 10 % or less of each other , I forgot the spec , so look into this . Fritz's Dodge Ram Tech

 

[csnider]

great!

Much appreciated. .

Chuck

 

[csnider]

OK,

finally got around to checking compression today. .

Warm engine would pump up 460 lbs after 7 strokes. one cylinder would do 450 all the rest 460. is that enough to give it a clean bill of health? Thanks for your time

 

[JFaughn]

7 is a lot , it should get most [ 80% ] of the way there by 2nd or 3rd .
10% of 450 is 45 , so your good there .
Then there is a leak down test , to determine where its going if bad .
It would see your way ahead of yourself , looking for a ruff running , I would disable fuel to one cylinder at a time while eng is running , to find a cylinder that is not doing well , then try a variety of things to find out why .
As long as the injectors are out , popit test them .
What area are you in , you find someone like me that has the popit tester .

 

[csnider]

Thanks for the info,

changed to a old stock set of injectors after the compression test. . Idled better but still has a "surge" like rythm to the power. . Phump, phump, phump phump, as I accelerate hard, runs smoother at cruis when not accelerating hard. Actually the drone of the exhaust sounds smooth & even but there's almost a slight rythmic surge instead of a smooth power delivery. Has a good amount of pwer and runs real cool exhaust temps with even temps at the exhaust ports... I'm thinking my injector pump is getting wierd?... I have two trucks . the other one although not quite as "turned up" runs very "electric like" . Maybe I'll do a compression check on that one and see how close it is. to the rough running one. .

I already did a new lift pump and checked for air leaks on the suction line on the rough one ,so I was hoping the injector switch out would reveal it.

Not yet though. . Thanks again for the help. .

i will say this about the injector pump. . It was turned up to 210 hp at the rear wheels (stock injectors and turbo then!)about 80K before I got it so the (IP)could possibly be tired. I turned it down some when I got it as i added a fuel pin,high flow turbo, better intake setup and 4" exhaust. Truck has 155K on it now. . started noticing rougher running a couple months ago . Starts RIGHT up with at most one revolution just click the key and it's running..... So I was thinking the compression test might reveal a soft cylinder among the six but they were all dead on except the one about 10lbs lower. . Oddly , every once in a while it runs smoother for a bit then goes back to it's now usual way... . I'll figure it out eventually I just don't want to start throwiing money at it by "shotgun" fixing it... rebuilt IPs are expensive