Engine/Transmission (1998.5 - 2002) What to Expect- Compression Testing

[Partyat33]

I suspect I have low compression. Truck starts very hard when cold and makes huge amounts of smoke until it warms up. Condition is improved by plugging it in. So, I am borrowing a compression tester. Can anybody tell me what type of results are normal ? I rebuilt the engine from scratch a few months ago and I am wondering if I have a ring problem.



Thanks



Dennis

 

[y-knot]

You will have to roam around in thew Cummins manual for the compression test procedures and correct values. My service manual states that the manufacturer does not recommend the dealers do a compression test, sorry. They do give the compassion ratio's but that means nothing.

 

[Nickaru]

Are the grid heaters working? Sounds like a cold start problem if the smoke is white. Fuel contamination is another suspect. My $. 02

 

[Partyat33]

I believe the grid heaters are working based on the battery voltage behaviour. Its done this since I rebuilt it, even in the middle of summer. Had quite a few tanks of fuel in it as well, so don't think thats it either. Might be timing. I have a manual so I will look up and see what it says. I appreciate the suggestions. I gotta find the problem.

 

[AKAMAC]

Have you checked the valve clearance?

 

[Partyat33]

Checked the valves a couple of times, thought maybe it was leaking by, but I don't think so.

 

[Snow man]

Do you have excessive blow by?Did you put in a thicker head gasket, thicker head gaskets will typically cause smoke til ti warms up from the reduced compression.

 

[A Johnson]

If a Cummins manual has a compression spec it's news to me( I will qualify this by saying I haven't looked at a manual in a long time). A few years ago we were working on an issue and the factory asked us to do a compression test, we then asked them for specs and they couldn't give them. I suppose someone in Indiana has a spec, but remember it is dependent on crank speed.

Basically I suggest if you want to do the test, do a comparative test and you should probably be within 10% or so between all cylinders, providing your crank speed stays the same.



A Johnson

 

[JR2]

Do you have a compression tester for the cummins?? If you don't I belive snap on has one for about $100. A buddy of mine had to buy one and take it to the dealership for them to use on his truck as they had never done a compression test on a Cummins before.

 

[Partyat33]

I did put in a . 020 over gasket with . 007 shaved off the head. But I will also say I put in a . 020 over gasket prior to the rebuild and it did not exhibit this problem.

As far as the compression test, I think I am looking for consistent numbers between cylinders as a start. I will see where that takes me.



I am going to see Kirk and Destry at Iron Diesel, they have a tester, I don't know what kind it is.



Dennis

 

[GregFisher]

what color smoke, basic rule of thumb, white smoke low comp. water in fuel or advanced timing. black smoke overfueled, retarded timing, lack of air.

personaly im not a big fan of compression testing, that usually only tells you how good your batterys are. i prefer leak down test, but in your case with a complete rebuild there's many possible factors. i think we realy need more info???