Manager Forum

Compression spec?

It just says within 25 % of one another' but what if there all under 300? Like between 250-300; I cannot find what the readings are supposed to be anywhere.

I was hoping someone knew what a normal # might look like say 350 +

Typically you should see 400+. At about 330 the engine will not start on its own. You start getting below the 400 mark, it indicates a developing issue. Keep in mind battery condition and cranking speed affect compression. And, the engine should be at least 150 rpm while checking compression.

I had a battery charger to each battery and had no cyl above 300. I was getting bubbles in the fuel filter. With a few of the glow plugs out the bubbles go away im just thrown off by the overall low comp #'s and the fact no one gives a spec. Im pretty sure at this point its injectors but am torn by the overall #'s

Have run into a few of these where the fuel filter on the frame rail is real dirty and one where the housing was cracked. The cranking rpm is a real important issue and we've replaced more than one set of batteries because some zipper head used undersized ones or replace only one. If your getting air in the system it may be in the rail filter area.

Another thing we run into a bit is the harnesses to the glo plugs getting brittle and not feeding the plug. This will cause a bit of unburned fuel and will effect the compression. If the oil smells like it's heavily contaminated with dsl fuel it may be the glow plug harness or plugs themselves. When you scan the system and get a contribution code check the harness and glo plug before you go for the injector. Can't say about this particular system but i do know for earlier ones there were International injectors and Ford ones. Look identical but incorrect will cause a rough idle after slowing down from a hard acceleration.

bubbles in fuel would go away with certain glow plugs removed. Repalced all injectors and now its on the road again good to go.

Sounds like compression was getting up through the injector pintle or past the copper washer at the bottom of the injector. Seen both already.

Thanks for posting.