290 p.s.i. to 320 p.s.i. compression good?

[ChrisKringle]

At 100k started getting excessive rough idle at start up along with slight miss just off idle along with rough miss at freeway cruise speed when accelerating.



Feared the worse, bad injector, probably washed a cylinder, so had shop pull injectors and test compression first. They said it ranged from 290 psi to 320 psi, which sounded fine to them.



I said fine, I'm sending injectors to Don M for a rebuild and 90hp tips while ther're out and I'll be on my way. Also had shop throw on a Schwitzer300 turbo which is pretty cool.



Now for the question, have 110K on the odometer now and looked under the truck today and seen a light pulsating haze coming from the crankcase vent tube, looked like a faint steam pulsating rapidly.



Does your truck vent from this tube on a hot summer day, or are my piston rings toast and I should get a leakdown test performed at Cummins?? I do get a similar very faint haze out of oil fill cap if removed, but definately not a strong pulse of air that would indicate bad rings.



By the way, still idles extra rough at start up, still misses off idle, but now makes funny 'change in can' sound from injectors at mid to high rpm, after thousands spent on them.

 

[AABEN]

That is about what you should get. That is how the eng gets it air and keeps from high pressure build up in the eng. That is jest like letting a little gas of of you. GOOD LUCK

 

[WKruger]

Could also be bad valve seats and or guides. The older 24 valves were terrible for that. Had to let the temp gauge come up before you put a load on the engine. I'm not too sure if they fixed the problem.

 

[Vaughn MacKenzie]

Compression tests are fairly subjective on a diesel and not the best way to ascertain cylinder health. It's fairly dependant on how it's done (whether you take the 2nd, 3rd or 4th compression stroke or or highest reading it pumps up to). I have been told however that by the time you drop down to 250-275psi you have a lot of cylinder leakage.

For comparison I did a compression test on my '96 at 355k and the weakest hole was 500psi, the rest were 525-530. . . these numbers were the highest they pumped up to, usually by the 4th stroke. #1 came up the slowest since it's a little weak.

Final word though is do a leakdown and/or blowby test before deciding whether or not it needs torn into. There are instructions posted here before for a manometer setup to see how many inches of water your engine is producing at a high idle (2000 RPM) and I'll see if I can dig it up.

 

[ChrisKringle]

The cummins shop said the best way to tell was with a leak down test, around a $100. Damn I wish my shop would have told me that before I paid for injector R&I and compression test.

 

[ChrisKringle]

I thought I heard 460 p. s. i. from the factory, and I should be seeing around 350, nevertheless I still think a leakdown is in order.

 

[osiris]

I think that you also have to take into consideration your altitude I think that the higher altitude you are the lower your compression could be, not saying that its going to go rockbottom when you are up high just saying altitude plays into the equation as well...

 

[ChrisKringle]

Well I've been searching everywhere on the net, and something I just came across said 350 factory, and 300 used, but that was for a marine engine, that is much different than what Vaughn said above.



Does anyone know what the HPCR 325/600 engine should show on multiple cranks?

 

[Vaughn MacKenzie]

Before worrying too much about the compression test you might give the blowby test a try:

Blowby Test - Diesel Bombers

 

[ChrisKringle]

Yeah I am going to get the blowby done just to see what's going on. Or maybe I'll just leave it alone cause it runs good?

 

[osiris]

I dunno it almost sounds like the injector(s) might be bad again? I had some of the same problems you are describing and 5 out of six injectors were bad again... Don M took care of them and Richard at browns diesel is helping out alot as well... you should give him a call

 

[ChrisKringle]

Well I actually sent my injectors to Don M at the same time that I had the injectors out for a compression test (around 8-10000 miles ago, just a couple of months ago). I chose to have him rebuild them for $125 each or whatever it was, and install Flux 2 tips which are rated at 100hp. Well, they didn't work the first time the shop installed them, loud knock from one cylinder after a few minutes of running them, so then I have to pay the shop hour rate to remove them, send them back, then pay to reinstall again. 2 weeks went by. Guess it was the shops fault for not cleaning injector tubes, supposedly.



I agree, I don't think my injectors are working properly cause of white smoke, rough idle at start up, miss just off idle, coins in can sound at mid rpm.

 

[osiris]

yeah that is what it sounds like to me like i said i have had mine rebuilt by don and then put about 4 K on them and they were trashed again... are you running any aftermarket fuel filter and are you running a pressure box?

 

[TCDiesel]

Osiris, I hope this time you are putting the Correct rail on, if at least eliminate it as part of the cause?Factory rails may not support aftermarket injectors, it has been the consensus around here that in most cases it only time before it shows its ugly head...

 

[ChrisKringle]

Osiris, I hope this time you are putting the Correct rail on, if at least eliminate it as part of the cause?Factory rails may not support aftermarket injectors, it has been the consensus around here that in most cases it only time before it shows its ugly head...

Oh I didn't know that, I'm just saving for the dual cp3 kit from PPE. As of right now, I drive it as a tow vehicle with pressure box off and TST on 1 and 1. I haven't raced or anything.



Mark from TST told me over the phone he does not recommend any aftermarket fuel filtration for the HBCR. He says Cummins tested the high pressure fuel system in fleet service for many many miles. This was a few month ago when I called him inquiring if I could add a FASS fuel filter to the FASS95 he sold me. He was a Cummins Engineer so I guess I'm not adding additional filtration. I do run the Baldwin 5micron filters though.

 

[osiris]

i believe what happened to mine injectors was bad fuel and improper installation the first time around... we will see what happens when i get my truck back