Compression Loss and Gain
Correct VIN 1HTMMAANXCH683095 Complaint of intermittent power loss and shutdown. After shutdown won’t restart for 20 to 30 minutes or longer. No codes. Have been able to recreate one time only. During no start engine crank speed sounded high. Did a Navistar Engine Diagnostics (NED) Relative Compression Test (RCT). All 6 cylinder were at about 9 RPM. Waited a bit and ran RCT again.
Still no start but speed up to about 12. Got called away. Some time later it started right up.
Cannot figure out what would cause loss of compression on all 6 cylinders. No engine brake.
RCT speed back up to mid 30’s which is normal. See attachment. Have not been able to recreate since.
This was brought to us after another shop (which is pretty good) had taken multiple stabs at this including replacing all injectors. With NAV remans.
When running it runs great which is odd because cylinders 1 and 2 are dead.
Dead cylinders confirmed by cutout test and Navistar Cylinder Performance Analyzer (CPA) Injector Misfire Detection program (IMD) Also confirmed RCT by running CPA RCT+ . Did not have CPA+ hooked up when I had the no start.
Proceeding with caution on the diagnostics because the other shop is good and has a real good NAV guy.
Rex, EPA 10, That sounds like sticking rings. I do find it odd that they will free up. I'm not a huge fan of the RC test. I've had plenty of funny results. How does it sound? That's what I rely on more. Does the fan rock or kick back when you stop cranking? The health report codes I saw were from last month, and they wouldn't affect this issue.
Truck came from another shop... question... did they clear any history codes? How many miles? What is general condition of truck? Any history of overheating... any sparklies in the oil on dipstick? Galded piston... egg shape crank journal... bent crankshaft can do this exact thing (personal experience on that one: no fun at all). Not familiar with your cranking, electronic diag test... are you…
Michael, eng was to temp. Had just come back from a 15 minute road test to get to temp. I then did a cylinder cut out test. Confirmed the two bad cylinders. Imediately after that was the crank no start. No sparkles in the oil, oil sample is back from lab. About 47 ppm aluminum and iron is up a bit also but under 100 ppm. Details on your crank story? On the no start the cranking RPM was as…
Can you pull vc and confirm injectors are dumping oil on 1 -2 .with low compression those 2 cylinders shoujd be white smoking bad if it’s too low to fire ...it’s not going dead from low compression..if it’s that low should not start at all cold .would start better hot ..unhook particulate filter and check on smoke ..can you take intercoorer hose off at intake to eliminate starving fior air…
Marvin, Odd thing is it is barely repeatable. Only did the crank no start on me once. Based on some ideas here and something about the way it ran with the intake hose off has me thinking ITV. Hope to do some tests tomorrow.
Kevin, I posted the wrong VIN. Correct one is CH683095. I edited my original post. The attachment is also wrong. But it is close enough to what we saw when it came in. I was told years ago in a case file that the RCT is not reliable on the … (EPA 07) engines. On the EPA 10 engines I found it to be close enough. The attachment is also wrong. But it is close enough to what we saw when it…
Rex I’m not real familiar with the RCT in NED? Is the rpm differenc the difference compared (Relative) to the slowest cylinder? can you explin the test Please?
Josh, hi! See my explanation to Michael. I will get a screen shot of where the test is. Have to be hooked to an ECM to see it. Short version, ECM can watch the piston speed. So it see what it is close to or at TDC. Since it is compressing air that will be it's slowest speed. After TDC and ignition it goes much faster. ECM takes the speed at about 30 degrees ATDC. The difference is the number on…
I’m thinking outside the box. what if the rings are sticking, but I would find that hard to believe on all 6 and enough to cause a shutdown situation. is there an intake throttle valve? if this sticks closed it wouldn’t let any air into the cylinders and could definitely cause no compression in all 6
See above. I like that idea and it makes sense. Now you have me thinking about what a stuck open EGR valve would do . At first thought it shouldn't effect compression. Problems like this make me miss drinking!
Rex I actually Have had a stuck open egr valve on an egr 466 and it did cause a no start but not due to loss of compression, it was flossing the combustion chamber with exhaust gas instead of oxygen. it was trying to start and almost would start but would stop in a second.
Josh, EGR valves cause a whole host of issues and so do ITV's. Often with no codes. Had a 2008 ISC the same time as this. Regen problems. Will know for sure first of week but I think an EGR valve and sensors may have fixed it. Monday I'm going to block the intake and see what happens.
Josh, see my post above. Looks like a faulty ITV. Guess I never knew or thought about what happens to compression if there is no intake air.
Let's put aside the no codes for a moment... all things being good (or good enough to run intermittently) I have not heard any talk about blue exhaust smoke or major crkcs blowby... so normal crank speed with ok compression is ~ 150 - 200 rpm... with all the "good" things being good it starts... it has combustion. So if everything remains as is but we no longer inject fuel (no combustion) would…
Michael, 2014 so EPA 10 level. Has not shut off on us yet. Hard to tell on blowby because it does have a DPF and is an open crankcase system. Have not looked for floaters in the tank. Yet. I'm thinking crank speed would stay the same fuel or no fuel but will have to verify. May drop the cans off. The DPF can hide issues. Josh has me thinking about the Intake Throttle Valve. Was running it…
This morning I blocked the intake and reran the RCT test. Compression tanked. Got as low as 1 !! Opened it up just a skosh and got to almost 5. I am advising customer to replace ITV. Thanks to all especially Josh. It helps a lot getting some different ideas. Helps kick me out of my rut. Hope this is the right way to update and close this.
Rex, not sure if you remember me but you let me borrow an engine ecm for test purposes about a year and a half ago. I told you hoepfully I could repay the favor one day. glad you were able to get it figured out. this is a great resource