lmorris Posted October 14, 2011 Share Posted October 14, 2011 I had posted on another thread elsewhere about a 6.4L that had the right side glowplug harness out of the valve cover and lost 12 L of oil soon after we did the rad. Well here it is. Customer has truck chipped and lifted with all the aftermarket goodies like exhaust and intake. He pulled out to pass a bunch of trucks in the highway and blew out the harness from the valve cover. How much crankcase pressure do you think is necessary to cause this? Quote Link to comment Share on other sites More sharing options...
Keith Browning Posted October 14, 2011 Share Posted October 14, 2011 I think the answer to your question is in performing a crankcase pressure test. If crankcase pressure is what is causing the glow plug boots to blow out of the valve cover I would say it is excessive but you need to TEST it and PROVE it. Quote Link to comment Share on other sites More sharing options...
cbriggs Posted October 14, 2011 Share Posted October 14, 2011 Last one I had do that had over 30 before 2000 rpm. I think it was around 12 at idle. Had a big hole in one of the pistons. Quote Link to comment Share on other sites More sharing options...
lmorris Posted October 14, 2011 Author Share Posted October 14, 2011 After further testing #8 is down 13% on relative compression and crankcase pressure is around 13 at idle and pegs our gauge at 2000 rpm. It puffs like a steam train at idle. Customer has been told depending on cause of failure this may not be warranty. He has given us the ok to go further. So up next is the fuel leak tests. Unfortunately it came to us with only 2 liters of oil in it, so checking for overfilled oil won't happen. Its starts to rattle like it has a leaky injector after running for a bit though. Quote Link to comment Share on other sites More sharing options...
cbriggs Posted October 18, 2011 Share Posted October 18, 2011 There are pics in photo post (a ways back) of the 6.4 I had with a hole torched in a piston and almost thru the cylinder wall from a bad injector. Quote Link to comment Share on other sites More sharing options...
Brad Clayton Posted October 18, 2011 Share Posted October 18, 2011 That injector was like a frickin' laser beam. Quote Link to comment Share on other sites More sharing options...
cbriggs Posted October 19, 2011 Share Posted October 19, 2011 I likened it to a plasma cutter. Quote Link to comment Share on other sites More sharing options...
lmorris Posted October 19, 2011 Author Share Posted October 19, 2011 I liked the way Brad described it better. All you need to do now is mount the injector onto a shark. Quote Link to comment Share on other sites More sharing options...
Brad Clayton Posted October 20, 2011 Share Posted October 20, 2011 or some mutated seabass. Quote Link to comment Share on other sites More sharing options...
lmorris Posted October 21, 2011 Author Share Posted October 21, 2011 No compression on #8, rest are 300 PSI. Nothing on the mist test. Nothing on the high pressure pump leak test. Glow plug and injector tip both look good. The valve train looks good. Really curious as to the loss of compression. Will post a pic when I get the head off. Update: #8 piston is split in 2 right along the pin line. There are a few little pieces in the pan, thus it also has a couple of holes in it. Given the condition of the other cylinders, which are fine, we are assumming a faulty piston or the injector stuck open. Quote Link to comment Share on other sites More sharing options...
ktmlew Posted October 29, 2011 Share Posted October 29, 2011 300 psi on the other cylinders sounds about 100+ psi low doesn't it? What is a good number on these? I would have assumed 420-450? Quote Link to comment Share on other sites More sharing options...
Jim Warman Posted October 29, 2011 Share Posted October 29, 2011 We live at about 580 meters above sea level. Bear in mind some of this could be the nature of our compression tester.... we have never, ever seen readings much above about 350 PSI... for my part, if I see 325ish on our gauge, I may not actually consider this as "good" but I might see it as "acceptable". A compression test is only one step in a comprehensive determination of a cylinders ability to seal compression. We are looking more for even values than absolute values. Depending on my findings, I might crank the engine "dry" about 6 compression strokes watching the reaction of the gauge on each stroke... I might crank the engine to achieve "absolute value". I might repeat the test "wet" or I might "leak" the cylinder in question. Before I do any of this stuff, I'll do a power balance and relative compression if available and likely a crankcase pressure test as well. We need to avoid reading too much into a situation. Speaking of "relative compression".... Ford watches the crankshaft trigger wheel for rpm variations to "assume" cylinder sealing ability. Back in the 80's, Sun Equipment was marketting engine analysers that used starter current draw to assume cylinder sealing ability. So far, one seems about as accurate as the other for leading or misleading the tech. Quote Link to comment Share on other sites More sharing options...
ktmlew Posted October 31, 2011 Share Posted October 31, 2011 300 psi on a 7.3L is a bad sign...did they drop the compression ratio dramatically on the 6.4L? Of course that assumes a decent cranking speed. Quote Link to comment Share on other sites More sharing options...
Brad Clayton Posted October 31, 2011 Share Posted October 31, 2011 Never seen any good Powerstroke engine below 400 psi and I am in the mountains! If it don't hit 400 psi in my bay then there is cause for concern. Quote Link to comment Share on other sites More sharing options...
lmorris Posted October 31, 2011 Author Share Posted October 31, 2011 We too were a little perplexed at the 300 psi readings, until we tried it on a new truck and even borrowed our closest dealership's gauge. 300 psi is normal for us. Quote Link to comment Share on other sites More sharing options...
Jim Warman Posted November 1, 2011 Share Posted November 1, 2011 That's our experience, too. I've yet to see one even close to 400 PSI using our gauge. Quote Link to comment Share on other sites More sharing options...
Gary_P Posted November 4, 2011 Share Posted November 4, 2011 if the piston is not melted, I would not think the injector was held open Quote Link to comment Share on other sites More sharing options...
BrunoWilimek Posted November 4, 2011 Share Posted November 4, 2011 300 psi on a 7.3L is a bad sign...did they drop the compression ratio dramatically on the 6.4L? Of course that assumes a decent cranking speed.7.3 is 17.5:1, 6.0 is 18:1, 6.4 is 17.5:1, 6.7 is 16.1:1. Quote Link to comment Share on other sites More sharing options...
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