I was going to do an engine change on a 2006 F150 5.4. Before I removed the donor motor I decided to do a quick relative compression check. The results were not good. Next I checked the compression on each cylinder . After 5 or 6 strokes the results varied from 75 PSI on the low side (cylinder 1) to 175 on the high side (cylinder 6). The vehicle was a burn so running the engine was not an option. Next I did a cranking test to compare No. 1 to No. 6. The results are below. Maybe someone could fill me in a bit at what I'm seeing. A leak down test with some smoke added on No. 1 showed leakage through both intake and exhaust valves. Maybe I try it again with a faster sweep.
5.4 Cranking Compression
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Hello,
when you did the compression check did you use a mechanical gauge?
also, number 1 cylinder is off, i dont know much about these engines but i think they use a 3 valve head with roller finger followers? and VVT, perhaps remove the valve cover and inspect the valves for cyl. 1 to make sure valve train looks ok. -
The vehicle was a burn so running the engine was not an option. Next I did a cranking test to compare No. 1 to No. 6. The results are below. Maybe someone could fill me in a bit at what I'm seeing. A leak down test with some smoke added on No. 1 showed leakage through both intake and exhaust valves. Maybe I try it again with a faster sweep.Comment
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Bob did you happen to have a battery charger hooked up when you did the relative test? . reason I asked is I always get a bad wave forum with a charger hooked up. what looks different to me is the amplitude rise on the cylinder after the bad one. I usually see a higher amplitude after the bad hole.Comment
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Below is a screen shot of a 7.3 diesel with one bad cylinder. you can see the next cylinder has just a little higher amplitude, this is what I usually see. bob your screen shot may be showing a bad cylinder and then then next one week?
20171027-2048-2.jpgComment
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I'd of probably used an amps clamp around the battery lead, connected the scope to a CMP or CKP sensor to measure position, and used a RPM measurement for cranking speed. Using these methods you could then see individual cylinders for starter current draw, cylinder speed and each relative compression to each other. Hence if you knew the starter current draw should be a given value x, lets say 300 amps, then checking the peaks at each cylinder would show weak compressions by comparisons.
Hope that makes sense!Comment
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I'd of probably used an amps clamp around the battery lead, connected the scope to a CMP or CKP sensor to measure position, and used a RPM measurement for cranking speed. Using these methods you could then see individual cylinders for starter current draw, cylinder speed and each relative compression to each other. Hence if you knew the starter current draw should be a given value x, lets say 300 amps, then checking the peaks at each cylinder would show weak compressions by comparisons.
Hope that makes sense!
Makes sense to me, but what doesn't make sense to me at all is that an archaic ancient Counselor 2 has a wonderful cranking amps test with nice IDS like bar graph display compared to the ragged POS hump displays of the later more sophisticated vantage , modis , Verus platforms, that for this test at least makes those handhelds seem like Tinker Toys, LMAO. Why?
Well gotta Love looking at an Iowa Class Battle ship shooting off it's big 30"guns like I shoot off my mouth, but I have to admit technology marches on, and it's a shame one of those tiny ugly Lego block looking stealth destroyers could take out an Iowa class battle ship from an internet controlled drone from 200 miles away without firing a shot.Attached FilesLast edited by Witsend; 10-29-2017, 05:43 PM.Comment
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funny, I remember when i posted a nice pico scope bar graph when someone was asking about a pressure transducer and seemed no one liked the bar graph the pico scope makes, instead they wanted a wavy graph. i guess its snap on fan boys sometimes...Comment
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Holy ****! It's like the best cranking amps test display screen ever. How the hell was THAT lost?
I've never even seen a Counselor in person and now I want one just for that.
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5.4 Relative Compression
Hey Bob,
You might want to add a synch signal from an ignition source to the relative compression and in cylinder pressure tests. On the relative compression it will help identify the weak cylinders(s) in the firing order. It will show you valve train timing issues on the in cylinder pressure test. Good friend of mine, Brandon Steckler, has done a lot of work with this type of testing. I'm pretty sure he's posted some of it on iatn. If not let me know and I'll get some info to you.
Later, BobComment
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I'm not sure how that COP #1 trigger reference will work off the primary circuit if each coil on a Ford has that goofy multi strike spark discharge setup. I think I would suspect the cylinder with the miss fire code , high misfire counts, power balance test deficit, and confirm the low compression hump from relative compression test without a #1 trigger reference . Confirm that suspect cylinder with a low compression by testing that particular cylinder with the High misfire count or power balance test is indeed low with a compression gauge.Comment
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I'm not sure how that COP #1 trigger reference will work off the primary circuit if each coil on a Ford has that goofy multi strike spark discharge setup. I think I would suspect the cylinder with the miss fire code , high misfire counts, power balance test deficit, and confirm the low compression hump from relative compression test without a #1 trigger reference . Confirm that suspect cylinder with a low compression by testing that particular cylinder with the High misfire count or power balance test is indeed low with a compression gauge.
Agree that there are easier and faster ways to identify problem cylinders. Was leaning more to using an ignition synch with the pressure waveforms.
BobComment
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