Compression Test Question
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Senior User
Joined: Dec 2012
Posts: 373
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From: Arlington, Texas
Compression Test Question
Heading up to Harbor Freight tomorrow to buy a compression test kit and finally calm my nerves. I have never done a compression test before, so I was wondering if you guys can walk me through this or give me some advice?
Elder User
Joined: Mar 2012
Posts: 534
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From: Quaker Hill
Disconnect 42 pin connecter, pull VC. Pull all GP's. Crank engine over a few times with VC resting on to blow out excess oil that went into GP holes. Thread fitting in carefully (Harbor Freight fitting cross threads easily) crank it over with gauge hooked up, probably 5-6 revolutions. Take the reading, release the pressure, repeat on next cylinder. You'll probably have to put your batteries on the charger while this is going on. You have to have good RPMs for an accurate read. We got between 340-380 on a 7.3 with 362k last week, and around 400 on another one with 80k miles. On the high miles engine, I had to pour a tablespoon or two if oil down the GP hole, but the engine had sat a while, low on oil with several oil leaks. They read 0 at first, til I poured the oil in, blew it back out and then took the readings. Good luck.
Thread Starter
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Senior User
Joined: Dec 2012
Posts: 373
Likes: 0
From: Arlington, Texas
Disconnect 42 pin connecter, pull VC. Pull all GP's. Crank engine over a few times with VC resting on to blow out excess oil that went into GP holes. Thread fitting in carefully (Harbor Freight fitting cross threads easily) crank it over with gauge hooked up, probably 5-6 revolutions. Take the reading, release the pressure, repeat on next cylinder. You'll probably have to put your batteries on the charger while this is going on. You have to have good RPMs for an accurate read. We got between 340-380 on a 7.3 with 362k last week, and around 400 on another one with 80k miles. On the high miles engine, I had to pour a tablespoon or two if oil down the GP hole, but the engine had sat a while, low on oil with several oil leaks. They read 0 at first, til I poured the oil in, blew it back out and then took the readings. Good luck.
Lead Driver
Joined: Jun 2013
Posts: 5,647
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From: north of Minneapolis, MN
IMO...just best to jump the solenoid.
Lead Driver
Joined: Jun 2004
Posts: 6,303
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From: Amarillo, TEXAS!
The one in the HF kit doesn't fit, but Mityvac has an adaptor that fits in the glow plug port. However the quick connect fitting doesn't work with the compression gauge from HF. I took my Mityvac adapter to a hydraulic shop and had them cut off the male quick connect fitting and put a 1/8" NPT fitting on it instead. Then I just removed the schrader valve from one of the extra fittings in the HF kit and threaded it in. It was less than $5.00 to have the fitting changed. The Mityvac part number for their adapter is MVA5605.
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Senior User
Joined: Dec 2012
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From: Arlington, Texas
Yeah, I read up on the HF this morning before I headed out and just decided to get a good kit from NAPA in case someone around here might need a test in the future. That one needs an adapter too!!! Just going to cruise junk yard row tomorrow and find the snap on or Mac tool truck to snag the adapter. I hope all of this gives me good karma to the engine compression gods..
Some of the pins in my 42 pin connector look corroded a little bit. Is that normal?? Also my turbo blade is NASTY!! Wanna see some pictures ?
Some of the pins in my 42 pin connector look corroded a little bit. Is that normal?? Also my turbo blade is NASTY!! Wanna see some pictures ?
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Lead Driver
Joined: Jun 2004
Posts: 6,303
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From: Amarillo, TEXAS!
Also my turbo blade is NASTY!! Wanna see some pictures ?
Lead Driver
Joined: Jun 2004
Posts: 6,303
Likes: 576
From: Amarillo, TEXAS!
Neither of those look too bad to me. My connector didn't have quite that much corrosion, but it's a Southern truck (FL and TX). But on my old compressor wheel it isn't even obvious that it ever had corners! The early '99 filter housings were pure trash.
EDIT: I see you're in Arlington. How has the weather been down there while I've been stuck here in CT?
EDIT: I see you're in Arlington. How has the weather been down there while I've been stuck here in CT?
Thread Starter
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Senior User
Joined: Dec 2012
Posts: 373
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From: Arlington, Texas
Neither of those look too bad to me. My connector didn't have quite that much corrosion, but it's a Southern truck (FL and TX). But on my old compressor wheel it isn't even obvious that it ever had corners! The early '99 filter housings were pure trash.
EDIT: I see you're in Arlington. How has the weather been down there while I've been stuck here in CT?
EDIT: I see you're in Arlington. How has the weather been down there while I've been stuck here in CT?
Thread Starter
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Senior User
Joined: Dec 2012
Posts: 373
Likes: 0
From: Arlington, Texas
Neither of those look too bad to me. My connector didn't have quite that much corrosion, but it's a Southern truck (FL and TX). But on my old compressor wheel it isn't even obvious that it ever had corners! The early '99 filter housings were pure trash.
EDIT: I see you're in Arlington. How has the weather been down there while I've been stuck here in CT?
EDIT: I see you're in Arlington. How has the weather been down there while I've been stuck here in CT?