Compression test procedure

psdguy95 · Sep 22, 2011

I would like to do a compression test on my truck but i have some questions.

1. Should i remove all gp's?
2. Do i need a special type of tester or will any type work?
3. How many cranks of the motor should i do?
4. What specs should i be within?
5. How high should the numbers on my compression gauge read?

onebad7.3 · Sep 22, 2011

psdguy95 said:
I would like to do a compression test on my truck but i have some questions.

1. Should i remove all gp's?
2. Do i need a special type of tester or will any type work?
3. How many cranks of the motor should i do?
4. What specs should i be within?
5. How high should the numbers on my compression gauge read?

1. Yes
2. The thread is M10x1.0
3. I crank it 5-6 times to get a good reading.
4. You should be around the 400 psi mark. If your anywhere from 365ish and above you'll be ok. As long as the lowest reading is within 75% of the highest reading.
5. As long as the gauge goes to 500 you'll be fine.

When you pull the glow plugs out, don't let oil run into the cylinder. It will make your numbers a tad higher than what they are. I'd used a little compressed air to blow the oil away from the glow plug.
I have another truck with jumper cables on the truck i'm testing, so the batteries won't get run down. Cranking fast at first and then slower and slower can give you lower readings.

TrailerHauler · Sep 22, 2011

onebad7.3 said:
1. Yes
2. The thread is M10x1.0
3. I crank it 5-6 times to get a good reading.
4. You should be around the 400 psi mark. If your anywhere from 365ish and above you'll be ok. As long as the lowest reading is within 75% of the highest reading.
5. As long as the gauge goes to 500 you'll be fine.

When you pull the glow plugs out, don't let oil run into the cylinder. It will make your numbers a tad higher than what they are. I'd used a little compressed air to blow the oil away from the glow plug.
I have another truck with jumper cables on the truck i'm testing, so the batteries won't get run down. Cranking fast at first and then slower and slower can give you lower readings.

Pretty spot on, that's how I've done all mine.

psdguy95 · Sep 22, 2011

Thanks guys. Ill get the battery charger out. And ill post up my numbers.

MossBack · Sep 22, 2011

75% seems a Tad high for differential pressure. I thought it was 15-25% ?

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psdguy95 · Sep 22, 2011

Well i just found out all 3 of my compression gauges only go up to 300. :doh: Ill see if i can find one at school tomorrow.

onebad7.3 · Sep 22, 2011

Yeah I screwed my percent up:cursing:

Just post the numbers and we will tell you if its ok

MossBack · Sep 22, 2011

onebad7.3 said:
Yeah I screwed my percent up:cursing:

Just post the numbers and we will tell you if its ok

Ur cool bro I was curious as I want to test mine too. I just about dropped 200 on the snap on diesel compression tester. It is a combo kit for like 10 different Diesel engines. But ill just go the harbor frieght route I guess.

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psdguy95 · Sep 22, 2011

97F250psd said:
Ur cool bro I was curious as I want to test mine too. I just about dropped 200 on the snap on diesel compression tester. It is a combo kit for like 10 different Diesel engines. But ill just go the harbor frieght route I guess.

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How much is the harbor frieght one?

MossBack · Sep 22, 2011

psdguy95 said:
How much is the harbor frieght one?

40-50 the problem is making the connector to thread into the gp hole. U have to be able to wiggle around vavle springs. Snap on kit has a flexible hose, while some people Fab there own. All in all I bet the snappy kit is worth it for safety and reliability

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psdguy95 · Sep 22, 2011

True true. Do i have to disable the injectors when i do this too? Or can they stay plugged in?

psdguy95 · Sep 23, 2011

I was searching around on harbor freights website and found some stuff. This kit is specifically designed for the 6.9 and 7.3 engines.

http://www.harborfreight.com/14-piece-diesel-compression-tester-set-46800.html

They also have a 12 piece kit that's cheaper but this one seems a bit better.

Bushwakd · Sep 25, 2011

psdguy95 said:
True true. Do i have to disable the injectors when i do this too? Or can they stay plugged in?

When you disconnect the main wiring harness to the under valve cover harness does that not interrupt any power signal going to any injector. I believe it does. But any ways since the glow plugs are unplugged and removed just unplug the injectors and remove the UVCH and gasket and get it out of the way.

psdguy95 · Sep 25, 2011

Wow. I realize how stupid of a question that was now. :doh:

Tom S · Sep 25, 2011

It takes an adapter that has a flex section in the center.

MossBack · Sep 26, 2011

Adapter

My snap on guy has a different brand that is a complete kit with one of these and a few others for most diesel engines. IIRC it was like 250 ill find out thursday and if it is that close in price to HF ill buy it.