Checking engine compression

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Nov 3, 2002 | 12:17 PM

fiend

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Checking engine compression

I'm looking at buying a truck, and I would like to see what kind of condition the engine is. I've been told to check the compression, so i'll take it to a mechanic to do it. But how do I know what's a good or bad compression?

Also what to look for to check if the tranny is bad? The E4OD is in there.

Nov 3, 2002 | 02:05 PM

Ford_Six

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From: The Big, Oregon

Checking engine compression

The compression should be 130+, and all the cylinders should be within 85% of each other to be considered healthy. As far as the tranny, check the condition of the fluid. If it is nice and red, and smells good, it is good. If it is brown and burnt smelling, it is bad. In between is a judgement call, but if it is red and burnt smelling, they are trying to pull a fast one on you. The tranny is really burnt out, and they JUST changed the fluid in it.

Jared

Nov 3, 2002 | 03:07 PM

fiend

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Checking engine compression

>The compression should be 130+, and all the cylinders should
>be within 85% of each other to be considered healthy.

Is that the same for a 302? What do you mean by be within 85% of eachother?

Nov 3, 2002 | 03:49 PM

Ford_Six

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From: The Big, Oregon

Checking engine compression

That's the same for just about any modern engine. By within 85%, I mean that the lowest pressure should be no less than 85% of the highest pressure. If the highest were 150psi, the lowest should be no less than 127. Be especially careful to get readings from the #'s 7&8, as these engines sometimes had a crossfire problem on these cylinders.

Jared

Nov 3, 2002 | 09:30 PM

sand man

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Checking engine compression

the amount of compression is not as important as the fact that they are all about the same compression i have been told by quite a few people that if all the cylinders are within 10 PSI of each other then you have a good engine, as an engine gets older it is quite common for the compression to go down but for a better chance at a smooth idle make sure all cylinders are within 10PSI. good luck, hope you get a good one

Nov 4, 2002 | 09:31 AM

jimandmandy

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From: Running Springs CA

Checking engine compression

Ford lists 75% as the wear limit for compression, they do not give a number in psi. Clean, red fluid is not enough to tell if an E4OD is any good. If the truck has over 100,000 miles and there is no record of a transmission rebuild, be aware that you are probably looking at $1200-$2000 within the next 20,000 miles.

Jim

Nov 4, 2002 | 05:51 PM

MustangGT221

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From: Topsfield, MA

Checking engine compression

https://www.ford-trucks.com/dcforum/DCForumID18/1445.html

Theres all you need.

Primary rig is Green Thunder:
95' F-150 XLT 4x4, 302, 5 spd, MSD 6A, Flowmaster Exhaust, Sunroof, Clear corners w/ Diamond headlights, CD player with 2 10" subs and some 32" BFG Muds