94ford5liter

I've checked practically everything on my motor to see what's wrong with it. Everything pretty much checks out fine, so i've narrowed it down to an internal motor problem or a computer problem. The motor has 140k so I wouldn't be suprised if it was bad. To compression test it you take all the spark plugs out and put the tester in each cylinder correct after firing it for 4 seconds? I was also wondering what should the compression of each cylinder be around?

BADNOTCH

I am not sure how much compression you should have, but when you are running the test make sure your lowest cylinder to highest compression readings are no more than 20% apart. If it is more than 20% that is probably the bad cylinder.

94ford5liter

could a bad timing chain also cause a big power loss, its never been replaced and it has 140, im guessing that could be bad..

luckythirteen13

with that many miles on it, change the chain. a new chain wont help much but it will making timing more reliable.
as for the compression test. you want them to be 10% variance at the most for a performance engine. 20% is fine on a stock car but if your going for performance you want 10%. and for the number, 140-150 is really good for how many miles you have on it. dont be dissapointed if you get 120psi. the main thing is that all are within 10%

94ford5liter

could it be a computer problem then if the timing chain doesnt affect it much? I bought a gtech and it did 0-60 in 8.9 seconds so something is definitely ****ed up lol...

94ford5liter

ran the compression test, here are the results:
4th back driver side - 125
3rd - 130
2nd - 134
1st = 131

4th back passenger side - 130
3rd back - 126
2nd back - 131
1st - 125

Quik

sell me the car for a good price. ill take real good care of it. i promise

tinman

With that kind of readings you have NO problems.........

white93 GT

yea those are great numbers on my 120k mile motor all are within 90 to 100 psi......it sucks.....but i did run a 15.5 up here in colorado so that around a 14.5 at sea level.

Greybeard

A compression test will give you some basic info, and at the same time, can help in troubleshooting. The best test is a cylinder bleeddown. With some inexpensive valves, a Harbor freight HVLP regulator and guage assy and some plumbing fittings you can adapt any compression tester that uses standard airline quick disconnect fittings into a very useful bleed down tester. I built mine in an afternoon including the trip to Lowes and Harbor Freight for under $30 (I think my compression tester was $24.95 at Advance..) I will gen up a drawing and post it when I get a chance.

Using only the compression tester, the only reliable compression figure is warm cranking at WOT. After the motor is warmed up, disconnect the ignition module connector, I always connect a battery charger so that the last cylinder gets as good a turn as number 1.

Open the throttle all the way to the stop (I use a length of padded 2x4 between the seat and the throttle pedal. The WOT switch shuts off fuel in the start-crank mode. Crank for 4 seconds, record the reading and reinstall the plug then go on to the next cylinder. I always reinstall the plugs snug as I go along so that the compression is an accurate picture of what happens at a warm start-up. When all are complete, wait 5 minutes for the starter to cool (or pour a quart of chilled water on it to speed the process...) Then using a standard squirt can, repeat the process and note the readings to see if the loss is in the rings or valves. Two squirts of oil should improve the compression by a few pounds up to 10 on a good cylinder. If you see a 20-30 pound or more rise on more than a couple cylinders, try a can of Seafoam or other upper cylinder cleaner to see if the rings are coked up and simply not sealing because of the carbon buildup. I just had this problem in my 97 Nissan PU. Every oil control ring was gummed up and there was a ton of carbon in the ring lands that caused poor ring seating and oil consumption. I used a can of Seafoam (I heard about it from an NMCA racer buddy who had used it on his tow vehicle; I'm not endorsing it beyond my own experience but it worked for me )

If any adjacent cylinders are low, I'll follow up by pulling both plugs and checking compression while putting a finger on the adjacent cylinder to feel for blowby from a bad head gasket.

If all cylinders are within 10% but under 130 or so, or if a couple are out of the 10% range, I would do a bleed down test just to find out what's wrong before taking it apart.

FOR ADVANCED CALCULATIONS, TRY: (NEED TO SUBSCRIBE, BUT IT;S A GREAT TECH SITE)
http://www.smokemup.com/auto_math/pressure_ratio2.php