low compression?

[GREASE FIRE]

right now my truck will only start if it is warmed up, the block heater was plugged in, or i use starting fluid. If it sits overnight without the block heater, even in warm weather, it will not start.
Less than a thousand miles ago it started right up with no problems....
but it seems now that low compression could be the problem since i have checked everything else out.

has anyone ever used one of those harbor freight compression testers? are they "good enough" for our purposes? if so, what kind of numbers should be i be looking for?
the engine only has 170K but i have no idea what the previous owners did with it - perhaps it got a lot of abuse.

thanks,
paul

 

[gatorman21218]

What did you all check out? Glow plugs and relay? glow plugs can go bad after one start (especially the autolite/champion brand) what about the starting system? Batteries, starter and the cables. Really look over those cables. Is the motor spining really fast when cranking? if not i suspect a starter/electric issue.

As for compression the book says "pressures are considered normal if the lowest reading cylinder is within 75 percent of the highest"

then the chart says highest - lowest: (260 - 195) up to (440 - 330)

 

[icanfixall]

Several members have tried the harbor freight items with very poor results. Most couldn't continue to work for the 8 cylinders or the fittings that go in the glow plug holes was ruined. They are of a very poor quality tool at best.Usually anything above 250 will start the motor. If you are in the 350 and above range then you have a good motor. My rebuilt motor has 530 lbs on all cylinders but you can read below of all the work I did. It pays off too. If you try to do a compression test don't squirt any oil in the cylinders like a gasser. These motors burn oil for fuel and... We have an oil cooling jet showering the bottom of the piston when these motors run or turn over. They act as a cooling of the piston... Thats a good thing...

 

[milightfo]

kinda off subject but i used a harbor freight volt meter on my truck a while back it showed 19 volts charging,long story short it drove me crazy trying to find out why it was so high and come to find out it was the cheap HARBOR FREIGHT meter....you get what you pay for,try a different guage

 

[f-two-fiddy]

Ditto on the HF Comp tester. JUNK!

 

[rhkcommander]

i bougght one online that seems decent but it has a 90° angle at the end that goes to the glow plug hole

 

[Black dawg]

have you checked voltage to the plugs?

 

[dyoung14]

just because it wont crank even if its hot outside when its set all night, most idis wont crank few will so dont worry about it too much, your glow plugs aint working