Well here's a little update. Got the compression testor and they were all a little low but I think this is do to a starting problem. The motor cranks over extremely slow, i finally realized how bad it actually was when I counted the strokes for the compression test. All of the pulleys are free, it has a "newer" used starting motor, and I cleaned the grounds, still too slow. I am going to disassemble the spare motor and see what I can do with it, I've worked on quite a few electric motors.

 

It dosn't mater how slow the motor is turning to check the comp. 3 or 4 complete turns is enough. Any thing over 100psi is good. You said your sure your getting spark or I would suggest the electronic dist. pick up in the dist. Very common on that motor also crank sensor but only if no spark. Check for out of time. Take out any spark plug, have someone tap starter, put your finger over the plug hole and when you feel the compression stroke stop turning instantly. The rotor under the dist. cap should point to that wire.

 

Well, my theory was that velocity would force more air into the compression tester. Even if I was wrong, it still is turning way to slow(probably 1 revolution of the crank every 1.5-2 second) which can only hinder the starting situation. Like you mentioned, the next thing I'm looking into is the timing.

 

The stroke length is the same fast or slow.Speed dosn't increase the volume in the cyl. If its spinning so slow and your getting fuel to the injectors the plugs should soaked,and you may have washed down the cylinders with fuel which will lower compression do to lack of oil around the piston rings.Check your oil to see if you have gas in it. It should be easy to smell. if so change the oil and filter. You should find out why its turning so slow. Check ground from battery to eng. block.

 

Yeah, actually it does. Cranking speed effects the amount of air sucked into the cylinder by creating more vacuum at the intake. A slow turning engine will not create as much of a negative pressure differntial, hence less air being packed into the cylinder. A simple test, place your hand over the throttle body and compare the "suction" you feel both fast and slow. To get a decent (and repeatable) compression test, the rig needs a well charged battery and decent starter.

If you think about it, would expect the engine to start if it was turning that slow?

BTW, what were the cylinder compression readings?

Cheers.

 

Yes the motor would start if it was turning slow as long as everthing was working, spark and fuel and it didn't stop turning. Speed of crank will not stop it from starting. It's not a lawn mower with a mag.were you need to create the spark by pulling it fast. It has electronic ign. the spark will be there no matter how slow it turns . Just need spark and fuel and you got fire in the hole. Have you never had an almost dead battery and just before it almost stops cranking have it start?. Im sure you have. Only if it was it flooded would a faster spin help. I"m not saying that it shouldn't be spinning faster but it should still start.

 

Very, very seldom, and that was in an engine where the compression was known to be good... which is an "unknown" in this case...

The other problem with a low battery and electronic ignition, is low supply voltage. Below certain voltage thresholds, which vary from device to device, coils refuse to fire, sensors can't maintain constant reference voltages, etc. So, it's just another variable to add to the problem.

Personally, if I were 250Cherokee, I'd get my battery and starter working as they should and do the tests again.

Cheers.

 

The readings were inbetween 90-110 with it turning that slow.

I appreciate the input but you guys are acting like I'm not doing anything about the starting issue. Like I stated, I have cleaned the grounds, tried 3 different batteries, put a different starter motor in, and ensured that all of the pulleys were not binding. At this point I have the spare starter motor disassembled and am cleaning it and checking on the brushes.

Hopefully I can get it turning over faster and retry the compression test for the hell of it. But still, shouldn't it run at 90-110psi per cylinder?

 

have you starter tested for amp draw
the new used one may be no good ether

if it bad cleaning it wont help

 

Well I put the the cleaned starter motor in and installed new plugs and what do you know, it fired right it. Note to self: don't be cheap next time, $10 of plugs could mean the difference between running and not running.

On a side note, it has a blown steering line, slight header leak, and is leaking antifreeze from a flange but that's all minor besides the exhaust leak.