No compression??????

[JMF350]

Here goes.... I've got a '91 F SuperDuty with a 7.3. On cooler mornings (50-60 degrees), when I go to start it, sometimes it will hit, but not start. I can do a quick either shot, it'll hit, start for a half second, die. Now the messed up part.... if I go to restart it, it will crank over like a gasser with all the plugs out (but without the swoosh sound). Let it sit for 5-10 minutes, it has compression again. Do it all over again. Again, if it hits, but doen't start, it cranks over with no compression. If I plug it in over-night, it will start OK, but if I don't let it idle for 5-10 minutes, try to give it any fuel at all, it developes a miss and may die. If it dies.... you guessed it, no comp. Another thing, if I let it get heat in it, 10 mins. or so.... it runs and pulls STRONG!!! Runs great. Also, on the no compression cranking.... if I get mad and just crank it like this for a while (30-60 seconds), it will blow the oil filter off (well, the o-ring anyway). Any ideas

 

[Zookie400]

im running out the door so i cant stew on this one now. ill ponder it on my drive to work, this sounds very funny with oil filters blowing out and whatnot.

 

[trackspeeder]

The hard starting is an air leak in the fuel system. Could be the return lines or the fuel filter. Or both.

Now the blowing oil filter? You got me stumped.

 

[Dogman]

Whats your mileage? Pull your oil filler cap and see if your getting any kind of compression out the oil filer. If you do you my have bad O rings on the injectors, broken compression ring on the piston or pistons, motor slap wore-out. I would start with the injectors O-ring there cheep like 11 bucks or so for the O-rings. Sounds like a blow-by problem.

 

[JMF350]

The filter thing is weird as heck.... cranking, it will blow off, running it won't Pulled the filler cap.... not blowing air out. We though of a stuck piston ring, or a valve hanging open, or a head gasket seap... thing is, what are the odds on a hit and miss, that it doesn't start, and all 8 cylinders have the exact same thing happening. Let it sit 20 seconds, try to crank, it WILL have compression on a cylinder or two. The longer it sits before trying again, the more cylinders it will pick up.
I should have said more about the actuall start-up/ giving it throttle and it dies scenario. If it starts, and I try to take it to 2000 or more, it will start missing and die (with a no comp. crank to follow). Now if I just rev it to 1500-1800 rpm's, and can let off of it soon enough, it will still develope a miss (pretty sure the dead cylinders are due to low to no compression), but not die, and eventually, it will smooth back out. It is truely one of those "you have to see and hear it to beleive it" things.

 

[Dogman]

What oil are you running?

Another thing, if I let it get heat in it, 10 mins. or so.... it runs and pulls STRONG!!! Runs great.

I'm thinking oil may be the problem. If the oil is to thick when cool, the oil pump can have a hard time moving it and it can have some adverse problems come around. Like injectors not firing, blowing hoses and filters and so on.

I would look at putting your winter blend oil in "If you have not done it" and see what happens.

 

[JMF350]

15-40 Rotella. It could be an oiling issue, but blowing off at 180-300 cranking rpm's and not 600 rpm's at idle? The customer had to have the truck back, so I told him I'd do some research. Thanks for the input guys. It figures that this isn't a common ordeal, as these are the trucks I usually get stuck with.