Trouble cranking when warm!

n0nka · #1 02-06-2007, 11:38 PM

Yeah, I know this one sounds backwards, but it's my daily driver and I'm afraid I'll find myself walking to work one day soon if I don't figure it out. First thing in the morning, the engine cranks fine. (even if I have to start it 2 or 3 times. It's been fairly cold out here in S. Illinois lately.) If the engine's warmed up good, and I park it for a short period (10 min. - 3 hours?) it barely turns over enough to start. Sometimes it sounds like I barely get in one revolution. Just when it seems the starter has given up, and comes to a complete stop, the engine comes to life, and runs fine. It's a 77 CJ-7 with late 60's or early 70's GM 350 (Yes Jim, it's got the Quadratrac transfer case.)

Any ideas? I'm pretty stumped. I only have two theories, and both are quite a stretch.

WAG 1) The engine is running way too hot, and nearly seizes up if it hasn't had time to cool back down. (factory temp gauge read hot, $10 WalMart replacement reads cold, I haven't had the Jeep long enough to have a good feel for what's normal, but the radiator gets plenty warm, so I know the water's flowing.)

WAG 2) I know the timing chain has better than 1/2 inch of play in it. I don't think I'm hearing a rod slap, but when the engine is warm I do have some sort of knock when its under a load. Could the timing chain be stretched so far that it's firing the piston while it's still on the up-stroke?

Thanks, Mark
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JeepDawg · #2 02-06-2007, 11:49 PM

Your timing it too far advanced. This will cause to both run hot and have trouble starting. What is happening is that the starter is fighting the early ignition....

That knocking you are hearing might be pre-ignition.

Do this quick test...with it hot, remove the wire from the coil...then try to turn it over....it if cranks fine...then timing is your problem.

If this is the case then take the time to learn about your timing and how to set it properly....

Jim_Lou · #3 02-07-2007, 06:40 AM

My WAG1 is a poor battery cable connection.

WAG2 is a funky solenoid.

If you can get it to the shop we can figure it out pretty quickly. I should have some play time this weekend.

WILL · #4 02-07-2007, 12:09 PM

I vote for bad wiring connection or famous GM hot start solenoid problem.

n0nka · #5 02-07-2007, 10:00 PM

Thanks for the great advice guys!
I'll bet on the timing problem. I've had bad solenoids and wiring before, and although they fit my description above (and trust me, there's plenty of potential for bad wiring under this hood and dash), they don't sound like what I'm observing right now.

[ QUOTE ]
Your timing it too far advanced. This will cause to both run hot and have trouble starting. What is happening is that the starter is fighting the early ignition....

That knocking you are hearing might be pre-ignition.

[/ QUOTE ]

As a matter of fact, when I really step on the gas, sometimes the pinging lets up, or goes away till the engine catches up. Does "vacuum advance" lay off the timing a bit if you really mash the throttle?

I'll try to check/adjust the timing this weekend. The timing chain will have to wait till the weather is better. I'm looking forward to replacing ALL the wiring, but that's a job for this spring or summer.

Thanks again for the advice guys. I'll let you know this weekend how it went.

V/R, Mark

Jim_Lou · #6 02-08-2007, 07:14 AM

[ QUOTE ]
when I really step on the gas, sometimes the pinging lets up, or goes away till the engine catches up. Does "vacuum advance" lay off the timing a bit if you really mash the throttle?

[/ QUOTE ]

The vacuum advance is gone away by 3/4 throttle or so. Wide open the mixture gets a lot richer which also reduces the tendency to ping.

n0nka · #7 02-08-2007, 08:34 AM

That's good to know. I was worried I might have a weak piston rod. But that didn't explain the knock going away. I'll bet if I leave it this way for too long I Would end with a bad rod, or who knows what else. I'm going to hit the sack for a little while. I just spent 14 hours straight working on a training package for my troops.

Thanks, Mark

JeepDawg · #8 02-08-2007, 10:24 AM

Have you tried to crank it with the coil unplugged and the engine hot?

n0nka · #9 02-08-2007, 01:24 PM

Not yet. I'm off today. My daily commute is about 2 miles. So it barely has a chance to get warm.

n0nka · #10 02-20-2007, 05:50 PM

Sorry it took me so long to get back on-line with an update: Thanks for all the great advice guys. you were all right on target.

[ QUOTE ]
I'll bet on the timing problem. I've had bad solenoids and wiring before, and although they fit my description above (and trust me, there's plenty of potential for bad wiring under this hood and dash), they don't sound like what I'm observing right now.

[/ QUOTE ]

As it turns out, I did have a bad battery, and a bad alternator. (Is crow better BBQ or smoked??)

[ QUOTE ]
Have you tried to crank it with the coil unplugged and the engine hot?

[/ QUOTE ]

I didn't disconnect the coil, but I did have trouble cranking it even with the ignition turned off.

[ QUOTE ]
Your timing it too far advanced. This will cause to both run hot and have trouble starting. What is happening is that the starter is fighting the early ignition....

That knocking you are hearing might be pre-ignition.

[/ QUOTE ]

I got the timing light out Wednesday and the mark was off the chart. Way up on top of the harmonic balancer. Pulling the vacuum advance hose brought it right down to about 3 or 4 degrees, so I didn't adjust anything. I just capped the port on the carb and left the hose off. No more pre-ignition when the engine is warmed up either. It sounds much better on the highway. Side effect; Idles like a Harley.

Should I be concerned about leaving the vacuum advance off for now?

thanks, Mark