1977 CJ5 starts, dies after 10sec, wont start for a half hour

[Scott1S]

Hello all. My dad left me his jeep, and I'm trying to get it working just well enough so that someone who can really appreciate it can take it and drive it all the way to their house. He used to love this old thing, taking it prospecting out in the desert, but he made all his own modifications and its quite the kludge now.

It was running ok at first, except would overheat after 8-10miles in a phoenix summer. I had a shop look at it, and they said that the electric fan that was added to help cool the radiator wasnt working, and they didnt want to even attempt messing with the "custom" wiring job on this thing. I found that the fan was unplugged, optimistically plugged it back in, and now the jeep starts, runs cleanly for about 10 seconds, then stops. It doesnt sputter or slowly die, it just stops. And it wont restart until I've let the engine sit like 30 minutes. I unplugged the electric radiator fan right away, but it's never come back. I've checked fuses and wiggles wires, nothing. I should also say that my dad added a 2nd fuel pump that you manually start and get up to 3psi before turning the engine over. In the past i've been able to leave that on and it all works, so I dont think this is a fuel pump problem. The pressure is still high when the engine cranks without starting.

I saw a related forum post here:
http://www.jeep-cj.com/forums/f2/engine-starts-then-dies-11008/
But what's different for me is that I have to wait a while before the engine will start, and also I'm pretty sure I can eliminate the fuel pump as the problem.

People have mentioned ground problems and relays. If that might be the problem, can anyone suggest which relay I should start with? Or a very simple test, like wiring the ignition coil straight to the battery?

Thanks for any help, and I apologize in advance that my knowledge base here is pretty low.
-Scott

 

[Torxhead]

So have you checked for any spark at the plugs after it dies out, this would confirm an ignition problem, which could be a coil, ignition control module, or pick up coil. I don't think you should leave out fuel as a possible issue yet.

 

[Saddle Tramp]

What Torx said. Is it an AMC V8? With 2 fuel pumps do you still have a return fuel line to the tank? Ignition module? They will act like that but that comes under checking for spark.

 

[scott2s]

Thanks Torx and Saddle!

[I'm the OP, but I havent been able to log in for the last few days, and the email reset doesnt work either. I couldnt figure out how to contact the admin, so I finally gave up and made a new user acct!]

Torx, I checked for spark (plug out and grounded to block), and I'm pretty sure the spark is strong at first and then gets either weak or hardly noticable, so I think you are right. Of the 3 spark components you mentioned, can you suggest a test that can help me narrow down on the problem? Like powering the ignition coil straight from the battery? Does the fact that it takes ~half hour to recover shed any light on the likely culprit?

Saddle, there is a sticker under the hood that says AMC engine AMC 304 . I'm not sure about how the return lines work on the fuel pumps yet, but since it worked before I messed with the electrical system I'm guessing we can put that lower on the list.

Thanks! -Scott

 

[Torxhead]

As I recall, you should get around 1.35 ohms between the positive and negative posts on the coil when it is disconnected from the vehicle, and while running it should not get hot. The ignition control module should not get hot to the touch either. The '77 and older ignition systems I am not too familiar with and advise guys to dump them in favor of a newer system. With a carbed engine the oem style fuel pump is all that you need and it should put out around 4 or so p.s.i. Sometimes guys will add an electric pump to fill a carb that has dried out after sitting awhile. A big issue here would be to determine if the problem is fuel or ignition. If it is running out of gas it would empty the carb float bowl also.

 

[Saddle Tramp]

Stock, there is the main line of course that runs from the tank pickup to the mechanical pump at the side of the block. From there the line leaves the pump and goes to the fuel filter in an area close to the front of the carburetor. The filter has one port in and two ports out. Install the filter so that outlet port closest to the edge of the filter is up. The lower outlet goes to the carburetor while the upper goes to the return line. The return line takes any extra fuel or air in the line back to the fuel tank and without it the motor may not run properly.

I would also check the coil.

 

[Lumpy Grits]

How hot does the coil get? Can you hold your hand on it?
Also-Loosen the gas cap and see what that does to to prevent vacuum lock in the gas tank.
I would also change the fuel filter to start with.
How much gas and how old is it in the tank?
LG

 

[ksouthw80]

I agree coil. saw this on a car we restored and sat , being started here and there. cheap start anyway.

 

[ksouthw80]

moisture in the distributer along with wires would be my next venture...

 

[Turbogus]

Not that I'm anyone's expert but in the FSM there's a procedure for checking from the battery, starter relay, coil, Ignition Module to plugs. As I've recently gone through this myself I'm leaning towards coil.
That being said, with any new aquistition I always count on changing all filters, oil, coolant and spark plugs. What puzzles me is why there are two fuel pumps on your rig, unless it's a fire-breathing 401 or a Chevy Rat motor in there.