Riddle Of A Problem A 1979 Cj5 Help!

I own a really nice CJ5 that has taken me years to restore with original parts, added a lift kit, fat tires, killer stereo you get it.

We run it around Seattle in the summer with my project managers and we go to Mexi Friday's and have a good time and it's never given me a problem until I took it on a road trip.

Seattle is bad (wont get into politics) so I decided in August of 21 to take a trip to Montana to formulate an exit strategy. I noticed on this trip, starting in Idaho, that when the day wore on, and it got hot, a phenomenon occurred that has cost me 10K with no end in sight to solve.

IT ACTS LIKE ITS OUT OF GAS...blub blub...….blub.....blah dies.

Did the usual checks for gas, oil, etc. not the issue. I noticed that when I left it sit for an hour or two the jeep will start right up, run great but when it gets hot or starts to get hot blub...blub....blub...blah dies.

The whole second part of the trip home was drive 2 hours, sit for 1 hour. Horrible stranded on the side of the road in 90 degrees no top or AC.....I noticed that the longer I let it sit, the longer it would drive before dying.

I also noticed that when I made it gas stations and removed the locking gas cap, there was a "whoosh" sound as if it was under pressure, so on the way back I decided to leave the cap off and to my astonishment it drove much better, but eventually it would die again, but it had more power and response when the cap was off.

On my way to the cabin (I know I should of been thinking) I had to 4x4 up this road and I accidently broke some springs so now I am limping back to Seattle literally 3 hours, then 1 to cool, etc, etc. Sometimes it would not start unless I left it for three hours it was so bad.

So....I call all over Seattle and cannot find a mechanic that knows/wants to take this on, so I take it to the dealer thinking they would certainly know, and they tell me "we don't work on American Made Jeeps", so I find an old school mechanic (or so I thought) who said he would fix the springs and diagnose the dying issue and it was there that I began to pay. The ship had my jeep for months before they called me saying it was done claiming difficulty of parts.

First invoice was $7700.00 (I did get new tires and springs) so 3K of it went to the tires and springs, with 1500 of it going to wheel bearings, and the balance going toward the fix. I paid the invoice in full, it is a 79 and I figured I needed the work anyway, thinking my Jeep was fixed.

Here is what is what was on the invoice that I paid last year:


Symptoms and Diagnostic Trouble Codes

Customer states the engine dies after filling the gas tank.
Possibly put on a smaller carburetor.
Engine seems to run better fuel cap off.
Fuel gauge is inop.
Vehicle seems to wander going down the road, check suspension.
Engine has oil leak.
Check for tune up parts.

Work Description:

Checked and found there is a fuel leak coming from the top of the fuel tank, removed the fuel tank and found the fuel level
sender is cracked and the hard fuel lines are not flared at the ends where the soft fuel lines connect onto them, recommend
replacing the fuel level sender, fuel hoses and flaring the fuel lines.
Driver side front leaf spring is broken.
Need to start with replacing the valve cover gasket for oil leaks.
There is oil in the distributor.
Front wheel bearings are loose and are very rusty, and front axle shaft universal joints have play in them.
Brake fluid has 300ppm of copper content in it.
Rear marker light is out.
Passenger high beam is out.
Reverse lights inop.
Tires Are cracked.

Fixed:

Replaced the fuel level sending unit, fuel hoses, and found the breather hose was plugged off, replaced the plug with a
breather vent.
Replaced the front wheel bearings and races, and the universal joints on the front axle shafts, spindle bearing and seals,
replaced all the gaskets on the manual locking hubs.
Replaced the distributor, checked spark plugs and checked good.
Flushed the brake fluid.
Replaced the tires.
Removed the valve covers, found them to be a little bent at the sealing surfaces, straighten them out, and reinstalled with
new gaskets.
Cleaned all oil residue, off of engine ran engine and found the oil pan gasket is leaking.

I get the Jeep back July of last year, in the garage it goes it was raining, got busy with work (covid killed us) and soon the rain/snow were back and it sat until two months ago March 1, 23 when it was a sunny day and I could not contain myself and I took the Jeep out (has no top) and drove around. Guess what? I am at a stoplight, take a sharp turn to the right gun it, and it dies same symptoms. Won't start.

Then it starts clicking. Alternator. So I take it back, they give me the song and dance about it being a 79 "and one should expect issues" and promise me they will fix it. They replaced the alternator, and then they called me the other day after replacing the ignition as well and told me that they leave it running for 4 hours, and it dies and they can't start it. Same thing IT ACTS LIKE ITS OUT OF GAS...blub blub...….blub.....blah dies.

What could be causing this??????

Please help I love my Jeep and would hate not being able to drive this thing but I am besides myself trying to figure out what's wrong. I do have a larger carb, but not sure how that ties into it but that's just me guessing.

 

I’m by no means an expert on this stuff, but my first thought would be that, once the engine gets up to operating temp, the heat slowly creeps up the intake and carburetor and eventually causes the fuel to boil in the carb bowl. If you’re currently running a standard/thin gasket between the carb and intake it would be very cheap and easy to try a thicker gasket or a phenolic spacer underneath the carb.

Also, the trip where you first noticed this contains some higher elevation driving. Fuel boils at a lower temperature at higher elevation, again pointing to a possible fuel boiling problem.

when it dies, if you pop the hood and listen closely you may even be able to hear the fuel boiling/percolating

 

@boopiejones I agree it sounds like a possible vapor lock. Something else that might help besides the spacer is a return line. You could place a filter like shown between your fuel pump and the carb and route a return line back to the tank.

 

Does your cap have a vent in it? My cap leaks, good or bad, I don't fill it to the top, or park it on a side hill when full.

 

Yeah sounds like a classic vapor lock. The size of the carb is not the issue, just hot gas in the carb. A phenolic spacer would help..

 

Also re route fuel lines away from heat, or insulate them. The previously mentioned return line will also help, if you don't have that.

 

I too have had this issue when traveling cross country. My final resolve was the fuel filter. The fuel return port on cheap replacement filters don't have any restriction. The original filter had a very tiny hole in the return port. Basically if you blow thru the filter and put your finger over the primary out, you should get very little air flow out the return line, if it flows freely thats bad.
I can't explain why it worked when cold and dies when hot, but it does.
Good luck, hope you find your resolve.

 

Vapor lock seems most likely but there is also a possibility the ignition coil is on its way out.

 

Sounds about right. Or cheap crap modern condenser?

 

The '79 CJ was loaded with emission garbage. If you live in an area without testing, remove what you can. Install fuel injection and an HEI.
A return and vented tank would help. You did not say if this was a V8 or 6 cylinder.

 

My v6 was acting very similar. Replaced the coil and issue went away.

 

I would go with the coil that doesn't require a ballast and eliminate another point of failure, unless you are doing a restoration.

 

Either or both vapor lock and the coil could be the problem. Vapor lock can also be caused by a clogged tank pickup screen or line. With that, your fuel pump is trying to pull a vacuum and you effectively lower the boiling point of the gasoline. Add to that a bit of heat and it will boil. The first thing I would do is check your fuel pressure at the carb. You can use a cheap gauge for this but one teed off the fuel line that you can leave in-place driving it would be best so you can observe what happens when it quits. If you still have fuel pressure when it quits, then look at the coil. You can also remove a plug and see if you still have spark when it quits.

Having a shop do all your work on an old Jeep can be prohibitively expensive and most of the problems are not difficult to fix. The first thing you should do is purchase or download the Factory Service Manual (FSM) and enjoy a little bedtime reading-------

 

I hate shops. I hate dealerships.

One question I have is did the engine temp creep up before it shut down or did it stay cool?

Take a cellphone video when you drive and share the part when it dies have a buddy try cranking right away.

Pull the fuel tank and make sure it is clean.

My 4.3 chevy eventually went fuel injection because it never ran right.

i'ld bet it's a $20 part

 

Exactly what I did.

 

$1,500 going to wheel bearings, were they at least 24 carat?
$3,700 going to "the fix"? What Fix?

Any shop worth a bean should have been able to fully diagnose all of the points Fino said above. ESPECIALLY if they were in possession of it when it did it again and they reported to you "cannot get it started".

You need to stop unloading the parts cannon at this and dive in and check the vital things while they are happening.
1. Does it have spark when it happens
2. Does it have fuel pressure when it happens
3. What is your temps showing at the time it happens
4. Backfiring exhaust or carb

You've gotten good advice above on what to check and doesn't require a wallet unload to verify those things.

 

The "IT ACTS LIKE ITS OUT OF GAS...blub blub...….blub.....blah dies" sounds exactly like my '76 jeep (the yellow jeep in my avatar). Mine has a chevy 350 and generates a lot of heat. On hot days or climbing a long hill offroad, the jeep would act like it's out of gas and die. @ITLKSEZ and @Fireball were there to witness the problem first-hand. When the jeep cooled off, it would run fine again until it heated up again. On my jeep, the metal gas line passes close by to the exhaust header underneath. It was suggested the gas in the metal line was being heated to vapor and the mechanical pump up front couldn't pull the fuel through the heated line. About a year ago, I removed the mechanical pump and installed an electric fuel pump under the jeep by the gas tank. I routed rubber fuel hose all the way from the pump's outlet, along the frame, to the carb. I kept the hose line away from the exhaust header. I have not experienced the "blub blub blub...dies" problem since that day.