Fuel Issue -- Pulling My Hair Out!

I've been having a fuel issue with my 59 CJ5. The vehicle has a rebuilt 134 engine. I have had this issue for at least 3 years. I've had it this long because (1) I don't drive it a lot, and (2) it only happens when I'm on a back road miles from help. This makes it not much fun to drive and difficult to diagnose. By the time I get it towed back it runs fine. I can't recreate the problem around home no matter how much or how long I drive it.

This is what it does: when I drive it off the highway for about 2-4 miles it dies. It will typically restart after about 20 minutes, but the problem then re-occurs. At first I thought it was vapor lock as some of the fuel line ran close to the exhaust manifold. I rerouted the fuel line but that didn't solve it. Without going into all the details, I have replaced the fuel tank, the fuel filter (twice), the carburetor and the fuel pump. Since there isn't anything left in the fuel system, I thought it might have be an electrical problem so I replaced the coil, points and condenser. It still happens.

I thought maybe I had a non-vented fuel cap but its the correct cap, and once it stalls, it still won't start even if I remove the cap altogether.

The last time it stalled I was able to see that the glass bowl on top of the fuel pump only had about 1/4" of fuel in it. No amount of turning the starter would fill it. I finally got it filled by pouring gas down the carb and firing it about 6 times. This leads me to think I've got a bad fuel pump, even though its not very old.

I should add that the fuel tank was full so it wasn't due to fuel sloshing around inside the tank causing the pickup to suck air.

The problem only happens on rough dirt or gravel roads, it never happens on pavement regardless of how I drive it, including going up grades steep enough to require me to downshift to second. I plan to test the pump next, but I'm not sure how much fuel it should produce over a given period of time. Any ideas on that, or any other ideas on what might be wrong?

I'd sure like to figure this out while I still have some hair ;-)

Mike

 

X2 Next time it happens hotwire the coil and see if it will start. Is it an old coil? May be losing continuity from the jostling.

 

I had a subaru once that had one of those silver paper seals off of a bottle of heat in the tank and it would plug up the pickup line and kill the engine. I finally found it after taking the tank out and looking inside. didnt do it all the time just enough to make it a car you couldn't trust to drive. ditto on the above also disconnect the fuel ine and crank it over to see if anything comes out.( be carefull squirt it into a bottle or something )

 

Next time it happens verify whether it is a fuel or spark issue. That will help narrow it down. Just check for spark and remove air filter from the carb, operate the throttle with engine off and check for a solid, steady spray of fuel. If a strong steady stream then it is ignition. If weak or just dribbles then a fuel delivery issue.


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This has been such a long process I didn't include every detail in my original post. It is probably not an electrical issue as I installed a brand new coil, points and condenser just before the last stall. I did not check for spark last time it stalled so I guess I can't rule it out 100% however, I did do a pretty complete check of the fuel system after it stalled. I could only get a couple of very weak spurts of fuel from the accelerator pump when I worked the throttle. The glass bowl on the fuel pump was almost empty and would not fill by turning the engine over. The glass bowl finally filled by prime starting the engine half a dozen times. It ran for a while after the bowl filled but stalled again about 1/2 mile later. My tow crew ran out of patience at that point so we hitched it up and headed back.

The fact it would prime start but not run also suggests fuel and not electrical.

Chuck 123 has an interesting suggestion, but I don't think its that because after the last stall I field replaced the fuel filter which is about 8" away from the tank and fuel was free flowing as I wrestled to get the new fuel filer back on. I do plan to check the fuel pump output, but its running fine now so I doubt it will show much. I need to get it to stall again for that to be meaningful.

I was also thinking that maybe the problem was too full of a tank. When it stalled it was on a hill with a little bit of side slope. When I removed the cap quite a bit of fuel spilled out. I wonder if that could be blocking the tank vent. I'm grasping at straws... I think I may drain off a couple gallons, replace the fuel pump and try it again.

 

Glass bowl not sealing good on the pump, allowing air to enter the system? Perhaps exacerbated by the rough road? (grasping at straws too...)

 

Years ago I had 2 similar problems (different vehicles) but was not specific to on/off road use. What I found was 1:The flexible fuel line between hard line from tank and fuel pump was slowly decaying internally. Small bits of the hose would flake off reducing the fuel flow and caused similar conditions as you discribe. Replacing the line fixxed the problem. 2:On another vehicle, I also found a small bit of debris in the tank. Cleaning the tank fixxed that one.

 

My first thought was vapor lock but that wouldn't explain why it only happens on back roads. Vapor lock would explain why it starts again after some cooling off time but it would happen regardless of road conditions. My second thought is fuel pump, maybe 53Flattie is on to something. Did it act this way on the old fuel pump or did you only start having this problem after it was replaced?

 

I'm convinced (now) its not vapor lock. In addition to the fact it only does it on steep bumpy roads, the last time it stalled I checked and the fuel line under the vehicle was cool. Under the hood it was hot, but no hotter than anything else under the hood. Plus I cooled the entire line off with water and it still didn't start. I don't remember exactly when I replaced the fuel pump, but I'm pretty sure I have had the problem the entire time I've had this pump. I've heard that ethanol in fuel can degrade the rubber sections of the fuel lines. I would not mind replacing them, but what is the alternative? I'll check for bits of rubber when I tear it apart.

 

Oh, one more thing. I found a fuel pump without the glass bowl but it was listed as for a 1959 Jeep Pickup with the 134. I'd like to try one without the bowl to eliminate the possibility 53Flattie mentioned. Any reason the pickup pump won't work?

 

maybe next time it shuts off, manually pour some gas into the intake to see if it will fire. If it does, then it is probably a fuel delivery issue. If it doesn't at least misfire or cough, then probably electrical. pretty much the same thing nick said. Its hard to diagnose these over the web. Just make sure all the components are there: fuel, air, compression, blue spark and timing. Its a simple engine.

 

Are you absolutely sure it is not in fact flooding? Bumpy off-road use and high fuel pump pressure can override the float valve in Carter YF, especially since some kits provide an oversize inlet valve. Many people use a pressure regulator for this reason.

A flooded hot engine might take 20 minutes to restart...

 

I vote plugged gas cap vent.

 

Had not thought about flooding as a possibility. I don't think its that because I was able to prime start it and that would only make a flooded situation worse. Also, the carb is a Solex; don't know if they have that same problem. I'm not running a fuel pressure regulator. I've not always been able to prime start it when it stalls so this is still something I'd like to look at.

I maybe need to retract my conclusion that its not vapor lock. I checked the gas line again last night and it runs within about 1" of the exhaust pipe as it runs along the frame rail. I covered it with rubber hose to try and insulate it, but maybe that makes it worse? Can't dissipate the heat? The fuel line is not original so I'm not sure where its suppose to run. Does that sound right that it would run along the frame rail, parallel to the exhaust pipe? That might explain why it only stalls during back road conditions -- grade makes the engine work harder (heat) but the speed is very low so the exhaust heat isn't blown back as it would be at 40 mph.

 

25+ years of no problems, overhauled F134 started vapor locking. Electric fuel pump pressure regulator problem solved. pin hole in fuel line???