78 2f highway speed chug/cough - possible water in fuel (1 Viewer)

[Lschumm]

over the past two days ive been driving my 1978 Fj40 from Denver up to Spokane where I go to school. It’s been running fantastically other than an issue that’s starting to worry me

- back story, I left my gas cap in Cheyenne at the station but didn’t realize it until a few hundred miles later. During this time the cruiser developed a cough at high speeds in 4th gear, anywhere from 50+ (will normally cruise 60 no problem with no wind or hills). I drove through some fog, heavy wind, and blowing snow at this time. I bought a new cap so the system is sealed up again.

The cough occurs randomly and you can feel the engine lose power as if dying. The cruiser then jolts quite noticeably for 4-5 seconds and then regains power and accelerates again. It would do this occasionally but usually could go a an hour or two between fits. I assumed it was some water that got in the fuel tank while I had no cap, and that the coughs were just water going through the engine.

Today I’m not so sure though. It’s been having the cough almost all day (about 150 miles so far) but only at high speeds in fourth gear. I’m beginning to worry it could be something else. Carb from changing altitudes? Bad spark plugs? Ive driven almost 900 miles so far, by the end I’ll be around 1100. I’ve had the cruiser for about 3 years and never experienced this.

Has anyone had this problem before or know what could be causing it? Any help is greatly appreciated.

Thanks!

 

[scott fasken]

Try a bottle of HEET to take out the water if it got some. Also it can freeze at night a headache, had mine die in Eagle, CO when you FJ40 was new.

 

[scott fasken]

They sell it in many gas stations

 

[47coeman]

Sounds like you have water on your gas yes heat or a water dispurser would be the thing to get

 

[Pighead]

Check your fuel filter too. Might be restricting flow and starving the engine at high speeds.

 

[scott fasken]

Yes that could be a solid point also.

But it is funny to hear the words High Speed with a FJ40....

 

[4x4veteran]

Check your fuel filter too. Might be restricting flow and starving the engine at high speeds.

Do it now.

 

[1MOA]

New fuel filter, Heet and fill the tank up till you can't get another drop of gas into the tank or filler tube and run the thing on a long trip. Also if you can park the vehicle in a warm location for as long as you can ( it can be a under ground garage that is even just a few degrees above freezing) will help.

 

[POTATO LAUNCHER]

If the fuel cap you put on is a universal type it may not be venting now causing a vacuum effect. Ethinol gas simply sucks also. Buy the lowest octane available. Both of my Cruisers do this on that craptastic gas.

 

[TimeIsMoney]

I had some surging in my 78 last week. Turned it to be a small piece of debris in my main idle jet, Weber carb.

 

[cbmontgo]

Smog pump bearings might be locking up. Is there a burning smell immediately after? I had a similar issue and that's what it was. Just my $.02.

 

[cbmontgo]

Love the 40, by the way.

 

[Living in the Past]

If the fuel cap you put on is a universal type it may not be venting now causing a vacuum effect. Ethinol gas simply sucks also. Buy the lowest octane available. Both of my Cruisers do this on that craptastic gas.

78 did not have a vented gas cap. The emissions system is suppose to keep gas fumes from escaping. A vented gas cap would allow fumes to escape.

 

[Lschumm]

Update:

Purchased some HEET from the gas station after another 50 miles or so. Didn't change the chugging/sputtering at high speeds. Continued to get worse throughout the day, but I did end up making it through the blizzard to Spokane. Cruiser still got me home in one piece!

Hills were rough, only about 20mph max in 3rd, and lots of sputtering. I checked air filter, but really do think it has something to do with the fuel filter because it wasn't ever at a consistent speed or RPM, but more of a certain "umph" level. This makes me think it's

related to the amount of fuel entering the system.

Refilled with premium in Coeur d'Alene (less ethanol) and added an injector cleaner. Was noticeably better for the last 30 miles into Spokane, but would sputter lightly past about 50. Luckily traffic was only moving about 40 anyways because of the snow, so I wasn't holding up too many more people in the right lane

Will change fuel filter tomorrow and update with results.

 

[shawnfj40]

Did you say that you are running a Webber?

 

[Lschumm]

Update 2:

Finally got around to changing the fuel filter this morning. Took her for a spin on the highway and she won't manage much past 50 still. Started up and ran perfectly, even after sitting for nearly a week. Also still runs normally at low speeds around town, no coughs/sputters/chugs/shutters of any nature.

When I inch closer to about 50, there is almost a point when I can feel the car begin to lose power very slightly. If you let off the gas, the engine decelerates as normal. But, if I keep my foot where its at, then the shutters begin to follow about a second after. If I lift off once the shutters begin, they almost immediately stop and I can ease back onto the gas very gingerly, trying to avoid more shutters.

Any other thoughts/suggestions? Shawnfj40 I believe its the stock carb, I haven't changed it and I don't believe the previous owners did either. Carbs are not my territory though, so I really don't know...

Thanks for all the help so far

 

[SteveH]

For whatever reason, I suspect insufficient fuel flow. You have the classic symptoms of a fuel pump that can't keep up with demand. If you have changed the fuel filter, and you believe the tank isn't full of crud (debris that will clog the next filter), you can try this:

Perhaps just for test purposes (but maybe for long term), try adding an electric fuel pump inline to bump up the flow to the carb. I would mount the pump very low for best results. I mounted mine under the pass. floor on the frame. You can try a cheap vibrator type pump, or a better, Carter motor-driven electric pump (Carter P4070 Electric Fuel Pump | eBay).

If the truck runs great on the highway after that, you have at least diagnosed the problem, if not found the root cause. I fought fuel system issues on my '78 FJ40 for 15 years (various hot soak and vapor lock issues) and finally installing fuel injection.

 

[Solace in Solitude]

If, by “highway speeds”, you mean when you have the pedal to the floor, trying to make it up a hill under load, it could be your secondary.

When “under load”, the secondary kicks in and tries to suck “mass quantities” of fuel (compared to when the secondary is not in use).

Any leak in the fuel delivery system will cause the secondary to suck air instead of sufficient fuel... the engine will chug and sputter and shudder and die... but will start back up immediately because the secondary automatically disengages when the engine dies, or you ease off the pedal.

Check your carb sight glass and make note of the fuel level... then drive until it dies again... switch the ignition off... safely coast off the road... check the sight glass and let us know what the fuel level is... by switching the ignition off, you are capturing the fuel level when the failure occurs.

I also have a ‘78... I experienced this with a fuel filter that didn’t fully seal.

Check your fuel lines and filter for leaks (pinholes, poor connections, etc.).

Also, vacuum leaks rob your engine of power.

I searched and searched for a vacuum leak, to no avail, until I realized the dissy vacuum advance was leaking.

I replaced the dissy with a new DUI, with new advance module, and regained beaucoup power.

 

[Solace in Solitude]

Oh, as @SteveH said, it could also be your fuel pump not keeping up... but, I think you’ve tried a new pump... with a spacer or without?

My ‘78 didn’t need a spacer.

I run Carter electric fuel pumps, one per fuel tank... but I changed to electric to prevent potential fuel dump into the crankcase... and to provide an immediate backup, in the event of a pump failure.

 

[emac]

So, it studders when its under heavy acceleration or fuel demand. Fuel starvation or secondary issue. If the pump is fine then I would clean the carb.

FWIW, I have never put ethanol fuel in my 40 since the restoration (new tank, pump,rubber lines, filter and carb). My son was almost out of fuel and put some ethanol fuel in it. Within a couple of miles it started running like crap. After chasing a few unicorns, I took the carb apart and cleaned it out real good and all was back to normal. The ethanol must have loosened up some gunk in the hard lines after the filter and clogged it up. Ethanol is evil. When they switched to ethanol fuel, all the gas stations had to replace tanks because the varnish build up would be loosened by the ethanol. I hate it so much, I put a tank in at home and have conventional fuel delivered for boats, mowers, and old cars.

Good luck keep after it!