bad stumble 4wheeling (1 Viewer)

[lovetoski]

Headed out early yesterday am to go 4wheeling with my son. (Goal was Gallagher Head Lake, north of Salmon La Sac in Washington State.) Truck drove fine over Snoqualmie pass and for the next few hours. After about 90 minutes of 4L (rough trail, but nothing severe) we began to have a stumble, or maybe call it a mis-fire. Temps were mid 80's, we were mostly going uphill, 4000 ft altitude. The stumble got worse, truck became very hard to drive. Idled fine, just wouldn't run w/out missing/stumbling at 1500 rpm and over. We stopped a couple of times to ponder the problem. Both times we stopped, the truck ran fine again for a short while afterwords. The third time we stopped, I resolved to replace the fuel filter. The stumble felt/sounded to me like a fuel problem, and I thought perhaps the fuel filter was clogged.

Hijacking my own post mid-way through, this is where I discovered how dumb I can be. I opened my spare parts box, pulled out the fresh OEM filter box, opened it, and it was empty! Maybe I bought an empty box? Maybe I spaced out and used it already...I have no clue. Pretty dumb. But, the "air" filter for my axle breathers has the same inlet/outlet size as the Toyota fuel filter, so I swapped that in instead. There are a couple of lessons in this...

Back to the real story...truck ran fine again after the filter swap. But, afterr 15 minutes or so, the stumble came back again. I turned around to head home, hoping that whatever the problem was it wouldn't prevent us from getting home (3 hours away at this point). Given that it felt like a fuel delivery issue, I was thinking fuel pump...though mine is only 4-5 years old and with less than 15,000 miles on it. It's a NAPA though, not OEM.

We got home fine. Truck ran strong, even back across Snoqualmie Pass. That seems to rule out a fuel pump (I think?)

Next I am thinking carb...and I did have a carb adjustment done a few months ago. The truck failed emissions (again) and the emissions shop worked on the carb to get it to pass. I remember that they said they reduced the fuel level (adjusted the float I suppose)

Could this be the source of the problem? Lower than needed fuel level ok on road, but problematic in rough uphill off-road?

Open to any and all suggestions...

 

[jrhaze]

I had the same problem the other day however mine is a 3B not the 2F. No idea if the same thing could apply to the 2F?

Anyways I had the exact same symptoms and intermittent . . . turns out it was a faulty ignition harness. Replaced that and problem solved.

Just though I'd throw it out there in case there is a chance it could apply to you and your problem.

 

[Kurtis]

Sounds like a vacuum leak. Sometimes when the engine bay heats up a cracked hose will start leaking worse. If your lines are old I'd start replacing them. Another source of vacuum leak can be the booster hose or the brake booster itself.

 

[BlueCruiser84]

I know nothing about that area. When you say that the truck ran fine on the way home was this over pavement or still off road?

You may have had some crap in your tank that got dislodged with the rough driving and clogged up the fuel filter. You'd think if it clogged after you replaced the "fuel filter" that it wouldn't have run well on the way home, though. Also, the fact that you replaced the filter with a breather filter could affect it, although I couldn't tell you the technical differences between the two.

Have you driven it since?

 

[mdennis]

have you grounded your fuel cut off solenoid

 

[Benjaman]

Could be lots of things! check the easy stuff first, like air cleaner(if those road were real dusty), or lose vacuum hose. Float level in carb(if yours has a sight glass). Hook up a timing light and bring up the rpm's, watching the mark, should be smooth and not miss.

Headed out early yesterday am to go 4wheeling with my son. (Goal was Gallagher Head Lake, north of Salmon La Sac in Washington State.) Truck drove fine over Snoqualmie pass and for the next few hours. After about 90 minutes of 4L (rough trail, but nothing severe) we began to have a stumble, or maybe call it a mis-fire. Temps were mid 80's, we were mostly going uphill, 4000 ft altitude. The stumble got worse, truck became very hard to drive. Idled fine, just wouldn't run w/out missing/stumbling at 1500 rpm and over. We stopped a couple of times to ponder the problem. Both times we stopped, the truck ran fine again for a short while afterwords. The third time we stopped, I resolved to replace the fuel filter. The stumble felt/sounded to me like a fuel problem, and I thought perhaps the fuel filter was clogged.

Hijacking my own post mid-way through, this is where I discovered how dumb I can be. I opened my spare parts box, pulled out the fresh OEM filter box, opened it, and it was empty! Maybe I bought an empty box? Maybe I spaced out and used it already...I have no clue. Pretty dumb. But, the "air" filter for my axle breathers has the same inlet/outlet size as the Toyota fuel filter, so I swapped that in instead. There are a couple of lessons in this...

Back to the real story...truck ran fine again after the filter swap. But, afterr 15 minutes or so, the stumble came back again. I turned around to head home, hoping that whatever the problem was it wouldn't prevent us from getting home (3 hours away at this point). Given that it felt like a fuel delivery issue, I was thinking fuel pump...though mine is only 4-5 years old and with less than 15,000 miles on it. It's a NAPA though, not OEM.

We got home fine. Truck ran strong, even back across Snoqualmie Pass. That seems to rule out a fuel pump (I think?)

Next I am thinking carb...and I did have a carb adjustment done a few months ago. The truck failed emissions (again) and the emissions shop worked on the carb to get it to pass. I remember that they said they reduced the fuel level (adjusted the float I suppose)

Could this be the source of the problem? Lower than needed fuel level ok on road, but problematic in rough uphill off-road?

Open to any and all suggestions...

 

[justin85-60]

It could be many different things. All have been mentioned, but I do have to go with JRHaze on this one. I had a wiring issue on my old 60 (2f). It was the fusible link right by the alternator. There was some kind of short in it. It ran like crap sometimes and great others. Turned out that if you moved the fusible link around while it was running like crap it would magically run fine. Just throwing it out there, don't limit yourself in your search. Good luck.

 

[lovetoski]

Hey guys,

Thanks for the responses...a bit of additional background...in the 8 years I've owned this truck, it's always run well. A Local emissions shop adjusted the carb to increase the chance of passing smog (didn't pass, but spent enough to get my tabs anyway). It's only after they did something that the stumbling started, and it does it only on steep sustained off-road conditions.

Sounds like a vacuum leak...If your lines are old I'd start replacing them. Another source of vacuum leak can be the booster hose or the brake booster itself.

Replaced all vacuum lines last year, and my vacuum guage reads steady.

I know nothing about that area. When you say that the truck ran fine on the way home was this over pavement or still off road?

You may have had some crap in your tank that got dislodged with the rough driving and clogged up the fuel filter.

Have you driven it since?

The drive home was on the freeway, approx 90 miles worth, including over a mountain pass. Ran fine. So unless I am missing something, this suggests there was no clogging of the fuel filter.

have you grounded your fuel cut off solenoid

Yep - 2 years ago. Has run fine since then until this last trip.

Could be lots of things! check the easy stuff first, like air cleaner(if those road were real dusty), or lose vacuum hose. Float level in carb(if yours has a sight glass). Hook up a timing light and bring up the rpm's, watching the mark, should be smooth and not miss.

Air cleaner is brand new. Fuel level in the sight glass is smack in the middle. I didn't get a chance to check the timing though.

Since it ran fine on the freeway, which given the brick shaped "aerodynamics" of a cruiser requires a heavy foot to hold 60-65 mph...I think the basic fuel delivery system (pump, filter, carb) are fine.

There's something I don't understand about the effect of sustained steep bumpy uphill.

I am stumped.

 

[Wile E Coyote]

The lowered float level is leading to slight fuel starvation on those long, steep uphill inclines. If it's troublesome enough, then another carb adjustment is in order.

 

[lovetoski]

The lowered float level is leading to slight fuel starvation on those long, steep uphill inclines. If it's troublesome enough, then another carb adjustment is in order.

Makes sense - thanks. I checked the FSM, and searched MUD, and the only reference I found to adjusting the float level requires a partial dis-assembly of the carb. Did I miss something?

 

[Kurtis]

This shows my utter lack of patience but this exact issue is why I got rid of a 150k 2f with strong compression and now have a fuel injected 5.7 and automatic under the hood now. I have to admit that the last year and 15,000 miles have been the most enjoyable, reliable, and fuel efficient miles of my cruisers life. If you can call 14 in town and 17 on the highway efficient. But with 8" of lift and 35s i'm not complaining.

I would dig into the carburetor, when I had this issue I tried everything on the fuel delivery/ vacuum side of things to no avail. Before I ripped mine out I was really thinking that I was having problems with a sticky float or dirt clogging a jet. Mine was really sporadic. It would drive perfect have great power ( for a 2f) then out of no where just cut out and leave you without power trying to make a left turn on a busy street. That's what put me over the edge and out she went.

What happens when you pull the choke when its having the rough idling problems? The choke would always allow mine to run when this issue would happen.

 

[lovetoski]

What happens when you pull the choke when its having the rough idling problems? The choke would always allow mine to run when this issue would happen.

I didn't try that - thankyou!

Understand your sentiments re going to EFI and a V8...not quite ready to swap out what's under the hood...not that I haven't thought about what my options are...

 

[klinetime574]

Definitely sounds like a carburetor setting/ vacuum leak. Because people claim that the Aisin carb is the best off road. Check the settings on the carb and make sure the emissions shop reconnected everything right. Because I'd imagine they had to unplug a few hoses to adjust the carb.

 

[lehiguy]

Spark plugs, old wires? Run the engine in the dark, the darker the better. Watch for lightening storms on your wires. Could be crud in the carb float bowl that intermittantly obstructs the jets too. Could be a sign that an FI V-8 is in your future.

 

[FJ40Jim]

The float bowl is in front of the carb body. The main jets are at the back of the bowl. When the truck is pointed uphill, the fuel in the bowl is covering the jets. IOW, it is not a fuel slosh carb starvation issue.

If you think it is fuel related, it's probably too much fuel. The head pressure above the jets is increased going uphill, so the main circuit is running richer than on flat, then the bouncing starts sloshing fuel out of the bowl vents & down the venturis. See if there is black smoke visible when bouncing up the trail and running bad.

 

[lovetoski]

If you think it is fuel related, it's probably too much fuel.... See if there is black smoke visible when bouncing up the trail and running bad.

OK, cool. If there is black smoke, what would I do to reduce the amount of fuel?

Note - an emissions shop recently "tweaked" the carb to help it pass emissions (I still failed). Not sure what they did. Though they did say the carb is running rich, and there's fuel in the oil.

Probably I need to have it rebuilt...

 

[FJ40Jim]

OK, cool. If there is black smoke, what would I do to reduce the amount of fuel?

Note - an emissions shop recently "tweaked" the carb to help it pass emissions (I still failed). Not sure what they did. Though they did say the carb is running rich, and there's fuel in the oil.

Probably I need to have it rebuilt...

Yes, new float, needle & seat, lowered float level... could all help the situation.