1978 FJ40 2F Odd fueling issue (Solved!) (1 Viewer)

[TaylorDurdan]

Here's a weird one! I searched the forums high and low and haven't found this issue yet, let's see if you guys have any ideas.

The problem:

Truck seemingly drives ok, maybe a little light on power, but overall ok. As soon as you hit 40mph in 4th gear, the truck will buck violently and not go any faster. Letting off of the gas will stop the bucking, but there's really no way to tip toe past the 40 mph mark.

Once bucking, you can shut off the engine and coast to the side of the road and see that there is zero fuel in the sight glass window on the carb. Start the truck up, and carb will refill properly at idle. I can now recreate this issue in 2nd, 3rd, and 4th gears. It's RPM based. If I drive long enough in 2nd gear at the same RPM that it takes to achieve 40mph in 4th, it will also starve the carb.

"Solutions" so far:

Initially, just like anyone rational, I assumed vapor lock. The cooling fan in the engine bay that blows on the carb works, too, btw.

So far, I have:

• replaced the fuel tank for brand new OEM unit (original was leaking from the seams, so it needed replacement anyway)
• ran a temporary 5/16" soft fuel line from tank to fuel pump in case of suction line obstruction
• installed brand new OEM fuel pump
• pulled carburetor apart and set the floats to OEM spec
• blocked off fuel return port in case it was allowing too much to bypass the bowl
• pulled the "fuel cut-off solenoid" and cleaned it, ensuring that it works (it does)

I think next I should pull the feed line from between the pump and the carb and make sure it is clean and flowing freely.

Has anyone seen the actuation cam on the crankshaft wear down enough to not pump the fuel pump effectively? I would assume something catastrophic would have had to have happened internally for that to be the issue. This truck was restored by someone else and I've been fixing so many issues, though. I wouldn't put it past whoever did the resto to use some worn-out crankshaft at this point.

 

[TaylorDurdan]

I just removed the hard feed line from the pump to the carb and blew air through it. It appears there are zero obstructions.

I now have zero ideas why I would not be able to supply enough fuel to the carb to keep the bowl full.

 

[samatulich]

Vent the filler cap (just crack it open), you maybe experiencing vapor lock.

 

[Solace in Solitude]

I know the actuation cam will wear, but I’ve not heard of it wearing so much it will no longer drive the pump.

Hook the fuel return back up... and try venting the cap.

If you pull the feed line, from the carb, find out of there is a screen filter in the carb feed port... maybe it needs cleaning.

I think you bypassed the frame-rail hard-lines, to test with a soft-line... but, you should clean your hard-lines, make sure your soft-lines are not cracking and your clamps are good.

Is your fuel filter clean? Note: I had your issue and found the fuel filter was allowing the pump to suck huge quantities of air, when the secondary kicked in and increased the fuel demand. My filter was a replaceable element aftermarket glass filter.

The carb expects/needs a lot more fuel when the secondary kicks in... Have you tried the secondary paper clip test, to ensure you secondary is functioning properly?

Aisan 2F Carb Secondary Paper clip test ?

Just finishing up on my tune up on my 82 FJ45. I did the secondary shaft vacuum paper clip check but do not remember what is considered expectable as in shaft travel on the secondary's shaft. I have been searching the Mud site for an answer, I know I saw it but just need so guidance in locating...

forum.ih8mud.com

Consider borrowing or buying an electric fuel pump... install it temporarily, in-line with the oem pump... see if it makes a difference... might encourage/discourage you dropping the pan to check the actuation cam... could always carry the electric pump as a trail spare.

I removed my mechanical pump and run a pair of these, one per tank... provides me emergency backup, should a pump fails. Amazon.com: Carter P4070 In-Line Electric Fuel Pump: Automotive

 

[TaylorDurdan]

Test driving with the gas cap loosened made the driving condition worse, surprisingly. I don't know why I spaced on even trying that first. At under 30mph, the truck was undriveable and bucking. I keyed off the engine during the bucking and coasted off the road. Carb was empty. This time, though, it took much longer to refill the fuel in the sight glass at idle. I wonder if someone connected the vent/evap system incorrectly and that's my root cause. This truck is 100% OEM configured and the customer does not wish to de-smog or remove any factory systems.

I have removed many electric fuel pumps from these trucks due to running issues, but I did plan to install one temporaily just to see if that fixes my issue.

I have done the paperclip test and the carb is functioning as designed as far as I can tell.

That screen was damaged by whoever "rebuilt" the carb during this truck's restoration. I was smashed into the carb housing. I removed it and torn down the carb completely to clean out an remaining foreign matter.

The filter is also a brand new OEM unit. All parts are from Toyota; no third party aftermarket. I had started with the filter, but didn't mention it since I bypassed it entirely with the soft line. I thought maybe the cad-plated spring clamps the previous shop installed on his fuel lines might be causing air to get sucked in on the suction side, so I replaced them with actual clamps. All with zero results.

 

[Solace in Solitude]

I love my electric pumps!! I’ve carried an oem pump, in my trail spares, for 3 years and never reinstalled it.

Try an electric to rule out the actuation cam wear.

Here’s the fuel line routing, including the fuel separator.

fj40 fuel separator libe routing - Google Search

:

 

[SteveH]

I fought endless flooding and starvation issues on my '40 before installing TBI, but after TBI I discovered another problem - when the fuel tank is low, I can hear the electric pump cavitating. I also see more air in my clear, plastic fuel filter mounted before the pump. I cannot see a reason for this, but the problem is there. When my gas tank is more than half full, the TBI system is very happy. When lower, I get starvation issues under some conditions. This summer, I plan to attack this, and perhaps install an in-tank pump.

Anyway - the short version is this: is your gas tank mostly full?

 

[TaylorDurdan]

Yeah, the tank just got put in this week and filled. I think I need to make a soft line between pump and carb and toss in a clear filter to watch what's happening.

I wonder if I can recreate this high-ish RPM pump failure in neutral....

 

[TaylorDurdan]

I love my electric pumps!! I’ve carried an oem pump, in my trail spares, for 3 years and never reinstalled it.

Try an electric to rule out the actuation cam wear.

Here’s the fuel line routing, including the fuel separator.

fj40 fuel separator libe routing - Google Search

:

Thank you for that. I'll have to double check what all has been done to make sure it was done correctly. I know this is going to be something simple.

 

[samatulich]

Have you checked for vacuum leaks at the carb?

 

[3_puppies]

got a pic of the new pump on the block? I've got a guess.
I think it was @Pin_Head who stated a way to check the pump flow.
remove gas line feed from carb, direct it into a container, remove coil wire, it should pump 1 cup of gas in a minute???

maybe Pin_head will chime in

 

[ducktapeguy]

I had a similar problem when I first picked up my 40. Car ran fine until about 40mph. Turned out the PO had the input and return lines reversed. The return line has an orifice in it to restrict the flow, when put on the input line it worked fine until you started needed more gas, then the bowl would run dry.

Disconnect the input line to the carb and check the flow. Also there might be a fine screen on the input line that's clogged (not sure if it was on my 40 or jeep but one of them had a fuel filter at the carb.)

 

[Solace in Solitude]

got a pic of the new pump on the block? I've got a guess.
I think it was @Pin_Head who stated a way to check the pump flow.
remove gas line feed from carb, direct it into a container, remove coil wire, it should pump 1 cup of gas in a minute???

maybe Pin_head will chime in

Good point!

You don’t have a spacer on that new pump, do you?

Should pump 1cup in 15 seconds ... see second post here Fuel /air mixture problems?

 

[3_puppies]

Good point!

You don’t have a spacer on that new pump, do you?

Should pump 1cup in 15 seconds ... see second post here Fuel /air mixture problems?

that was my thought on the fuel pump, but wanted to see a pic.

I thought 1 minute seemed like a long time, 15 seconds is much better.

 

[tls3601]

Mechanical OEM fuel pump for me, zero issues!

 

[TaylorDurdan]

Good point!

You don’t have a spacer on that new pump, do you?

Should pump 1cup in 15 seconds ... see second post here Fuel /air mixture problems?

No spacer on the pump, bolted directly to the block.

I had a similar problem when I first picked up my 40. Car ran fine until about 40mph. Turned out the PO had the input and return lines reversed. The return line has an orifice in it to restrict the flow, when put on the input line it worked fine until you started needed more gas, then the bowl would run dry.

Disconnect the input line to the carb and check the flow. Also there might be a fine screen on the input line that's clogged (not sure if it was on my 40 or jeep but one of them had a fuel filter at the carb.)

I have the correct line going to the correct spot on the carb. The screen on the input had been destroyed by the previous shop. That was removed, cleaned, carb dismantled and cleaned out of all debris.

Currently, I have the return blocked off because I thought maybe the internal rubber 'valve' and restrictor was ruined and letting too much bypass the float needle.

I'll have to check the volume of the pump. At this point, though, Everything is brand new from tank to line to pump, so I can't imagine what else it could be aside from the carb itself having an issue.

 

[TaylorDurdan]

Have you checked for vacuum leaks at the carb?

Yeah, I smoke tested the intake manifold/carb system

 

[Dizzy]

Wasn't '78 a transition year for fuel pumps? I saw a video about the amount of camshaft reach among different 2F vintages.

 

[Catfish28]

Had a similar issue on my 78 with oem pump, carb, etc. ended up being a punched soft line between the hard line running along the frame rail and the filter. Happened after I bolted the filter to the mounting bracket.

 

[65swb45]

If you’re running out of gas, either it’s not getting to the carb fast enough, or the carb is not letting it in fast enough.

Do the bottle test.