Fj40 wont idle (1 Viewer)

[Unicroc404]

So I know those horse is likely beat to death. But my 1979 fj40 wont seem to idle without the choke pulled out. Adjustment screws don't do s*** and I've sprayed the entire thing down with carb clean looking for a leak. Nothing as of yet. Any suggestions or ideas on tracking this nightmare down?

 

[B y r o n]

Possibility of debris in the idle circuit. Maybe time for a clean and rebuild.

 

[whitey45]

Classic california choked emissions disaster!! If you dont drive it often, idle jets likely plugged due to our s***ting ass ethanol gas!!!

 

[DeskJock]

Classic california choked emissions disaster!! If you dont drive it often, idle jets likely plugged due to our s***ting ass ethanol gas!!!

Searched 3 years for a CA 1975 for this very reason.

And - agree, if your not driving your rig weekly - gas turns to goo.

 

[Unicroc404]

Well, I'm in texas but it definitely has all its smog equipment. I will say it is missing its pre heater hose... but from what I've read that shouldn't have anything to do with it yeah?

I suppose next step is a rebuild

 

[DeskJock]

If your able to demog - I’m running the City Racer OEM carb and it was plug and play on my rig.

 

[Unicroc404]

If your able to demog - I’m running the City Racer OEM carb and it was plug and play on my rig.

Was is already tuned?

 

[Grayscale]

Was is already tuned?

Yes, on my Racer OEM carb. Not exactly plug-and-play, but really close.
However, it might not be the carburetor. I'm thinking that a rusted open EGR valve might do it. What about the classic crack on the intake manifold, could it be to the point where you are pulling exhaust air?
There are two different things that the choke does, one is the attenuation of vacuum in the carb throat, the other is the idle kick-up. So can it run with a little application of constatnt throttle pedal after you push the choke in?

 

[charliemeyer007]

Give it a heavy dose of fuel system cleaner in tank, take it out for a good hard run for several hours to try and use up the fuel in the tank. Fill tank with good hi-test gas and see if it runs any better.

So has it ever idled correctly? Did it just start needing the choke to run?

 

[DeskJock]

Was is already tuned?

Umm - don’t think so. Prev owner installed fuel injection via a throttle body and did a large cap distributor that had been modified

The Computer failed and I put a one distributor and the city racer carb - and it stated right up.

Runs good?

 

[Roastchestnuts]

Dont forget about the fuel cut solenoid If thats bad/disconnected it wont idle right.

 

[DeskJock]

Dont forget about the fuel cut solenoid If thats bad/disconnected it wont idle right.

Good call.

 

[Unicroc404]

Yes, on my Racer OEM carb. Not exactly plug-and-play, but really close.
However, it might not be the carburetor. I'm thinking that a rusted open EGR valve might do it. What about the classic crack on the intake manifold, could it be to the point where you are pulling exhaust air?
There are two different things that the choke does, one is the attenuation of vacuum in the carb throat, the other is the idle kick-up. So can it run with a little application of constatnt throttle pedal after you push the choke in?

I was unaware of a intake crack issue, where exactly does this typically happen? That makes alot of sense actually.

 

[Grayscale]

I was unaware of a intake crack issue, where exactly does this typically happen? That makes alot of sense actually.

The damage is from hot exhaust directly under the intake manifold. The 'heat-riser' used the exhaust gas to directly warm-up the intake manifold. It was intended to 'atomize' the fuel charge, during cold-starts, which means that the exhaust manifold had a mechanical flap, controlled by a bimetal spring to control the heat. Too much complexity for its day.

Now, you can buy a thin solid plate to go in place of the gasket between the stock exhaust manifold and the intake manifold, to accomplish some the thermal exchange without the direct exposure of exhaust gasses on the aluminum intake manifold. I suppose by skipping the exhaust manifold with headers, I'll probably have more fuel contamination of the crankcase oil, and a bit worse gas mileage.

 

[Unicroc404]

The damage is from hot exhaust directly under the intake manifold. The 'heat-riser' used the exhaust gas to directly warm-up the intake manifold. It was intended to 'atomize' the fuel charge, during cold-starts, which means that the exhaust manifold had a mechanical flap, controlled by a bimetal spring to control the heat. Too much complexity for its day.

Now, you can buy a thin solid plate to go in place of the gasket between the stock exhaust manifold and the intake manifold, to accomplish some the thermal exchange without the direct exposure of exhaust gasses on the aluminum intake manifold. I suppose by skipping the exhaust manifold with headers, I'll probably have more fuel contamination of the crankcase oil, and a bit worse gas mileage.
View attachment 3700844

Oh wow what a nightmare.

 

[Grayscale]

I don't actually know that it is a vacuum leak there. However, it is easy to get to, after you figure out the vacuum piping. Mine's a '75; I'm fairly certain that our manifolds are different. I have a '71 intake manifold that shows no problems. I'm still guessing that it is the EGR valve, I think that it is cast iron, and, we see the steam, indicating that there is water-vapor in the exhaust - just a guess.

 

[avicenna110]

Second on fuel idle solenoid. I just had this issue on my car, the solenoid is controlled by the “computer”. My engine fuse was blown so the computer wasn’t functioning. Check the fuse and the solenoid.

 

[numby]

As a preliminary open the hood up, put the trans in neutral, and set the handbrake. You can then stand outside the vehicle, reach in the window, and turn the key to "on". You should hear the idle solenoid click. NOTE: Unplug the OVCV connector at the charcoal canister or it will click too...along with any other relays you've added.

 

[bdog75]

my '82 FJ40 had the same issue. I found the connector on the harness to be rusty that connects to this control module. its located on the firewall behind the clutch pedal. I used a file from a gas welding tip cleaner that fit into the terminals and cleaned them up. The problem went away for me.

 

[1911]

my '82 FJ40 had the same issue. I found the connector on the harness to be rusty that connects to this control module. its located on the firewall behind the clutch pedal. I used a file from a gas welding tip cleaner that fit into the terminals and cleaned them up. The problem went away for me.
View attachment 3713265

That is the emissions "computer" that controls when the fuel cut solenoid on the carb opens and closes. The connections from the wiring harness to the circuit board inside were cold soldered, and are well known for cracking with age and making an intermittent open circuit. It's possible to heat and re-flow the solder to fix it, but an easier way is to just ground the wire to the FCS where it enters the box. Then the FCS will be always on with ignition.