FJ60 Intermittent Stall at Idle

[Rzeppa]

Didn't you say that disconnecting the idle solenoid had little effect on the idle? That sounds like something has been adjusted to compensate for the solenoid. That thing should be able to kill the engine at a resonably low idle.

That is right Bruce. I have the idle speed screw set such that the throttle plates are partly open all the time. Sometimes it idles at 1200 RPM when it is like that, other times maybe down to 1000. I know stock is 650 but it won't run that low and never did. When I first got it and it ran great the idle was a little high at about 900 or so. No matter what she won't idle much lower than 900 or so. Which may be related to:

With the relatively low vacuum, the sound this engine makes (very throaty for a non-header stock 2F) and the knowledge that at one point this was a MAF engine I suspect the cam is a long-duration model. MAF used to really push long-duration cams ("RV Grind") back in the day. I doubt that is the root-cause of my problem but it does explain why it won't make 14" of vacuum to actuate the vacuum switch.

I remember Bruce Miller's 2F powered 60 that Mark Whatley built had a long duration cam and idled like crap. Of course that rig had a quadrajet too, which is pretty high flow for a 4.2, even at idle.

 

[Rzeppa]

And just to reiterate - the solenoid does click when you unplug it and plug it back in, and I have verified battery voltage is present at the connector when the key is turned whether the engine is running or not. And I have bypassed the computer ground by pigtailing the connector straight to ground at the computer.

 

[60wag]

So are you sure you don't have a vac leak? Maybe cap off all of the vac operated devices at the manifold (including the brake booster) and see what kind of vac can be measured at the intake manifold? An idle speed of 1100 would drive me nuts.

 

[Rzeppa]

So are you sure you don't have a vac leak? Maybe cap off all of the vac operated devices at the manifold (including the brake booster) and see what kind of vac can be measured at the intake manifold? An idle speed of 1100 would drive me nuts.

Of course I am not 100% sure I don't have an unintentional* vacuum leak. But I have to remember that she ran fine before smog, and all I did was retard the static timing, add some heet, replace the air filter element and change out the primary jet. After smog I put the old jet back in and re-advanced the static timing to exactly where it was, and have now run a couple tanks of fuel through. And this is totally intermittent but only occurs under one condition: When rolling to stop, disengage the clutch and foot off the throttle. If you roll to a stop very gently (slow rate of deceleration) she usually won't die, only when stopping quickly.

*Both the HIC system and the HAC system introduce intentional vacuum leaks. The HIC system introduces air directly into the manifold through the PVC valve tubing, and the HAC introduces air directly into 3 places in the carb: idle, primary and secondary circuits.

A very odd observation I had written about earlier in this thread was that when I remove the vacuum line from the HAC diaphragm of the distributor the idle speed picks up. While it is disconnected, if you plug the end of that line with your finger the idle goes back down.

 

[60wag]

Maybe you booster is leaking and stopping quickly creates a big enough leak to stall it? Do you have an in cab vac gauge so you can watch it while stepping on the brake pedal?

 

[Rzeppa]

Maybe you booster is leaking and stopping quickly creates a big enough leak to stall it? Do you have an in cab vac gauge so you can watch it while stepping on the brake pedal?

Somewhere earlier in this thread Steve Helmreich suggested checking with a gauge and I had replied that I have a portable gauge and a T that I can run from inside the cab. I guess it is easy enough and worth checking, but I haven't done that yet. I appreciate all the suggestions, they are helpful!

I suppose interpretation might be an issue. If it stalls I bet any vacuum would go away in a hurry, right?

And of course having the brake depressed at a dead stop does not make it stall, nor does simply slowing down.

 

[SteveH]

Even thought I recommend hooking up a gauge, I think a brake booster leak big enough to kill the engine would create a noticeable sound or other sensation (pedal feel) such that you wouldn't need a gauge - just thinking out loud.

I would also run a test by temporarily disconnecting the HAC valve (mine never seemed to make any difference) and get rid of anything that could be overreacting during this delicate return-to-idle time frame.

Are there any dash pots on the throttle that keep it from snapping shut under decel? This his how my '66 Mustang would stall - when you floored it, and then suddenly backed off, it would snap the throttle shut and die, due to too much gas and no more air. Many later carbs (GM, Ford) had dash pots that prevent the throttle from snapping shut and overfueling the engine. When these dash pots were defective/missing, you'd get an off-throttle stall. I just don't recall if FJ60s have such a device.

 

[Rzeppa]

Even thought I recommend hooking up a gauge, I think a brake booster leak big enough to kill the engine would create a noticeable sound or other sensation (pedal feel) such that you wouldn't need a gauge - just thinking out loud.

True. I had a leaky booster in my '76. It never made the engine run any differently, but just made it hard to press the brake pedal enough to stop! Because I didn't know better back in the 1980s, I drove it like that for however many months and ended up burning up exhaust #5. That was an expensive lesson.

I would also run a test by temporarily disconnecting the HAC valve (mine never seemed to make any difference) and get rid of anything that could be overreacting during this delicate return-to-idle time frame.

That's an interesting idea. I *think* the HAC is supposed to always be on when above a certain elevation (about 4,000 feet), and always be off below that. There is actually some hysteresis according to the manual, but at 7,000 feet it should always be on.

Are there any dash pots on the throttle that keep it from snapping shut under decel? This his how my '66 Mustang would stall - when you floored it, and then suddenly backed off, it would snap the throttle shut and die, due to too much gas and no more air. Many later carbs (GM, Ford) had dash pots that prevent the throttle from snapping shut and overfueling the engine. When these dash pots were defective/missing, you'd get an off-throttle stall. I just don't recall if FJ60s have such a device.

What is a dash pot? Nevermind - Wiki to the rescue:

"A dashpot is a mechanical device, a damper which resists motion via viscous friction. The resulting force is proportional to the velocity, but acts in the opposite direction, slowing the motion and absorbing energy. It is commonly used in conjunction with a spring (which acts to resist displacement)."

I don't think so. There are at least 4 vacuum diaphragm actuators on the carb. Choke breaker, AC idle kick up, secondary actuator, and a fourth one I forget what it does (manual isn't in front of me). I have watched the AC idle kick up operate as the compressor cycles on and off.

Instead of disconnecting just the HAC, I wonder what would happen if I disconnected both vacuum advance diaphragms from the distributor and drove around?

 

[SteveH]

Since mechanical advance provides (allegedly) 80% of all spark advance, all you should notice with the vacuum advance disconnected is just a bit less power. Go for it.

 

[Rzeppa]

Since mechanical advance provides (allegedly) 80% of all spark advance, all you should notice with the vacuum advance disconnected is just a bit less power. Go for it.

I don't know if it is quite that much, but certainly more than half. I know the manual says HAC is 7°. I don't know what the spark control advance is. But yeah, I've done that before. When I first got my Jim C. carb for my 71 I still had the stock retard distributor on it so I capped off the ported vacuum on the carb until I could install a non-USA advance distributor. It wasn't bad, but definitely got more kick when I got the proper distributor.

 

[BreckBJ44]

The HAC starts to open and allow a second air addition channel to the carb at around 2000 feet. It maxes out and is at full open at 4000 feet so here, the HAC does the same as running with that hose connected to the air cleaner. It does however allow for a richening of the mixture when dropping below 4000 feet which I used to do often in my 87 60. I still would have to do a lean drop idle set If I was staying down there for long...

I will be bringing my whole complete 60 Harness with me when I come back down to town tomorrow night. Let me know a good way to get it to you as I (as always it seems) will not be able to make the meeting due to a work commitment.

 

[Rzeppa]

The HAC starts to open and allow a second air addition channel to the carb at around 2000 feet. It maxes out and is at full open at 4000 feet so here, the HAC does the same as running with that hose connected to the air cleaner. It does however allow for a richening of the mixture when dropping below 4000 feet which I used to do often in my 87 60. I still would have to do a lean drop idle set If I was staying down there for long...

I will be bringing my whole complete 60 Harness with me when I come back down to town tomorrow night. Let me know a good way to get it to you as I (as always it seems) will not be able to make the meeting due to a work commitment.

Thanks Kraig. Yeah I studied the manual quite a bit, and the HAC bleeds air into all three carb circuits, primary, secondary and idle. And of course advances the distributor, 7° according to the manual. What I am trying to wrap my brain around is what might (1) intermittently adversely affect either timing or mixture ONLY under the dynamic condition of rolling to a stop AND (2) was something that somehow got buggered up when I changed the jet and timing for smog and somehow didn't get fixed when I put the old jet back in and put the timing right back where it was. I have certainly been keeping (3) in mind: it just came up on its own and had nothing to do with the smog stuff, which is where the majority of these suggestions have been running.

 

[BreckBJ44]

I'm back in town if you want to play with that computer. I live downtown but will be heading south tomorrow and over the weekend if you are around.

K

 

[BreckBJ44]

One silly question... do you engine brake when this happens? Maybe you are backfeeding pressure somewhere into the system?

I was thinking that if the engine runs a vacuum when running at idle or above, wouldn't engine braking actually put positive pressure into the system if a check valve wasn't working properly? Just an idea.

K

 

[Rzeppa]

One silly question... do you engine brake when this happens? Maybe you are backfeeding pressure somewhere into the system?

I was thinking that if the engine runs a vacuum when running at idle or above, wouldn't engine braking actually put positive pressure into the system if a check valve wasn't working properly? Just an idea.

K

No, just the usual way to come to a stop. Shift into neutral around 10 MPH or less and then push down on the clutch pedal while braking to a stop.

I did eliminate one more system today. When I went out driving, I disconnected the HAC distributor advance line and plugged it. I did get one stall, so that ain't it.

 

[trucruiser]

Jeff,
Any status updates? Chompin at the bit here.
I picked up a carb, not new or rebuilt but rather low mileage. Im gonna try this out and see if it changes anything. Im still battling the same issue.

Carlos

 

[Rzeppa]

Jeff,
Any status updates? Chompin at the bit here.
I picked up a carb, not new or rebuilt but rather low mileage. Im gonna try this out and see if it changes anything. Im still battling the same issue.

Carlos

Hi Carlos, last update was unhooking the HAC vacuum advance line at the distributor diaphragm and plugging the line. It really did not make any difference. I drove around and got one stall.

Two things I haven't tried are (1) removing the solenoid and idle mixture screw and spraying that idle passage with carb cleaner and (2) popping the top off the carb and looking to see if there is any debris in the bowl. I have been avoiding these 2 steps because they are time consumng and kind of a PITA. As I was explaining to Ricardo at the meeting, we can take the top off our '71 carbs in about 15 minutes, maybe even less, but on a darn 60 it takes almost that long just to get the air cleaner cover off! There's a lot more junk on a 60!

We are taking her on a road trip to Ouray next week, but I don't expect any problems other than the intermittent stall when rolling to a stop. She runs great on the road, and once you stop she'll sit there and idle all day.

 

[subzali]

for giggles you could try the brake booster line. I know it doesn't make sense, but weirder things have happened.

 

[Rzeppa]

for giggles you could try the brake booster line. I know it doesn't make sense, but weirder things have happened.

Of course. I haven't completely discounted vacuum leaks, but I keep asking myself "What has changed?" and also have noted that you do not have to press on the brake for the stalling to occur as you roll along. There was one instance on our road trip where Linda went to change gears and left the clutch depressed for longer than just the gear change without pressing on the brake pedal, and she stalled.



There was another instance where we drove through a torrential downpour outside of Gunnison and she bucked and stumbled. At the time I figured it was either a fuel delivery issue or an ignition issue based on the seat of the pants symptoms. After the road dried out and she dried out under the hood (one of the fender splash shields is missing on the distributor side) I surmised that she was leaking HV from the plug wires. I will replace the plug wires and get a new splash shield, and halfway expect this to be my root problem!

 

[trucruiser]

Last night I finally got a chance to swap on the other carb i picked up , and it seems to have cleared up my symptoms, It now idles great and during my test drive last night it wouldnt die at stops. Idle is right aroung 700 RPM's and its very smooth.
One observation was my carb mounting nuts were loose, I dont think that was the cause of my problem but im sure it had some effect.

Cheers