Hesitation & anti-diesel solenoid (1 Viewer)

[pavlis613]

Been wrestling with a major hesitation situation with my 71 FJ40. Been floundering around for over a month.

Truck idles great, and once you get past a massive flat spot it runs great again. But there is a 'dead zone' between (roughly) 1200 and 1800 rpm. If you let the gas pedal linger in this zone the engine will die.

Here's what we've done:
-carb rebuilt by well-respected local guy
-new ignition parts-Pertronix, rotor, cap, plugs, coil, wires.
-new vacuum lines (vac readings 18-22)
-new air & fuel filters
-compression tested: 124-133
-timed and idle set at 680 (idles great)

None the things we've done or tried over the last month have worked.

Today, just before taking off the carb for a trip back to the rebuilder, I tried one last thing. I disconnected the anti-diesel solenoid---on the premise that the 'hesitation' was so massive and complete that it felt like the fuel was actually being shut off in the first moments of acceleration. Which is what I'm told is exactly what the solenoid supposed to do when you turn off the key.

At any rate (and sorry this is so long) it seemed to work! The nice smooth idle went away, but for the first time since I've owned it, the truck rev'd smoothly. Even from the lumpy idle.

Has anyone ever heard of this before? Does it make sense? Are these solenoids available to buy anywhere? (I have looked.) Can the solenoid be removed?

Help.

 

[thebigredrocker]

Congrats on owning a 71

Aisan carb correct?

What do you have timing set at now?

Stock retard dizzy with vacuum retard canister capped or plumbed into the VSV? If the not so popular retard dizzy is what you have, FJ40Jim recommends capping the vac fitting and bumping timing up to 10°. Doing this will disable the retard function and use the internal weights for advance only.

When you unhook the idle solenoid your engine should die. A possible reason it didn’t die is because you have the idle speed screw turned in too far. This screw cracks open the primary butterfly plate enough to pull fuel from the main nozzle. It’s supposed to be barely cracked open.

That is a '71 carb.

Do not connect any vac hose to the '71 vac retard distributor. Just set base timing to 10*BTDC and run as mechanical advance only.
Cap off manifold vac fitting (#3).

Cap the giant hose fitting on the air cleaner lid that used to feed clean air to the AIR pump. It's just letting dirty air right into the top of the carb.

Install large diameter oil-proof hose between currently capped air cleaner barb and fitting on valve cover. Maybe available from Toyota?

There is a rubber seal that should be in the neck of the air cleaner to seal it against the carb air horn. Get a new one from Toyota.

Back the idle mix screw (#1) out 4 or 5 turns to get a decent idle. Adjust the idle speed screw (hidden on back side of carb) to get the desired idle speed. If it will idle at 6-700RPM, then turn in idle mix screw until idle speed starts to drop, turn back out to achieve peak/smoothest idle.
If it will not idle correctly, then it likely is running too lean due to:
-manifold vacuum leak
-plugged carb idle passage
-warped carb body &/or air horn.

HTH

FJ40Jim also commented in the thread beliw
Fast Idle

 

[thebigredrocker]

Also remember to gap your spark plugs. Oregon FJ just solved an issue that sounds similar to what your head scratching on. Turned out his spark plug gaps were to tight.

 

[pavlis613]

Congrats on owning a 71

Aisan carb correct?

What do you have timing set at now?

Stock retard dizzy with vacuum retard canister capped or plumbed into the VSV? If the not so popular retard dizzy is what you have, FJ40Jim recommends capping the vac fitting and bumping timing up to 10°. Doing this will disable the retard function and use the internal weights for advance only.

When you unhook the idle solenoid your engine should die. A possible reason it didn’t die is because you have the idle speed screw turned in too far. This screw cracks open the primary butterfly plate enough to pull fuel from the main nozzle. It’s supposed to be barely cracked open.



FJ40Jim also commented in the thread beliw
Fast Id

Congrats on owning a 71

Aisan carb correct?

What do you have timing set at now?

Stock retard dizzy with vacuum retard canister capped or plumbed into the VSV? If the not so popular retard dizzy is what you have, FJ40Jim recommends capping the vac fitting and bumping timing up to 10°. Doing this will disable the retard function and use the internal weights for advance only.

When you unhook the idle solenoid your engine should die. A possible reason it didn’t die is because you have the idle speed screw turned in too far. This screw cracks open the primary butterfly plate enough to pull fuel from the main nozzle. It’s supposed to be barely cracked open.



FJ40Jim also commented in the thread beliw
Fast Idle

Aisin carb.

Timing set at 7*

The dizzy is plumbed to the VSV.

The engine does die when I disconnect the solenoid, but it can be started with a little bit of choke. It idles poorly - around 800 rpm - but as I said it's the first time I've been able to use the throttle without the engine practically dying as it passes through the 1200-1800 rpm range.

I guess my question is this; is there an underlying logic to the fact that the hesitation disappeared with the solenoid disconnected. From my perspective, the truck rev'd smoothly from about 800 rpm and up and it's never done that before.

The other thing that maybe isn't clear is how massive this 'hesitation' is. As mentioned if you hold the throttle in the dead zone you can literally shut off the engine. That seems like too serious a thing to be simply a timing issue. [Just trying to make sure everyone understands that the prob isn't just an annoying little hiccup or stutter---it's a massive, engine-croaking event. ]

Thanks for the quick response, guys. Can you give me your opinions on the possibility of the solenoid playing some part in the problem?

 

[pavlis613]

Also remember to gap your spark plugs. Oregon FJ just solved an issue that sounds similar to what your head scratching on. Turned out his spark plug gaps were to tight.

Thanks. Will check the gaps tomorrow.

 

[thebigredrocker]

I’d take the VSV out of the loop.

 

[thebigredrocker]

With engine WELL warmed up, Was your vacuum a steady 18+ at idle when the solenoid was hooked up? Does the solenoid make an audible click when you turn the key to ON?

As I mentioned earlier, with the ICS disconnected, I don’t think it should idle if your idle speed screw is properly adjusted. Sure it may start, but it should die if you plug the idle crcuit like you did by diconnecting the wire. If your primary butterfly is too far open at idle the carb will pull fuel from the main nozzle. I’d back the carb adjustment screws that reside in and around the throttle cable out. The screw that opens your throttle butterfly plate should barely make contact. On your carb base or “throttle body”, screw the brass idle mix in til it just bottoms out. Take care not to force it in too far and gouge the tip. FJ40Jim recommends then backing it out 4 full turns or IOW 1440°‘S.


I had a huge hesitation on my 71 that turned out to be a manifold vaccum leak. It was hard to find. It was the #6 cylinder. Hopefully you don’t have a leak.

Pretty common for the old brake boosters to leak. I pulled my booster hose from the check valve side. Stuffed the smooth end of a drill bit in it to plug it. My booster was indeed leaking, plugging it improved running condition. I’ve since replaced it with City Racer’s replacement booster.

The aisan carb’s don’t like vacuum leaks.

 

[pavlis613]

With engine WELL warmed up, Was your vacuum a steady 18+ at idle when the solenoid was hooked up? Does the solenoid make an audible click when you turn the key to ON?

As I mentioned earlier, with the ICS disconnected, I don’t think it should idle if your idle speed screw is properly adjusted. Sure it may start, but it should die if you plug the idle crcuit like you did by diconnecting the wire. If your primary butterfly is too far open at idle the carb will pull fuel from the main nozzle. I’d back the carb adjustment screws that reside in and around the throttle cable out. The screw that opens your throttle butterfly plate should barely make contact. On your carb base or “throttle body”, screw the brass idle mix in til it just bottoms out. Take care not to force it in too far and gouge the tip. FJ40Jim recommends then backing it out 4 full turns or IOW 1440°‘S.


I had a huge hesitation on my 71 that turned out to be a manifold vaccum leak. It was hard to find. It was the #6 cylinder. Hopefully you don’t have a leak.

Pretty common for the old brake boosters to leak. I pulled my booster hose from the check valve side. Stuffed the smooth end of a drill bit in it to plug it. My booster was indeed leaking, plugging it improved running condition. I’ve since replaced it with City Racer’s replacement booster.

The aisan carb’s don’t like vacuum leaks.

Thanks, Rocker.

The engine was well warmed. (I've burned through almost 3/4 tank of gas since the tuning/testing started.) The vac did drop off dramatically when the flat spot hit but I assumed that was due to the drastic drop off in revs.

If there is a vac leak significant to cause this dead zone effect would the engine still be able to run as well as it does below the dead zone (idle) AND above (revving in the 2000-3000 range is smooth and powerful) ?

I have tried taking the VSV out of the vacuum system, but wasn't sure of the best way to do it---can you tell me how to route the hoses? I'll give it another try.

As to manifold leaks, we have tried several times to find one. Carb cleaner spray, oil beads, WD spray. Obviously there are places on the manifold that are impossible to see let alone test. Any advice there?

 

[Solace in Solitude]

Don’t overlook the dissy vacuum module, when looking for vacuum leaks.

Finding that leak wore me out... I had completely overlooked it.

 

[pavlis613]

Don’t overlook the dissy vacuum module, when looking for vacuum leaks.

Finding that leak wore me out... I had completely overlooked it.

We looked at mine. The vac module was getting vacuum and the mechanism inside it wasn't frozen. We tried to separate the module from the diss, but it wasn't going to come off easily and we didn't want to break it.

Can you tell me how you tested yours? How you fixed it?

Thanks.

 

[thebigredrocker]

You can use a handheld vaccum pump to apply suction. If you see it rotate the points plate and hold then no leak. If it moves the points plate and the plate immediately returns, then you have a leak.

Retard dissy the plate moves clockwise.


Besides the dissy, what all do you have hooked up to the VSV?

 

[pavlis613]

Thanks for that info. I'll try it tomorrow.

One VSV port goes to the diaphragm on the carb, the other two go to ports on the carb. Not really sure what they all do. Do you?

 

[thebigredrocker]

The diaphragm on the carb is often called the choke breaker, CB or choke pulloff. At full choke, when your rig starts the CB linkage automatically cracks open the choke plate a bit. The CB also has a linkage connected that funtions as a throttle positioner. I’ve seen FJ40Jim mention the TP can be removed.

Your carb should be sitting on a insulator that has a small driver side port you can hook the CB into. The insulator also has a big port in front for the PCV valve.

The port on passenger side of fuel bowl is a manifold vac emissions port. You can cap it.

You mentioned 3 ports on the carb. Do you have a passenger side vac port near the idle mix screw? On the throttle body? If so, that’s a good source of “ported vacuum” for an advance dissy.

Cap your retard dissy if that’s what you have.

Big port on valve cover should plumb into a port on the air cleaner.

 

[FJ40Jim]

Reconnect the ICS. It is obviously functioning.

Rev the engine up to the "die-off" speed. Place hand over carb to choke off most air into carb.

If choking off air improves running speed & smoothness, then engine needs more fuel.

If choking off air kills engine worse, then it is drowning in fuel.

It is not a vacuum leak, because that would be worst at idle. It is not a weak ignition system because it would get worse as revs/load increased.

HTH

 

[Dizzy]

For the sake of Rocker's analysis, if you have opened the idle mix screw excessively, and the primary throttle plate is basically closed because air is entering from, let's just say the vapor purge or brake booster line, then when you do give it some throttle, would that not create a fuel-starved condition which is most pronounced just above idle?

Does the choke breaker's throttle positioner get tripped when vacuum reaches the choke breaker diaphragm, or do you have to depress the gas pedal to let the throttle positioner screw free?

 

[FJ40Jim]

For the sake of Rocker's analysis, if you have opened the idle mix screw excessively, and the primary throttle plate is basically closed because air is entering from, let's just say the vapor purge or brake booster line, then when you do give it some throttle, would that not create a fuel-starved condition which is most pronounced just above idle?

No. If the idle mix screw is over-rich, then it will be over-rich up until the carb transitions mostly on to the main circuit.

Does the choke breaker's throttle positioner get tripped when vacuum reaches the choke breaker diaphragm, or do you have to depress the gas pedal to let the throttle positioner screw free?

The vacuum is strong enough to move the TP, even when the throttle is pressing against it at idle.

 

[pavlis613]

The diaphragm on the carb is often called the choke breaker, CB or choke pulloff. At full choke, when your rig starts the CB linkage automatically cracks open the choke plate a bit. The CB also has a linkage connected that funtions as a throttle positioner. I’ve seen FJ40Jim mention the TP can be removed.

Your carb should be sitting on a insulator that has a small driver side port you can hook the CB into. The insulator also has a big port in front for the PCV valve.

The port on passenger side of fuel bowl is a manifold vac emissions port. You can cap it.

You mentioned 3 ports on the carb. Do you have a passenger side vac port near the idle mix screw? On the throttle body? If so, that’s a good source of “ported vacuum” for an advance dissy.

Cap your retard dissy if that’s what you have.

Big port on valve cover should plumb into a port on the air cleaner.

Sorry for my ignorance, but what is a retard distributor?

Reconnect the ICS. It is obviously functioning.

Rev the engine up to the "die-off" speed. Place hand over carb to choke off most air into carb.

If choking off air improves running speed & smoothness, then engine needs more fuel.

If choking off air kills engine worse, then it is drowning in fuel.

It is not a vacuum leak, because that would be worst at idle. It is not a weak ignition system because it would get worse as revs/load increased.

HTH

Because it idles so well below the dead zone and revs smoothly and with power above the dead zone, I've always thought that the basics of vacuum, fuel, and ignition were sound. And that it had to be something very specific. Which is what led me down the ICS rathole.

I'm running out of things to try.

Could it be some piece of carb linkage that's malfunctioning. Or not functioning?

It's my (very) shallow understanding of the way carburetors work that there are "circuits" that manage the different fuel/air/whatever requirements of the engine as different load and rpm states are needed.

Is there carb linkage that is in place (or should be) specifically to handle the engine demands between idle and 2000 rpm?

The heat control valve in the exhaust manifold is frozen solid. I've assumed that the good high end performance meant it is frozen open and once the engine is warmed would not be a factor. Might it though?

Some other obscure widget?

THX

 

[FJ40Jim]

Most 69-75 USA distributors have vacuum retard. That is a largely useless smog control device. It is more useful to have a vacuum advance distributor.
Regardless, the type of vacuum controlled timing the truck is equipped with is not germane to this diagnosis.

Perform the simple diagnostic test and report back if it is leaning out or drowning. We'll go from there.

 

[pavlis613]

Most 69-75 USA distributors have vacuum retard. That is a largely useless smog control device. It is more useful to have a vacuum advance distributor.
Regardless, the type of vacuum controlled timing the truck is equipped with is not germane to this diagnosis.

Perform the simple diagnostic test and report back if it is leaning out or drowning. We'll go from there.

The engine "revives" when I put my hand on the carb.

 

[FJ40Jim]

Excellent work, that narrows it down considerably! It would seem that it is running lean when transitioning from idle circuit to main circuit.

Possible culprits include:
restricted or too small primary slow jet,
restricted or too small primary main jet,
primary & secondary boosters mixed up....