Builds The 60 known as Mamabear: a tale of rust and good times. (5 Viewers)

[HemiAlex]

The stumble and misfire is back. After a round of frantic diagnosing and parts replacing, it’s driving terribly.

-checked for vaccum leaks. Couldn’t find any.
-inspected all vaccum lines. No cracks.
-replaced the city racer with a factory aisan. No change
-inspected and replaced the distributor cab, rotor and plugs. No fouling or issues there.
-replaced the fuel filter. Looked better since I’ve replaced the fuel tank.

Valves were adjusted about 15,000 miles ago in January, distributor was rebuilt by JimC last year, intake gasket was replaced before Xmas, fuel tank done a few months ago...and we just got done with a trouble free trip of 3,000 miles stopping at every gas station we saw.

It was idling poorly the other day, and stalling at idle. I played with the carb and it got better. The following day it went away. Now it’s bucking under any load, not accelerating past 2000 rpm, it will buck back after a shift and has a ton of hesitation.

If it is a tank of bad fuel, I’ve topped off 12 gallons somewhere that i trust, added iso HEET Incase there is water in the fuel and I’m trying to burn out most of this tank of fuel so I can drain the tank completely.

It just figures that I start playing with our 40 and this truck throws a fit.

I’m out of ideas.

 

[klinetime574]

What about the ignition coil? Not too familiar with testing one but I’m sure you could find it in the manual. Maybe even plug wires. Or it could be getting hot and acting up.

 

[HemiAlex]

Coil is a year old oem and ignitor seems to work.

I swapped in my back up coil and ignitor, same thing. Nothing changed.

 

[klinetime574]

Hmm. No vacuum leaks, what reading were you getting at idle? Should be a steady 21-ish.

If you’ve ruled out all fuel (carb, filter), air (no vacuum leaks), and spark (ignitor, coil, wires, dist, plugs). Then you’ve got a conundrum. Of course we’re assuming all parts are good. Swapped parts and not swapped parts.

I want to know the problem lol

 

[HemiAlex]

It’s right at 19 inches of vacuum. Good for what the motor is.

I’m wondering if it’s starved for fuel under load from a bad pump (recent kyosan) or it’s all bad fuel.

The fuel will be drained tomorrow morning.

 

[mattressking]

It’s right at 19 inches of vacuum. Good for what the motor is.

I’m wondering if it’s starved for fuel under load from a bad pump (recent kyosan) or it’s all bad fuel.

The fuel will be drained tomorrow morning.

If you have gas in middle of sight glass at idle, wouldn’t assume fuel pump. Is ICS hooked up? Or white wire grounded ? Do the idle issues occur after warmed up? If you stop the truck and let it cool down (not sure what ambient temps are but sub 80s) does the issue go away then come back when warmed up?

Charcoal canister properly venting?

Stupid but loose plug wires on distributor cap/plugs?

I had this but it was temp dependent, found multiple leaks on IM gasket so I sealed it up (no machining) and bolted back up, no issues. Did that a day before SAS, 4K miles later, still good.

Could try choking the carb at idle, (people call it the okie rebuild on here?) see if that would resolve debris in carb from bad fuel before assuming fuel system.

 

[HemiAlex]

Fuel didn’t look great. This is a 7 year old tank.

It drove fine on the way here and after about 15 mins it started misfiring under load.

Let’s see if it was all fuel. Just drained 15 gallons out and I’ll go get a full tank of non ethanol 93 today.

 

[HemiAlex]

It isn’t the fuel. It is also definitely not the plug wires. I swapped a set in just now.

The only tidbit I got about another possible avenue is about the distributor.

The air gap for the reluctor is .008-.016".
Anywhere in that range is fine. The signal generator is a go/ no-go type of thing. It either generates a timing pulse or not. It cannot cause a weak spark, but it could cause an intermittent spark. The igniter will not consistently fire one cylinder, but not another. It will either shut down for good, or misfire erratically. The igniter doesn't know if it is hitting #1 or #4 or whatever. It just makes a spark after it gets the trigger from the dizzy.

I’ll swap in my spare distributor tomorrow. That’s all I’ve got.

 

[mattressking]

When you swap carbs....are you using the same FCS? Or does each carb have its own solenoid?

I never saw anything about temperature dependent but "started misfiring after 15min of driving". So can you say that its fine when cold but once hot, the issue appears?

If so, somewhere to me sounds like a vacuum leak. Have you checked vacuum hot and cold if so?

When you say it is misfiring, that would mean that you can pull one plug wire at a time and hear additional misfire at idle, if one doesn't change the idle, usually thats the cylinder that is culprit. Does choke assist in issue?

If you drive past a certain rpm, say 1600rpms, does the issue go away or is it misfiring all the way through powerband?

 

[HemiAlex]

If you have gas in middle of sight glass at idle, wouldn’t assume fuel pump. Is ICS hooked up? Or white wire grounded ? Do the idle issues occur after warmed up? If you stop the truck and let it cool down (not sure what ambient temps are but sub 80s) does the issue go away then come back when warmed up?

Charcoal canister properly venting?

Stupid but loose plug wires on distributor cap/plugs?

I had this but it was temp dependent, found multiple leaks on IM gasket so I sealed it up (no machining) and bolted back up, no issues. Did that a day before SAS, 4K miles later, still good.

Could try choking the carb at idle, (people call it the okie rebuild on here?) see if that would resolve debris in carb from bad fuel before assuming fuel system.

ICS is hooked up and working, no extra grounding. I can hear the click. It seemed to be temp related over time.

Charcoal canister is bypassed since I'm running the Rest of world non-smog carb.

Plug wires were tight and checked.

Intake gasket was resealed in January and has been good. Choking the carb worked for me in the past as a fix for a few weeks, but this used Aisan was spotless inside.

 

[HemiAlex]

When you swap carbs....are you using the same FCS? Or does each carb have its own solenoid?

I never saw anything about temperature dependent but "started misfiring after 15min of driving". So can you say that its fine when cold but once hot, the issue appears?

If so, somewhere to me sounds like a vacuum leak. Have you checked vacuum hot and cold if so?

When you say it is misfiring, that would mean that you can pull one plug wire at a time and hear additional misfire at idle, if one doesn't change the idle, usually thats the cylinder that is culprit. Does choke assist in issue?

If you drive past a certain rpm, say 1600rpms, does the issue go away or is it misfiring all the way through powerband?

Each one has its own solenoid. Same issues with both. It was completely fine until that 15 min mark.

Hot vacuum is 18. Not bad for the 690 idle on a really tired engine.

It was across all cylinders. I unplugged a plug wire, and that really sounded like a dead cylinder. This is completely uniform across it all. A true general misfire.

You can hear small pops at idle, but most notably at a 2000 rpm with load or no load, the the break up starts.


I replied to all of this for sake of completeness, but we are 99% sure we figured it out. I want to put this down as a record so nobody else has to fight what I went through.

I was honestly ready to pop my spare distributor in. It was getting bad. I had thoughts of pulling the 2F out if that didn't work.

Then, I messaged an land cruiser guru who works for a builder that a friend recently purchased a truck from. I explain the situation and he responds with something completely out of left field.

"Have you tried unplugging the tach wire to the coil? There are two separate connectors that go into the ignitor, one supplies the tach and I've seen this cause an odd stumble before. It's either a malfunction in the tach or perhaps the amplifier for the AC is going bad. The most recent one I dealt with bypassed the AC amplifier and had a separate switch to power the AC Clutch. He didn't care that the tach didn't work..."


My mind was blown. I unplugged the first wire and the truck wouldn't fire up. Plugged that one in, unplugged the next one and saw my tach was dead and the compressor wouldn't kick on. I drove around til the truck got to 187* and then I started flogging it for the next 30 mins. No issues. The truck ran flawlessly. It would have started messing up by now. I've driven it the last two days for at least an hour every day with no issues.

I can live with a known issue. I purchased a used AC amplifier and I'm going to try that next. I think since that is the only complex board on the truck, its not unreasonable for that to be causing interference, or maybe messing with the load of the ac compressor to cause this misfire. Once I swap my newer one in, I'm going to de-solder the RPM sensing portion of my old amplifier and try that. I never start the truck with the compressor on anyway, so it isn't a big deal. I really doubt that the tach is what's causing an issue, but I'm willing to throw another used one on for the sake of testing. It really felt like it had a soft touch rev limiter in place. The only thing that's smart enough to break and try to act like that is the AC Amp.

If anyone has to deal with this kind of strange issue....I'll document it as best I can. I never in a million years would have gone down this route if I hadn't reached out for help.

 

[Gretsch]

Man good stuff. Thanks for sharing.

 

[dogfishlake]

People that see this will be thanking you for posting it for years. Nice fix, or road to a complete fix at least.

 

[HemiAlex]

People that see this will be thanking you for posting it for years. Nice fix, or road to a complete fix at least.

That’s what I was hoping for. I’ll catalog what I do to fix it this. I’m budgeting for the amplifier, a tach and possibly an ac compressor.

I thought “how could we drive a truck without ac...”

Then I remembered that we just brought this home.

 

[dogfishlake]

That’s what I was hoping for. I’ll catalog what I do to fix it this. I’m budgeting for the amplifier, a tach and possibly an ac compressor.

I thought “how could we drive a truck without ac...”

Then I remembered that we just brought this home.

View attachment 2083310

Haha. Yes!

 

[klinetime574]

X2 about figuring that out

The FJ40 has crotch AC. Can’t beat that.

 

[HemiAlex]

I replaced the ac amplifier and it’s still acting up. I also reconnected the ouput wire on the coil, and disconnected the ac compressor wire.
The misfire didn’t go away.

I’m going to go into more diagnosis and check the wiring back to the tach with the wiring diagram.

I’m still stumped. Glad the truck is running great, upset that the ac won’t work.

 

[HemiAlex]

I think I fixed it.

I unplugged the emissions computer and it wouldn’t run.

I did the “green wire” mod to simulate the early one wire idle control solenoid on the pre emissions 2F by grounding the green wire to the body and eliminating the emissions computer. Every thing is plugged back in, no misfires. It must have been fluttering the ics due to a bad emissions computer. I could resolder the connections but I’d rather keep it simple.

 

[gregnash]

I think I fixed it.

I unplugged the emissions computer and it wouldn’t run.

I did the “green wire” mod to simulate the early one wire idle control solenoid on the pre emissions 2F by grounding the green wire to the body and eliminating the emissions computer. Every thing is plugged back in, no misfires. It must have been fluttering the ics due to a bad emissions computer. I could resolder the connections but I’d rather keep it simple.

I think I have a spare emissions computer laying around somewhere if you want to borrow to test. I know I purchased way back when I did my head thinking mine had gone bad and it really was my ICS dying.

 

[HemiAlex]

I think I have a spare emissions computer laying around somewhere if you want to borrow to test. I know I purchased way back when I did my head thinking mine had gone bad and it really was my ICS dying.

I may take you up on that. Right now I’m happy that it’s working.