2F Hesitation/stumbling at various RPMs

[Yankee]

If the manifold assembly has never been machined flat by a machinist in the past, it’s guaranteed to be warped and not sitting flush on the head. At this point- all virgin 2F manifold assemblies are warped. Mine was warped in 1988 when the engine only had 42K on it.

Does the bolt holes that connect the intake and exhaust to the engine head need to be machined as well after the front surface has been machined flat? I'm suspecting that my issue might be that since the surface was machined flat, the bolt doesn't sit evenly between the intake and exhaust holes. The bolt, when torqued down to the head, torques the exhaust side down but not the intake as the surface is slightly below the exhaust side. This is making me think that the intake wasn't getting fully bolted down since its bolt holes are not even with the exhaust holes. Does this sound reasonable? If the holes are not even, is there a process to get the bolt hole sides to be even that isn't guess and check?

 

[mattressking]

Does the bolt holes that connect the intake and exhaust to the engine head need to be machined as well after the front surface has been machined flat? I'm suspecting that my issue might be that since the surface was machined flat, the bolt doesn't sit evenly between the intake and exhaust holes. The bolt, when torqued down to the head, torques the exhaust side down but not the intake as the surface is slightly below the exhaust side. This is making me think that the intake wasn't getting fully bolted down since its bolt holes are not even with the exhaust holes. Does this sound reasonable? If the holes are not even, is there a process to get the bolt hole sides to be even that isn't guess and check?

You won't like what I'm going to say but the best method to machine these things flat is to loosen the assembly, put new gaskets in, leave the 3 mounting bolts very loose, then clean the mounting surfaces to head and bolt down tight without gasket to head. Then tighten the 3 bolts that combine intake to exhaust manifold.

Once tight and aligned, then you put on a surface plate and measure run out, not to exceed .5mm. If it does, time to machine, if it doesn't, I highly recommend stock gasket with copper rtv to seal up versus machining.

Folks like the Remflex but they are sensitive gaskets, I'm not much of a fan long term.

 

[OSS]

This is a common issue. The half circle bolt ‘flange’ on the exhaust manifold doesn’t line up with the corresponding intake manifold one— so only one of the manifolds gets clamped tight to the head at that spot.

The workaround is to use half circle washers as shims — set on the low flange to level out the difference so that the bolt or nut will compress the pair evenly.

Advice on whether I should buy a Land Cruiser

What do you mean has caused you some excitement? I don't wanna talk about it.

forum.ih8mud.com

@2mbb

 

[Yankee]

I got some washers and cut them in half to use as half circle washers, but the issue is that the washers are too thick (even just being around 1.5mm) and cause the intake flange to be higher than the exhaust flange which would then be the opposite problem. The difference between the intake and exhaust flanges height wise is about 0.5mm. Is there something a machine shop could do to make these flanges even? I tried having the machine shop I usually go to do something about the flanges but the guy I was talking to just said to use half circle washers as well and that they couldn't do anything. Maybe if I talked to a more experienced person at the shop they would know of something they could do. Any suggestions for what I could ask them to do to help?

 

[Yankee]

Hello again!

Bringing a dormant thread back to life with some updates. I ended up taking my manifolds into a different machine shop that was able to machine the bolt ear holes flat as well as fix some other issues on the manifolds. I also took my carburetor in and got it rebuilt.

I only just got the carburetor back so that's why things have been dormant here without any updates. However, I'm not out of the woods just quite yet. After putting everything back together, I grounded my white ICS cable to my carb as my carb rebuilder guy told me to do like so.

After doing all of that, I started the 60 up and had the choke pulled out and it was idling fine until it was mostly warmed up and I had the choke all the way down. Once it was warmed up and I put the choke down, it sounded like it was backfiring a little and sounding rough. Could be timing, but I'm not sure yet. The biggest issue I have is that now when I rev the motor up to 2k rpm, the motor instantly wants to stall and fall on its face. I have a video here showing exactly what it's doing.

New video by Zachery McLaughlin

photos.app.goo.gl

Hopefully that link works. If not, let me know and I can find some other way to upload it.

My question is: did I incorrectly bypass the ICS and that's what's causing the sudden drop off? My fuel pump is new, my lines seem fine, so I'm unsure if I did something wrong there.

 

[OSS]

Try grounding the wire that connects to the vacuum switch. Unplug the wire from the vacuum switch and ground the wire to the body.
Then see if that helped anything.
@Yankee

 

[Yankee]

Try grounding the wire that connects to the vacuum switch. Unplug the wire from the vacuum switch and ground the wire to the body.
Then see if that helped anything.
@Yankee

View attachment 3679784

I just tried that and it didn't help anything. I'm wondering if maybe it's an ignition issue? Maybe something to do with my igniter/solenoid?

 

[Pighead]

What is your timing set at?

 

[OSS]

I’m still circling around the possibility that it’s a FCS malfunction issue due to the Deceleration Fuel Cut System.

I extracted the section on the Deceleration Fuel Cut system from the emissions manual.

Go through it’s troubleshooting pages to make sure it’s working correctly.

You’ll notice that at above 1800 rpm and decelerating, the system actuates the FCS (when everything is working correctly). If the system has gone haywire, it can actuate the FCS solenoid above 1800 rpm always — which would create the exact same symptoms you’re seeing.

 

[Yankee]

I’m still circling around the possibility that it’s a FCS malfunction issue due to the Deceleration Fuel Cut System.

I extracted the section on the Deceleration Fuel Cut system from the emissions manual.

Go through it’s troubleshooting pages to make sure it’s working correctly.

You’ll notice that at above 1800 rpm and decelerating, the system actuates the FCS (when everything is working correctly). If the system has gone haywire, it can actuate the FCS solenoid above 1800 rpm always — which would create the exact same symptoms you’re seeing.

Thank you for sending over those docs. I went through those pages and it seems that everything is working as intended. The FCS is actuating (clicking) when the positive connect and disconnects, and the vacuum switch is showing continuity. Could the FCS still be operating incorrectly even if it's clicking?

 

[OSS]

The FCS is controlled by the emissions computer. It’s not impossible for the emissions computer to malfunction, though it’s rare.

Just to rule it out, you could wire the FCS with temporary jumpers so it’s always energized no matter what, then do a test run with the engine.
If it’s still sputters & stumbles as before at higher RPMs, then the problem isn’t the FCS or the emissions computer.
It would be nice to rule these two unknown variables out to help find the culprit.

 

[Yankee]

The FCS is controlled by the emissions computer. It’s not impossible for the emissions computer to malfunction, though it’s rare.

Just to rule it out, you could wire the FCS with temporary jumpers so it’s always energized no matter what, then do a test run with the engine.
If it’s still sputters & stumbles as before at higher RPMs, then the problem isn’t the FCS or the emissions computer.
It would be nice to rule these two unknown variables out to help find the culprit.

How would I wire it to be always on? As I posted earlier, I grounded the white wire of the FCS to the carb. Would it be different than that?

 

[OSS]

It’s power source (12v+) is fed through the wire that connects to the wiring loom. The green plug.

Unplug it and connect jumper wires to the plug. If that’s not something you feel comfortable doing, then just move on to something else and assume it’s ok.

When the ignition key is turned on, you can hear it click. The click is the solenoid being energized and the plunger snaps opens, allowing fuel to flow.
But when the engine is running, you can’t hear what it’s doing. If the emissions computer is flipping it off at higher RPMs, you can’t tell if that’s actually what’s happening.

 

[Yankee]

It’s power source (12v+) is fed through the wire that connects to the wiring loom. The green plug.

Unplug it and connect jumper wires to the plug. If that’s not something you feel comfortable doing, then just move on to something else and assume it’s ok.

When the ignition key is turned on, you can hear it click. The click is the solenoid being energized and the plunger snaps opens, allowing fuel to flow.
But when the engine is running, you can’t hear what it’s doing. If the emissions computer is flipping it off at higher RPMs, you can’t tell if that’s actually what’s happening.

So I should just remake the original connection like in this (crudely) drawn diagram I made? Visuals really help me so I thought I'd try to draw it out haha. From what it sounds like you're saying is to just remake the original connection to the plugs with jumper cables.

 

[OSS]

This thread linked below has some more comments on the Fuel Cut Solenoid.
(Your engine problem may not be caused by the FCS turning off unexpectedly, but it’s good to rule it out).
@Spike Strip has a good comment on that thread.

FJ60 fuel cut off solenoid

forum.ih8mud.com

 

[Yankee]

This thread linked below has some more comments on the Fuel Cut Solenoid.
(Your engine problem may not be caused by the FCS turning off unexpectedly, but it’s good to rule it out).
@Spike Strip has a good comment on that thread.

FJ60 fuel cut off solenoid

forum.ih8mud.com

So I've tested the FCS using both the battery and with the regular plugs and it's clicking, so that should mean that it's working correctly. I'm starting to wonder if it has something to do with either my spark plug wires, distributor, or coil. Anyone know how to test the coil or distributor?

 

[Yankee]

Another update y'all: I tested the spark plugs wires and the cap and rotor of the dizzy and all of them look/tested good. I ordered a new OEM Denso coil thinking maybe the coil is on the fritz, but I installed the new one today and the sputtering around 1600-2000 rpm is still present. Going to now do a fuel pressure test to see if it's either a fuel or air related issue. Any ideas?? I'm starting to run out of them haha.

 

[SoCalViking]

Another update y'all: I tested the spark plugs wires and the cap and rotor of the dizzy and all of them look/tested good. I ordered a new OEM Denso coil thinking maybe the coil is on the fritz, but I installed the new one today and the sputtering around 1600-2000 rpm is still present. Going to now do a fuel pressure test to see if it's either a fuel or air related issue. Any ideas?? I'm starting to run out of them haha.

Just found this thread -- any update since July? My FJ60 has the stuttering issue but not getting the sputtering noise you are experiencing.

 

[Yankee]

Just found this thread -- any update since July? My FJ60 has the stuttering issue but not getting the sputtering noise you are experiencing.

Hey there!

Yes, I meant to update this thread since I had last posted.

When August rolled around I essentially gave up on figuring out what was wrong and decided to take it to a local classic car shop that my family and I had taken some of our classic cars to. The shop was closer than the Landcruiser shop I had taken my carburetor to which was important since my FJ60 was non-op and I had to tow it down. When the shop took a look and ran some tests, they narrowed the issues down to the carburetor and noted that it was running extremely lean. They decided to take the carb off and send it down to Ace Fuel in California for them to run tests and see what was going on.

Ace Fuel, after running some tests, agreed with what the shop said about the carb and recommended a full rebuild. Despite already having the carb rebuilt by a Landcruiser shop that costed me close to a grand and 3+ months of my time waiting, I decided to let them rebuild the carb again. When they rebuilt the carb, they discovered that the Power Valve was replaced and was defective, the Idle Solenoid O-ring was incorrect, and the Float Drop Spec was wrong. This meant that the previous shop (note: it was a Landcruiser shop) rebuilt my carb incorrectly. Once they rebuilt the carb and sent it back to my shop up here, the truck ran so much better, but still had a power sag at full throttle so they sent it back free-of-charge to have the carb tuned more. The shop received the carb shortly after and it ran even better, albeit some sag at full throttle. I am chalking the power sag to being vacuum-related since the shop didn't route the vacuum lines correctly for a desmogged application, which I don't blame them for.

I picked up the Landcruiser shortly after and it's been a dream since. It's been running perfectly fine besides the vacuum leaks that I just need to get around to re-routing, but I couldn't be happier. Hopefully this thread here will be able to help someone else down the road. When in doubt, check the carburetor again.

TLDR: Got carburetor rebuilt by a Landcruiser shop to fix stuttering issue, waited 3+ months and paid close to $1k, issue still persisted and pulled my hair out checking everything else, gave up and sent cruiser down to a different shop, found out carb was rebuilt incorrectly/with defective parts, rebuilt it correctly, now it runs like a top.

 

[Ry24000]

I picked up the Landcruiser shortly after and it's been a dream since.

It's been running perfectly fine besides the vacuum leaks now it runs like a top.

Really? OK? does it run like a top with those vacuum leaks? Did you fix them or what?