Stumbling During Acceleration/Reving (1 Viewer)

[bcolvin]

Hi All,
I recently have been having a stumbling issue during acceleration and or reving the engine. Before a couple days ago the LC was running great. I have checked a bunch of threads in which this one seemed to be on the right track but I wanted to verify and get any thoughts with you all.

I have a 1984 FJ60 Desmogged by me following the desmog guide. Carb and Dizzy have been rebuild by Jim C within the past year. I have replaced all of the existing vacuum lines as well. I have a new fuel pump (three months old) and a one year old fuel filter. Over the past year my tachometer has been working intermittently which I assumed was either a grounding problem or a broken tach. I separated the green tach clip near the ignitor/coil. It seemed to work better yesterday. Today not so much when I tried to move the LC. It idles fine and runs with choke out well... just stumbles with choke in during accleration. My vaccuum off the brake is around 17... I live at about 7K ft.

I also checked the solenoid on the deceleration fuel cutoff and it clicks when unplugged/plugged in and the solenoid there was loose/not grounded well and now it is which I thought also may have fixed the issue yesterday but now no go. This was recommended in a thread by @OSS

Does this sound like the Emissions Computer or would the green wire/white wire mod be the solution? Let me know what you think or next steps could be. Thanks a bunch for your time.

 

[g-man]

that link is mostly about EGR valve problems. You say you are de-smogged so I assume there is no EGR. In that case, fuel or vacuum problem. Possibly something electrical. Did you solve this?

 

[bcolvin]

that link is mostly about EGR valve problems. You say you are de-smogged so I assume there is no EGR. In that case, fuel or vacuum problem. Possibly something electrical. Did you solve this?

I did not solve it yet. Definitely no egr. I did check for vacuum leaks but not at the manifold. I check the bolts on this but I did replace the gasket and reseal a year ago. I’m betting on electrical. I have the parts to make the jumper for the green wire mod. The more I have been reading on this the more this seems plausible. Thanks for the reply

 

[g-man]

I thought the green wire mod was to fix an inoperable ICS? To my understanding a correctly working ICS would open during acceleration and close during deceleration. So, you would feel more of a hesitation during deceleration and at idle and not feel it while accelerating. I'm guessing this could more be a problem of vacuum leak or fuel starvation.

 

[Seth S]

All of my starting, idling, stalling, driving issues went away after I gave in and did a full service of the intake/exhaust manifold side of the engine. It was about $1000 of parts and machine shop work but it’s what was needed after 30+ years

 

[bcolvin]

All of my starting, idling, stalling, driving issues went away after I gave in and did a full service of the intake/exhaust manifold side of the engine. It was about $1000 of parts and machine shop work but it’s what was needed after 30+ years

I’ll check the torque on the manifold bolts when I get back in town. I did a resurface on the manifold, new hardware, and bolts during my desmog about a year or so ago. Thanks for the suggestions.

 

[Gretsch]

I have a new fuel pump (three months old) and a one year old fuel filter.

I'm guessing this could more be a problem of vacuum leak or fuel starvation.

What kind of fuel pump was installed? Aftermarket?

I believe the input signals for having the EC activate/deactivate the ICS comes from the tach signal and the vacuum switch on the inner fender. I guess its possible your tach problems could contribute to poor ICS operation but my guess this is nothing to do with the ICS. The click test really does not tell you anything other than the ICS can work and not that it actually is at the right time. When I was sorting out issues with my ICS, it clicked all the time when testing this way, but never worked correctly during normal operation. For clarification, the green wire mod you speak of is to simply bypass all the controls of the ICS and keeping it open whenever the key is on.

I also checked the solenoid on the deceleration fuel cutoff and it clicks when unplugged/plugged in and the solenoid there was loose/not grounded well and now it is which I thought also may have fixed the issue yesterday but now no go.

Is this to mean you did the green wire mod and it did not work or you found it had a bad ground somewhere which you fixed? FYI, fixing the grounds is essentially what the green wire mod is doing. Not sure in your post which you have done here. You can easily test the 'green wire mod' by just running a set of jumpers off the open ICS plug before you get into permanent modification of the ICS circuit. Your symptoms of ICS functionality are opposite what normally happens with a malfunctioning EC/ICS control. Idle is an issue, not accelerating. I would just rule out the ICS as the cause of this issue by running jumpers on the plug and see if your issue goes away. But its likely something to do with something else.

The emissions computer needs a signal from the tachometer to control the fuel cut solenoid that’s used with the Deceleration Fuel Cut circuit. The computer needs to know the rpm to trigger the FCS at the right time.
The Deceleration Fuel Cut circuit is also controlled by the Vacuum Switch. If that switch no longer works, you’ll get that dying feeling above 1700 rpms.

From another thread but lays out the inputs for the ICS control. The jumpers will bypass all this so try that and move on to other more likely things.

Has anything been done to your coil? I had a failing coil that would cause my truck to hesitate at high RPM like you describe. I believe tach signal comes off the coil.

If your tach is intermittent as you mention, then maybe thats a possibility. HTH

 

[bcolvin]

What kind of fuel pump was installed? Aftermarket?

I believe the input signals for having the EC activate/deactivate the ICS comes from the tach signal and the vacuum switch on the inner fender. I guess its possible your tach problems could contribute to poor ICS operation but my guess this is nothing to do with the ICS. The click test really does not tell you anything other than the ICS can work and not that it actually is at the right time. When I was sorting out issues with my ICS, it clicked all the time when testing this way, but never worked correctly during normal operation. For clarification, the green wire mod you speak of is to simply bypass all the controls of the ICS and keeping it open whenever the key is on.



Is this to mean you did the green wire mod and it did not work or you found it had a bad ground somewhere which you fixed? FYI, fixing the grounds is essentially what the green wire mod is doing. Not sure in your post which you have done here. You can easily test the 'green wire mod' by just running a set of jumpers off the open ICS plug before you get into permanent modification of the ICS circuit. Your symptoms of ICS functionality are opposite what normally happens with a malfunctioning EC/ICS control. Idle is an issue, not accelerating. I would just rule out the ICS as the cause of this issue by running jumpers on the plug and see if your issue goes away. But its likely something to do with something else.



From another thread but lays out the inputs for the ICS control. The jumpers will bypass all this so try that and move on to other more likely things.

Has anything been done to your coil? I had a failing coil that would cause my truck to hesitate at high RPM like you describe. I believe tach signal comes off the coil.

View attachment 3031182

If your tach is intermittent as you mention, then maybe thats a possibility. HTH

@Gretsch thanks for the detailed response. Your threads are what I have been following. I used a kryosan fuel pump which I believe is the oem. I relatively confident not fuel delivery problems since it idles so well but not at higher rpm’s.

I’ll be back in town tonight and will try the jumper and see if the grounding does anything. If not I’ll look into the coil. This has not been touched since I have owned the vehicle. Again thanks for the suggestions.

 

[Seth S]

Something as simple as the wrong plugs (wrong like el cheap brand) with worn electrodes or improper gap can cause running problems

 

[micruz60]

Putting this in for thought: check the resistance values on all your sparkplug wires from distributor, also check the wire from coil to distributor.

 

[bcolvin]

I made the jumper and no dice. Where I am at currently, is good vacuum and running at idle. No issues. When gas/accelerator is pushed sputter and dying. When throttle is pulled out engine will run fine even when gas pedal is depressed.

The LC was running great last week and for months prior and it was a more "all of a sudden" the studdering came about. Although one month ago I did notice that I had one big studder on a hard acceleration but did not think much of it. I would think that spark plug cables and such would see issues at idle and progressively get problematic. I will definitely check these though as I am digging around for solutions.

List of items to poke around on
Coil and igniter
Spark plugs and cables
Vacuum leaks around manifold.... checking bolts etc


As always thanks for taking the time to help me learn more on the Land Cruiser.

 

[fjc-man]

Your new fuel pump was mounted with a new Bakelite spacer right? Fresh fuel filter?

 

[bcolvin]

Your new fuel pump was mounted with a new Bakelite spacer right? Fresh fuel filter?

Yep. Both less than 4 months. I will replace the fuel filter with another tomorrow just in case. I think I have a spare. I am currently making sure there are no ground issues on coil/ignitor. Thanks

 

[bcolvin]

Yep. Both less than 4 months. I will replace the fuel filter with another tomorrow just in case. I think I have a spare. I am currently making sure there are no ground issues on coil/ignitor. Thanks

Well my attempt at grounding and adding a second grounding wire and checking all grounding did not pan out. Will be back at it tomorrow. Thanks for the suggestions

 

[bcolvin]

Thanks all for the help. I ended up switching out the coil did not help but seems to start a bit quicker. @Seth S you were spot on. I picked up some carb cleaner and sprayed around the base of the carb and intake/exhaust manifold. I noticed a bit of reving up when sprayed around the center of the manifold. I was pumped to figure out that I could access all of the manifold bolts without taking the carb off.

I loosened all of the bolts and then followed the FSM torque sequence and specs. Now everything seems to be running great. Again I appreciate everyone's suggestions and help I definitely checked up on all the suggestions.