83 FJ60 surges with tach hooked up

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Hey guys, I just purchased a 83 fj60. it runs great when the black tach wire at the igniter is unhooked. When this wire is hooked up the engine idles smooth as it should but as soon as the RPMS hit 1800 or higher on the tach it surges like the ignition is being turned off for a second, its worse when its being driven. Is this signs of a bad igniter? or bad tach?
 
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That's a strange one. If it's got a/c it could be related to the a/c amplifier . Tach signal goes to the amplifier as well. You could disconnect the amplifier temporarily to test. There are 3 wires with ring connectors screwed on the back of the tach. One of those could be loose. Or it could be the igniter.
 
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That's a strange one. If it's got a/c it could be related to the a/c amplifier . Tach signal goes to the amplifier as well. You could disconnect the amplifier temporarily to test. There are 3 wires with ring connectors screwed on the back of the tach. One of those could be loose. Or it could be the igniter.
it does have a/c although not functional at the moment. from the diagrams I have seen I thought the tach signal wire goes directly from the igniter to the back of tach. Where is the a/c amplifier
 

OSS

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This is what I think might be happening:
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.

Check the function of the vacuum switch. Or ground the wire that connects to it.
 
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This is what I think might be happening:
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.

Check the function of the vacuum switch. Or ground the wire that connects to it.
I did some testing on the fuel cut switch today. I hooked a test light inline with the solenoid to determine if it was switching on or off when at the 1800rpm and the light stayed lit the whole time indicating its been operating as it should. does the 83 have an emissions computer and if so where is it. I thought the FCS was triggered just by the change in vacuum.
 

2mbb

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The pulse wave signal used to monitor the engine speed goes from the coil/igniter to three locations: Tachometer, A/C amplifier and Emission Control Computer. The Tach doesn't do any more that translate the signal into a meter deflection. If the engine is pulsing above 1800 RPM, the tach is not causing it. The previous posts are correct that it may have something to do with either the A/C amplifier or Emissions computer.

Make sure the A/C amplifier is turned off (blue button on the heater control is not depressed) or unplug the harness from the a/c amplifier. The amplifier is located under the dash mounted on the front of the A/C plastic ducting.

Also you might try disconnecting (temporarily) the emissions computer.

Isolating the individual systems should help narrow where the problem is occurring.

1632233394792.png
 
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The pulse wave signal used to monitor the engine speed goes from the coil/igniter to three locations: Tachometer, A/C amplifier and Emission Control Computer. The Tach doesn't do any more that translate the signal into a meter deflection. If the engine is pulsing above 1800 RPM, the tach is not causing it. The previous posts are correct that it may have something to do with either the A/C amplifier or Emissions computer.

Make sure the A/C amplifier is turned off (blue button on the heater control is not depressed) or unplug the harness from the a/c amplifier. The amplifier is located under the dash mounted on the front of the A/C plastic ducting.

Also you might try disconnecting (temporarily) the emissions computer.

Isolating the individual systems should help narrow where the problem is occurring.

View attachment 2792228
Okay I figured it out! I removed the tach wire from the plug going into the emissions computer and it now works as it should. Im assuming I should look for a new emission computer. All th smog stuff has been removed so maybe I could just leave it alone?
Thanks guys!
 

Spike Strip

Let's Go Brandon !
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@1983Landy

It sounds like the desmog was not done correctly. You don't need the emissions computer if you're desmogged, unless you want to keep the deceleration fuel cut circuit (it helps prevent backfiring).

Is the ICS (carb solenoid) still have the normal two-wire connector or is the white wire grounded?

@Engineer8000 offers a service to repair the Emissions Box as they are long NLA from Toyota and trying to find a good used one, particularly these days, is unlikely. He also examines/repairs the NLA A/C Amplifier.

You can check his vendor thread

 

2mbb

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Nice. Reading through the emissions manual, the engine speed is used by the emissions computer for two maybe three circuits, Exhaust Gas Recirculation and Deceleration fuel cut and Air Injecction...but the Air injection used the deceleration fuel cut being on or off to do different things. Download a copy of the 2F emissions manual and you try disconnecting the devices that are controlled by the engine speed via the emissions computer to identify the root cause. As spike say's your desmog may not have been done correctly causing intermittent vacuum leaks, etc.
 
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@1983Landy

It sounds like the desmog was not done correctly. You don't need the emissions computer if you're desmogged, unless you want to keep the deceleration fuel cut circuit (it helps prevent backfiring).

Is the ICS (carb solenoid) still have the normal two-wire connector or is the white wire grounded?

@Engineer8000 offers a service to repair the Emissions Box as they are long NLA from Toyota and trying to find a good used one, particularly these days, is unlikely. He also examines/repairs the NLA A/C Amplifier.

You can check his vendor thread

Yes the fuel cut switch on the carb still has the two wires going to it and its been tested to determine if its opening and closing which it is. I tried unplugging the emissions computer while it was running and it died. I will look into how it was desmogged.
 

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The ICS is controlled through the Emissions Computer by switching open/close to ground. If you ground the white wire off the solenoid to the body of the carb you bypass the emissions computer.

A few pix would help us not have to guess so much.
 

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