JC-4 vacuum pump observations

[RF_Burns]

After reading a post about the JC-4 vacuum pump capabilities, I decided to test mine. Mine pumps down to 9" of vacuum and restarts at 6". That is
too low for my liking.

I was sure I read where someone had made adjustments to the JC-4 to increase its vacuum, but I can't seem to find it. So being brave I took it apart
and found a small circuit board with an electronic sensor for vacuum. The board is mounted with the components against the housing, but there appears
to be a surface mount IC and a power FET to drive the motor. I had posted a link to the operation of the JC-4 recently. From that document I'm sure
the IC is likely a microcontroller, so making modifications to its operation is not really feasible.

My next step is to wire directly to the motor to see how much vacuum it can actually pull. Unfortunately the case has a rubber seal which has swollen
in length so is impossible to re-use. I'll need to find something to replace the seal before I can test it.

I'll post my findings. If it can produce some decent vacuum, I can use something like a Superior K058 adjustable vacuum switch and a relay to control
it.

--
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.
Hubler 1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that

 

[Ken H.]

Bruce,

Pete Pappas, ex-GMCer modified JC4's for better vacuum. He sent me
instructions which I'll continue to hunt. The mid involved an added screw
threaded into the top of the housing and ball point pen spring, or
similar. Seemed to me like a little too much of a kludge for me so I never
tried it.

Ken

> After reading a post about the JC-4 vacuum pump capabilities, I decided to
> test mine. Mine pumps down to 9" of vacuum and restarts at 6". That is
> too low for my liking.
>
> I was sure I read where someone had made adjustments to the JC-4 to
> increase its vacuum, but I can't seem to find it. So being brave I took it
> apart
> and found a small circuit board with an electronic sensor for vacuum. The
> board is mounted with the components against the housing, but there appears
> to be a surface mount IC and a power FET to drive the motor. I had posted
> a link to the operation of the JC-4 recently. From that document I'm sure
> the IC is likely a microcontroller, so making modifications to its
> operation is not really feasible.
>
> My next step is to wire directly to the motor to see how much vacuum it
> can actually pull. Unfortunately the case has a rubber seal which has
> swollen
> in length so is impossible to re-use. I'll need to find something to
> replace the seal before I can test it.
>
> I'll post my findings. If it can produce some decent vacuum, I can use
> something like a Superior K058 adjustable vacuum switch and a relay to
> control
> it.
>
>

 

[RF_Burns]

Thanks Ken,I was sure I read something about a mod. I took a look at the sensor this afternoon. It appears to have a magnetic plunger with 3
electrical terminals so likely a Hall-Effect sensor to the plunger. I think a better idea would be to bypass the existing electronics and power the
motor with a vacuum switch operating a relay.

I bypassed the controller to power up the motor and measured the max vacuum at just a tad under 20". I also confirmed from the circuit board that the
motor is powered from pin B. I used a hose to the vacuum gauge, so I'm not sure how long it will take to pump down a booster.

just my findings.

--
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.
Hubler 1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that