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Author Topic: '87 R10 - TBI to Carb conversion.  (Read 2742 times)

Offline PushrodV8

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'87 R10 - TBI to Carb conversion.
« on: March 19, 2017, 06:16:12 PM »
Hello Chevy folk.
I'm just about finished getting the engine buttoned up but was hoping to get a confirmation on the vacuum system.

Does the '87 have a vacuum line for the A\C vents?

I have the brake booster \ transmission valve \ pcv covered but I'm seeing a Tee fitting heading across the firewall ledge up top.

Thanks and happy Spring to you all. 8)
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Online bd

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Re: '87 R10 - TBI to Carb conversion.
« Reply #1 on: March 19, 2017, 06:28:30 PM »
Welcome to the site!

The tee connects to the vacuum reservoir on the driver side of the firewall and to a plastic spaghetti line that runs through the firewall into the back of the A/C selector panel.
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Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline PushrodV8

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Re: '87 R10 - TBI to Carb conversion.
« Reply #2 on: March 20, 2017, 03:40:07 PM »
Thank you sir, I appreciate that.

Ok, now that I have everything pretty much all cleaned up and the wiring harness tucked away I noticed that this truck doesn't have a TH350 but a TH400 transmission.

Does anyone know what method is used originally to perform the kickdown function?
Was it controlled by the ECM in conjunction with the TPS?

That's pretty much the last thing I need to get wired in now. I see people using little NOS throttle micro switches to close a 12v contact to the electrical detent, is that the best method?
Thanks again!
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Offline VileZambonie

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Re: '87 R10 - TBI to Carb conversion.
« Reply #3 on: March 20, 2017, 05:00:51 PM »
The detent switch attaches to the accelerator pedal assembly. When the switch closes it energizes the detent solenoid.
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Offline PushrodV8

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Re: '87 R10 - TBI to Carb conversion.
« Reply #4 on: March 20, 2017, 05:26:45 PM »
Right on.
For sure, yeah I already know how they function I mainly just needed to know if it's routed through the ECM?

If it's just a simple set of contacts on the the pedal itself then it's probably fine just the way it is. If it isn't wired separately then I'll need to route a new wire from the pedal to the transmission bypassing the main harness.

I don't recall seeing it in the diagram I found online.
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Offline VileZambonie

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Re: '87 R10 - TBI to Carb conversion.
« Reply #5 on: March 20, 2017, 06:46:30 PM »
Oh yes if you have the factory setup then it is controlled by the ECM.
Let me see if I can dig up a diagram for you.
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Offline VileZambonie

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Re: '87 R10 - TBI to Carb conversion.
« Reply #6 on: March 20, 2017, 06:49:13 PM »
Attached
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74 GMC, 75 K5, 84 GMC, 85 K20, 86 k20, 79 K10

Offline PushrodV8

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Re: '87 R10 - TBI to Carb conversion.
« Reply #7 on: March 21, 2017, 11:34:34 AM »
Sweet, thank you.

Come to think of it, I believe I'll be good just leaving it factory wired since the trigger is from the pedal.
I originally assumed it would have been triggered by the TBI \ TPS which has all been removed.

At this point I have the ECM still in place for the speedometer. (I recall reading that was needed)

So in theory as long as the ECM doesn't apply "safety\disable logic" in the sequence to disable the kickdown (based on the missing oil pressure sensor \ coolant temp sensor \ or tach signal) it should continue to function like it is.

Does that sound right?
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