Engine stumbles when you hit brakes even with vacuum for booster disconnected...

[KRBishop]

If its an ESC engine(which is seems to be per your comments) it seems like you have a short somewhere. You are getting a flashing check engine light in conjunction with the stumble. Find the short. If your mechanic just wants to remove everything instead of finding the actual problem, find another mechanic that isn't afraid of actually troubleshooting an issue instead of throwing a bunch of parts at it.

Maybe you could talk old boy into looking at some of the vacuum routing? I've never seen so many caps on one engine in my whole life!

The only thing capped at the moment in those pictures is the cruise control.

 

[KRBishop]

If its an ESC engine(which is seems to be per your comments) it seems like you have a short somewhere. You are getting a flashing check engine light in conjunction with the stumble. Find the short. If your mechanic just wants to remove everything instead of finding the actual problem, find another mechanic that isn't afraid of actually troubleshooting an issue instead of throwing a bunch of parts at it.

Appreciate the feedback. The research I have seen show eliminating the ESC actually helps with a lot of things. It was my call, but again, thanks for your POV.

 

[Bextreme04]

Appreciate the feedback. The research I have seen show eliminating the ESC actually helps with a lot of things. It was my call, but again, thanks for your POV.

Troubleshoot and verify, don't just through parts at it. You can fully bypass the ESC function without removing or replacing anything. I still think it sounds like you have a shorted wire somewhere.

 

[KRBishop]

Troubleshoot and verify, don't just through parts at it. You can fully bypass the ESC function without removing or replacing anything. I still think it sounds like you have a shorted wire somewhere.

How do you bypass it?

 

[Bextreme04]

How do you bypass it?

Google "bypass ESC distributor". I would post some links, but they are in competing forums.

 

[KRBishop]

Troubleshoot and verify, don't just through parts at it. You can fully bypass the ESC function without removing or replacing anything. I still think it sounds like you have a shorted wire somewhere.

I see how... by connecting the black and green wires from distributor... so you can just run the truck like that with no issues?

 

[Bextreme04]

I see how... by connecting the black and green wires from distributor... so you can just run the truck like that with no issues?

I wouldn't say that... but it will keep it from doing the ESC function and locks it into a regular HEI. If you do that and it is still having the issue, then switching to a non-esc HEI probably wouldn't fix it either.

Supposedly the 305's were very sensitive to detonation and that's why they have the ESC. Without it, you can't run as much initial advance without detonation and supposedly power and mileage suffers from it. I have zero personal experience with it though, so take it for what it's worth.

 

[KRBishop]

UPDATE... took out ESC distributor... installed regular HEI vacuum controlled distributor, re-timed, adjusted carb and runs like a top! Idles great and acceleration is fine. Thanks for all the help

 

[Camar068]

glad you got it

 

[Vbb199]

You said 84, c10. Didnt say what transmission.
Is it a 700r4?

Brake switch, or maybe it was CC switch disengages lockup, but it may have another function i am unaware of.

 

[Vbb199]

Oof, i see now, the stupid ESC and its compliant distributor.
Yeah, those are garbage on those older squares.
The esc retards timing when it hears a knock, and theres a good possibility the esc was also drastically retarding the timing with the brake switch.

Glad you ditched that junk and solved your issue.

Now that its old news, replacing that distributor wasnt the issue, bypassing that ESC module would've been the fix.... @Bextreme04 was right, there was even a GM service announcement about those faulty ESC modules, with a way to bypass it.

By 1987-1988, they got the esc and knock sensor down pat its in very primitive form with the introduction of TBI, and they work well for what they are with their singular ks on the pass side of the block.