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

KRBishop · Apr 21, 2021

bedwards said:
Just a hunch, but take your connector off the brake light switch and see if it does it. You have cruise control in one of your pics and it turns it off with the brake light switch if I'm not mistaken.

Thank you... I actully disconnected the cruise control vacuum and plugged it as well when I disconnected the booster vacuum line and it still does it! No vacuum lines connected to brake at all and it still stumbles when brakes applied like it does in the video. So crazy

Brake like switch is in brake assembly though, right?

KRBishop · Apr 21, 2021

Waylon said:
If you have some extra wire and crimp terminals, build yourself a jumper wire to test it. Just disconnect the B+ wire at the distributor, plug in your new wire and run it straight to your battery positive terminal. An alligator clip at the battery would be best. You will have to disconnect it to kill the engine.

I can't disconnected battery + wire... the wires are all connected in one plug like this: https://www.autozone.com/external-e...3omSBf6M-U1oz4OA_iBoC78wQAvD_BwE&gclsrc=aw.ds

Octane · Apr 21, 2021

Sounds more like a vacuum leak somewhere to me.But its always iffy to diagnose anything sight unseen.

KRBishop · Apr 21, 2021

Octane said:
Sounds more like a vacuum leak somewhere to me.But its always iffy to diagnose anything sight unseen.

Thanks to everyone for all the help.. The truck had a new alternator and distributor wires and plugs installed in a few months ago and was running great...

About 3 weeks ago when I came to a stop at red light it started to stumble as if it wanted to die...

It took a bit for me to realize that it was related to pressing brake pedal. As mentioned, in gear, wheels chocked, with no brakes applied... no stumble.

Since issue started...

I put in another set off plugs
I had it timed perfectly
Tested with multimeter at battery
Ran smoke through system and saw no vacuum leaks
Disconnected booster vacuum line and plugged it along with disconnecting cruise control vacuum line and plugged it
Just disconnected brake light switch

Truck still stumbles only when in gear and brakes applied. Out of gear and brakes applied, no issue. Still need to figure out multimeter at distributor.

If booster vacuum disconnected and plugged and it still does it, that rules out a bad booster, right?

bedwards · Apr 22, 2021

The brake light switch should be under the dash on the back of the brake pedal lever

KRBishop · Apr 23, 2021

bedwards said:
The brake light switch should be under the dash on the back of the brake pedal lever

Yes, thank you... tried that as well and when disconnected still having issues...

DanMcG · Apr 25, 2021

Well it's not a vacuum issue, so chances are it's electrical, but I'll be damned if I got a clue.

It sounds like there could be a wire that gets energized when put in gear under the dash that is getting shorted out when the brake pedal moves and contacts it.
That's all I got.

gotyourgoat · Apr 25, 2021

What is that rectangle above and between the speedo and fuel gauge. It's blinking along with your stumble. Choke?

Octane · Apr 25, 2021

With more than 20 professional amateur mechanics failing to rectify the issue sight unseen,it might be time for the pros to take an in person look at it. Lol

KRBishop · Apr 25, 2021

gotyourgoat said:
What is that rectangle above and between the speedo and fuel gauge. It's blinking along with your stumble. Choke?

Check engine light comes on as it stumbles. Dropping at mechanic tomorrow... still can't figure it out lol

Josho · Apr 26, 2021

It's possible the torque converter is failing or vacuum modulator is bad

Rusty Nail · Apr 26, 2021

KRBishop said:
Check engine light comes on as it stumbles. Dropping at mechanic tomorrow... still can't figure it out lol

Did ya ever think about pulling the codes out of the computer? It's pretty easy to do.

KRBishop · Apr 26, 2021

Rusty Nail said:
Did ya ever think about pulling the codes out of the computer? It's pretty easy to do.

Funny you should say that and I did try that and it wasn't showing any codes... I finally brought it to my mechanic because I exhausted everything I could do and he thinks it is the electronic control module because the vehicle is originally from California so it has all kinds of admissions on it… the electronic control module controls the distributor… he thinks if he replaces it with a vacuum controlled distributor and eliminates the computer it should solve the issue. Were gonna try it.

His only slight issue is that he thinks it may also affect the carburetor which is also part of that system but thinks he could bypass it if not I have to put on a new carb .... I guess we will see!

Rusty Nail · Apr 26, 2021

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!

Good pics though. Looks like you stand there with a rag sometimes.

Bextreme04 · Apr 26, 2021

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.

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

KRBishop

Junior Member

KRBishop

Junior Member

Octane

Full Access Member

KRBishop

Junior Member

bedwards

Full Access Member

KRBishop

Junior Member

DanMcG

Full Access Member

gotyourgoat

Full Access Member

Octane

Full Access Member

KRBishop

Junior Member

Josho

Junior Member

Rusty Nail

Full Access Member

KRBishop

Junior Member

Rusty Nail

Full Access Member

Bextreme04

Full Access Member

Similar threads

Latest posts

Forum statistics