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ABS connection to brake booster


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CRINTIMIDATOR
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Feb 27, 2015, 6:52 AM

Post #1 of 10 (1421 views)
ABS connection to brake booster Sign In

1991 GMC K1500 5.7. Engine runs fine til it warms up then when you apply brakes hard, engine will stall. If you pump brakes, rpms will raise then fall til it stalls. New master cylinder and brake booster. Wondering if ABS module or ABS Hydraulic Unit can affect the vacuum on booster if either goes bad. Have not found any vacuum leaks anywhere.


Tom Greenleaf
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Feb 27, 2015, 7:37 AM

Post #2 of 10 (1410 views)
Re: ABS connection to brake booster Sign In

1991? I don't think ABS messes with vacuum in power assist? Try this: Engine off, deplete power assist by depressing brake pedal till it feels hard. Hold there and start engine and pedal should fall some with renewed assist.


It should also hold power assist long after engine is shut off for a couple stops or at least one decent one. If not vacuum is leaking and everything from check valve to even new booster in question. If somehow master and booster are not compatible with pushrod to master things could be messed up there,


T



Discretesignals
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Feb 27, 2015, 5:21 PM

Post #3 of 10 (1388 views)
Re: ABS connection to brake booster Sign In

If you have a vacuum gauge, connect it to the intake manifold. What it is the vacuum at idle with engine warmed up? If you have low manifold vacuum to begin with, activating the brake booster can kill the engine.

I found one person's perception of an engine running fine may be different than another person's. We had a customer with a dead misfire and they swore up and down the engine was running fine and had plenty of power.





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.

(This post was edited by Discretesignals on Feb 27, 2015, 5:24 PM)


CRINTIMIDATOR
New User

Feb 28, 2015, 7:09 PM

Post #4 of 10 (1364 views)
Re: ABS connection to brake booster Sign In

I appreciate the responses. Had the transmission rebuilt around four months ago and after it was installed, truck just died on way to work, like three weeks later. After sitting for around an hour cranked back up and he discovered the distributor was shot. Replaced the distributor and everything was fine till it started stalling at stops and when you put it in gear. Replaced brake booster and just about every sensor and module including new computer on truck. Ended up buying new crate motor (original had 275,000 mileage) and after installation, still doing same thing, stalling when you put it in gear. I am thinking it is in wiring but he has so much time invested he is bound and determined to figure it out himself. Vacuum seems to be fine when he checked it.


Discretesignals
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Feb 28, 2015, 7:15 PM

Post #5 of 10 (1362 views)
Re: ABS connection to brake booster Sign In

Now your saying it stalls when putting into gear. You stated before it was stalling when your pumping on the brake pedal.





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.


CRINTIMIDATOR
New User

Mar 1, 2015, 7:06 AM

Post #6 of 10 (1351 views)
Re: ABS connection to brake booster Sign In

  If you are in park or neutral, if you pump the brakes it will raise rpms but if you switch into drive or reverse and hold brake, it will stall. If you hold brake lightly it doesn't stall. If you are pressing brake hard it stalls every time. Also stalls when driving in traffic and coming to red light or stop sign. After you stop the rpms will start acting erratic and then it will die. Starts right back up.


Tom Greenleaf
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Mar 1, 2015, 7:41 AM

Post #7 of 10 (1347 views)
Re: ABS connection to brake booster Sign In

Booster check valve and grommet. Not vehicle specific but did you replace those?


This is all over the place but seems it leaks vacuum to me exacerbated by brake use that does use vacuum but only till it's at max intake manifold vacuum then quits taking vacuum. Check valve hold that for the time you aren't touching brakes at all - get it?


If that leaks or maybe hose to it with just some motion of booster and master assy it might leak vacuum on hose to it. All of that if booster was replaced should have been new IMO and fit tightly even without clamps.


If you just plugged that (don't drive the thing) you lose power assist but then will find touching brake pedal at idle or in gear - clear area for low powered brakes it could move, it shouldn't effect the way the engine runs at all. Then when hooked up if it does and constantly it's leaking.


Perhaps a quick (usually don't notice) stumble to recharge vacuum for next use but if idle speed is staying normal you really wouldn't notice and if not find out why AND once holding brake at a stop the consumption of more vacuum stops unless you are pumping it away.


ABS - I don't think it's involved with this part at all. You could probably just pull the fuse for it which puts it back to regular brakes and a dash light should light while fuse out,


T



CRINTIMIDATOR
New User

Mar 1, 2015, 11:31 AM

Post #8 of 10 (1335 views)
Re: ABS connection to brake booster Sign In

He has discovered if he unplugs the temperature sensor the truck idles fine and doesn't stall when you put it in gear. Replaced with oem but when it is plugged in it stalls when you put it in gear. He checked the check valve on booster, seem to be working properly.


Tom Greenleaf
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Mar 1, 2015, 11:58 AM

Post #9 of 10 (1332 views)
Re: ABS connection to brake booster Sign In

Getting to be a waste here. Which sensor, one for fuel delivery that would cover the vacuum leak your booster probably causes? That or the one for a gauge which would do nothing for this.


Nothing conclusive for tests or proper anything on this so far. If someone is just going to tell you it's all fine and you believe it than why is there a problem? Thread is messed up,


T



Discretesignals
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Mar 1, 2015, 6:34 PM

Post #10 of 10 (1286 views)
Re: ABS connection to brake booster Sign In

I've ran into one of those where when you pressed on the brake the engine would stall out. What happened on that one was the brake lamps and the fuel pump share the same ground point on the frame. The ground had a bad connection and when the brake lights were operated that would cause the fuel pump to quit or slow down due to the voltage drop happening across the poor ground point.

Unplugging the temperature sensor (ECT) will cause the engine puter to add more fuel because it will think the engine is running cold. Maybe the low fuel pressure when the brakes are applied is being offset when you have the ECT unplugged. Just a theory.

Fuel pump ground is located somewhere in the back on the left frame rail...I believe.

You could also do a voltage drop test on the pump ground circuit to see if it has excessive voltage drop when the brakes are applied for confirmation.





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.

(This post was edited by Discretesignals on Mar 1, 2015, 6:36 PM)






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