warthogcrewchief

Over the weekend I have been testing the brakes. About one out of every five or six times, the engine dies after I come to a complete stop when I slam on the brakes.

I just got done doing a complete overhaul of the braking system, of which, the vacuum booster was replaced. I figured the vacuum booster would have been the cause, but with a new vacuum booster, and the engine still dying occasionally, I think I can rule out the vacuum booster.

Before I replaced the vacuum booster, I tested the engine dying after a stop both in drive and in neutral. With that, I think I can rule out the transmission.

Sometimes I can hear the RPM of the engine drop when I apply brakes.

Could the brakes be too much of an overload for the vacuum system or a potential leak in the system?

trainwreck91

no check engine light? could be a few things. EGR valve is bad, you can take it off and take it to autozone for free testing or the throttle position sensor or even an oxygen sensor. might even just need to turn up your idle. might just be too low. but i'm almost 100% sure it has nothing to do with your brakes!

warthogcrewchief

I agree, I doubt it's with the brakes as I've changed EVERYTHING on the brake system...well, almost everything. I do think the idle may be a little low. At idle, there is an ever so gentle miss.

The RPM is sitting around 500, and if I'm not mistaken, it should be closer to 750-1000.

A low idle would explain why the engine bogs down a little bit when applying the brakes.

On the plus side, a low idle would probably increase fuel economy.

Joe In NY

rpm is 600 RPM factory. Clean out your throttle body and run Chevron fuel system & injector cleaners. Also, make sure your spark plugs are in good shape. Do this and the motor should run smoother. Mine did after throttle body clean, injector cleaner, and new plugs.

warthogcrewchief

Thanks. The RPM is right on at 600 RPM. I was thinking about how I wanted to attack this...fuel or air. I know it has a recent (within a year) distributor and plug wires. Plugs, MAS clean, and fuel additive doesn't take much time or money at all to do.

Thanks for the input. It helps to validate what I was thinking.

in2pro

Just trying to run through my head what happens when you step on the brakes...
vacuum will change..
What engine loads are changing?
is it a really at braking or is is rapid deceleration?
Idle air control?
Throttle position sensor?
does it do it if you shift out of gear?

Joe In NY

Actually, need something very important. What year, model, engine?

warthogcrewchief

The make/model/year is a '97 C1500 Suburban 2X4, 5.7L Vortec. I thought it was in my signature line...I'll have to double check that.

When I was doing some maintenance test runs (while the brake booster was bad) I would slam on the brakes from about 30-35 MPH and the engine would die just after I came to a complete stop. I would then place it in neutral to restart with no problems during restart.

To verify it wasn't a tranmission problem, I was able to duplicate the same results while in neutral.

While doing another maintenence run/emergency stop after I replaced the booster and master cylinder, I have only had it happen once more out of five stops.

The primary fuse/relay box is loose (located near the firewall,driver's side, under the hood). The inboard side is bolted in and the outboard side plastic retention tab is broken/missing. I suspect that might be an issue. I have acquired (legally) a new/used fuse/relay box mount from a parts truck. I plan on changing that out this week.

I'm also planning on doing what Joe in NY suggested: fuel treatment, spark plugs, and cleaning the throttle body & MAS.

A little voice in the back of my head is saying to check the vaccum lines.

warthogcrewchief

Couldn't find any Chevron fuel cleaner, was going to use STP fuel cleaner, but the guy at the store suggested Lucas fuel cleaner. I'm used that with a full fuel tank earlier this week. After about 100 miles, no noticeable change.

I pulled the throttle body just a little bit ago. Also got a new throttle body base gasket, but it was just fine...replaced it anyways. Cleaned out the throttle body. The idle in the butterfly was completely clogged with carbon. Cleaned it up and put everything back together. Started right up with a slightly high idle, but that seems the normal for a cold start until it gets warm. Haven't driven it yet. It does sound a little smoother. I will check the idle here in a little bit while I take her out for a short drive.

I think I still feel a little bit of roughness. If this doesn't fix it, I'll pull the spark plugs and check them, along with new plug wires (which appear to be newer).

73shark

FWIW, Techron is Chevron's name for their FI cleaner. It's the only thing I've found that works.

Gotta love those A-10s. Tremendous airplane!