Engine running rough after changing brake booster?

[kxnomore]

Hi guys,
I needed a new master cylinder, as it was leaking fluid very slowly out of the back by the booster. But after changing it out, the brake booster started leaking air badly, so I figured it was a coincedence, and I ended up changing that out with a brand new rebuilt unit.

But now the engine is running like crap (within 10 minutes after installing the booster). It can't be a bad vacuum, though, as even when I plug the vacuum line going to the booster, there is no change. It's almost like I lost a cylinder, as it's shaking almost out of the truck. Does anyone have any ideas of anything where a booster could cause the engine to run rough?

Thanks in advance...

[ChevLoRay]

What about the hose from the manifold to the booster? The check valve in the booster or in the hose from the manifold? Sounds too much like it is a vacuum leak to just dismiss it, to me.

[kxnomore]

I'll try that as soon as I get off work in an hour or so. The hose is relatively new though, but maybe it got twisted or something. It also smelled kind of strange, almost like it was burning berry juice? Does brake fluid smell sweet when it burns, or just smell like burned engine oil? It didn't smell like coolant though.

I will also run a compression test just to be sure it isn't something else.

[cdowns]

check all the plug wires to make sure you didnt loosen one either on the plug or pull one off the dizzy while you were changing the booster and master cyl

[724x4a/cchevy]

Sounds like you have a vacuum leak somewhere. That's the only affect to the engine that a power brake booster would have.

[724x4a/cchevy]

I've heard stories of the seals leaking. When the seal leaks the engine would suck brake fluid out of the resevior. Have you noticed it smoking or mysteriously dissapearing brake fluid??

[67'sgota4541]

check your spark plug's #7 esspecially,if booster had a vacuum leak it may have fouled the plug.

[kxnomore]

well, that got my hopes up that last one. Welcome to the board by the way... The plug looked okay though. it was a little lighter than the number one plug, actually. I'm out of time for tonight, but this has to be something simple. The vacuum was registering only 13 or so, and I could have sworn it used to be more like 15 or 16. I'm not sure if it's due to my moving to a higher altitude. The carb idle is tuned okay, but does altitude (7,000 ft) cause a lower vacuum? The needle is bouncing a bit, too.

But tomorrow I'll pull all the plugs and do a quick pressure test just in case, and put in new plugs and check all the wires, etc. I did notice the vacuum advance wasn't working, so that's a small leak, but didn't change the overall vacuum when I plugged it. I'll let you all know what it was if I find it.

Here's a pic of the truck. It's a 72 3/4 ton highlander.

[Jtrux]

15 or 16 is pretty low. 21 to 24 would be more like it especially on a stock motor.

[SCOTI]

Your 'new' part could be bad. Swap it for another & see if the problem persists.

[boostin20]

You should have 15-16 at idle. You will only have 20+ under decel while in gear. If the engine was fine before the booster change, there's no reason to do compression or leak down test. Look at vacuum system one more time. 724 is right about the booster seals possibly leaking and sucking fluid. Have you ruled this out?

[soba_03]

Sounds like a bad booster. Plug all the ports. If it idles then replace lines one at a time. You might find one internaly colapsing or a hole that you might not see. Also if you ported in the bottom of the carb check to make sure you didn't move the carb of loosen up the fitting, and check carb base nuts. Of course you can check this with some carb cleaner or WD40 at the carb base. Good luck

[steelhorse]

A bouncing needle on a vacuum gauge is usually a sign of a sticking or bad valve.A compression test is in order.

[re1]

That is a beautiful highlander seat,
any details where you got it recovered.

[BLACK AND BLUE 67-72]

Bouncing needle usually is valve related, like a broken spring, mine did this. Could just be a coencidence.

[pumpkin]

If it ran fine before changing the booster, and with the new one runs bad. I would suspect that the idle mixture was richened up to compensate for the old leaking booster.

[kxnomore]

Okay guys, I've got an update and it aint pretty. cylinder #4 has given me its all, but she's no longer holding any compression. Well, 30 lbs, actually. It was nice while it lasted...

So that was one heck of a coincedence, but the brakes had nothing to do with it.

On a related note, when I held the shop air to the cylinder at top dead center, air was rushing out the exhaust, so it must be a stuck or bent exhaust valve. I'm not sure it's worth just getting this one valve fixed, or replacing the whole engine. I only was told it was about 3 or 4 years old and was a full rebuild. It's a '78 400 c.i. small block with solid lifters. And a bad valve. The head number is 3947041 with a date of C18 70, and a stamp of GM 13. Oh yeah, all other cylinders were exactly 160psi stone cold.

Any recommendations?

[ETsC10]

Originally Posted by kxnomore

...I'm not sure it's worth just getting this one valve fixed, or replacing the whole engine...

I'd pull the head and get it to a machine shop. If you need the truck now, slap on a used head until the repair is made. WAY easier (and cheaper) than replacing an engine.

[ChevLoRay]

Originally Posted by kxnomore

Okay guys, I've got an update and it aint pretty. cylinder #4 has given me its all, but she's no longer holding any compression. Well, 30 lbs, actually. It was nice while it lasted...

I'm not sure it's worth just getting this one valve fixed, or replacing the whole engine. I only was told it was about 3 or 4 years old and was a full rebuild.

Any recommendations?

In '76, I bought a '65 C-10 with a dead miss in one cylinder. I had recently been recalled to my future long-term employer and didn't have money to burn. So, I pulled the bad head and had it repaired....the one valve that was the problem. At that time, it had over 75K miles on it, but when I reinstalled that head, and buttoned everything back up and adjusted it all out, all was good. I drove the truck until late '80, when I sold it to a friend who drove it for several more years. The last time I saw it was in '99, when it left for CA.

So, you know my opinion is to just get the one fixed that is bad, and drive it.

These are tough economic times, you know......

[BLACK AND BLUE 67-72]

Pull your valve cover and check your springs, make sure one isn't broken!!!! I had the exact same problem with mine, I thought i had a bad valve and was starting to pull the head and when I pulled the valve cover I saw the broken spring....

[kxnomore]

I'm with Chev lo Ray. these are rough times. I got the head off today, and the one valve is visibly sunk down in the head. I'm off to the Machine shop Monday morning to just fix this one valve. the springs looked good, and the cylinders had a small ridge that was more visible than actually worn. Plus the other cylinders had good compression. I checked the valve lift and it was the same as the others.

So hopefully it won't be too costly at the machine shop. Thanks to everybody for your advice.

[soba_03]

pull off the valne cover and back the exhaust rocker nut a few turns to the left (lefty loosey) and do a compression check.. see if you can buy some time.. if the valve was set a bit on the tight side you might have enough spring to get it to seal for a bit longer... just a thought...

[boostin20]

Glad you could find the problem quickly. Hopefully you get out of the machine shop for a couple hundred bucks.

[justcuz]

Should be less than that! I just had my heads redone and they replaced 4 valves, all new seals valves regound. $300.00 including the gasket set (Felpro)