No brakes when engines cold!!! (1 Viewer)

[Brayden3223]

When my engine is cold I have no brakes assist, it’s bloody scary. Feels like it’s almost impossible to get the car to pull up but I don’t believe it’s anything to do with the brake booster, I have a FZJ80 Aussie spec and the same day the brakes stopped working properly the engine also started running poorly. It was after a 4 hour drive, 300km drive non stop. The day after that drive, I hopped in the car and it wouldn’t idle,if I try to drive, it feels like I’m towing a invisible caravan and smells insanely rich. it would stall and shake and brakes wouldn’t work. When the car gets halfway on the temp gauge it begins to idle but still rough and brakes begin to work again. If I’m cruising at low rpm on a freeway or something, the car begins to shake like it’s vigorously misfiring. Doesn’t throw any codes. Could this be a vacuum leak? I can’t see how it would affect my brakes? All feedback appreciated. I’m almost ready to take it to a mechanic if I can’t find the issue soon, and I’m meant to go away for a trip in 2 weeks

 

[Pighead]

Sounds like a bad brake booster diaphragm

 

[Brayden3223]

Sounds like a bad brake booster diaphragm

I did think that, the only reason I lean away from this is, I disconnected the whole brake vacuum line and blocked it and it didn’t change my idle or how it ran at all

 

[Pighead]

I did think that, the only reason I lean away from this is, I disconnected the whole brake vacuum line and blocked it and it didn’t change my idle or how it ran at all

you mean it still ran poorly with the brake booster disconnected?

 

[Brayden3223]

you mean it still ran poorly with the brake booster disconnected?

Yeah, I disconnected it from the intake manifold, I know I would have no brake assist when it’s disconnected but I just wanted to confirm that, that wasn’t causing the poor idle, as it seems the 2 issues correlate

 

[Pighead]

Well then, the other way around perhaps. is your engine running so poorly that it cannot generate vacuum enough to assist your brakes?
it would have been too convenient if a new booster solved all of your problems.

 

[Brayden3223]

Well then, the other way around perhaps. is your engine running so poorly that it cannot generate vacuum enough to assist your brakes?
it would have been too convenient if a new booster solved all of your problems.

I’m hoping it’s something simple, the only vacuum lines I haven’t really looked at, at this point is the ones under the intake manifold because I don’t know how to get it off, few bolts on there are hard to reach

 

[gummycarbs]

Well, well, well, if it isn't the guy with obvious vacuum leaks who insists he doesn't have any vacuum leaks...

I’m still searching for it! This is among a few small problems I’m currently facing! But there isn’t any vacuum leaks at all

Replace *all* of your vacuum hoses, including everything under the upper intake. Doesn't matter what your throttle body cleaner experiment says, you have vacuum leaks.

The upper intake manifold isn't difficult to remove, but you'll want a very long socket extension (like two feet) to get to a few of the bolts from underneath.

 

[Brayden3223]

Well, well, well, if it isn't the guy with obvious vacuum leaks who insists he doesn't have any vacuum leaks...



Replace *all* of your vacuum hoses, including everything under the upper intake. Doesn't matter what your throttle body cleaner experiment says, you have vacuum leaks.

The upper intake manifold isn't difficult to remove, but you'll want a very long socket extension (like two feet) to get to a few of the bolts from underneath.

I feel attacked

Nah I appreciate it, is there any other things I should do when the intake manifold is off?
And is it just the 2 rear bolts that need to be done from underneath?

 

[gummycarbs]

is there any other things I should do when the intake manifold is off?

Clean the carbon out of it, which may well be contributing to the problems you're seeing. Check the operation of the VSV and check valve and replace if necessary (honestly, I'd just replace the VSV because it's hard to get to and lasts decades).

Oh, and the coolant hose that's hiding under there.

is it just the 2 rear bolts that need to be done from underneath?

Not sure. I did mine four or five years ago. I just vaguely recall having lay down to access a couple of bolts toward the rear, but maybe it was all of them.

 

[Rusty Marlin]

Its a bunch of them, most of them are more easily accessed with a long extension from laying underneath. I bought a 3 footer for this job.
A wobble adapter just behind the socket will help with a couple too.

 

[Kernal]

I forget, is there a nut or two you have to get from below also??

I just remember it being difficult to find the 1-2 more rearward ?bolts looking up from below. Ended up marking them from above with yellow paint I sprayed on my finger then quickly reached down from above to dab the paint on them. After that I was able to find them along with a good light. FWIW

 

[robnicko]

Couple of questions,
Have you put a vacuum gauge on the motor to see what its measuring?
Have the the valve clearances been checked?
When you disconnected the booster was there strong vacuum evident from the hose with engine running?
Is the throttle body clean and butterfly seating correctly at idle?
Is it running LPG? if so can you post some pics of the engine bay & setup?

 

[Dave 2000]

Adding to the above:

Your vehicle is not listed in your signature, so just throwing this out there, the UK diesel 80's have the brake booster AND a reserve tank, so if EITHER of them have a leak your brakes will not work properly, having said that if yours is petrol then the vacuum is created 'downwind' so's to speak, that is after the butterfly valve, you have less braking power (or more accurately less vacuum) when the throttle is wide open, this is the reason for the non return valve so that the booster is held at vacuum immediately after you come off the throttle along with your engine having cut out and with the auto transmission not driving the engine then no vacuum.

Also are you blocking the pipe that you disconnect from the booster to see if engine idle improves (petrol only)?

Regards

Dave