When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
With the car running at idle what should my vacuum readings be, on my 85s3 5spd
This is the reading after running car , engine off,
2
Here is a reading at idle,
where should the readings be .
Where are you measuring that? I'm currently chasing a vacuum problem (see my ongoing thread regarding ISV/ICV replacement). I think it should be 19-22 in-Hg at idle, but from what I am learning, there are essentially two separate vacuum "circuits." The one for the brake boost, vacuum reservoir and HVAC system uses one-way valves to draw it down and then basically provide a constant vacuum source with which to operate stuff. The other one comes off the throttle body and is for things that need to see whatever current manifold vacuum is, e.g. the line to the EZF, fuel dampers, AC kickdown, and I think the auto transmission if you have that. I measured 21 in-Hg at the tee off of the brake booster and thought that meant I was good, but on advice here, measured it at the front damper and got 0 (found one disconnected vacuum line, fixed it, and now I'm at 9 in-Hg...so more to do).
Where are you measuring that? I'm currently chasing a vacuum problem (see my ongoing thread regarding ISV/ICV replacement). I think it should be 19-22 in-Hg at idle, but from what I am learning, there are essentially two separate vacuum "circuits." The one for the brake boost, vacuum reservoir and HVAC system uses one-way valves to draw it down and then basically provide a constant vacuum source with which to operate stuff. The other one comes off the throttle body and is for things that need to see whatever current manifold vacuum is, e.g. the line to the EZF, fuel dampers, AC kickdown, and I think the auto transmission if you have that. I measured 21 in-Hg at the tee off of the brake booster and thought that meant I was good, but on advice here, measured it at the front damper and got 0 (found one disconnected vacuum line, fixed it, and now I'm at 9 in-Hg...so more to do).
measuring from the test port off of the brake booster hvac connection.
For that location, your low reading might be indicative of a bad check valve and an HVAC diaphragm leak. However, I don't think (someone please correct me if I'w wrong here) this measurement location is telling the whole story. Try it at the EZF or the vacuum line attached to the front fuel damper, and see if you get a different reading.
Curious, does your Heater Control valve "close" all the way when the engine is running?
You should be able to observe it going from fully closed to fully open, and that is a good indication that the HVAC system is OK and you have enough vacuum to pull it closed.
Curious, does your Heater Control valve "close" all the way when the engine is running?
You should be able to observe it going from fully closed to fully open, and that is a good indication that the HVAC system is OK and you have enough vacuum to pull it closed.
I would find your brake venturi valve. It's a Y configuration, the angled arm goes to the brake booster. Of the other two arms one goes to the plenum, and one goes to the throttle body. Inspect the venturi for leaks, the measure vacuum in the line to the plenum. That should around 20.
Good luck,
Dave
So brought home the company smoke machine, attached to the hose comming.thanks off the venturi to the booster, activated the machine for 20 +minutes and no leaks in the booster side of the system, I was really hoping to find smoke comming.thanks from the wheel well, no leaks in the system, so why don't I have enough vacuum.
I suggested measuring the vacuum at the venturi hoses. The two that don't go to the brake booster go to either the throttle body or the plenum. The plenum should have the most vacuum at 20mm. If it doesn't, I would be surprised, after your leak test. You can try connecting the brake booster directly to the plenum. If that is better you make have internal problem with venturi.
Good luck,
Dave
I would find your brake venturi valve. It's a Y configuration, the angled arm goes to the brake booster. Of the other two arms one goes to the plenum, and one goes to the throttle body. Inspect the venturi for leaks, the measure vacuum in the line to the plenum. That should around 20.
Good luck,
Dave
Ok so measured at the year 2in then measured at the booster 1in so I think my venturi is bad took it apart the small seal inside is collapsed so will take it to work and replace the seal, also noticed the rubber 4 way to is somewhat loose on a vacuum line, will have to try and source one.
Ok so measured at the year 2in then measured at the booster 1in so I think my venturi is bad took it apart the small seal inside is collapsed so will take it to work and replace the seal, also noticed the rubber 4 way to is somewhat loose on a vacuum line, will have to try and source one.
so today I replaced the o-ring inside the venturi and the hoses comming. of the venturi, so I took new readings today at idle I now have 1in at the check valve, and 2 in at the intake so if I have 2 in at the intake but only 1 in at the bypass valve where can I be losing the booster the venturi , if I test at the test port at the 4 way connector it measures only .5 of an in can some pls advise me on a correct path, 85 928s3, new one way valve new hvac valve rebuilt brake booster, brake pedal is still very still,even connected the booster directly to the intake and the brake pedal is still very stiff.
06-01-2017, 12:17 AM
How much vacuum?
