3.2l manifold vaccum ideas

sleepdoc · 01:00 AM

Hi All,

I have been working through the fuel system componets on my 3.2l
while investigating an idle surging problem. After reviewing the numerous posts here and elsewhere about this common problem I had a couple of ideas in regard the "vacum leaks" issue.

First what do you think about pulling off the airfilter system from the
air flow meter and presurizing the intake system with commpressed gas to try to hear small leaks? I have an ultrasonic leak detector but can't detect any leaks over the cacophony of the runnig engine. If there are no leaks in the hoses or at the intake manifolds, I would expect to hear gas leaking through the open valves and out the exhaust. Anyone tried this?

Second idea is that at normal idle running conditions there ought to be a known vacum reading in the intake manifold. With the AMF closed, and the Idle control valve disconnected, We should have a known vacum that the system in good repair generates. Anyone know how much that value is. Can we use it to convince ourselves that vacum leaks are not a problem?

What do you think?

best Mark

dean · 11-30-2004, 03:55 AM

The first idea won't work cause there will be a valve open. Use carb cleaner to find the leak.

I think 12-18 inches vacume is a good idle reading

Dean

sleepdoc · 11-30-2004, 09:14 PM

Hi Dean,

What if i was to close off the exhaust and pressurize the entire system.
I think the rings would hold 20 psi

best Mark

RoninLB · 11-30-2004, 09:21 PM

did you check the vac line where it enters the brake booster with the ultrasonic? I've got one and it seems pretty accurate at finding vac and exhaust leaks.

sleepdoc · 11-30-2004, 09:33 PM

Hi RoninB,

I checked all the vac lines I can find, No brake booster in my car a 914/6 conversion.

Today I tried disconnecting the O2 sensor (new), powering the heater circuit, and running at idle until at temp. The O2 sensor reads .8v
If I open the idle bypass screw or open the oil filler the reading drops minimally to .75v. What do you think is causing such a rich mixture?

best Mark

nhromyak · nhromyak's Garage

Did you check and/or clean the ISV?

sleepdoc · 11-30-2004, 10:10 PM

Hi nhromyak,

Yes removed it, cleaned with carb cleaner, run both directions under direct visualization good quick movement.
Also by using John Walker's trick with an old relay I was able to try to adjust the idle so that the ICV doesn't have to do much work.

best Mark

dean · 12-01-2004, 03:35 AM

Hi Mark,
Closing off the exhaust might work. Give it a shot.

Dean

sleepdoc · 12-01-2004, 07:53 PM

Thanks Dean,

I will let you know what happens. I don't really think this is a vacum leak problem, I can't hear any, especially now that the O2 sensor experiment suggests a rich not lean mixture. I plan to try it to definitively state no leaks. I will report the result.

best Mark