What is the normal vacuum for a S type R?
Getting 15 psi but poor power brake booster performance.
Booster passes smoke testing.
Fuel trims are high also.

 

Fuel trims may mean an air leak and so lower vacuum.

What are they at idle and how much do they drop if you rev somewhat and hold for a few secs at the higher revs?

 

I have an 06 str and checked vacuum last year. 19 to 20 in/hg at idle. Very good i think

 

How are you doing the smoke test? Most cars have a check valve, where the large vacuum hose connects to the booster.

Did you remove the check valve? If not, no smoke would have flowed into the booster, rendering the test ineffective.

If you did remove the check valve, did you check for smoke under the dash, where the pedal pushrod passes through the firewall? If not, you'd have missed a potential leak there.

One quick way to check if the booster is leaking and preventing normal manifold vacuum from developing:
​​​​​
Disconnect and plug the large vacuum line to the booster. Do NOT drive like this, as considerable pedal force will be required to stop. Start the engine and see if the vacuum reading increases. If so, you’ve got a leaking brake booster or check valve.

 

Hi Wrenchead,

I assume you mean 15 inches of Mercury (inHg) of vacuum rather than pounds per square inch (psi)?

There are lots of places to lose vacuum on the 4.2L S/C engines. The first thing I recommend is to look for any oil leaks around the top of the engine. if oil is getting out, unmetered air is being inhaled under engine vacuum. The oil filler neck and cap, cam cover gaskets, spark plug tube seals, the O-rings on the stem of the crankcase vent valve ("PCV valve") and the dipstick tube O-ring are common places to find oil/air leaks. On N/A engines the VVT solenoid gaskets are another common leak point.

Other common leak points include the main air intake pipe between the MAFS and the aluminum intake pipe to the throttle body. Look for cracks in the accordion pleats of the plastic pipe, and check that the hose clamps are secure and not overtightened at the air filter housing end..

The O-rings in the Norma connectors on the ends of the crankcase/part-load breather hose and full-load breather hose harden and leak. The fuel injector O-rings harden and leak.

The plastic quick-connect fitting where the hard plastic brake booster pipe connects to the right side of the intake elbow breaks and leaks.

In addition to the dipstick tube O-ring, the O-ring(s) on the dipstick itself can leak air.

Air leaks at the intake manifold gaskets can cause vacuum loss/lean running, and leaks at the exhaust manifold gaskets can also cause lean running.

To smoke test these engines, smoke must be injected at several points while other points are blocked off - main air intake, oil filler neck, crankcase vent valve port, both ends of each breather hose, the brake booster pipe, oil dipstick tube, etc.. Remember not to inject smoke onto your MAFS or it can be contaminated (I remove it prior to any smoke testing). To fill the intake manifold with smoke, remember to prop the throttle plate open. And your smoke machine should be set to provide sufficient pressure. I generally use 8 or 10 psi for intake leak detection, sometimes more. A lot of the cheaper smoke machines are regulated to just 1 psi for safe EVAP system work, and their usefulness for engine intake diagnosis is limited.

Cheers,

Don

 

I pulled the vaccum line off the booster and plugged directly to the booster. And yes no leaks inside, under the dash. Check valve tests OK too.

 

I'll get the exact readings this weekend. Stay tuned.

 

I am smoking from the aluminum elbow from the Mina kit after the MAF.
PCV and booster lines plugged
Replaced the o-ring at the brake booster line 2 years ago so should still be good. Saw a little smoke around the EGR valve. Can't tell if the leak is at the EGR gaskets or the gasket between the EGR solenoid and casting.
Smoker runs at 15 psi so should have enough pressure. Otherwise the car runs Ok.
Big concern is the wooden brake performance
Going to get my inspection camera out next to try to pinpoint the exact location of the smoke.

 

Okay, good to know.

Is the check valve on the end of the hose, and plugs into a grommet on the brake booster? If so, has that connection been tested? Seems you've tested the components themselves, but not the connection between them.

Not sure of the best way to test. Probably run at idle and observe the fuel trim while spraying some starter fluid on the connection. If the fuel is trimmed back, that means the starter fluid is being drawn in.

 

With the booster vacuum line installed on the booster smoking from the intake tests the connection at the booster.
Removing the line at the booster shows smoke entered the booster during smoking.

 

Hmm, that doesn't sound right. Seems like the check valve is letting air back into the booster.

 

Final got back to the car on the weekend.
Short term fuel trim on banks 1 & 2 after starting are -16 and -12.
At 2K rpm go to -9 and -8.
After warmed up at idle -25's for both.
l'm confused.
Negative trims tell me I 'm running rich.
Poor brake booster performance was thought to be low vacuum because of a leak... Lean condition.????

 

Fuel trims are -25, changing to -8 to -10 @ 2K rpm.
This tells me I'm rich...too much fuel.??????

 

Sorry, when I removed the booster line the check valve stays on the line side. Booster is now open...just a rubber grommet hole.
​​​​

 

Hmmm. Any chance your MAFS was contaminated by the smoke machine?

Off the top of my head, some possible causes of rich running are leaking fuel injectors, excessive fuel pressure, obstructed air filter, MAFS out of calibration, or a misbehaving throttle body. A failed Engine Coolant Temperature Sensor (CTS or ECTS) can also cause rich running by prompting the ECM to mistakenly continue cold-start fuel enrichment even after the engine has reached full operating temperature, but the ECM won't know anything is wrong because it is responding to an incorrect signal from the CTS.

Can you tell via Live Data that the fueling system is going Closed Loop?

Cheers,

Don

 

It's trims with properly warm engine (hot cat convs) that reveal most but -25 would be very rich if that's what they are.

 

Checked again today after a long warm up and still at -25 on both banks and is in open loop condition.

 

obviously fix your fueling issues first but the 03-05 active booster is more complicated than it looks. if you have any doubts just replace it.

 

What coolant temperatures are being reported by the CTS when the engine is cold and warm?

 

187°F, so seems OK