What's up everyone, I'm a new member. Got an 06 5AT coupe back in December. I've been reading the boards for a while. The DIY section was a lifesaver - so far I've installed a z-tube, pop charger, 5/16 plenum spacer, and 6000K Philips bulbs.

Need some of your expert advice though. I installed the plenum spacer about 3 weeks ago, and it seems like the car has slowly been losing power, at least according to the butt dyno. If I gun it from a standstill, I accelerate like a rocket, but if I hit the gas from a roll, the car lags hideously, especially around 30-40 MPH. I've also noticed a hissing noise coming from the plenum area, near the vacuum line on the left. But according to Tony at Motordyne, some noise there is normal. For the life of me, I can't remember how it sounded before the install - but I don't remember that much of hiss. I reset the ECU and it didn't seem to do much, so I'm thinking it isn't related to the computer remapping due to an increase in airflow.

I've searched through the forums and it looks like the telltale signs of a problem with the spacer install are a rough idle and fluctuating RPMs when you hit the gas. I don't have any of these issues, just the lag/hesitation. Do you think there may be a problem - that this is the beginning of a leak? Or am I crazy and I've just gotten used to the extra power?

Thanks.

P.S. I've checked all the connections, the rubber around the oil cap, the gaskets, and I own a torque wrench, so I'm not terribly concerned about the bolts.

 

Have you checked for vacuum leaks with propane or carburetor cleaner?

 

I just installed mine about 2 weeks ago and immediately heard a hiss and rougher idle. I retorqued the bolts and found a few that weren't tight enough. Started her up and have been trouble free and smiling ever since. Also make sure the rubber "oil-filler boot" isn't pinched in between the plenum and the spacer. Try retorquing just in case.

 

Welcome to the Driver boards, aero .

If I recall correctly, I had to retorque (60 inch-lbs.) the 6 (six) bolts, which sit on top of the upper collector/plenum, over a period of a couple of months. I do routinely check them from time to time, but they have been fine. You may want to check the said out and retorque them, if required. Good luck!

 

+1...
If the bolts on the upper plenum aren't torqued down correctly, you could have a leak. The upper and lower plenums have to seal properly w/ the spacer. Just make sure you don't over torque the bolts.

 

Thanks for all the replies. I torqued the main (6) bolts to 40 inch-lbs then 80 inch-lbs per the MD instructions, but my wrench does have a 6% error, so it's possible I may have under-torqued by about 5 inch-lbs. I figured it wouldn't have had that much of an impact, but it sounds like the bolts may be the prime suspects. The rubber around the oil cap is definitely out of the way, and I'm 99% sure the gaskets are okay (no folding over or anything). I guess I'll take it apart this weekend and retorque the bolts. If that doesn't work, I'll have to get more creative.

 

I just installed my spacer this weekend I am also having the exact same problems as you are. I thought that it was just normal. Please keep me updated on your progress.

 

I (and many others) had to re-torque the center bolts several times over a period of about a month before they staying tight. You might want to check that if you haven't already. Just remember to do it when the plenum is cold.

I hope you figure out your problem.

 

I would loosen everything that was moved/removed during the install, check all the connections, and retighten. IMO, the main suspect would be the fittings/installation of the intake tube to the throttle body and also the vacuum line attached to the intake tube. Make sure all vacuum lines that were touched during the install are removed and reinstalled. If that's not the case then I'd look at the 6 central plenum bolts. I had to torque mine to almost 100 in/lbs to ge them to stay tight.

What kind of tranny do you have and what gear are you using when going WOT in the 30-40mph range?

 

You could spray some carb cleaner in the area you think it's leaking. If the idle goes up, then you got a vacum leak somewhere.

 

Thanks for all the tips guys. I'll check the intake tube and vacuum lines, then the main bolts. If I still can't resolve it, I'll try the carb cleaner. I'll let you know how it goes.

Dave, I've got a 5AT. I'm not sure exactly which gear I'm in when the lag occurs. I've heard that the 5ATs have a tendency to hesitate in 3rd though. That's why I wondered if this is all in my head. Especially since the car is fast as hell off the line.

 

Your description of fast off the line but slow from a roll sounds like something else is going on.

Its hard to say without being there.

As for a potential leak, the effect of an air leak is only noticable at idle or at very low throttle positions. (Not at or near WOT)

If you have a small leak that is large enough to affect the idle it will typically show itself as a hissing, squeel or rough idle. But these types of leaks won't affect performance when you hit the gas because the relative flow rate through a hypothetical leak (equivalent to 1/16" - 1/8" diameter) the relative flow area through an open throttle body is so much larger the leak does not have the capasity to tangibly change the air mass flow rate or affect the A/F ratio.

If the leak area was much larger (like 1 square inch) it would have the ability to affect WOT performance. But if this was the case your car would never be able to idle.

Basically what this means, if your car idles good, you don't have a leak.
Or even if there was a leak small enough that it doesn't affect the idle, it certaintly can't affect performance when you tip in the throttle.

And if you don't have a leak, there is either something else causing the problem (or there may not be a problem at all).

The best thing you can do to trouble shoot the problem is to simply remove the spacer and see what happens.

If you remove the spacer and you still notice the problem, there is either something else wrong with the car or possibly the butt dyno.

Either way, start a trouble shooting process and post your results.

I'll help out.

EDIT: Do you have any kind of aftermarket intake? Others who ran into your same situation went through extensive troubleshooting. ...it was found that their MAF was fouled up by over oiled filters.
After a quick cleaning of the MAF the problem disappeared.

 

I had the same thoughts initially. The car idles somewhat smoothly, no fluctuations in RPM, but I can feel a little tiny bit of shaking when I grip the steering wheel. The main symptoms are a hiss coming from the plenum area and the lag/hesitation from a roll. I listened to the hiss last night and narrowed the location down - it's coming from the left side of the plenum, about 3-4 inches in front of the vacuum line (toward the front bumper). I'm not sure if that's the normal hiss referred to in the MD spacer installation guide, or if it's a sign of a leak.

I do have a pop charger and z-tube installed. I was very careful with the MAF and throttle body though.

EDIT: to complicate matters, there may be another factor involved. I live in Virginia, and the weather has been changing wildly the past few weeks. The week I installed the spacer, it was pretty cold (we had snow), but then we hit temps. up to 84 degrees 1-2 weeks later, which is around the time I started to notice the lag. It makes me wonder if it's all just due to heat soak throwing off the butt dyno.

 

Ahhhh. Popcharger.

80% of the time when there is a problem with your symptoms, its oil on the MAF hot wire.

If you can, try to clean off your maf with 90% isopropyl alcohol or carburator cleaner. After spraying it, blow it off (gently) with an air hose.

I'll bet that clears it up.

-----------------

And there is one other important factor that may be working.
The air temperature (as you noted).

Air temperature makes a huge difference on power output. I've done a series of dyno tests mapping the effect of air inlet temperature. With inlet temperatures from 50'F to 120'F in 10'F increments. And I did dynos at each inlet temperature.

Surprisingly, the peak power didn't change all that much... only about 8 HP... but the TQ changed massively. From 50'F to 90'F the TQ fell ~20lb-ft. And it was fairly linear to about 5KRPM where the different plots began to converge.

Cold air is for your car like an MREV is to a REVUP engine.

 

Speaking of temperature, it got cold again today (32 degrees) and everything seems fine. On the way to work I had good acceleration from a standstill and from a roll. It makes me wonder if the "problem" was just decreased midrange torque due to the large increase in air temp.

I'm still going to troubleshoot tomorrow though. I'm just afraid I may be trying to fix something that isn't broken. I'll let everyone know the results once I take it for a test spin.