engine/power restricted??

[rjpiselli]

Last night I finished replacing the oil check valves, which requires the intake manifold to be removed. This was done purely as a preventive maintenance thing; prior to this project the car ran and had full power. After the job there is a severely noticeable reduction in power. it seems like the car is holding itself back. what doesn't make sense is the car idles perfectly fine, not lights on the dash, engine is as smooth as can be. but when your at WOT it feels like its going to start to take off and then just doesn't.

My first thought was the intake flapper. But the arm is fully extended out when the engine is off; and immediately goes in upon starting the car. Also, it is my understanding that this flapper moves at 5k rpm. im experiencing a restriction across all rpms; most noticeable between 2k-4k rpm. again, the engine is smooth and accelerates uniformly, but just does so noticeably slower. there isn't the thrown-in-the-seat feel it had before doing this project.

I did disconnect the battery during the project; and since completion have put about 50 miles on the car, nothing has changed. With the IM off i also replaced the pcv valve, and replaced all vacuum lines and hoses, as well as changing out plastic connections for brass. My next step is going to be taking the IM back off and going over all of the electrical connections/vacuum lines and the flapper system, but I'm predicting that i wont find anything that stands out.

Any help would be great. Does the IM flapper only take action at 5k rpm? Am i on the right track with that? Something else i should check?

EDIT: the car is a 2004 S4 6MT

[jakeoboy67]

doublecheck your connections at the front of the intake manifold+ vacuum lines that you disconected .

[rjpiselli]

doublecheck your connections at the front of the intake manifold+ vacuum lines that you disconected .

roger that.

[R&Cs4]

x2 on a vacuum leak. Also, do you hear any whistling or hissing noises from the IM?

[rjpiselli]

x2 on a vacuum leak. Also, do you hear any whistling or hissing noises from the IM?

I don't. I was very meticulous in ensuring that everything went back as it was removed, or better. I listened around for vac leaks after the first test drive and even unplugged a couple lines and was able to confirm that they aren't plugged or anything. Nevertheless I must have missed something.

despite the fact that it appears to be functioning correctly, I am still thinking that something is up with the IM flapper.

[jvitelli17]

I am in the same boat! did the oil check valves and i don't feel the butt dyno preforming well. I don't hear any hissing or out of normal noises, however my idle isnt bad but i notice a ever so slight fluctuation from 800-780 and back every now and then. I did NOT replace my PCV and seems like i have OEM clamps so with a smell of oil after hitting it i will be replacing the PCV next weekend but i doubt that is my main problem.

Let us know what you find when you disassemble, i am curious to know if i missed something too!

[rjpiselli]

Ok so after removing the IM and looking over everything I noted the following:

No bad, disconnected vac lines.
No unplugged connectors
All bolts were tightened down
Flapper arm requires only enough force to overcome the spring to manually work
*perhaps the key* two of the wires for one of the knock sensor connectors are exposed.

So I am obviously going to repair this. But my question is this; could the knock sensor be responsible for a reduction in power? It is my understanding that they monitor the engine for knocking and retard the timing according. That reduces horsepower, correct? I will be repairing this likely by the weekend and will report back with the results in mission horsepower restoration.

[R&Cs4]

Ok so after removing the IM and looking over everything I noted the following:

No bad, disconnected vac lines.
No unplugged connectors
All bolts were tightened down
Flapper arm requires only enough force to overcome the spring to manually work
*perhaps the key* two of the wires for one of the knock sensor connectors are exposed.

So I am obviously going to repair this. But my question is this; could the knock sensor be responsible for a reduction in power? It is my understanding that they monitor the engine for knocking and retard the timing according. That reduces horsepower, correct? I will be repairing this likely by the weekend and will report back with the results in mission horsepower restoration.

If your engine is pulling timing, it could definitely be caused by that. Have you scanned w/ Vagcom?

[rjpiselli]

I haven't scanned it with vagcom for lack of access but can only assume these two wires are causing a faulty reading by the knock sensor.

[JimmyBones]

I haven't scanned it with vagcom for lack of access but can only assume these two wires are causing a faulty reading by the knock sensor.

Did you torque the knock sensors to the correct spec? Knock sensors will give the wrong reading if they are loose and you will break them if you over tighten them.

Did you make sure that the MAF boot was on tight. I have had to replace the clamps on a few cars now because those they got weak from normal use over time.

[jmcS4]

Did you torque the knock sensors to the correct spec? Knock sensors will give the wrong reading if they are loose and you will break them if you over tighten them.

Did you make sure that the MAF boot was on tight. I have had to replace the clamps on a few cars now because those they got weak from normal use over time.

i didn't have to remove the knock sensors when i did my service

BUT i did forget to connect the bank one knock sensor that clips the intake manifold. car was down on power and shot flames anytime i shifted

[rjpiselli]

Did you torque the knock sensors to the correct spec? Knock sensors will give the wrong reading if they are loose and you will break them if you over tighten them.

Did you make sure that the MAF boot was on tight. I have had to replace the clamps on a few cars now because those they got weak from normal use over time.

I did torque them down properly, but will double check them. Maf boot was on securely but will also keep that in mind.

[rjpiselli]

i didn't have to remove the knock sensors when i did my service

BUT i did forget to connect the bank one knock sensor that clips the intake manifold. car was down on power and shot flames anytime i shifted

I'm thinking my issue is def knock sensor related bc it seems to be backfiring when I shift as well.

[jvitelli17]

Did you torque the knock sensors to the correct spec? Knock sensors will give the wrong reading if they are loose and you will break them if you over tighten them.

Did you make sure that the MAF boot was on tight. I have had to replace the clamps on a few cars now because those they got weak from normal use over time.

What is the torque spec for the knock sensors? I took all four off mine when i did the service to clean the crude off them, Should have left them alone! I just tighten them down because i couldn't find the torque specs online...this can be my prob too because vagcom showed one knock sensor having open circuit....

[jmcS4]

I'm thinking my issue is def knock sensor related bc it seems to be backfiring when I shift as well.

I know u said you check them but recheck them lol. I didn't realize I forgot to connect them until I scanned the car and saw the codes. It's hard to fit a hand in there to connect them

[rjpiselli]

What is the torque spec for the knock sensors? I took all four off mine when i did the service to clean the crude off them, Should have left them alone! I just tighten them down because i couldn't find the torque specs online...this can be my prob too because vagcom showed one knock sensor having open circuit....

I believe the proper torque is just under 18.5 ft lbs

I know u said you check them but recheck them lol. I didn't realize I forgot to connect them until I scanned the car and saw the codes. It's hard to fit a hand in there to connect them

yeah I def have them plugged in, but like I said there are 2 exposed wires on a single connector. so im thinking repairing the wires is going to end up solving my issue. thanks for the heads up though!

edit: someone please correct me if that's not the right torque for the knock sensors

[rjpiselli]

Just an update: I repaired all of the exposed wires for the plugs on my knock sensors and once again went over my vac lines before reinstalling my IM. there is a very tiny plastic vac line that connects to the front of the IM and runs to the back and goes into a Y along with 2 other tiny vac lines that are the same very small black plastic material. upon putting that back into the Y the tip pretty much just fell off. It was a little cold (43F) so that may have played a role, but im thinking that this brittle thing was damaged upon the first reinstall of my IM.

Anyway, the knock sensor plugs wires were all deteriorated and cracking and the copper was exposed and of course touching one another; my personal opinion is that this is what caused my noticeable reduction in power; but it could have also been vacuum related. in any event it now seems to be restored to its original running condition and after approx. 50 miles there have been no problems detected.

thanks for the pointers on this guys!

[jvitelli17]

Just an update: I repaired all of the exposed wires for the plugs on my knock sensors and once again went over my vac lines before reinstalling my IM. there is a very tiny plastic vac line that connects to the front of the IM and runs to the back and goes into a Y along with 2 other tiny vac lines that are the same very small black plastic material. upon putting that back into the Y the tip pretty much just fell off. It was a little cold (43F) so that may have played a role, but im thinking that this brittle thing was damaged upon the first reinstall of my IM.

Anyway, the knock sensor plugs wires were all deteriorated and cracking and the copper was exposed and of course touching one another; my personal opinion is that this is what caused my noticeable reduction in power; but it could have also been vacuum related. in any event it now seems to be restored to its original running condition and after approx. 50 miles there have been no problems detected.

thanks for the pointers on this guys!

Did you torque them down to 18.5? and which lines are you talking about? I was going to rip into mine this weekend and recheck torque on knock sensors. I reconnected the small vacuum line on the front of the IM but the only one i know about was the small line that runs on top of the IM. I just want to check everything when i take it out.

[rjpiselli]

Did you torque them down to 18.5? and which lines are you talking about? I was going to rip into mine this weekend and recheck torque on knock sensors. I reconnected the small vacuum line on the front of the IM but the only one i know about was the small line that runs on top of the IM. I just want to check everything when i take it out.

Yes the knock sensors are torqued to 18.5 lbs. the little line im talking about is connected to a Y on the drivers side right by the oil filter housing. It is a small hard plastic line that goes in 3 directions: 1. over the manifold to the passenger side of the engine; 2. towards the back of the engine on the drivers side about 6"; 3 to the front of the intake manifold. the 2 that go to the back of the engine go into some sort of solenoid or something, im not sure what they do; but I know that they are brittle. anyway, mine are connected to the Y with a 1/2" long piece of rubber hose that slides over the Y and slides over the plastic hard lines. Seems like a dumb design and I cant imagine why they wouldn't have just been rubber hose the full length, but never the less I removed the broken chunks and reattached them using a piece of rubber hose like it was when I got in there. the one that runs to the front of the IM runs along the drivers side fuel injectors. I'd check all 3 of the lines that go into that Y as like I said, they seem really brittle.

edit: "I reconnected the small vacuum line on the front of the IM but the only one i know about was the small line that runs on top of the IM" it sounds like you are talking about the same line I am. just check the ones that connect to the same wishbone that this one does.