Power loss after secondarys open

[MOSHO92]

I replaced all my intake manifold gaskets on Friday to cure a leak and hopefully fix my lean condition.

After testing it, I dont think I have the leak anymore (doesnt feel jerky due to timing retard) but I have a new issue.

On WOT there is ample torque up to 3950rpm... then as soon as the secondarys open up there is a noticable loss of power (even passengers can feel it). It feels slightly sluggish up from then until redline.

I plan on getting it dyno'd soon for the A/F ratio, but until then....Do you have any ideas?

Thanks.

 

[MelectroK]

Are the secondaryies visually opening???? Maybe there stuck but the computer thinks there open and dumps more fuel.

 

[MOSHO92]

Are the secondaryies visually opening???? Maybe there stuck but the computer thinks there open and dumps more fuel.

Good call. I strongly beleive that they are opening because I can hear them...But it does sound quieter than it did with the vacuume leak, maybe only one bank is opening

I'll check tonight..

I'm also going to try swaping MAFs and see what that does for me...I'll get back in the morning.

Thanks

 

[MOSHO92]

Epiphany

WOW...Great call on that MelectroK. The rear bank is sure enough stuck closed I never would have thought of that.

Is there a way to oil the butterflys without removing the manifold again?

Oh and I did check to see if the vacuume line running to the bank was pinched. It wasn't.

Thanks again!

 

[AutoSHO]

Loosen up all the nuts for that set of butterflies and re-tighten them. Check to see if you can get them moving freely. if not, you can pull them off and remove the 2 philips head screws holding the actuator on, and then separate the butterfly assemblies by simply pulling them apart. At that point you can dribble some lubricant into the pivot points. However, that shouldn't be necessary.

 

[sdpatt]

Are the secondaryies visually opening???? Maybe there stuck but the computer thinks there open and dumps more fuel.

The EEC will cause only as much fuel to be injected as called for by the sensor inputs and programmed A/F ratio tables. The MAF sensor output has a great effect on the measure of fuel injected. The EEC doesn't have to "think" the secondaries are open, it knows whether they are open or not by the volume of air inhaled by the engine.

Verifiy that you can fully articulate the "stuck" secondaries with a finger on the actuator cam linkage. You should be able to move the lever thorugh its full range with just a finger. Try it out on the front bank to see how it should move.

This will verify that there isn't a mechanical obstruction that is preventing the butterflies from opening. The gasket replacement and reassembly may have interfered with the proper operation of the butterflies.

If the rear bank butterflies are stuck closed, be aware that they are closed by vacuum and opened by the spring pressure in the vacuum diaphragm actuator. The vacuum is either not being released in that bank by an obstructed vacuum line or there is an obstruction or friction preventing the actuator from rotating the shaft to the open position.

 

[MOSHO92]

With the engine off (no vacuume, butterflys should be open) the rear bank is fully closed. If I use a screwdriver and pry the tab just a little bit to start the rotation (it doesnt take much force to do this) then the spring pops it open the rest of the way. It feels like it is gummed up or not properly lubed. I didnt think that they needed lubrication to function however, so there is the possibility that a piece of old gasket is stuck in a joint causing some extra friction.

I will try a few things when the motor cools tonight and get back to you. Thanks for the suggestions.

 

[Racer X]

Hang on a sec...

You mean that with the engine off with no vacuum, the butterflies are supposed to be open?

 

[AutoSHO]

Yup. Watch as someone else starts your car, they will close either while cranking or as the engine starts up. Same with shutting it off, they will open back up after the car has been turned off.