Sluggish SHO

[evox15]

I have a 94 SHO ATX. It seems to me that it is really sluggish on the take of and takes for ever to get into higher rpms, once it finally gets up to around 4500 it really takes off (but what good does that do me after I've been left in the dust). Does anyone know what might be causing this, I read maybe the secondaries where open, how do tell if they are open or closed. Also the transmission seems to shift very violently from 1-2 and 2-1. If I punch the car in drive it shifts right at 3000 rpms and doesn't go any higher, the only way to get up there is to manually shift it.

Any help is appreciated.

Erik,
[email protected]

 

[sdpatt]

I'll let the ATX owners help you with the transmission problems. You do have something very wrong.

The secondaries as they are called are the second set of 6 shorter length, larger diameter intake runners. These are closed off at the interior face of the intake plenums by a set of butterfly valves operated by two vacuum diaphragm valves, one on each side that operates on three intake runners. These butterfly valves are held closed by vacuum from the intake manifold applied to the vacuum actuators. The butterflies are opened when the electrical solenoid valve on the rear center of the intake is opened by a signal from the electronic engine control (EEC) computer. The springs in the actuators then open the butterflies and let the engine breathe through both the long, narrow intake runners and the larger secondary runners. The secondaries are opened by the EEC at 3,950 rpm when the torque curve of the small runners only crosses the curve for both sets of runners open.

The easiest ways to prevent the secondaries from closing is to disconnect the electrical connector to the solenid valve or unplug the vacuum supply line from the rear plenum. The only consequence of the connector being off is the secondaries never closing. With the vacuum line off, you will hear a distinct hiss from the tap on the rear intake plenum. Take a look and see what you find.

Welcome to the Forum and good luck with that transmission.

 

[edmontonsho]

I read maybe the secondaries where open, how do tell if they are open or closed

You should be able to tell if they are oppening at the correct time if you can hear the sound of the motor all of a sudden change at 4000.

 

[BlackOnBlackATX]

Hey Erik, im having a little trouble understanding your shifting problem, can your explain it again? i get the part about the violent 1-2 and 2-1 shifts but could you explain about the problem you have where it wont go past 3000 rpms? thanks man.
Bob

 

[evox15]

upon inspection of the engine, I think that perhaps the harsh shifting is due to a worn front motor mount, when I put it in drive, hold the brake, and give it gas it looks like the motor tilts backward about 1.5 to 2 inches. If the overdrive is off and it is given full throttle approximatley at how many rpms is it supposed to shift at? The car does shift a little later than 3000 (it was late and I couldn't remember exactly the shift point) upon rechecking today I think it was at about 4300-4500, is that normal, it just seems that alot of the cars power is up higher than that.

Thanks,
Erik

 

[jelloslug]

When I got my '90 the secondaries electrical connection was unhooked. I did the seam thing yous did, I even got the "secondaries are now open sound" at around 4000 RPM like normal, it was just slugish till then.