Frequency Valve/Oxygen Sensor Control Unit

[cay-ahe]

My car had been getting some suspension work done and went in running fine. When I picked up the car it seemed to run fine but since it is a track only car I basically ran it around the parking lot and into the trailer. I took it to a local Dyno to get dyno certified for NASA racing. Once on the Dyno it was obvious the car was not running right and was running dangerously lean.

I hope this can help others trouble shoot a car that all of a sudden is not running right including (lean)backfires, won't accelerate, won't take initial throttle input, boggs down basically runs poorly. Sometimes it started easy other times it didn't.

So we went through the thought process of fuel delivery issues, fuel filter, fuel pump, filter in the tank. Changed the filter and pump, hooked up fuel presssure equipment and all looked good. Still ran like crap and seemed to be getting worse hard to start now. Possibly bad gas the car has pretty much not moved for 3 months. I checked for vacuum leaks nothing obvious, using starter fluid on all the lines easy to reach, throttle intake area, injectors, nothing stood out.

Not knowing much about the CIS system I was reading as much as I could about it. I could not tell if the Frequency Valve was working. I read descriptions of it pulsing and didn't know how to interpret that. Now I know that it is more of a buzz or rattle that is like one of those prank hand buzzers. It was not working.

With the help of a very experience 911 tech it was narrowed down to a loose connection on the Oxygen Sensor Control Unit. Here is my latest high performance mod.

He also found a suspect wire grounding and changed the relay. All is well now. I ran the car on the Dyno again yesterday and confirmed I am back to having my massive 180hp and more importantly good air/fuel ratio. Problem solved basically with a couple of tie wraps.

[KNS]

So what did you do? It looks like you zip-tied the connector plug to the brian. Those O2 brain boxes are over $600.00! glad your fix was an easy one.

[Superman]

That little "ice cube" relay next to the brain sometimes fails. A good part to carry in the trunk. According to JW.

[LM3929]

Is that a protection bar in front of the control unit?

Is it possible to get a top view of the box?

Thanks LM

[john walker's workshop]

sometimes as simple as a blown fuse. the one for the domelight. no power to the relay=no power to the computer=no power to the freq valve.

[cay-ahe]

Originally Posted by Superman

That little "ice cube" relay next to the brain sometimes fails. A good part to carry in the trunk. According to JW.

Absolutely agree.

Originally Posted by LM3929

Is that a protection bar in front of the control unit?

Is it possible to get a top view of the box?

Thanks LM

What looks like a protection bar is just the bar to adjust the seat aft and forward, it's nothing special.

[tcar]

Originally Posted by john walker's workshop

sometimes as simple as a blown fuse. the one for the domelight. no power to the relay=no power to the computer=no power to the freq valve.

frequency valve, dome light and CLOCK, too.

Another frequent problem with those in targas, sunroofs, and convertibles, is carpet getting wet and affecting the relay or control unit.

[tcar]

What are the blue things on top of the box?

Seat cover straps?????

[john walker's workshop]

prophylactics.

[porsche930dude]

I had a fuel enrichment control unit go bad. Its that little silver box strapd onto the big one. The electronics inside were practicly dust. Anyways iv been having a problem with my domelight/ buzzer. Sometimes very rarely when im driving it goes on for a bit then shuts off. Can this be related to the computer or is it on a different part of the circuit just off the same fuse?

[cay-ahe]

Originally Posted by tcar

What are the blue things on top of the box?

Seat cover straps?????

Seat belts that go up through the seat on a six point set up.