Is a '81 RoW supposed to have Lambda control?

munsonbw · 12-04-2007, 05:12 PM

I have been taking the cold months to go through my SC in better detail than I ever bothered before. One thing that I have always found odd was the frequency valve; its wiring just did not look like something Porsche would have ever done. From what I read on the board here in recent months, I wanted to make sure my warm up idle hunting was not a result of a malfunctioning lambda control. To my surprise, there was no control box under the pass. seat. I traced the wires back to this thing:

Which is a K-Jetronic control unit of some sort from DC Johnson and Co in CA. The troubling thing is that it does not have any inputs from the throttle switches, because it turns out I do not have any on my TB! Only input is the O2 sensor and then the box powers a relay for the frequency valve. I haven't checked the duty cycle at all yet. Here is the frequency valve plumbing:

My fuel distributor has part number 0 438 100 097 which is correct for an 81 RoW car. What I don't know is if I am supposed to have Lambda control. Given the fact I do not have any of the throttle switches and no harness under the seat for the control brain, I would guess not. If the frequency valve should not be there, what will removing it do to the mixture? Currently the car runs well and I have run it for 10k miles since I bought it with no issue. During my head stud replacement I felt the everything in the engine looked normal. Plugs never have shown any signs of lean running, actually the contrary. All of the fuel lines look pretty professional. I just don't like the thought of some unknown lambda box working at WOT, doing who know what... presumably targeting 14.7:1

I do have a LM-1 unit, so I will hook it up soon and try to get some AFR numbers. Anyone know how to get a tach signal to Megasquirt from the Bosch CDI? I have a MS from another car that I could use to data log with the LM-1 rather than just watching a gauge.

TIA,
Ben

Head416 · Head416's Garage

Well, you seem to know more about these systems than me, but I can let you know that there's no Lambda in my car, nor evidence that there ever was. (Not exactly conclusive, but you can make of it what you will.) Good luck.

DARISC · 12-04-2007, 10:36 PM

Gray market RoW SC's have no Lambda system. Federalization required smog pump & cat.

munsonbw · 12-05-2007, 02:49 PM

Interesting, no lambda... any ideas what would have been done to the control pressures or other components to adjust for the frequency valve? Any else had one of these on their RoW? From what I know of the Lambda system you can't just pull the freq. valve off and disconnect the brain, the fuel distributor is calibrated to work with the lambda on the lower control pressure. Wonder how it works when lambda is added to the non equipped FD.

stevemfr · 12-30-2007, 06:55 AM

Hey Ben,
I used to convert gray market cars 20sumpin years ago :-o . Your car is a gray market vehicle that was converted (federalized). DC Johnson was one of the bigger suppliers for aftermarket FI-lambda controls back in the 80's. The EPA didn't stipulate how the vehicle was to be modified on an individual certification - that was left up to the modifier. The EPA highway/city cycle test had to be passed just like the OEM's, tho. A smog pump was not necessarily required.

Assuming your system is still operational (do you feel the valve buzzing with the motor running?), unplugging the frequency valve will kill your catalytic convertor. It's actually not the fuel distributor that's calibrated to run with the frequency valve, but the WUR-control pressure (the valve is plumbed between the control pressure line on the WUR and what looks like the fuel return line, so that should be correct. I wouldn't have left the frequency valve floating in the air like that, tho, but mounted somewhere. I usually mounted them on the FD with an AC hose clamp). The control pressure is set somewhat higher (=leaner) with a frequency valve and the FV reduces the control pressure to lambda, so unplugging the FV might leave you lean at WOT.

About the only way to check your mixture or the operation of the system is to add a second o2 sensor bung ahead of the cat and check the mixture while driving with a wide band o2 sensor.

Its funny, I haven't even thought about this stuff in years, and this is my second post in the last day on this topic ( HELP! What do I do with this 3.0L? ).

Good luck!
Steve