View Full Version : Fuel enrichment switch

Dead Skunk
09-09-2002, 07:11 AM
Anybody know what kind of power loss I would experience if the switch weren't working? In comparing notes with another GTI driver on shift points and RPM at various places on the track I concluded that it might not be working. Together we tested it with an Ohm meter and it's not doing anything. I'll replace the switch and harness before the next race, but I'm just curious about how much power I've been missing.

Warren Martin
Dead Skunk Racing

Bill Miller
09-09-2002, 05:28 PM
I'm pretty sure the FTE switch takes the freq. valve duty cycle from 50% to 65% and takes the O2 sensor out of the equation and runs the system in open-loop mode. You can wire up a manual switch and just kick it on when you go out for the pace lap and kick it off after the checker flies.

Edit: Sorry, I don't know how much power your actually giving up. You should get an A/F mixture gauge though, because you could be leaning out at the top end w/o the FTE switch doing it's job.

MARRS #25 ITB Rabbit GTI
SCCA 279608

[This message has been edited by Bill Miller (edited September 09, 2002).]

Dead Skunk
09-12-2002, 08:09 PM
Thanks Bill,
Switch and wiring have been fixed,so I'll see if there's any difference at the next race.

Dead Skunk
09-16-2002, 10:23 AM
Bill Miller
I've ordered an EGT guage and thermocouple. What temperauture should I see as normal operating range?

Bill Miller
09-16-2002, 04:13 PM
Something around 1300 deg. F should be good. I'm sure there are a few (Mark C., etc.) that will chime in.

MARRS #25 ITB Rabbit GTI
SCCA 279608

09-16-2002, 09:30 PM

Greg Amy
09-16-2002, 10:29 PM
<font face=\"Verdana, Arial\" size=\"2\">Anybody know what kind of power loss I would experience if the switch weren't working?</font>

If I remember my wiring diagrams and KJetronic details from when I was racing my GTi in Showroom Stock (yep, mid-to-early-1980's) it does the exact same thing as the temperature sensor on the port side of the head in the water line. That switch changes the duty cycle and goes open loop when the car is cold (just as Bill said). The full-throttle switch does the same thing on full throttle after the car is warmed up.

So, if you want, you can just take those two terminals on that water temperature sensor, connect them together, and you'll get the same thing. I remember it made a nice little kick in the pants...

(Shame on you for thinking we used to do that when we raced the regular Rabbits in Showroom Stock!!!)


Joe Craven
09-18-2002, 11:42 AM
OK, here is what I'm reading. Shorting the water temperature sensor requires negates the need to connect the FTE wires to the switch?


Bill Miller
09-18-2002, 04:59 PM

I think you're talking about the thermo time switch, which controls the cold start injector. AFAIK, it does not make the lambda sensor go open-loop. You were getting a 'nice little kick in the pants' because you were dumping extra fuel into the motor (but not through an open-loop O2 sensor). Now, there's an interesting question, what happens is you short the cold start injector _and_ have the O2 sensor run open-loop???

MARRS #25 ITB Rabbit GTI
SCCA 279608

Big Money Mike
09-25-2002, 11:53 AM
Ive been playing with the full throttle switch on my 84 GTI also. Im an aspiring racer starting to build a car and dont know much, but, I had a surging idle and bucking hard under acceleration problem that I cured by sticking the full throttle switch wide open. The richening effect smoothed everything out and it runs like a champ. Im wondering if since the car is old as heck, if the injector rings are worn out and leaking extra unmetered air into the motor causing the problem in which case I can replace the seals and unstick the full throttle switch. I read about someone else having this problem on the vwvortex.com board. Any thoughts?

09-25-2002, 04:08 PM
Injector seals are about a 5 minute and $3.50 job. I'd also look for any other leakes in the intake manifold side of the house.

Some of those rubber hoses might look good, but are burned from the heat of the exhaust on the bottom side.

Tim Linerud
San Francisco Region SCCA
#95 ITB GTI, GP for 2002

Eric Parham
09-26-2002, 05:11 PM
Yes, the thermo-time switch only controls the cold-start injector. BUT, there is a switch at the end of the head on at least some cars (those with single-wire O2 sensors), in addition to the full-throttle switch, that also makes the frequency valve on the fuel distributor's control pressure line run open-loop. However, THIS open-loop setting is LEANER than the full-throttle switch's open-loop setting. I don't remember the exact numbers, but, whatever the mixture setting is, I think the duty cycle is something like 60% for the full-throttle switch and only 55% for the temp switch. As I recall, there's also a difference in computers where only some of them allow the full-throttle setting to override the warm-up setting if it's already in an open-loop mode. Keep in mind that if it isn't set correctly, closed-loop operation may have it operating at anything from a 5% to a 95% duty cycle, so 60% only richens the mix if it was running LESS THAN THAT in closed-loop (i.e., it's actually possible for the full-throttle switch to LEAN the mix if the adjustment screw is set too lean)...

Bill Miller
09-26-2002, 08:03 PM

My understanding of 'open loop' on the freq. valve is that it operates at it's max. duty cycle, 65%. I also don't understand how there could be 2 'open loop' settings. Either it's open loop or it isn't.

MARRS #25 ITB Rabbit GTI
SCCA 279608

Eric Parham
09-27-2002, 09:03 PM
"Open-loop" just means that the CIS-lambda system is NOT reading or using the signal from the 02 sensor (i.e., that it is not using a "feedback" loop). As indicated, there are at least two open-loop modes for the CIS-Lambda computers that came in most GTIs and Sciroccos, and the modes do provide different duty cycles for the frequency valve. Somewhere, I do have a copy of the Bosch Fuel Injection Performance Manual. If memory serves, I think that's where I first read about the different modes (although the Bentley manuals may cover it as well).

I hate to mention things that I'm NOT SURE of, but I've also heard a RUMOR that SOME computers may also have a third mode (undesireable for racing), that leans the mixture to a "limp-home" mode if it detects certain problems. My guess is that this isn't a mode at all, but just a non-operating frequency valve, FWIW.