Setting TR Fuel Mixture

JRV, are there "plugs" for the adjustment holes? This may be a totally stupid question, but I don't recall seeing any plugs on my Fuel distributors. Would this then be a air leak?

Hi Jeff,

from the factory there are two plugs covering the two sealing screws...first the little caps/plugs must be removed to reveal the sealing screws underneath, ten the sealing screws removed to allow access to the Allen Mixture Adjuster Screws down inside.

Regards, JRV

Thanks JRV...I AM missing those items! I just ran out and checked, and with a thin screw driver stuck through the adjustment holes, I push down on the plunger and the screw driver follows along. Would the plugs be something I can buy from Rutlands?

Jeff: If you are missing those items (screws and caps), then, you have a vacuum leak.......which has to affect the engine. I have screws on mine, but no caps. The screws are VERY important, to stop any vacuum leak. I will measure mine, if you want, and then you could buy some metric screws, if that is what you need. I wouldn't be concerned about the caps.

Thank You Hank....if they are just ordinary screws I can do some trial and error till I get the right ones. Well it seems I have stumbled onto yet another thing wrong on my car, I always wondered why it would act "wierd" sometimes. I am going to be a TR expert when I get this car done. But no matter what, I've enjoyed doing it. And when I get my next fcar I'll know exactly what to look for.

Jeff: If you have been driving without the screws, thus causing a continuous vacuum leak, then you will have to be surprised, at the performance, when you plug these holes up.

As far as the screws go, you will have to know the RIGHT length.....you don't want it too long, since it will interfere with the sensor plate arm. I could get that for you, but not until tomorrow, since my TR engine is in another location.

Jeff and Hank,

Although the screws are essential to prevent a "false" air leaks, then is an alternative solution which will ease the mixture set-up. Back in the late 70's, early 80's, VW used a "stick pin"...a rubber plug, with a wire steel handle that covered the FD mixture hole. In that the plug was removeable without tools, mixture set-up was a bit quicker.

Regards,
David

There is some great information here, but it has created a few more questions regarding the DC measurements, "The Bosch FI Manuels state that duty cycle will be 50% when the mixture is stoiometric (14-1)"
If the duty cycle was at say 75%, would this indicate that the mixture was set too lean and the Frequency Valve had to "fire" more to get the mixture to be correct when read at the O2 sensor? It seems to me that the FV is just "fine tuning" an incorrect mixture setting. Question 2, could a car with a DC reading of 75% still be running correctly; the FV is just having to work more to bring the system into spec at the O2 sensor? Question 3; Is there a DC point that you would you recommend readjusting the mixture? My DC figures are almost 75%, but the car recently passed the Ca. emissions test ( I realize this test is after the cat, but there is some relevance with this info)

Thanks,
Mark

Mark,

I honestly can't answer your questions. I only use an Exhaust Gas Analyzer and do my checking/testing before the cats. after cat test (for me) are only to tell Cat efficiency or just for a heads up on adjustment needs..

For example...in the glowing Header Thread the numbers after the cat were good pre-cat numbers. After I saw the HC numbers were very low for a 2v 308 I realized several things ..the car had cats, the tests were after cats, the cat efficiency was really good and that the CO pre-cat was double or more what it should be.

Exhaust gas testing before the cats should become SOP if it's not already...imo. And here quoteing from the Bosch Manuel on Duty Cylce: "When the sensor is hot enough to send the right kind of "hot" signals, the control unit switches over to operate in a closed-loop mode. You should see the needlefluctuating at the middle, typicaly between 45-55%. A swinging needle indicates closed loop operation- normal idle-warn engine, warm lambda sensor."

Regards, JRV

Hi again JRV,

Very good topic here.

Regarding my issue - Mr. Foley has been a godsend here, has been helping me out immensely. To refresh, 328 spontaneously developed "popping" in idle and irregular surge in RPMs. No overall change in performance.

Parts changed to date include: plug wires/extenders/plugs/O-2 sensor/protection relay/fuel injectors/thermo-time switch/exhaust gaskets/this weekend all intake gaskets.
Items checked include: wiring harnesses & grounds, TDC&RPM sensors, fuel pressure, AAV, coolant tank thermostatic switch, alternator, CSI, intake & vacuum hose integrity. With the help of Mr. Foley have exchanged Jetronic & Microplex ECUs, coil units, and protection relays into his car...which ran like a top. We see (at my baseline mixture setting) similar values of 68% cold 72% warm and 74-76% hot. Swinging needle on my V/O O-2 sensor (plugged in) when running. O-2 sensor voltage at that point (baseline setting) 0.886mV. Except my car is symptomatic.

Don't think I'm forgetting anything above? Have striven not be thorough (smile). Next step I am thinking is to check that camshafts have not jumped a tooth - rear intake about 2-3mm from centerline of timing belt cover pointer.

My gastester CO mixture checker is not that impressive - does give a reading, but not sure it's trustworthy. So not much help here. Still have no access to exhaust gas analyzer.

Now interestingly when I twist mixture screw 1/4 turn rich duty cycle goes up (to 80-odd%) which seems strange. And improves, but does not eliminate popping sound & irregular idle. Disconnecting O-2 sensor (running open loop) makes my eyes water and again almost, but not quite, resolves syptoms. I have in my notes disconnected DC was 60%.

Very strange. If cams in alignment then will change caps/rotors (already cleaned x2). Suggestions from here? (smile)

Take care,
Carl