Throttle Pot. Voltages

[Gerry Attrick]

Having a general poke about last night, and decided to check the throttle settings. All OK except for the throttle pot voltages. I have 4.3v between green and yellow; 0.325v between green and red (-ve wire first). I looked at the data given in the Dutch Rover SD1 Owners Club (reproduced in the Epistles) and this shows the 0.325v being between yellow and red. Feeling a panic, I searched the PH site and found Wedg1e's comment that 0.325 should be between green and yellow. This morning, I checked with Dicky Mint's article in the TVR Wedge Pages (which appears to have come from the same source as the Dutch one) and this shows 0.325v between green and red (like mine!!).

OK - so the big question is, "Which is correct?" Or does it vary depending on which day of the week the car was built or the brand of coffee drunk by the fitter at TVR?

[dickymint]

Doesn't matter about the colours - as long as you're getting the readings. Personally i think 325mV is too low (i use about 370-380mV with a 0.005" gap.
Also i get a different reading depending on wether the engine is running or not.
You having problems? or just fettling?

[Gerry Attrick]

I was just tinkering, as the first sign it's going off tune is when the idle becomes unstable. I was beginning to assume the reason was that the ECU was getting a full throttle signal when it was idling.

Why do you use 370-380mV with a 0.005" gap, rather than the spec figures? Is there an benefit??

[dickymint]

Gerry Attrick said:

I was just tinkering, as the first sign it's going off tune is when the idle becomes unstable. I was beginning to assume the reason was that the ECU was getting a full throttle signal when it was idling. Why do you use 370-380mV with a 0.005" gap, rather than the spec figures? Is there an benefit??

From memory the EFI spec is 325mV +/- 25mV with a zero gap (zero gap for SD1 maybe but you need at least 0.002" for a Wedge).
370mV when the engine is running works for me especially better at low revs.
The manual says to check the voltages at the ecu, but most people check it at the multi-plug. Maybe (only maybe) checking at the ecu would result in a lower reading?
It just seems to go better for me and it sorted my "lumpy idle problem"

[Gerry Attrick]

Many thanks. I'll give it a whirl, and see if there's any effect. Maybe it will reduce the sensitivity, and I'll get more and less .

[chunder]

325mv is spot on - any more and fuelling is being enriched.
Dickymint - when you say you upped it to 380 did you just adjust the TPS position or did you move the throttle linkage stop so that the butterfly was open wider as this would also allow more air at idle ?

I think the butterfly gap should vary according to the specific engine characteristics - size, cam, state of tune etc and be somewhere between 2 and 7 thou. Then idle speed and mixture can be set through altering a combination of the plenum and AFM bypass screws.

Just wish I could get it right on mine !