Most of us who have bog standard Rover Flapper Efi Systems know we must adjust our throttle pot to be 0.325 volts above zero at the idle position of the throttle?

It's not Zero nor 1.0 volts. It's 0.325 Volts. But WHY?

I cant recall ever seeing a written explanation (reason) in any "Rover" documentation and although I have heard a few different opinions none ring true.

UNTIL NOW!

In another forum I was explaining that the Rover ECU "FULL LOAD ENRICHMENT CIRCUITS" are triggered when the throttle pot reaches 4.3 volts at 90 degrees of rotation, or full throttle.

Feedback from some members indicated this was not common knowledge yet that fact is clearly described in the original Rover Technician Training Manual. See below, a scanned image from page 14 of that manual.

It then dawned on me that to guarantee the ECU would see a full 4.3 volts at 90 degrees of rotation, a small offset at idle position is needed.

So, if normal tolerances for analog circuit components (say 5%) apply, then, if for some circuit tolerance reason the full load enrichment circuits saw something lower than 4.3 volts, they may not be triggered.

Now, 0.325 volts is 7.5% of 4.3 volts so by specifying a 7.5% offset, this would ensure that the circuits were always triggered at full throttle providing there were no overt mechanical reasons preventing full 90 degree rotation.

For the first time in 14 years, and without the benefit of the designers' knowledge or reasons, this seems like a good explanation of why the setting is so specified.

Can anyone throw a different light on this subject?

Interesting. Mine never gets that high (only around 3.5v) for some reason. The throttle plate opens fully and I've had the pot apart and it's clean and not worn through the track.

Perhaps I'll adjust it sometime to to give 4.3v at full deflection and see what happens.

I actually tried this the other day. The throttle pot is the original type. With idle position at 325mv, full throttle read 3.3v. Swinging the pot as far as it will go in its adjustment slots gives ~0.6v at idle and 3.65v at full throttle. Just barely scraping up to the 3.7v figure suggested as a minimum in your EFI guide.

There did seem to be a slight improvement at full throttle acceleration, but I'm still not entirely happy with the pick up from low revs at full throttle.

The pot appears fine and there's no voltage drop across the connector. I wonder if low supply voltage is the culprit. I guess it's a 5v supply, do you know off-hand what voltage I should see on what wires?

Was wondering if my throttle pot is the cause of my rough running & reluctance to start??

Cheers for the info, Ramon. I'll check for 4.3v on red/green and also the resistance.

The car doesn't have cruise control, and I'm doing the test by operating the linkage by hand in the engine bay. That is a good point though, once I can get the proper voltage this way I shall have to check I can still get it using the pedal.

The car has impressive peformance, but not having had a known-working one I have no frame of reference. It's hard to try to describe without making the car sound much worse than it is. Going from 2000rpm in 2nd gear, there's almost a diminishing return on opening the throttle, 75% doesn't give quite 1.5 times as much acceleration at 50%, and 100% isn't quite twice as much as 50%. Accelerting through the revs at full throttle it feels slightly choked, and the sound is off-beat (I've no idea if this is characteristic), perhaps like a very, very slight missfire (but without vibration, smoke or poor performance). At least until around 3500-400rpm where it feels better. I don't think it's my imagination when I say that since adjusting the pot, full throttle now feels a bit better.

I wouldn't be surprised if the engine wasn't getting its enrichment.

I'm guessing the airflow meter doesn't register "full throttle"? I'm used to later systems where the main load sensor is a MAP or MAF sensor with the throttle pot just increasing responsiveness by pre-warning the ecu of an impending full load situation.

Hello Bloke,

Punx0r wrote:

The car has impressive peformance, but not having had a known-working one I have no frame of reference. It's hard to try to describe without making the car sound much worse than it is. Going from 2000rpm in 2nd gear, there's almost a diminishing return on opening the throttle, 75% doesn't give quite 1.5 times as much acceleration at 50%, and 100% isn't quite twice as much as 50%. Accelerting through the revs at full throttle it feels slightly choked, and the sound is off-beat (I've no idea if this is characteristic), perhaps like a very, very slight missfire (but without vibration, smoke or poor performance). At least until around 3500-400rpm where it feels better.

Let me give you a SUBJECTIVE frame of reference for a 3500 Efi on song from 2000rpm in second gear when you hit the loud pedal.

Think of a Saturn 5b Moon Rocket and double it. There will be a lot of local noise, a kick in the arshe, you are part of the upholstery, with no hesitation until the engine tops out at 6000 rpm and it coughs because the lifters stop responding.

Anything less and your efi system is crap.

Quote:

I wouldn't be surprised if the engine wasn't getting its enrichment. I'm guessing the airflow meter doesn't register "full throttle"? I'm used to later systems where the main load sensor is a MAP or MAF sensor with the throttle pot just increasing responsiveness by pre-warning the ecu of an impending full load situation.

Lets examine what should happen.

You open the throttle 25% and the air flap in the AFM opens a similar amount.

Then 50% the flap does the same.

Then 75%, the flap does the same again, so

At 100% throttle open, the AFM flap is also wide open.

All very crude logic but remember, the throttle plate and the flap are in the same tunnel so when one opens the other must follow because there is nothing else involved in trying to prevent the AFM Flap from opening - UNLESS THE AFM HAS BEEN TAMPERED WITH.

So, if you think the AFM flap is not opening fully then neither is the throttle. QED

While all the above is going on the throttle pot must be screaming at the ECU acceleration enrichment circuits to double pulse the injectors with more fuel and at full throttle the throttle pot must tell the ECU, "Please give me full load enrichment".

The way you describe your current status, none of that is happening.

It seems to me that until you sort all that out by performing all the recommended tests, you might as well go for a ride-on lawnmower, it would be a lot quicker.

Right, I found some time after work to do a few quick tests:

Voltage between yellow/green is 4.36v - so all good

The resistance on red/green goes from 1.9k to 4.5k, it's smooth, but there's a spike (5-7k!) at about 5 degrees of opening (I assume this is the "cruise" position). I'm at a loss to explain why the resistance is that high at closed throttle.

I found that this test has to be done with the sensor disconnected, otherwise the readings are very strange (starts at 1.9k and finishes at 1.5k).

Next, I removed the inlet hose and took a peak at the throttle plate to find it only opens approx. 85% at full throttle. I disconnected the rod that connects the quadrant to the spindle and found it to be about the same. Then I noticed part of the spindle was fouling a jubilee clip on the plenum vacuum pipe. Moving this let the throttle open fully, giving a voltage of 4.35v (admitedly, starting at 0.66v, so probably 4.0v in actuality).

The odd thing is that the quadrant part of the linkage still only allows ~85% opening. Closer examination shows two tangs on the quadrant, 90 degrees apart that run with another pair of 90 degree tangs. It's these that's stopping the throttle opening fully. With the throttle closed, it's hanging on the cable, with approx a 4mm gap between the stop tangs on the quadrant.

Obviously someone has been messing with the linkage at some point in the past.

After adjusting the cable to move the quadrant, I'm going to have to move the crank on the end of the throttle spindle to match. It's current dead horizontal with the throttle closed. Will this be ok?

The throttle pot was in good condition inside when I last had it open, but I didn't oil it before reassembly. I'll reclean and oil it before condemning it for the out-of-spec readings above.

So I'm all right adjusting the throttle linkage hither and dither? I wanted to be sure there wasn't a carefully procedure for setting it before I started messing with it.

I shall do something with the throttle pot. If memory serves, the resistance was ok when I lasted had it apart and cleaned it. As mentioned though, I didn't oil it, and it may have suffered as a consequence.