Stepper Motor Question?

Aye Up,

As part of a first in-depth service since I bought the v8 D1 (1997) back in April, I removed the stepper motor for inspection/cleaning the day before yesterday. It was very heavily carbon’d up.

I cleaned all the muck off it, did the same with port that it screws into and then refitted it.

The vehicle had been starting on first flick of the key and almost instantly settling within the prescribed tick over rpm with both a cold and hot engine.

Since I have cleaned the stepper the engine still starts immediately but the revs immediately rise to around 1200 rpm and then drop back to just below 1k when cold and down to normal tickover when hot.

Which is correct - the increased revs or as previous?

Associated to that, does the stepper plunger require to be set to any specific length before putting it back into the plenum i.e. some kind of calibration or does the ECU adjust it accordingly regardless of what position the plunger is in on replacement?

And an aside (I suspect), I doubt that this would have a bearing on the above but I ought to mention it as I had carried it out just before the stepper clean - I had also fitted a new dizzy cap, rotor arm and plug leads and new plugs. The old plug gap was less than 25 thou and I suspect that they had been fitted straight from the boxes and not gapped. I set the new ones to 0.8mm.


Thanks

it starts and idles high when cold, it's meant to, and then idles at 750 to 800 when warm, its meant to.

However.

if you want to adjust the idle , you need to block off the stepper and adjust using the screw under the protective cap near the throttle. That is for fine adjust. Too much and the air intake will whistle. For coarse adjust then bend the throttle stop tab

Aye Up Henry B,

Thanks for the response

That’s good to hear that mine now appears to be functioning correctly when starting from cold, and idling correctly when hot, but are you saying that when starting from hot the revs shouldn’t initially rise to 1200 as one does?

Enzian said:

Aye Up Henry B,

Thanks for the response

That’s good to hear that mine now appears to be functioning correctly when starting from cold, and idling correctly when hot, but are you saying that when starting from hot the revs shouldn’t initially rise to 1200 as one does?

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Aye it should rise to 1200 for a few seconds then drop down after a period.

Aah, right-o, in that case job done.

Would I then be right in saying that if the revs rose as high as 2k rpm, that would not be correct?
I’m thinking of an initial cold start on a winters morning and oil circulation!

Enzian said:

Aah, right-o, in that case job done.

Would I then be right in saying that if the revs rose as high as 2k rpm, that would not be correct?
I’m thinking of an initial cold start on a winters morning and oil circulation!

Click to expand...

1200-1500 is the Max i'd think it should go tbh.

Hmmm, I posed that question as I know someone with one that does hit 2k - that’s why I was wondering whether a new one needs the plunger to be set in a certain position before you stick it in the plenum.

Come to think of it, back in the day of manual chokes I have no doubt that when starting on full choke engines did rev way above 1500!

Out of interest (and as an FNG on the site!) are there any members who were previously employed as fuel injection specialists, maybe even on D1s, or are currently employed in fuel injection?

I was wondering whether some of the problems I’ve been reading about in some recent posts (i.e. DV8) were occurring when the D1s were still dealer current or are only coming about as the engines/systems have aged?

The EFI ECU looks after the idle rpm, the the base idle is set at the factory and hence the tamper proof plug in the throttle housing never to be touched again, however if the engine has been interfered with the base idle adjustment can be carried out following a procedure briefly mentioned in post #2.

It was only the 3.5 (flapper) that had both speed and mixture adjustment and both of those had tamper proof plugs when the vehicle left the factory.

When I fitted a Janspeed cat back system to my disco the idle speed instantly went up to 2500rpm and stayed there for two minutes while the ECU did its bit and brought down the revs to the normal 750, just shows the affect a free a better flowing exhaust system has.
As normal cold starting the engine starts and runs at 1200 for a couple of seconds, then depending on ambient temps drops within 15-20 seconds to the idle speed somewhere around 750rpm, which could change slightly depending on electrical, AC load on the engine which again the ECU looks after. All much the same as modern day cars.

Thanks for that additional info Discool, very useful, I am getting a better idea of how the efi system works all the time.
But is it relevant as to where the plunger on the stepper is when it is initially fitted or will the ecu adjust it appropriately no matter where it starts out?

Yes it will readjust via the ECU, unless of course something prevents that happening, it’s so easy to move the existing setting just by handling as I found out... Oops.
But not a problem even reused the large fiber washer as I didn’t have a replacement, that was at least 10 years ago and never been there since.