Stepper disconnected - loads better

[taylormj4]

At the previous suggestion of a PHer, I disconnected the stepper motor today after warmed up and revs settled down, then went for a drive.
Big improvement, smooth overruns with almost undetectable shunting, revs don't stay high or increase when I change gear any more and when going into neutral at lights etc. Starting from cold is great, no more 1800rpm and having to wait for revs to drop down and then same again at first few traffic light stops.

So questions:
1. Why is this the case, fault or just rubbish management by the ECU
2. Will it cause any harm leaving it disconnected, e.g. ECU taking the huff and going into limp home mode.

Cheers, Matt

[neal1980]

Mines been disconnected for years was much better.

In really cold weather just a bit of throttle till shes warm.

I often hear this limp home mode, does the Lucas even have that??

[taylormj4]

neal1980 said:

Mines been disconnected for years was much better.

In really cold weather just a bit of throttle till shes warm.

I often hear this limp home mode, does the Lucas even have that??

Yeah, I believe so. It's a default, will run every engine but not terribly well, fuel map that the ECU drops into should one of the main sensors fail so the ECU doesnt't know what the engine is doing - I guess something like a lambda sensor failure or similar. Stepper motor not talking is probably not serious enough to cause limp home.
Presume you have taped up or sealed the open connector from the loom in some way ?
What revs does yours do at idle then. Mine is slightly elevated because I disconnected it when it was still slightly cold. Wondering if that might be better than stepper completely closed down ?
I can tolerate a slightly raised idle in place of the massively better manners the car now has, beautiful overruns with no shunting, much more driveable. If I did a track day, I might reconnect the stepper as the revs held high during gear changes promoted smoother gear changes and less likely to loose the rear end when changing down.

[Naybr]

This is very interesting! I thought that the Stepper only 'stepped in' when the car was stationary...

If this is so, why does disconnecting it make such a difference when driving?

Can someone explain what's happening here?

[macdeb]

I think it's also to have the revs higher for a moment whilst on downshifts. Might be wrong but something like that.
ROB

[v8s4me]

I had this high revs/tick-over with my V8S. Turned out to be a broken wire on the connector for the tune resistor. Now that's fixed it's much better. It's still not perfect so there must still be a fault somewhere. Maybe worth having a look?

Edited by v8s4me on Thursday 21st April 23:55

[rickprice]

Is there a right and wrong time to disconnect this? Should I wait until warm, or do it when cold? Will it make any difference?

Rich

[Barkychoc]

rickprice said:

Is there a right and wrong time to disconnect this? Should I wait until warm, or do it when cold? Will it make any difference?

Rich

If you disconnect when the engine is cold (but running) you will most likely end up with a slightly high engine idle speed when warm.

If you disconnect when warm you'll get normal idle speed when warm but slightly slow / maybe a tendency to stall when cold.
This is the way to do it.
The engine must be running when you disconnect otherwise the idle control is fully open and you'll get 1800 - 2000 rpm idle

[Alexdaredevilz]

macdeb said:

I think it's also to have the revs higher for a moment whilst on downshifts. Might be wrong but something like that.
ROB

That's the speed sensor

[Andy chimaera]

i just tried it and it seems to tick over really high, so thought i best plug it back in lol

[taylormj4]

Andy chimaera said:

i just tried it and it seems to tick over really high, so thought i best plug it back in lol

Hi Andy,
The way I did it was start up from cold, revs are high at around 1700. Wait for engine to warm up and revs to drop to around 1000, then whilst engine is running, disconnect the connector to the stepper motor. The engine must be running when you disconnect as the ECU alters the stepper position when you turn the engine off. The revs should not change as you disconnect as the ECU loses control of the idle speed.
Matt

[Andy chimaera]

taylormj4 said:

Hi Andy,
The way I did it was start up from cold, revs are high at around 1700. Wait for engine to warm up and revs to drop to around 1000, then whilst engine is running, disconnect the connector to the stepper motor. The engine must be running when you disconnect as the ECU alters the stepper position when you turn the engine off. The revs should not change as you disconnect as the ECU loses control of the idle speed.
Matt

i tried that, it seems to drive okish at the time, but then start it from cold and it dont tick over very well, it ticks over too low and cuts out, although my car runs poorly any way, lots of shunting and very twitchy etc etc, i must say, it always ticks over on the button, 1200 when cold and when warm always drops to 900 every time. am i supposed to plug it back in for cold start or something?

[rev-erend]

Jules used to recommend putting a cap over the pipe then drilling an 8mm hole in the cap - then replace the rubber pipe over it.

This had the effect of lessening the air bleed effect and over reving..

Well worth a try.

[taylormj4]

Andy chimaera said:

i tried that, it seems to drive okish at the time, but then start it from cold and it dont tick over very well, it ticks over too low and cuts out, although my car runs poorly any way, lots of shunting and very twitchy etc etc, i must say, it always ticks over on the button, 1200 when cold and when warm always drops to 900 every time. am i supposed to plug it back in for cold start or something?

Actually I have now experienced this also. I started mine up yesterday, coldest morning since I disconnected it, and revs started oscillating up and down, getting more and more variable until it stalled. Had to reconnect the stepper to get it going, then disconnected again.

Does anyone (Blitzracing?) have a wiring diagram that says what each of the 4 wires are for ? Two for power to the motor and 2 for the control signal (step in / step out). Does the ECU use a +ve voltage for step one way and -ve for step the other way etc ?
Thanks.

[taylormj4]

Thought some might be interested in some more feeedback on this disconnection of the stepper motor. I've been drivng it daily for over a month now without the stepper connected. The weather is warmer, which is of course helping, but overall still so much better. The car is now a pleasure to drive including great manners in traffic, barely detectable shunting.

Will not be reconnecting the stepper, although I have sealed up the connectors in anticipation that I may have starting problems in the winter. However, on colder days, I am finding that a small throttle opening on start up provides the same and warm up for only around 15secs is necessary before driving off.

The thing that interests me for more investigation is, when I shut off the engine I have always heard a loud sucking noise as the engine comes to a halt, which I presumed to be air being drawn into the engine that became audible due to the engine shutting down. However, interestingly since disconnecting the stepper, this air noise now does not occur. Why would that be ? Could the sucking noise be an air leak somewhere that is now somehow shut off due to the stepper being permanently near-closed ?

[BrianMillar]

taylormj4 said:

Does anyone (Blitzracing?) have a wiring diagram that says what each of the 4 wires are for ? Two for power to the motor and 2 for the control signal (step in / step out). Does the ECU use a +ve voltage for step one way and -ve for step the other way etc ?
Thanks.

The stepper motor has four wires going to it.
One pair of wires drive the valve open the other pair to drive the valve closed

The wire pairs are:

Orange – Blue/Grey
and
Green/White - Red/Green

I cannot remember which pair does what though

The resistance of each pair should be 40 – 60 ohms

[BeastMaster]

Thought I would add my bit. Disconnected my stepper motor also(while warm and engine running) as intermittent fast idle problem was taking away some of my enjoyment of the car.

Have been running like this for 3.5 months and am very pleased that the idle is now very stable. I have once in this time manually adjusted the idle speed by way of the bleed valve on top of the plenium, probably because the stepper motor valve had gummed up a little.

Apart from getting rid of the idle problem I had also noticed that the car seemed to run a lot better, a bit more throttle response and sounding a little more crisp so was well pleased.

The only negative being a cold start which is tricky as a little bit of throttle is required for around 20secs at 2000rpm to get past the fuel enrichment prog.

After a recent throttle cable break I have removed the plenium to make fitting a replacement easy, while apart I cleaned 18 months of crud (as the engine breaths into this area) polished the trumpets and decided to fit a blank over the stepper motor housing so that the bypass was eliminated. This has allowed me to reconnect the stepper motor to the ecu again so although it is being controlled no air is being bleed through it. I have to report a further improvement in the engines character

For info my car does not run the cat map, and has always been well behaved apart from the intermittent idle problem

Andy

[BliarOut]

How do they behave when you whack the throttle shut?

[BeastMaster]

BliarOut said:

How do they behave when you whack the throttle shut?

Running without stepper in my case is only a positive experience and can see no negatives except for the cold start niggle to keep it running on throtle, and this is not a big problem, after all in teaches heel and toe. - Andy

[V8 GRF]

As far as I understand it the stepper is/was the modern replacement of the 'choke' (remember them?, so really only effective when the engine is cold so once the engine is warmed up it plays no part?