Switchable stepper motor ?

[WokingWedger]

Okay, I am fed up with the stepper motor hanging on to revs.

Please DONT TELL ME TO CLEAN IT !

You shouldn't have to clean every time you use the car!

Engine has just been rebuilt by John Eales and fitted by a respected TVR specialist.

Ran sweet as a nut for a few trips out then the old problems started. Revs hanging when you come off the throttle. This was fixed temporarily by adjusting the base idle (stepper was trying to compensate for incorrect base idle apparently)

All good for 2 days use.

Now its racing away again. (even makes changing gear awkward)

I disconnected the stepper (when hot) and it runs perfectly, but of course it wont idle when cold.

Now just a thought !

Can I put a switch in one of the leads to the stepper motor, so that once warm I can switch it off ? (switch mtd in the car obviously).

Which lead should the switch be spliced in to ?

Any thoughts ?

PS I don't want to fit an after market ECU.

[WinstonWolf]

Can you try a different stepper? Better to cure the fault than work around it IMO.

[Pupp]

A cheat that can work is to put a restrictor in the hose between the stepper housing and the throttle casting. Idea is for the bypass circuit to allow just enough air for idle and cold start but not enough for the revs to soar when it randomly opens. Can't remember the ideal drilling size but its a couple of mm or so and will come up with some searching.

Better fix is to junk the 14CUX and go aftermarket

[Barreti]

Probably something you've already done, but have you used PTFE tape when refitting the stepper?

[yknot]

Are you sure the problem is with the stepper motor, do you have Rovergauge software or the Ecumate diagnostics??

It may be that the TPS is going out of range on tickover and throwing the ECU into a tizz or maybe the speed sensor???

Could be many things but don't just assume the stepper motor is faulty as it gets a lot of unwarranted bad press!!

HTH

Edited by yknot on Sunday 21st December 17:02

[blitzracing]

Its not just the stepper - the throttle pot voltage has to be correct, and no speed reading- either of these are wrong it can hold the idle high. The ECU has a target idle, depending on engine temp and the ECU will switch into idle mode, or drive mode depending on the sensor input. Both ECUmate and RoverGauge will display these values- plus the stepper position- typically this should be about 30% open (60 steps) to show its adding additional air to the base idle setting. If you stepper is dropping to zero, you have an air leak somewhere. You would be far better looking at these readings than trying to bodge it- the system does work if every thing is in balance.

[WokingWedger]

Thanks everybody.

Stepper is sealed with ptfe tape (or was prior to rebuild - so better check).

I have tried the restrictor without success.

I have ordered a Rovergauge cable ( due soon).

What should I look for when the Rovergauge is connected ? What is the tell tale ?

It just seems once it has don its job when the car is cold it shouldn't be interfering !

[SILICONEKID345HP]

WokingWedger said:

Thanks everybody.

Stepper is sealed with ptfe tape (or was prior to rebuild - so better check).

I have tried the restrictor without success.

I have ordered a Rovergauge cable ( due soon).

What should I look for when the Rovergauge is connected ? What is the tell tale ?

It just seems once it has don its job when the car is cold it shouldn't be interfering !

PTFE ! They come with a sealing ring (washer)