Tickover problem - prob not stepper motor

[MrMCI]

Hi All,

Hope everyone has been out enjoying the weather today.

I am just after a bit of help, I still have tickover problems despite cleaning and re-installing the stepper motor. I remembered to use the PTFE and sealing washer and to clean inside the hole. I was amazed by how clean it was, I have seen some pics of holibally coked examples.

Now the issue is what to look at next. To summarise my problem:

Ticks over fine when cold and when trundling in slow traffic. When I come off a duel carridgeway / slow down from 70MPH ish about 50% of the time the revs die. Sometimes the ECU catches it at about 250rpm and restores but sometimes it just dies.

I think it must be something to do with the new speedo sensor but dont know how to test. Any ideas?

Thanks and enjoy the rest of the weekend.

Mark

[blitzracing]

The "new speedo sensor" ? The symptoms you descibe could be could be the speed sensing input to the ECU from the speedo calibration unit found under the dash. This appears as a fixed pulse train above 3mph on pin 39 on the ECU (black and white wire). You can measure it with an oscilloscope- but I dont know what a DVM would have to say about such a signal however. I would think you would get some sort of reading on an AC input, that should fall to 0 when the car stops. The Steve heath ECUmate can tell you whats going on.

[MrMCI]

Ok, I suspected it may be due to the speeds sensor. I have swapped from the old magnetic type to a Steve Heath optical sensor. I know that my car is an early 500 and Steve had to make me up a special connector to attach to my speedo. I wonder if I have lost the feed to the ecu.

What would happen if I just disconnected the feed to the ECU? why does it need it?

[blitzracing]

Are- as far as I understand it the speedo calibration unit was only used on the Ford gearbox set up, not the older LT77- so if that means you have a pulsed signal from the diff you will still need a speed input to the ECU. This bit on the ACT website is quite good (3/4 of the way down) about it. The original Lucas set up used a very simple chopper disk or read switch to produce the signal, so it was literally on-off-on-off as the car moved forward. You need this signal to get the stepper to control the idle when it the ECU sees the car is stopped.

http://www.actproducts.co.uk/category/lucas-inject...

[carsy]

Shouldnt a properly set up base idle stop the car from stalling in these conditions.

[MrMCI]

That is what I was hoping to hear :-) just need to confirm that is the best approach before I go fiddling. If I turn up the base idle will it lift the idle all the time or should the stepper compensate?

My car is a bit odd, I have the ford gearbox but the GKN diff.

[carsy]

Get the car up to temperature and then if you can get it idling properly disconnect the wiring to the stepper. The stepper is then out of the equation and that is effectively your base idle. Give the car a drive and see what happens.

[MrMCI]

In case anyone was interested, after a bit of diagnosis with Mark Adams and Steve Heath....both of whom are heros. It looks like my problem is due to my wiring and may affect other Griff and Chimera owners who go to a Steve Heath speedo sensor.

The wiring harness to my instruments has 4 pin plugs as opposed to the larger 7? pin multi connectors of later cars. It looks like putting the sensor in has lost the speedo feed to the ECU affecting the control of the stepper motor.

I hope the fix is reasonably easy (a jumper wire from the speedo to the control box) but it does mean taking the dash out again. I will confirm if it works so that any others with similar problems now or in the future can resolve.

[MrMCI]

ok.....problem fixed thanks to discussions with Steve Heath and Mark Adams.

There is definately a warning for those who fit the improved Steve Heath speedo sender to 1994 and earlier cars. If you dont have the 7 pin multiplug on the back of your speedo (mine is a 4 pin) you have to do some of your own wiring.

In summary the speedo sender sends its signal into a little control box that feeds the ECU, this box in turn also feeds the speedo. You need to make sure that Steve's little box of tricks is on the input to the control box NOT the input to the speedo (as i first fitted)otherwise your ECU looses a sensible speedo signal input and you will have weird tickover problems.

If anyone gets in this situation PM me and I can explain further.

Mark

[EGB]

MrMCI said:

I had exactly the same. Fixed it with a 2mm plastic insert between the plenum throttle stop. Butterfly remains very slightly open on tick over to stop stalling in my case. On carburattor RV8s this was done with a screw. I think this could be a nuisance problem with a "lazy" stepper?

Hope everyone has been out enjoying the weather today.

I am just after a bit of help, I still have tickover problems despite cleaning and re-installing the stepper motor. I remembered to use the PTFE and sealing washer and to clean inside the hole. I was amazed by how clean it was, I have seen some pics of holibally coked examples.

Now the issue is what to look at next. To summarise my problem:

Ticks over fine when cold and when trundling in slow traffic. When I come off a duel carridgeway / slow down from 70MPH ish about 50% of the time the revs die. Sometimes the ECU catches it at about 250rpm and restores but sometimes it just dies.

I think it must be something to do with the new speedo sensor but dont know how to test. Any ideas?

Thanks and enjoy the rest of the weekend.

Mark