V8 stalling

[sparkypete]

Hello peeps


I seemed to have a problem with the tick over on my 4.0 V8S. On the way home tonight the car ran great, when i came off the motorway and slowed at junctions and lights the car would not tick over and the revs fell. This was the story until i got home,turned of the engine to open garage and started her up again, all was well, tick over back and OK.

Any help and advise as to what to try would be greatly received.

many Thanks

[GreenV8S]

Perhaps a sticky stepper motor?

[sparkypete]

Stepper was replaced last Nov and the car has not covered many miles since,

[GreenV8S]

sparkypete said:

Stepper was replaced last Nov and the car has not covered many miles since,

Why was it replaced, perhaps this is some long-standing problem that has been misdiagnosed? For example wiring fault/poor connection to the stepper motor, rather than the stepper itself at fault?

[sparkypete]

Thought the same myself, the connection to the stepper checks out OK, removed it to chack it, as aspected very clean, maybe faulty unit?.


What next anybody

Thanks

Pete

[pugwash4x4]

more info pleas- what is it, what's it in, is it bog standard, have you had any problems in the past, how many miles, and whats it's servcing like?

quick thing you could try is to stick a jumper over the mouth of the inlet manifold and see if the car stalls- if it doesn't then you have an air leak in the system somewhere behind the MAF sensor.

[sparkypete]

Pugwash, its a 4.0L TVR V8s stnadard I think apart from polished and ported heads which was done 20000 miles ago by previous owner, its currently at 57000 miles and it appears to have been regulary serviced.

All help and advise is welcome.

Pete

[GreenV8S]

Get the engine warmed up and idling nicely, then disconnect the plug to the stepper motor. If the problem still occurs with the stepper disconnected you know it's nothing to do with the stepper motor or associated logic, and must be something more fundamental.

I'm suggesting this as a temporary test to diagnose the problem, not as a cure. But if you decide that you're happy to run it like this there's no reason why you shouldn't run it like this indefinitely. Just be aware that the stepper motor is still free to move and may slowly adjust itself, so the idle speed may gradually move up or down. If you plan to disable the stepper motor permantly then you shoul lock it off or replace it with a fixed restriction.

[sparkypete]

Well went for a run this morning and guess what, the idling was all over the place again, anyway did what V8S recomended and the tick over is now bob on, it does not stall or race, looks like good bye stepper motor.

i assume no harm will come to the engine if it is removed ??

[GreenV8S]

sparkypete said:

i assume no harm will come to the engine if it is removed ??

You don't need a stepper motor. The ECU and engine are both happy without one. The only problem you'll find is that the idle speed varies with engine temperature and you might have to help it with the throttle for the first couple of minutes on very cold mornings. However, I ran mine as a daily drive for a year or more with no stepper motor and I didn't find it any trouble at all. In fact it was much more pleasant to drive because it eliminated that slight doubt that you get sometimes when you come to a halt and the stepper is a bit slow to respond.

In my case I had no choice because my new manifold doesn't have any provision for a stepper motor. Other people have removed the stepper motor from the standard manifold and replaced it with a plug, then adjusted the base idle speed to get the idle right. Others have simply unplugged the stepper and left everything else alone. The problem with this last approach is that the stepper motor can gradually move and mess up your idle speed. If you plan to leave it like this I'd suggest finding some way to lock the stepper motor, or replace it with a plug.

[seight]

.....and if your stepper motor is open fully when you disconnect it then next time you are on the motorway and lift off expecting to slow down you may not! Throttle may be closed but air will still be fed by stepper motor.

[sparkypete]

I wait until the engine is warm and ticking over at the right RPM, and then disconnect it whilst the engine is still running, that way the stepper is at the right position, this will do until I remove it altogether and set the base idle correctly.

Edited by sparkypete on Tuesday 3rd July 18:56

[GreenV8S]

seight said:

.....and if your stepper motor is open fully when you disconnect it then next time you are on the motorway and lift off expecting to slow down you may not! Throttle may be closed but air will still be fed by stepper motor.

This is why you get the engine warmed up and idling correctly and *then* disconnect it.

If you disconnect it with the stepper fully open then I doubt you'd get as far as the motorway because it'll rev its nuts off as soon as you start it!

[seight]

I read in an old email from someone in the know that you could get an error 48 if you run without the stepper connected. Apparently the ecu tries to reset the stepper at startup by counting the 'click' to go as far as poss in each direction. Have you ever had any probs with a std ecu showing an error?