Classic LSE cutting out at idle...

VogueLSE4.2 said:

But more head scratching required...

Replaced the stepper motor today with a new one and it made absolutely no difference...car starts and revs but cuts out once I let off the throttle.

Next step is the throttle potentiometer. I've located this but haven't taken it off yet. It doesn't appear to have any adjustment, will I find a screw to turn when I take it off? How do I go about adjusting it?

If it's the potentiometer, why do they become faulty?

Thanks for all the help so far folks.

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1: See my earlier post, early throttle pots have slotted holes, late ones don't but you can enlarge the holes with a needle file to create some adjustment.
2: You will not find a screw to adjust if you take it off.
3: Adjustment is easy, plug in a multimeter, check throttle pot for base voltage and scaling. If it needs adjusting, loosen fixing screws and rotate it to get the right base voltage. (Do a search in the V8 section as I suggested)
4: Potentiometers become faulty because they wear out.

I've taken the potentiometer off this morning and see that there is a flat spade/blade coming out of the sensor, which when the sensor is in place fits inside a female slot inside the inlet plenum. None of it appears to be adjustable?

I've managed to get the car to idle by tightening the adjuster on the butterfly, but this is a bodge and the car sounds rough.

Shall I just buy a new potentiometer and hope for the best?

is the hose and airways clear from plenum to stepper motor

Diagnostics could be good to see if the Stepper motor 'Steps' are within the desirable range....

Useful info (based on the Rover V8 in a Morgan) http://www.gomog.com/allmorgan/GEMS/GEMSbyPoole.pdf

Idle setup is on page 82 or 83 (around there)

VogueLSE4.2 said:

I've taken the potentiometer off this morning and see that there is a flat spade/blade coming out of the sensor, which when the sensor is in place fits inside a female slot inside the inlet plenum. None of it appears to be adjustable?

I've managed to get the car to idle by tightening the adjuster on the butterfly, but this is a bodge and the car sounds rough.

Shall I just buy a new potentiometer and hope for the best?

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A new potentiometer is expensive for what it is but up to you.
I have already told you how you can get some adjustment, use a round or half round needle file to elongate the mounting holes on the potentiometer body, this should give a small amount of adjustment. Perhaps you have misunderstood, the adjustment is made by physically moving (rotating) the potentiometer but only a small movement is needed. But before you do anything you need to check the base voltage then check resistance and scaling, the values should change smoothly with no spikes. With the potentiometer removed, rotate it and make sure the movement is smooth, if there is any sticking or notchiness then you'll probably need a new one. Have you done a search in the V8 section?

1: Multimeter plugged in to throttle pot, engine off, throttle closed base reading 0.27v.
2: Grab throttle linkage and slowly pull to wide open throttle, watch voltage increase, you are looking for any spikes in voltage. At WOT the reading shoule be in the range of about 4.8v - 5.0v
3: To attach multimeter probes, push them in to the back of the connector plug, on mine, the wires I am measuring across are RED and GREEN, the green one is the ground wire, the red is the signal or output wire, the yellow wire is the power supply. Note, IIRC the wires changed colour on later models.

Now, moving on and just for laughs,the easier way to check out this stuff and other things is to get an ECUMate. Just plug it in to the diagnostic plug and away you go, you can see what the ecu sees.

Thanks for the detailed info - I hadn't fully understood what you meant by adjustment on the throttle pot but I do now. I have tested it and it's working fine, so it's neither the stepper motor or the throttle pot.

If I tighten the throttle cable, I can get the car to idle badly, but it will keep running. When I try to drive it like this, it sounds and feels hellish, like not all cylinders are firing, sounds slightly Subaruesque.

The EFI warning light of an exclamation mark without a circle appears after a short time also.

VogueLSE4.2 said:

Thanks for the detailed info - I hadn't fully understood what you meant by adjustment on the throttle pot but I do now. I have tested it and it's working fine, so it's neither the stepper motor or the throttle pot.

If I tighten the throttle cable, I can get the car to idle badly, but it will keep running. When I try to drive it like this, it sounds and feels hellish, like not all cylinders are firing, sounds slightly Subaruesque.

The EFI warning light of an exclamation mark without a circle appears after a short time also.

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O.K. so you are happy stepper is working and throttle pot is in the right range. Throttle pot doesn't as far as I know cause EFI warning light to come on so the issue is somewhere else. You say you can get an idle by tightening the throttle cable. On that basis I would be looking at the air flow meter or you have an inlet air leak. Worst case may be failing (or failed ) O2 sensor(s) or possibly ECU.

I would suggest the best way forward is firstly to check out the air flow meter - go in the V8 section and do a search, all the necessary info is in there. If the AFM checks out I would strongly recommend taking off the plenum and ram housing then giving it all a good clean, check and set the throttle disc clearance, reassemble, set base idle and then see what happens. While you are tinkering you may as well check the fuel and coolant temperature thermistors.
Also remember that if the EFI warning light is on the ECU is in limp mode and is just running a basic map that essentially says dump lots of fuel in, your MPG will be in single figures and the plugs will soon soot up, if you drive it like you stole it it runs a bit better (guess how I know!) but you need to sort it. HTH

Ok...I found a pipe had come off that attaches to the plenum near the throttle butterfly - once this was attached the car started and idled perfectly.

Problem solved...or so I thought.

As soon as I drove the car, it felt sluggish and the EFI warning light came on more or less immediately. It will drive ok, but sounds like it's not running on all cyclinders and is sluggish with a big drop in power.

Rovacom wouldn't speak to my car, so I haven't got any info on what the fault code is. The vacuum advance module however has been found to be faulty, and I intend to change this next, but would this cause the EFI warning light to come on?

a faulty sensor on efi side presumably

VogueLSE4.2 said:

Ok...I found a pipe had come off that attaches to the plenum near the throttle butterfly - once this was attached the car started and idled perfectly.

Problem solved...or so I thought.

As soon as I drove the car, it felt sluggish and the EFI warning light came on more or less immediately. It will drive ok, but sounds like it's not running on all cyclinders and is sluggish with a big drop in power.

Rovacom wouldn't speak to my car, so I haven't got any info on what the fault code is. The vacuum advance module however has been found to be faulty, and I intend to change this next, but would this cause the EFI warning light to come on?

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O.K. so some progress then. First up, replace vac advance and see what happens. Do check all wires and connections in the ignition system and check the ignition timing.
If vac advance is sorted and the problem is still there you have the headache of deciding if the misfire you appear to describe is an ignition problem or an EFI problem. Normally I would say an ignition misfire shouldn't cause the EFI warning light to come on but that is only true for a non-cat motor. If the O2 sensors see a rich mixture the ecu will try to compensate, same if it is too lean but if the ecu can't achieve the right mixture it will fault.

You say Rovacom can't talk to the ecu. I have no experience of Rovacom, could it be your cable? if not, you may have to consider a replacement ecu. It is entirely possible the ecu is dying, I had one that intermittently stopped reading the air flow meter, drove me nuts trying to sort it but put in a good second hand ecu and not looked back. A spare ecu is always handy in any event so something to think about.

I've bought an ECUMate, but I've got the same problem as I had when I connected it to Rovacom - it can't connect to the ECU so I can't pull the fault code.

I've got a Tornado ECU chip fitted, could this be causing the communication problem or be faulty, sending the ECU into fault mode?

Any tips on removing the ECU as it appears to be pretty securely mounted?

I'm struggling to find a replacement LSE ECU to swap out to see if a different one works, I assume the ECU is different to the one fitted to the 3.9, as these seem to be much easier to get hold of?

Doubt it is your chip. Post up your location. There may be help on your doorstep.

VogueLSE4.2 said:

I've bought an ECUMate, but I've got the same problem as I had when I connected it to Rovacom - it can't connect to the ECU so I can't pull the fault code.

I've got a Tornado ECU chip fitted, could this be causing the communication problem or be faulty, sending the ECU into fault mode?

Any tips on removing the ECU as it appears to be pretty securely mounted?

I'm struggling to find a replacement LSE ECU to swap out to see if a different one works, I assume the ECU is different to the one fitted to the 3.9, as these seem to be much easier to get hold of?

Click to expand...

Ecu is easy to remove, just needs a little patience. I wouldn't have thought a Tornado chip would prevent communication but I'm no expert on that.

As for an ECU swap, I am not aware of any difference between the 3.9 and 4.2 ECU's both are Lucas 14 CUX and as you have cats, the fuel mapping is controlled by the O2 sensors except at WOT. The injector pulse is triggered off the ignition coil and modified by the inputs from the various sensors so I can't see any issues in there. HTH.

Right...I've been a plonker.

I was connecting the ecumate to the air suspension connector, hence why I was getting no response. I've found the correct connector now but...the car won't start at all so I've got a new problem.

It'll turn over fine but won't fire. I've had this problem in the past and it turned out to be a loose wire on the ignition amplifier. I've taken the clip off the amplifier and both wires have snapped off as they were brittle, so I'm going to re-do the wiring into the connector and hope that gets it going so I can pull the fault code from the ECU using the ecumate.

As the two wires have snapped off the connector, can anyone tell me which one goes where on the connector? (One wire is white, the other is white with a black stripe)

Also, I'll need to replace the two small metal clips that crimp the cables and slide inside the purple insert in the clip - what are these called?

Finally, I found a loose, black rocker switch under the driver seat, any idea what purpose this serves?

Thanks for the input on this so far...I know it's growing arms and legs.

Rocker switch could be the Air Suspension isolation switch.

cooltide said:

Doubt it is your chip. Post up your location. There may be help on your doorstep.

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Thanks, the car's in East Calder, between Edinburgh and Livingston.

Hmm bit far for me. When I replaced the amp wires, I just used 2 prong fork connectors and cut a prong off

VogueLSE4.2 said:

Right...I've been a plonker.

I was connecting the ecumate to the air suspension connector, hence why I was getting no response. I've found the correct connector now but...the car won't start at all so I've got a new problem.

It'll turn over fine but won't fire. I've had this problem in the past and it turned out to be a loose wire on the ignition amplifier. I've taken the clip off the amplifier and both wires have snapped off as they were brittle, so I'm going to re-do the wiring into the connector and hope that gets it going so I can pull the fault code from the ECU using the ecumate.

As the two wires have snapped off the connector, can anyone tell me which one goes where on the connector? (One wire is white, the other is white with a black stripe)

Also, I'll need to replace the two small metal clips that crimp the cables and slide inside the purple insert in the clip - what are these called?

Finally, I found a loose, black rocker switch under the driver seat, any idea what purpose this serves?

Thanks for the input on this so far...I know it's growing arms and legs.

Click to expand...

Yep you are a plonker but don't feel too bad I'm pretty sure we've all done it!
Anyway, first up, you dont have to have the engine running to pull fault codes, plug in Ecumate, turn on ignition and if there are stored fault codes you'll be able to get them.
Ignition amp wires - not sure which amp you have, two pin or three pin. Anyway on a two pin one, the white wire is ignition live and is spliced in to the coil + feed. The white with black stripe is connected between the ignition amp and coil -ve. Unfortunately I don't have a wiring diagram for a '93 but the ignition circuit is the same as far as I know. So, the white wire goes on the front pin and the white with black stripe on the back pin. While you're in there, check the condition of the connectors at the coil end, these are also likely to be brittle and corroded, if so, replace them.

The black rocker switch is indeed to disable the air suspension.