Poor Running

[daveyboy]

I have a 1991 Maestro 1.6lx automatic, had this car about 5 years and its never missed a beat, that is until now.
The car starts no problem but has difficulty revving and the idle is very poor sometimes cutting out, i thought it may be ignition related and as all the components were original as the car only has 40k on the clock i replaced rotar arm, distributor cap, plugs and leads. this seemed to cure it for some 20 odd miles, i took it out this evening and from cold did about 3 miles and it ran fine, came back to it an hour later and the old symptoms are back with avengance!! the car starts, idles terribly, you can rev it but its as though it is missfiring or has too much choke?? been an auto its barely driveable, i have never touched the carburettor on the car as it has always up until this time ran like clockwork. the breather pipes are all good, dashpot on carb is ok i am wondering if it could be the stepper motor or o rings not entirely sure as never had this before i would appreciate any input, i know it sounds sad but i have always been so impressed with the cars reliability i would really like to sort it as its been a god send to me when my modern cars have been off the road. And also as parts seemingly are more difficult to get hold of if it is sounding like the carburettor any ideas where i could source the parts from?
thanks Dave

[Tram2468]

Hi Daveyboy,
Many moons ago I had a 1.6 petrol monetgo which suddenly started running very erratically. My local car mechanic said looks like a very simple problem, lifted the bonet then made it run worse and then properly - simple solution check the small bore vacum pipe that runs from the Carb to the ECU, mine had a bend rubber piece at the carb end that was split.
Over to you Sherlock......

[G Force]

Hi Daveboy. I would say that almost certainly sounds like the vacuum switch diaphragm has split.

The vacuum switch is connected to the side of the carb by two short rubber pipes, it then has a further vacuum pipe connected to it.

Prise the valve off of the two pipes and remove it from the carb, pull off the vacuum pipe and suck on the valve where the vacuum pipe was connected.

If you can suck air through the valve or you get a mouthfull of petrol the valve needs renewing. Part number LZX 2292.

If its not the valve let us know and we will advise further.

Gary:)

[daveyboy]

Hi Gary,

i have been looking tonight and i cannot see such a thing on my carburettor, i have the stepper motor on the left handside and what looks like a valve on the other with 2 wires onto it.
i have rechecked all the breeathers to the ecu and the trap that is fitted in between the carb and ecu and all pipes are good with no leaks, the breathers to the carb which run to the back of the engine are all clear too and in good order. i can hear the stepper motor working, and as yesterday the car starts easily runs the tickover is not excellent but then it plays up, i did find if i held the revs at a constant speed it starts to splutter and my only way of describing it is to say its as though its a car with a manual choke thats on and its over fueling? if i rev it harder it clears a bit buts its no wear near as smooth as it used to be, disconneting the stepper motor wiring makes no difference as either does disconnecting the wiring to the valve on the other side of the carburettor. it does smell rather rich too in my opinion, however i have not touched the carburettor settings at all so i am at a loss really :confused:

[G Force]

Hi Daveboy, It is possible that your car being a 1991 MY may not have the vacuum switch fitted as it was deleted on the very last Maestros that were made.

If that is the case, then from your description I would agree that it does sound as though the engine is running rich. There are a few main causes of this.

Have you noticed anything odd happening with the temperature gauge? is it registering cold all the time or reading 1/4. If the temperature gauge works OK then the problem is more than likely with either the carb stepper motor O rings or the carb is flooding due to a worn float chamber needle and seat assembly.

The stepper motor O rings can be done by removing the stepper motor whilst the carb is still on the car, but to replace the needle and seat you will need to remove the carb to strip it. You should still be able to get the needle and seat kit, the part number has been superceded and I don't have it, but it was GSU 104 if that helps.

If the carb is flooding you can often see drips of petrol or fumes coming from the float chamber vent pipe that runs from the carb down the back of the engine towards the floor just in front of the heater box drain. Another sure sign that the carb is flooding is if you remove the overrun fuel cut off valve by taking out the 3 screws that fix it to the carb, if the valve body is wet with petrol then you should definitely replace the needle and seat assembly and reset the float hight.

If you remove the overrun fuel cut off valve (the solenoid with two wires connected to it), even though I don't suspect this is a problem at this time I would recomend cleaning it out and making sure it is fully closed, then leave it disconnected and tape up the wires, as this valve its self does stick and cause many running probs.

Cheers

Gary:)

[daveyboy]

Well i replaced the o rings on the stepper motor and it made no difeerence :(
so i removed the carburettor and fitted a new float chamber needle and seat kit. the car now starts as it always did, runs the same but if it cuts out it wont restart if left it starts when its cooled down :giveup:
i have cleaned the orfco valve and it is closed, i am at a loss now not sure what to do with it. Getting some seriuos grief as we could really do with it running at present, i am sure its fuel related as the plugs i fitted earlier in the week are black with soot so some how its running far too rich but i dont really know why.
you go into a motor factors now and mention maestro and people laugh at you, i asked if they knew of anywhere where i could get my carburettor reconditioned they said no, anyone got any ideas i wouldnt mind spending a few quid on it to get it up and running as its mint but i cant go on like this for much longer
oh and the carb isnt flooding or letting petrol pass through the overflow pipe

[E_T_V]

Ok if it is running too rich then one thing to check would be the autochoke. It lives in the top of the glovebox. Unplug and replug the electrical connector for it many times (the connections give trouble). Is the engine temperature gauge working properly? I.e. starting from cold then going up to the middle when the engine is warm?

Also check the wiring to the temperature sensor as this is used to control the autochoke mechanism. I'm guessing that the autochoke is being left on for some reason and this is causing the overfuelling and eventual cutting out.

[daveyboy]

hi yeh the temperature gauge is working well starts at cold and rises to midway or just under as it always has done, i will go and check the connections now and report back cheers

[E_T_V]

That is good news, as when the autochoke ECU goes faulty the gauge also goes to pot too.

[daveyboy]

well i have checked all the connections and unplugged lots and replugged and cleaned up the temp sensor and it starts as usual but wont tickover well, its as though the choke is fully on, it will rev past 3,000 ok i assume as its burning the fuel?? but if let tickover stops and wont restart :(

[E_T_V]

What happens if you disconnect the temp sensor. If the idle speed increases but the engine then runs better then it would point at a faulty temp sensor.

[daveyboy]

if i disconnsect the temp sensor nothing happens it still runs as before.
i have today rechecked everything else and adjusted the mixture to weaken it, the car starts all of the time now even when hot, but will still not tickover and still sounds really chokey as though its running on choke, also if you try and rev it at times its got what i can only describe as a flat spot which clears and then the car will rev freely,it dosent like been held at a constant rev either it isnt smooth after a few seconds and you either have to rev harder to clear it, not sure what to do i can source a brand new carburettor for £165 but if its not this i am at a loss as i dont want to spend that much and still have it running badly :banghead:

[G Force]

Hi Daveboy. very sorry to hear that you have not been able to get to the bottom of this problem yet.

I think before you replace the carb you need to establish whether the auto choke is working as it should do otherwise you could change the carb and still have the same problem.

When the engine is cold, have a look at the stepper motor then get an assistant to turn on the ignition for the first time. You should notice the pin of the stepper motor extend out fully.

As the engine warms up the pin should retract gradually until eventualy a clearance should exist between the pin and the linkage. If this is working correctly then I would expect the fault to be with the carb its self or a blockage in the air filter or inlet trunking.

If the stepper motor does not behave in this way then either the stepper motor is not responding to what the ECU is tellling it to do, or the ECU is faulty and not driving the stepper motor correctly. Or the ECU is not recieving the correct information from the sensors or it is responding wrongly to the sensor info.

If you get an incorrect response from the stepper motor, remove the coolant sensor plug and bridge the two wires of the plug with ign on. if the system is working as it should this should fully retract the stepper motor, turning off the choke. If this happens then it is likely that the coolant sensor is faulty.

If the stepper does not respond at all then check the continuity between the coolant sensor wires and the ECU in the glove box. If ok check the continuity between the 5 wires to the stepper motor and ECU. Rectify any shorts or open circuits as necessary.

If there are no problems with the wiring between ECU and stepper motor or coolant sensor, check all the earth paths (black wires) from the ECU to earth.

If all the earth paths are OK check for 12v ign on at the ECU plug on the white wires. If you don't find a problem then try another ECU.

Best of luck with it :)

P.s. does your car have a catalytic converter fitted?

[daveyboy]

hi Gary

no the car has not got a catalytic convertor on it.
i think i may be getting somewhere, with the engine cold and an assistant turning on the ignition the stepper motor extends out fully, with somewhat of an un smooth manner i must add, i couldnt run the car for long as the fumes were are bad and someone else was working in the garage and with the rain i couldnt go outside to run her up fully. so with the ignition on i bridged the two wires on the coolant sensor wiring the stepper motor makes a funny noise but will not retract fully it is as though the motor is trying but not working so i am assuming that the choke is staying on all the time? the stepper motor isnt as smooth as it used to be thinking back it used to make a prominant noise. i will have to run the car up tomorrow and get to temp and see if the motor behaves in another way. i phoned my local factors to price a stepper motor and they tell me its no longer availible, any ideas if i do need one as to where i can get one?

[G Force]

hi Gary

so with the ignition on i bridged the two wires on the coolant sensor wiring the stepper motor makes a funny noise but will not retract fully it is as though the motor is trying but not working so i am assuming that the choke is staying on all the time?

Did you get chance to run the engine with the coolant sensor wires bridged?
Hopefully you didn't and you find the car runs OK with the wires bridged, (wishful thinking here) :)you might experience a bit of a misfire still if the plugs are sooted up. If this is the case then you need to fit a new coolant sensor.

When you observe the stepper motor retracting it may appear not to retract fully, but if you open the throttle and put your finger on the pin it will move in further, this is normal. The only force pushing the pin in is the throttle return springs, so when the throttle reaches its stop the pin stays in contact with the fast idle lever giving the impression that the pin has not fully retracted, this could be what you are seeing.

If the engine still runs rich with the coolant sensor wires bridged due to the choke staying on, it is not necessarily the stepper motor that is at fault. It could be a wiring problem between ECU and stepper motor, a faulty ECU or the stepper motor. You would be best to check continuity between the 5 wires from stepper motor back to the ECU first.

As for a replacement stepper motor if you need one in the end I am sure someone on here will have a spare one or a spare carb. You could have trouble finding one from a late maestro like yours as they are very rare. The best match for your car will be a late montego with the ERIC engine management system.

Good luck

Gary:)

[daveyboy]

it was geting late when i got in this evening but i got a mate to help me check the continuity across the 5 stepper motor wires and fuel ecu all is well there so the wiring to that is ok.
the noise the stepper motor was making was still puzzling me so i took it off and took it apart cleaned it out and put it back together in the off (pin fully retracted position) refitted it to the car and turned on the ignition the pin came out with no noise and i bridged the coolant temp sensor and the pin retracts so this is apparrent to be working as it should.
the car however refused to fire up for some reason :censored:
so i shall try tomorrow or possbily thursday to keep the car running long enough to see how it all behaves when it warms up
i am really grateful for the help and advice in this matter i would be totally stuck without it.
i will keep you posted as i am pretty sure i still havent solved exactly what causing this to happen.

[G Force]

refitted it to the car and turned on the ignition the pin came out with no noise and i bridged the coolant temp sensor and the pin retracts so this is apparrent to be working as it should.
the car however refused to fire up for some reason :censored:

i will keep you posted as i am pretty sure i still havent solved exactly what causing this to happen.

Hi Daveyboy. OK the car not starting? hopefully this might be nothing too sinister (more wishfull thinking:) ) Were you trying to start from cold with the coolant sensor bridged? or it may be just a case of the carb being empty & not quite time enough cranking for it to refill??

If the car will run ok once the stepper motor is fully retracted and warmed up, but the choke comes on and the mixture goes rich if you reconnect the coolant sensor, Fit a new sensor.

Let us know what is happening once you get her running again,

Cheers

Gary:)