Over-fuelling on an MG 2.0i

[SimonR]

Hi All,

I'm sorting out a few problems with my Maestro and one of them is that before I took it off the road, it was over-fuelling rather severely. The engine ran fine but smelt very petrol-ly and a tankful didn't last long. I hate to think what kind of mpg I was getting.

The car is a 1990 2.0i MG spec, with K&N filter. The only fault that I know may affect the fuelling is a slightly blowing exhaust manifold (yet another thing I'm addressing shortly!) but the blow disappeared when the engine warmed up.

Is there a fuel mixture adjustment that needs to be made? - or am I possibly suffering from a faulty sensor / airflow meter?

Any advice gratefully received.

[Russ]

Hi Simon,sounds like the fuel pressure reg. Give me a call when you get chance

Russ

[E_T_V]

First thing to check would be the ECU temp sensor. Check its resistance when cold and hot and see if anything seems amiss. If wrong the engine will effectively be running on "choke" all the time.

[AndyB]

Long time back I did quite a lot of checking out on the fueling side, to sort out bad running. Had a scrap MG Montego and another spare Maestro MG engine so was brave enough to try out a few things with bits in my garage.
As per Russ's comment, I was curious about the pressure regulator, I also wanted to check the injector flow rates and pattern.
I was getting a high CO reading.
Now usual safety messages - beware pressurised fuel, no fags, cold engine, have plenty of rags ready for mop ups. If unsure or not confident, don't do the below :
First, remove the injector rail with the injectors still on the rail, fuel in and out hoses still connected, injector connectors removed and fuel sensor switch disconnected. With it all sat on the cylinder head did the following :
Made a tee connection in the fuel line at the fuel filter out, ran the tee output to a 0-50 psi pressure gauge. At the pair of relays you can make a link to run the pump (through the resistor). Compare the pressure with the manual (about 38 psi with no vacuum ? - haven't got the manual to hand). I compared three rails doing this and found them all within 1 psi.
The regulator basically regulates the whole system at that pressure from pump out right past the injectors to the regulator, so you can measure it anywhere, the fuel filter the most conveniant break-point. Excess pressure is relieved out from the regulator and returns to tank.
Flow / pattern. Flow I think is 160cc/min. Get a tall thin jar, weigh exactly 160 grams of water into it, mark the height. Dry it !
Get a spare injector connector, cut in and extend the leads to two croc clips. Connect to first injector. Put one lead on battery, hold jar under injector and connect 2nd clip to battery. Injector will flow. Time 60 secs and it should come up to the mark. Also view the pattern.
Repeat with other 3 injectors, all should be same and of course a uniform spray.
One of mine was high flow, one had bad pattern.
I don't think the polarity matters on the injector.
From the three rails I had I made up two sets of checked out injectors and pressure regs.
CO check bang on after that.
Ran this method past Roger Parker years ago and he was fine with this as a minimal kit check method, yet effective.
E_T_V I'm curious, do you mean the fuel temp sensor on the injector rail ? Trying to remember, is this a switched output (ie closed - open). I think this sensor is aimed at detecting high temp after switch-off, as the latent heat in the exhaust heats up the fuel rail and makes restarting a hot engine more difficult. What happens if Simon just disconnects one spade from the sensor ?
PS Simon, what do the plugs look like ? - with your description they should be black !
By the way, nearly all the bad running issues I had were in the stepper at the air throttle (the gunge area !) This area causes most slow running problems, but not what Simon has.

[E_T_V]

No I meant the ECU temp sensor, the one that is in the coolant elbow to tell the engine how hot it is. If it fails the ECU assumes a cool engine so that it'll still start ok, but of course then it overfuels as effectiuvely the car is running on choke all the time

[oseerees]

No I meant the ECU temp sensor, the one that is in the coolant elbow to tell the engine how hot it is. If it fails the ECU assumes a cool engine so that it'll still start ok, but of course then it overfuels as effectiuvely the car is running on choke all the time

.... in the coolant 'elbow'?
You mean 'thermostat housing'.

When this sensor failed on mine - I mean really failed - everything went 'mad'!
Temp gauge will rise and fall dramatically, engine will cut out, sometimes restart fine, able to drive very short distance, then judder, cut out again, gauge go mad again... well that's what happened when mine failed.

Just shoved a replacement sender in and immediately car was normal again.

No harm in changing it, but I would check injectors, stepper, bunged up throttle housing, etc.

[Russ]

the other thing that I know people have had trouble with in the past ,is the ECU being damaged as a result of a short when conecting the battery and touching the spanner on the airflow meter. This often results in damage to the PCB in the ECU which ive seen a couple of times and both were resoldered and were ok

[SimonR]

Chaps, many thanks for all those really useful replies.

Russ - I'll give you a call when I've got a moment - I've been somewhat hampered by the weather, Marshall Rover's parts department and an ailing Daimler that ate up my weekend ;-)

E_T_V - year I know the sensor you mean and had wondered the same thing. I've got a spare that I can substitute but do you know how the resistance redings would change with temperature?

AndyB - Interesting stuff I may well do the same thing and see what I get in terms of spray patterns and volumes. I'll alsko take out the plugs and see what they look like - you're right, they should hopefully tell their own story.

I'm busy with the front suspension at the moment but will get round to this shortly!

Cheers all.

[E_T_V]

I'm not sure on the resistance values. I think they may be in the factory manual though. I would guess it would start at a high resistance (2k ohms maybe and then drop to a few hundred ohms with a hot engine), but they are only guesses.