Efi Running Rich

[Grim]

Hi,

 

Having averaged 17mpg on a tank of fuel on my newly fitted injection system, i think i have a slight problem.

 

The CO level can be adjusted so it is correct at idle when warm, so it shouldn't be the temperature sensor (it runs like a bag of spanners when cold and the ecu adds more fuel in, but runs okish when warm).

The throttle position sensor and air flow meter both read correctly, and there is an electrical connection to the ecu for both.

It is not a fuel leak, as there is clear evidence of increased soot in the exhaust and on the plugs.

It shouldn't be a faulty injector as all of the plugs are equally sooty (i would expect one to be worse than others).

 

So as far as i know, that leaves the fuel pressure regulator, which could be setting the pressure too high, or such like.

 

Can anyone tell me if that is possible, or if i have missed any points.

I am assuming the ecu hasn't gone into a limp home mode as it can get a reading from the sensors, but i don't actually know for sure; how is it possible to check?

 

Andy

[Guest chris brown]

Check the vacuum pipe from the fuel pressure regulator to plenum hasn’t collapsed as it sounds like you are over pressurising the injectors.

[Grim]

it looks ok, but i haven't checked if it is blocked yet.

[Grim]

ok, it's not blocked, i've checked the fuel pressure and it seems to respond normally to sharp throttle openings.

 

Does anyone know what the fuel pressure should be?

 

I really don't know what else could be wrong? could the ecu be dodgy?

[Guest elwe]

If the engine runs OK apart from being rich I think its unlikly it is the ECU.

 

Could one of the sensors like the coolant temperature or air flow meter be broken or giving duff readings? That would sound far more likly to me.

 

Most of the sensors work on resistance, are all your wires and connectors OK? I believe the coolant temp sensor has lower resistance the colder it gets. Therefore if you have some extra resistance in a dodgy connection the ECU won't come off warm up enrichment.

 

This is how those cheap 'gain 10bhp' mods on ebay work. They put a low value resistor in one or more sensor circuits to trick the ECU into running rich. Most production cars are setup for economy, best performance is achieved when running slightly richer.

[steve in stockport]

andy

sounds like you need to start swapping parts over to try to eliminate the fault.

have got a few bits knocking about, so if you want, pm me and you can borrow what i have in the spares box and if one of the bits cures the problem i'm sure we can come to an agreement.

are you coming this way over christmas, as if you are you could colect the parts on your travels

 

steve

[Grim]

Could one of the sensors like the coolant temperature or air flow meter be broken or giving duff readings? That would sound far more likly to me.

 

Most of the sensors work on resistance, are all your wires and connectors OK? I believe the coolant temp sensor has lower resistance the colder it gets. Therefore if you have some extra resistance in a dodgy connection the ECU won't come off warm up enrichment.

i've checked each of the sensors as described in the injection troubleshooter on the northwest site (with the observation that one of the pin numbers is wrong), and they correspond to the correct values, so i know it is not a sensor. The method described there includes the wiring to the sensors, so it's not that either.

It shouldn't be the coolant sensor, as that would give high co at all times, but i'm somehow able to have a good level at idle when warm (awful when cold). I'll recheck it though.

 

sounds like you need to start swapping parts over to try to eliminate the fault.

have got a few bits knocking about, so if you want, pm me and you can borrow what i have in the spares box and if one of the bits cures the problem i'm sure we can come to an agreement.

are you coming this way over christmas, as if you are you could colect the parts on your travels

 

steve

 

Cheers, i may be coming your direction, i'll let you know when i do.

 

Andy

[Grim]

ok, i think i've fixed it now, the performance is back up to where it should be, just have to get the co levels set again.

It was a wiring problem.

[Guest chris brown]

Let us in on the secret then. What was wrong

[Guest salty_monk]

Must be something really silly or simple otherwise he would have told us already

[Grim]

it was a broken wire in the loom. Alas now i have a randomly surging idle speed, but that'll be the idle control valve, or perhaps an air leak (the brakes intermittantly go unservoed, so i can guess where it might be)