Signs of Tired Injectors

Mon Feb 27, 2012 7:20 pm

I'm chasing what I believe to be poor fuel economy for an M20B20.

No drivability issues, asides from the fact that I don't seem to be able to make the fuel last. £20 gets me ~1/4 of a tank, which is lasting about 65 miles before the light is back on.

I've ohm'd out the coolant temperature sensor, got identical resistances from both the ECU plug and the sensor directly, effectively ruling out C191 corrosion (approx. 225 ohms@ just under 1/2 on the temperature gauge).

Pulled a few spark plugs, healthy tan colour. I'm leaning towards a dodgy spray pattern from the injectors, although I'm uncertain as to the characteristics of worn injectors. Would I expect to see the plugs a bit more blackened/ some sign of running rich?

The other cause I can think of is the coolant temperature sensor is giving 'cold' readings for too long before warming up, and I'm driving longer distances with a richer mixture before the sensor lowers resistance. Does that happen?

Any insight/ thoughts welcomed!

Joe

Mon Feb 27, 2012 9:06 pm

320's were never good on fuel, even when they were new

Mon Feb 27, 2012 9:42 pm

when my injectors were done the car was hard to start
i had the injectors serviced and now it starts just fine
http://www.injectortune.co.uk/
cannot say that it changed the cars economy but i only get that sort of mpg on very short trips
i dont think the six pots make the best economy i think most go the lpg route

Mon Feb 27, 2012 10:36 pm

That's kinda where my thoughts were heading: 7miles to work is barely time to warm up the block. I'm relatively sure my old 2.7 got better mileage than this 2.0 does.

Thanks for the input Parkin10, I have no real problems with the car asides the fact that the MPG is crap. Maybe it's time to start looking to put an LPG conversion in the boot. Although even a conversion needs time for the car to warm up before it switches over to the propane, right?

Tue Feb 28, 2012 8:56 am

yes warmed for the lpg
im on the school run every day 3/4 mile there and back never gets warm really costs a mint with a 2.5 toying with the idea of a zafira dti (some one kick me quick)

Tue Feb 28, 2012 9:09 am

The older (mixer) type LPG system (perfectly adequate for E30s) will start and run happily from cold on LPG, although it will start from cold more quickly on petrol, and power will be limited in cold weather until things start to warm up after a few hundred yards.
Once warmed up from overnight, it should start and run normally on LPG for the rest of the day, with no petrol usage at all.
I have two M50/52 engined BMWs in daily use running multi point injection LPG, and both of these have been 'tweaked' to change over at a much lower temperature than they should do.
They both change over within seconds of the engine starting at any air temperature over about five degrees, and again, as long as you don't try to use the full performance for a few hundred yards, they perform perfectly.
Certainly preferable to wearing your engine with bore wash from petrol.

Tue Feb 28, 2012 4:00 pm

JoeDiese wrote:I've ohm'd out the coolant temperature sensor, got identical resistances from both the ECU plug and the sensor directly, effectively ruling out C191 corrosion (approx. 225 ohms@ just under 1/2 on the temperature gauge).

sorry to kind of hijack but how do you do this?

Tue Feb 28, 2012 7:55 pm

Brian, is there a decent source for information on LPGing an M20?

Prey: multimeter set on resistance between pin 45 of the ECU plug and any ground on the chassis.
Compare against reading taken directly from the plug...

Wed Feb 29, 2012 9:27 am

try these
http://www.autogas-lpg.co.uk/
http://www.lpgc.co.uk/index.htm

Wed Feb 29, 2012 7:19 pm

there's a simple lpg system suitable for an M20 for sale in the parts section by bristol_jer