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MG MGF Technical - MGF 1.8i Misfire on acceleration

Been scratching my head over this one anyone help! The engine appears to misfire/flat spot when accelerating under load up through the gears 2/3/4/5 (when warm). It is only momentary 3/4 times at approx 1500 to 2500 RPM range then clears. Engine idle is not 100% and you can detect a slight misfire again, but only a 50/100 drop in rpm is detectable coupled with a slight "put" "put" from exhaust!! Checked plugs, new leads, new HT coil, checked dizzy cap, new ECU temp sender (brown one), checked throttle for sticking(at manifold), checked air filter appears ok(little dirty light black soot). No ECU light or other tell tales.Also put some optimax in and did not notice a performance change! Any thoughts or theories greatly appreciated!
Andrew

Hi Andrew,
(here I am, having just read my guestbook on site) :)

This failure sounds quite similar to the one I had.

*Idle high* intermittant over more than half a year.
http://www.mgfcar.de/high_revs/index.htm
Later a juddering engine on accelerating ... aswell intermittant.

Finally I put it down to bad connections of the ECU connector.

Assume it's not been the spade connectors (male/female) but the crimp connections of the sensor wires inside the big black ECU connectore.
Theý are tiny 0.25 square mils only in big spades.
I re-routed and put the sensor wires in _no force 2 spade connectors_ curves and this did the trick (at mine).
My car suddenly stoped starting When I playe at the connector. (See pics regarding loos cable tie on this page.
http://www.mgfcar.de/starter/start.htm

Try going in that direction and move sensor wires, colour marked in this sheet.
http://www.mgfcar.de/mems1.9/mems1.9.htm

(hope this makes sense)

HTH
Dieter
PS mit freundlichen Gruessen an die Gattin :)
Dieter K.

Dieter,

Many thanks for your reply! I will look at the items you suggest. More info: A friend who is a trustworthy mechanic and replaced the head gasket this april succesfully (water in oil brown scum on dip stick and coolant loss)used a scanner to download the ecu (connected under steering wheel RH drive!)and picked up a fault with the Coolant temp sender/wiring. As I have changed the sender and cured an oil leak that contaminated this connection perhaps it is infact wiring from sender to ECU? The fault cleared when engine was running. Danke for alles. Will feedback when succesfull!!!!

Andrew
Andrew

Andrew,

ECU failure batch stores any failure with sensors.
No final evidence though.
If you disconnect or short circuit the sensor connection while the engine is running, it will store a failure aswell.

However, may be you have the skills to measure the input voltage of the coolant sensor.

http://www.mgfcar.de/mems1.9/ect_Dsc02526.jpg
(notice, don't take the *minus* voltage to serious, cause I poorly mixed the instrumnent +/- and measure wire colours on that pic)
More stuff about sensors @ http://www.mgfcar.de/sensor/index.htm

Good luck
Dieter
Dieter K.

This thread was discussed between 02/11/2004 and 05/11/2004

MG MGF Technical index

This thread is from the archive. The Live MG MGF Technical BBS is active now.