Poor running when coolant thermostat opens!?

[Chim_Pete]

I have had a developing problem for a few months whereby the car ran badly when warm (and only below 2000 rpm) after the battery was reconnected, but only for the first journey... I put this down to the possibility that the ECU was 'learning' for this first drive and then sorted itself out.

I left the car standing for a while over Christmas etc. and now the problem has developed to the point I can't use it. It starts fine from cold and revs and drives happily, then it seems as soon as the thermostat opens to allow water to the radiator it starts running lumpy and missing but only below ~2000rpm. By keeping the revs up it can be driven, but let the revs drop down and it will stall and refuse to restart until it has cooled.

I have swapped the ECU coolant temp sensor which made no difference, bled and fully topped up the coolant/radiator, checked the HT lead connections, cleaned the stepper motor valve all to no avail.

Does anyone have any experience of such a problem? I can't fathom how/why the thermostat/coolant circulation should affect anything; unless Its coincidental with that critical temperature value affecting something else...

I'm guessing its fueling related (or possibly ignition?), but don't know why it should be so closely related to engine temperature. It even does it with the bonnet up, so I would guess its not temperature affecting the HT leads for example.

Any thoughts appreciated as its driving me nuts!

I haven't got an fault code reader, but that may be the next logical step...

Thanks,

Pete.

[blitzracing]

Get the Steve Heath ECU mate ,it does both fault codes and sensor data (more importantly). The fault code reader in its own is somewhat limited.

[Chim_Pete]

Yep, its looking like that is the way to go; for this and future issues!

[gavgavgav]

Do you have a spare ignition amp to try out? They can have strange behaviours when hot.

[TVR Thunder]

+1 for Steve Heath's ECU mate. Excellent piece of kit!. Takes the guesswork & expensive 'Change it until it works!' philosophy out of fault finding!

[wacjac]

i had a similar problem recently. once the temp had got to around 70 deg it would start to misfire. amongst other things in the boot was an old ignition module. changed that and had no problem since. Tho the wires to the coil were cleaned up at the same time.

[carsy]

I bet ignition amp.

[SILICONEKID340HP]

Coil breaking down when it gets hot ..Everyone know`s that including my granny

[gruffalo]

I had this happen on my old 400, was the fuel temp sensor, sometimes a little reluctant to start when hot as well.

[Chim_Pete]

gavgavgav said:

Do you have a spare ignition amp to try out? They can have strange behaviours when hot.

Its on its third ign amp since I bought it in 2006! I did wonder about it, but last time it was ran poor all the time, not just when it was hot. I will try my old amp to see if that makes any difference, otherwise I guess another new one may be on the cards.

Thanks.

[scotty_d]

SILICONEKID340HP said:

Coil breaking down when it gets hot ..Everyone know`s that including my granny

Or the ignition amp, or a lead , Had all 3 of these issues when i had my old chim the first 15-20 miles where great then it was breaking down under heat and load.