Cold running engine splutters

[oswaldx]

My Early S2 Elise '51 plate, K series, 73k miles runs fine on the whole and starts fine, but from cold, it is OK up to about 2500 rpm, but splutters if you try to gain more revs untill the temp reads about 72.( it's as if it's not getting enough fuel) There is no temp reading below this (is this normal?). Once warmed up, it goes fine, but even on long runs, the exhaust tail pipes are always a sooty black - never a pale grey that I've normally associated with correct mixture. I've changed the ECU Temp sender and no difference. What are the thoughts? Throttle potentiometer ? engine map gone potty ?(and no - I don't try to rev the nuts off it until its warm!)Thanks.

[bananamana]

I wouldnt go above 2500 rpm until its 85 - 87c anyway...

[oswaldx]

It's less stressful to allow revs to build gently than to labour an engine in lower gears. However, it shouldn't stutter if you ask it to - it wouldn't have done that when new.

[Gad-Westy]

oswaldx said:

It's less stressful to allow revs to build gently than to labour an engine in lower gears. However, it shouldn't stutter if you ask it to - it wouldn't have done that when new.

Sounds odd. The usual suspect for this kind of problem is the ECU temp sender, but you've already changed that. One thing that struck me as odd was that you're not getting a reading below 70 degrees. I'm not sure about the S2 but the S1 reads from about 45 deg upwards. Maybe another S2 owner can confirm whether this is correct or not. I beleive on the S2 the dash and ECU use the same sender so its just possible that your new sender isn't working or you have a problem with the wiring downwind of it. As a first check, a good clean of your earth points would be a good idea.

[marcpardoe]

Can confirm, no reading on my S2 Elise under 70!
Its the same on my S2 Exige!

[oswaldx]

mine being an early S2 has 2 temp senders - one for the gauge, one for the ecu. Why? I can't figure out ! Reassuring to hear that others don't read below 70 or so. what does that leave ? Throttle pot ? Ecu re-map ? Did change battery soon after getting car last june. Not sure if problem existed then or not in the warmer weather it's less noticeable. Are there any other sensors that could cause this ?

[LivinLaVidaLotus]

Look in your manual, there should be (There is for Yota cars anyway) and entry on how to reset the throttle position sensor - try that, see if it makes any difference.

[hbaumhardt]

Whilst the S2 has 2 temp sensors fitted, the blue one does nothing and the black one runs both ECU and dash display and doesnt register until 70/72.

[oswaldx]

thanks for that knowledge. Just a case of figuring out what's the cause of the problem now then as that seems to rule out the ECU temp sender.

[hbaumhardt]

Could be a lambda sensor problem e.g. heating elements not working correctly so giving odd readings after idle but then the probes work fine when warmed by exhaust gasses.

Try disconnecting the post cat lambda (remove left rear wheel, wire runs up behind wheel arch liner) and if no joy also disconnect the pre cat Lambda (4 wire block on the left hand side of the crank case). Its Ok to run the engine with them disconnected for a while, MIL light will be on but should go out after a couple of starts once reconected.

[jondude]

A cheap and easy thing to do first of all, is to run the car as empty as you can, then fill up with fresh, new petrol. Try the high octane, detergent stuff.

This MAY be all the car needs - you may have some duff petrol in there.

The air filter is cheap, too - and it needs to be both clean and sitting perfectly in place, or you will get the symptoms you describe.

You should rule the above items out before doing the expensive stuff!