Stumble/hesitation on heavy acceleration

[bzguy]

Hi all, since last week I'm the happy owner of a 1991 Lotus Elan SE with only 59.800 km's on the clock.(I will introduce myself in another topic).

Everything fine, but I notice some hesitation/stumble when I accelerate hard.

Max boost is 0.65 (car is not chipped), checked the spark plugs (they're new), and I have already ordered Magnecor leads (as the leads are stamped 1990 I intended to replace them anyway)

A friend of mine lent me his Elanscan cable, tomorrow I will hook it up and do a quick "paperclip" test to see if it throws any codes.

Any quick thoughts what could be the cause ?

I was thinking spark plugs, leads, ignition coils, clogged injectors, CAS, ...

[John_W]

It could be as simple as incorrect plug gap. Make sure it's 31 thou. My car developed a mysterious misfire last year, and after trying all the complex things, I decided to try the simple ones and the correct plug gap fixed things immediately.

Otherwise do a search on "misfire" for other ideas, eg look at this thread viewtopic.php?f=38&t=16495&p=218218&hilit=thou#p218218 . Elanscan probably won't pick up a misfire unless it's a sensor issue (eg CAS/HES).

John

[HJ2]

'new plugs' so:

[bzguy]

The car came with new plugs, but indeed I didn't check the gap. Must be 0,8 mm, right ?

I managed to do the quick "paperclip" test : code 13 : O2 sensor ?!

But how can a faulty O2 sensor make the car hesitate ?

[HJ2]

You could unplug the sensor and see if it makes any difference.

[alan e]

You say the car is not chipped in that case your SE will not have a o2 sensor fitted, you can fit a sensor to make it closed loop but you will have to fit a chip or fit a S2 ECM which may work not sure if that's possible or the sensor will not work, look on the left side next to the turbo is there a blanking plug that's where the sensor is fitted.

[bzguy]

Alan : I just looked : there IS a sensor just left next to the turbo.

Now I'm confused

Car has no chip as far as I know, max turbo pressure is 0,65

So, to check if it makes any difference, I can just unplug the O2 sensor ?

[HJ2]

Ik zou het gewoon proberen kerel!
Maar eerst de bougies checken hoor.

[alan e]

Alan : I just looked : there IS a sensor just left next to the turbo.

Now I'm confused

Car has no chip as far as I know, max turbo pressure is 0,65

So, to check if it makes any difference, I can just unplug the O2 sensor ?

Yes just unplug it and see if the engine starts to run rough.

[alan e]

Ik zou het gewoon proberen kerel!

with what ever HJ2 said

[HJ2]

Hahahaha!

Welcome to the Forum bzguy!
Finally the best Lotus for you after all the other cars you've tried!

[bzguy]

Ik zou het gewoon proberen kerel!
Maar eerst de bougies checken hoor.

Tomorrow I will get a set of gap checkers ; 0,8 mm is right ?

[HJ2]

yep!

[alan e]

Alan : I just looked : there IS a sensor just left next to the turbo.

Now I'm confused

Car has no chip as far as I know, max turbo pressure is 0,65

So, to check if it makes any difference, I can just unplug the O2 sensor ?

Yes just unplug it and see if the engine starts to run rough.

Also check if the seal on the ECU as been cut/broken if so you may have a chip fitted and change to closed loop

[bzguy]

OK, I have some surprising news, see pictures hereunder :

- there is an O2 sensor installed :

IMG_0006.JPG

- the car has been chipped, by Superchips Ltd ; however no idea what it's supposed to have changed on bar etc ...

FullSizeRender.jpg

[bzguy]

I re-connected everything, no fault code anymore.

But I haven't started the car yet

Tomorrow I will get gap gauges ...

[Giniw]

Sorry for the little off topic, but:

you will have to fit [...] a S2 ECM which may work not sure if that's possible

My SE which had no catalyst when it left Hethel (according to its VIN) now has both a lambda sensor and a S2 ECM (but no catalyst). I don't know when or why it has been installed, but it works well.
(I can't be sure the lambda sensor is actually read by the ECU though, maybe it's just a fake one )

[bzguy]

Same here, no catalyst, and oxygen sensor

[Giniw]

Yes but mine is not chipped, it just has a stock S2 ECM.

[alan e]

In the true Lotus way just because the plug for the sensor is there it may not be wired back to the ECU check the Wiki under converting a SE to closed loop it may be its never been wired but its still worth disconnecting the sensor when the engine is cold and then starting it to see how it runs its also worth saying which town or city you live just in case there is someone close that can give you a helping hand.