Stumble/hesitation on heavy acceleration

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Stumble/hesitation on heavy acceleration

Postby bzguy » Mon 10.04.2017, 00:26

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, ...
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Re: Stumble/hesitation on heavy acceleration

Postby John_W » Mon 10.04.2017, 16:17

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).

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Re: Stumble/hesitation on heavy acceleration

Postby HJ2 » Mon 10.04.2017, 16:35

'new plugs' so: :agree:
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Re: Stumble/hesitation on heavy acceleration

Postby bzguy » Mon 10.04.2017, 16:58

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 ?
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Re: Stumble/hesitation on heavy acceleration

Postby HJ2 » Mon 10.04.2017, 17:08

You could unplug the sensor and see if it makes any difference.
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Re: Stumble/hesitation on heavy acceleration

Postby alan e » Mon 10.04.2017, 17:45

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.
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Re: Stumble/hesitation on heavy acceleration

Postby bzguy » Mon 10.04.2017, 18:08

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 ?
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Re: Stumble/hesitation on heavy acceleration

Postby HJ2 » Mon 10.04.2017, 18:11

Ik zou het gewoon proberen kerel!
Maar eerst de bougies checken hoor. :wink:
Last edited by HJ2 on Mon 10.04.2017, 18:17, edited 2 times in total.
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Re: Stumble/hesitation on heavy acceleration

Postby alan e » Mon 10.04.2017, 18:15

bzguy wrote: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.
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Re: Stumble/hesitation on heavy acceleration

Postby alan e » Mon 10.04.2017, 18:17

HJ2 wrote:Ik zou het gewoon proberen kerel!


:agree: with what ever HJ2 said :D
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Re: Stumble/hesitation on heavy acceleration

Postby HJ2 » Mon 10.04.2017, 18:26

Hahahaha!

Welcome to the Forum bzguy!
Finally the best Lotus for you after all the other cars you've tried! :clap:
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Re: Stumble/hesitation on heavy acceleration

Postby bzguy » Mon 10.04.2017, 18:28

HJ2 wrote:Ik zou het gewoon proberen kerel!
Maar eerst de bougies checken hoor. :wink:


Tomorrow I will get a set of gap checkers ; 0,8 mm is right ?
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Re: Stumble/hesitation on heavy acceleration

Postby HJ2 » Mon 10.04.2017, 18:31

yep! :smt023
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Re: Stumble/hesitation on heavy acceleration

Postby alan e » Mon 10.04.2017, 18:34

alan e wrote:
bzguy wrote: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
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Re: Stumble/hesitation on heavy acceleration

Postby bzguy » Mon 10.04.2017, 18:48

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
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Re: Stumble/hesitation on heavy acceleration

Postby bzguy » Mon 10.04.2017, 19:03

I re-connected everything, no fault code anymore.

But I haven't started the car yet ;)

Tomorrow I will get gap gauges ...
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Re: Stumble/hesitation on heavy acceleration

Postby Giniw » Mon 10.04.2017, 19:04

Sorry for the little off topic, but:
alan e wrote: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 :-D )
Last edited by Giniw on Mon 10.04.2017, 19:19, edited 1 time in total.
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Re: Stumble/hesitation on heavy acceleration

Postby bzguy » Mon 10.04.2017, 19:13

Same here, no catalyst, and oxygen sensor ;)
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Re: Stumble/hesitation on heavy acceleration

Postby Giniw » Mon 10.04.2017, 19:20

Yes but mine is not chipped, it just has a stock S2 ECM.
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Re: Stumble/hesitation on heavy acceleration

Postby alan e » Mon 10.04.2017, 19:47

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.
Last edited by alan e on Mon 10.04.2017, 20:52, edited 2 times in total.
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