Unknown serious engine fault - PLEASE HELP

[JossElan]

My Lotus has an intermittent engine fault which is not registering a fault code (with the paperclip test). It usually starts with a small judder* followed by the engine light coming on, the judders will then become more frequent and then the engine will start running rough. If I continue, it will really start cutting and juddering and the engine will start cutting out when I lift off the accelerator. Can anyone help!?

*the initial judders feel like a half-second loss of power and I get corresponding lurch forward.

[JossElan]

I should also point out that sometimes the light will go off and it will run fine for a bit; if I'm driving at a steady pace.

[rip]

Hi,

CEL coming on but not giving a fault code is unusual.
It does not sound like a major issue though. I would call something mechanical major such as the engine not turning or a massive oil leak.
I suspect a CAS fault although at the moment there is not much to go on.

[Giniw]

Hi, if there is no recorded fault code after the engine stops and the CEL was on, couldn't it be an electrical problem with the ECU being not properly energized?

[Rambo]

This may be a red herring.......

...but what exhaust system do you have on your car ? And are you on full boost when this juddering, lurching forward or power loss takes place ?

Just a thought

[clemo]

Hi, if there is no recorded fault code after the engine stops and the CEL was on, couldn't it be an electrical problem with the ECU being not properly energized?

my guess too

[JossElan]

Hi all,

Thanks for your replies so far. I've just had the exhaust changed. It was a Lotus original and is now a PNG Sports Exhaust; however, the fault has been present with both.

[Brit-Car-Nut]

With no details or fault codes, I think you will waste less time and money if you take it to one of the M100 specialists for diagnosis.

The possible list of causes is quite long and without some understanding of the M100, you will most likely end up replacing a lot of un-necessary parts trying to figure it out yourself.

Then again, maybe you like a real challenge or funds tighter as mine...

[Rambo]

With no details or fault codes, I think you will waste less time and money if you take it to one of the M100 specialists for diagnosis.

The possible list of causes is quite long and without some understanding of the M100, you will most likely end up replacing a lot of un-necessary parts trying to figure it out yourself.

Then again, maybe you like a real challenge or funds tighter as mine...

And if you go down this route you will need to update your location in your profile. Because without knowing if you live at Lands End or John o Groats we can't recommend your nearest M100 specialist or knowledgeable LEC M100 owner

[JossElan]

Profile updated. I'm in between Marlow and Henley, Bucks.

Well, actually, right now I'm by the side of the road waiting for the RAC after trying to limp her home!!!!

[JossElan]

I think its time for a specialist to have a look - Any opinions on Hofmann's in Henley, Steve Williams in Maidenhead or SGT in Taplow?

[Simon_P]

First do some free diagnosis yourself

Check battery terminal connections
Check engine earth - wire and croc clips from the braid on the chassis to the plenum
Check CAS is tight and hasn't slipped.

Is it ok when cold ? and then deteriorates when hot
Only happens under load?

[JossElan]

Thanks Simon,

I'll have a look at these tonight.

Is it ok when cold ? and then deteriorates when hot
Only happens under load?

It tends to begin after a couple of minutes, usually after applying load but not full boost, and then develops to full cutting-out over the next 5-10 mins; however, sometimes the light will go off again and I can drive for extended periods - although by this stage I'm nursing the car and diving as steadily as possible; keeping the revs below ~3k. After I broke-down last night it would start but then cut-out after 1-2 seconds; however, I waited for an hour and then it started fine and I drove the rest of the way home (very gingerly!).

[Danevansgolf]

If I was you i would either change the spark plugs or when the engine is hot, take the plugs out and see if there are any cracks on the ceramic parts. Plugs only cost a tenner. I've had a similar problem, which turned out to be the plugs, which had hairline cracks in them. Only found them when I took them out hot, and the cracks were visable. Good luck

[JossElan]

Update: Just taken it to my new local specialist (SGT, Taplow). They struggled to get the car to communicate with the Élan scan but finally got a Code 34 - MAP sensor fault. They've ordered a replacement (~£200) and I'll provide an other update when it's been fitted.

Thanks for all your advice

[muley]

Pleased to hear that progress has been made.

£200 seems a bit steep, IIRC I paid about £20 for mine. Listed as for a VOLVO something or other.


Jim

[Brit-Car-Nut]

The MAP sensor is a standard 2BAR unit used in a lot of cars, mostly GM influenced. The most common aftermarket part number is Standard Motor Products AS4. Prices vary wildly but it is most important to make sure you are getting the 2BAR version as there is a 1BAR part that basically looks the same and the electrical connection will work. The best way I found to be sure is to make sure the connection area key is RED/Orange in color.

I found some on eBay for $15.00 a while back.

AS4b.jpg

[muley]

Update: Just taken it to my new local specialist (SGT, Taplow). They struggled to get the car to communicate with the Élan scan but finally got a Code 34 - MAP sensor fault. They've ordered a replacement (~£200) and I'll provide an other update when it's been fitted.

Thanks for all your advice

FWIW, they didn't need to struggle with Elanscan, they could have used a paperclip.


Jim

[JossElan]

The paper clip test wasn't generating a fault and even the Élanscan took a few attempts to connect. More importantly, I've been done up like a right kipper!!! They ended up charging me over £400! Don't think I'll be taking my car back there again. There was another (red) Élan there too, apparently with the same problem. Wonder if they got shafted too!

[clemo]

The paper clip test wasn't generating a fault and even the Élanscan took a few attempts to connect. More importantly, I've been done up like a right kipper!!! They ended up charging me over £400! Don't think I'll be taking my car back there again. There was another (red) Élan there too, apparently with the same problem. Wonder if they got shafted too!

Well the good news is you are back on the road .
If you initial diagnostic of unknown serious engine fault had have been the case then you could have been thousands down .

SGT though ... one to remember (or forget)