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Changed Exhaust Manifold - Full Throttle On Startup


Best Answer Frazer stuart , 27 January 2018 - 10:09 PM

Right I've got it sorted. It's a silly, quite embarrassing mistake but I thought I'd post it rather than leave the thread unresolved.

There's 4 studs which come out of the inlet manifold, go through the throttle body then through a plate (which holds the fuel lines and moisture trap). You bolt those down to secure it all.

During reassembly I managed to get that plate between the inlet manifold and throttle body. It created a decent sized gap between the two so loads of air was getting sucked in. Difficult to see right down the back in the dark!

Changed it round and all fine (apart from a wandering idle but that's a Story for another thread)

Thanks for your help everyone in trying to get it sorted Go to the full post


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#1 Frazer stuart

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Posted 21 January 2018 - 03:38 PM

Hi guys,

Hoping someone can help a rookie out.

Car is a 93 cooper spi.

This weekend I changed my exhaust manifold from standard to a maniflow stage 2 lcb. I managed to leave the y piece at work (doh) so I have only got as far as fitting the 2 bits which attach to the block. I have then refitted everything else (intake manifold, throttle body, air box).

I wanted to start it up to run some water through the coolant system so that I can circulate that, flush it out tomorrow, refill coolant and fit the rest of the exhaust system.

So I went to start it up and (apart from being crazy loud due to no exhaust) it just instantly runs like it's on full throttle!

I'm a rookie (this is by far the toughest job I've done on the car) and I've followed the Haynes manual.

The throttle cable seems to rest back to closed just fine.

Anyone have any ideas?

Could the lack of full exhaust system be affecting the lambda reading? Not sure if running super rich would seem like full throttle?? Or maybe an air leak, or something to do with the stepper??

Ps when I fill the rad with water, it only takes 1 litre, but 2 came out. Is that normal? The plan was to run it and top the rad up as the water level goes down but I obviously didnt get that far haha.

Thanks so much in advance! :)

#2 lawrence

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Posted 21 January 2018 - 04:13 PM

Put the exhaust on fully. Theres no point in expecting the car to run nicely when you have half a zaust.

Regarding the rad. Standard side exit?

#3 nicklouse

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Posted 21 January 2018 - 04:21 PM

dosent the Y piece have a sensor in it? if yes then the system will be trying to run with a false reading.



#4 Frazer stuart

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Posted 21 January 2018 - 04:31 PM

Lawrence - yeah fair point about the half exhaust. I'll fit it all up once I get the y piece and try again.

Yeah standard side mounted rad. Drained it by removing the auxillary fan switch. Put that back in and refilled.

Nicklouse - the lambda is in the piece of the manifold which I have fitted, where the 2 outer ports join (probably better to be in the y piece like you say so it reads all 3 cylinders, but hey). The piece containing the sensor is fitted to the car but the sensor is only 50 cm from the open end of the pipe, because the rest of the system isn't fitted. So maybe it's reading loads of oxygen and overfuelling??

#5 Frazer stuart

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Posted 21 January 2018 - 04:39 PM

I get that incorrect lambda readings could cause overfuelling, but wouldn't the car also need access to air to run like it's on full throttle?

So maybe I'm looking for an air leak as well? And a big one because it really was flooring it!!

#6 nicklouse

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Posted 21 January 2018 - 04:41 PM

if it was a carbed car then yes an air leak would cause the same issue. injection i dont know.



#7 Frazer stuart

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Posted 27 January 2018 - 10:09 PM   Best Answer

Right I've got it sorted. It's a silly, quite embarrassing mistake but I thought I'd post it rather than leave the thread unresolved.

There's 4 studs which come out of the inlet manifold, go through the throttle body then through a plate (which holds the fuel lines and moisture trap). You bolt those down to secure it all.

During reassembly I managed to get that plate between the inlet manifold and throttle body. It created a decent sized gap between the two so loads of air was getting sucked in. Difficult to see right down the back in the dark!

Changed it round and all fine (apart from a wandering idle but that's a Story for another thread)

Thanks for your help everyone in trying to get it sorted




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