Air purge pump and another connection

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DWH
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Air purge pump and another connection

Post by DWH »

Hello. Some help please.
Having had the sports exhaust and some other work carried out at Lotus Bits last week, the car is running very well and the 120 miles journey back was totally uneventful and smooth, except for the potholes in the roads.......
I did however notice after stopping for some food that the air purge pump was not operating. Having opened the bonnet when I got home, I found that all the pipe work to the pump was missing and after removing both the fuses in the relay housing that is cable tied to the purge pump, found that one had blown.
The fuses were both originally 2amp but the closest I have spare is a 3amp fuse. I have yet to run the car up to temperature to see if this has solved the non-working pump but what do these fuses and the relay control ? And where should the missing tubing connect to on the air-box ? and does the pump suck air out of the air box or blow fresh air into it ?

Image

Also, I found that the lower spade terminal on the "thing-a-me-jig" at the front of the engine was not connected.......what is the "thing-a-me-jig" and should both wires be connected ? Photo shown below

Image

I emailed Lotus Bits last week but haven't had a reply.

Thanks
David
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Re: Air purge pump and another connection

Post by amarshall »

The relay switches power on when the ignition is off, and off when the ignition is on - the power goes through the thermal switch on the cylinder head so the pump should only run when the engine is hot and not running.

I can't remember if it sucks or blows (suck would make sense - weaken the mixture by removing it rather than adding more air to an already rich mixture), but the rear tube vents down through the bottom of the engine bay and the front one connects to a spigot on the underside of the airbox. Chances are that yours won't work as the motors burn out. There's a thread on how to replace it in Technical Articles.

The "thingamajig" is the throttle jack used to keep revs up when the aircon compressor is running. (may also prevent throttles closing too quickly in some circumstances). Yes, both connectors should be on it - but one may have been taken off because it isn't properly adjusted.
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Re: Air purge pump and another connection

Post by DWH »

Thanks Angus. The pump was working fine when I delivered the car to Lotus Bits. I'll try and take it out tomorrow for a run and get it up to temp to see if replacing the fuse has sorted the problem.
I'll put the lower spade terminal back on and see what happens......the car hasn't got air-con and don't think it ever did so it seems odd to have a "throttle jack" fitted or was it fitted to all cars ?

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David
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Re: Air purge pump and another connection

Post by amarshall »

A little voice is telling me that is has something to do with emissions control as well - hence my comment about stopping the throttles closing too quickly. It isn't present on all cars - just the HC with all the messy plumbing for emissions control systems.


Discussion from 2005 : http://www.lotusexcel.net/phpbb/viewtop ... w=previous
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Re: Air purge pump and another connection

Post by alanbell »

the purpose of the purge pump is to suck hot air out of the plenum chamber after switch off thereby enabling easier starting. personally i think it is a waste of electricity as i never found it made any difference. it would switch off after a few minutes and heat soak probably put the temperature up again. mine has been binned.

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Re: Air purge pump and another connection

Post by Lotus-e-Clan »

I disagree.

The purge pump IS worthwile for hot starting - the issue is they run too long and eventually burn-out.
Peter K

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Re: Air purge pump and another connection

Post by DWH »

Could someone out there with easy access to their car please confirm which wires should be connected to the top and bottom terminals of the throttle jack please so I make sure it's round the right way.
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David
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Re: Air purge pump and another connection

Post by Doc Si »

Mine is connected the same as yours....the yellow wire to the top terminal.

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Re: Air purge pump and another connection

Post by DWH »

Thank you.
I'll reconnect and see if there's any difference. As I said at the beginning, the car has never run so well as it is at present, so thanks to Lotus Bits for that. The flat spot that was evident at around 2,400 rpm has gone and the car picks up cleanly and smoothly.
Looking forward to getting some proper use from the car this year.
Here's hoping for lots of decent weather this weather......unlike today sadly..

Thanks
David
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Re: Air purge pump and another connection

Post by tonypoll »

I think the purge pump only helps on a hot day - when a build up of petrol vapour in the airbox causes an over rich air-fuel ratio upon re-starting?
Therefore you should see no difference at this time of the year (February).
On a hot summer day it should make re-starting easier as you are pulling in fresh air to the carbs, so getting the correct air-fuel ratio.
I agree: ( 'it sucks') it removes the air-fuel vapour from the airbox, pulling in fresh air.

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Re: Air purge pump and another connection

Post by amarshall »

Checked mine - yellow wire at the top.

I've definitely found that the purge pump helps, in all weathers - mostly when filling up on the way to somewhere else. As long as it gets to run for 5 minutes or more it eliminates the embarrassing churning and WOT manouevres that used to be required to start it.


(but then, I'm also one of those freaks who starts it from cold with the choke rather than pumping the throttle pedal)
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Re: Air purge pump and another connection

Post by Lotus-e-Clan »

I'm the same sort of freak Angus ...I just need to get out more, then I'd be exactly like you..except I have no hair, and I'm smaller. :)
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Re: Air purge pump and another connection

Post by amarshall »

Lotus-e-Clan wrote:I'm the same sort of freak Angus ...I just need to get out more, then I'd be exactly like you..except I have no hair, and I'm smaller. :)
I'm getting there - on both counts :(
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Re: Air purge pump and another connection

Post by kerry watkins »

We also start the car by pulling the choke out. We also depress the clutch. Was told many many years ago that it took a little pressure off the engine! Must be getting old :shock:
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Re: Air purge pump and another connection

Post by excel tel »

my purge pump has always been disconnected and sometimes crank over a bit to start when hot but not such a problem that i really feel i need to do anything about it.
I have also left the throttle jack disconnected as i find it just hold too many revs on, between gear changes it will still be reving 2-3000rpm
Also dont like the way that it acts on the end of the throttle linkage,in my mind it feels like its twisting the throttle linkage unevenly and more likely to put the carbs out of balance.

Cheers Terry

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