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Throttle solenoid?


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Hello,

Confused .com here

My Excel Service Notes for the Ignition and Fuel Supply show a Throttle Solenoid. My Component Location Diagram , bracketed under the RPM Speed Sensing Relay, calls it a Throttle Jack. The RPM Speed Sensing Relay is not shown on the Ignition and Fuel Supply Diagram, but a Decel relay is.

Grateful if someone could either shoot me or tell me what is going on.

Thanks Brian

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  • 1 month later...

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On 07/04/2019 at 20:22, Grizzly said:

Grateful if someone could either shoot me or tell me what is going on.

Thanks Brian

They're different names for the same device which is designed to open the throttle slightly to stop the engine stalling. :thumbup:

Cheers,

John W

http://jonwatkins.co.uk

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Hello John,

Thanks for your reply

I had sort of figured this out, but don't yet know how they work. I have the parts, just waiting for my engine rebuild to be finished and then I'll have a go at the electrics. 

These devices are mentioned a lot wrt Lotus Turbo engines (going wrong) fitted to Esprits

I'll just follow the manual and, for once, do as I'm told

 

Brian

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  • 10 months later...

Sorry to bring this up again

My research leads me to conclude that the throttle jack solenoid valve shown on Sheet 3 of my Service Notes Electrical schematics is not actually needed even if AC is fitted. The biggest factors in my decision is that it is only mentioned wrt early Turbo Esprits where most are removed and that I can find no details on  line of what they look like. So, even though my original Excel engine wiring loom has wire connections for one not fitting one should give no problems re idle speed when the AC is on. I should be grateful if someone would confirm this for me.

Tidying up the engine wiring loom then would see the removal of the wire from the Decel relay to Diodes D12 and D11, the removal of these same Diodes and the wire to Diode D10 leaving diode D10 only in the Radiator Fan and Heater Circuits. That should be OK should it not?

Thanks

 

Brian

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What was the research that led you to conclude the throttle jack wasn't needed?  My car has A/C but it doesn't work so the jack isn't necessary but, I would have thought that, with working A/C, the compressor load would drop the idle speed too low or it could be that you get a dip in speed below idle on decel and the jack is there to stop that stalling the engine.  It won't be powerful enough to open the throttles by itself but it will prop the throttle open when you lift off.  It'll be interesting to see what you find when you try it.

S4 Elan, Elan +2S, Federal-spec, World Championship Edition S2 Esprit #42, S1 Elise, Excel SE

 

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19 hours ago, Grizzly said:

The biggest factors in my decision is that it is only mentioned wrt early Turbo Esprits where most are removed and that I can find no details on  line of what they look like.

I had an '89 Esprit Turbo with a throttle jack fitted for the air con which I disconnected as it wasn't used.

Here's a pic of an original vacuum solenoid vale for the EBP & throttle jack part number A082M6421F from SJSportscars, but mine didn't look like that. :thumbup:

image.thumb.png.ffc24f4cdeb6e3ec42b84e135cc7d832.png

Cheers,

John W

http://jonwatkins.co.uk

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Thanks for your comments guys - so what is the throttle jack for?

I, too, was of the understanding that it kept the engine revs up when the car was idling with the AC on, which is why I am trying to get to the bottom of it as I can find more info on Hen's teeth than I can on this 

It seems to serve a different purpose on turbo cars with EPVB valves (which also fail)

I have seen the photo on SJ's website, but am not sure that that is all there is too it (we're not friends so I won't ask them)

Maybe a chat to Mike at Lotusbits or Garry Kemp might be the way to go

Trevor - a big ask - is the throttle jack still fitted to your engine? Is so some pictures would be good - better still if you will remove it can I have it?

 

Thanks

 

Brian

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3 hours ago, Grizzly said:

Thanks for your comments guys - so what is the throttle jack for?

I, too, was of the understanding that it kept the engine revs up when the car was idling with the AC on, which is why I am trying to get to the bottom of it as I can find more info on Hen's teeth than I can on this 

I believe  that's correct, I think I read it in the Esprit Workshop manual. From memory, it was about the size of my index finger with a couple of spade ends on one end & a spring loaded plunger on the other which popped up when the solenoid was activated. 😀

Cheers,

John W

http://jonwatkins.co.uk

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10 hours ago, Grizzly said:

Thanks for your comments guys - so what is the throttle jack for?

I, too, was of the understanding that it kept the engine revs up when the car was idling with the AC on, which is why I am trying to get to the bottom of it as I can find more info on Hen's teeth than I can on this 

It seems to serve a different purpose on turbo cars with EPVB valves (which also fail)

I have seen the photo on SJ's website, but am not sure that that is all there is too it (we're not friends so I won't ask them)

Maybe a chat to Mike at Lotusbits or Garry Kemp might be the way to go

Trevor - a big ask - is the throttle jack still fitted to your engine? Is so some pictures would be good - better still if you will remove it can I have it?

 

Thanks

 

Brian

Hi Brian, my plan is to (one day) get the A/C working and, therefore, plan to keep the throttle jack.  Unfortunately, my car is in a lock-up away from my house so I won't be able to get a picture for a couple of days but I will when I can.

S4 Elan, Elan +2S, Federal-spec, World Championship Edition S2 Esprit #42, S1 Elise, Excel SE

 

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My '90 N/A has a throttle jack but doesn't have aircon. I understood it was something to do with emissions, to stop the revs dropping back quickly to idle between gear-changes. Mine does work but I've never managed to successfully adjust it to work as described in the manual. Either seems to hold the revs too high for too long or not at all. Currently disconnected...

Not worth starting anything now...🍺

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Guys, this thread has two very different engines mixed up.

 

The SE Esprit onward had the Throttle jack, used to overcome the EBPV. This was controlled by the ECU/ECM.

Some of the Excels (and other carb'd earlier engines) had a Throttle Jack, mainly used to up the idle so that the Air Con doesn't cause it to stall. This was a fairly basic circuit and the engine has no ECU/ECM.

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  • 2 weeks later...

Sorry for the delay.  Finally got to the Excel today.  Battery was flat and had parked it with the driver's door near the wall but got it jump started and brought it home to put on the drive.  Which means I've now got pictures of the throttle jack.

y4mSto10_RQ2NHcgX3cRAp38W91Bt4p663L8PJNq

y4mwzHqnypGqv6DUVlgbEeR-leFLju5GsczyEY3i

 

Hope these help.  If you need more, let me know.

S4 Elan, Elan +2S, Federal-spec, World Championship Edition S2 Esprit #42, S1 Elise, Excel SE

 

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Hello Trevor

Many thanks for the trouble you've taken and for the photos. Now we know what one looks like - but I've never seen anything like it before, despite many hours Googling.

The throttle jack discussions on line all talk about Esprit problems which does not help as on Esprits it has a different function and is vacuum operated - as shown on SJ's website.

The throttle jack on the Excel appears to be electically operated as indicated on my schematics and as verified in your picture, so, I'm afraid, no further forward in finding one.

It also appears to be a "long "way from the carbs and not in direct contact with the carbs. 

https://www.dellortoshop.com/contents/en-us/p631_Lotus_20_and_22_type_throttle_lever_for_Dellorto_DHLA.html shows an operating arm for carburettors which I had imagined would be moved by the action of the throttle jack, but I cannot make sense of it all

Am I chasing something that is in fact superfluous and is now obsolete because it is not needed?

There must be Excels out there that run perfectly well without one?

Any one got one off the car for research?

Thanks

Brian

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That is exactly what I have on my '90 N/A Esprit. The 'plunger' on the bottom of it acts on the carb/throttle spindle to hold the revs momentarily when the throttle is closed. At least that's how understand it's supposed to work but, like I said, I've never managed to adjust mine correctly even though the solenoid does operate when powered up.

Not worth starting anything now...🍺

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There is a lever from the throttle spindle for the solenoid to push against when energised.  In the second photo, you can make out the adjustable screw against which the jack pushes.

S4 Elan, Elan +2S, Federal-spec, World Championship Edition S2 Esprit #42, S1 Elise, Excel SE

 

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That is what I had figured

I don't know what the idle engine revs should be so, for arguments sake, say 1600 RPM. This is sensed somehow by the engine speed sensor (don't ask me how - as a Civil Engineer  boxes that don't appear to do anything but actually do without moving is Black Magic) . If the engine revs drop to say 1400 RPM the speed sensor senses this and activates the solenoid, moves the plunger against the throttle lever and increases the engine revs to 1600 RPM plus a bit (?) and stays there until the throttle pedal increases the RPM as you drive away, whereupon the throttle jack solenoid is deactivated and the plunger returns to park position - how? -Spring return? -until the next time.

Simple theory

In Practice it is just a spring loaded solenoid that you can buy for pence on eBay. But the ones I've seen on eBay come with a warning that they must only be energised for a few seconds otherwise they overheat - which no good if you're stuck on the A55 on a hot day in a traffic jam with the AC on trying to get into Llandudno unless you sit there with you're foot on the accelerator pedal and watch the engine revs like a hawk and missing when it is you're turn to move forward by a foot ar so!

So what solenoid could be used.

I know there has been some discussion on here re the use of solenoids to replace the boot opening device - what were they and how were they activated / returned?

Determined to get to the bottom of this

 

Brian

 

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I think that the 'speed sensor' must pick up a signal from the ignition/rev counter circuitry to tell it when engine speed drops too low. There could be many possible situations causing this - between gear changes, upon sudden stop, when a/c engages, when engine fans engage, and also when a gear is selected on an Excel SA. It may also be useful in cold start situations, meaning less choke is needed. Upon receiving the signal from the speed sensor, the relay then activates the jack which opens the throttle slightly. Looking at the parts list it was fitted to SEs and SAs, not before.

My car is fitted with an SA gearbox. It has fuel injection instead of carbs, and idle is set artificially fast in order that the engine can tolerate the load from the gearbox in Drive. Idle speed without load is then controlled by retarding the ignition. This is not very efficient, so I think a throttle jack is the way to go for me - then I can set the idle speed as it should be and the jack will open the throttle as load dictates. It could also improve my cold start performance. If you find a good alternative let us know!

I seem to remember that Rover cars of the 80s and 90s with MEMS engine management used a stepper motor to control idle - progressive, so more precise than the throttle jack.

Cheers, Richard

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I'm still pondering the control of the throttle jack, be it a solenoid or a step motor. Both require a polarity change to reverse the operation push to a parked retract position (or a spring in the case of a solenoid). I know nothing about the workings of the speed limiter / sensor (amongst many other things) but I cannot imagine it having a reverse polarity circuit - just on on-off switch to energise the end device. It is possible to design an automatic reverse polarity circuit using three relays, but I haven't figured that out yet. It would be "bulky" unless some one could design and build a mini-circuit on a pcb for mounting in a relay holder.

So for now, as my engine is in lockdown, I'll do nothing until I can get the speed limiter working off the engine and explore the output pins

Unless, of course, someone comes up with the answer

Brian

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