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Punchline is something to do with Jaguars. Pa-dum-pum kssshhh!
Actually, my full-throttle micro-switch was broken.
There’s your problem right there.
Internally shorting. So, full throttle enrichment all the time! Anyone know what the % increase here is? I know that if you run the ECU full lean and drop the fuel rail pressure to 18 psi it counters this enrichment. So, quite a bit.
I’ve no idea when this switch failed, I’d tested it middle of summer or so and it was functional. Very glad to have found it finally. The connection boots covered this area and hid the cracked case.
The circuit and the switch is normally open. At full throttle it closes and that triggers full enrichment. Just use a test light see if the switch is passing current or not when it is in its normal state with the throttles closed, and if it does when the microswitch lever is activated by your finger - which is what the capstan does when at WOT. this is one of two devices on the car (USA spec only, UK just have one such device). The second device is a vacuum switch (on the cabin end of the A bank inlet Manifold) which is held open by manifold vacuum when the car is running at anything but WOT.
Easiest test for this switch is to trip it by hand with the car idling. If you idle changes significantly then the switch works and so does your vacuum-based WOT switch if you have one.
As Greg said, the micro switch is normally open and the vac switch is normally closed but held open by 1 in. of vacuum or more. Both switches provide a ground to pin 5 on the ecu when activated.
Proper test ( 16cu ECU )
Checking pin 5 with the car off should show a ground. If not vac switch is bad.
Disconnect the vacuum switch electrical connectors and pin 5 should NOT show a ground. This confirms the wiring.
Tip the micro-switch and pin 5 should show a ground. This confirms the micro-switch functions
Reconnect the ecu and start the car. Now, at idle, reconnect the vac switch.
No change in idle confirms the vac switch opens.
Unless, that is, the micro switch casing is cracked and flexing, but is held together by the rubber boot on the side connector. Then the end connector can shift and close the switch. it may be intermittently shorting and at other times not. This could go on for more than a year and almost drive you mad.
Thats is the real reason for the post. I just wanted to give a heads up that this can happen, and be hard to detect.
Heres a closeup of the broken micro switch. You can see that the missing piece was not bonded to the case base. Only the corner of the case top was holding this corner together. And the side connector flexes against it when the switch is tripped. Eventually that case top edge failed. The top is less than a millimeter thick. Poor design choices here by Burgess. Current micro switches are beasts by comparison. But this one did last a long time!
When I say top and base I’m referring to the photo. The switch is upside down in the photo. When mounted, none of this was visible.
Last edited by JigJag; Mar 19, 2019 at 09:19 PM.
Reason: Add a picture
I purchased some after market limit switches from RS Components
842-1745
Both normally open and normally close.
Choose the right combo - holes line up perfectly.
Thanks for that link Dukejag! I was digging through Google results and this helped me filter them. But I think I'm gonna drop some serious dough ( $11 ) on this Honeywell environmentally sealed version for use in Zone 2 hazardous locations. Not that I'm worried about this switch causing an explosion, but simply for the sealed case and robust design. I'll modify the mounting slots to accommodate the lever length if they do not offer a longer replacement roller arm.
The pictured version of this micro-switch definitely doesn't have a long enough lever to reach. This one's lever can move 7.7mm towards the switch to the second pivot point. This makes it 27.8mm. Probably adequate with alterations to the mounting slots.
They do offer a version with a 29.98 mm ( same as original ) roller lever. I'm working with a rep trying to find those.
Those switches are nasty - no sealing at all. They were quite commonly used as clutch lever switches on motorbikes - I always kept a spare. The Honeywell switch looks promising.
The V15W2 is a beast. No question, it’s the best made micro switch I have seen. But they’ve not released the 3cm arm version yet. I had a standard 3cm roller Honeywell on hand so I used that for now. I did test fit the V15W2 and it kicks in at around 50% throttle opening using the default slots with the arm pictured above. Not bad, if I’m over 50% throttle I’m more likely heading to wot than just cruising at 80mph. But for now I’ll stick with a std. one that trips closer to 70% and fab up a new bracket for the new switch.
This got me thinking. A WOT indicator light is in my future.
Finally found the cause of my over-richness.
