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I have an intermittent issue with the fuel pump not priming on my Lotus Elise S2 111S K series. It appeared to randomly not prime but I have been running OBDII checks (no fault codes found) and when I leave the ignition on for a period and then turn off and on then it primes fine and appear to do so from that point onwards, until the ignition has been off for a while (normally overnight)

I believe this is a faulty MFRU and once the ignition has been on for a while (10 minutes) and the MFRU has physically become warm due to the heat from the ignition being on, it appears to work.

Does anyone know how I can test the Fuel Pump Relay? What pins on the MRFU are involved here?
 

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Be careful not to get stranded. While this may not be your exact issue, especially because your fuel pump eventually pumps fuel. And one thing to consider is, if ithe K is wired like the 2zz, the fuel pump is tied into the immobilizer and that relay is known to go bad. My fuel pump immobilizer relay went bad and I spent forever hunting down the real problem. There are a few videos/threads about how to cut out the immobilizer and I recommend doing it while hunting down the rest of this issue. Good luck!
 

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Discussion Starter #3
Be careful not to get stranded. While this may not be your exact issue, especially because your fuel pump eventually pumps fuel. And one thing to consider is, if ithe K is wired like the 2zz, the fuel pump is tied into the immobilizer and that relay is known to go bad. My fuel pump immobilizer relay went bad and I spent forever hunting down the real problem. There are a few videos/threads about how to cut out the immobilizer and I recommend doing it while hunting down the rest of this issue. Good luck!
Thanks for your response. The immobilizer relay is clicking over when the I turn the key to the fused position (lights on) and the engine is turning over fine - just not getting any fuel. If I don't disarm it then nothing happens when I try to start the car. Is this what ou saw?
 

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Check the Inertia Switch. I have seen quite a few go bad lately.
 

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2005 Elise LSS Saffron Yellow
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Inertia switch, immobilizer relay, and MFRU relays can all figure into this. Given that the inertia switch and MFRU are in the engine compartment (essentially out in the weather) it's not surprising they can cause problems.

Further, just because you hear a relay click does not mean that it necessarily is working properly - the contact points on the relay can get corrosion on them (notably on the earlier MFRUs with the open frame relays) and fail to switch power even if the coil and moving parts are doing as they should. Likewise, the cold solder joint problem on the MFRU can affect the points connections as much as the coil connections.
 

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Similar to what Matt ^ said, start unplugging things and putting a jumper wire across the fuel pump circuit until it works. For example, remove the connector to the inertia switch, put a wire across the two wires, and see if that works. Same for the immobilizer. You don't actually have to be able to start the car, so don't worry about jumping things like the starter, just listen for the prime.
 

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Discussion Starter #7
Check the Inertia Switch. I have seen quite a few go bad lately.
3 wires on the inertia connector. I guess I jump the two outer wires (higher gauge)? These are black and purple and the middle wire is white with orange stripe.
 

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3 wires on the inertia connector. I guess I jump the two outer wires (higher gauge)? These are black and purple and the middle wire is white with orange stripe.
Sounds like the same colors as the Toyota one, so you are right - jumping the purple and black should allow the pump to run

1263279
 

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Discussion Starter #9
Sounds like the same colors as the Toyota one, so you are right - jumping the purple and black should allow the pump to run

View attachment 1263279
Tried that and still no priming. If the immobilizer relay was not working then the engine would not turn over on the K Series and it is turning over fine. Is it easy to directly power the fuel pump? I feel the pump is doing its job when it gets power but can't guarantee this is the case.
 

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Tried that and still no priming. If the immobilizer relay was not working then the engine would not turn over on the K Series and it is turning over fine. Is it easy to directly power the fuel pump? I feel the pump is doing its job when it gets power but can't guarantee this is the case.
That just means the inertia switch isn't the problem, so go to the next component in the chain and jump over it.

One misunderstanding is that the starter and fuel pump have seperate relays, so having the starter work does not mean the immobiilzer fuel pump relay also works. Trust me, I've been there, haha. Currently my fuel pump is jumped at the immobilizer but not the starter, so I still have some security. The pump circuit is fried though and has to be jumped (for me).
 

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Yea the starter and fuel are separately stopped by the immobilizer. In the s2 you can remove the seats and back panel to get access to a pain in the ass mini hatch which let's you power the fuel pump if you have a power supply.

I'd hunt down mfru next.

Good luck!
 

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Discussion Starter #12
That just means the inertia switch isn't the problem, so go to the next component in the chain and jump over it.

One misunderstanding is that the starter and fuel pump have seperate relays, so having the starter work does not mean the immobiilzer fuel pump relay also works. Trust me, I've been there, haha. Currently my fuel pump is jumped at the immobilizer but not the starter, so I still have some security. The pump circuit is fried though and has to be jumped (for me).
Bypassing the Immobiliser for the fuel pump circuit APPEARS TO HAVE FIXED IT!!!!!!!!!

The pump is priming rather proudly as soon as I turn the key. All other immobiliser functions are still working as before (eg starter, alarm etc.) Join 2 wires and the problem goes away. Ironically my Lotus garage opens tomorrow so was thinking of getting them to take a look.

I do not believe I can a new silver box immobiliser part. Look at the Cobra site but can't seem to get spares/replacements. Any ideas?
 

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I'd recommend bypassing the starter portion of the immobilizer too ;)

Then make sure your insurance is up to date and forget about "fixing" the immobilizer.

The alarms will still work, and you wont get stranded!
 

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I have an intermittent issue with the fuel pump not priming on my Lotus Elise S2 111S K series. It appeared to randomly not prime but I have been running OBDII checks (no fault codes found) and when I leave the ignition on for a period and then turn off and on then it primes fine and appear to do so from that point onwards, until the ignition has been off for a while (normally overnight)

I believe this is a faulty MFRU and once the ignition has been on for a while (10 minutes) and the MFRU has physically become warm due to the heat from the ignition being on, it appears to work.

Does anyone know how I can test the Fuel Pump Relay? What pins on the MRFU are involved here?
I don’t think the fuel pump primes when you turn the key with the immobilizer still flashing, correct? That’s why I’ve seen people suggest to turn off the immobilizer (push large button on fob) before turning the key, as it will start easier if the pump is primed. I’m guessing that wasn’t your issue since you said intermittent priming, but just wanted to mention the obvious solution just in case.
 
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