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Discussion Starter · #1 ·
I just read the other threads on this and I am having some problems figuring out what the problem is with my car.

I went to the drag strip the other day and my first launch my car hooked pretty good but then just died. There was no drama, it just lost power and rolled to a stop. I had to have the car towed home as it would crank but not start. I do not have any wiring diagrams so please be specific.

The car was running fine and I even autocrossed it several times with no problem. Here are the important details followed by my questions:

1. The car is turbocharged and had a bigger fuel pump installed.

2. The inertial switch was "disabled" by Monkeywrench racing when they did the fuel pump and other work. It looks as if the inside was taken out as it will not trip no matter what. (I did however previously discover it was left dangling and was dragging on the axle so the rubber cover and a little plastic on the outside is ground off. I had moved it about a week prior to the event)

3. The fuses all have power and are all good.

4. I have a fuel pressure gauge and it does not have any pressure at all.

5. One time it blew a fuel pump fuse (at least that is what Monkeywrench told me it was and it acted the same way) They replaced it at the time with a larger one and it started right up.

6. The fuel gauge was not working correctly once before after I got it back from Monkeywrench. They found a loose ground? (No problems since then)

7. Along with the fuel gauge, the speedometer also every once in a great while will not work. I then shut it off and restart it and it will work.

8. Once after washing it in a spray off car wash the car would not start but cranked. (at that time I am not sure if it had fuel pressure). This was after having it back for a week following problems #5 and #6. I took it back to Monkeywrench for them to diagnose. It started at their shop after being trailered there and they were not really sure why.

9. My door locks and alarm were not working right prior to all of this. I could not get my car to lock/ unlock on a regular basis. (Just prior to this happening I did accidentally lock and unlock the doors which was not normal)

OK, so at this point I am guessing that it is either the fuel pump relay or the fuel pump itself (but the pump only has about 1500 miles on it). We checked the wires and there do not appear to be any bad connections.

My Questions I need help answering:
1)Where is the fuel pump relay located? Can I check it?
2)What color wires are the power wires for the fuel pump? I want to check the pump itself but could not figure out which wires power it.
3)What are your thoughts on the inertia switch being "disabled"?
4)Do you think the door locks or alarm have anything to do with this?
5)Am I on the right track and is there something else I should be checking?

Thank you for all of your help. I need to get my car running again.:panic:
 

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Any chance its shorted here?

"The inertial switch was "disabled" by Monkeywrench racing when they did the fuel pump and other work. It looks as if the inside was taken out as it will not trip no matter what. (I did however previously discover it was left dangling and was dragging on the axle so the rubber cover and a little plastic on the outside is ground off. I had moved it about a week prior to the event)"
 

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Discussion Starter · #3 ·
Any chance its shorted here?

"The inertial switch was "disabled" by Monkeywrench racing when they did the fuel pump and other work. It looks as if the inside was taken out as it will not trip no matter what. (I did however previously discover it was left dangling and was dragging on the axle so the rubber cover and a little plastic on the outside is ground off. I had moved it about a week prior to the event)"

I don't know? Is there a way to bypass it to check? Any idea what an inertia switch cost or how long they take to get? I could just look at getting another if I can't figure this out. We thought there was power going to the fuel pump but I am not sure because we didn't know which wires were the correct ones.
 

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Discussion Starter · #5 ·
The Fuel pump relay is in the Multi-Function Relay Unit on the bulkhead under the fuses.
Is the muti function relay the square box directly below the two fuse boxes? Is there a way to test the relay and also, does anyone know which wires are the power wires to the fuel pump?
 

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Yes, you can check if you have 12V at the "purple" inertia switch wire with the engine ignition on. The fuel pump wires are both black. Also check fuse R1 in the engine bay.
Michael
Is the muti function relay the square box directly below the two fuse boxes? Is there a way to test the relay and also, does anyone know which wires are the power wires to the fuel pump?
 

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Discussion Starter · #8 ·
Ideas?

The fuel pump system is really easy to diagnose. Just follow the circuit diagrams and it will nearly trouble shoot itself...

Here's a link to the diagram on my website:

http://www.boefabrication.com/lotusElise/manuals/elise_north_america_1-16.pdf

Good luck,

Phil
Thanks for the diagrams. We have to look at it again tonight. We had checked the wires to the fuel pump for power and there was power at one of the black wires so we thought the fuel pump was bad as it wasn't running. After removing the pump and checking it, it turns out that the pump was good after all. Any ideas? I am thinking about the Multi Function Relay as the culprit but we have to study the wiring diagrams a little more. Any help would be appreciated.
Derek
 

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Discussion Starter · #9 ·
We think that the ground wire on the fuel pump may be the problem. Plugged the pump in today again and it worked. The ground wire has a cut in it and didn't look like it was spliced together well. When we checked the wire there was a lot of variance in it, especially when it was moved. I am hoping that that was the issue as yesterday there was power to the pump but it wasn't running. It seems like the only obvious issue.
 

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3)What are your thoughts on the inertia switch being "disabled"?
That is an extraordinarily unsafe thing, especially on a modified car. Replace/fix it immediately. Doesn't matter what someone is doing-- larger fuel pump, swirl pot, etc-- there is absolutely NO good reason to disable it.

4)Do you think the door locks or alarm have anything to do with this?
If the alarm/immobilizer have been played with, they'll certainly prevent the car from starting and cause all sorts of other weirdness. Check the white molex plug behind the plastic trim panel behind the seats. It's the one with a bunch of black wires running to/from it. Note any weird splices or other fumbuckery.

The Alarm box itself and CDL modules are under the dash-- the dash cover has to come off to get at it properly.

There aren't that many things that'll prevent the fuel pump from priming/running. The inertia switch, immobilizer, and pump power itself are the big ones. It would be a very good idea to pull the technical manual for the car so you have a reference. Well worth the $25.
 

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Simba is spot on about the inertia switch. It's a gadget worth keeping...

Here's a tip. The inertia switch is before the alarm immobilizer. So even if the black or purple wire going to the inertia switch have fire, doesn't mean it's getting to the fuel pump, as the immobilizer can interrupt it... If you get really stumped, just hot wire the pump with a relay and run your own ground. Use the inertia switched wire as the trigger for your relay and the chassis as a ground. I have a pic of my relay on the website (but it doesn't show much)... It's really easy to do and get around that whole immobilizer and crappy OEM wiring issue...

Good luck,

Phil
 

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Wow. It is simply unforgivable and irresponsible to disable the inertia switch. I am finishing up my TRACK ONLY car with standalone ECU and disabled immobilizer and have taken all steps necessary to be sure that the inertia switch is part of the fuel pump control circuit.

I would not let a shop with that kind of judgment change a light bulb on my car.
 

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Keith- Just to clarify for viewers at home- you're referring to what Simba and I are calling the inertia switch, right? The "immobilizer", as we're referring to it, is a component of the alarm system. I know what you meant, just clarifying for someone that may not:D

Cheers,

Phil
 

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For clarification, the Inertia switch is not controlled by the Immobilizer (or the reverse), it is simply a single pole, double throw switch that isolates the Fuel Pump and unlocks the doors. It just so happens that the Immobilizer is in the Fuel Pump circuit.
 

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If you think its the pump.

  1. Check for voltage at R1, both sides to be sure, failure there means a fault between the battery and the relay
  2. Check for voltage on the ECRU/MFRM RMC1 (purple 2.0) ,no reading here is a fault between R1 and the MFRM
  3. Check MFRM/RMC2 Green 0.5 and RMC2 Black/Purple , for a reading, that controls the relay for the fuel pump, so if its not energized, the ecu signal isn't coming on. (Check wiring to ecu)
  4. Next step is to check pin 1 (purple 2.0 ) at the inertia switch (presuming the wiring is still there) then pin 3, (black 2.0) which feeds the immobiliser.
  5. then pin 1 immo feed, (black 2.0) if no reading there fault is betwen the inertia switch and immo.
  6. then pin 6 immo out, (black 1.0) if no reading , fault is probably the immo
  7. last step is the fuel pump (black 1.0)


reading the list of faults though, i think i'd be looking for a grounding problem, loose connection or wire gone bad. its possible the relay is being overloaded and has died.
 

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Also to simplify diagnostics you can just run directly from MFRC/RMC1 (purple 2.0) to the fuel pump B 1.0 (comes from immo 6).

to recap you're taking the purple wire which feeds pin 1 of the inertia switch, straight to the live side of the fuel pump (just don't mix up the ground and live side of the pump! )
 

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yes I meant the inertia switch should always, always, always be part of the fuel
pump control circuit. It does not have to handle the actual power current (although mine does), but I really see no reason to disable it. At the very least, leave it in series with the relay control circuit.

Charlie's suggestion is excellent, but he did say for diagnostics - don't leave that bridge in place after you find the fault.
 

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FYI, the immobilizer will not allow the car to crank -- at least that's how it works on my 07 Exige S -- so it's probably not the immobilizer. My hunch is it's more likely gonna be the inertia or wiring issue with fuel pump -- do you hear the fuel pump when turn the key?

Since you said this happened right after a drag launch (which is pretty hard on these cars), I'd suggest Inertia got triggered -- assume you've tried reseting it?

Rob
 

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We're attempting to help Derek diagnose the problem right now over email.

This car came to us originally with many wiring issues caused by a very questionable turbo install done elsewhere. We spent dozens of hours undoing the damage and got the car running extremely well but have seen some unusual function on the fuel pump circuit. Last year it blew a fuse at one point for no apparent reason and was fine after replacement. No physical cause was found. We had not modified that part of the wiring at all. Could be a funky ground or something more complicated. The problem could not be reproduced at the time making diagnosis very difficult.

We'll continue to assist with the diagnosis as much as we can.
 

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Lotus runs the same configuration i posted on track cars with kill switches, its mainly a street car safety feature.

If the inertia switch is disabled, i doubt its a g force. But drag race means a lot of extra load, which could mean fried MFRC or wiring.

if you wanted to maintain the inertia but bypass the immo, just bridge it after the inertia switch instead, pin 3.
 
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