11Budlite Posted June 17 Share Posted June 17 I'm trying to locate the fuel pump relay on my 2019 Caterham 310S. I'm assuming that it should have a heavier gauge Yellow/Green wire coming from the 87 terminal of the relay and it's switched by the ECU. The Y/G wire goes to the inertia switch on the firewall and then on to the fuel pump connector at the tank. I've looked at all 6 relays I can find on my car and don't see one with a Y/G wire coming out of it. Any ideas? Link to comment Share on other sites More sharing options...
JohnCh Posted June 17 Share Posted June 17 If the relay wiring on the Sigma is the same as the Duratec, the relays are grouped in sets of three that are then connected to create the six-relay string you see in the fuse box. Unfortunately, sometimes Caterham switches which group of three starts the string, but the FP relay should be in either position 2 or position 5. Group 1: Starter > Fuel Pump > Cooling Fan Group 2: Reverse Light > Flasher > Ignition I just took a look at the back of my fuse box and I do see the Y/G wire snaking its way towards that relay. It might be worth pulling the suspected relays and checking continuity to the inertia switch. BTW Assuming the Sigma operates like the Duratec, there is a module on the left of the fuel tank that functions as the PWM control for the fuel pump. That could be another area to check for a problem. Link to comment Share on other sites More sharing options...
11Budlite Posted June 17 Author Share Posted June 17 Thanks John. Unfortunately the Sigma layout is different than the Duratec. There are 4 relays on the firewall in front of the fuse box, and 2 others on the drivers side near the steering column. I posted photos of the 6 relays on a previous thread here: I'll check all the relays for continuity to the inertia switch even if they are different colored wires, and also check for a module on the left side of the tank. I don't recall seeing anything there when I had it apart before. Link to comment Share on other sites More sharing options...
MV8 Posted June 17 Share Posted June 17 (edited) I assume there is another wire on the inertia switch that goes to either the relay, ground, or the ecu. I assume there is another wire on the pump that goes to ground or power. All we know from you posts is there is a wire between the pump and inertia sw that is yel-grn that can be for pump ground or power. Disconnect the battery negative terminal, then continuity check the wires at the inertia sw and pump to ground and post what you find. Does the sigma have two fuel lines on the fuel rail or one? Edited June 17 by MV8 Link to comment Share on other sites More sharing options...
11Budlite Posted June 17 Author Share Posted June 17 32 minutes ago, MV8 said: I assume there is another wire on the inertia switch that goes to either the relay, ground, or the ecu. I assume there is another wire on the pump that goes to ground or power. All we know from you posts is there is a wire between the pump and inertia sw that is yel-grn that can be for pump ground or power. Disconnect the battery negative terminal, then continuity check the wires at the inertia sw and pump to ground and post what you find. Does the sigma have two fuel lines on the fuel rail or one? The inertia switch has a Y/G wire going in and a Y/G wire coming out of it, no other wires. One of those wires goes to the fuel pump, I'm assuming the other one goes to the relay. The Sigma has only one line going to the fuel rail. I'm at work now and won't be able to do any more checks until tomorrow pm. Link to comment Share on other sites More sharing options...
JohnCh Posted June 17 Share Posted June 17 With a single fuel line, you should have the PWM controller I mentioned earlier. Here is a picture of mine. It's a Ford item so I bet the version used on the Sigma looks very similar or is even the same part. Link to comment Share on other sites More sharing options...
MV8 Posted June 17 Share Posted June 17 Colors don't mean much. Sounds like it may be a kit car with a Brit engine wired like a Ford with creative color codes (no judgment!). Disconnect the negative battery cable. Unplug the inertia switch. Set the dvm to beep on continuity (when leads are touched together). Have someone hold one dvm lead to the inertia sw connector pin while you probe each relay socket to find the fuel pump relay. Pump driver at the pump should have two ecu wires, two for pos and neg pump, ground, and one from the relay through the inertia sw. Link to comment Share on other sites More sharing options...
11Budlite Posted June 17 Author Share Posted June 17 Thanks guys, I'll be checking those ideas out tomorrow. Link to comment Share on other sites More sharing options...
11Budlite Posted June 19 Author Share Posted June 19 I guess I never mentioned why I'm trying to find the FP relay. The issue I'm trying to fix is the FP energizes whenever the battery is hooked up whether the ignition is on or not. It's getting the signal from the ECU because it builds pressure then shuts off like it would normally. The attached photo shows the connection at the FP. The Y/G wire at the FP does go to one side of the inertia switch. I checked for continuity between the other Y/G wire at the inertia switch and the relays and was unsuccessful. I'm probably going to have to unwrap some of the harness to see what I'm missing. I also found this Caterham with a similar issue: https://www.pistonheads.com/gassing/topic.asp?h=0&f=101&t=1895605&i=0 I know I've seen this connector in the dash wiring, so I'll be checking that diode as well. This is a distinct possibility. Didn't see a PWM controller on or near the FP/tank. With the help of JohnCh, we've noticed that the Sigma FPA is different than some of the Duratec FPA's which have the PWM controller on the side of the tank. There's a possibility that the controller is part of the FPA on the Sigma model because it's quite a bit more expensive. https://caterhamparts.co.uk/pumps-senders/3000-fuel-pump-sigma-and-duratec.html https://caterhamparts.co.uk/pumps-senders/5501-fuel-pump-seven-485-model.html I don't think this is related to my issue but it's always good to understand how things work. I also took the tunnel cover off and will check to see if that helps me locate any of the issues. Link to comment Share on other sites More sharing options...
MV8 Posted June 19 Share Posted June 19 There are many reasons it could be more expensive but there are only four wires (including the fuel level and grounds), so an integral controller is very unlikely. It could be the ecu performs the controller task. I would determine if the ecu E connector pin 9 is getting power whenever the battery is connected and ensure the key is in the off position. You should be able to find this MRFU by touching theground cable to the battery and listening for the click. Link to comment Share on other sites More sharing options...
JohnCh Posted June 19 Share Posted June 19 1 minute ago, MV8 said: but there are only four wires (including the fuel level and grounds), so an integral controller is very unlikely I noticed the same thing, but it is possible that the ECU controls the main FP relay instead. The MBE simply switches that programmable output to ground when the engine is over a specified rpm to ensure the pump won't continue to run if the engine stalls. It doesn't send any signals to adjust the pump speed based on a table or a fuel pressure reading like more sophisticated systems. As @11Budlite states, it's likely not the issue but interesting to understand nonetheless. The fact that one fuel pump assembly is over 85% more expensive than the other tells me something is significantly different. Or it's just another example of head scratching pricing from Caterham Link to comment Share on other sites More sharing options...
MV8 Posted June 19 Share Posted June 19 (edited) Looks to be a Ford C-Max or Mazda 3 fuel pump assy listed by CAT for the sigma and duratec, but $40-100 (3M519H307AV) like the ones below instead of $500 plus shipping. ebay pump Another Ebay Fuel Pump Edited June 19 by MV8 Link to comment Share on other sites More sharing options...
11Budlite Posted June 20 Author Share Posted June 20 So I had a little time to do some investigating last night. I had the inertia switch and FP connected, but all the relays removed from their sockets. Connected the battery and the FP runs for a couple of seconds and then shuts off. That's with ALL the relays removed, at least the (6) I can find! The (2) Y/G wires from the inertia switch are wrapped together and travel to the maze of wiring under the ECU. I started unclipping the different harnesses and will see if I can trace where the other Y/G wire goes and maybe I can make some sense of this. Link to comment Share on other sites More sharing options...
11Budlite Posted June 21 Author Share Posted June 21 (edited) I had a chance to do a little more investigating early this morning. I was trying to identify all the relays and the wires that go to the different relay terminals. I have one relay that I'll call #4 that's located on the bottom of the (4) joined relay block on the right side of the passenger firewall. It has the following wires connected to the relay terminals: 86: P/U (Purple/Blue) 85: B/R (Black/Red) 30: N (Brown) 87: B (Black) This has me confused because the black wire at the 87 terminal has continuity to chassis ground. I always thought the 87 terminal was used to send power to the device you were trying to power up. Fuel pump, cooling fan, etc. Is there any situation where the 87 terminal would be hooked up to ground? Edited June 21 by 11Budlite Link to comment Share on other sites More sharing options...
CBuff Posted June 21 Share Posted June 21 (edited) . Edited June 21 by CBuff Sorry pocket post Link to comment Share on other sites More sharing options...
MV8 Posted June 21 Share Posted June 21 I would determine if the ecu E connector pin 9 is getting power whenever the battery is connected and ensure the key is in the off position. You should be able to find this MRFU by touching the ground cable to the battery and listening for the click. The main and fuel pump relays are within the MRFU. It seems clear from the "pistonheads" discussion, so I don't know why you are performing unrelated tasks. Link to comment Share on other sites More sharing options...
11Budlite Posted June 21 Author Share Posted June 21 1 hour ago, MV8 said: I would determine if the ecu E connector pin 9 is getting power whenever the battery is connected and ensure the key is in the off position. You should be able to find this MRFU by touching the ground cable to the battery and listening for the click. The main and fuel pump relays are within the MRFU. It seems clear from the "pistonheads" discussion, so I don't know why you are performing unrelated tasks. Where's the MRFU? Still haven't located it. Link to comment Share on other sites More sharing options...
MV8 Posted June 21 Share Posted June 21 Is it not where John said his was? Next to the fuel tank? Link to comment Share on other sites More sharing options...
JohnCh Posted June 21 Share Posted June 21 @11Budlite checked and it's not next to the fuel tank on the Sigma. Looking at the photos on PistonHeads, it appears it may be behind the engine. Note what looks like the red 12v+ battery cable. Anyone recognize that location? BTW although the PH thread calls it a MFRU, Ford lists it as a fuel pump control module (AU5A-9D370-FC). It doesn't control any other circuits. Link to comment Share on other sites More sharing options...
MV8 Posted June 21 Share Posted June 21 I spy yellow/green wire in the pic above. The module is next to the heater valve. See second page of pistonhead topic, 2019 , 2020 post for the wiring which includes yel/grn. Link to comment Share on other sites More sharing options...
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