Red hot fuel pump relay
Discussion
Hello all Hopefully somebody can help me out here. My T350 has been cutting out when i've been driving along. I've finally traced it to the fuel pump relay. When i removed the relay, the pins were too hot to touch. When the relay cools down the car will start. I've ordered a new fuel pump relay but i don't believe that this will cure my problem. I believe that the new relay will also get hot and do the same thing. My question is what would cause the fuel pump relay to get so hot in the first place and how do i go about stopping this from ever happening again? Any help would be greatly appreciated.
Hello Martin
As above, bad fusebox connections will cause overheating, check for this first and if ok see below
Too high a current draw will also cause overheating
Jogging my memory and taking a quick look through Google I think your fuel pump relay powers the fuel pump and power steering pump but I could be wrong and don't have the time right now to delve deeper
If your relay does power both pumps as mentioned above - You need to get someone to measure with an Ammeter what current each pump is drawing through the relay, it would be best to push the correct terminals into the fusebox relays socket terminals 30,87 and the other 87 and measure the current from terminal 30 to 87 and 30 to the other 87 with the engine running
Because it's difficult to get at that relay socket to test things you could add fly leads to those terminals that are to be pushed into the fusebox relay socket and measure the current at the end of the leads that will be more reachable
Those above leads will need to be 30/40 Amp rated cable
Once you know what current each pump is drawing you will need to ask someone what their pumps draw so as to be able to make a comparison or post the current draws to this topic and see what people think
As above, bad fusebox connections will cause overheating, check for this first and if ok see below
Too high a current draw will also cause overheating
Jogging my memory and taking a quick look through Google I think your fuel pump relay powers the fuel pump and power steering pump but I could be wrong and don't have the time right now to delve deeper
If your relay does power both pumps as mentioned above - You need to get someone to measure with an Ammeter what current each pump is drawing through the relay, it would be best to push the correct terminals into the fusebox relays socket terminals 30,87 and the other 87 and measure the current from terminal 30 to 87 and 30 to the other 87 with the engine running
Because it's difficult to get at that relay socket to test things you could add fly leads to those terminals that are to be pushed into the fusebox relay socket and measure the current at the end of the leads that will be more reachable
Those above leads will need to be 30/40 Amp rated cable
Once you know what current each pump is drawing you will need to ask someone what their pumps draw so as to be able to make a comparison or post the current draws to this topic and see what people think
Thank you both for your replies. I checked how many amps the fuel pump was drawing. It was about 5.7 amps. Which I believe is not too bad. Anyway, my new relay turned up this morning. I fitted it and then went for a long drive. I let the car get up to temperature and then pulled over to check if the fuel pump relay was getting excessively hot. It wasn’t. Thank god. I drove around for a bit more and then drove home. I let it idle on the drive. Checked the relay and it was still good. I’m shocked that my only problem was just a fuel pump relay. I expected the problem to be far worse. Like a new fuel pump or a new fuse box. So, now I’m waiting for the next problem to arise. Who knows what it will be but it will be something. Thanks for your help.
really glad it is sorted - 2016 I drove my S1 to Le mans and the hot ambient mid to high 30s did my fuse box in - obviously some loose or dirty contacts heated up and the whole thing started to melt. Thank god for LV Euro Recovery, they flew both of us home and the car came later, best £26 I've ever spent.
I spent the winter fitting a new fuse box
Once sorted just go and enjoy driving it.
I spent the winter fitting a new fuse box
Once sorted just go and enjoy driving it.
Update. My fuel pump relay is still getting red hot and the car cuts out once it’s up to temperature. A few days ago I fitted a new fuse box and hoped for the best. No such luck. The fuel pump relay still gets red hot and eventually the car cuts out. If you leave it 10 minutes the car will start but it will cut out again when it gets warm. What on Earth is going on? Could both fuel pumps be on their way out? Do I have a bad ground from the fuel pumps? If so, where exactly are they earthed to? If this isn’t the problem, what else could it be? Any help or advice would be great.
Another update. I’ve done a voltage drop test on the fuel pumps. I’m getting a reading of 0.8 volts on the positive side on both pumps. On the negative side I’m getting a ridiculous reading of 270 volts. I’ve done the test about 10 times now and it always reads about 270 volts. This is impossible. I was hoping to see readings of 0.5 volts on the positive side and the negative side. Also, something else is happening to my T350. If I leave it on the drive in the sunshine all day and then try and start it, the car won’t start. The fuel pump isn’t priming. If I open the bonnet and let some kind of breeze in there and wait a few minutes the car will start. If I leave it in my cold garage the car will always start without fail. Obviously I have some kind of heat/fuel/electrical problem. I did run a couple of earth cables from the fuel pumps to a decent earth. I was still getting the ridiculous reading of 270 volts on the voltage drop test. On a 12 volt system. So to recap, the car will start and run fine from cold. Once it’s up to temperature and the fans start cutting in the car will just die. It can’t be started for at least 10 minutes until it’s cooled down. This problem is really starting to get me down. I’ve put a new fuse box in, new HT leads, new coil pack, new spark plugs, new relays, re-earthed the fuel pumps. It’s getting to the stage of worst case scenario which is ECU replacement. I’m not sure if they can be repaired by Paul Smith. He has repaired my dash ECU and my dash binnacle. Any ideas what my problem could be? Any help would be fantastic.
Hi David. I’m putting the positive probe of the multimeter on the posits battery terminal. I’m then taking the negative probe and back probing the positive connection of the fuel pump connector. The one under the inspection hatch in the boot. I have two fuel pumps so I’m testing two positive wires. Then for the negative side I’m putting the negative probe on the negative terminal of the battery and then back probing with the positive probe to the negative black wires of the fuel pumps. I have ran two new earth cables from the fuel pump connector to a decent earth.
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