Apex MCX fuel pump question

[obr]

I was asked to look at a MCX Apex today, they could not get the fuel pump going. This sled has a true 420hp, and has the extra pump. The extra pump is conected through the contact going to the stock pump. Neither of them will start.

The relay to the pumps is clicking when we put the ignition on, but there's no power to the contact. The relay is closing when the ignition is on, and opens again after some seconds. We tried switcinh the relay from another sled to be sure, but that didn't help.

My next guess was that the wire might have broke, but I have a guestion. Is the relay wired directly through to the contact that comes from the fuel tank, or does the relay go through the MCX box or through the ECU and then to the contact? We did switch ecu's but that did not work...So the only thing left if this is the problem, is the MCX box.

The guys that had the sled, had both pumps running to get all the race fuel out of the sled, the sled had not been started for a season.

 

[vipertonytro]

As far as I know the mcx box has nothing to do with fuel pump power. That comes from the stock fuel pump wire. Did you take a test light and see if the pump is getting power? How about running a jumpper from Bat pos to pump positive? Does pump run then? Then check your ground wire. I have known mechanics who miss this step, just because it has power they think it is okay. Needs a good ground too. Reverse your test light hook negative lead to batt positive and touch light to ground on pump if it doesnt light you have no ground. If you already checked the relay did you test the wire from there to pump for continuity? Process of elimination you will find the problem

 

[obr]

didn't have the time, but will try again tomorrow probably...I know there's no power to the stock pump, the problem is somewhere between the relay and the contact up on the left side to the stock pump. Is it only the wire between there, or some connections that I've missed?

 

[vipertonytro]

Stock fuel pump Harness follows fuel line up on the left hand side of the sled as your sitting on it. Pull the cowling off behind the guage cluster that has four allen head screws. it is the one your ignition switch is on. On the left side there is a rubber wire protective cover. Under it are a multitude of connectors. The fuel pump harness has a connector in there.this is usually where most guys tie in for the aftermarket pump. I would assume a bad connection. Follow the pos wire from aft pump to this point and you will probably find your problem. Good luck

 

[obr]

Thanks, that is the contact where the extra pump is connected, and that is the cotact that has no power....from there it goes into harness, and I'd have to splice the harness to follow it I guess....But between this contact and the relay, there'n nothing more then a wire?

One guy also told me that if there was a block in the fuel somewhere, and the fuel pressure was high, the pumps would not start. So this might also be the problem...

 

[vipertonytro]

Your friend is right if the line is already pressured up the pump would not start However if the line was pressured up your sled would start Get an ohm meter and check continuity from pump wire to wire after pump relay. If no continuity there is a break somewhere in between. Did you run a jumper to the positive wire yet? like I said it is a process of elimination. Rule out the pump first then move on from there.