vipernicus42

iTrader: (4)

Hey Guys,

So the other day I'm driving along and the whole car dies on me. I pull over and check the engine bay fuse box and my big 60amp main fuse blew so bad that it's blackened! So I look around for any source of a short, couldn't find anything, so I put my spare 40amp fuse in its place. That fuse didn't blow right away so I tried to get the car started.

The car would crank, but wouldn't fire. After troubleshooting ignition for a while, I pulled the plugs and realized they were dry. I gave a few taps of the pedal to shoot some accelerator pump shot, cranked again, and it caught, burned off the gas and died. After a few times the float bowl was empty. I confirmed my suspicion by drizzling some gas down the carb throat, and again it burnt off the gas then sputtered and died.

My Mallory Comp 70 has less than two seasons on it, but I couldn't hear it when cranking (I usually can't hear it unless I have the bin out and I'm really listening for it or I have the door open - both of which were true in this case)

I unplugged the fuel pump to test if any power was getting to the connector during cranking. After blowing the "Engine" fuse in the fusebox under the dash twice because I had my multimetre wires plugged into the wrong spots (the load testing spots) I put a good fuse in there, wired my multimetre correctly and I'm not getting ANY voltage showing at the connector when cranking.

So my pump may be good (or it may be blown) but I'm not getting anything at the connector.

My next test is to hook jumper wires from the battery to the fuel pump to check that it isn't blown, then I have to continue troubleshooting the electrical problem.

As it stands:

1. All fuses in the engine bay and under the dash are OK
2. I can crank it and start it if I supply fuel
3. The fuel pump connector doesn't get voltage when I crank
4. Everything else in the car appears to work fine except my "Media Deck" headunit. I'm assuming this blew its fuse when the main one went, I'll have to take it out and test, but it's not connected to the fuel pump circuit so I'm not too concerned about it.


I can't for the life of me figure out what would blow the main fusible, or why everything now works except the fuel pump. I don't want to have to pull the carpet to start tracing the fuel pump wiring, so what do you guys think? Any ideas?

Jon

Rx-7Doctor

iTrader: (13)

Jon,

The only standard things on your year if you have the fuel pump hooked up to the original wiring from the old pump is that either the fuel pump relay is bad or the trailing ignitor is bad.

I'm sure you probably checked for the tach working or not when you crank?

The only thing that blows a fuse is excessive amperage through the circuit that it is protecting.

Could be a wire shorted to ground somewhere or the pump just died.

vipernicus42

iTrader: (4)

Why would the trailing ignitor affect the fuel pump?

I had thought about the fuel pump relay, I plan to check it tonight if I can find it. According to the FSM it's up under the dash so hopefully it won't be *too* hard to reach.

I replaced the leading ignitor when I thought the problem was ignition related but the trailing ignitor is hard to get to because the alt is in the way. I'll remove the alt and replace it tonight and we'll see what happens!

Jon

gsl-se addict

iTrader: (3)

The main fuse blowing concerns me a bit. Even if the fuel pump or whatever was shorted, it should only blow the fuse in the fuse box inside the car. Power goes like this:
******---------headlight link
battery-------------- main link---alt/fuse box in car
******-----------retractor link

So it goes from battery to the fusible link block. From there is splits between the headlights, retractors, and main. The main connects to the alt and main fuse block.

If anything after the main fuse block shorted, only the fuse in the block would blow (since they are all under 60A..unless you have some circuit that is not protected). This means that your short probably happened between the battery and the fuse bblock inside the car. The battery + terminal could have shorted if the battery isn't strapped down good. Alt coud have a short (or short between the alt output wire and ground). Or could be a short in the wiring between the main link and the fuse block inside the car. My guess would be the battery or the alt/alt wiring.

This could have blown your other fuse too.

Go back and test all fuses to make sure they are good. The fuel pump should have power when cranking or the car running. The fuel pump is controlled by the FP relay. This is in turn controlled by the ECU. The ECU gets it's 'cranking' input from the 'Start' terminal on the ignition switch and gets the 'running' input from the trailing ignitior.

If it was a bad trailing ignitor, I would expect fuel while cranking. I've seen this happen many times. With a bad trailing, you usually can start, it will run for a few mintues (until fuel bowls dry up) and then it dies. So:

1. track down the short so it does not happen again (concentrate your search to the engine bay)
2. test all fuses inside the car
3. check/replace fuel pump relay. You can also just bypass it so the fuel pump runs when the key is in the 'ON' position (like the S1/S2 cars).
4. check spark on trailing. See if tach bounces or pull a sparkplug wire
5. check ECU

vipernicus42

iTrader: (4)

Wow, thanks for the clarification!

My best guess for the short that killed the main fuse is the battery. I've been over the whole engine bay a few times, and the only thing I can think of is if the battery's side-terminal cap jostled enough that the side terminal for + came into contact with the rad mount, it would ground out the + and cause all kinds of not-so-good stuff.

The car did die shortly after a corner, though I didn't think much of it because I was already out of the corner when it actually died.

There is no power to the fuel pump whilst cranking, so that means it's probably not the trailing ignitor. I'll replace it anyway just to be sure.

So...

1. I'll search again, but I think I can just get away with tightening down the battery clamp and adding some electrical tape to the side post covers.

2. All fuses inside the car have been tested for continuity with my multimetre

3. I'll take this as my next troubleshooting step - I'll try bypassing the relay completely to get power to the pump when the ignition is in the on position. I know that the "Engine" fuse in the fusebox under the dash does indeed get power when the ignition is on, so the fuel pump relay *should* be getting power, so I should be able to bypass it and see what happens.

4. Like I said I'll replace the ignitor with one I borrow from Project Keiko and see if that fixes anything. I've got an inductive timing light so that should flash a bit if I'm getting spark through those wires.

5. I'm not sure what to check for the ECU, I don't know how one would go about testing it. I think I'll leave this as the last possible troubleshooting step since I don't want to have to pull the carpet on both cars to swap ECUs just for a test. I'll jump the Fuel Pump Relay first, and go from there.

If it is the fuel pump relay, I'll probably take the one from Keiko and just wire that one up as a bypass S1/S2 style. It would drive me crazy to have my DD wired up that way, but the other car wouldn't be an issue.

Jon

Kerebrus

iTrader: (30)

I kind of have a similar problem.. lately the 20amp fuse that runs power to the fuel pump keeps blowing out. One way I know I can get it blown fast is by drive the car hard which in about 10 minutes it would just die and the fuse would be blown. Although for about 3 days the fuse hadn't blown once until yesterday where it was quite a hot day and after going to the bank, once I got bank in my car it wouldn't start and the fuse was blown, then again about 40 minutes later went to lunch got back in the car and it wouldn't start because it was blown again. We checked how much fuel is going to the carb and it didn't seem like the right amount so my mechanic said the fuel filter is probably clogged which is causing strain on the FP but in previous experiences when my fuel filter was clogged that usually led to excessive bogging due to lack of fuel, which hasn't happened once yet. I personally think it must be the fuel pump?

This is the fuse that keeps blowing:

Kentetsu

Jon, my stereo is tied in with the fuse that runs the fuel pump. You might want to double check.

Also, if the trailing ignitor is bad, then the fuel pump will not run.

Good luck.

vipernicus42

iTrader: (4)

Alrighty, well I got the problem fixed!

It looks like whatever caused the short had enough time to overload a few circuits inside the car before it blew the main fuse. Among the casualties were the Fuel Pump Cut Relay, the fuse that runs my Media Deck, and the fuse for that main "Engine" circuit.

I'm fairly sure that one if not both ignitors got fried since I had to change at least the leading ignitor before the car would start on jerry can gas in that parking lot.


So for those who are interested, here's how I tracked it down.

For good measure, I replaced the other ignitor right off the bat with the second one from Keiko. I did this first since I knew where the ignitors were and how they connected so it was a very easy task to do first. Next I pulled my stereo out in case a short in the wiring there was the culprit. I found that the 10amp fuse that's on the stereo's positive line was blown right apart inside, so I replaced the fuse, but left the stereo unhooked, just in case.

With the ignitors both replaced and the stereo out of the picture, I hooked my multimeter to the connector for the fuel pump and cranked it. No dice.

I had already figured out that when the ignition is in the "on" position the "Engine" fuse in the fuse box under the dash gets power. So I looked to the next part in line - the Fuel Cut Relay.

As the guys covered above, the Fuel Cut Relay is the relay that stops the fuel pump from getting power unless the car is cranking or running. It has 4 wires. Two of them are positive coming from that "Engine" fuse at the fuse box, which carries power as long as the key is in the "on" position (Black/White). One (Blue/White) goes to the fuel pump positive, and the other (Black/Yellow) is the signal from the ECU that tells the relay to close the circuit and let current from one of the Black/White wires go across the relay to the Blue/White wire.

The relay is bolted up under the dash with one 10mm bolt and is surprisingly easy to get at. Here's what it looked like:




Figuring that it was pretty easy to get to the relay, I'd just swap it for the one in Keiko and see what happened. I went over to the parts car, got under the dash and was surprised to find this:



Aparently I'm not the first person to blow a relay! So I stole the jumper wire and hooked it up to bypass the relay. I hooked one of the black/white wires directly to the blue/white wire.

Then I turned the ignition and my multimeter sprang to life, showing 12v on the fuel pump connector. So I hooked up the connector and *Bingo* the pump started pumping.

I started the car and let it run for a little while. It looks like my coolant temp gauge isn't working (thankfully my e-fan and its thermostat are!), and I don't know what else in the car got affected by this. I *still* don't know what actually shorted out to cause this, but here's hoping that I can track down and fix any remaining problems and that this never happens again.

Jon