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Main Fuel Pump- Shorting?

4202 Views 18 Replies 6 Participants Last post by  bianchi2
The car ran great for 3 trips this morning. I shut it off to wait for a friend, put the key in the on position to listen to music. I started hearing an intermittent electrical shorting sound, like a lot of electricity was arcing somewhere. It's coming from the main (external) fuel pump, and the car won't fire. The "drive relay" under the shelf behind the passenger seat clicks simultaneously.
I had to leave the car at work. Not cool since this is the first time I've been able to drive it in 4 months. Can I rule out that a fuel system fuse has blown since that theoretically cuts the power? Does this sound like "replace the main pump" to everyone else?
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Ok- I just pulled the main fuel pump and tested it on my other car's battery... it's working. Maybe that drive relay then??
The drive relay sends power to the fuel pumps (there are two - the other is inside the gas tank) only when the engine is running (it gets a tachymetric signal from the coil to know the ignition is ignitioning).

The drive relay can go bad but check a few other things first. Is the ignition system working - do you have spark? What is system voltage during cranking? It can sound like it is cranking over OK but if system voltage drops below ~ 10.5V the computers will not power on to send the make spark/squirt fuel signals. Check the flywheel sensors. If one (or both) fail the computer will not know the flywheel (and thus the crankshaft) is turning. It uses those sensors for ignition timing. Remember: no ignition = no fuel.
Ok, so not the relay. The fact that it was clicking probably means it works too, huh? After consulting my Dad (literally the most capable and tech-savvy person I've actually met), I put the fuel pump back in with the intention of trying it again now, as it may have overheated from running the car, then sitting with the key in the on position. If that's not the case, what may have caused the "shorting sound" could be the hose clamp that almost touches the positive connector... I wrapped the clamp and connector in electrical tape just in case. Would have tried to start it then, but I left the Alfa key at home. Figures.
ghnl- I don't have flywheel sensors anymore, and just put in an RML electronic distributor with Bosch blue coil. I'll check for spark again, but it was performing flawlessly before.
The ECU and relays are under the package shelf behind the passenger seat. If there is arcing back there it could sound like the fuel pump.
jcslocum- I thought it may have been coming from there, so I pulled the shelf out. That's when I found that the drive relay was clicking too. The "shorting" sound was definitely coming from the pump though, no doubt.
3 great trips then sit and listen to music with key in "on" position but engine off. Did you check the cranking voltage like Eric (ghnl) suggested?

I know that will not lead you to the arcing sound but might get you running again.
The "shorting" sound was definitely coming from the pump...
I'm not sure what this 'shorting sound' is. IME a short circuit is usually a brief bzzt immediately followed by either a blown fuse (hopefully) or melted wires &/or ruined electrical component (often accompanied by escaping smoke).
I did check the voltage, it's about 13.2 at rest, 13.0 with the key in "on" but not running, and 11.5 during cranking. The sound was a "bzzzzt" sound, followed by a few seconds of silence, then repeat. Identical to the sound of arcing electricity while you connect a battery, but a little louder. I say the sound "was" because it didn't happen anymore after I removed/reinstalled that pump and wrapped the connectors in electrical tape. Unfortunately it's still not firing, but I did find that the plugs are not getting power. Then I checked across the coil during cranking, and it's not getting power either. I also checked the fuel rail... and there's definitely fuel in there. Plenty of it. The fuse behind the passenger's seat is good, but I haven't checked the one that's somewhere under the coil-ish, I couldn't find it and didn't have my shop book.
Then I checked across the coil during cranking, and it's not getting power either.
Across the coil? As in from the positive terminal to the negative terminal? If so, that would explain the no voltage reading.
To check for voltage at the coil, ground one voltmeter lead and the other lead goes on the coil positive terminal. Turn on the key and take a reading.
Thanks Papajam. I checked from POS to hard ground today- 11.5V with key in "on." Same with NEG to hard ground... is that supposed to happen? Can't find anything wrong anywhere otherwise. Seems like fuel is getting to the injectors, power until the coil but no sparks, battery output is good, all accessories work in "on" key position. Here's some pics that probably won't really help, but they're pics and I know BB'rs love that stuff.
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You doing some engine cooking while driving? Looks like you got some French bread bakin away there!
Key On Engine Off (KOEO) coil voltages are normal (although a bit on the low side).
Please verify the coil wires assignments;
coil positive - green/black (Alfa), red to aftermarket ignition
coil negative - yellow, white/black & small white (Alfa), black to aftermarket ignition. The large white wire should be taped up and out of the way.
Papajam- my coil wiring is identical to that except instead of a yellow wire I have a thicker black wire... I will trace it later today. Jcslocum- haha, but if it does it's job, the bread will never toast.
...instead of a yellow wire I have a thicker black wire... I will trace it later today.
That wire, whatever the color, is the RPM signal for the fuel ECU. Easy way to test this is to disconnect the wire at both ends (which means disconnecting the fuel ECU connector). Do a continuity test from the coil end of the wire to pin #1 of the ECU connector.

I'm beginning to suspect that the no spark may lie with the aftermarket ignition...
Ok, I disconnected the big plugin from the computer behind the passenger's seat, then tested from what looks like pin 1 in the diagram I have, then tested the one at the other end just in case, since nothing is labeled in the connector or the diagram. The pics below show my first test point, which read like an open circuit, then my second test point, which read under 0.3 ohms (the wire I was using to reach tested at 0.3 ohms by itself, and I got the same reading from this pin). Last pic shows how my other multimeter lead was connected to the coil's thick black wire to get those readings. I also tried reading from the white wire in case it USED to be yellow, and got no readings.
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I called RML this morning and went through a few checks (including hooking a light bulb to hard ground and the coil negative, then cranking and watching for it to flash... which it didn't). Papajam- looks like you're probably right, I think something shorted and fried my new dizzy's circuit board. I've had an auto-resetting circuit breaker hooked up to the fuse 7 spot for about a year since it kept blowing and I couldn't find the problem. I thought it just controlled the tachometer, but it very well may have caused my current issue (as a side note- I don't think that the RML parts were faulty. I don't want them to get bad press if it was in fact another issue in my car. They are being very helpful with me trying to fix this).
Just to "close out" this thread, here's the end: My Spider has an intermittent short somewhere that is linked to the #7 fuse. I can't find it, partly because it's intermittent. That short seems to be what caused my electronic dizzy to fry. RML fixed and returned it to me, I put it in the car (with no #7 fuse in place now), and she runs great. Now that I have the timing right, there's definitely more power above 3k, and it doesn't taper off by 6k like it used to. :)
just a note here, with a little work you can instale a honda civic in-tank f.i. pump..i have had mine in my car for a year now, works great..
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