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Electrical Gremlin - Fuel Pump Blowing Fuses - Please Help
So the new alternator is installed. When a multimeter is hooked up to the battery it reads an error. When the battery is at rest it reads 12v.
We found an exposed wire coming from the alternator and going into the loom.
We taped that up.
Started up and still reading error on multimeter when running.
It wouldn’t start after this...no fuel pressure and I couldn’t hear the fuel pump.
Blown fuse. Put in a new 15amp fuse...turned key and blown fuse. Same with a 30amp...click at the fuel pump and instant blown fuse.
Also found a blown 5amp fuse in the ECU.
Any thoughts here? Is my fuel pump dead or shorted? Planning on getting a new fuel pump today and installing tomorrow. When we pull the old one, testing it.
We could use more details about your car in order to help out;
Year, model, 12a, 13b, EFI?
Did you do anything to it? When did this start? What were the symptoms?
Related to your other thread about Alternator problems?
https://www.rx7club.com/1st-generation-specific-1979-1985-18/bad-alternator-help-80-sa-1141323/
1980 12a, 48mm dellorto, MSD ignition, Mallory fuel pump...new optima red top. Has been running like a champ until 2 weeks ago when it died on the way home...just cut off.
Got a new alternator, but it was still having issues. Taking a deeper dive today with a buddy who is a mechanic we started finding issues.
First with the wiring harness from alternator to loom, and then with blown fuses to the fuel pump.
As crazy as this sounds, check your ground connections from the negative side of the battery to A) drivers side strut tower, B) starter long bolt. Also, it's beneficial to run an extra ground strap from the negative terminal to the alternator mount bolt to create a clean ground for battery charging.
Rationale; if the ground at the starter is intermittent or loose, the fuel pump circuit can become the ground, blowing the fuel pump fuse. If you're using the stock wiring, as you should, then the fuel pump has a Circuit Opening Relay which cuts power to the fuel pump in the event the engine dies. The signal for this safety relay is carried across wires too small to function as a ground, hence the fused connection.
if you're blowing fuel pump fuses, it's likely NOT the pump, but this can be easily tested by running 12v to the pump to be sure it's not seized. If you bypass the fuel Pump safety circuit, you may be masking the true problem. Check those grounds, and make sure you have good connections,
That picture of the bare wire looks toasted around the edges. I suspect more electrical issues involved. Stop buying new parts and diagnose this by some of the methods mentioned. Will save you money and time.
Spent 7 hours yesterday, and 2 hours on the phone with GSLSEforme trying to diagnose the issue, and the fuel pump isn't the issue, the short is between the fuse box and alternator.
Cannot thank Mike enough for all of his help.
We have isolated the short coming from the fuse box, specifically the 15amp Main fuse for the ignition. We disconnected all harnesses in the engine and it still lit up a test light with the negative connected to the bottom of the fuse clip and the test light touching the other end. The melted wire is the red/white that is the main wire leading back to the fuse box. The red/white wire does not continue to the alternator after the melted harness which is a possible issue too. Next steps are to peel back the harness from the loom to the fuse panel and from the connector to the alternator to see where the short is happening.
I am not a mechanic and may not be explaining this properly.
A lot of work left, but it looks like we are starting to get a clearer picture on what we dealing with. Electrical problems suck!
Pro-Tip: Add this information to your Signature Line as part of your profile to make troubleshooting easier in the future:
"1980 12a, 48mm dellorto, MSD ignition, Mallory fuel pump...new optima red top." - )Think about adding mileage on your car, plus any other mods you may have done)
Yes, electrical issues truly do suck, because they're often not intuitive and require a lot of effort to track down,
Pro-Tip: Add this information to your Signature Line as part of your profile to make troubleshooting easier in the future:
"1980 12a, 48mm dellorto, MSD ignition, Mallory fuel pump...new optima red top." - )Think about adding mileage on your car, plus any other mods you may have done)
Yes, electrical issues truly do suck, because they're often not intuitive and require a lot of effort to track down,
Still have a lot to learn with electrical diag, but as I was taught this sounds like short to ground issue. Ohm out the power wire for the fuel pump to ground (make sure it is a clean ground to get a good reading), if it reads OL that's not the problem then. Also, being that other fuses were blown, ohm out the fuel pump power to the other circuits - that'll tell you if they're shorted together (which they may be judging by melted insulation). If you do have a short to ground, keep your meter connected and move down the line disconnecting and ohming out connectors until it reads OL, that'll help narrow it down. Same goes for if they're shorted together.
Also, do not ever replace a fuse with a higher amperage fuse. That's how electrical fires can start!
Turns out a previous owner wire the MSD coils incorrectly...the Positive on the Negatives and vice versa causing damage to a coil and causing timing issues. Through researching the wire diagram, I rewired new coils correctly, and voila, no more blown fuses. Fuel pump hums away, and the car runs like its never run before.
I still need to make sure that there isn't an issue coming off the wiring harness from the alternator to the main red/white connection.
Here is what I've noticed right off the bat...the timing was messed up. The car hogging gas, burning a small amount and sending the rest out of the exhaust...no wonder it stunk to high heaven and got horrible mileage! No wonder it bogged down when first started and had to warmed up for 5 minutes before I could go anywhere. No wonder at high RPM in second gear it would sputter...the list goes on and on.
Now it fires right up and I can put it into gear and be on my merry way. The engine seamlessy pulls through all gears smooth as butter and is super responsive at all rpm ranges. I don't smell like I've been on a 1980's pontoon boat all day. It's so much quieter. I filled up yesterday and drove 45 miles and my fuel gauge was just under F...before it would have been at 1/2 a tank.
Things I am going to sort next:
- idle RPMs are high and it appears to be running a bit rich; need to adjust carbs
- getting new plugs
- rewrapping electical and cleaning it up
- getting new suspension bushings
I thought the car drove well when I got it...I was so wrong...I am literally blown away by what this little car can do.
Thanks again for all the help and I know I'll be coming back soon with another list of questions.
01-25-20, 11:41 AM
