Blowing the 30A Fuel injector fuse!
 

About 3 weeks ago my car died while sitting at the drive through at McDonalds. Had it towed home and I assumed it was the fuel pump.

Car is a 2000 NB!

1) Swapped the fuel pump to a Deatschwerks 320lph unit and tried to crank it over. No go. :(

2) I tried plugging and unplugged the main relay and it clicked so it's fine.

3) I have swapped over to coil-on-plugs and wiggled the wiring harness to the coils and BOOM! It cranks over and no issues.

4) Fast forward a month my car dies while idling in traffic and causes a 3 mile back up. :(

5) Checked the fuses and notice that the fuel injector fuse popped so I pull another fuse pop it in it's place and that gets me to the parking lot right before the fuse blows again.

6) Tried to replace the fuse again and it blew so I had the car towed home.

Two weeks goes by and I finally had time to work on the car.


1) Disconnected the harness to the coil packs and tried to start it and the fuse didn't blow.

2) Reconnected the harness - Attempted to start the car and it doesn't turn over and the fuse didn't blow.


What gives? Any help would be greatly appreciated.

-B

Doesn't turn over = starter not turning or engine not firing up and running on its own?


For what it's worth, the ignition coils are not powered by the INJ fuse. (Unless you changed the power take-off point when you did the COP conversion)

For the NA, the only thing between the coils and the alternator/battery is the 80A main fuse.

For the NB1, they go through the MAIN, IG KEY and ENGINE fuses.

For the NB2, they go through the MAIN and IG KEY fuses.

But it's pretty much impossible for the coils to blow the INJ fuse on any year.

Starter will turn over and I can smell some gas from the tail pipe so it's getting fuel. But it won't start.

-B

Well, somethin' be all broke up in your engine management, yo!

(possibly two somethings, given the two distinct failure modes.)

The ignition system is *probably* not causing the INJ fuse to blow, unless you tapped power from somewhere other than the stock location to drive the coils.

The fact that when you are getting fuel without ignition (assuming that the INJ fuse hasn't blown yet) points to something else entirely.

Troubleshooting more than one problem at a time sucks royal ass. It's why us forensic engineers get paid what we do. :D

Can you revert back to a completely* stock ignition setup for the time being?



* = 100%, no foolin', bone-stock.



Incidentally:

https://www.miataturbo.net/attachmen...1&d=1367659221

I disconnected the harness to the coils and tried to start the car and the fuse didn't blow. Car is a 2000 NB!

-B

5/5/13 updated!

1) Inserted another fuse, turned on the ignition key to the ON position - Fuse good

2) Try to crank car over - Fuse popped

3) Inserted another fuse, left key to the ON position

4) Jump F/P & GND terminals in the diagnostic port - Fuse blow.

What does this mean? Short in the fuel pump?

How can I test the fuel pump without blowing the fuse?


-B

1) Disconnected the plug at the fuel pump & jumped the F/P & GND terminals. I can also hear the relay under the dash click when I jump the terminals. - Fuse still intact!!

2) Tried to crank the car over with the fuel pump connector unplugged - Fuse still in tact!!!!

Err....I'm assuming I gotta yank the fuel pump and see what gives?



-B

Solved the problem! I feel like a complete dumbass!!!

I yanked the fuel pump and at first everything looked normal till I inspected the wires leading up to the pigtail.

This is what I found!

https://www.miataturbo.net/attachmen...ine=1367822566

When I installed the fuel pump I soldered all of the wires so ensure a secure connection. I also used heat shrink tubing to insulate the wires....what I didn't take into consideration was that the tubing I used was not rated for gasoline! It took about a month for the heat shrink tubing to partially dissolve and short out. :(

So I didn't have chemically resistant heat shrink tubing so I used old school butt connectors to keep the connection tight and insulated. Here is the result:

https://www.miataturbo.net/attachmen...ine=1367822566

Reinstalled the fuel pump assembly, installed the 30A fuse, and jumped the diagnostic terminals. The fuse didn't blow! So I cranked the car over and it started!

Thank GOD for the 30A fuse because a short in the fuel tank means that my little Miata could have blown SKY HIGH!

On the positive side I did discover:

1) A bunch of vacuum hoses that were cracked. This would explain why I was getting sporadic surging and funky idling at times.
2) The radiator hoses were also feeling spongy so those need to be replaced.
3) I also discovered that my valve cover gasket and the PCV valve were shot so those need to be replaced.
4) My throttle body and upper intake manifold was caked with oil so those need to be cleaned.

-B

I'm honestly surprised that more cars don't explode due to wiring faults inside the fuel tank. Speaking as an engineer, the combination of sub-par electrical connections and a seaked vessel full of pressurized hydrocarbon vapors scares the shit out of me.

Seriously, it seems to me that one out of every hundred cars on the road should be pulling an Apollo 13 every single day.