5 replies to this topic

[Don]

Hi guys,

My '94 died on me while exiting AMP a few weeks ago. I got it towed back to our spot and ran through a few tests. I could not hear the FP so, removed the FP and tested it on a 12v source, it seemed to be functioning. Jumpered the F/P and GRN connection under the hood and the car started up. A bit later, I started the car again (with the FP/GRN jumper still in place) and the fuel pump relay started smoking under the dash. Weekend over because I could not find another one locally ...

I recently bought a new fuel pump relay, but still no luck. The FP does not seem to be working, no voltage on the plug into the FP, tried jumpering the FP/GRN connection ... nothing. No ECU codes appeared to be stored (jumpered GRD to TEN, engine light came on for a few seconds and then went off when ignition was on). I checked the wiring into the FP relay ... I get 12v on two of the wires and about 1.6v on the green wire when trying to start the car. The 1.6 volts on the green wire does not sound right (from what I have been reading on the Internet), but I am not sure what that means.

What should I be looking at next?


Thanks for any help that you guys can provide.

Don

[jschwarz]

I'm finishing up my car and went through the same things you've checked. FP to GND the relay clicks and the pump goes to work but without the relay doesnt click and the pump sounds like it isnt working. Ive checked the wiring and relays with similar results to yourself. I'm a day or two away from having it ready to attempt a start to see if it does fire. Im told the things are vacuum activated and why it appears not to be working.

I'll let you know what I find

[Brandon]

Hi guys,

My '94 died on me while exiting AMP a few weeks ago. I got it towed back to our spot and ran through a few tests. I could not hear the FP so, removed the FP and tested it on a 12v source, it seemed to be functioning. Jumpered the F/P and GRN connection under the hood and the car started up. A bit later, I started the car again (with the FP/GRN jumper still in place) and the fuel pump relay started smoking under the dash. Weekend over because I could not find another one locally ...

I recently bought a new fuel pump relay, but still no luck. The FP does not seem to be working, no voltage on the plug into the FP, tried jumpering the FP/GRN connection ... nothing. No ECU codes appeared to be stored (jumpered GRD to TEN, engine light came on for a few seconds and then went off when ignition was on). I checked the wiring into the FP relay ... I get 12v on two of the wires and about 1.6v on the green wire when trying to start the car. The 1.6 volts on the green wire does not sound right (from what I have been reading on the Internet), but I am not sure what that means.

What should I be looking at next?


Thanks for any help that you guys can provide.

Don

I've got a '96 and ran into a eerily similar problem last year. When mine went TU, it was the morning after driving it off the trailer after arrival at a track.

There's 2 separate circuits that operate the fuel system on the 1.8s (can't speak for the 1.6s) - one is the relay, the other is the pump.
Each circuit has a fuse - the relay's is in the box under the hood (it may actually be part of the relay itself - can't say for sure), and the pump is under the dash, driver's side. Swapping the relay did nothing as did toying with the injector module or fuse. I didn't think to try the FP-to-GND option to even see if it would start but I imagine it would not have.

Turned out to be the actual pump fuse under the dash. I don't recall the specific fuse number (here's a link to a thread with pics - you'll have to register to view them, sorry: http://forum.miata.n...ad.php?t=388280) but I certainly felt foolish after dropping the car off at the shop nearby only to learn it was a fuse.

So a lost race weekend, coupled with feeling stupid picking up the car from the shop (hindsight being 6'3" meant I probably wouldn't have found it myself regardless) for such a minor repair, I've gone out and invested in these fuses that light-up when blown (I don't believe these are the brand I purchased but representative): http://www.cooperind...tmatcmaxid.html

Best of luck - HTH,
Brandon

[DES4]

Point is: If a fuse blows, it's telling you there's too low of a load on the circuit... is the fuel pump pulling too much current? Blown fuses are symptoms of problems.

[Don]

I checked all of the fuses (I did not have a manual with me at the track to tell what each fuse was for, so pulled all of them).

I sorted out part of my problem ... a previous owner used a '90-'93 relay in the car (which is a '94). For this to work, they swapped the green wire in the relay harness over to the opposite side of the relay plug. I purchased a '94 relay, so it did not work with the modified wiring. After correcting the wiring, the car will start with the F/P to GRND jumper in place ... but not without the jumper. I need to start looking at the ECU and whichever inputs signal it to engage the relay. I borrowed an extra ECU from the shop that built the car, so I'll start with that.

[Don]

I still have not sorted out this no start issue. The car will start with the F/P to GND jumper in place (diag port under the hood). When the jumper is in place, the light green wire from the ECU to the FP relay is grounded (FP runs). With the jumper removed, the light green wire from the ECU to the FP relay shows ~5v (no fuel pump at this point). I have swapped out the ECU and CAS and still no luck. The ECU has to be missing an input signal and not triggering the FP relay, but I have not been able to figure out what it could be. There are no codes stored in the ECU.

Could a bad coil(s) or MAF stop the ECU from engaging the FP relay? I have not tested spark yet (seems like this should have been one of the first things that I tried) ... although I do have spark when F/P to GND is jumped.