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Old 09-08-2008, 09:55 AM   #1
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Default Might need to borrow your spare parts

In the process of fixing the 50 problems I've found so far on my newb Miata project, I'm probably gonna be needing to borrow a few parts soon.

Possibly a PCM, MAF, TPS, and crank PS.

I realize you can test most of these things, and I have tested a few others. Checked resistance at injectors - ok
checked resistance at CPS - ok
watched pulses at cam PS - ok

Seems like there might be a short in the wiring going to the Cam position sensor. Intermittently, if you jiggle the connector w/ key on, you get fuel pump power, and other times you get nothing. The white/red wire is my suspect, as I know it goes to the fuel pump relay. Even w/ the fuel pump relay harness jumped and fuel pump running, the car still wont start. Crank position sensor was found way out of adjustment as well.

Just wondering if anyone was local to me, I'm in Northern KY, 41042 zip.

I'm trying to figure out this basket case. To give a short background, I bought the car not running but already had the turbo on it. Nothing was done correctly, I think the OBX mani is even installed upside down for some reason.... ? WTF?

I'll update w/ what parts I end up needing and hopefully someone can help or I'll even pay shipping to get the parts I need to check if you aren't local. I know even w/ a discount the MAF and CPS are insanely expensive.

Thanks
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Old 09-08-2008, 10:38 AM   #2
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This is for the '96 in your sig, right? Have you plugged in an OBD-II scanner? I'd think there would be some stored codes given what you are describing.

Some advice:

1- Wiring diagram: http://www.madracki.com/miata/wiring.html

2- The white/red wire at the cam sensor does not go to the fuel pump. It's the main switched +12 supply for most of the engine electronics. Pretty much everything except the ignition system, actually.

3- The cam sensor is a dual-output device, it gives both cam position (two pulses per cam rev) and crank position (four pulses per cam rev.) The sensor down on your crankshaft is used for misfire detection only, the engine will run without it.

4- I don't think it's physically possible to mount an exhaust manifold upside-down. The bolt pattern is such that it only goes on one way.
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Old 09-08-2008, 11:09 AM   #3
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It would seem my car is a 1995.5. The title says 96, but looking at wiring diagrams for a '96 in Mitchell OnDemand it shows the fuel pump relay being under the rear of car and if I look at wiring diagrams on a '95 it says fuel pump relay is under sterring wheel (where mine is) but then YES, it has an OBD2 connector and I used my ScanGaugeII to scan it for engine codes and it had none stored. Using the ScanGaugeII I was able to read throttle position setting and it said it was a 10% open while no tension was on it and even after I played w/ the adjustment screw.... at WOT it only read 73% open.

The white/red at the cam sensor does go to the fuel pump relay... it even shows it that way in the link you posted on page 9 of the 1996 wiring diagram. But it says fuel pump relay is under rear of car which is not true on my car, mine is under the steering wheel. The same white/red goes to the injectors and EGR solenoid valves as well as IAC and purge solenoid and to the main relay as you said.

To check to ensure it would read codes, I pulled the crank position sensor and got a code, cleared the code, reconnected the sensor and no codes came back.

The cam sensor passed both tests, 2 pulse and 4 pulse. Although, I believe Mitchell told me to test it use 5 revolutions to obtain the 4 pulse signal from the white wire to ground and then switch to the blue/yellow wire and 4 revolutions got 2 pulses. However it said to test, it tested accurate.

I made the statement about the manifold because the OBX emblem is on the under side... I guess another engineering flaw? haha I hear this thing is gonna crack a lot, I'm really looking forward to welding the holy hell out of it. :(

Last edited by Project84; 09-08-2008 at 11:26 AM.
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Old 09-08-2008, 11:50 AM   #4
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It would seem my car is a 1995.5. The title says 96, but looking at wiring diagrams for a '96 in Mitchell OnDemand it shows the fuel pump relay being under the rear of car
How many wires on each one of your ignition coils? Not the plug wires, but the connector underneath- three or four wires per coil?

Not being specifically familiar with the '96 model, I question Mitchell in this regard. On the later cars, the fuel pump relay (also called the Circuit Opening Relay) is under the steering column, and on the earlier cars it's also under the steering column. I do not think Mazda put the FP relay at the back of the car on any year.

Using the ScanGaugeII I was able to read throttle position setting and it said it was a 10% open while no tension was on it and even after I played w/ the adjustment screw.... at WOT it only read 73% open.

This is not necessarily symptomatic of a TPS failure. They're pretty coarse devices, and as long as it has a low value when closed, a high value when open, and a smooth, transition between the two then it is not likely preventing your car from starting. If it read high all the time, then I could see it perhaps being in flood clear mode. But that's probably not the case here.

The white/red at the cam sensor does go to the fuel pump relay... it even shows it that way in the link you posted on page 9 of the 1996 wiring diagram.
Ok, I phrased that badly. My point was that it isn't a control wire or anything. It's just power. And you've already proven that the FP isn't the problem by jumpering it on.

The same white/red goes to the injectors and EGR solenoid valves as well as IAC and purge solenoid and to the main relay as you said.
Yes, and to the ECU as well. It's pretty much the main power feed for all of the engine operating circuits, with the exception of the ignition coils.


It sounds like you know your stuff and are on the right track here. This sort of basket-case car can be tricky. Can we assume that you've already checked and verified that there is in fact neither spark at the plugs nor activity at the injectors? It'd be really ironic if this turned out to be something simple like a clogged fuel filter or swapped plug wires.
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Old 09-08-2008, 12:01 PM   #5
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checked for plug wire location and all were correct, checked spark on each wire, had great spark. Coils have a 4 wire connector BUT only 3 wires feed into this connector. The main blue wire has been cut and bypasses a harness before entering the coils, I'm guessing it was shorting inside the harness so someone just jumped around it. DIdn't check coil resistance, although like I said, spark is there for sure.

I haven't checked fuel pressure but pulled the feed line on the passanger side below the intake and it had some mega pressure on it. Replacing fuel filter today probably anyway. NOTE: Should I get some more worm-gear clamps for all the fuel lines now that I have the 190 HP installed? The rubber lines swelled nicely (kinda scary) when FP was running.

One thing to note is that the times I got the FP to run intermittently by jiggling the cam position sensor connector I could feel all 4 injectors firing at once. Makes sense too because if there is a short in the white/red wire somewhere, it does tie into the FP relay and each injector. I'm just not clear and why even when the FP was running the car still wont start. Seems like there is going to be more then 1 problems beneathe all this. Which is why I'm asking to borrow a PCM because I know at one point someone had the EMB hooked up and the previous owner said he removed it to try to get the car running thinking it was causing problems. It has the plug & play harness, so no wiring was hacked back there.

Thanks for all the interest in my problem, I appreciate the input.

Also worth noting is the car will start on starting fluid... and yes, I've used it wisely and not just dumped it into the intake and fired it up. lol Wondering now if I have 12 volts to the injectors... I wonder if the ground in the PCM is causing problems?
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