90 Turbo

iTrader: (3)

Ok so I have been chasing a problem with my car.
I have swapped the engine and alsorts of stuff but I think this is just miata stuff.
So the car starts but when I go to rev it it will not rev past 3.5k there is clicking noise under the dash which is the fuel pump relay but it is not stopping for no fuel the car is not seeing rpm's so it does not spark till its back under 3k.

Now here is the funny part if it twist the key to start it will rev all the way. I only did this a few time for worry of my starter but it sure is true.

I got under the dash and the yellow and black denso relay attached behind/on the steering colum is clicking when it hits the 3k and the tach zeroes out but I believe that is the fuel pump relay could it being bad cause this?

Or is it something with the ignition key switch.

Savington

iTrader: (31)

It's a fuel related issue. When you turn the key to start, it jumps the FP relay and blips the fuel pump (since the stock car relies on airflow to run the fuel pump).

90 Turbo

iTrader: (3)

why would the tach on the dash and the Tunerstudio go to 0 much quicker than the actual engine and why does the o2 not show lean.
A fuel pump relay is 90 bucks. Not cheap.

90 Turbo

iTrader: (3)

Here is a log I thought it was the Cas triple checked the extended wire and swapped it with a working spare same exact thing 3k then it dies. I thought about buying another till I noticed how much it reved with start switched on.

Savington

iTrader: (31)

Jumper your fuel pump and see if that fixes the problem.

90 Turbo

iTrader: (3)

Thanks for your help Savington I really appreciate it.
So are you saying I jump something inside the diypnp or inside the relay?
If inside the diypnp could you please be more specific what do I jump to what.
12+ to fuel pump pin or something

Savington

iTrader: (31)

Jump FP to GND in the diagnostic box.

Joe Perez

iTrader: (8)

Sounds like he doesn't know about the box.

Raise the hood, and look around the area of the driver's side shock tower. You will find a little black plastic box, about 1.5" square. Flip the lid off the top and you'll see a bunch of terminals, and a printed legend on the lid.

Locate the two terminals labeled FP and GND, and stick a jumper wire between them. You'll know you've got it when you can hear the fuel pump running with the key on but the engine not turning. Be careful in there- you can blow **** up if you jumper the wrong wires.

Start the engine and see if the problem has gone away.

FWIW, the relay itself is almost certainly working fine, presupposing that you're right about this being strictly RPM-related.

90 Turbo

iTrader: (3)

well this is the wierdest thing. I loaded an old tune and it was working but the tps was not set right so I used the tps calibrater and then it died and now will start but not run and it is very lean now. So I will check presure tomorrow and replace relay if needed.
Just makes no sense something in the diypnp is not controling the pump right maybe?

90 Turbo

iTrader: (3)

Fuel pressure is there. I sucessfuly tested the fuel pump with the jumper. The pump real burdens when I squeze the return with pliers.
I will reload firmware and see if that gets the injectors firing in the morning.

redrider706

iTrader: (4)

What all did you change since the car ran well last time? Did you change the crank and cam trigger setup? I had a similar issue when I went to a 01+ setup from a 90. The issue was the polarity of the "Ignition Input Capture". I had to flip it and the car started to run smoothly and rev good.

90 Turbo

iTrader: (3)

OK same as before will start but the second you disengage starter it dies.
Rev with starter engaged it revs.

Braineack

iTrader: (62)

But was the Fuel Pump jumper still in place?

90 Turbo

iTrader: (3)

Yes the jumper was in. I specificly tried it that way to take it out of thing that could be causing this.
Does the diypnp even know I am turning the key to start. It is my understand that the computer knows I am cranking because the rpm is below what I set 350rmp for me.
Anyway all the same leave the starter engaged and the car runs all the way to 7k.

Braineack

iTrader: (62)

the MS knows you're cranking if your RPM is between 1 and the number you have set as the cranking RPM.

unsure how the starter can be engaged and you can rev to 7K...doesn't that cause "awful death noise"?

is it maybe possible your ign. switch is not switching power correctly?

90 Turbo

iTrader: (3)

Brain that is what I am thinking its the only thing that makes sense is the key ignition is bad or something.

90 Turbo

iTrader: (3)

Wait I missed redriders comment so you are saying change ingition input caputre in Ignition options tab to falling edge?
Is there any chance this will hurt anything?

Joe Perez

iTrader: (8)

Just as an FYI, the reason we were telling you to jumper the FP relay:

On the 90-93 cars, the FP relay is normally driven by a mechanical switch closure inside the AFM, not by the ECU. This switch closes whenever any airfllow at all is moving through the sensor. But during cranking, there is no (or very little airflow), so these cars also were equipped with a wire leading directly from the starter circuit to the FP relay, causing the relay to close whenever the starter is turning.

Now, in the MSPnP configuration we assume you have removed the AFM, and the MS is driving the fuel pump relay directly. (DIY did a neat hack to make this possible, and it's this hack which requires that the ST SIG fuse be removed on all '90-'93 cars running an MSPnP or DIYPnP.)

The theory was that the MS was, for some reason, shutting off the fuel pump. Given that you describe this problem as being RPM-sensitive, and ALSO cured by turning the key to start, it's still the only logic explanation I can think of. (RPM sensitive points to the ECU in general, and fixing it by turning the key to start suggests the fuel pump, as this would be driven by the starter circuit.)


However, I just double-checked the wiring diagrams for the '90-'93 Miata, and the location of the ST SIG fuse is such that its removal would break the path between the starter circuit and the fuel pump relay.

Which leads me to ask: You DID remove this fuse before ever operating the MS in the car, correct?

90 Turbo

iTrader: (3)

Yes the fuse is missing for sure. I had a buddy helping me with the car and he kept saying I needed a fuse there.
Thanks for your help with this guys.

I figure either the starter engage forces the ground to be solid or the key ignition is messed up. I found a link to a cleaning guide I am going to try tonight:
Cleaning the Ignition Switch (1990)

90 Turbo

iTrader: (3)

My question is when it was doing the 3k limit earlier it was the fuel pump relay that was clicking when it hit 3k so is it possible I am getting a intermiten power problem to diypnp or inside it?