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Old 01-01-2013, 08:43 PM   #1
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Default New build, motor starts but won't stay running

Sorry for the nubular thread. With three little kids running around, and a full time job etc I'm lucky to get out to the garage let alone trouble shoot!

New build. Eagle rods, weisco pistons. FM2. New DIYPNP from a member here. He was running well with ID1000's, and most stuff basically the same as me, so it should at least run a bit.

It primes, starts, and then leans out and dies. It dies more quickly if I'm on the throttle at all. The only way to keep it going or build any revs is to pump the gas pedal.

Gas has been in the tank a while, I'm sure it's not great, but I don't think that can be the problem. Could be a fuel filter, but why would it start like that and the accelerator 'pump' seems to supply fuel.

Any ideas?

Happy 2013!
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Old 01-01-2013, 10:10 PM   #2
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Your goin to have to pull the laptop out and do some sort of tunning. I'm sure the cranking tune is good enough but the after start and idle tune is made for a differant motor. Plug and play is very relative when u buy it from another Miata owner.
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Old 01-01-2013, 10:58 PM   #3
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Ok, thanks. I'm absolutely new to tuning. The way it's acting is so extreme. Almost like its getting no fuel at all other than starting prime (and when I pump the pedal). I'll go in and richen up some values and see.
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Old 01-01-2013, 11:27 PM   #4
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Either:

The req fuel value you have entered is inappropriate for your injectors,

Your VE table is way too lean in the idle region,

Your afterstart enrichment / warmup values are too low, or

Your timing is way off.

First start with a new ECU always takes a bit of coarse fidgeting to get it stable.
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Old 01-01-2013, 11:37 PM   #5
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Also check the IAC startup table. You may have to increase the initial step value since your setup will be slightly different, and it may have been tuned for warmer weather. I'm assuming you are running closed loop.
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Old 01-01-2013, 11:56 PM   #6
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Good point- until everything else is at least close to being correct, it can be helpful to change the idle mode to "PWM Warmup" and just key in some duty cycles in the neighborhood of 40-50%, just to get the IAC valve stable while you work on everything else. Closed-loop idle will get wacky if the fuel and ignition are way off.
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Old 01-02-2013, 04:19 AM   #7
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Can you jump FP and GND and see if that changes anything?

Also, check the vacuum lines to the fuel pressure regulator. If you place your MAP line there, make sure it's t'd, and not stealing all the FPR's vacuum
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Old 01-03-2013, 05:37 PM   #8
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Alright, I'm also going to throw this in the MS EMS part of the forum. With the addition of a proper AIT sensor (GM), getting it running enough to get an initial time on it (10deg), and going to PWM warmup mode for the idle, I've managed to keep the car running long enough to warmup completely. It idles.. sort of.
If I step on the accelerator at all (just a bit or all the way or anywhere inbetween) it richens up and revs for just a moment, then the WB shows it running to full lean and it dies (like two seconds). It reacts the same no matter what the coolant temperature is.
My goal here is to get it to work even just a little bit. And I'm at the 'completely new and pretty much clueless' stage of tuning. I have a little bit of sense though, so here's what I tried: 1/ Could it be reading incorrect manifold pressure? Unplug the vacuum hose, engine quits. Apparently that's working, and it should be since the ecu came off a working car. 2/ Add fuel to VE1. I selected all and increased in increments of 10. The mixture richened, and now it 'idles' at 2000 rpm and 12.0 AFR. Didn't make a difference when I tried to rev the motor. AFR goes to 18+ and it dies. You can feel it take the acceleration enrichment and right after that the pedal feels dead (motor doesn't react to it).

Thoughts: The VE table certainly will need tuning for this car, but I don't think that's the problem. Likewise with timing and IAT temperature. TPS has been calibrated. I probably need to mess with that again as I turned the screw on the throttle body, but it works. Probably not the problem. Fuel filter: Could be, but it runs and gets gas. A clogged filter might mess with things, but it would be more likely under load. Plus, the motor reacts the same if I even just crack the throttle.

Fuel pressure: I'm a little unclear how this is working. It's a 94 with a 99 engine, so I'm using the 99 rail and the 94 fuel pressure thing turned upside down on the end of the rail. Should work.

This whole damn thing is complicated by a military move that is taking me to HI (from Washington state)... Sunday. It will suck to leave this car parked for years.

Anyone know anyone in Seattle that knows miatas and how to deal with MS?
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Old 01-03-2013, 06:00 PM   #9
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I don't have anything to add other than sympathy for your frustration with suddenly having to move. Good luck!!
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