I Messed Up- ST SIG HELP
 

Hey guys, I did something stupid. I started my car with the ST SIG 10A fuse still in. I have a DIYPNP V1.5. Which transistor, and possibly anything else, did I most likely fry? I think it is the one in spot Q17 but I'm not entirely sure.

Side note, why does my car only idle when the fuse is in place and not when I take it out? The IAT sensor does go into pins 1 and 6 of the AFR pigtail, yeah?

Cheers!

If this is a '90-'93 Miata, probably the TIP125 in the high side driver section.

Oh, right. I have a '90 with the stock 1.6. I'll check that out in a minute. Is it likely that anything else would be messed up? And what about the IAT sensor pins with the AFR pigtail?

it was working because the AFM controls the fuel pump, since you probably blew the transistor on the MS and it sounds like you still have the AFM in place.

But it also depends if you bought your DIYPNP with that circuit populated/wired or not.

I have removed the AFM. I installed the IAT sensor right by my TB and connected the wires to slots 1 and 6 on the factory AFM connector. Those are the right slots aren't they?

I'm going to take a wild guess here and say that until you replace the damaged transistor on the MS board, the car isn't going to run (with or without the ST SIGN fuse) after you remove the AFM.

With the transistor blown, the MS isn't able to control the fuel pump. With the ST SIGN fuse in, the starter circuit is powering the fuel pump during cranking, then the mechanical switch inside the AFM takes over once there's airflow.

You could work around this problem by placing a jumper wire between pins A and B of the AFM connector, or between pins F/P and GND of the diagnostic connector under the hood on the drivers side shock tower, which will cause the fuel pump to run all the time when the key is on. This creates a potentially unsafe situation wherein the fuel pump will continue to run in the event of a ruptured fuel line.


I am, admittedly, taking some liberty in translating your original post, presupposing that when you say "why does my car only idle when the fuse is in place and not when I take it out?" what you really mean is "why does my car only START when the fuse is in place..."[/i] With the AFM still installed, I'm guessing that you could have started the engine with the fuse in place, then removed the fuse and the engine would have kept running.

Thank you for detailing that all out for me. I will replace the transistor as soon as I can tell which one exactly it is that I blew. Can you help me with that? They all look fine to me.

Also, my AFM is indeed removed and I have installed the IAT sensor by my TB.

And my car was idling last night for a minute or so with the fuse in and the AFM removed. Here is my setup
https://www.miataturbo.net/attachmen...ine=1434468941

TypicalSteve responded to me via PM, which I post here so as to retain one single thread of conversation:

Two options occur to me:

1: The transistor isn't blown, however your ECU was clearly assembled at a shop located directly above an Indian burial ground, or

2: Are you sure about that full minute?

Reason I ask is that once the fuel system is primed and the engine running, it'll take a little while for the fuel pressure to drop and stall the engine while it's just sitting there idling. Not a full minute by any stretch of the imagination, but maybe 10-20 seconds of runtime after the fuel pump is shut off might be plausible before the engine sputtered to a halt.

The car was most definitely on and idling for at least a minute. I then shut it off, though, and it was unable to maintain idle after that. But it did do it once.

Is there a sure fire way to tell if the transistor is blown or not? Shouldn't I be able to test the continuity with a voltmeter or something?

When you key the car on, it should prime the fuel pump for 3 seconds. If it doesn't, that transistor is blown out, and you'll have to solder a new one in, ~$14 from DIY.

If you need the car to run, jumper FP and GND in the diagnostic box. The FP will be on when the key is on, which is annoying, but it'll work.

Okay, that's pretty straight forward. Thanks.

Is there any way to tell if the FP is priming other than just listening to it?

That's pretty much it.

The NB having a returnless fuel system, you can't hear fuel moving under the hood as with the earlier cars. Easiest way is to open the fuel filler and stick your ear against it while someone turns the key on.

its under the green board.

Alright, cool. I will probably order that resistor today then.

Thanks

transistor.

honestly, I'd wire 4O to FP and then jump the wire in my AFM connecter when you install your AIT sensor and call it a day.

I meant transistor... And Okay I will do that and post a pic to verify that it's all correct.

Thanks

FP to 4O puts the fuel pump output to the AFM connector. you then have to jump that pin in the AFM connector to the fuel pump relay itself.

Would that method be better than just grounding the FP in the diagnostics box?

Schematically, it's identical. Less convenient to install, but also less likely to fall out.

I'm still struggling to understand why the engine is running with the AFM removed if, in fact, the transistor is fried.

I couldn't tell ya. I just know that I have the AFM removed with IAT sensor installed to slots 1 and 6 on the connector. Last night, I hadthe fuse pulled out and it idled for at least a minute. I would post a data log but I didn't record one. I can post my tune, though.

Maybe the transistor isn't fried.. But it should be... So I don't know.

FWIW, my miata can and will siphon fuel from the tank, that was with RX8 yellow injectors.

I had the fuel pump relay removed, and it still turned over and would idle but nothing else. I was purposely trying to run the lines dead, twice, two separate times, and it did it both times. I've pulled my charcoal can and honestly have no idea what I've done with it there, it's possible I had pressure in the tank helping feed the fuel down the lines.

My transistor was certainly fried too, like a giant chunk of it missing. I replaced it and pulled the fuse and all is well in the world.

I will take off my sequential module when I get off work and check out the transistor. I will probably just jump the FP to Ground in the diagnostics box (with care so it won't come undone) and call it a day.

Until I get bored enough to buy a new transistor and install it on the board.

I believe it's underneath the sequential board, like all the way underneath on the other side of the DIYPNP.

I don't know how you can't find it, it should be obvious. TIP 125 - high side driver, it's fricken' labeled for you on both sides even.

https://www.miataturbo.net/attachmen...ine=1434487883

yes, cause the MS controls the fuel pump in that config--its how i wire all my 90-93 DIYPNP units

FP jumped in the box means it's always running with key on.

Just to recap, I have a '90 with a DIYPNP and started it with the 10A ST SIG fuse in place- oops. I just jumped F/P to GND in the diagnostics box for now so the fuel pump will come on (and stay on) whenever the key is in the on position.

I am using the attached base tune and it will startup and idle pretty well. I even drove it up and down the street once. I noticed that the car won't produce boost at all. My boost gauge shows me vacuum pressure and the vacuum pressure going to 0 when I give it gas but it will not ever rise above 0.

P.S. I don't know how to post my tune and/or datalog of it idling...

I guess this means that I have a boost leak somewhere... Would having 3mm ID silicone boost/vac lines cause a boost leak? Or is it most likely just tightening down everything again?

you has boost leak.

That would have to be a large boost leak.

Much larger than a 3mm hose.


This may seem like a silly question, but we've been giving very little in the way of hard data and nothing in the way of pictures: Are you sure that the turbine wheel inside the turbo is spinning freely?

Yes, the turbine wheel spins freely. I can either spin it by hand or watch it while I give it gas from the engine bay. It appears to be moving very freely and everything.

I don't have hose clamps or zip ties around any of my boost/vac line connections, though, either. I have them going from MBC to turbo and wastegate, intake mani to BOV, and intake mani to boost gauge. Should I zip tie or clamp those connections? They seemed really tight with the 3mm hose so I didn't bother with it.

P.S. I tried just turbo to wastegate as well. It's a Hallman Pro MBC if that would mean anything to anyone.

its not the vacuum lines. you have a blown coupler or something.

I bought every single one of my couplers new like 2 weeks ago. I guess I could just Tighten all down more?

One of your couplers is off or not tightened enough. I would go and check every single one of them very carefully.

Okay! I'll do that when I get home from work and post an update. Thanks for the help!

I also installed an aftermarket waste gate actuator.. Is it possible that my waste gate flapper door is opening early?

Okay guys, I double checked all of my clamps, couplers, and lines. They all seem very tight. I am still not going over 0 PSI according to my boost gauge when I drive it.

Where should I look to now? I took videos of the turbine, gauges at idle, and gauges under load. Will be on Youtube shortly

Here is the video:

http://www.youtube.com/watch?v=zqt_7...ature=youtu.be

I took everything off and put it all back on today. Boosts safely up to 8 psi now!! THANK YOU ALL SO MUCH FOR ALL THE HELP.

I truly appreciate it.

your car sounded like it was running on 2 cylinders in the video.



you need to l2t.

I can assure you it was/is running on all four. The issue was an exhaust leak where the exhaust housing mates to the manifold. That's why it sounded like a lawnmower and also explains the obnoxious back firing up in the engine bay. I bought locking nuts and those seemed to work.

What does l2t mean?

learn to tune.

your AFR targets can be 10:1 at idle but it's not going to hit it if you don't tell the MS to use EGO at idle. You need to tune your fuel map, im surprised it can even idle that lean (assuming you didn't botch the AFR calibration).

I'm in the process of learning now. Under load, the AFR's look solid IMO. I'm still working on idle and returning to idle. I calibrated my AFR gauge according to the instructions in the manual.

And to be fair, that video was taken with the horrid exhaust leak. The AFR's are a lot better at idle now. I will post a new video either today or tomorrow.

okay, yeah an exhaust leak will throw off readings like that.

I am going to look into AE and the fuel map after work tonight, though. I might be coming back for more tech help! Haha.