1999 Miata with turbo, injectors are run in parallel, they are high impedance 550's out of a turbo FC RX-7, on 4 amp setting.
TOG (currently)? 5.806
IOT (currently)? 0
Minimum on time? 1.5
Injector size? 550 cc/52.373 lb
Number of Injectors? 4
Expected Horsepower? 300 @ crank
Phased or Sequential? Phased
Turbo? How much boost? 15 psi max
MAP sensor BAR? 2
Rev limit? 7400
Running latest firmware and WINTec software. ISC valve is turned off/unplugged per the TEC GT instruction manual. I have tried playing with the bypass screw on the throttle body to no avail (backed it out gradually).
Basically I can crank the car and it will start but will not hold an idle, dies almost instantly. I can ankle choke it, and get it up to operating temperature, but RPMs fluctuate when I do so.
When playing with the IOT, if I go positive, it will maintain an idle around 500-750, but according to the LC1, running crazy rich and acts like it's running on three cylinders. Pulling fuel out of the VE table causes it to start fluctuating and die.
If I go negative with the IOT, the car will fluctuate and die. Holding the throttle, the more negative I go, the more wild the fluctuations get.
Revving it up with the throttle, the car sounds great, makes all the right noises, but when it comes back down it will die unless I hold the throttle, in which case it performs as stated above.
I think I'm missing something very simple, but can't seem to figure out what it is?? Any thoughts?
1999 Miata with turbo, injectors are run in parallel, they are high impedance 550's out of a turbo FC RX-7, on 4 amp setting.
TOG (currently)? 5.806
IOT (currently)? 0
Minimum on time? 1.5
Injector size? 550 cc/52.373 lb
Number of Injectors? 4
Expected Horsepower? 300 @ crank
Phased or Sequential? Phased
Turbo? How much boost? 15 psi max
MAP sensor BAR? 2
Rev limit? 7400
Running latest firmware and WINTec software. ISC valve is turned off/unplugged per the TEC GT instruction manual. I have tried playing with the bypass screw on the throttle body to no avail (backed it out gradually).
Basically I can crank the car and it will start but will not hold an idle, dies almost instantly. I can ankle choke it, and get it up to operating temperature, but RPMs fluctuate when I do so.
When playing with the IOT, if I go positive, it will maintain an idle around 500-750, but according to the LC1, running crazy rich and acts like it's running on three cylinders. Pulling fuel out of the VE table causes it to start fluctuating and die.
If I go negative with the IOT, the car will fluctuate and die. Holding the throttle, the more negative I go, the more wild the fluctuations get.
Revving it up with the throttle, the car sounds great, makes all the right noises, but when it comes back down it will die unless I hold the throttle, in which case it performs as stated above.
I think I'm missing something very simple, but can't seem to figure out what it is?? Any thoughts?
Thanks!
Shane
A couple of questions - what is your timing doing while this is going on? Is it moving around or holding steady?
Also, what is your injector pulsewidth when this happens? Seems like this shouldn't be an issue with 52lb injectors, but it never hurts to check. _________________
Information is not knowledge
Knowledge is not wisdom
Wisdom is not truth
-FZ, Joe's Garage
I can probably help here as I have a very similar setup (although I am sequential on low impedance injectors) it'll be a day or two before I can access my laptop for bin files though. _________________ Steve.
Visit the home of the "slowMX5"
A couple of questions - what is your timing doing while this is going on? Is it moving around or holding steady?
Also, what is your injector pulsewidth when this happens? Seems like this shouldn't be an issue with 52lb injectors, but it never hurts to check.
I've changed the timing map to 14 degrees over all the zones it travels in while the engine is fluctuating. The dashboard reads a solid 14.1 degrees of timing, 3% duty cycle, pulsewidth drops down to ~1.4-1.5 when engine decelerating and a smidge higher when rising up.
The engine RPM fluctuates no matter where I hold it... took it up to 2500 and 3000 RPM with gentle throttle application, still fluctuates just faster/narrower oscillations. Whatever is causing that is the root problem (my guess). The higher I take the IOT the more it smooths out at higher RPM, but low RPM it bogs and acts like it's overfueling. I had it at +0.5 IOT and holding it at 3000 RPMS is almost steady but still fluctuating slightly, A/F mixtures reflect this. Yargh!
I'll do some more checking to make sure that there is nothing mechanically wrong, but I feel like I'm butting my head up against a wall here. What am I missing?? LOL!
A couple of questions - what is your timing doing while this is going on? Is it moving around or holding steady?
Also, what is your injector pulsewidth when this happens? Seems like this shouldn't be an issue with 52lb injectors, but it never hurts to check.
I've changed the timing map to 14 degrees over all the zones it travels in while the engine is fluctuating. The dashboard reads a solid 14.1 degrees of timing, 3% duty cycle, pulsewidth drops down to ~1.4-1.5 when engine decelerating and a smidge higher when rising up.
The engine RPM fluctuates no matter where I hold it... took it up to 2500 and 3000 RPM with gentle throttle application, still fluctuates just faster/narrower oscillations. Whatever is causing that is the root problem (my guess). The higher I take the IOT the more it smooths out at higher RPM, but low RPM it bogs and acts like it's overfueling. I had it at +0.5 IOT and holding it at 3000 RPMS is almost steady but still fluctuating slightly, A/F mixtures reflect this. Yargh!
I'll do some more checking to make sure that there is nothing mechanically wrong, but I feel like I'm butting my head up against a wall here. What am I missing?? LOL!
S
So when the fluctuations happen, what is the injector pulsewidth? If it's dipping down in to the 1.4-1.5mS range (or lower), it could be that the injector spray pattern is getting unreliable. Maybe try setting the min injector on-time to 1.5 or so as an experiment.
I had similar issues with unpredictable mixtures at idle/low loads (I run six 150lb injectors) - sometimes it would be 12:1 sometimes 20:1. I had to bump my MIOT up to ~1.5mS to alleviate the problem. _________________
Information is not knowledge
Knowledge is not wisdom
Wisdom is not truth
-FZ, Joe's Garage
The 99+ Miatas run a returnless fuel system. The pressure regulator is in the tank next to the fuel pump.
The 99 shop manual calls for 53-61 psi at idle measured at the rail... this is quite a bit higher than the 38-42 we're used to seeing on the earlier cars that have a return line, so the injectors are pumping more fuel than expected... to the tune of 20-30%! That would explain a lot of things
I'll test fuel pressure in the morning and see what we've got, but I think this is the problem...
We were reading 62 psi at the rail. We swapped out the FPR out of a 90, which dropped it to 45 psi and VIOLA! Up and running smoothly. At 62 psi our 550's were pumping nearly 670cc worth of fuel
Just curious why your not running full sequential? What is your estimate for peak duty cycle? If low enough wouldn't you benefit from running sequential at idle?
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