1.8's with the returnless fuel rail suffer the most because the fuel is trapped in the rail with nowhere to go, and nothing to do but to heat up the injectors until the hot fuel escapes into the engine.

I had to do this on my '99;



it ain't pretty, but it works (for me).

 

Those style injectors (flow force, ID, etc), are the worse, I'm guessing because they're smaller and therefore more prone to heat soak? Not sure. But I've never had an issue with the NA sized injectors, or even the slightly older NB style.

There's a mat based or clt based option, switch to coolant based, since the injectors sit on the head, not in the intake. I believe the last car I tuned had this issue with ~40 MAT readings.

Tune it by watching the wideband once it starts. Really helps to wire directly to the battery. Then just choose a time, around 5-10 minutes, to keep the engine off while tuning. Personally, i shot for 12-13:1. My taper looked like the ones posted here, I just tuned ase percentage. Do this for every 5-15 degrees, however precise you wanna be, or follow your ase table temps.

 

Hmmm...I'll play around with rwayatt's settings tomorrow. In the meantime, I wanted to share that I had the lean condition on startup after the engine had been sitting still for 4 hours in 45* air temps. The CLT was 70* and I figure the fuel couldn't have been any warmer than that. Shouldn't the injectors have been able to handle those temps?

And I'm not saying I disbelieve the problem is with hot fuel hitting the injectors, but I figure these things must be used in OEM installations all the time. I'm guessing that big car manufacturers wouldn't accept fuel injectors that cause lean conditions because the fuel is too hot. People who buy Fords and Chevys in Phoenix expect their cars to run correctly, right?

 

your AIT is not heatsoaked, and your engine is already warmed.

your fueling simplly does not change based on the engine demands.

As you idle and it drops from 17AFR to ~14AFR but the PW remains roughly the same -- in the low 2.0ms range. Youre idling at the same VE table % 57.7 throughout the log and you only have about 5% fuel enrichments from warmup, which as they reduce you actually richen.

So at 1,400-1,300RPM, after the car starts, you're asking for the exact same amount of fuel as 850RPM later in the log.

and why is your spark advance so high? is there any reason why you're idling at more spark advance than the car demands at WOT? Something is telling the MS to add 5° of spark above the already ridiculously high spark table number.

why does your log show 100%TPS during cranking?

why is your battery voltage so low?


I don't believe ASE is your issue. You dont really need it when your car is already warmed up. and it only should last 2-3 seconds.

You richen up as your RPM better matches the fuel that your injecting. So either lower your cranking idle table and targets so the idle duty starts running the car at 850rpm or tune your fuel map so you actually have the fuel required when idling 1200-1400RPM. and then fix your spark while youre at it before you melt your pistons.

 

Y'all are blaming the fuel a lot. Resistance goes up with temperature, injectors are just solenoids. Its more just the injectors heating up on the head and not being cooled until fuel starts pulsing through them. I'm sure the warmer fuel they get at first doesn't help though.

 

this is a legit issue for NB returnless guys.

 

Oh definitely. I'm just worried people will start suggesting fuel coolers.

 

Yeah this ^^ is the root cause. The returnless system acerbates this because the heated fuel in the rail just sits there like a heater until it flushes out (unlike the full-return system).

 

Thanks, Brain. It looks like I've got some trouble in my tune that's goes beyond the fuel temp issues others are seeing. If we need to, I'll start a new thread to drill into my specific issues.

In the meantime, I can't comment on your PW and spark advance questions because I didn't tune those. I've sent an email to my tuner asking him to jump in with those answers. I can answer some of the questions though.

I started and stopped the engine a few times and in this particular case the engine cranked but didn't want to start. I hit the throttle to put the MS in flood clear mode and the engine started.


Not sure about this one. The battery is pretty new. Voltage may have been a little low because of the multiple starts. Voltage looks OK to me once the engine is running.

Glad to hear that. I was trying to match the settings suggested on this thread but the numbers sure seemed strange. Maybe we'll fix the other issues and then dial in the ASE.

I'll let my tuner, Nate, comment on this. Totally agree that I don't want the mixture to be as lean as we're seeing.

 

I started a new thread at Warm restart and idle issues - Miata Turbo Forum -Boost cars, acquire cats. because I don't want to derail this thread about hot fuel injectors.