Carloverx

Hey all, I'm finally tuning my car for power and seem to be prematurely maxing my injectors. I suspect it's either a tune issue (i'm new to this), or, albeit less likely, a issue with the combination of parts.

Note:

1. My MAP SENSOR is reading very high compared to my in-car boost gauge. You'll see 19+ "Boost psi" below, while my gauge never surpasses 15.
2. I'm trying to dial the car in on the street as best as possible before heading over to a dyno sometime in the near future.
3. Feel free to provide any additional thoughts outside of the primary injector question.

Setup:

1. 99 Miata Newly built 1.8 with low comp (8.5:1) pistons and Manley Rods
2. DIYPNP running speed density
3. GT2871R (essentially a China charger)
4. Flow Force 640cc injectors (oem rail, pump, etc.).
5. Stock 4.3 rear with a 6 speed trans and a (temporary) 195/45/15 tire
6. Timing map is a slightly tweaked version of Braineak has used on other cars (it's my start point for now).

As you can see, according to the Virtual Dyno, the car is making well under 250hp. (Remember, low comp pistons and it's all a work in progress). I'll continue to manipulate timing and boost as I become more comfortable, but in the mean time, why am i maxing my injectors?

18psi

iTrader: (76)

it calculates duty cycles based on all the injector parameters and fuel requirements you input into the tune. and the map sensor is also out of calibration. so this is most likely a tuning issue.

Savington

iTrader: (31)

If the MAP sensor is correct, then you're down to 41psi of effective base rail pressure at 19psi. You could also be maxing out the stock fuel pump.

If the MAP sensor isn't correct, you should stop tuning, because everything you're doing will be down the drain when you finally fix the MAP sensor.

Carloverx

Incredibly quick, concise, and informative feedback! I really really appreciate it (and all your historical posts for that matter).

Tonight/tomorrow I'll thoroughly investigate my MAP sensor calibrations and fuel pump if necessary and will report back with my conclusion/results. Thanks again!

18psi

iTrader: (76)

NP, your minimum vacuum is -9.4
clearly it's not calibrated right or faulty (or the engine is seriously hurt, which is not the case)

Savington

iTrader: (31)

Full vacuum should be ~13-15kpa (~12.5psi).

Carloverx

So, I'm struggling a bit here with getting the MAP sensor to read correctly.

The log above was had its "Common MAP Sensor" set to "MPX4250" (with default values of: 0.0 Volt and 5.0 Volt at 10 and 260 respectively).

• Here're the data points I captured with this setting (PSI based on in car boost gauge):
  1. Engine off: @ 0psi : 98kpa
  2. Idle/Vacuum: @ -18psi : 35kpa (at 1,050rpm)
  3. WOT: @~14.5psi : 210kpa

• Next,I began experimenting with the MAP Sensor 0.0volt and 5.0volt values in tuner studio (creating "Custom" MAP sensor settings).
• Although I didn't make extreme changes it didn't look like adjustments to either would have got me anywhere closer to the 0 to negative kpa i should see.

Question: What other parameters can/should i be adjusting to impact how my MAP Sensor is reading reading pressure?

stefanst

iTrader: (1)

If your MAP sensor is a MPX4250, then the standard settings in TS are correct. If they give you the wrong values, then either your connection to the MAP sensor is questionable, or the sensor is broken. Fiddling with the settings is pointless in this case.

Savington

iTrader: (31)

35kpa is reasonable for idle, but not for overrun.

18psi

iTrader: (76)

where is it tapped into the source?

Carloverx

• It's tapped at the upper/back vacuum source on the intake manifold (borrowed image below)
• It runs across the firewall and enters the cabin in the factory hole in the firewall a few inches from the brake booster.
• Once in the cabin, I'm using a tee to also feed my boost gauge from the same incoming line.

18psi

iTrader: (76)

That port should be fine. But you really shouldn't share the line for the gauge too, at least it's not recommended.

Carloverx

Whelp, I'm still stumped. After giving this a lot of thought, here're the only possibilities I've come to:

1. The map sensor IS calibrated and reading correctly. This likely means:
- The Injectors actually are maxed
- The vacuum signal actually is weak on overrun
- The boost gauge is reading low

(This seems like an unlikely combo, but could something else be causing these there symptoms?).

2. The map sensor itself is faulty. (I'll order another just in case).

3. The Mega Squirt itself is faulty (Reverant built, so unlikely).

4. The voltage running to the map sensor is faulty.

Ugh.

stefanst

iTrader: (1)

I don't see anything in your log that would indicate any trouble with your MAP sensor. Forget PSI. How many kpa when idling? how many with the engine not running?

18psi

iTrader: (76)

Both are posted above

Savington

iTrader: (31)

You maxed the fuel pump. It looks the same as "maxed out injectors" unless you know what you are looking at.

Test it this way: Back fuel in your 210kpa row off by ~5% and do a single pull. If AFRs don't change, back it off by another 5%. If AFRs still haven't changed, but your DC% has dropped by a bunch, then the fuel pump is maxed out.

stefanst

iTrader: (1)

I see 35kpa for idle @ 1050rpm and 98kpa with engine off. Both seem about right. 210kpa at max boost also looks OK. The only indication that there's something off is the boost gauge reading 15psi when the MAP is at 210kpa. 15psi boost would be 203kpa. Close enough.
Just not sure where the perceived MAP issue is...
Also 250 rwhp on VD with 210kpa off a chinacharger on a poorly tuned car with uncertain VD dyno factors doesn't seem outlandish to me either.

I second the fuel pump guess.

Savington

iTrader: (31)

Aha. That log shows a 109% barometric fuel correction and a baro reading of 80kpa. OP, where do you live?

Carloverx

New Jersey (08833)

stefanst

iTrader: (1)

I have FF640s as well and get a PW of 12.5ms and AFR of 12.3 at 175kpa, which is my max.
You get 13.1ms and 11.3 AFR at 175kpa. So that's pretty damn good agreement.
Now at 210kpa I would roughly expect 210/175 * 13.1 ms = 15.7ms , just extrapolating from the lower value. Add 10-20% for reduced flow caused by lower pressure differential and we'd expect 17.3ms to 18.9ms.
You're at 18.7ms and your AFR is up. Your fuel system is maxed out. Convert to return-style system and upgrade pump.