O2 sensor fluctuations, MAP sensor reading wrong?

[b_rinner]

Attached is the tune i currently have and the log from a run using that tune. If im missing things please tell me but what immediately jumps out at me is that during idle, after a rough startup, the 02 sensor readings start fluctuating pretty wildly and that once i give it alittle throttle, the boost gauge starts reading ~1.2psi (reading above the throttle blade) but the MAP sensor (a 2 bar sensor) reads ~40kPa. Are those normal things and/or have i missed something in the tune (more likely).

6 adjustments to airflow taking away airflow numbers 6.hpt
log from tune 6.hpl


vehicle info is a 383 sbc, with 48lb/hr injectors, procharger, 91 octane pump gas.

[twenglish1]

What is the part number of your MAP sensor? Need to start with making sure the MAP Sensor Linear, and the MAP Sensor Offset parameters are set correctly. Are you talking about the O2s switching from below 480mv to above 480mv? As in how closed loop fueling feedback normally works? Going to need the fuel injector part numbers as well, and you are using a vac/pressure referenced regulator, correct? It is likely starting rough because your VE and MAF need work, and it starts running better once the O2s warm up and closed loop control starts making corrections.

[b_rinner]

MAP sensor part number ECC1175 from advance auto

As for the O2 sensors, i just wonder if the switching back and forth is not normal, or something that i havent done correctly with the tune.

The injectors are from fiveomotorsports.com and they are apparently delphi injectors. (see attached injector info sheet...of which i dont really know what to do with)
injector sheet.jpg

Correct, the regulator is vac/pressure referenced (came as part of the procharger kit) and fuel pressure is 60-61 psi.

[blindsquirrel]

This is what happy, healthy narrowband O2s look like in closed loop:
screenshot.22-04-2025 22.14.55.png

You don't know what to do with that injector data because it's not what you need to work with the factory PCM. Quality injectors cost more for a reason, it's not just profiteering. If you can decipher what the Delphi part number is, and they are unmodified Delphi injectors, you should be able to find real data for them (but depending on what they are, it may not be in GM format). If not, just cross your fingers and poke some random numbers into the tune. Maybe roll some dice? I don't know. Don't buy mystery injectors only to find out after they have your money that they don't have full data available.

Also stop buying house-brand electrical parts from the corner parts store. These days even real genuine brand name electrical parts from reputable sellers are a crapshoot, the rebranded bottom of the barrel offshore crap... you're punching yourself in the face. Just stop.

[b_rinner]

This is what happy, healthy narrowband O2s look like in closed loop:
screenshot.22-04-2025 22.14.55.png

........Also stop buying house-brand electrical parts from the corner parts store. These days even real genuine brand name electrical parts from reputable sellers are a crapshoot, the rebranded bottom of the barrel offshore crap... you're punching yourself in the face. Just stop.

lol ok...thats a fair point...i deserve that.

[Alvin]

The map sensor scalar and offset if it's what I think it is would be 200 and 8 can you find out if what you have cross references to 12615136?

There is a chance the injecotrs you used might have been used in something that you can grab injector data from. Else you'll want to find a different injector. It makes a big difference.

Also with this os. You'll need to delete the map sensor pid in the scanner and add the one for the custom OS. It will say something like Map sensor - 2 Bar

The map sensor pid you are using will only show 105kpa (basically no boost)

[blindsquirrel]

2006 Cobalt 2.0 has two 3-wire sensors with identical package style. I can't find anything for 'ECC1175' that says whether that is the SCIP sensor (1-bar, 19418088) or the BARO sensor (2-bar, 19418810/12615136).

[Alvin]

Easy way to know for sure he's got the correct one is to start the car, log, let it die.. make sure map reads atmospheric

the 2 bar custom OS's won't see map right until the engine starts or tries to start

[b_rinner]

The map sensor scalar and offset if it's what I think it is would be 200 and 8 can you find out if what you have cross references to 12615136?

There is a chance the injecotrs you used might have been used in something that you can grab injector data from. Else you'll want to find a different injector. It makes a big difference.

Also with this os. You'll need to delete the map sensor pid in the scanner and add the one for the custom OS. It will say something like Map sensor - 2 Bar

The map sensor pid you are using will only show 105kpa (basically no boost)

how about i get the 12615136 map sensor and get that done with so I know the correct values?

ill work on getting the correct MAP sensor PID added

[blindsquirrel]

https://www.rockauto.com/en/moreinfo.php?pk=16524721

I think that's the 2-bar because of the applications it lists... if it was the 1-bar it would list all kinds of platforms. I just haven't found any sources that specifically show ECC1175 and which GM numbers it crosses to.

If it is the 2-bar, the settings need to be 200 linear/8 offset. If it's the 1-bar it is 94.43 linear/10.34 offset.

[b_rinner]

ok its been a hot minute but heres what ive done:

I got the AC Delco MAP sensor 19418810 (which i believe is the correct 2 bar map sensor). I set the linear and offset to 200 and 8 and when logging Key on engine off, It reads Barometric of 87 and MAP of 0.

My issue is this, at the exact time of reading 87 kPA, i checked the airport weather station about 3 miles from my location and it said current barometric pressure was ~102kPA. I believe i have done the 2 bar MAP PID selection correctly but why is there the difference? In order for me to get the Barometric reading on vcm scanner to match the true reported barometric pressure...i had to have an offset of ~24......that doesnt seem right? How am i messing this up?

[blindsquirrel]

Weather report barometer is corrected to sea level, it's useful ONLY for seeing trends that come with weather changes. It is not the actual raw uncorrected atmospheric pressure for the location.

https://www.weather.gov/epz/wxcalc_pressurealtitude

Altitude vs Barometric Pressure - Document ID_ 839729.pdf

[blindsquirrel]

This might be useful as well: https://aviationweather.gov/data/met...=KMEI&hours=24

Put your nearest airport code in. Make sure to click the 'decoded' toggle at the top.

edit: nevermind, 'decoded' view should be set in the URL already.

[b_rinner]

05302025 tune 20 run with map 200 and 8 settings 2000rpm showed 2psi boost gauge.hpl

using the links you provided gave me the same barometric pressure.

also, now my concern is that as seen in the above log, when running at ~2000 rpm my boost gauge (located at the intake hat) reads ~2psi and the MAP is reading ~30 kPA.....???? that seems off. Did i buy a crap 2 bar MAP sensor?

[blindsquirrel]

Why would you expect pressure before the throttle blade in the intake tubing to be equal to pressure after the throttle blade in the manifold?

[blindsquirrel]

Also, 'same barometric pressure' means the same as what? Which of the several numbers you've given is the same?

[b_rinner]

Ive been doing some reading of other post with similar questions...let me see if i understand this correctly. With a supercharger:


The increased airflow above the throttle blade causes a pressure increase above the blade. Because the engine is running, it is consuming air at a given rate per RPM due to numerous factors. As the throttle blade opens, the supercharger provides more airflow to the manifold. Without the supercharger MAP would be some variation of a vacuum.....WITH a supercharger the MAP should be some variation of positive pressure depending upon how much airflow the engine is capable of consuming. (if the engine can match the airflow exactly from the supercharger, the MAP should in theory be about zero meaning not a vacuum and not a high pressure sitting in the manifold.....IF the engine is being provided with more airflow than it can naturally consume then it backs up in the manifold and shows at a positive pressure......if the engine can consume MORE than what is provided then it causes a vacuum in the manifold and shows as a 'less than zero' pressure)



How much of what I said (if any) is true? (or am i just being dumb?)

[blindsquirrel]

Faulty reasoning, based on misunderstanding. Unless the throttle is fully open, pressure will always be higher in front of the blade compared to behind the blade. Even with the throttle fully open there will be some pressure drop because the throttle body itself is a restriction, even if the blade & shaft were completely removed.

What kind of device is measuring your 'boost' pressure, in front of the throttle? Just a Bordon-tube style mechanical gauge? Or a sensor? And if it's a sensor/electrical gauge is it calibrated as closely as the OE MAP sensor and its associated circuits are?

You are leading yourself astray with what-ifs. None of this is how you diagnose a MAP sensor.

[b_rinner]

fair...

the boost is being measured by a mechanical gauge (which can probably be faulted for not being entirely accurate)

[blindsquirrel]

If the supercharger (or turbo, or whatever) is moving more air at 2000 RPM no-load than the engine needs to hold steady with such small throttle opening, then of course there will be much higher pressure upstream of the TB compared to what's in the manifold. If pressures were equal on both sides the engine would effectively be WOT.

'Higher pressure' means the same thing if it's a N/A engine (atmosphere is higher pressure than what's in the manifold) or boosted engine. It's just that the boosted engine can supply higher than normal atmosphere to the throttle inlet. The throttle restricts airflow, the engine's natural state is WOT.