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Won't Richen on Boost

gottarollwithit

Cooks with motor oil
Joined
Aug 23, 2008
Location
nut Sac, Cali
I've been happily running a 3" exhaust, 36lb injectors, and 15g/19t hybrid for years now. With kids, smog, etc i've decided to revert back to stock.

So, it's wearing all stock sensors, stock injectors, lh2.2 engine management, stock exhaust system, and old 15g.

If i slowly lean into the throttle and bring it up to 7 psi (max stock boost with out an MBC), my AFR's do not richen up. Usually just stays at stoich or leans out a little to 15-16. Also kinda feels like it's bogging when in boost, almost as if timing is being pulled.

Any ideas?? What controls AFR when in boost???


I was under the impression that the MAF keeps it at stoich when not in boost, then the O2 sensor sees my exhaust leaning out when in boost, then richens the mix.
 
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One bit of enrichment you should see is the richening of the mixture on throttle transition. When you open the throttle quickly the change in vacuum going to the fuel pressure regulator is supposed to cause a quick spike in fuel pressure for accel enrichment. Seems like that's not happening. A stuck diaphragm in the fuel pressure regulator can cause that.
 
I think a better way to explain it is:

If I slowly roll into the throttle and boost, fuel enrichenment does not occur.

If I sharply depress the throttle and cause a downshift/rapid increase in engine speed, the rapid enrichenment spike occurs, then quickly goes back to 14ish:1
 
Well that's just evidence that you are supposed to have a performance enhanced Volvo. :cool:

My understanding is enrichment under boost is going to be detected by the ecu. It should get a higher load signal from the EZK and then richen the mixture for high load. It should also be reacting to the Mass Air Sensors increase in airflow.
 
Possible that i damaged the O2 sensor and its not seeing the leaned out mix? Thus its not communicating it to the ECU?.. Or, is 6PSI with a 15g such a small amount of air that my O2 sensor cant see it?
 
The O2 sensor absolutely does not control fueling during boost. The MAF does and the O2 is there for cruise/steady state fueling.

If you aren't seeing boost enrichment, I'd say there's a problem somewhere else.
 
So what does control fueling during boost? I didn’t touch anything aside from the exhaust, turbo, injectors, and maf.

I changed to the greentop injectors? Would injectors from an lh2.4 car matter?
 
So what does control fueling during boost? I didn?t touch anything aside from the exhaust, turbo, injectors, and maf.

I changed to the greentop injectors? Would injectors from an lh2.4 car matter?

The way I understand it, under acceleration the ECU gets a reading from the AMM(MAF) and matches that reading up to a table for air pressure/rpm and uses that to know how much to fire the injectors. As boost rises the fuel pressure regulator also increases the fuel pressure to the rail, adding more fuel.

Did you change the ECU? Is it a turbo ECU?

Is the vacuum line connected to the FPR? Is it good?

Does the AMM part number end in -007? That is a LH2.2 AMM
 
So what does control fueling during boost? I didn?t touch anything aside from the exhaust, turbo, injectors, and maf.

I changed to the greentop injectors? Would injectors from an lh2.4 car matter?

The MAF is an actual reading of the amount of air an engine is consuming...so...

The ECU has fuel maps that are based on load vs RPM, and that load signal is a calculation based on a lot of data (MAF flow, air temp, coolant temp, etc). This is a pre-programmed fuel map that is the 'base' data. The O2 sensor is a modifier that alters fueling during cruise conditions to remain as close to 14.7:1 as possible. When the engine gets into any boost (or very very low boost) the ECU ignores all O2 data and runs off the pre-progammed map. If you're not getting proper fueling under boost, then there's something affecting the ECU's main data, like an improper MAF, dead coolant temp sensor, dying fuel pump, low fuel pressure, too-small injectors, etc etc etc. The O2 is most definitely NOT the culprit.
 
Glad you guys are here to clarify my poor understanding of this.

I find it hard to believe that my MAF coincidentally took a dump at the same time as the reversion. I never changed or touched it during the reversion.

Are there different versions/sizes of the green top b230ft injectors?? I threw in whatever I usually smog test with - not 100% sure they’re the original injectors. They definitely came from a 740 or 940 though.

Yes, FPR has proper vacuum, never touched the turbo ECU, and it is indeed an 007 MAF
 
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