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I have a Chevrolet Lacetti 1.6 gasoline 2007 model and I got error code p0172. This model has not MAF sensor and the MAP seems to be ok. Also with the OBD2 scanner I have LTFT -9% and STFT -27%. The calculated engine load at idle is 43% and both O2 sensors are 0.9V. I changed the upper O2 sensor but still is high(0.92V). Also the car is stalling. I cleaned the EGR valve and the pcv valve is ok. Any help,please?
I would expect to see 18-25%ish for the MAP at idle. @ 43 % the PCM thinks the engine is under load and will fuel for it, but your engine is a idle, so there is a major fuel correction. Do the Fuel Trims improve; ie. go positive with increased load and RPM?
At Key On, what is your BARO PID read?...............................Should should be within +/-1 of what your local weather station states.
At idle what does the MAP PID Read?
BARO - MAP will give you the intake manifold vacuum. You should be 16-21 in HG.
Couple of option, a skewed Map Sensor, or an air leak in the intake.
This is a MAP Speed Density Engine. Any increase in manifold pressure increases the MAP voltage, the PCM interprets this as increased loaded and it will add fuel for it. If the O2's are working correctly they will remain rich and the PCM will start removing fuel.
A vacuum leak would have a raised idle RPM on this engine.
Having Negative Trims and Higher Calc Load at idle on this engine is indicitive of an exhaust restriction, or engine valve timing or tight valves.
It would be nice to know what the how the trims behave with higher engine load and RPM. Do they improve? Or stay Negative? That would give us much clearer diagnostic direction.
Never stop Learning.
Last edit: 5 months 2 weeks ago by Paul P.. Reason: Content
The following user(s) said Thank You: Noah, 70monte
2.Or does it stall put in gear and trying to increase engine rpm?
3.Does the Engine Lack Power?
4.Is there fuel in the engine oil?
5.When snapping the throttle what is the highest you can get the Map Pid? and the CALC LD, want to see min 70-75% CalC Load.
6.If Sensor 1 O2 is reading rich, is the Sensor 2 reading rich as well? (If the second is lean, one of them is not reporting correctly)
7. Engine Coolant level has not gone down?
8. Verify with a scan tool the IAT and ECT are within a few degrees when cold, and that the ECT does get to 180-190 operating temp.
Need a little more data please. The fact that the trims don't change at higher Engine Load rules a few things out.
So far, Fuel Pressure(high), Leaking Injectors, Exhaust restriction, and engine Valve/timing are suspects
1) yes
2) yes, mostly when it is cold.
3) yes
4) I think so.
5) I think 80%. I'll try and come back.
6)They are both high. First is about 0.95 and second at 0.94.
7) I had a little leak from hose that goes to the water canister, so I do not know for sure but I do not think so.
8)Ok. I'll check and come back.
Thank you. It is a puzzle.
At this point to rule out a few things, pull the first O2 and run the engine, it'll be in open loop, but is there any improvement in power and trims? This will rule out a plugged catalytic convertor.
Get a fuel pressure guage and verify the fuel pressure. I do not know the Spec on this system.
Also, the vehicle is Multi Port Injection? Is there a pressure regulator on the fuel rail with a vacuum line? or is there a fuel pressure sensor? It will be the 3 wire variety?
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