Help P0420

[ysteve]

I have 3.4 and no codes. Nobpdy cant find the problem. I checd alredy everithing and still no power an hard upshift?

[BNaylor]

Originally Posted by ysteve

I have 3.4 and no codes. Nobpdy cant find the problem. I checd alredy everithing and still no power an hard upshift?

Head Scratcher! Just a suggestion but have you started looking at an internal engine problem?

3.4 is known to have flaky intake manifold gaskets. Both UIM-Throttle Body and LIM. Are you losing any coolant?

How about a compression test on each cylinder? Minimum is around 105 psi. Normally good cylinder compression is around 125 - 150 psi. Test is run with all spark plugs removed and with fresh engine oil.

Other possibility is your torque convertor clutch (TCC) not working properly. Maybe it is staying locked up?

What brand spark plug, heat range, and ignition wires are you using?

[ysteve]

No iam not loosing any coolant. I think owner before fix gasket. About spark plug and wires acdelco (brandnew). (fuel and air filter new as well, pcv, cat)
The symptoms is like engine cant breath, like cloged cat. But i put Direct Fit, maybe aftermarket one but this dosent metter. Only thing i newer changed its o2 sensors.
How i can check injectors for carbon. Cause when car is hot i feel little vibration(onthe neutral), dosent idlle smooth (no codes of misfire)

[BNaylor]

Originally Posted by ysteve

No iam not loosing any coolant. I think owner before fix gasket. About spark plug and wires acdelco (brandnew). (fuel and air filter new as well, pcv, cat)
The symptoms is like engine cant breath, like cloged cat. But i put Direct Fit, maybe aftermarket one but this dosent metter. Only thing i newer changed its o2 sensors.
How i can check injectors for carbon. Cause when car is hot i feel little vibration(onthe neutral), dosent idlle smooth (no codes of misfire)

Ok I guess we can rule that out.

Have you tried running any fuel injector cleaner like Lucas through the gas tank?

02 sensor is a possibiity but I doubt it. When accelerating or when power is needed the PCM is in open loop mode which means the 02 sensors are out of the picture (inhibited). They are used at idle after engine warms up to proper operating temperature, cruising, etc. Closed loop mode only.

On the 3.4 you can manually clean injectors by removing the throttle body and upper intake manifold plus anthing else in the way like electrical connecors and vacuum lines. Then you remove each fuel injector rail with the injectors intact. You can leave the fuel supply pressure and return lines connected to the rail or disconnect them. However, once injector is pulled you should put in new o-rings.

Have you checked out the EGR valve and tried cleaning it and make sure passages from exhaust to UIM are not carboned up. Make sure EGR spring loaded pintle is clean and moves freely. Spray pintle with WD40. An EGR valve stuck open could cause loss of power and rough idle. Doesn't always give an error code or SES light either.

Good luck!

[ysteve]

I tryed Two tank with fuel injector treatment. What about EGR i didnt know that, where is location of that bastard?
Thank you. Your help is apreciated.

[BNaylor]

Originally Posted by ysteve

I tryed Two tank with fuel injector treatment. What about EGR i didnt know that, where is location of that bastard?
Thank you. Your help is apreciated.

You're welcome. Important thing is not to give up.

The EGR valve is located between the throttle body and the ignition coil modules. It is that cylinder looking object sitting upright. When called upon it passes hot exhaust gases back into the intake to help reduce certain emissions. There are 2 10mm bolts that hold it to the flex exhaust flange and 2 10mm bolts that hold it to the upper intake manifold. There is one electrical connector. Be careful with it because replacement is expensive. Good luck!

[ysteve]

Thank you. I am gonna check EGR tommorow.
I have one more thing never touchen, its a radiator. Sinse i boght this car, i never flush it. Can it be some heating issue. My gage shows inthe midde between 140-260. Manual says its normal. Its just, when engine is hot you can feel vibration better than on cold.

[ysteve]

Hi BNAYLOR3400, today i checkd the EGR valve and its fine. What else it could be?

[BNaylor]

Originally Posted by ysteve

Hi BNAYLOR3400, today i checkd the EGR valve and its fine. What else it could be?

Good question.

Final suggestion, run a vacuum test if you haven't already done so with an automotive vacuum gauge (0 - 30 hg). Acceptable engine vacuum is nothing less than 15 hg but more like around 18 - 20 hg when good. You can tee off of any intake manifold vacuum line. If your power is that bad maybe the test will show something.

Also, take the engine rpms up to 2500 rpms and hold steady when running the test. See if vacuum slowly drops off below 15 hg or towards zero. It is does then there is a problem possibly a restricted exhaust even though you changed the CAT out. Good luck!

[ysteve]

Thank you. I will answer Satturday.