PDA

View Full Version : I seriously need your help: M62TU timing



justanewbie
11-12-2012, 01:35 PM
Hi All,

I had to do the infamous chain guides on my car and a friend offered to do this whilst I was working away. He did it all, except he did not use the proper timing tools to re-time the engine.

Anyway, since then, I have re-timed the engine several times, the last time with the assistance of a BMW specialist (using the appropriate tools).

It is now smooth as silk, however, still running rich by way of observing the fuel trims.

From a cold start it goes from 0 to -15 on the Short Term Fuel Trims. The Long Term Fuel Trim is about -13 on bank 1 and -14 on bank 2... not enough to trigger the Engine Management Light but still not great.

Other bits I have done/replaced are:

- replaced 2 front oxygen sensors with new Bosch ones.
- tried another MAF.
- replaced intake manifold gaskets
- replaced vent pipe under intake manifold
- replaced rear crank case vent valve
- replaced fuel filter with regulator.
- replaced the valley pan.
- swapped over injectors from a M62TU 740i facelift.

Looking at the rear o2 sensors, I believe they should be fairly static at 0.45v... I have also tried swapping these for another working set. Could the fluctuating voltage of these be pointing me to a CAT problem?

Any help would be really appreciated!

Timm
11-12-2012, 04:25 PM
The post-cat sensors should show a higher reading (0.5V or so) than the pre-cat sensors (showing that the Hydrocarbons have been combined with Oxygen to produce CO2 and H2O) - but they will still show some movement that follows the pre-cat sensors except that the signal is delayed (showing the oxygen storing capability of the converter).

If the post-cat sensors just follow the pre-cat sensors the catalytic converters are dead.

das borgen
11-12-2012, 04:36 PM
The post-cat sensors should show a higher reading (0.5V or so) than the pre-cat sensors (showing that the Hydrocarbons have been combined with Oxygen to produce CO2 and H2O) - but they will still show some movement that follows the pre-cat sensors except that the signal is delayed (showing the oxygen storing capability of the converter).

If the post-cat sensors just follow the pre-cat sensors the catalytic converters are dead.

but that doesn't explain the running rich portion, which is the real problem there

Timm
11-12-2012, 05:24 PM
Sorry, I only answered this question:

Could the fluctuating voltage of these be pointing me to a CAT problem?

I'll try harder next time!

justanewbie
11-12-2012, 05:36 PM
Thanks Timm.

In so far as the CATs, I am just having a stab in the dark... big guess(!) given the engine has now definitely been re-timed correctly as I have done it myself!

Timm
11-12-2012, 05:41 PM
Well, it's worth trying all possibilities Mak - but I wouldn't say that your fuel trims are that far off to start with.

justanewbie
11-12-2012, 05:44 PM
Approximately -14 Long Term on Bank 1 and 2... I thought -5 to +5 was the 'optimal' range? I am sure I am not far off setting the CEL/EML.

justanewbie
11-13-2012, 07:34 PM
The following is a video monitoring the fuel trims after warm-up and driving a short distance:

http://i115.photobucket.com/albums/n292/justausername2006/th_VIDEO0042.jpg (http://i115.photobucket.com/albums/n292/justausername2006/VIDEO0042.mp4)

Following is focusing on rear (post-CAT) O2 sensor voltages:

http://i115.photobucket.com/albums/n292/justausername2006/th_VIDEO0044.jpg (http://i115.photobucket.com/albums/n292/justausername2006/VIDEO0044.mp4)