90 bonneville cam sensor failure

[MERC_DoD]

My 1992 bonneville has an intermittant SES light coming on. I had it scanned and scanner read "cam sensor failure". I replaced the cam sensor but still get the intermitant SES light. What now?

[HotZ28]

Have you checked the magnet in the cam gear? Remove the cam sensor and look through the hole. You may need to turn the engine over to see if it, (if it is still there)!

[MERC_DoD]

I will check in the morning, but would'nt the SES light stay on if the magnet had come off? AND if it did come off what is the fix?

[HotZ28]

Intermittent CELs are common with the magnet failure, especially if the magnet is just damaged and not completely dislodged. If you have high mileage on the engine, it would be best to pull the front cover and change the timing set & tensioner when you replace the interrupter/magnet! Click Here & Here for the procedures.

[MagicRat]

I had the same problem on my Bonneville (3800 V6)

Just a bit of background...... the signal from this sensor is only relevant when the engine is cranking over at initial start up. The ECM uses it to place the EFI into the correct sequential injection routine. Without the signal from the sensor, the EFI goes into a batch- fire mode, where the injectors fire off in groups of 2, instead of sequentially.

Now, in my experience, the batch- fire mode produces slightly more power, with no loss in fuel economy. I suspect that wide open throttle emissions may be slightly higher, though, and the idle was a bit rougher.

I found this out because my cam sensor failure occurred only when the engine is warm, When the engine was cold, the sensor worked properly.
Therefore, cold starts resulted in sequential EFI, Warm starts resulted in batch- fire EFI with the resulting power boost.

So......... I ended up just living with the 'problem', it was easier and more rewarding than actually fixing it.

[MERC_DoD]

Thanks for the input guys...still driving it right now. Have not had the opportuinty to work on it yet. Seems like there are always 10 others things that need doing!

[MERC_DoD]

well there seems to be some rattle coming from that area, and at 244000 miles i guess I should replace the timing chain and maybe in the process I might find the rattle. So lets see... timing kit 72.00, new gasket for cover,maybe a serpetine belt...anything else? I wonder what a shop would charge. I hate working outside in the gravel driveway in the cold!

[HotZ28]

You should call around for some estimates, this is not a "gravel driveway, in the cold" job! In addition to parts mentioned, you will need a tensioner & new interrupter (magnet) along with all gaskets & seals.

[Jrs3800]

Originally Posted by MagicRat

I had the same problem on my Bonneville (3800 V6)

Just a bit of background...... the signal from this sensor is only relevant when the engine is cranking over at initial start up. The ECM uses it to place the EFI into the correct sequential injection routine. Without the signal from the sensor, the EFI goes into a batch- fire mode, where the injectors fire off in groups of 2, instead of sequentially.

Now, in my experience, the batch- fire mode produces slightly more power, with no loss in fuel economy. I suspect that wide open throttle emissions may be slightly higher, though, and the idle was a bit rougher.

I found this out because my cam sensor failure occurred only when the engine is warm, When the engine was cold, the sensor worked properly.
Therefore, cold starts resulted in sequential EFI, Warm starts resulted in batch- fire EFI with the resulting power boost.

So......... I ended up just living with the 'problem', it was easier and more rewarding than actually fixing it.

The Cam sensor is a Cylinder #1 TDC reference, This is a pulse that is used all of the time in conjunction with the crank sensor so that the Engine will run in true SFI mode... Without this say you have a Code 41, the ECM/PCM( depending on year ) will run off the last good known fueling sequence... You might have a point where you start the car and it runs like garbage... Shut it off and start it again and chances are it will run better.. This system does not go into batch fire mode... I have also has this problem on my 91 Bonneville, that gave me the excuse to replace the timing chain too.. I replaced the Magnet with a new GM part.. Not a very expensive fix, pretty cheap in my book..