Help please

Simon, Is it possible that the Oxygen sensor is poisoned? I did not see it on your check list. Might be a good idea to throw a scope on it and not rely strictly on scan tool data. Adaptive strategies can be very deceptive sometimes.

I have not scoped it yet but the scan data was showing 800mv on both sensor 1 and 2 but they don't seem to be fixed there sometime they will show under 450mv, I checked the Heater circuit and that's was ok ,, again it was running fine before head gasket replaced etc.

Hi Simon, I agree with Donny, I've seen many o2 sensor fail after an event like this. In our shop when we're quoting a head gasket repair due to coolant entering the combustion cycle we factor in new sensors.

How would be best to test the o2 before replacing just to prove a point ??

It looks to me like if they are sitting at 800mv you have your answer. That tells the PCM rich. The way diagnostic executives in the PCM work is often counter intuitive. If the sensor is fixed rich the PCM starts adjusting the fuel trim. If that gets out of the limit or "clip" preset in the PCM "Rules" it will generate a code and in many cases a fail safe strategy will take over and substitute a

Thanks for the reply I shall test the o2s when I'm back in work . And I'll let you all know when it gets fixed .

Donny and Scott have both given you good advice. I have seen many coolant poisoned O2 sensors that reported a false rich condition. The PCM relies on the information it gets from its sensors to control fuel flow. If the O2 tells it the system is rich it will reduce fuel delivery to compensate. A quick test to see if the sensor is lying would be to remove it and see if it's dark from all the fuel

Have you tried checking the temp sensors. they can cause a rich condition. Another possibility would be to check the fuel pressure regulator. These are just suggestions

Hi yes the Coolant sensor works fine and shows correct voltages at cold and hot Inlet temp all ok aswell. The fuel pressure is regulated in the tank and fuel pressure is at 55psi with no real fluctuation.

I am not familiar with this model so pardon me if I talk about parts that are not on this vehicle. Make sure that MAF is facing the correct direction. Some MAF sensors can be installed either way. Make sure MAP is connected to correct port. You may want to remove the injector rail and cycle the key. Make sure that the injectors are not dripping un-metered fuel into the intake manifold. Check the

HI it is a speed density engine so no maf sensor. Map sensor works and reads fine and is connected tithe correct port. Tps is all ok. Evap has been blocked and no change. Cam timing checked 5 times and very definite marks, also I scoped cam crank correlation and perfect. All new chain and tensioner aswell. I would have to re check the 5 gas readings again. MaybeI should remove the

o2 sensor test: connect the scope to the signal wire set it to 10 sc screen , you can use scanner but is not responding fast enough, at idle create a vacuum leak the sensor should read lean less than 200 mv and stay there as long as the leak is present let it be some second plug it back the leak ,I like brake booster line I manipulate the amount of leak with my finger , the sensor should go

Hi Simon, Is it possible that a ground was broken or left off the cylinder head? Check the voltage drop between engine, body and battery. Should be just a few tenths of a volt if any. Since it appears the engine ran fine but with coolant loss before the repair, the problem was introduced during the disassembly and reassembly. Go over the steps again. It is likely something is not in place. It

There are only 3 earth wires at the back of the head and all connected and the engine is earthed ok . I will re check everything on Monday when I am back in work . Thanks for all your replys so far guys.

Check for debris/carbon stuck in EGR valve pintle causing EGR valve to hang open. I have found this on two GM models that would not allow it to idle properly. The one had carbon pieces stuck in pintle very soon after a head gasket job. Carbon can get dislodged during a repair like that and get stuck in EGR valve.

Thanks for the reply but it does not have an egr

Simon, Does this vehicle have front and rear O2 sensors? If it has a rear O2 sensor, does it agree with the front O2?

Yes it does ,, I'll have to double check but I think they both read about 800mv but they aren't stuck there, but also don't fluctuate (sensor 1 i mean ).

Hi Simon, MAP can be effected by camshaft timing which you have checked. A slipped reluctor can wreak havoc. A sheared camshaft pin or key are also becoming more common. Some timing gears have a stamped pin that can be flattened on assembly if off some. Some timing components have no key. It sounds like you scoped the CAM/Crank carefully and compared to a known good signal. If the O2 sensors

Thanks for the reply , yes I have triple checked timing and all the keyways for the cams and crank are good and intact and timing is perfect. I shall get some data for you guys when I'm back in work , again thanks people for all your replys.

I WOULD CHECK FUEL PRESSURE AND SMOKE TEST FOR A VACCUM LEAK.

Hello Simon I see there hasn’t been any activity on this post for 2 months. Did you resolve the issue with this vehicle. If so can you please post what the solution was, it may help others with the same or similar issues who look at your post for information. Thanks.

HI. This job is still on going at present , i have found a fractured crank sprocket that could be causing incorrect cam timing but the parts are on backorder so I am still waiting for them . I haven't forgotten lol.

Thanks Simon. An in-cylinder pressure transducer could tell you if the crankshaft timing is off in relation to the marks on the gears.

Yes I know but unfortunately I don't have one at the moment .. as soon as my parts come in fingers crossed it sorts the problem and I will post the picture of the fractured component.

FIXED . fault was incorrect cam timing due to fractured crankshaft sprockets all parts replaced and re-timed and now runs prefect.

Simon, thanks for posting the fix for this vehicle.

This was the culprit.