brandboZ28

I bought my 96 WS6 about 4 years ago. It needed some work but after changing the plugs and wires, it ran great until about 6 months ago. The car is modded with LT/dynomouth exhaust and a Pro 5.0. Its got Taylor wires with heat sleeves but otherwise everything is stock. The car is throwing codes for the rear 02's(headers), EGR(headers), MIL malfunction(burnt bulb), and a MAF code. I scanned the car and the MAF reads 5-7 at idle which seems a bit low but Im no expert. Im switching the MAF out with another tomorrow to see if that helps. The car starts up and runs great until it reaches operating temp where it starts to miss/stumble. The O2's seem to be cycling ok and the miss seems to come and go during a wot blast which also leads me to believe that the O2's are fine since at wot, the car goes to open loop but again, Im no expert. Another thing that is puzzling is that at idle, the car will run fine until it hits operating temp and then starts to "tick" out of the exhaust and begins to pop and backfire(loading up on fuel). I thought this would be due to a burnt valve but a compression test showed no such thing. Will a burnt valve always show up on a compression test? Any ideas before I start ripping it apart? Haha. Thanks

my1994z28

I would try replacing the temp sensor in the water pump..I only say this because your saying that once it reaches operating temp you have the problem..The PCM is linked to that sensor,it could be pulling timing causing the stumble.

95zsean

When it reaches operating temp it goes into closed loop and if your Maf or o2's are bad it will run like crap...

The valve will show up on the compression test so its likely no that. And your right about the o2's they are not taken into account when at WOT, so start with the MAF...

Injuneer

It isn't unusual to see the MAF readings 6-10GPS, depending on idle. If the reading is in fact low, check the intake elbow for a tear or the bottom edge off the throttle body. Look for a vacuum leak.

If the exhaust is "ticking" - out the end of the pipe, or in the engine compartment? - an exhaust leak will screw up the O2 sensor.

In general though, it sounds like an O2 sensor problem.

brandboZ28

The tick is out of the back of the exhaust. The engine bay sounds good. Ill inspect the exhaust further but I know everything is welded up so unless a weld broke(which is a possibility), the exhaust should be good. I have the different MAF that Im going to install in the morning and cross my fingers. Ill play with the O2 sensors and temp sensor after that. Thanks guys.

Injuneer

"welded up" - You can't weld the exhaust manifolds (or headers) to the heads - that's where a leak will hurt your O2 readings.

brandboZ28

The MAF didnt fix anything. Oh well. The exhaust manifold gaskets are fine. No leaks there. On to the O2 sensors. Thanks.

brandboZ28

A quick update. I replaced the O2's this morning and there is no change in how the car runs. The low coolant light has come on so the new found thirst for coolant has me a little concerned. Im going to replace the temp sensor since its cheap and hope for the best.

Update to this update. I replaced the temp sensor in the waterpump and also found a vacuum leak on the intake manifold. Still no luck. I guess its time to start digging into it in more depth.

Guest47904

The low coolant light doesn't automatically mean low coolant. You have to actually look at the level. The coolant level sensor is like any other capacitive type sensor. They go bad ALL the time. We have all had a bad one. Cleaning it rarely helps.

Disconnect one of the O2s and see if it then runs ok even after warm. This will prove a control problem.

If so have a look at the wiring that goes down the passenger inner fender where it is covered with foil. If you have headers and the wiring was not moved, it gets cooked under the foil. Mine did just what yours did but never threw a code. Wires were burnt to a crisp.