96 Taurus - At Wit's End!

[thedalaimama]

Sorry for the long post, but I'm trying to include as much info on possible on what my car is doing and what I have already tried.

I have a 96 Taurus GL Sedan, 6 cylinder 3.0 L Vulcan engine. About 3 months ago, it blew a head gasket and the engine hydrolocked. Mechanic was initially going to replace the engine, but got the engine to turn over and ended up finding that only one of the heads took a hit - there were three small cracks in the valve seat, but no warping and the other head was fine. Had both of them machined and head gaskets replaced, along with new spark plugs, oil change, radiator flush. Two days after I picked the car up, the check engine light started flashing and car began idling rough. Original mechanic didnt have equipment to diagnose and thought it might be a sensor.

Did a quick OBD check, got a reading that cylinder #6 was misfiring. Car only does this when it gets to operating temperature. I had the light reset, and when I ran the car for short trips, the light stayed off and car didn't idle rough...once it got warm, the light came on, started flashing, and idle problems came back. When I drive, the light goes from flashing to staying on steadily.

There is no overheating, no black or white smoke coming from the tailpipe. Oil and antifreeze are both still clean and I haven't lost any of either. Took the car to Ford for a pin-point diagnostic, and they found one plug was cracked, had one bad spark plug wire, and recommended a fuel injector flush. I replaced the plug, the plug wires, got the fuel injectors flushed...and it's still doing the same thing. I've had suggestions from a bad coil pack to something internal. I guess my question is really where do I go next? I just want to find out what the problem is, so I can decide if it's worth fixing. Was wondering if the Ford diagnostic should have picked up a bad coil pack.

Thanks for your time and for reading my post.

[Airjer_]

Maybe check compression on that cylinder when its warm.

[shorod]

Since replacing the plug, plug wires, and the injector flush have you verified the diagnostic code is still for a cylinder #6 misfire? If so, the compression check suggested above is a good next step. Fortunately cylinder #6 is up front and easy to get to. Obviously if the compression results are poor there's not much need in continuing. However, if the compression is good or even borderline, while you have the plug out for the compression check, I'd suggest you swap the plug with a neighbor. Visually inspect both plugs to see if the one from #6 shows evidence of coolant, excess fuel, or looks normal. If you have a spare plug wire that will reach, you might try swapping out the plug wire as well. See if the misfire follows the plug/wire set or stays at the cylinder. If the compression is decent and the misfire doesn't follow the plug/wire, then you're pretty much down to an injector issue. You may be able to borrow a noid light set from your local auto parts store and comfirm that you still have injector pulse when the engine is warm. If you happen to have a handheld oscilloscope you could gain more information by backprobing the injector wiring and checking for pulse with the injector still in circuit. It would be good to get a baseline reading as well so you can compare the pulse amplitude with what the amplitude when everything is running well.

As for whether or not the dealer should have been able to pick up on a bad coil pack, sure, if they were looking for it. However, if they found a cracked plug and bad wire, they really didn't have much reason to pursue it further unless you specifically asked them to test the coil pack and you were willing to pay the extra diagnostic time. Visually inspecting the plugs and wires is pretty easy and quick. Electrically testing the coil pack is not so quick and easy, and also isn't always conclusive.

-Rod

[plymouthsrock]

Anti-freeze is tough on fuel injectors, sounds like it's been narowed down to that. 3.8s were notorious for taking out injectors after a head gasket failure.