1997 Town Car - advice needed on vexing miss - p0306 code

[mikeamondo55]

Hello all!
Sorry in advance for how long this will be to describe..... I have a 1997 Town Car Exec series with 145k miles. Her name is "The Mary Todd".... She's been throwing the cat converter code for bank 2, every couple thousand miles for the past 2 years, so I assumed my new engine miss was the cat finally giving up the ghost.... however, after having Monro put a $555 cat on her, she is still missing..... here are the details:

THE MISS: Heading on level ground or downhill, she runs fine. Head up a small hill, cruising in Overdrive, and as the rpms drop, the missing begins. Kick in some throttle or turn off the over drive, forcing a lower gear, and she'll shift down and the miss goes away. Let her shift back into over drive whill still heading up the hill and it returns. Crest the hill onto level ground again, rpm increase and throttle is reduced and all is good..... so it misses under load at lower rpms. BEFORE the new cat, it had gotten quite bad, and included missfires / back fires through the throttlebody, and after being driven on the interstate for an hour or so, or up a steep mountain, the valves would begin to rattle badly. Now, AFTER the new cat, it runs much better,.... but the miss is still strong. The valves however, did not rattle after interstate driving.

THE CODE: I checked the engine codes with a basic scanner and got p0306, missfire detected, cyl 6. Cleared the codes, drove home last night and about 40 miles today, miss getting worse as we went, but still as described above. CEL came back on and blinked at me for a short time. Checked it and the code was the same - P0306. Cleared again, and drove another 40 miles or so, missing the whole time.... no CEL, but I checked for codes and it showed P0306 again.

THE HISTORY: Brand new plugs last week. Fuel filter, air filter and plug wires in late 2010 or early '11... about 25,000 miles ago. O2 sensors - brand new on the side with the new cat... original (Im guessing) on the other. Monro claimed they couldn't get the old ones out and sold me two new ones (without asking, mind you). Total bill (with a 30% off coupon) for psgr side cat and sensors $683. Never going back.

CARBON?: The guy at Monro had seen the misfire codes, so he pulled some plugs, saw some carbon (apparently) and tried to sell me a carbon cleaning for $177.... I declined. The backfiring through the throttle body only occurred for a couple days after the new plugs were put in last week... so how bad could the carbon be?

So.... any suggestions on where to start? In the last two weeks, I've but 1200 into the old girl, and we all know she's not worth too much more than that! But I'd sure like to get another year out of her!

 

[Town]

I don't understand how you can hear your engine intake/exhaust valves make a noise at any speed or load. The valves are silent running. The operating mechanisms can make noise. What you may be hearing is detonation, the pinging sound from an engine that is firing the fuel mixture too early and the shock wave bounces around the combustion chamber doing a lot of damage by eroding the metal.

Your ignition system has a wasted spark feature, it fires two plugs at the same time, one on the compression stroke and one on the exhaust stroke. The exhaust stroke firing is the wasted spark and there should not be enough fuel in the cylinder contents to burn but the intake valve is open for the overlap to intake so if the cylinder does burn fuel then the expanding gasses will have a track to the throttle body. Perhaps a leaking injector richening the mixture.

When you see the check engine light flashing then the misfire is more likely detonation and is very hard on the engine and will damage piston material through erosion and break piston rings, get off the throttle when this happens. Generally the spark plug is not causing the fuel to burn early, it is a hot spot in the cylinder head that could be carbon deposits from excess fuel or oil. Carbon buildup from excess fuel or more likely excess oil being burned.

Carbon on spark plugs that are a week old is not normal. But it sounds like more plugs are involved than just #6. What is your oil consumption like? Can you see blue smoke from the tail pipe on startup or after slowing down then accelerating?

There are several possibilities that might fit your symptoms:
1. bad oil seals on the valves leaking oil into the cylinders and burning to cause deposits that affect engine operation;
2. a bad injector on cylinder 6. Perhaps dribbling fuel into the intake and making the mixture too rich to burn properly. It can be tested or replaced.
3. low compression on the engine in general with cylinder #6 even lower and not able to support proper combustion;
4. sounds like the ignition system is up to date with replacements, the coil packs being the only item not mentioned;

Good luck.

 

[mikeamondo55]

Thanks for the detailed response! As far as the valve noise... Not sure what to say.... Many vehicles I have owned have occasionally presented what I have called valve rattle.... The whole top of the engine makes a noise that is rather obviously the valve train.... Can be related to low oil, but also mistiming, over heating and oil breakdown, etc. either way, its irrelevant.... It was doing that before the new cat was installed and seems to not be doing it now.

The car does not use oil and there is no smoke at any point, so I don't think there is seepage. The injector is a likely culprit..... But would one ,misfiring cylinder create a jerking severe miss, jerking several time a second? I guess even at 2000 rpm, it would misfire over 30 x sec....

Another hint, perhaps. The car is almost out of gas and the miss seemed to get worse the lower the tank got. My Subarus will suffer fuel pump weakness that goes away with a full tank (more pressure).... Ever see anything similar on Town Car's? Where is the fuel pump, anyway? Of course, that should effect all cylinders and not just #6...

How hard are injectors to change? Never done them.....

 

[mikeamondo55]

Oh.... And how do you clean out carbon if its there?

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[Town]

If you are not using oil then cleaning carbon from the combustion chamber should not be a problem. Many carbon cleaning processes are bad for the CATs.

The fuel pump on your car is at the bottom of the tank as per most cars and uses fuel to cool the pump as most cars. Running the car on low fuel is not recommended. Condensation in the tank increases with low fuel levels and moisture is absorbed by the ethanol in the gas to make for poor combustion. You will get bad performance (missing and flat spots and rough running) if this is the case.

The P0306 was caused by similar occurrences on at least two consecutive drive cycles to set a DTC. But misfires occur frequently and can affect driveability and do not get recorded because the conditions are not the same or not consecutive drive cycles.

Attached is the procedure to replace an injector on your car.

Good luck.

 

[mikeamondo55]

Are aftermarket fuel injectors okay, or do I need to go to Ford?

 

[paulgress]

I'll put my 2 cents in. When I had my 96 Towncar, I too had a miss. It ended up being the Coil for that particular bank. Also, a missfire allows unburned gas to exhaust, which will put carbon deposits on your sparkplugs and damage your catalytic converter. So it all adds up. Try replacing the coil.

 

[paulgress]

I'll put my 2 cents in. When I had my 96 Towncar, I too had a miss. It ended up being the Coil for that particular bank. Also, a misfire allows unburned gas to exhaust, which will put carbon deposits on your sparkplugs and damage your catalytic converter. So it all adds up. Try replacing the coil. Oh also, if you have a weak spark, your engine may not misfire on level ground or going downhill, when you press the gas pedal you increase the resistance between the spark gap of the sparkplug, thus requiring more voltage to jump the spark. This also adds up to the coil. I didn't see if you replaced your wires, but this will also cause the same symptoms.

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[mikeamondo55]

Well... looks like the culprit is a bad wire, but I didn't figure it out before I bought a new coil.... ugh. So for anyone with these symptoms in the future..... here are my recomendations.

A missfire in a particular cylinder, generating a P030X code, can be caused by a lot of things, including a bad coil, wire, plug, injector, injector seals, and probably several other things. In diagnosing, start with the cheapest first and SWAP, don't REPLACE!

Today, I bought a new coil and replaced the one corresponding to my misfiring #6 cylinder. I SHOULD have just swapped one coil for the other. 97 and earlier Townies have two coil packs, one in front of each cylinder head. Had I just swapped them, I would have seen the same code and known that both were good. As it happened, I put on a new one, and still had my miss. Just in case I had put the new one on the wrong side, I put the old one I removed in place of the other one, and still had the same miss and the same code. Now I know the coil was good and the plugs were only a week old. That left the wire or a problem with the injector topping the list. I had ignored the wires because they are only 2 years old.... big mistake! I then swapped the number 6 wire with the number 2 from the other side, which was about the same length and drove home. Of course, she was still missing like a bi-otch, but when I checked the code at home.... you guesed it! The P0306 code was now P0302. Misfire on number two cylinder! My two year old wire is toast. Tomorrow, I will change the wires and hopefully that will fix it. If not, my next step would be to swap the plug from six with another one.... should not be necessary, though.

My lessons (I'm sure, very obvious to more seasoned DIY's on here) are thus:
1) Don't assume fairly new parts are okay and fail to test them.
2) Make a list of potential culprits and start checking from the CHEAPEST, not necessarily the most likely.
3) If there is more than one of something on your car... ie spark plugs, wires, coils..... you can SWAP them to figure out which is bad.... and it helps if you have a scanner ($30 at Advance) and the problem identifies a cyclinder.... (obviously, all problems won't create as good a road map as this one did).
4) A cheap code scanner is a god-send. Seriously. Everyone should own one.

Hope this helps others along the way. If it's not fixed with the wires, I'll post a follow up. Thanks for input and help! The Mary Todd shall ride again!

 

[mikeamondo55]

Oh... and a note about the catalytic converter. I did not have to have my Cat changed right now. Monro Muffler, I'm convinced, is a profit center geared toward taking every last dime they can... and if they happen to fix your car in the process, well that's okay, too. In my case, the Cat on that side was bad... she'd been throwing the code for two years... so I was going to need to change it anyway. I'll likely sell her in a year or so, and buyers run from a bad cat code like the car's on fire. It needed done.... it's just that it likely would have been 200-300 less somewhere else. Cheaper parts, cheaper labor... more effort in pulling and reusing my O2 sensors.