solitarycheese

I've been trying to chase down a misfire for a while. The car still runs well, but idles a little rough (misfire can be heard from exhaust and felt in the car).

When it first started happening (March...), I would get a P0301 first, then all cylinder misfire codes (including P1399 and P0300) a little while later. I changed the spark plugs (NGK 7772), swapped coil packs around (no change), and did a compression test (248, 241, 235, and 247psi, respectively).

I was still DDing it when one morning the CEL started flashing. I had it towed to my mechanic, who redid the valve adjustment (was out of spec), and we had the injectors sent off for flow testing and cleaning. One of the injectors was off (I didn't see the report), but was supposedly good after cleaning. The CEL went away and I got the car back.

Now, I can feel the car misfiring again, but I had no CEL until I disconnected the battery. After the idle learn was complete, the CEL (P0304) came back. If I clear it with my scanner, it stays off; however, if the battery is disconnected the CEL will come back shortly but go away and not come back if I clear the code. Short & long term fuel trim is -3% and -1.6%.

At this point, I'm thinking I'm going to replace the cylinder 4 injector...perhaps it was the one causing problems before and cleaning wasn't enough.

The only other thing I can add is I have an intermittent P1457 code - only happens occasionally if the car gets really wet. It doesn't show any symptoms and stays off when I clear it.

franky

Why don't u swap the #4 coil to a different cylinder n see if the cel pops up for that cylinder.

As for the p1457, check the condition of the o-ring on the fuel cap.

Billman250

P1457 is not related to your problem. It also has nothing to do with the gas cap or the fuel tank ability to seal.

Based on what you've done, leakdown would be my next step. Think of a leakdown as a high precision compression test. It will show problems even if the compression is good.

Did you find any tight valves during the valve adjustment?

If that pans out, I'd be looking at which way the fuel trim is leaning. Be sure you complete a few good trips without a ecu reset before you look at the trim.

solitarycheese

Thanks for the advice. I didn't do the valve adjustment and didn't ask my mechanic. Short fuel trim is still at 3%, long term 1.5%.

Weird...CEL turned itself off yesterday after driving ~15 miles with it on, but came back today while idling.

06Estukay

I would take a second look at the valve adjustment. If too tight, the ecu will throw misfire codes.

MM3Kwolik

I would strongly urge you to follow Billmans advice. You more than likely have burnt valves which may have also destroyed the seats and prematurely worn the guides.

I had a 2006 come in on Wednesday with what I had diagnosed as a burnt valve for me to do repairs, turns out 6 exhaust valves (3 out of the 4 cylinders) were severely burnt and had worn the guides beyond the service limit and distorted the seats. Funny thing is that 2 of the 3 bad cylinders showed a perfectly normal compression test. Motor only had 36K miles on it so I suspect this one was yet another DBW car that came from the factory with tight valves.

Replaced the head with a reconditioned unit so that the customer only had to stay overnight once (had originally planned on that anyway), and he's back home now with a perfect running and driving vehicle.

solitarycheese

Are burnt valves something an experienced mechanic could see while doing the valve adjustment? They've seen my motor twice with the valve cover off. I had a valve adjustment done in January when I bought the car. When I took it back to the same mechanic in May, they redid the valve adjustment saying it was out of spec, which makes it seem like they didn't adjust them properly the first time.

xxmass

I experienced some misfire codes. All 4 cylinders and then a few individual. I had been running only Mobil fuel and attribute the misfires to grabbing a few tanks of gas from non Mobil stations. It took 4 ten gallon fill-ups (Mobil) before the misfires ceased. The codes were thrown at cold engine startup and shortly after while also experiencing the dipping idle. I now run with my cabin air fan at three bars and also my running lights on at all times. No dipping idle and no misfires.

I run a Scanguage e. This short term code and dipping idle occurred at 125k miles. Outside air temps at 80+ degrees.

MM3Kwolik

No, burnt valves are only visible with the head off the car, BUT any experienced mechanic can and should be able to properly diagnose them with the aid of a leak down test as Billman had stated. You'll be able to see where those gasses are going (rings, intake valves, exhaust valves, etc). You can have a motor with perfect compression across the board with a head full of burnt valves causing misfires. Is it common? No. Can it happen/Has it happened? Yes.

sillyboybmxer

is it possible to give a "how long does it take" for running with too tight of valves before its too late??
I ask because I had been getting misfire codes, I would reset it and wait for it to appear thinking it was something else as it happened commonly after getting gas, after running fuel injector cleaner, etc. So I reset and reset multiple times and finally found it was coming on at idle only. I got a valve adjustment done and it was fine ever since. 12k miles later and its still good. Just wondering how many times "resetting" and waiting like I did could contribute to the problem of burnt valves.