360 - Misfire Problem - Suggestions?

Hi All,

The car (2000 Yr with 52k) developed a misfire the other day. I was able to establish that the cat on the 5~8 bank was a lot hotter than the 1~4 bank. Slow down flashed briefly a few times and the CEL lit up.

Pulled code - P0152 which is an O2 sensor circuit (upstream bank 2 sensor 1) high voltage.

Pulled all plugs - thought I'd find one or two wet and black but there was really very little between them all.

Swapped all coil packs bank to bank.

Car had been powered down overnight. Started and found misfire still present. Using an IR temp probe I established that cylinder #5 wasn't firing.

Swapped coil between 5 and 6 but 5 still wasn't firing.

Took out and grounded the plug and started engine - spark is present and strong.

Put plug back in and went for a short drive. Cat on left bank got red hot 500c within five minutes. Checked exhaust ports at the manifold and found #5 about 150 degrees Celsius lower than the others on that bank - circa 150c for #5 and circa 300 for the rest. Interestingly the ports at 1~4 were quite a bit hotter, mostly in the 380c range.

Thoughts anyone? Any contributions gratefully received.
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Hi Eddie,

Thanks for your input. I had the inlet manifold off for a heat exchanger renewal a few months ago and all new gaskets were put on then. I've checked all around each of them as best I can with a boroscope (externally) and from what I can see they all appear intact with no sign of discolouration of the paper gaskets.

Unfortunately I can't upload the OBD reports (HTML file not allowed it seems) but I can report that long term fuel trim was at +15% both banks prior to killing power. With just 20 minutes running time since re-boot both banks are in the +3% to +4% range.

Long term fuel trim has historically been in the +10% to +14% range. I put this down to running a more open exhaust than standard. Unfortunately I don't have LTFT history from prior to the installation of the Agency Power exhaust box which was a couple of years ago now.

As regards the brake cleaner test, what do I expect? Car is pretty noisy, particularly on cold start as exhaust rattles and farts a fair bit until there's a bit of heat build up and things tighten up a tad. If inlet leaking do I expect the engine to try to stall or to rev up like it's on nitros?

Cheers!

 

Going to try to post up a bit of the OBD data......

Print screen to Paint and save as Jpeg - might be too small to read.

First report is for bank 1~4 - o2 numbers are 129, 128, 111 and 133.

Second report is for bank 5~8, numbers are 131, 128, 111 and 162.

Unfortunately I know next to nothing as to how to interpret the numbers. My suspicion is that the sensor code error was caused by something upstream which caused the cat to overheat and generated the o2 sensor code.

Good suggestion on the injector. I can certainly try that after I've done the brake cleaner test. Might see if I can blag the loan of a pressure gauge also.
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Eddie, my OBD reader (ScanTool) only connects to one bank at a time. When I connect I get option to connect to ECU11 or ECU14. The first report is when connected to ECU11 which I understand is the 1~4 bank. The second report is when connected to ECU14 which I believe is the 5~8 bank.

Whenever connected the system only ever reports for "Bank1" - I guess it sees the individual ECUs as relating to a single-bank engine.

Appreciate your input!

 

Good idea Aldous, I know where I can borrow one. Might also hear a broken valve spring knocking around in there if there is one! (sigh).

 

I checked back my logs and last time was about five months ago - circa 1,800 miles in meantime. Not an awful lot of miles but a good third of them were on track so she was well-run if not long-run!

 

Reporting back with the solution found……..

I tried the brake cleaner spray check and noticed no difference whatsoever.

I wasn’t at all convinced about the possibility of the injector being plugged given that my cat was overheating which I took to mean that there was fuel being dumped without being burned. However, having taken off the fuel rail previously for another job I knew it wasn’t a biggie so I went ahead and swapped #5 and #6 injectors just to see would it make any difference. It didn’t!

Using a long breaker bar held to my ear, (I’ve ordered a stethoscope Voicey – very cheap as you say), I wasn’t immediately too impressed with what I heard but the noise from the other side was much the same so after a few minutes I determined that there wasn’t anything materially different from side to side.

Back to the spark plug…... I had previously tested by unscrewing it and leaving it to rest against the gearbox. There had been sparks a-plenty and because I was running with a cylinder open I must admit that I did not stand and observe for very long. I went back and tried this test again, but this time I put an old plug into the cylinder and as a consequence I felt easier about taking my time to examine the spark properly. I found that the spark was not jumping from the central electrode tip to the earth electrode as it ought to. If the spark plug was resting on the gearbox there was plenty of spark, using heavily insulated pliers I pressed the spark plug tightly to the gearbox case and the spark disappeared. Release pressure somewhat and again the sparks started. On closer examination (and particularly if I actually opened the gap between the plug and the ‘box), I found that the spark was actually coming off of the threaded section of the plug to the box. I can now only assume that the spark plug is damaged internally and is shorting to ground before it comes to the central electrode tip and that there is/was absolutely no spark at all when screwed down tight into the cylinder.

I then connected the coil to the “old” spark plug I had in #5 and low and behold all is well in my F-car world.

The last time I can recall "needing" to change a spark plug was when I used to ride a two-stroke LC350. Since then, I’ve changed plenty of plugs but only because of service interval etc. I had become so accustomed to plugs basically lasting for ever that I never thought to check it thoroughly until other options had been exhausted.

So, I’m pleased to confirm a happy and very inexpensive ending on this occasion. Sorry to have wasted anyone’s time and thanks to Eddie, Aldous and Tom for the contributions.

Tom, thanks indeed for the offer. I’d have taken you up on it this weekend if I hadn’t gotten to the bottom of it.

Aldous, I get out on Mondello and Kirkistown without a hitch. There's a possibility of a group of us travelling to Anglesea some time in the future. I'm a little nervous about making that trip and being told I'm above noise regs. but I understand that they do hold various muffler bungs on hand for just such eventualities and they do their best to try and get people compliant so as not to waste the day.

Thanks again guys!

 

Cheers Eric!

Thanks Eddie, really appreciate your input.

Hey, no time like the present (or rather the 26th of Next month!).......

Our next outing..... http://octane.ie/forum/showthread.php?t=61851

... and our last ..... http://octane.ie/forum/showthread.php?t=61789&highlight=octane+12

An eclectic mix of vehicles but almost everyone knows each other and there's no messing on track, with respect given by all to others around them. I'm sure I could get you on the list if you fancy!

Edit: It goes without saying that B&B available at my place!

 

Car has been running fine since i threw in the old plug a wee while back but I got around to measuring the fuel pressure today.

Bank 1~4 bang on the money at 50 psi or 3.45 bar

Bank 5~8 a bit shy at 40 psi or 2.75 bar

There doesn't seem to me to be any discernible noise diff between the two pumps (as tested with my new Eur9 stethoscope!) so perhaps it's the regulator?

Thoughts? Wait till it gets worse? Is the pressure regulator a separate part or built into the pump? Are these components serviceable at all?