Misfire Advice

[Ivan_Good]

Ok, I've had a misfire since last Wednesday. It started at the end of a 40 mile trip. Initially at 80mph, it felt like I'd dropped a cylinder. I pulled over, and it was firing on all 6. As I pulled off 1st gear and 2nd felt fine, but the problem became more apparent with each gear change, as the engine was loaded up more.

For example, if I dive at 50mph in 6th gear, and put my foot down, the car will struggle to gain any speed at all. It make no difference if the engine is hot or cold. The only thing tht has changed, is the mis fire isn't as noticable as at first. But is still present, and my fuel consumption has increased slightly.

Its been on the computer this evening, and no faults found. [smilie=icon_cry.gif] [smilie=icon_eek.gif] [smilie=icon_cry.gif] :rollseyes:

I currently have the engine covers removed for access. The best plan I can come up with so far is to buy 3 new spark plugs, and 3 new coils, fit to front, then rear, to prove out possibility of faulty plug/coil. Not what I wanted to do, but cant think of any better idea. (it has just had new plugs fitted)

Anyone got any ideas?

 

[Big Iain]

Sounds like a coil on the way out to me. Fingers crossed its not one of the front three.

 

[Ivan_Good]

Hope it is just a coil, not bother if I have to take the plenum off, I've got all the engine covers off, so only a 10 min job.

 

[Kett]

Coil on it's way out methinks...


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[Redsalive]

I hope it's the coil. I had something similar recently, felt like it was misfiring under load, turned out to be a dodgy fuel pump. There was also no faults logged on the diagnostic.

I'm not sure as I'm crap with anything car related but I think someone mentioned that if there was a genuine mis fire on one of the cylinders it shows up in the history in the diagnostics?

 

[Ivan_Good]

Ok, coils have been ruled out, I've changed them today. As I'm still using the car, over the week the symptoms have slightly changed. Last Wednesday there was a definate significant misfire, under load.
Bit harder to tell, as I'm leaving the engine covers off till the things fixed. I would currently describe the fault as being sluggish/flat. All 6 plugs look identical, clean on the the tips, but higher up, towards the threaded section they are black, not brown?
Still no fault code being thrown up?????

 

[Matt]

What's the state of the exhaust system? I had a similar thing on my honda once and it was the backbox being blocked and corroded inside

 

[Ivan_Good]

Hard to say Matt, outside it's lovely and shiney, but inside?? It's on the original exhaust as far as I know

 

[rustedandrotten]

Sounds like fuel, pump not delivering enough so could be filter, mucky injectors or a dodgy pump. Got to start with pressure test when idling and under load. See what is what and probably start with the simplest first, filter, if pressure still dropping pump, holding but missing, injectors.
good luck, seeing as you have ruled out plugs and coils. Many threads on pumps, Spike seems to be the guru on these.

 

[Ivan_Good]

I've got a filter, ready to do, I suspect that this had never been changed.

 

[shinji]

Spike the fuel pump guru did elaborate in a different post that should be around 55 PSI static and 52 PSI running.

 

[hualpa_jo]

The best plan I can come up with so far is to buy 3 new spark plugs, and 3 new coils, fit to front, then rear, to prove out possibility of faulty plug/coil. Not what I wanted to do, but cant think of any better idea. (it has just had new plugs fitted)

"Just had new plugs fitted"? It proved very useful to me, to start looking right where someone had been working. New doesn't mean good. I have come across high load misfires due to: Wrong plugs, wrong gaps, broken or even loose insulators. In all of those cases, you couldn't tell by just looking. Also not every new coil is working as it should. Again: Happened to me before and caused me hours of head ache!