Help diagnosing misfire

sparkymark75 · 9 Apr 2011 at 11:44

My wife's 2003 Scenic 1.4 16v Fidji is playing up. It idles rough, and sounds like it's misfiring.

The ignition coils were replaced about 22 months ago with ones I got of eBay. I took them out and checked the resistances on them and they seemed fine but I've replaced them regardless and it's not cured it this time.

I've hooked my laptop up to the ECU using OBD II compliant cable and software but no codes are being listed.

What else can it be?

mrk · 9 Apr 2011 at 11:54

Crack in one of the cylinders? Way to find that out is to pressure test each cylinder if I remember right.

Could be a number of things! You could check each HT lead as well, as a faulty lead could cause it misfiring. Were the spark plugs changed too when the coils were?

sparkymark75 · 9 Apr 2011 at 11:57

The plugs weren't changed when I changed the coils. Has to happen the month I'm skint after forking out £200 for road tax :mad:

Jez · 9 Apr 2011 at 11:58

Plugs coils MAF HT leads were what i was told to look at when i had a misfiring focus. Turned out to be the coil in my case.

mrk · 9 Apr 2011 at 12:01

Strange that the ECU isn't polling any error codes though, if it was really misfiring the code would have been logged along with which cylinder is causing the misfire to help you narrow down the fault - Unless your software is the one not able to read those codes?

Lashout_UK · 9 Apr 2011 at 12:06

When was the last time you changed the plugs?

sparkymark75 · 9 Apr 2011 at 12:09

I've tried a couple of pieces of diagnostic software and neither show me any error codes. Below are some screenshots from just now;

http://img163.imageshack.us/i/14323208.png

http://img810.imageshack.us/i/72253382.png

The software I got with the cable, PCMSCAN, is showing that there are 68 emissions related-DTC's stoerd in the ECU. Not sure if this is how may it can report on or the total number of faults.

zipp0r · 9 Apr 2011 at 16:43

plug leads?, plugs? whats the condition of the antifreeze? still the right colour and not smelling of petrol or highly pressurised after not being used for 24hrs?
id be looking at the condition of the plugs first, if u have a misfire one plug should look different to the others.
searching fault codes will show sensor faults e.t.c, but not things like a plug isnt sparking or headgasket going.
22months ago and u never changed the plugs lol! you think yours are long life ones?

sparkymark75 · 9 Apr 2011 at 17:41

And in that 22 months you'd be lucky if the car's done more than 5000 miles. Anyway, turns out it was the plugs. The car was getting a service at the end of the month and these were getting done anyway, just had to do them a bit earlier.