Misfire - coil replacement on 4.2

[rmaurer]

Hi all, I've got a slight misfire at the moment that is most apparent when pulling away at junctions. If the revs fall below 1500rpm and I accelerate then it starts to miss and the more you put your foot down, the worse it gets until revs are over 2000 when it seems to clear. Over the weekend, I noticed it seemed to get worse when I was caught in traffic (i.e. possibly temperature related)

I've hooked up my laptop to see if any error codes had been logged but everything looked ok, except for 1 throttle pot reading slightly lower than the other at idle. Both are in synch when above 25% though and rise without fluctuating.

I've checked and reseated all the HT leads and they seem to be ok (Magnecors, around 16 months old) so am looking at the coil packs. I saw this thread: www.pistonheads.co.uk/gassing/topic.asp?t=244616&f=6&h=0 and have ordered a coil (fingers crossed they're the right ones, I'll post if they aren't). The question is, how difficult is it to dismantle the fuel rail etc and replace the coil packs on a 4.2? The fuel rail looks like 4 allen bolts, do the injectors then lift out or unscrew from the inlets and will the rail still be pressurised? If anyone can offer any advice, I'd appreciate it! (even if it's a case of - wouldn't recommend trying)

Thanks,
Ross

[trackcar]

It's dead easy .. you might want to run the engine with the inertia switch disconnected to depressurize the fuel rail, but essentially it's as straightforward as it looks.
go for it.

[rmaurer]

trackcar said:

It's dead easy .. you might want to run the engine with the inertia switch disconnected to depressurize the fuel rail, but essentially it's as straightforward as it looks. go for it.

Thanks Jools, a job for the weekend!
Just been out to Eurocarparts as they couldn't charge my credit card (no idea why, but they're fairly local to me) and picked up 2x Citroen ZX coils. I bought one initially then compared it to the Cerbs while in the car park and they look identical so went back and got another - £25.63 each!

Typical London traffic though, took 15 mins to get there and 1hr 45mins to get back due to 2 major accidents closing both the A1000 and North Circular... This at least confirmed that the misfire is definitely worse when the engine is hot - it actually stalled on me twice just before I got home.

[trooperiziz]

rmaurer said:

Typical London traffic though, took 15 mins to get there and 1hr 45mins to get back due to 2 major accidents closing both the A1000 and North Circular... This at least confirmed that the misfire is definitely worse when the engine is hot - it actually stalled on me twice just before I got home.

I don't think there is anything more frustrating than getting stuck in traffic when you know your car is playing up at low revs. It's guaranteed that there will be a load of holdups when you have a poorly car!

[rmaurer]

Decided to have a go at replacing the coils as I was working from home today and the weather was too good to stay indoors! I took a couple of pictures along the way, hopefully they'll be useful to others...

After removing the top panel, I disconnected the battery as I was worried about welding the alternator live lead to the extension bar I was using when removing the front coil (left the boot open though in case I forgot to sort the alarm out when reconnecting the battery). I disconnected the throttle link rod from the passenger side and then removed the 4 allen screws holding the fuel rail on:



The injectors simply lift out of the inlets and once free, I disconnected all leads so the fuel rail can be moved out of the way. I also covered the injector holes in the inlet with some tape as I always end up dropping screws/nuts etc into the worst possible place:



I wasn't sure if the HT leads need to be connected in the same pattern to each coil, so jotted down the numbering quickly. You can then remove all the screws and connectors and remove the coils. At the same time, you get easy access to the big fuse so I changed that as well. Both coil packs were cracked and in a poor state:





The coils listed above (first post of the thread) from www.eurocarparts.co.uk are exactly the same, although only time will tell if they'll last...



I did spot another sensor below the coil packs just visible in the photo below (centre of the V, below the fuel pipe T-piece), not sure what it was though... Can anyone identify this, thought it might be the oil pressure sender?



Anyway, the new coils went in with a bit of jiggling and once I'd eased the injectors back into the inlets and reconnected the battery (remote blipper on standby to reset alarm), the car fired up first time! (Phew!) All in, it took around 3 hours although several neighbours came over for a chat... Not a difficult job, but I'll find out tomorrow if the misfire is now cured.

>> Edited by rmaurer on Friday 28th April 22:07

>> Edited by rmaurer on Friday 28th April 22:12

[keithyboy]

Good quality pics

[purpleheadedcerb]

Well done mate. Just goes to show that these cars aren't quite as scary for diy as some would have you believe.

[trackcar]

Excellent work .. just a shame your service agent hadn't replaced those coils before they got to that state, they're a known weak point and should be replaced as soon as they start to show signs of splitting ..

top marks to you though .. great job!

[rmaurer]

Quick update - just been out and the engine is a lot smoother although I seem to get fewer pops and bangs, presumably because the sparks are stronger and less fuel is getting into the exhaust. An improvement... but... the misfire is still there (not as obvious though), mainly when loading the engine at low revs. I'm concerned that my throttle pots are out and the engine needs balancing properly which I'm considering having a go at. I can't see how this would cause a misfire though. I'm also tempted to replace the leads, they're 8.5mm Magnecors and have been on the car for around 18 months. How quickly can they break down and cause problems as they do sit fairly close to the exhaust manifolds...?

trackcar said:

Excellent work .. just a shame your service agent hadn't replaced those coils before they got to that state, they're a known weak point and should be replaced as soon as they start to show signs of splitting ..

Thanks Jools, I'm finding this annoying as well. The car is only 1 month/1000 miles out of another £2k service and considering the amount of money I've spent on the car in the last 18 months it is frustrating...

[lafr]

Ross,

(yoda mode on) Step back from the dark side you should, an RV8 is the path to truth, it is, return you will (yoda mode off)

LAFR