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  1. #1
    VXRed
    Join Date
    11th February 2009
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    110

    Default Z28NET misfiring / very rough running

    Morning all,

    I've been asking in a few places already and getting a few ideas together, but I'm wondering if anyone here has had the same problem or can easily decipher what is happening.

    I've got a Signum 2.8 Turbo, so the baby 230bhp version of the VXR's Z28NET (also called the Z28NEL I think?)

    Quite a few months ago, I had a minor issue where I'd get some juddering under load from low revs... so say I'm cruising in 3rd gear, traffic slows down, revs drop to about 1.5k RPM... traffic speeds up, I put my foot down without changing down a gear, judder judder up to 2.5-3k RPM and it all smooths out. First step I took was to replace the spark plugs. Replaced all 6 with Bosch platinums of some description. The problem immediately went away.

    Once, and only once, back in November, I started the car up and it didn't feel like it was running badly but the exhaust note sounded lumpy. Engine light flashing so I turned it off and plugged in my code reader. P0300, P0305 and P0306. Cleared the codes and it's been fine ever since...

    ...until last Tuesday. Starts fine, drives fine... then randomly start getting flashing engine light and it starts to run rough. It's perfectly driveable but it vibrates quite heavily under load. Stopped, read codes. P0306 and P0130. Cleared codes, started it, no difference. Stopped and tried to start again, won't start now. Gave it a few cranks and eventually it started. Didn't seem too happy to start but it did, and once it did, all the problems have gone away.

    Three days pass, no problems at all... then Friday afternoon, it runs really rough from cold start with engine light flashing. Read codes, P0300, P0303, P0304, P0305, P0306. Cleared codes, started, still running a bit rough. Read codes again, P0306 only. Cleared, started again and it purrs nicely for another three days (odd that it seems to be three days every time).

    Monday comes around, driving to work, same again. Starts fine, drives fine, engine light starts flashing and starts running rough. Guess what? P0306 again on the code reader. Every time I clear it, this code keeps coming back and the engine still runs rough. Vibrating under load. Leave it to sit for a few hours, start it up again, still runs rough. Now we're getting P0300, P0302, P0303, P0304, P0305, P0306. Clear them and take it for a quick 5 minute drive, only P0306 comes back.

    When I first had the juddering issues months ago, it was suggested either ignition coil or spark plugs would be the culprit. As the spark plugs seemingly fixed it, I didn't do anything with the coils... now that P0306 is the consistent code, I went and bought a new coil and fitted it to cylinder 6 thinking that this coil must just be knackered and potentially the others are just because it's been thrown out of balance. As soon as I fitted it, it seemed to purr nicely... for about a minute. By the time I got it out of the car park, it started running rough again. Guess what? P0306.

    Few hours later, I put the original coil back in and swapped it for cylinder 2. No change. Put that original back in, swapped it for cylinder 3. No change. Put it back on cylinder 6, no change. I didn't have enough tools, time or effort to get to the back bank. Limped it home and took another look in the evening.

    Took out the spark plug from cylinder 4 and cylinder 6. The one from cylinder 4 looks OK, but the one from cylinder 6 is a different colour. It's like a brown colour. It's a crap picture due to lighting and space, but this is what they look like:



    So I swapped the plugs around and started it up again... To me, it felt like the problem had moved... but the codes still read P0306. I'm not sure if it had actually moved the problem, or if it was just me telling myself it'd moved because I'd moved the plug. A suggestion I had was air intake as well. I can't see any pipework problems at a glance, but I do have a Ramair cone filter which I've heard some say they don't like... It's been there for 7-8 months with no issues but I took it off anyway and put the stock airbox back on, no difference.

    Some people have mentioned they can be really picky over spark plugs... it's been running fine with them for months so it'd seem odd for it to not like them... but I've been told the recommended one from Vauxhall is an NGK PLFR6C-10G... Admittedly I've not bought a whole set, but I bought a pair and swapped one into cylinder 6 last night to replace the manky looking plug... no difference after running it for 5-10 minutes.

    At this point, I'd run out of time and I'm going to revisit it late this afternoon... I didn't particular fancy spending out nearly £100 on a full set of spark plugs to replace a set of perfectly good spark plugs. If it turns out that is definitely the issue, then I'll happily go spend it but I don't want to throw money at it unnecessarily.

    My next idea is to pull apart the back of the engine so I can get to the rear bank... check all 6 plugs for condition... Swap the new plugs around a bit to see if I get any change and swap the new coil about a bit to see if I get any change.

    But is there anything specific that anyone has known to cause this that might save me the trouble of messing about too much? I've had people mention possibly fuel filter, injectors, timing chain... At this point, I'd probably just garage it and get them to do it but if it's a quick, simple (and preferably cheap fix) that I've missed, I'd rather give that a go first.

    I'm not sure what chain rattle would sound like... I couldn't find a decent video of the sound. I did find one that wasn't clear but it didn't sound like it was misfiring like this. I found one video of the same problem, but no fix in the comments.

    This is what mine sounds like:

    https://youtu.be/9XTk6n903LE

    Any help would be great

    Thanks!

  2. #2
    VXRed
    Join Date
    11th February 2009
    Posts
    110

    Default

    I've just been out and pulled all the plugs. They all look relatively OK bar that one manky one that I replaced. They're all pretty consistent.

    I've put it all back together and started it up again... it still runs really rough, but now I'm getting the spanner light coming on and off every now and then. I've read the codes again and now I've got some new codes:

    P0190 - Fuel Rail Pressure Sensor Circuit
    P0353 - Ignition Coil "C" Primary/Secondary Circuit

    Seeing as you've got to dismantle a lot at the back of the engine, could this just be I've not plugged something in correctly? Or could it be the actual problem? The words "circuit" suggest I've not plugged something in, but I can't see anything unplugged and everything I remember unplugging is connected. Maybe worth just reseating all the connectors?

  3. #3
    VXR enough V6spike's Avatar
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    18th May 2013
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    1,749

    Default

    wow, quite alot going on there mate. Plugs and coils would be the first port of call, but you seem to have done that. GM plugs or the denso IKH24 are what most run. bosch super 4's for instance are not liked by our engines.

    Have you checked the vac pipes, jubilee clips and other associated stuff for leaks, cracks or loose items? i don't think chains are a likely cause (i could be wrong though) as they bring up a different code.

    Those codes certainly point to multiple misfires and likley to be fuel related or an intake issue.

    Give Nick150 a PM as he's a ninja on these engines.
    '55' Sapphire Black VXR Estate. Eibach Prosport all round, remapped by Rabbid. DO88 intake kit.

  4. #4
    VXRed
    Join Date
    11th February 2009
    Posts
    110

    Default

    Small update. I've just found one if the pins on the ECU bent!!!



    Managed to straighten it out and now the P0190 has gone away. P0353 still present though so I'm off to attack some coils

    Sent from my SM-G955F using Tapatalk

  5. #5
    VXRed blooded
    Join Date
    11th July 2014
    Posts
    359

    Default

    Stick with genuine GM plugs, which are NGK Iridium and work fine on standard and remapped cars. The plug gap for a standard car should be 1.0mm, the brown plug seemed to have a big gap, check all plugs accordingly.

    If you have a mapped car then the gap should be reduced to 0.7mm or 0.8mm, both are OK.

    A set of six plugs can be had for around £50 delivered from the likes of www.genuinepartsearch.com, also check www.carpartsconnexion.com and www.autovaux.co.uk. Some cars don't like the Denso plugs, no one I know uses Bosch.

    I have heard of at least two people having to replace the ECU.

    Is your car remapped or standard? Good luck sorting it, unless chains are the issue then it should be relatively straightforward, where are you located?

    Coil packs are a common fault as you know, Opie Oils sells them www.opieoils.co.uk and often you can get 10% discount, I think some have also used Eurocarparts too.

    I have no idea what your error codes mean, but as v6spike has mentioned, check all hoses at the back of the engine, and general check of all hoses and wiring too.

  6. #6
    VXRed
    Join Date
    11th February 2009
    Posts
    110

    Default

    Well, I managed to fix the P0353. Some numpty forgot to plug the cylinder 3 coil pack back in after he'd pulled the plugs to inspect....

    So the NGK PLFR6C-10G I was recommended in cylinder 6 didn't make a difference... but the plug in cylinder 2 looked a bit black... so I put my other new one in that cylinder.



    It seems.... better... but not better. If that makes sense. It's back to running how it was a few days ago where it was just about driveable... it vibrates at idle... vibrates a bit more under load and low revs but seems to smooth out higher up... but with a severe lack of power. Still faster than the Mini One I'm driving in the meantime :P initially, after putting these plugs in, it wasn't registering any fault codes... but it did eventually start to log P0306 again.

    Even though it's standard, I'd been recommended a 0.7mm gap so the Bosch were all gapped down to this prior to fitting. I think the brown plug may just be the crap picture. This is in the light:



    The rear bank ones all look like this:



    Thanks for the tip on places to buy. Oddly AutoVaux and their sister GPS don't list any spark plugs for my reg... but Opie Oils do them cheaper than anyone else does before discount... ordered another 4x plugs for £45 including next day delivery.

    I've changed the one coil and it didn't make a difference... so I was interested to swap them around to see if anything changes. I've already:

    Installed new coil on cyl 6. No difference.
    Reinstalled original on cyl 6. Installed new coil on cyl 4. No difference.
    Reinstalled original on cyl 4. Installed new coil on cyl 2. No difference.

    New one is currently sitting on cyl 6 along with a new plug. The only thing I haven't done is tried the new coil on the rear bank... or swapped any existing coils about. I was going to give this a go tonight but it'll be dark by the time I get home and if I've got spark plugs coming tomorrow, I'll only have to take it apart again so I'll wait til Saturday to try all that.

    I can't see any splits or cracks to any hoses on a visual check. Are there any in particular that are common to cause issues?

    Sent from my SM-G955F using Tapatalk

  7. #7
    VXRed blooded
    Join Date
    1st August 2016
    Posts
    322

    Default

    Could be wrong but the plug in the first pic looks very bad as if it’s running lean and getting hot could even be small flakes of alloy on that one.
    Might have mentioned before but you might do well to speak to teapot and see if you can try a spare ecu? If he still has it
    Vectra VXR estate 07

  8. #8
    VXR enough V6spike's Avatar
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    18th May 2013
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    The pipes at the back and those that go into the block above the 3 plugs at the back can be very brittle. easy solution is to replace them with silicone hose which is absolutely fine, or replace with the GM stuff. also check the clip on the front of the intake that sits under the slam panel just by the bonnet latch. check the 2 clips on the turbo and the one underneath that runs back to the IC.

    Also the pipes around the Boost Pressure sensor (x3) and the one that runs underneath the turbo.

    As said above probably worth looking at that ECU. the pins are probably week and not making a decent contact. Did you remove the ECU plugs when doing the rears?

    As steve says (Aka Dog_book) jump over to Vec C and chat to teapot about it.
    '55' Sapphire Black VXR Estate. Eibach Prosport all round, remapped by Rabbid. DO88 intake kit.

  9. #9
    VXR enough Jon1796's Avatar
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    24th August 2015
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    Might be worth a read.

    V6t mis-fire
    https://r.tapatalk.com/shareLink?sha...1&share_type=t


    Sent from my iPad using Tapatalk

  10. #10
    VXR enough Jon1796's Avatar
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    24th August 2015
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    1,183

    Default

    Also coil packs don’t always give a fault code even if faulty had that on mine V had no idea as it didn’t give any codes. If you can change all.


    Sent from my iPad using Tapatalk

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