Jump to content

the dreaded misfire.


Recommended Posts

ok, I'm really ****ed off today, and really need the help of anyone with knowledge of the 1.8t 20v specifically in the mk1 octavia vRS... since my last breakdown on the cumbrian run, with an almost undrivable car due to misfires, my mechanic has had it for a week, and still hasn't managed to fix it, as it appears to be running correctly now! *sigh. obviously they cant drive it fast, but have done about 8 miles of "normal driving" ect on several day, and not got any faults. the only thing the diagnostics computer (proper garage diagnostics, can read everything, and report live if something isn't working, i.e throttle position ect ect ) came up with was a fleeting code of "pressure variation" in the throttle body, but my boost gauge is connected to the inlet manifold, I know this can't be an issue, as I have all the correct boost at the correct times....

so lets brake down what I KNOW, and what has been ruled out....

starting with things changed/swopped over..

1) new plugs
2) replacement coil packs
3) replacement MAF
4) replacement hocky puck (breather valve) 
5) replacement temperature sensor, this did seem to cure the issue initially, but it has come back as bad as ever, but now seem to have resolved itself.

things it isn't

1) boost leak. all correct boost arrives in the manifold when it should.
2) fuelling. there is proper fuel pressure, and plenty of fuel going in, its popping , banging, and spitting fire out the exhaust when it misfires. all unburned fuel. no lack of fuel is causing this!

things it probably isn't

1) the wiring loom, yeah its a bit old, but its always been scabby, and my mech says, "yeah maybe if its going off when its wet, but not just hot"... I can buy a new loom for £45, but I have spent hundreds, don't have any money, and currently cannot afford to throw money at it!
2) injectors, apparently they almost never go wrong, and if they were fooked, it wouldn't just stop working again...
3) O2 sensor.... don't know the reasoning behind this, but my mech doesn't think thats likley.... again, it wouldn't then fix itself.

I am at a loss, very frustrated, and cannot think what it may be! Its going to ruin our trip to germany if we cannot get it fixed, I am climbing the walls with frustration..... I need some help! any ideas would be greatly appreciated, any help would be greatly appreciated. Getting quite stressed about it 1f641.png:( I simply don't have the money to just throw new parts at it randomly trying to fix it 1f641.png:( I understand that my tame mech can't do anything, if the car tells him there is nothng wrong in diagnostics, and its appears to drive perfectly ( I will cane its ass tomorow again, knowing it will break, and take it back next week, when my braided hoses arrive....)

help?

Thanks in advance. Dave

  • Sad 1
Link to comment
Share on other sites

So its an intermittent missfire that is the problem? 

 

If the coil packs are not new then I wouldn't rule them out, also the connections too them. Does the missfire happen randomly, only when hot/cold, only under boost?

 

Basically theres either a fault with spark delivery, fuel delivery or the amount of fuel being injected. I would be checking ignition components, fuel injectors (just because they don't often fail they still can). Maf, coolant temp sensor and O2 sensors all control the mixture so if ones not reading right it may make it run rich. I would say its worth getting the car to a garage with an ocilliscope and scoping the signals from the various sensors and coil packs for problems. You don't need a fault code too diagnose faults, but it does help. 

  • Like 1
Link to comment
Share on other sites

What injectors are you running?   I have a set of 348cc (does that sound about right?) that I can send to you in the post.  If they solve the problem you can send me some money for them.  If they don't,  just post them back when you can.   

 

Had your fuel filter been changed in the recent past? 

Link to comment
Share on other sites

16 hours ago, Jux said:

So its an intermittent missfire that is the problem? 

 

If the coil packs are not new then I wouldn't rule them out, also the connections too them. Does the missfire happen randomly, only when hot/cold, only under boost?

 

Basically theres either a fault with spark delivery, fuel delivery or the amount of fuel being injected. I would be checking ignition components, fuel injectors (just because they don't often fail they still can). Maf, coolant temp sensor and O2 sensors all control the mixture so if ones not reading right it may make it run rich. I would say its worth getting the car to a garage with an ocilliscope and scoping the signals from the various sensors and coil packs for problems. You don't need a fault code too diagnose faults, but it does help. 

its not intermittent.... it just seems to have randomly cured itself...  when it goes off its progressive... starts with a slight hesitation on slight throttle, then develops over a few miles into full blown missfire at all or any revs, under load or not, and stays that way. its not the coil packs or plugs , and even if I had (mathmatically unlikely) to have replaced 4 with 4 more faulty ones (one is new, three were from a fully running working faultless car) I couldn't afford to buy new ones anyway, on this kinda hunch.... it DOES basically seem to be overfuelling, which is why we replaced the temp sensor firat time it happened, and this seemed to cure it! it then ran perfectly for a couple of weeks of gentle driving to work and back.... then it went wrong when pushed to limits on the cumbrian run... same symptoms... I'm thinking the o2 sensor has to be the next thing to be changed, along with another temp sensor....

12 hours ago, Leeboy said:

What injectors are you running?   I have a set of 348cc (does that sound about right?) that I can send to you in the post.  If they solve the problem you can send me some money for them.  If they don't,  just post them back when you can.   

 

Had your fuel filter been changed in the recent past? 

its possible it could be injectors..... but they very rarely go wrong apparently... and if the did my tech says they would stay wrong, it wouldnt just cure itself and start working normally again.... but in case I do need them, will you PM me a price please? (thanks for the offer, and the offer of return!)

 

speaking to a tech on favebook last night, I will be changing the PCV one way valve too.... this one.... http://www.ebay.co.uk/itm/AUDI-TT-A4-1-8T-ENGINE-BREATHER-AIR-INLET-VALVE-035103245G-A570/201819103892?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m2749.l2649  and someone else suggest crank sensor.... 

 

gonna drive it today, and see what the crack is.

 

thanks all!

Link to comment
Share on other sites

Crank sensor generally throws fault code (can't remember it) and causes starting to be a little troublesome, when mine went would cut power around 4500rpm and go into soft limp mode.

348cc injectors are for the 210/225 1.8T's, AUQ are 312cc, rough idle and lumpy running are a symptom. Cheap fix could be new injector seals, small leaks are common, usually show up under smoke test.

Do you know what map is on it? How long has it been on? 

VCDS logging might help, not sure which blocks to log, fuelling, boost, timing.

 

 

Link to comment
Share on other sites

run the map for 30k mate... was mapped with its current hardware, and runs spot on, already been to the ring and round ect with that set up....

 

Bought one of the wiring looms you mentioned.... Ross (tech) has just mentioned the crank sensor... gives issues similar to what I'm having apparently.... but there are no logs of issues with the crank sensor...

 

idle and running was fine at the start of today... then started to feel flat at high revs, now the "hesitation" has come in on small throttle inputs... I foresee the big misfire following on soon , as it has done before.

 

can't take it to Germany :( upsetting.

Link to comment
Share on other sites

I am having the very same problem. Used to come up intermittent open circuit on cyl 4, so I changed the plug and short loom,  but it's still got the same fault as you with no codes being brought up. After inspecting most of the coil loom I think that this is the next step for me. Replacing the full loom, but this job looks quite intense to do cos it goes right back to the ecu and ya have to mess with plugs and stuff.

Edited by skidmoose
Link to comment
Share on other sites

its not "hot/under load" if we took it out now, and drove it for an hour, and caned it to death, it would work perfectly (and I have change all plugs and coils, first things I went to!) 

 

 

but, If we were to drive at high speed for a prolonged time, or on a track it would start to misfire, gradually at first, until undrivable...

 

I've replaced all the obvious things, and @skidmoose , I have bought the wiring loom, don't think I can tackle it at the momenent either, certainly not on my own, I will hand it to my mechanic next time though....

 

 

 

 

Link to comment
Share on other sites

It's getting proper frustrating now. Went to cadwell park yesterday for a time attack meeting (obviously not on the track) takes about 20/25 mins to get there and the drive is not a steady drive. Got there spent a couple hours there drove home fine not even a hick up. Went to a local event on the way home no problem, got home no issue's. Drove to work today which is about 10 mins away, just round the corner from work started the hesitation on light throttle. Parked up did my shift came out started and boom big misfire. Luckily this time it stored a code. Back to cyl 4 misfire open circuit intermittent. So at least I have something to work with, but it's so random no pattern to it that I a such an unriliable car at the min. Sharkrider I have been looking around and thinking of getting two 8 pin waterproof plugs and joining the loom near the coolant temp sensor to save going all the way to the ecu and messing around with the ecu plug. Just have to wait for the loom to come and see how it looks from there.

 

Anyone want a parts car if this doesn't work lol. Only joking but I am bored of spending money on this now. Well not bored but it is running out yall know what I mean.

Edited by skidmoose
  • Like 1
Link to comment
Share on other sites

hard work isn't it? I still havent seen my car back yet... generally been without it about a month now. I have the whole wiring loom, and a new pcv one way valve... just going to hand them over to the mech.... just eliminates another couple of things...

 

glad you got a code to help! I havent! lol...

  • Like 1
Link to comment
Share on other sites

I've given up on it. selling the abarth and the eunos, and getting a car to share with my other half, and that will be used for long trips ect.... the octy has been put into semi-retirement... just taking me to work and back (6 miles each way)  ... its just been to carlisle and back without issue though , about 1.5 hours driving...

  • Like 1
  • Sad 1
Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Recently Browsing   0 members

    • No registered users viewing this page.
  • Community Partner

×
×
  • Create New...

Important Information

Welcome to BRISKODA. Please note the following important links Terms of Use. We have a comprehensive Privacy Policy. We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.