vr6 running issue's more complicated please help

[duncgti 10]

This is going to be a bit of an essay but i hope someone on here will be able to help me out. I have a k reg vr6 that has has a bad misfire issue, i had a look on here and have since changed all plugs,leads,dizzy cap,rotor arm and king leads. I also read the isv could be causing the problem so i cleaned that and also changed the diaphragm for a new one which didn't help so tried another isv, again didn't help. next i changed the fuel filter which was really filthy very dark fuel came out of it which was worrying, i have also removed the incoming fuel line to check if i was getting fuel at the rail which it is. the fuel pressure regulator also got a clean and looks fine. Now this is where im stuck as i think the injectors could have got dirty due to the fuel filter causing it to under fuel the car will fire but cuts out straight away as soon as you come off the gas, im just going to list some things and see if you guys think it could be causing the problem.

 

Faulty injectors

Fuel pump relay

Fuel pump (apparently there's 2)

bad ground

lambda sensor (car has a decat)

maf sensor

anything ignition related?

 

im really stuck as this is my daily car and would like it fixed, i have got a spare passat engine i can get hold of for parts. Would vagcom show up injector faults? and im also going to do a fuel pressure test just in case. Again sorry for such a long list of questions i've come from mk1 golfs which are relatively easy in comparison.

 

Thanks Duncan

[Roger Blassberg 0]

Vagcom won't show up injector problems such as blocked microfilters or nozzles but it will show electrical failures such as earth and signal faults. Undo the big 42-pin connector on the side of the cylinder head, spray pins and socket with contact cleaner and reseat the connector - all the injector and ISV signals go through there.

It might be worth pulling out the injectors and having them serviced ([email protected] ). He charges about £70 plus postage. You can usually find a spare set on ebay for £20 -£30, they are the same as for the Golf VR6 AAA engine, (Bosch part no. 0280150956, VAG part no. 021 906 031A). Of course it's a fair bit of a fiddle to get at the injectors - you have to take off the inlet manifold, but I did mine recently and it made a big difference to the smooth running and the idle, as well as improved fuel economy.

 

Fuel pump relay is a cheap and worthwhile try as well.

 

I assume that the air filter is clean and that you have checked for air leaks on the induction side

 

 

 

MAF is a perennial problem, difficult to prove that it definitely is or is not at fault, but if you can get someone with a known good one to try it on your car that should narrow it down.

Where are you? I can help if you are near to St Albans/Herts Beds border.

 

Best wishes

 

RB

Edited May 21, 2012 by Roger Blassberg

[Rustynuts 0]

Check your wiring, check everything related to ignition so that includes all sensors. Misfire could be caused by a bad connection so check your plugs. I had a car that did this, I never got to the bottom of it. Sold it and later came across the second owner after me. He said that wiring to the MAF was at fault. It was intermittently breaking connection.

[VW_OwneR_85 1]

I had a car that did this, I never got to the bottom of it. Sold it and later came across the second owner after me. He said that wiring to the MAF was at fault. It was intermittently breaking connection.

 

hahah hello ;)

 

yea the way the maf wireing was routed it would allow water to flow down into the plug and flood the connection, i only found this out a few days after i brought it home, i was washing the bonnet with the car running , and it just cut out, i was like er??? tryed starting it up and it idled up n down and then idled realy low with the battery light comming on then cut out and would continue to do so,, you could drive it but it was terrible!! after i found the plug i blew it out and used wd 40 to displace the moisture, worked perfect!!

but even on damp mornings with a slight bit of moisture can effect it, the idle wont be right and your get a slight miss/hesitation up the rev range,

[duncgti 10]

Thanks for the quick answers guys, RB i shall try the 42 pin connector in a minute and see if that helps, as for the injectors the spare engine has everything still attatched and comes with a wiring loom so if there are any electrical faults i should be able to replace any damaged wiring, and also try the injectors off that while i get mine refurbished. I don't mind taking the inlet off as i can get it powdercoated befor refitting it so it tidies up the bay a bit. The car had been sitting for a number of years and due to this the engine loom is a bit tatty and the wrap tape is brittle and falling off in parts so i would like to re wrap that as well. And as for air leaks i have checked the induction side and everything seems fine i sorted that when i first got the car as there were splits in the intake hose etc,i live in ruislip which is just of the a40 uxbridge junction so not to far away from you.

Rustynuts- as for sensors which ones should i be checking? the plugs are new as is most of the ignition system i will try clipping the leads back onto the plugs just to make sure they are seated firmly.

Thanks again guys any more sugestions as to what could be the cause of this would be much apreciated.

[duncgti 10]

just to keep this up to date i went to check the 42 pin plug which i found wrapped in electrical tap..always a good sign, unwrapped it to find 42 crimp connections! hmmm so made sure they were all tight one had fallen out so re crimped it just to see if it helped and it can hold an idle now but still terrible. the next question is will a passat engine harness work in a corrado as the spare engine has a new loom? it is a slightly newer loom from an auto car but it still has isv not an electric throttle so im guessing its the same block but will the fact its auto mean the engine loom has other sensors etc??. I don't mind putting in a different loom if it means fixing it properly. please help :(

 

Dunc

[duncgti 10]

does anyone know if the passat vr6 obd1 loom will fit the vr6 without any issues? because if it does i can start stripping out the old loom and check injectors etc.

 

Thanks

[duncgti 10]

anyone know about the loom

[Rustynuts 0]

Not sure of the definitive answer on this. However, if you need to strip yours out anyway you could then compare the two side by side perhaps?

[duncgti 10]

yeah i think thats what im going to have to do but i didnt really ant to strip the fuseboard side, i was going to remove the plug and solder it onto my existing loom so i didnt have to take the dash out!

[Rustynuts 0]

It is not as horrible as you think.

 

However, if you are going the soldering route, you could just compare the two in situe, the wire colours will be the same hopefully, if you come across different colour wires in the plug vs your tangled mess of wires then you know it is different. If not, you are game on. Then it is happy soldering.

[fla 9]

we had a bit of a tinker with the car today, cleaned out the isv, the dashpot was sticking a bit so we think that accounts for the cutting out.

Managed to remove three of the leads to check for a spark - rear bank were ok, but the front bank (near the front of the car) was a strange one. When the lead was removed from Cylinder 1 (LHS) there was no audible change in engine note, but there was a spark from it. The other two leads we couldnt get off, but hopefully will have a bash next weekend. Its a strange issue in that the misfire doesnt make the car shake as though it is a 'sequential' misfire. It was low on power too.

Couldnt get VAGCOM on it either - does anyone have the 2+2 leads we could borrow?

 

Assuming the spark plugs are all getting a spark, my only thoughts would be the injectors opening or providing an even flow, which hopefully we should pick up next look on the car. Other suggestions?

 

btw, good to meet you Duncan, Mk1 looks superb ;)

[duncgti 10]

thanks it was good to meet you to, thanks for all the help! hopefully we'll get to the bottom of it.

[duncgti 10]

right more updates! the loom has been fully soldered but it hasn't cured the misfire, i decided to remove the injectors and send them off for flow checking and cleaning, these have now been refitted with new o rings and manifold/throttle body gaskets and everything checked and cleaned. After putting it all back together.....still misfiring!! im really starting to struggle to think of anything else it could be, im getting fuel, air, and spark so my next plan is to do a compression test and try a different ecu and run vagcom. Does anyone have any other ideas that could cause a misfire like this?

 

Thanks Duncan

[dannyboy78 0]

Hello mate, i had the same problem, car would stall when i dipped the clutch or came off the throttle, was an intermittent issue, did as you have,injectors dizzy etc, turned out to be a intermittent fault with the alternator, it would work fine then would stop charging and after 2 mins the car would stall, new alternator problem solved! worth letting the car tick over and put a volt meter on the battery for 10 15 mins and see if its taking a charge,if it starts dropping you know the alternators naff.

[Roger Blassberg 0]

Have you and Hasan absolutely ruled out any problems with the MAF ?

 

I work close to you and could come round with mine to do a quick swap over of the MAF.

 

Let me know.

 

Best wishes

 

RB

[StArRaDo 10]

Man this sounds fun :shrug:

[buttles 0]

Have you checked the Fuel Pressure Regulator? Think it's 4 Bar normal and 3 Bar at idle. Get a guage on the fuel rail to check it's switching.

[duncgti 10]

heey guys thanks for all the advice! had a good day today, got one off my mates round to help me out today and got a compression test done on the engine. Whilst taking the plugs out we noticed a few were coked up and in a bit of a sorry state. We ran the tester compression was fine on all cylinders so we decided to clean the plugs up and give it another run. Car started and ran perfectly! firing on all cylinders, we think the reason for the misfire was due to poor injector flow causing the spark plugs to get coked up and not spark efficiently causing the problem to persist when the new injectors were fitted. Should have taken them out earlier really but as they were only a few months old didn't think they would be the problem, a note for the future always start with the simple things first :) feels good to be driving a working corrado again, went for a nice long drive just to make sure it was ok. Thanks again for all the advice i'll get some pics up of the cleaned up bay.