VR6 misfiring under load - this will be a tricky one!

[boltonjon 0]

Hi guys - i'm new here, but at least i've found some cool folks with similar attraction to these damn VR6s..

Welcome from the UK!

OK, the car runs rough and misses bad under load and really struggles to build up revs. So far the following has been checked/replaced:-

On-board diagnostics checked and good

New VW HT leads

New coil

New plugs

Compression ratios good

Temp Sensor

Air Flow Meter

Distributor, cap & rotor

Crank Sensor

Knock sensor is checked/good

cam timing good

no airleaks which i can feel/hear

Any ideas????

[xyber 1]

Has the airflow meter been checked or replaced as they can have a fault that doesnt show up

[ip 0]

Wow sounds similar to my issue (VR6 Missfiring problem (stuttering)).

http://www.vr6oc.com/e107_plugins/forum/forum_viewtopic.php?233995.last

Perhaps a litle different as mine runs sweet at idle and above 2000rpm. However, thought I'd give a quick list of stuff I've dug up while trying to fix mine:

1. Alternator output voltage (unlikely but can be an issue). Battery be 12v when engine switch off and approx 13.5 when running. If regulator fails, the alternator can overvoltage the engine which ruins ignition timing etc...

2. ECU and Fuel Pump relays. ECU relay in particular has reputation for failure but fuel pump realy has been know to go too. Not easy to test, just replace or borrow from another Golf.

3. Fuel Pump (seems possible). I bought a fuel pressure test kit from ebay for £10. Dead easy to use, put in series with fuel line and start car up. Instructions can be found with a quick google search. Should read 3.5bar when ticking over and peak at 4bar when throttle blipped. When engine switched off, fuel pressure should remain for a few mins.

4. Cam sensor (called G40) can go too (at least on coil pack models). Not sure if this applies to yours. If not the sensor itself then the magnet which should be attached to the cam can rattle loose throwing up timing errors.

5. Xyber is bang on, MAF does not really ever throw up a fault code, just drifts out of cal. As such only way to test is to replace.

6. When you replaced plugs, how did they look? Healthy (grey brown matt finish) or sooted up/melted. This should tell you a lot (sooty = rich running, melted = lean).

7. Odd one but a bunged up CAT can cause all your symptoms. If the matrix crumbles inside the CAT then it can flip over and block exhaust flow causing missfires etc. Easy to test, if it's failed, will rattle really badly when engine is revved. Not really likely but thought I'd mention it.

Not sure if any of that helps (didn't fix mine) but hopefully gives you a couple of new ideas. If you fid out what is wrong with yours then lease post as I'm really losing my rag with mine.

Cheers, ip

[gav_113 0]

sounds like fueling maybe (filter/pump)???

[xyber 1]

Might be worth giving the throttle body a damn good clean aswell with IPA or other electrical contact cleaner