Rich running Golf

Dale Owner/Technician New Zealand Posted   Latest  
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Driveability
2005 Volkswagen Golf Comfortline 2.0L 5-spd
Rich Running

Help, what am I missing here??? Golf is actually a 1.6 (BFQ engine) that we replaced a leaking thermostat housing/coolant distribution pipe assembly on. Customer drove away and short time later returned running on 3 cylinders with fault codes for cyl4 misfire, egr fault, and O2 sensor fault (no freeze frame data on our Autel). All plugs were rich fouled, number four the worst (compression is slightly low on that cylinder at 130psi, vehicle has done about 250000km and not well serviced).

Cleaned plugs and road tested. Fuel trims showed rich throughout (cruise at 50km/h -12 to -16) and number four fouls again within fifteen minutes of driving.

I've eliminated the following: MAF sensor, ECT sensor, O2 sensor (B1, S1) (friendly local panel beaters had an identical car). Fuel pressure is exactly to spec, injectors are not leaking (at least statically), no vacuum leaks, blocked off EGR which stopped code logging (weird, as EGR was spotlessly clean and could be actuated via scanner), no exhaust restrictions, no intake restrictions, repaired a couple of high resistance connections at the fusible links above battery, TPS appears OK I think (reads 13% at idle).

My next step on Monday will be to start checking earths, but would love to know if anyone has any thoughts on what I've missed here. And how the heck we could have caused it by replacing the thermostat housing!

Cheers!

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Albin Diagnostician
Washington
Albin Default
 

When Using your fuel trim numbers, are you using generic OBD2 data, or the VW enhanced data? The reason I asked, is because there is a big difference between the two. The generic data is not very accurate. What do the spark plugs look like, after a test drive and it has fouled the #4 plug? My first thought is there is an injector imbalance, such as an injector or two are not the correct injector…

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Dale Owner/Technician
New Zealand
Dale Default
 

Hi Albin, fuel trims are from VW specific software in Autel. All four plugs are fouling, number four just appears to quit firing first, the rest are pretty black and not far off doing the same. As mentioned, compression was slightly low on this cylinder, which I think is why. Car is a regular with us and fault had only occurred since we worked on it. Will do some more comprehensive road…

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Victor Owner/Technician
Florida
Victor Default
 

What are your injector pulse width readings at idle?

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Randy Diagnostician
California
Randy Default
   

By pass ect sensor with paper clip

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Dale Owner/Technician
New Zealand
Dale Default
 

Have tried a different ECT, and engine temp in live data is good.

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Randy Diagnostician
California
Randy Default
 

check grounds

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David Mechanic
United Kingdom
David Default
 

Hi Dale, are there two temp sensors in the housing . If so could they or their wiring plugs be mixed up ? Also you say that the temp Readings look ok in live data what does the temp gauge read ? Could it possibly be that the new housing is faulty ie causing coolant not to flow round a sensor ? Just a few thoughts that might help . Regards Dave T....

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Dale Owner/Technician
New Zealand
Dale Default
 

Thanks Dave, the housing came with a new ECT sensor and has a connection for the electric thermostat. Plugs are not interchangeable, and we refitted the old temp sensor with no change. Temp gauge on dash comes up nicely and sits bang on half.

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Dale Owner/Technician
New Zealand
Dale Default
 

Good idea re the housing itself - it is the only thing we changed. Might pull it off again tomorrow and have a real close look at it.

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Albert Owner/Technician
Pennsylvania
Albert Default
   

I agree with David Tate. My first thought would have been new housing is faulty beings that was the only thing that was replaced. And Yes I would check all the grounds maybe for whatever reason they were disturbed Good luck

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David Mechanic
United Kingdom
David Default
 

Hi Dale just had another thought customer has not put diesel in it ! Regarea Dave T...

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Dale Owner/Technician
New Zealand
Dale Update
 

Looks like I've gone off on a tangent here! So, cleaning up the chassis earth connections under the battery has sorted the rich running - fuel trims now where they should be. BUT number four spark plug still fouls and drops the cylinder! Now it takes about thirty minutes of driving rather than fifteen, and the other three plugs stay clean. Rechecked compressions - all good on 200 (not sure…

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Randy Diagnostician
California
Randy Default
 

Are those bosch spark plugs ???

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Dale Owner/Technician
New Zealand
Dale Default
 

Denso. No good?

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Randy Diagnostician
California
Randy Default
 

Putt oem plugs in it . That type of plug is junk . Looks just like plug bosch made no good you might be going down rabbit hole . Next step I would try oem plug

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Albin Diagnostician
Washington
Albin Default
 

Any chance you have an exhaust gas analyzer to take a sniff of the exhaust? I think some chemistry numbers would answer a lot of questions here. Another great test would be some secondary ignition waveforms. Since the oxygen sensors read from all four cylinders, you can't get a very good indication what is happening in the #4 cylinder. That is where the secondary ignition would shine. Now, you…

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Greg Technician
Colorado
Greg Default
 

Hi Dale, I'm curious what your fuel trims look like on the generic side of the PCM - vw likes to substitute to half value (or so, if I recall) on the mfg side when there are rich issues. Other than that, I would be looking at current of all injectors if you have a single fuse to pull from, include a trigger from one of the ign coils, or something to get you sync'd so you can see if extra…

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