832 votes
I ended up checking the ignition timing again, put in a new coil, new knock sensors, put in another fresh set of plugs, set the DPR MA to +5, and I failed my emissions test with the same results.
I just replaced my oem densos with some Bosch plugs that were labelled as being pregapped 1.1mm. I wanted them to be 1mm and checked with a gauge and Lo and behold they were already at 1mm. Whacked them in and improved my fuel consumption immediately.
I took it back in after setting the DPR to 2.5± 2.5 mA, checking again for any vacuum leaks, tightening down all the exhaust components, and changing out the spark plugs (again). I also checked the O2 sensor, it was fluctuating between .1v-.7v continuously.
To be honest the last plug VW went with , the 101905601F (OEM clones Bosch copper nickel FR7HE02 Or NGK ZFR6T-11G (5960) Copper Nickel, Beru BRU-Z272 copper nickel ) for the 2.5 is best. It’s one shade cooler and will have less spark knock. You have more timing.
I ended up leaving them as is and the car seems to be working fine.
As long as the Bosch ones match the factory specs then I’m sure they are fine as many other parts and sensors on these cars are made by Bosch.
when I worked for a Chevy dealer we hated Bosch plugs. Chevy's just don't seem to like them, they were often the culprit in misfire diagnosis.
I'm still not entirely convinced that it is weak or under ignition versus over fueling. Either way it just seems like it's having a hard time burning the fuel that it is getting. I still can't help but wonder about the Bosch Platinum 2s. I have had good luck with them before my Mark 2 GTI and the car did run well with them for a good 10 days before all of this started.
Update: went Bosch for the plugs and ngk for the coils, the manufacturer plugs and coils were still in as if no one has touched them since the car was bought, I’m the third owner I believe. Each spark plug was toasted, easily double the recommended gap, and once I put the first two coils in (pulled code P0300, P0301,P0302) the problem entirely went away (coughing and sputtering exhaust, slow to accelerate, car shaking between 20-40 mph, rough starts) so I knew it was a go ahead for the rest of the coils. Feels like a whole new car all around, I can tell the engine is thanking me by what she’s putting out now ????
The best plug I found for a shovel is a Bosch Platinum WR8DP.
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