Former VWDieselParts.com Forum

Have to pass a yearly emission test. It is done by 5 quick full throttle applications, about 30 seconds apart. The opacity during the 5 "runs" is averaged and should be below 40%.

I have some questions regarding pump "tuning" to pass.

Does timing advance help (lower the opacity percentage) or does retarding help?

What other adjustments do you recommend/have used to pass similar emission testing?

Thanks

Welcome. Where are you from? California? Based on what I have read about opacity, if you are only looking to pass an emissions test, then I would simply turn the full load screw counter clock wise until you have just enough power to get to where you need to go and back.

gunnar13 wrote:Have to pass a yearly emission test. It is done by 5 quick full throttle applications, about 30 seconds apart. The opacity during the 5 "runs" is averaged and should be below 40%.

I have some questions regarding pump "tuning" to pass.

Does timing advance help (lower the opacity percentage) or does retarding help?

What other adjustments do you recommend/have used to pass similar emission testing?

Thanks

If your engine is in reasonable condition, simply do as hj says and back the max fuel screw out half a turn. Additionally, remove inlet manifold to pump boost line and drop in to the barb a small nail with a 3 mm head then replace line. this will remove the 'call' from the turbo for extra fuel from the pump. Not sure of your opacity scale, but for me here in the UK the limit for the Quantum is 3 or 3.5%, and my Q gets between 0.4 and 0.5% which is actually modern TDi levels...

Seems like you could also plug or disconnect the boost enrichment line on the injector pump. Have also heard of folks adjusting the throttle cable or stop so you don't get as wide open throttle as possible.

Are these test under load,
or just reving in neutral?

Because there probably won't be any boost if it's not under load,
so plugging the line won't do anything.

maybe a turn of the screw on top of the spaceship would reduce off-boost smoke levels.

I would make sure timing was tuned to the advanced side of "the zone", and as a couple others suggested, back off the full load adjustment until you can barely stand to drive it. (mark the original position and a slight turn makes a BIG difference) and screw in the throttle arm stop to limit full throttle (again marking original position first).
Also, if you are adding oil or anything to the fuel, drain it or use what's in the tank and add clean, straight pump diesel for the test.

Thanks for all your suggestions.

The test is done without load. I really do not think is very scientific, considering that the parameters such as rate of application of the throttle, length of time at full throttle etc are not controlled. In either case, the car has to pass.

Again, thanks.

gunnar13 wrote:Thanks for all your suggestions.

The test is done without load. I really do not think is very scientific, considering that the parameters such as rate of application of the throttle, length of time at full throttle etc are not controlled. In either case, the car has to pass.

Again, thanks.

What the testing station testers have never been able to explain to me , is why do they rev the crap out of my engine, and take it to a speed that would be well over 100mph if in 5th gear

Here in Van we have a driving test for opacity... Part of it simulates merging on to a freeway, which seems to be pretty much pedal to the floor accelerating up to at least 80 km/h if not more. Jezzie puts out a fair bit of smoke during that part of the test...

My last opacity test came back at less than 1% even though I had a big black cloud during the highway acceleration test. The limit here is 30%. All I did was knock the max fuel screw down about 1/4 turn before the test, but I really don't think I needed to even do that.

Make sure your engine is good and hot first, and try and find a time of day when you're not going to be sitting idling waiting your turn to get tested more than a couple of minutes. Diesels like heat!

gunnar13 : RELAX . it is simple . Learn the lingo so we all read
from the same page.There are 2 screws to adjust for minimum smoke .. Even
the worst engine will pass Screw # 1 is called the full load stop it
is like a dor stop .It is not connected to anything inside pump.. We can
remove it from pump no problem . Screw # 2 is the idle adjustment.
And that is all , you wll pass.

The # 1 screw is RH about 5 turns. total. .. # 1 and 2 are
very sensitive so? small adjustments are in order.
Let us know your LOCATION,

hagar.