Spark Plugs - pre ignition issue

[vwtype53 at yahoo.com (Benjamin Harder)]

--- Jason <jason@scirocco.org> wrote:
>
> Ben, some questions:
> 
> 1.  How is it on cool evenings and mornings?  If it still does it, 
> something changed, because it didn't do it this spring when it was cool out.

The pinging is minimal to nil on cool days... but gets worse on hot days.


> 2.  Have you done a compression check to see what your effective 
> compression really is?   (Mine puts 195-205psi, and can take only about 9' 
> before I start hearing pinging on 93).

Nope, but as soon as I borrow the tester I'll check this out...

> 3.  Perhaps the Schrick 260/276 cams are resulting in hotter exhaust 
> manifold temperatures, which is resulting in the pinging... and causing you 
> to not be able to advance to stock timing.

Doubt this one... cams shouldn't really affect the actual air/fuel ratio...
just how that air/fuel gets into the cylinders and when.

> 4.  Since the advance on the 16V is vacuum-actuated, perhaps the additional 
> air you're flowing is causing more of an advance at higher loads than would 
> normally be the case.  Check your total advance with and without the vacuum 
> line connected and compare it to that of a stock 16V at 2000, 3000, and 
> 4000rpm.  (I'll do mine if you need me to).

Not sure about this.

> 5.  IIRC, isn't it the KS Box that controls RPM and Load-Dependent ignition 
> advance?  Since we already know that something is kooky with your KS Brain 
> (i.e. it doesn't do shit), perhaps you should swap it out with another and 
> see what happens.

Actually, I think I just may have a defective knock sensor... but still,
I should be able to drive the car without the knock sensor having to do
its job... I would just lose performance when the KS tries to  take away
timing... don't want this to happen in the first place.  ;)

> 6.  Since it's so difficult to get a true reading of ignition advance at 
> idle with your cams, who's to say that just averaging the timing mark is 
> actually where the timing is set to?  It could be that your timing is, in 
> fact, advanced further than the reading shows, but the KS Brain is 
> interpreting the lumpy idle as knocking, and continually messing with 
> timing?  Disconnect the KS brain and see if the timing is less jumpy at 
> idle.  If not, measure timing at 1500rpm (or as low as you can get a smooth 
> idle) and use that to interpolate base 1000rpm timing compared with another 
> 16V.

When I disconnected the KS brain, the car dies!  hmmm...

> 7.  Another possible crutch would be to use a ridiculously low temperature 
> thermostat.  Your car runs fantastically cool oil temperatures, but IIRC 
> you'll see "normal" (i.e. needle on the LED) water temps.  Reduce the water 
> temp and you'll cool the head some more.

Yeah, the car runs cool already... I have the 80 C thermostat in currently.

> 8.  Did any of the plugs you remove indicate that perhaps only one cylinder 
> was experiencing the detonation?  Check it out -- if so, it might be a 
> partially-clogged injector that is causing one cylinder to lean out.

All the old plugs looked the same, however, they were quite grey...
almost a little bit white looking.  Too lean still?

> 9.  Where is your O2 sensor?  Stock location, right?

Yes

> 10.  Could it be that the wiring in your A/F gauge is causing an O2 sensor 
> reading that is too high, resulting in your Fuel box leaning out the 
> mixture more than it should?  The gauge shows you running just lean of 
> stoich, but hey, you never know...
> 11.  Do you have a pyrometer (or whatever those non-contact high-temp 
> thermometers are called)?  If so, check the temp of each runner on the 
> exhaust manifold and see if one is running much hotter than the 
> others.  That would indicate a potential source for the problem...
> 12.  It does also ping under full-throttle, right?  If so, we can ignore 
> the O2-sensor arguments. ;)

 Yup, happens primarily under full throttle... O2 is probably not the issue.

All I know is that the engine runs much stronger with the *supposed* timing
set to 6-8 degrees... when it's cool out and there's no pinging of course.
Once retarded to 4-6, the engine is less "happy" to rev but will not ping.


=====
Benjamin Harder
86 Scirocco 16v
80 Scirocco 16v
93 Passat GLX

http://www.geocities.com/vwtype53/

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