worf928

Gary, That's the way my GTS' temp gauge behaves. And it is reading almost 20 degrees low. Do you have any reason to trust your gauge?

Does anyone have the specs for the 'other' temp sensor? The one across the bridge from the NTC-II?

Regardless of the documented accuracy or inaccuracy of the sensor, it is good metrology practise to have independent measurements with different measurement technologies before relying on a single sensor for critical data. I believe that I have this covered.

I have three sources of temp data John: an external IR thermometer, the dash gauge, and Hammer data from the NTC-II. I have verified that these measurement sources provide data that are very close to each other on my '91. So, my metrology process is calibrated and uses triply redundant data sources. Because of the latter I've ordered a new sensor for the GTS dash gauge (if for no other reason than to determine its specs.)

I agree that one should not rely on the NTC-II data solely. However, since 928s have the dash gauge asking for NTC-II data will give two independent measurements.

John Speake

OK Dave, I would take the IR as a reference, if the other two agree, then that's a bonus :-)

Bill Ball

I thought I'd pipe in about a local guy's 70K mile 95 GTS automatic that has bigtime pinging that we are working on together.

The car pings a lot under mild or heavy acceleration. No real clear temperature relationship. Worse with load.

- Has recent rebuilt MAF
- We swapped in another GTS EZK and LH which made no difference.
- We checked cam timing - right on.
- Owner did a water injection treatment - no change. Maybe not aggressive enough.
- We checked compression and 2 cylinders are 205 to 210 on 6 strokes. Most others are 200, a couple 195 and one is 190.
- Single tip Bosch copper heat range 7. The plugs do develop shiny black deposits on the metal case ring.
- The car does burn some oil, mostly under spirited driving -- as much as a half quart in 100 miles -- but less than half a quart in 500 miles of freeway driving.

I don't know the status of the in-tank fuel pump or whether the injectors have been cleaned. The owner has run several cans of SeaFoam in the gas.

We may look at the in-tank fuel pump and injectors based on a few positive reports here, or perhaps the GT EZK EPROM. However, the high compression in at least a few cylinders and some apparent oil burning issues lead me to want to work on that.

Possibly more water injection treaments may help to decoke the cylinders, but with all this oil being burned, no wonder there's a pinging problem.

I plan to do a leakdown test to make sure we don't have bad rings. I recall that the elimination of oil drain holes in the pistons, keeping more oil on the cyinder wall, was a design element of the GTSs, but even so, not all of them ping or burn a lot of oil.

Any other things we should look at?

Note - the car also idles about 950 RPM. Not erratic, just high. Idle adaptation fails, with the idle rising to 1500 RPM during the procedure with either the Spanner or Theo's 928 Diagnostic. Haven't figured that out yet either. A battery disconnect takes the idle back down to 950.

sweanders

Fuel pressure ok?

Have you tried changing to a "low octane setting"?

Nicole

I was under the impression that only the 1992 and maybe some early 1993 modelsl had this - no?

Bill Ball

Haven't checked the fuel pressure directly, but we can do that.

Ah, yes, the coding plug. So, low octane would be the pattern at the bottom, correct?

Bill Ball

Hi Nicole:

No, I think all years, but I'm not 100% sure. The early GTS issue was weak rods, IIRC. Anybody confirm?

Vilhuer

AFAIK all GTS have blocked piston oil holes. There are two different versions of pistons though. Difference is in piston skirt thickness and oil ring design.

Bill Ball

OK, so pistons and rods changed in the GTS over the production years. Anyway, I do believe this car has evidence of coking from oil burning, and the contribution of the lack of oil drains in the GTS pistons and the nature of the GTS oil control rings are mentioned as a cause, although oil burning seems to be awfully variable if this is the main reason.

We'll continue to pursue other causes and remedies. We'll do a leakdown test anyway for evidence of bad rings, as well as other suggestions like fuel pressure.

John Speake

I understand from AdrianSE that Porsche changed to drilling the later GTS pistons, as seen on warranty replacement engines.

He certainly drills the pistons on all his GTS based race engines.

ROG100

Bill,
Of the 3 GTS's I have been involved with the pinging went away after we changed out the intank pump.
In all cases the ITP was toast and after replacement no pinging and the car performed better.
ITP are $142.86. Sorry could not miss the sales opportunity 8>)
Roger

heinrich

210 is way too high isn't it? You must have carbon?

cobalt

I agree. If you have a borescope you might want to do a visual inspection.

I was under the impression the GTS should only use the 3 electrode plug. My local guy was factory trained on the 928 and worked at a local dealership exclusively working on 944 and 928's for over 10 years in the 80's and 90's before going independent. He made a comment to me about only using the factory style plugs which I believe are the triple electrode. What are the odds the single electrode plugs haven't been doing the job properly?

Just a thought.

worf928

Yup. The spec plug is the 3-electrode copper. However, I have not been able to find a source for them other than through Porsche at big bucks per plug (and I'm not 100% sure you can even get them through Porsche anymore.) For all the vendors I tried the SKU number for the 3-'trode plugs is linked to +4 platinums. IOW, if you order 3-pins coppers you get +4 platinums. I tried this twice, got +4s, returned them and gave up.

If anyone has a source for the 3-electrode plugs at a reasonable price...

cobalt

I was told not to use the 4 electrode plugs and would be better with the 2 electrode if I had to compromise. IIRC 928 specialists have them listed but I don't know if they have stock and I must assume you already tried.

So it sounds like if I find a source to buy a few sets and keep them in reserve.