'88 930 Hesitation When Accelerating Above 4K RPM

73ess · 09-20-2009, 11:03 PM

I recently purchased an '88 930. It seems to run fine accelerating from idle up to around 4000 RPM, but above that I'm getting only a max of .75 BAR on the boost gauge and then feel some pretty bad hesitation. It feels just like the clutch is slipping, but I'm guessing it's something either ignition or fuel related. The car had been sitting for a couple of years without much driving. Any ideas on what could be causing this? Recommendations on where to start troubleshooting the problem?

73ess · 09-22-2009, 09:38 AM

Still trying to resolve. Any tips?

john walker's workshop · 09-22-2009, 09:41 AM

fuel systems gum up from sitting. have the injectors cleaned and put a fresh set of plugs in for starters. new fuel filter too.

willtel · 09-22-2009, 10:57 AM

My car suffered from similar issues about a year ago. I ended up refreshing the ignition system with new plugs, plug wires, distributor cap, and rotor and it seemed to clear up. You may also very well have some boost leaks due to old vacuum lines or bad intercooler seals.

In the future you would be better off posting these questions to the dedicated 930 forum, http://forums.pelicanparts.com/911-930-turbo-super-charging-forum/?daysprune=. Our cars are different enough that they makes us play in our own sandbox.

Tyson Schmidt · 09-22-2009, 12:33 PM

Also pull the intercooler and have a close look at all hoses that recieve manifold pressure. You may have a split in one that opens up under boost.
This will not only make you lose boost pressure, but also make it run rich, as the incoming air is getting metered by the sensor plate, but not all of that air is getting to the engine.

Check the hose for the power brakes too, both up front, and from the engine to the rear tunnel.

911st · 09-22-2009, 12:41 PM

Sounds like an air leak. With some air leaks they do not show up until under boost. Thus you will run well until on boost (4k rpm). Then air is forced out after it has gone trough the fuel Metering assembly.

Check the seal at the inter-cooler as that seems to be the issue often. Again, if it leaks you're motor will go very rich on boost.

Also might check you timing with a timing light. Disconnect your vac lines at the dist and plug. You should be at -26 at 4000rpm. Then when you hook back up the vac lines you should be close to +1 deg.

911st · 09-22-2009, 12:42 PM

Great minds!