Quote:
Originally Posted by mitsy
Its rough on idle and wont rev past 3000 without a struggle the car does have quite a loud hiss even with the air intake buttoned up the reason i asked about leaded fuel it has a red fuel cap not green for unleaded
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I think all 928's start out with red fuel caps.
The variations ROW-vs-US-vs-other specialty markets include different coding plugs for the brains, giving more or less advance and fuel, reading oxy sensor or not, and there's a low-octane jumper that retards the timing some for poor fuel quality when installed.
If you have a US car, forget about using leaded fuel or a lead additive.
Remember that tetraethyl lead was added to motor fuel as an anti-knock agent, and many motors depended on it for valve stem/guide lubrication. Modern unleaded fuels in the US have 'other' ingredients to boost octane now, all of which have lower specific energy than the gasoline they displace in the blend. Adding lead doesn't decrease the amounts of the 'other' ingredients in the leaded fuels today so there's really no advantage for performance. The only purpose for the additives is to allow you to drive your original/unmolested/unrebuilt 1950's Pontiac to the end of its 50,000 mile life without worrying about excessive valve-guide wear. It's almost impossible to buy leaded fuel around here, save soe specialty race fuels and for older airplanes.
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The oil breather hoses connect to the boot between te MAF and throttle. Any air leaks there mean false air leaking in downstream of the MAF so no fuel is added to make up for the extra air. With the injection controller in closed-loop mode, it reads from the oxy sensor and compensates some. At higher loads (but not necessarily related to RPM's), control changes to open-loop, where the controller looks only at MAF signals; It's in that mode that MAF errors and air leaks mean serious power losses. You can see the oil breather hoses, and get to them with the air cleaner housing removed and the MAF removed. The hoses do get tired.
There's a RL thread worth searching that describes a tester for intake leaks using Home Depot plumbing parts, a natural gas pressure gauge unit used for testing new piping (also from H-D), and a bit of air from your compressor. Roll the engine to 45º before or after top center, add a little air, and it either holds pressure or you'll hear where it's leaking. Roger (928srus) has all the plumbing pieces packaged if you don't want to drive to Home Depot. If your oil system vents are plumbed with original hoses, it's a good idea to renew them anyway. There's an issue with cracking at the plastic oil filler neck too, but that needs the intake and the water bridge removed before you can comfortably replace the filler neck and gasket.