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Re: Turbo boost Analysis questions? 92 900T Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Fri, 28 Apr 2006 13:35:07
In Reply to: Turbo boost Analysis questions? 92 900T, jkel, Fri, 28 Apr 2006 12:25:49 Members do not see ads below this line. - Help Keep This Site Online - Signup |
I think your engine is running just a little lean, and that is promoting knock and the lack of full boost. You mention that the boost seems to dial back a bit, depending on air temp. Also, a whitish plug is running lean - it should be more of a grey.
Two reasons come to mind for running lean - too much air, or too little fuel. How is your idle? If the idle is smooth, it is unlikely you have a vaccum leak. Also, vacuum leaks aren't much of an issue at boost - leaks are now letting metered air out. But it is worth looking into.
The one that comes to mind is not enough fuel. Your fuel pressure may be a bit low, or the fuel flow. A clogged fuel filter can allow fine fuel pressure at low flow rates, but as flow increases (with engine speed), pressure drops off. The FPR also has to be working properly - it increases fuel pressure as the boost pressure increases. Make sure that hose from the intake manifold to the FPR is in good shape. Otherwise, the FPR won't increase pressure enough, and you'll run low on fuel at higher boost.
Make sure your throttle position switch is working and set properly. It provides a signal at WOT for fuel enrichment.
Lastly, clogged Injectors will reduce fuel flow. The suggestion of a can of fuel injector cleaner wouldn't hurt.
Try running a spark plug one range cooler. A hotter plug is more prone to knock. Yes, the manual has its recommendation. That's for a new car - yours has 16 years on the clock.
I'd also try dialing the timing back a couple of degrees. The loss of performance by running a hair retarded will be more than offset by the additional boost.
As cars age, some need higher octane, others can get by with lower octane. If your compression is good, you may even have a little carbon buildup that is increasing the compression, and making the engine more prone to knock. It's entirely possible that short of an engine rebuild, you won't be able to get full boost on available 91. I had a '86T that required 93 for full boost. In that case, a slightly cooler plug and slighty retarded timing may be your only choices in the land of low octane. And that's not a bad trade.
posted by 192.249....
, Fri, 28 Apr 2006 13:35:07 <-- Viewing This Message
, Fri, 28 Apr 2006 13:09:07, Sat, 29 Apr 2006 14:56:54, Fri, 28 Apr 2006 15:42:33
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