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Registered User
Join Date: Feb 2012
Posts: 17
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no power at 4000
1978 930. have all new vacuum lines and they are tight. Except for a faulty AAR the car runs great until it hits just over 4000 rpm. Then there is no power - even on boost. Feels like it is missing. I have adjusted the valves as well. Previous owner had bypassed the boost cut off switch but I have remedied that. Before I start with changing cap, rotor, fuel pump, fuel filter, accumulator, etc. I thought I would go to the well of all knowledge!! Any ideas on what is the logical progression to start on first??
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07-17-2012, 08:48 PM
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Registered
Join Date: Jul 2003
Location: Back in B'ham, AL
Posts: 3,459
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As always, before any of the above changes, check the WUR; many threads on that... The hot summer temps affect our cars badly.
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07-18-2012, 05:04 AM
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Registered
Join Date: Jul 2006
Location: S. Florida
Posts: 7,249
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"Any ideas on what is the logical progression to start on first??"
Check fuel system and control pressures and air fuel ratios when cold, warm, and hot at idle, cruise, and boost. If it's misfiring and rough when boost comes on it may be going too rich and that could be caused by alot of things including a simple small vacuum leak turning into a metered air boost leak. That can make the AFR go rich to around 9:1 at full throttle and 4000 rpm and the thing will chug, misfire, and blow dark grey hydrocarbon stinking smoke out the exhaust when you floor it. |
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07-18-2012, 09:05 AM
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Join Date: May 2008
Posts: 1,252
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http://forums.pelicanparts.com/911-930-turbo-super-charging-forum/682816-need-help-please-cutting-power-around-4000-rpm.html?highlight=power+4000
Had a similar symptoms uptop.. 1ST i thought my msd6al was conking out...The least expensive way 1st ..CHK all hoses-intercooler-afrs and every thing they said ^^^^^^^^^^^^^^^^^^^...Had a volt meter..chked all fuses...etc..etc.. Tightend up the wastegate-hoses-bolts..etc...etc..--Still didn't feel right. Changed plugs- ngks or denso copper cheap..& if u can do them... or clean them. Switched my coil///slightest leak that was almost not seen... Changed it to msd/epoxy (black one). Took out the distributor--cleaned it and changed the coil inside...Cost me approx. $35.00 autozone. *Getting an AFR-Meter is a big help* After all done. Kept my fingers crossed..Started great..Took it for some top-end runs...ALL GOOD. Last edited by wjfk32; 07-18-2012 at 09:24 AM.. |
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07-18-2012, 09:08 AM
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Registered User
Join Date: Feb 2012
Posts: 17
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Found that the over boost switch is bad. Grounded the switch and now pulls good through 5500 rpm. Thanks forum to all!!!!
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07-19-2012, 07:22 PM
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Registered
Join Date: May 2008
Posts: 1,144
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dr3358 are you going to get another boost switch, or are you just going to keep a closer eye on the boost gauge?
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'87, Modified WUR, Billet valve, 965 downpipe, Kokeln intercooler, GHL headers, Garrett T04B K27 hybrid, Tial w/.8 bar, WEGO IV, RarlyL8 dual out, LSD |
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07-21-2012, 05:40 PM
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Registered User
Join Date: Feb 2012
Posts: 17
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Replaced boost overboost switch and problem solved, except that now I loose power at about 5700-6500. Could be that the engine has close to 175k on it!!
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08-03-2012, 08:40 PM
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