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My Motor is Missing! (multimedia enhanced)
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bacook  
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PostPosted: Tue Aug 07, 2001 11:32 am    Post subject: Reply with quote

Hey Everyone!
After a recent "exhibition of acceleration", my 931 motor has started missing. In order to exploit technology and absorb as much internet bandwidth as possible, I have uploaded a video clip so you can hear what it sounds like.
Notice how it runs smooth for a few seconds, then rough for a few seconds. What is going on here? I checked to plug wires and timing, and the timing belt doesn't appear to have slipped. Any suggestions?
Here are the clips:
High Bandwidth (2.5MB)
http://members.rennlist.com/bcookt06394/931missing.mpg
Low Bandwidth (816KB)
http://members.rennlist.com/bcookt06394/931missing.rm
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Joes924  
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PostPosted: Tue Aug 07, 2001 2:29 pm    Post subject: Reply with quote

Somthing in the fuel department try moving around the injectors . Maybe pull em and put back in/ in diff. holes.
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Dave  
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PostPosted: Wed Aug 08, 2001 12:45 am    Post subject: Reply with quote

Check your coil it could be bad. Sometime they run got for a few seconds but then they get hot and crap out.
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wdb  
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PostPosted: Wed Aug 08, 2001 12:22 pm    Post subject: Reply with quote

my other car had a similar problem,turned out to be a loose battery terminal.
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Joes924  
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PostPosted: Wed Aug 08, 2001 2:58 pm    Post subject: Reply with quote

Does it turn over and crank good. fuel filter,injectors or loose connection. I had a rusty gas tank once and it sounded like yours.

[ This Message was edited by: Joes924 on 2001-08-08 14:59 ]

[ This Message was edited by: Joes924 on 2001-08-10 10:38 ]
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bacook  
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PostPosted: Fri Aug 10, 2001 11:14 am    Post subject: Reply with quote

Well, I tried another coil, reseated the ECU connections, reseated the injectors, and tightened the battery terminals. All that and the car is still missing. Any other suggestions?
I will get a compression tester this weekend and do that and a leakdown test to see if anything is broken.
Aaaarrrrggghhhh! At least my 924NA is reliable!
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eturbo924  
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PostPosted: Sat Aug 11, 2001 3:10 am    Post subject: Reply with quote

Did you check the ignition wires (spark plug wires)

Also since I can not hear the file I need to ask. Does the idle drop or stay constant with just a miss?

Eric
http://www.geocities.com/eturbo924
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Zuffen  



Joined: 31 Jul 2001
Posts: 1426
Location: Owasso, Oklahoma 74055

PostPosted: Sat Aug 11, 2001 4:03 am    Post subject: Reply with quote

did you check your rotor? how does it act across the rpm range?

_________________
Bob Dodd - 924turbo@cox.net
931 1982, 944 1982 euro, 924S 1988SE, 93 968 tip 06 Silver Cayenne S, 06 Black Cayenne S

I have Way too many cars, parts for the 931,944 and 951
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wdb  
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PostPosted: Sat Aug 11, 2001 5:32 am    Post subject: Reply with quote

its been my experience that an intermitant miss is not mechanical,a bent,burt,or stuck valve will cause a constant miss.it sounded like the exhaust was poping(not smooth steady exhaust flow)caused by unburned fuel igniting in the exhaust manifold. using insulated pliers pull the plug wires one at a time while the engine is idling,and youll be able to identify which cylinder is not firing right,because there will be almost no change in the idle speed when you pull the plug on the bad cylinder,but when you pull the plug on the three cylinders that are running well there will be a dramatic drop in engine speed.if you can isolate it to one cylinder,its a process of elimination.vacuum leak(spray carb cleaner around intake runner ,and injector for that cylinder,fuel flow(check injector,if you switch it youll still have miss just different cylinder), spark (check the hall effect trigger and pick up that are under the rotor)in the distributor as well as the obviousplugs wires,dist.contacts,check connections on the altenator.if these dont get it ,the only thing else I know of that would cause this is a bad ground on the control module.hope this helps
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larso  
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PostPosted: Sun Aug 12, 2001 3:28 am    Post subject: Reply with quote

could be:

-loose wire
-ignition module
-pressure switch for fuel cut off
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Joes924  
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PostPosted: Sun Aug 12, 2001 12:01 pm    Post subject: Reply with quote

fuel filter.
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bacook  
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PostPosted: Mon Aug 13, 2001 2:52 am    Post subject: Reply with quote

OK, so I checked each spark plug and when I disconnect each of them it doesn't run any worse. It is a sporatic miss, and it does indeed sound like a misfire. Carb spray didn't reveal anything, and I checked the under-dash ECU and the one under the hood for loose connections. The injectors are seated well, and I tried new plug wires and another distributor cap. The fuel filter only has a few hundred miles on it. The misfire is persistent even at higher RPMs.
I did notice that, when I unplug the wires from the in-tank fuel pump, nothing happens. Could a bad pump cause a misfire if the fuel pressure is low? I tried the same on my NA and it didn't make a difference, but that was just at idle. Also, keep in mind that this was a sudden break, likely due to being at redline too long. I still haven't done the compression check, but that is next.
DAMN!!! Anybody want to buy a very beautiful car that absorbs all your time and frustrates to no end? It's the perfect relationship!
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numbers  
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PostPosted: Wed Aug 15, 2001 7:40 am    Post subject: Reply with quote

Check your valve springs. Running it at high revs for an extended period, you may have broke one.
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wdb  
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PostPosted: Fri Aug 17, 2001 11:33 pm    Post subject: Reply with quote

let me see if I can lay this out so I can understand it better.cannot isolate it to one cylinder,that means its systemic.elimanates A (1)bad valve or spring.prolly not slipped timming belt;no mention of power loss.spark;replaced coil,notmuch else there between dist.and plugs to go wrong. vacuum leak;oxegen sensor would adjust fuel quickly and miss would hardly be noticable.fuel pump;when going bad draws excess current,would burn a fuse.pressure regulator;I dont know how it works to know if it could cause this type of problem.the cycling of low idle speed and high idle speed suggest to me that it is a sensor or electrical problem within the sensors circuit.I would check the o2 sensor for contamination (oil carbon etc.)and wires for loose or damaged connections.pressure regulator,some one else will have to help you with that.
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larso  
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PostPosted: Sat Aug 18, 2001 4:04 am    Post subject: Reply with quote

how easy does it start compared to before?

usually if the head gasket is gone it is always harder to start since starting relies on compression for quick starts.

-ignition module could be a possibility still.

-ignition distributor could have something wrong with it.
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