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Join Date: Jul 2002
Location: Sydney, Australia
Posts: 2,477
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When CDI's go bad - the symptons?
Can CDI's go a little bad but still work or do they just totally fail?
I'm chasing a misfire (3500-3800 rpms) on the track car - pulls cleanly to 3500 and from 3800 onwards but stutters in the middle. Could this be the CDI? - I have replaced just about everything else. Car has newly rebuilt/recurved distr, new points/plugs, MFI has been tuned on the dyno - any other clues as to what it could be?
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Cheers, Ryan 1969 911E (historic racer) 911ST replica (tarmac rally) |
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04-12-2004, 03:15 PM
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Join Date: Jul 2002
Location: Atlanta
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I heard about a weird one like this once, the pig tail (wire) on the dist. had frayed and was making contact intermittantly somewhere inside the wire....
Did you check the plug wires for continuity?? Just fishin
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erik.lombard@gmail.com 1994 Lotus Esprit S4 - interesting! 84 lime green back date (LWB 911R) SOLD  RSR look hot rod, based on 75' SOLD 73 911t 3.0SC Hot rod Gulf Blue - Sold. |
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04-12-2004, 06:29 PM
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Join Date: Mar 2002
Location: Portland, OR
Posts: 124
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flaky CDI
Hey, Ryan.
When my CDI started going south, it went intermittent on me. Worked cold, started the car every morning no problem. Once the car warmed up, it might or might not start mis-firing and backfiring (cannon shots from the muffler - scared the holy bejeesus out of me!). It would not hot start at all - no spark of any kind until I left it overnight. This repeated for weeks before I replaced the CDI. It took me so long to diagnose it because a) everyone told me it was either bad or good, so if it worked some of the time it wasn't the CDI, and b) because it costs too much to use the shot gun approach. So, it could be...
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Larry '77 930 w/mods "built with my kids' college fund" |
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04-12-2004, 08:39 PM
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Join Date: May 2003
Location: Manhattan Beach, CA
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A CDI can be intermittent, i.e. work sometimes and not other times,
a total non-op & not at a certain RPM range. The problem you describe in all likelihood is not the CDI. It's probably a fuel starvation at the 3500 to 3800. Since the engine is MFI, it should have a speed relay to shutoff the fuel on de-accel which occurs around 3000 to 3500. Make sure this is not interferring.
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Have Fun Loren Systems Consulting Automotive Electronics '88 911 3.2 '04 GSXR1000 '01 Ducati 996 '03 BMW BCR - Gone Last edited by Lorenfb; 04-12-2004 at 08:48 PM.. |
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04-12-2004, 08:45 PM
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Join Date: Jul 2002
Location: Sydney, Australia
Posts: 2,477
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Thanks all - A newly rebuilt CDI is being tested this afternoon - fingers crossed. If no change then a new coil will be trialled.
Loren - thanks, the speed relay is not hooked up so I know it is not that.
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Cheers, Ryan 1969 911E (historic racer) 911ST replica (tarmac rally) |
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04-12-2004, 10:03 PM
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Ryan,
I was going to ask you if you've tried another coil ....
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Matt Holcomb 1990 Mazda MX-5 (Miata) -- SOLD 1974 911 RS 3.0 replica -- SOLD 1974 911 Carrera 2.7 (MFI) -- SOLD 1976 911 2.7 -- SOLD |
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04-12-2004, 10:20 PM
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1974 Porsche 911 Carrera 2.7 2.7 MFI
