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Join Date: Sep 2002
Location: Johns Creek, GA
Posts: 1,392
Still no start- mmmm

I was hoping i would not have to ask for help / guidance, but here goes.

I had a no start issue about a month ago and I thought I traced to a bad coil (per my resistance readings and no spark at the plug). I read a several good informative threads on the topic and thought this was the issue. I installed a used old style bosh coil off a running 911 and the resistance on it was good. I went ahead installed a new Beru wire set, bosh plugs/rotor/cap as they all were fairly old. I tied to start it about 10 times and still no start. One thing different now is when the car is attempting to crank, on about half the ammempts the tach will read around 4k rpm, but the other attempts it will not read, or then start to read. When the no start first occurred a month ago, the tach would only bounch whenthe key was truned but would not read. I rechecked all the connections (ICU, coil wires etc) and the coil resistance all seem good. The Bosch OEM ICU is humming.

Iím thinking about my next steps in troubleshooting and would like comments / suggestions / tell me if I am off base for those more in the know:

1.) I want to make sure it is not a fuel problem. Both pumps seem to be working.
QUESTION: where is the best place to spray starting fluid in the fuel system to see if it will crank?

2.) this weekend when I have a helper, I will check for spark.

3.) The ICU is humming but I understand it could be bad.
QUESTON: is there any way to test it in the car to see if it is any good? I thought I read there is not a good safe way to do it. I could send it out to be tested and rebuilt if needed.

4.) Regarding the green coax wire from the distributer to the ICU 6 pin connector: I checked the connection to the distributer and it seems good. I believe I should have the single wire to the ICU (no connection mid way) so I didnít look any further at the coax. I want to check continuity. At the connection to the distributor, there is a green wire and black wire.

QUESTION: Do I check continuity on the green connection at the distributer to the 31d connection on the 6 pin ICU connector? Do I check the black wire on the connection to the 31/1 connection on the ICU connector?

5.) My ignition switch did not want to turn a intermittently about a month ago the same day this no start occurred. It would eventually turn and the car would start. The same day it would trun but then the no start.
QUESTION: should this be a non-issue since the key will turn and the pumps will run and the CDI is humming?


Any help / guidance in advance would be appreciated.

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Charles
79 930 #632
88 911 Cab
74 TR6
88 CRX Si

Last edited by cellison; 07-06-2012 at 10:06 AM.. Reason: clarify
Old 07-06-2012, 09:57 AM
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Aircooled Breakfast
 
Join Date: Dec 2007
Location: Wyoming
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Charles, Here are some quick thoughts, I'm sure others will offer more ideas. Check the basic stuff first:

How is your battery? Sometimes a weak battery will crank the engine and not properly feed the ignition equipment. What is the voltage with the engine not running?

If you can hear the fuel pumps running when you have the ignition on then it means that someone has disconnected the metering plate sensor. You can pull the air cleaner and push down on the metering plate to send fuel to the injectors but don't do it much as you will quickly flood it.

The CDI box normally makes a high-pitched whine which is generally considered a sign of health.

Definitely have an assistant help you check for spark which will help you to determine if it's fuel or ignition.
Old 07-06-2012, 10:23 AM
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Thanks Luft. i may need to make one clarification. i can hear the front fuel pump running, but I think the back one is running, but it may the be whine of the ICU i hear. the fuses are fine. i'll check the battery voltage.
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Charles
79 930 #632
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88 CRX Si
Old 07-06-2012, 10:48 AM
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Just because your CDI (ICU, in your vernacular) is humming doesn't necessarily mean it's producing spark. I thought the stock CDI's whined....as in high pitch, not a low pitched hummm.

Anyway, I'm too deaf anymore to hear the whine of mine - but then I'm not sure I should be hearing anything from my MSD anyway.

Maybe find someone from whom you can borrow a known good CDI, just to put that piece out of the equation. I think I've seen some tips on how to test these somewhere, but you may have to spend some time searching this forum to find it.

I'm a little suspicious of your ignition key symptom earlier (your point number 5 ). Just because you can hear the CDI energized and the pumps running with the key on and the engine not running, who's to say that when the key is turned to the starter position that the contacts which keep electricity flowing to the ignition and/or fuel systems isn't faulty? Your keyed ignition switch temporary fault seems just too much of a coincidence.
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Mark H. 1987 930, GP White, Wevo shifter, Borla exhaust, stock everything else. The result of a massive Pelicanite good will fire recovery effort. Truely an open book, ready for the slippery slopes to modification.
Old 07-06-2012, 11:31 AM
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beancounter
 
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tach weirdness may point to CDI, as the tach gets its signal from the CDI box. anyone local to you that you can swap a known good CDI box with just to test? AFAIK its the same part as in a 911SC, so that broadens the pool of possible "donors"
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Old 07-06-2012, 11:33 AM
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Sorry, but I didn't read much of your post...But, is your overboost switch grounded?
Old 07-06-2012, 11:49 AM
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thanks for the responses. i checked battery voltage and it was 12.7V. still haven't checked for spark as my helper took off to run errands. the CDI is whining not humming. i may look to see if i can borrow a cdi to swap out. QUESTION: do i actually need to remove my cdi/install the other one or can i just plug in the the donor and place it near the other one? there a a thread on Cdi, and it said if i recall you can test it but i think it said don't do it as her is high voltage. i'll go back and re-read it. i'll look at the over boost switch. i'll zero in on those items and if it still will not start, i'll look more at the ignition switch. any other ideas?
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Charles
79 930 #632
88 911 Cab
74 TR6
88 CRX Si
Old 07-07-2012, 06:12 AM
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beancounter
 
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I think you can just plug in the CDI
Old 07-07-2012, 06:19 AM
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Garage
Plug your CDI into the other car and see if it runs......less chance of frying the doner if something is wrong with your wiring.
Don't forget.....you'll need to ground the CDI.

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Last edited by pete3799; 07-07-2012 at 07:37 AM..
Old 07-07-2012, 07:17 AM
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