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Eagle Keeper's Avatar
 
Join Date: Apr 2001
Location: Panama City Fl.
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Help no spark!

Well I just finished installing the engine after a top end rebuid. Engine cranks fine but it wont fire up! I'm getting fuel but no spark. I can hear the CD box humming away. Any ideas!?!?!?

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Jason
F-15 Crew Chief (21 years)
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'71 914 (Sold)
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Old 06-03-2003, 09:08 AM
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Join Date: Oct 2002
Location: Kentucky/NY
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Only the basics

Check timing, check correct wires on correct plugs. Check
coil wire to dist. Check that connectors are down and tight
on plugs.
I'd try one thing at a time...no point in doing more if the first
thing you try fixes it. Also give you an idea what to check
if it happens again.
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Old 06-03-2003, 10:50 AM
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Also:
check connection at CD box
check connections to coil (properly connected?)
check "signal wire" to distributor (tends to break internally, I've been told)

Jerry M
'78 SC
Old 06-03-2003, 10:59 AM
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Thanks for the replys! I've tried everthing listed! Now I'm leaning to the coil because the CDI is humming away. I did all the voltage tests and everthing is good at the connector at the base of the CDI. But still no spark!!!
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Jason
F-15 Crew Chief (21 years)
'86 944
'71 914 (Sold)
'79 911 SC (Sold)
Old 06-03-2003, 12:49 PM
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Jason,

All the CDI-unit whining signifies is that it has power and the DC-to-DC converter circuit is working ... it doesn't mean the unit is getting a trigger signal, or that the trigger signal is being processed!

Did you check for continuity through the 600 Ohm pickup coil at the CDI-unit connector? If it is good ... check for low-level AC signal [less than 1 Volt peak-to-peak] while cranking with DMM set on AC Volts, Hz scale, or oscilloscope ... at the CDI-unit connector terminals #7 & #31d ... as shown in the following diagram:

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1973 911S Targa ... 'Annie'
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Last edited by Early_S_Man; 06-03-2003 at 01:22 PM..
Old 06-03-2003, 01:20 PM
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I did that ck I was getting the correct readings. I'm leaning to the coil because it's cheaper!!! But it could be the CDI.
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Jason
F-15 Crew Chief (21 years)
'86 944
'71 914 (Sold)
'79 911 SC (Sold)
Old 06-03-2003, 01:44 PM
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hey bud, i have a 70t, had the same problem and it turned out to be the points.
Old 06-03-2003, 01:53 PM
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Jason,

That was TWO tests:

1. 600 Ohms +/- 10 % at terminals #7 & #31d

2. 200 mV AC signal at terminals #7 & #31d during cranking or while turning removed distributor by hand

The only way to rule out the CDI-unit is to measure the 350 Volt to 460 Volt pulses at terminal 'A' of the coil ... with a scope, while cranking!
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Warren Hall, Jr.

1973 911S Targa ... 'Annie'
1968 340S Barracuda ... 'Rolling Thunder'
Old 06-03-2003, 01:55 PM
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Warren,

I didn't do the Ohms ck but I did do the mV ck on the distributor with the distributor removed and with it installed. I did get a slight drop when I was measuring it through the harness compared to when I was going straight off the distributer.
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Jason
F-15 Crew Chief (21 years)
'86 944
'71 914 (Sold)
'79 911 SC (Sold)
Old 06-03-2003, 02:06 PM
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You can use a 600v neon to test for output from CDI to coil
Get from Radio shack (called Tandy in UK)
and put a "clamp on" timing light on HT lead from coil to dizzy.
That'll prove it real quick.
Jeff

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Old 06-03-2003, 02:27 PM
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