SC will not start

[rfix'n]

Ran fine on saturday and then would not start on sunday. I've checked fuel and spark and have some concerns with each.

Spark - I put a spare plug on the coil lead, grounded and got a blue spark, not fat but blue. When I put the spare spark plug on a spark plug lead I get a yellow spark, again not fat but present. Checking the coil gives 700 ohms between 1 & 4 and 15 & 4. I'm not sure which is 15 and 1, one of them has a brown wire, I'm assuming this is the ground side, is that 1 or 15?

Fuel - If I pull an injector and have someone turn the motor I get a quick initial burst of fuel and then nothing. IF I turn the key to on and push up on the sensor plate I get plenty of fuel coming out of the injector. Should I be getting constant fuel while cranking with the starter?

Thanks in advance for your replies.

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Rob Fix
'78 SC Targa

[wckrause]

Rob,

I don't know if turning the motor with the starter will cause enough air flow to lift the sensor plate high enough to get your main injectors to start running. Even if they don't inject, the cold start injector should pump enough fuel to get the motor started. I'd suggest trouble shooting the cold start injector, and the thermotime switch.

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Bill Krause
'79 911SC Euro
MY PELICAN GALLERY

[rstoll]

Had some intermittent starting problems a while back. Especially on humid or rainy days. Changed cap, rotor and wires. Ok now.

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Robert Stoll
83 SC
83 944

[Doug Zielke]

Rob,
I think you hurt that green Targa playing with the Blue Bomber on Saturday!

Seriously, the "yellow" spark thing does not sound good. You should see a veritable lightnin' bolt! I'm going to think about your problem a bit, but in the meantime, you should be checking all the connections.

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'81 SC Coupe (aka: "Blue Bomber")
Canada West Region PCA
The Blue Bomber's Website

[rfix'n]

Doug - My first thought was that my car didn't play well with others! I have checked all plug wires and they test correctly for end to end resistance. I have not checked ground straps etc., yet. I wanted to test the coil but am not sure I'm doing it correctly or what the test results are telling me. Thanks for the replies.

[chrisp]

I just wanted to throw this out......is your airbox cracked? If you don't have the airbox blow off valve then maybe that's the issue. I have heard that when the box is cracked the car won't start. Of course if you have the valve then I have no other ideas.

[Bob W.]

If I remember correctly, according to the fuel injection manual there is enough air flow from a cranking engine to lift the sensor plate and start the fuel pump. In the summer, the cold start injector shouldn't come into play. The cold start injector works only on very cold days. I have to look in the manual to see at what temperature it will engage but I don't have it here at work.
How about trying to start it with either(quick-start). It should start any engine capable of starting. Then you can look for air leaks.
Bob W.

[wckrause]

Bob,

The fuel pump will definetly be on while the engine is cranking. The fuel pump relay circuit turns on the fuel pump when the key is in the START position no matter where the sensor plate is. Once the engine catches, and the key is returned to ON, then the sensor plate switch keeps the pump on.

I've seen specs for the thermotime, but I can't remember at what temp it starts to come into play. Anybody?



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Bill Krause
'79 911SC Euro
MY PELICAN GALLERY

[nhromyak]

As ChrisP stated, air-leak.

Check the boots, pop-off valve (you have one, right?).

Good luck.


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Nick Hromyak
'85 Carrera 7 & 9 Fuchs
Havin' Fun in Sacramento

[rfix'n]

Thanks for all the replies. Yes, I have a pop-off valve. I have checked for cracks in the airbox, none visible. As I understand it, if there was an air leak then the sensor plate would not lift and thus no fuel would get to the injectors. Tonight I will try and start the car while gently lifting the sensor plate, this will ensure fuel delivery.

I'm still concerned its a spark issue. Can anyone provide the correct test procedure for the coil or verify my numbers in the above post?

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Rob Fix
'78 SC Targa

[Early_S_Man]

Rob,

Sounds electrical, specifically distributor-related! Your coil is fine, as the secondary resistance spec is 650 to 790 Ohms. The primary is supposed to be 0.4 to 0.6 Ohms, but some digital multimeters read any low resistance as 1 Ohm, even shorted test leads! There are two or three versions of the CDI-system coil:

1. Terminal '1' is ground. Terminal 'A' is the hot side of the primary. Terminal '4' is the output of the secondary.

2. Terminal 'A' is the hot side of the primary. Terminal 'B' is ground. Terminal '4' is the output side of the secondary.

3. Traditional Bosch coils: Terminal '1' is ground. Terminal '15' is the hot side of the primary. Terminal '4' is the output side of the secondary.

Check the condition of the distributor cap, specifically the center carbon rubbing block that makes contact with the rotor.

Also check the resistance of all of the ignition wires. Coil lead should be 1000 to 2000 Ohms. Spark plug wires should be 3000 to 4000 Ohms.


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Warren Hall
1973 911S Targa
1992 Dodge Dakota 5.2 4X4 parts hauler

[wckrause]

"Tonight I will try and start the car while gently lifting the sensor plate, this will ensure fuel delivery."

Be careful doing this, those intake backfires are violent.

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Bill Krause
'79 911SC Euro
MY PELICAN GALLERY

[Early_S_Man]

As stated above, I don't think this is a fuel delivery problem!

Thermo-Time switch opens between 107 degrees F and 112 degrees F, so it is commonly mis-named as cold-start enrichment ... it REALLY should becalled NON-HOT RESTART ENRICHMENT!

The 'yellow spark' is the reason I suggested testing the spark plug wires, as it suggests a somewhat diminished-power spark at the plug, which suggests to those 'experienced of the OPEN BERU CONNECTOR clan' ... that the spark maybe is having to jump accross 'one too many' air gaps on its' path to the spark plug! Which, under cold engine start conditions, i.e., underhood temp at room temperature, the Bosch CDI-system is fully capable of doing, but it would be a (VERILY!!! VERILY!!!) lower-power spark in the combustion chamber!!!

[The above explanation inspired by John Muir! May he Rest in Peace!]
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Warren Hall
1973 911S Targa
1992 Dodge Dakota 5.2 4X4 parts hauler

[This message has been edited by Early_S_Man (edited 08-20-2001).]

[Doug Zielke]

John Muir??
Holy cats, Warren...I think he'd have us all riding around on horses!

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'81 SC Coupe (aka: "Blue Bomber")
Canada West Region PCA
The Blue Bomber's Website

[Early_S_Man]

Doug,

Not the John Muir of the 19th century who rode on horseback to show Abraham Lincoln his sketches of the mighty Redwoods!

Instead, the John Muir of the 20th century who toured a bit South of the Redwoods, down Baja way, and whose onboard spare parts kit for trusty VW transporter included: one spare distributor, cylinder and piston, connecting rod, engine bearings, cylinder head, rear axle and bearings, starter, generator, Voltage regulator, numerous spare tire tubes, bead breaker & tire irons, headlamps, tie-rods, front-axle bearings, wheel cylinders, etc. A man prepared for any forseeable roadside emergency caused by Pemex 75 octane petro-tailings, or large rock thru oil return tubes!!!

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Warren Hall
1973 911S Targa
1992 Dodge Dakota 5.2 4X4 parts hauler

[Doug Zielke]

Got it, Warren!
That Transporter must have been pretty full, if you consider the tools John must have taken along as well.

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'81 SC Coupe (aka: "Blue Bomber")
Canada West Region PCA
The Blue Bomber's Website

[wckrause]

If Warren says it's ignition, I won't dispute him, but if that does check out OK, I'd check the thermotime switch next. No matter what condition the rest of the CIS system is in, if the thermotime and cold start (non-hot start) injector are working, the motor will at least cough sputter then die. (If the ignition is working properly).

[rfix'n]

Well I'm convinced its spark related as well. However, when I got home this evening it started right up. I took her for a spin and she ran just fine. Still has a yellow spark though. A double check of the plug wires all test out fine. It's a new set that I built from Paccar wire this winter, I was hopeing for a failure here as it would be an easy fix.

I'm still unsure of the coil, as I understand Warren's post the primary test is between 1 & 15, this tests to 700 ohms and I think its suppose to be less than 1 ohm. I am going to cleanup my distributor this weekend, might be time for a new coil as well.

Thanks again for the posts and suggestions, and special thanks to Warren for explaining the primary & secondary on the coil.

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Rob Fix
'78 SC Targa

[This message has been edited by robfix (edited 08-20-2001).]

[Titleist 911]

Check the green wire connecting to the distributor. This was my problem on a "78 SC. It mimicked many other problems, especially the hot start.

[Early_S_Man]

Rob,

Yes, by all means check the two-pin connector on that green cable! If it is on its' dying legs, it may be fragile and ready to break/fall apart! From what I have heard, the $29 replacement cable is only from distributor to connector, so be careful with the connector and part going to the CDI-unit, as it is part of the whole wiring harness, and costs many $$$!

Military or IBM Twinax cable and connectors are a less expensive solution, but require more time to assemble the connectors and solder, etc.
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Warren Hall
1973 911S Targa
1992 Dodge Dakota 5.2 4X4 parts hauler

[This message has been edited by Early_S_Man (edited 08-21-2001).]