83 SC will turn over but won't fire

HDBrown · 02-02-2007, 12:04 PM

Can anyone suggest a good checklist to go down for an 83 911sc that will turn over but won't fire? Thanks.

1982911SCTarga · 02-02-2007, 12:10 PM

Three things: fuel; air; and fire (spark). And the systems related to each one.

Did you buy that car or are you poking and prodding?

Brian

HDBrown · 02-02-2007, 12:17 PM

Thanks - I havn't bought it yet, still "poking & prodding". You must have seen the listing or know the seller.

I can go about it intuitively, but I'm interested in knowing any of the common failure points for an SC. For instance, I had a Carrerra and I knew to carry an extra DME relay. One night it wouldn't start, I broke out the extra DME relay and voila! fired right up.

The seller claims that this car was running when he parked it. Assuming he is being truthful, I'm thinking (hoping) it is something simple.

Joe Bob · Joe Bob's Garage

The ONLY way to figure it out is to eliminate what it isn't. You will need two people, or long arms or a remote starter switch.

Pull a plug wire, find a suitable ground, hold the wire with an insulated glove or set of INSULATED pliers and crank the engine. If you get a nice fat blue spark....that's not it....no spark...that's one problem

Next, open the air box, lift the flapper and turn the key WITHOUT cranking the motor....you should here the fuel pump come on.....no fuel pump noise, no fuel......try using some Quick Start (Ether). Spray while cranking the motor, it should fire....if it does fire.....

If you do hear the pump and you have spark, it's probably out of time or has an issue with the cap or rotor.....

1982911SCTarga · 12:50 PM

Hank, I saw the ad (see my comments in the other thread).

I would try to get as clear an explanation from the owner of the symptoms that were present that caused the car to be parked.

On getting the engine started, there are some basic things such as the red fuel pump relay (see the inside of the fuse box cover for which position it's in). You also need to make sure that the battery has enough juice to get the engine running (check with a voltage meter). An '83 also has an oxygen sensor relay under the passenger seat. I'm not sure that a failure of that would result in a no start, but it would run poorly.

Begin with the obvious and work your way in.

No doubt, many others with more knowledge will offer their suggestions.

This could be an easy fix or a difficult one (with beaux coup layers of interactions). Good luck.

Brian

psalt · 02-02-2007, 01:04 PM

Hank,

Check to see if there is fuel in the tank, the 911 gauge has fooled many. Listen for the fuel pump when you lift the air sensor plate in the air box with the key ON. Be aware that on an SC, the cold start valve and the injectors spray when cranking and it is all too easy to flood the engine if it does not fire. You should also be able to hear the CDI box whine with the key in the ON position. Check for spark with a spare plug, and if there have been many attempts at cranking, pull a plug and see if it is wet. If so, clean and replace, or replace the plugs.

Paul

HDBrown · 02-02-2007, 01:38 PM

Gentlemen - thank you for the information! I'll let you know how it turns out. H.

Blanco · 02-03-2007, 05:08 AM

I had the same issue with my 82. It turned out to be the green wire from hell. It was not providing a trigger to the CDI. I went ahead and replaced the green wire and it cranked right up.

If your green wire is brown and brittle then change it. Mine had been field repaired with some electrical tape by the previous owner. It worked until the inside core was grounding to the outside wire.

surfdwn · surfdwn's Garage

Check the fuse for the fuel pump, located along the left side of the engine compartment. It will corrode over time and need cleaning. The wires often look like they get too hot in this area. I have had this occur on several cars.

David Nolen

HDBrown · 02-04-2007, 05:36 PM

Thanks to all for the advice. I passed on the non-operational "good deal" and bought a very nice 81 SC that has been well maintained and recently gone through with a "fine tooth comb" and a box of q-tips.

Early_S_Man · 05:45 PM

Hank,

Does the car have the factory alarm system with the keyswitch in the driver's door? If so ... a failed alarm control unit may be keeping the car from starting.

'82 SC Won't run

Here are some additional resources:

6-pin SC/Turbo CDI unit repair documentation

BOSCH CDI discrete components troubleshooting

http://www.st.com/stonline/books/pdf/docs/4347.pdf

http://bitsavers.org/pdf/ibm/generalInfo/223-6783-1_transistorTheory.pdf

http://bitsavers.org/pdf/ibm/generalInfo/223-6725-2_TekOscopes_Aug60.pdf

The 'usual suspect' list for SCs includes these items to check:

1. Fuel pump relay -- Red ... check for corrosion on relay pins or socket

2. Thermotime Switch + Cold-start Solenoid

3. Fuel pump

4. Distributor Green coax trigger lead to CDI unit ... replace if insulation cracked/missing or discolored brown

5. Distributor magnetic pickup coil -- test by measuring resistance at CDI 6-pin connector terminal #7 & #31b ... 600 Ohms +/- 10%, also look for 1 -2 Volt AC signal during cranking

6. Replace distributor coil lead with dedicated test lead and spark plug [KD Tools 2756 or 2757] with permanent ground clip. Test coil output while cranking. NEVER crank engine with coil wire disconnected [no load on coil] and CDI unit powered up!!!