CIS electrical gremlin, HELP!

[Mookster]

I have a '83SC

I have an intermitent bucking as I drive down the road.
When the bucking starts I can hear the O2 relay under the seat clicking like mad. I would assume it is electrical based on the relays clicking. The car sometimes stalls or the bucking ends. This problem happens at all levels of the RPM range and at any tempeture. It has been doing this for 2 years and it's getting old!

When the car is in the driveway and the O2 relay starts clicking the fuel pump relay clicks as well.

I have replace the O2 relay, the fuel pump relay, the neg battery cable, transmission ground strap, spark plug cables, distributor coil, lamda sensor, jetronic computer, rotor and cap, all plugs (several times), fuel accumulator, fuel pump relay fuse box plug, flushed the gas tank, and replaced the fuel pump.

I have disconnected the lamda sensor/connected the lamda sensor and the same problems still exit.

I have checked the 12 pin connection and CDI connection. The CDI unit whines when the car runs and appears to be working.
The air flow sensor moves freely. I have cleaned every ground connection I could find.

The valves have been adjusted, the mixture has been adjusted and tested by a qualified shop. The timing is correct.

The voltage tests completed at the battery, alt, and O2 relay are within specs.

If I cannot resolve this electrical issue in the CIS loop, is there a way to by-pass the relay and this gremlin?

I have had a qualified shop attempt to assist but no luck.

Your help/input is appreciated.

Any good shops in Tampa area you recommend?

[Mookster]

bump

[Rick Ilcisko]

I am having the same exact problem now with my 1983SC. Ive done every thing that you did and am working on the green wire (pulse module wire) to the distributor as I type this. If that does it Ill let you know. Keep in touch. Rick

[Mookster]

any ideas?

[john walker's workshop]

disconnect the over-rev fuel pump relay and see if that fixes it. it's mounted on the side of the cowl by the hood hinge, behind the gas gauge. 3x3x1 black plastic box with a white plug on the bottom.

[filou]

Do you have a wiring schematic diagram for your car ??? it is 83 Sc i believe !!! Something is cutting the juice to your O2 and fuel relay and that why the car is bucking. Are you able to read the wiring diagram ??
Yo need at least a Voltmeter and ohmeter to diagnostic your problems !!!
Do you hear your O2 relay click in a harmonic sequence or it is clicking at a random sequence ????
Let us know.
Filou.

[filou]

according to the diagram i have here in front of me (911 sc 82'), the juice to the O2 and fuel pump relays are in direct relationship with your RPM limiter switch. on that switch, the wring diagram indicates four connections : + and - to juice the RPM limiter switch and two usuable connections (like you would find on a regular relay). There are number by: nos 3 and 6 should the + and - for the switch and nos 1 and 4 outgoing juice to power the fuel pump relay. with voltmeter, control the juice at the connections 1 and 4 to see if there constant and also control at 3 and 6 to see if juice is also constant there. If the juice if constant going to the RPM limiter switch , you'll know that your power supply is OK. Is your juice coming out of RPM switch is not constant, you'll know that your RPM switch is shot. Try using a digital meter, even a cheap one, there are more sensitive at detecting voltage fluctuation.
Let me know if you found the problem.
Truly, Filou.

[tutzilla]

I hate to use this term but : Been there done that!
I had a similar problem with my 81SC. I would be driving and the O2 Relay under the seat would start clicking the car would buck a little and then lose power and die (search-runs 16 minutes and then dies). I ran thru the bentley manual with multiple tests, anywhere from trouble shooting fuel related issues(failed fuel volume test so I replaced the fuel pump) to electrical problems(tested fuel relay,rev limit circuit,removed after market security system,etc.).
To make a long story short it turned out to be a short in the CDI box. My P-Mechanic had a spare CDI box which I replaced and viola, problem solved. I opened the original CDI box and found a wire which had worn its self against the inside of the box. Once the car reached a certain temperature the box would ground out. Hopefully this helps! Rob.

[JK-81SC]

OK, since everyone is fessing up I'll jump in too. My '81SC is doing the same thing. Unfortunately it's in about 500 pieces right now, so I can't give immediate feedback on these suggested fixes, other than check my CDI box. I removed the engine/tranny to do some fixing, and then some house and medical bills had to be paid.

So, now I'm back to where I was a year later. I'm getting ready to ship the tranny off off to JW's shop, while I replace injectors and other engine maintence things.

What I will do tonight is take out the CDI box and check for any worn insulators.

Thanks to tutzilla for the help!

[filou]

What i was subjecting is: first found where the problem lies and THEN change the part. I don't like to buy parts (especially electricals which you CANNOT return once they've been installed). Sure, eventually you'll find the problem that way but at what cost !!!! Before i start spending money on parts, i'll make sure i know what was wrong.
IF it's not the RPM limiter switch, then you move on upstream from there and keep going til you find the problem. After that, you can, like you said, round up your suspisions to the remaining parts more likely to go bad in that case the CDI box which make total sense.
Intuitive versus logical thinking will always be the big debate over technological solution.
Truly, Filou.

[Mookster]

Thanks JW for your idea. I will checkout the rev limiter relay.

Filou,

1. I have the Bently Manual which does have the wiring diagram. I can read the diagram but I am not sure where the switches and relays are actually located.

2. I have a VOM. I have complete voltage tests at the battery, fuel pump relay, O2 relay, fuel pump and received normal voltage readings.

3. Just for kicks I did remove the back of the CDI box and did not smell/see anything out of the ordinary. Can the CDI be bench tested?

4. When the O2 relay clicks, it goes f'ing nuts. The car bucks like it wants to stall. One day I was working on the vehicle with both lids up and feul system started to do its wonder. The O2 relay was clicking as well as the fuel pump relay. This confirms my problem is most likely electrical.

If the CDI unit is untimately the problem, do people recommend rebuilding the unit, buying a used unit, or replace it with MSD/aftermarket unit?

From a cost perspective it appears the aftermarket units are cheaper. Are they better? 21 years on the oem part does not appear to me to be all that bad if replacement is warranted.

Additional input is appreciated.

Thanks in advance

[filou]

Mookster, do the relays go wild only under particular circonstances ???
i am still studying the diagram for your car and one other component which could disturb the current flow of the fuel pump relay is the air flow sensor contacts. Did you check those ???
If you look at diagram, i have Hayes book, wiring diagram for 911 sc USA 1982 models (diagram I of VI) line 16, you'll see the air flow sensor contact in line with fuel pump relay going to connection 85 on the relay for the fuel pump. Do you copy me ???
Check for good continuity or almost nul resistance when contacts close.
Let us know.
Filou.

[filou]

Do you know for sure if you sensor if correctly adjusted in relation with the contacts of the air flow sensor plate ??? Because if the sensor plate seat right at the near but not quite closure of the contacts of air flow sensor plate the contact will be most likely to go ON, OFF ON then OFF again kind of situation.
Make sense ???
Filou.

[niner11]

mookster, Look up German Tech in largo if this starts to drive you nuts after a while. PM me if you need more info, Chuck

[Mookster]

Filou,

The relay goes nuts intermittenly. No certain rpm range, temperture... I have gone months without the problem and then it starts again. Sometimes it happens daily. This is what makes it frustrating.

I am not positive the air flow sensor is adjusted correctly. I did move it up and let it down and it appeared to move without problems and back to its correct position.

Niner11,

Thanks for the wrench tip. I may need a new set of eyes on this one.

[tutzilla]

My P-Mechanic has an MSD in his SC that he is happy with. The only reason I changed mine out to another used original CDI box is because he gave me a good deal on it and it worked. Had I caught the chaffed wire in the CDI box it would have been an easy fix with just a piece of electrical tape. If you have any interest in my used box let me know, I am sure we could work out a deal on it(I would make sure it works).