electrical fubar, either pump or crank but not both

[7783911]

I admit this one is my fault, i was installing a light in the engine bay and touched a live wire to the metal box holding the 14 pin connector etc. Now the car wont start. If I crank it, i cant hear the pump going..but if i remove the 14 pin connector, the pump whirs away but obviously no cranking.

What could i have fried to cause that symptom? I checked the relays..fine. I checked the wiring to the 14 pin and the relay and every thing looks fine.

Suggestions (Timmy, I hope your out there!)

[Dpmulvan]

Did you check all your fuses??

[7783911]

yes, checked relays and fuses..is there some sort of "brain" that turns off pump if cdi is non functional...since i get pump to work without 14 pin connector but when connected i dont hear pump and am not seeing spark..maybe cdi is heart of all woes? How does one test the CDI?

[Dpmulvan]

Problem is probably where the hot wire came from and not what you touched in back. Is that wire still hot? You need flow chart and meter with continuity. You can’t work on these cars hot, lacking a fused dash et.
Hopefully somebody has a link or copy of flow charts.

[7783911]

The live wire i touched the rear metal fuse box with was a new one from the 3 fuse box in the engine bay..an unused slot for AC. Showing power to all of those inbounds from main harness, showing some power at 14 pin connector,,but have to see if CDI is culprit, could it block fuel pump from running (like a safety feature?) since fuel pump does run with 14 pin connector undone?

[Flat6pac]

The 77 has an automatic fuel pump start with the movement of the airflow sensor like the SC
You shouldn’t hear the fuel pump run as the starter is noisier.
Your red relay, in the front, remove and run a jump wire from 30 to 87a will turn the pump on. The numbers are on the bottom of the removed relay.
If you have fuel pumping, spark is your next consideration.
Bruce

[7783911]

Bruce, i have a 77 targa with 83 sc engine transplant. The fule pump when the key is "on" is noticable whine as expected. But when cranking cant hear any whine at all (me at back, helper at fron to listen). Seems we may be looking at CDI or possible AFS?

[timmy2]

Pull an injector when cranking and see if it is squirting fuel.
Not at the same time...
Pull a spark plug and see if it is firing or put a timing light on it.
Checking for spark is easier, so do that first...

[7783911]

Thanks Dennis

I did try the spark test without success but was curious why pump worked without 14 pin connected but why i couldn't hear the pump with the 14 pin connected...does the CDI (if its fubar) have some impact on controlling the fuel pump if an error is detected?...i will try the fuel supply now to further test...

I suspect the CDI

[7783911]

tested fuel with cdi plugged in and 14 pin inserted and got some fuel (not alot but not sure how much to expect..but definitely some). So now down to spark..wish i had a spare cdi to test with. any suggestions how to test CDI?

[timmy2]

Other than a timing light to check for spark, not really. (see link below)
I have a special device for my own testing, but that won't help you.

The CDI power wire may be the problem. It runs straight from the top of fuse 11 (counting from headlight back) to the white "t" connector and from there to the lower left fuse on the 3 fuse panel.
Check at the 3 fuse panel, or in the T connector for 12 volts with ignition on. (careful, that circuit is not fused)

There is this thread to read:
911 sc no spark solved

[7783911]

i have power on pin 5 and good ground on pin 1

pin 1 to 3 is 0 ohms which is correct?
pin 1 to 4 is only 606 which may indicate defective coil damage to the box?
pin 2-5 is 1 ohm..which indicates damage to fusible tach link in the box

pin 5 is 12.6 V
same 12.6 at fuse (position 3) and white connector (red from harness to red to 6 pin connector)

i could nt test 1 to 5 for capacitance

i will try to figure out how to test cdi for spark production and also test coil

[Walt Fricke]

778
The safety circuit for the fuel pump involves a switch over behind where the air metering disk is. With no air flowing the measuring plate sits at its lowest position, and the switch is closed. This grounds the fuel pump relay coil up front in a clever way such that it won't switch the pump current on. The air from starter turning the engine, and a running engine, lifts the plate up enough so this switch opens, the fuel pump runs, all is normal (I'm simplifying the relay wiring a bit). If your engine stalls, the fuel pump stops. Turn the key to the run position without the engine running, and no fuel pump.

However, if you disconnect this switch back on the engine, the pump will run when the key is turned to the run position, even without the engine turning. The fuel pump jumper relay jumper trick does the same thing, but it is easier if you can't remember which pins on the relay are which to pull the plug - if you have long arms, or have removed the heater air fan.

The switch line runs through the 14 pin connector back on the left rear of the chassis. So f you disconnect that plug, the fuel pump will run with the key on.

[7783911]

luckily a friend took his cdi and brought it over and we plugged it in..worked like a charm so i am sending off to repairs..thanks to everyone who offered advice, i did learn more with every posting! One day I l be as good as Dennis (ha ha..never!)