12V DC at the engine ground

[EAP]

Where do I start to look for a short??
I am showing 12V DC at all three of the wire terminals that attach to the left side engine ground. I am also getting 12V DC on each side of each injector connection while disconnected. I am testing with a multimeter. During my test of the engine ground I have all grounds (3 terminals) disconnected and am reading from the terminal to ground. The current is only present with the ignition key in the on position and the car will not start.

Any electrical guru's out there that can help?

I have just reinstalled the engine and am suspect of the alternator, ignition switch electrial portion or the DME . The engine will not run consistantly due to obvious fuel flooding. I have replaced new (from Pelican) the position sensors (seed and position) the CHT sensor, plugs, wires, cap and rotor.

I hope I have explained my problem well enough

Thanks for any and all help.

[ToddM]

Just need to start disconnecting stuff one at a time until it dissappears

I would be surprised if something isn't getting hot; the point of the short would be seeing the full battery load on it.

[EAP]

I should have added in my initial post. This is an '84 3.2 RoW...

Nothing is getting hot....I am trying to figure out the best place to begin disconnecting??

[john walker's workshop]

did you remember to reconnect the plug by the left rear shock? did you try swapping the black plugs for the flywheel sensors around?

[EAP]

Yep, I checked wire harness plug again today and it is connected. I also tried swapping the sensor plugs around too. This afternoon I removed the alternator and verified the wiring per diagrams on this forum. No stray voltage at the alt.

I am now taking a look at all common components with the engine grounds. The best I can come up with is either the electric portion of the ignition switch or the DME.

How often to the ignition switches go bad? I might just order one up and replace it.

I have attached a noid test light to the injector harness. There is an intermittant problem where the light will illuminate steady, not come on at all or flash with a dull illumination. So, it seems to be an intermittant problem that could point to the ignition switch as the culprit.

I sure could use some more suggestions.......

[RoninLB]

Originally posted by EAP


Where do I start to look for a short??
I am showing 12V DC at all three of the wire terminals that attach to the left side engine ground.

i guess battery is installed correctly ?

[EAP]

Oh yeah! The only grounds providing 12V DC are the engine grounds. I checked the luggage compartment and they are not providing current (checks good for ground). The car will turn over and is getting spark. It will run for a second and then die. I then have to pull the fuse for the fuel pump in order to keep the fuel from flooding the cylinders since the injectors are going nuts ( the injectors have 12V DC on both wires at the harness).

Is there a way to troubleshoot the ignition wires and switch??

[Mahler9th]

This sounds scary. I would disconnect everything that was disconnected for service, and ring out each circuit one by one. I would be very systematic and anal retentive, and keep a log at each step. I would use factory schematics. I do not think that it should take too long, and it should work. Having a knowledgable partner could be helpful to ring out the circuits. I would be especially careful examining the heavy cureent-carrying wires, eg at the starter.

Best of luck and let us know what you find.

[EAP]

Okay, I have a couple hours before work to take a look at it. I think I'll begin at the starter, it's the only component that I have not checked for correctness in wiring. My next step will be each component, to include the electrical portion of the ignition switch.

Wish me luck, and as always, I am open to suggestions....

[ToddM]

if you disconnect EVERYTHING you can then test the wiring

[911quest]

just a quick comment some times if the car is not running and the circuit is on a relay or ecm it will show a short to ground basically the relay is in the off position and its going to ground

[911pcars]

"Oh yeah! The only grounds providing 12V DC are the engine grounds. "

Is our terminology correct? 12VDC should NOT be available on any ground (the metal portion of the chassis or anything connected to it). Voltage should only be available from the battery or source wires connected to the battery.

If you're measuring 12 volts from the chassis, I'd suspect you have the battery connected backwards. Is the positive post grounded?

Sherwood

[EAP]

I am not an electron wizard so I rechecked connections to the starter and the alternator, everything looked correct. I have 12V at both sides of the injector connections as well as the throttle position switch connection (simple two wire switch behind the throttle linkage). And, 12V is present at the intake ground wires, I tested by removing the wires from the 10mm bolt and testing across a mulitmeter. Going from the ground bolt to each of the three wire terminals, 12V is present. Can anyone perform the same check and tell me if they are seeing voltage too. I am also curious to know if anyone has voltage at both pins of each injector while checking to ground with a mulitmeter.

BTW my stray voltage is present with the DME connected or disconnected to the harness....makes no difference.

I have ordered an ignition switch (along with other parts) today from my really good friend Jason at Pelican today. It's worth a shot.

Next will be to remove fuses and relays, as suggested above. Seems like a logical path since I am walking in the dark on this one.

[EAP]

Would the car turn-over and fire if the Batt. were installed backwards? And wouldn't the alt. smoke?? I'll check the Batt again tonight after work, I am willing to try anything. Then I will remove the negitive cable and check for voltage from cable to Batt terminal. I did check the luggage compartment chasis ground to the negitive battery post and there was no voltage present. I know it doesn't make sense to me either.

Thanks for the ideas, keep 'em comin'......

[911pcars]

A voltmeter checks voltage potential between source (+ terminal) and ground. Connecting a voltmeter between the a chassis ground and the neg. (–) post of battery doesn't measure available voltage. However, this connection does measure voltage drop, which should be <.1 V if there's a good connection and a circuit is ON.

If the negative battery post is grounded, then you're okay there.

When you checked the 3 wire terminals with the voltmeter, you verified each one is connected to an active source voltage (12V). ou weren't measuring the voltage available from the ground connection. If these wires are normally switched or ECU-activated and they're ON all the time, you should look further.

If the battery were connected backwards, yes, the starter might rotate, but in the reverse direction. However, I doubt if the solenoid would engage the pinion gear with the flywheel.

If car doesn't start, does it crank?
If it cranks, do you have spark?
If you have spark, do you have engine compression or enough of it?
Do you have fuel spray from the injectors?

I think you need to look at the overall no-start symptoms before tracing the myriad electrical paths.

MHO,
Sherwood

PS: BTW, I wouldn't replace components w/o verifying they need replacement. It can get expensive diagnosing malfunctions using that method with no guarantee that'll fix anything except for good luck.

[911quest]

your right the way I read it in my dyslexic state I thought he was checking Resistance

[EAP]

The car cranks without problem. I have spark and too much fuel. The engine will pop prior to flooding and with foot on accelerator it will actually run until it floods.
As for the voltage check. As I understand it, there should not be 12V present at a disconnected ground wire.... All three terminals ends attach at the left side of the intake (engine ground). By unbolting them and checking for voltage with the multimeter I expect to see 0V DC. With a continuity checker the light will illiminate when clamping to the wire and probing a ground....that just seems wrong.
Also, I have votage present at each side of the injector wiring connections. Per Bentley, there should only be voltage present at the red/white wire.....

Am I missing something......Thanks a lot 911cars as I am woundering if I am indeed checking the voltage correctly.

[Mahler9th]

I am still scared by this thread. I think checking continuity is the way to go. Is there continuity (short circuit = 0 ohms) between 12vdc at the battery or fuse panel, and those ground wires to which you refer? If so... yikes.

There aren't that many things to check if all you did was an engine removal and replacement. And since you are concerned about 12vdc and grounds, you can focus on those circuits. Ostensibly, some 12vdc circuit is not connected properly. There are only so many choices for 12vdc to check. Similarly, there are only so many ground circuits to check.

Do you know how to check continuity with a meter? That is what I would use.

I agree with Sherwood about the swapping of parts. Here is an example:

I have a good friend who just removed the engine from his wife's 993. She had the dreaded air circuit passage clogging and could not pass smog. My friend is very skilled and has good tools, but hasn't worked much on the newer cars. His main helper is a nationally-known member of the PCA tech group and a top dealer mechanic. Skill and experience beyond reproach.

They took apart the motor, got it all straightened out, and re-installed. The thing wouldn't fire. They did a "quick" troubleshoot and discovered that fuel was only dribbling into the rail. So they figured that somehow the fuel pump (in your case ignition switch) decided to fail whilst they were doing their work. When I heard the diagnosis I said... I would not believe it-- too coincidental. Well my friend bought a new 993 pump. Unfortunately to get the existing pump out, he ruined it. Put in the new pump. Same problem.

After about 4 hours of work and a fuel pump, he discovered that the fuel rail was installed backward.

[EAP]

I know what you about replacing parts to find the problem. I hope I have explained how I have been checking the continuity and voltage....
I have been using a multimeter "meter". I have stray current at ground wires that are not connected to the injector (as I stated, the injectors have 12V at both sides of the harness connector and only the red/white should have current). I also have 12V at the grounding wires while they are disconnected from the left side of the intake. Am I checking this correctly??

I have checked voltage using a multimeter set to DC Votage.

BTW,
During engine removal I have changed the DME Relay, CHT sensor, Speed and Ref. sensors, plugs, cap, rotor.
I changed the Speed and Ref. sensors after having intermittant spark and very intermittant power at the injectors.
I just found a thread where an '84 Carrera RoW owner had an internally shorted injector.......I will check that option as well.
What I obviously have is 12V DC connected to the harness at some point...I just don't know where. I have checked and re-checked the alternator connections and I re-checked the starter wiring.

[911pcars]

This is the way a typical circuit is created:

+12 VDC -----Switch--------Load-------------------------------Ground

The ground is a return path back to the battery to complete the circuit. With the switch closed, current will flow from battery to the load, then back to the battery via the ground. Some circuits place the switch on the ground side of the load, but same difference.

With a voltmeter connected as shown below and the circuit ON, the circuit should have source voltage (12V) all the way up to the load. After the load (to ground), there is 0 voltage. It's all "used up" operating the load.

+12 VDC -----Switch------->Load------------------------------->Ground
^ ^
--------------------->12V 0 volts ---------------------->0 volts

Sorry, can't help you with the injector circuit as I'm not totally familiar with DME, but it sounds like the system is trying to energize the injectors when it shouldn't be.

Sherwood