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Discussion Starter #1 (Edited)
My 85 GTV6 won't pass smog, so I have been running though various fuel injection diagnostics. Then I touched my multi-meter to this electrical connector (pictures below) while the car was running and it died and won't re-start. It'll turn over, but not start.

The connector is on the passenger side (US). I believe I was testing voltage from the O2 sensor, but certainly fried something when attempting to. This is my first go at L-Jetronic tuning. Seems I am learning the expensive way.

Any one know what I killed?
 

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Check all of your fuses as you most likely popped one of them. That certainly looks like the O2 sensor connector.
 

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Discussion Starter #3
Yep checked the fuses right off and didn't see anything. I'll take a closer look though to be sure.
 

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I am pretty sure that the heater in the lambda sensor gets it's power from the combo relay along with the injectors, fuel pump etc. So if you popped that fuse your complete FI would be dead. Listen to the combo relay when your helper turns on the ignition. You should hear it click if the fuse is good.
 

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You might want to check the fuel kill switch? The last picture you show, it's just to the right of your hand. Black rubber button. If that's not it, I'd be curious to know what you find out as mine is having starting problems too.
 

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Discussion Starter #6
Ed-

Good call on the fuses. Didn't look blown, but turned out it was. Been working through the Gordon fuel injection troubleshooting guide for the first time and it had also mentioned "It's possible and not too uncommon for fuse #5 and #8 to blow in such a way that they make contact and look fine but are not really carrying enough current."

Still unclear on why putting a voltmeter on the engine/fuel-injection side of the connector caused a surge. Guess I know not to do that again, though. Got off easy this time.
 

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Still unclear on why putting a voltmeter on the engine/fuel-injection side of the connector caused a surge. Guess I know not to do that again, though. Got off easy this time.
Yeah, you got REAL lucky. That's the O2 sensor heater connector, and it pulls 12V power through a fused relay. If you'd done the same thing with one of the other Bosch connectors you might've fried the ECU.

Do you have an old voltmeter? Many modern digital models are high impedance, meaning they won't do what yours did. In any case, it's always bad form to attach your meter to any wires that go back into the ECU harness.
 

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Still unclear on why putting a voltmeter on the engine/fuel-injection side of the connector caused a surge. Guess I know not to do that again, though. Got off easy this time.
The probe most likely touched ground while it was in contact with the 12v side of the heater circuit. It's a lot more exciting when you do it on a 120 volt circuit!
 

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Discussion Starter #9
Yeah - it was pretty dumb. I knew better, but it was late and wasn't getting a reading on the other side and just reflexively poked the leads on other side of the plug before thinking about it. I was sure I fried the ECU or AFM. Got lucky.

Interesting note about the voltmeter. It is newish, but a just a Harbor Freight digital. So you're saying there is a multi-meter out there that can protect me from myself? That would be nice, as electricity is not my forte.
 

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Some old volt meters, mainly analog types, have a low ohms/volt which means that they load the circuit when they are connected. Sometimes that is a good thing as solid state switches have a leakage current which can be enough to make a modern instrument think that it is ON when it is really off. But it is mainly a bad thing when trouble shooting high impedance electronics circuits. Your HF voltmeter has a resistance of about 1 million ohms on the DC voltage ranges so you don't have to worry about it blowing anything provided it is on a DC voltage range. It is a different story if it is on a current or resistance scale or if you accidentally ground the probe.
 

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But Mad North-Northwest
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Ed's probably right. One of those terminals in that connector is ground, so if you touched the probes together...POP. Glad it was an easy fix.
 

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So you're saying there is a multi-meter out there that can protect me from myself? That would be nice, as electricity is not my forte.
You could wrap your test probes with electrical tape or heat shrink tubing leaving only the end 1/4" exposed. That would reduce the probability of you shorting something. I have a couple of screwdrivers insulated like that for when I work on live 120 volts.
 

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Discussion Starter #13
Just to be sure (since electricity isn't my strong suit and this being my first attempt at L-Jetronic)...

I was actually touching the ground probe of the voltmeter to the chassis and then sticking the positive probe into the O2 sensor wire. Is that bad form with this system? Should I instead be sticking each probe into each of the wires in the O2 connector? (being careful not to touch the probes together in the process, of course).
 

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Your procedure is correct but somehow or another the 12 volt supply wire was shorted to ground. Maybe you managed to get the probe onto both connectors at the same time, possibly through a strand of frayed wire. Who knows?
 

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But Mad North-Northwest
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Just to be sure (since electricity isn't my strong suit and this being my first attempt at L-Jetronic)...

I was actually touching the ground probe of the voltmeter to the chassis and then sticking the positive probe into the O2 sensor wire. Is that bad form with this system? Should I instead be sticking each probe into each of the wires in the O2 connector? (being careful not to touch the probes together in the process, of course).
It depends what you're trying to do.

The O2 sensor has three wires. Two are in the Bosch connector and are for the heater...that appears to be what you blew. The single wire is the sensor wire.

To check the heater in the sensor, you measure resistance (Ohms) between the two wires on the Bosch connector on the sensor (sensor side unplugged from the harness, not the harness side). Should not be open or shorted...maybe 4-10 ohms or so.

If you want to monitor the sensor output with the car running, you clip your positive multimeter probe to the sensor wire (with it still connected to the wiring harness) and the negative multimeter probe to engine ground, and measure volts. This can be used to evaluate whether the sensor is working properly or if you have a mixture problem.

Very important to use a high impedance multimeter when doing this and have it set to VOLTS, not Ohms or Amps. If you go to the L-jet tuning guide at hiperformancestore.com it has some details on doing this.
 

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Discussion Starter #16
I think Ed hit the nail on the head…it's pretty tight in that connector and I think I must've hit both wire contacts. It was midnight and I was getting in a hurry to finish…not a great mix with electrical testing and my minimal expertise therein.

In response to Tom, yeah, I was attempting to test the sensor itself (not the heater) to then see if I needed to adjust the mix. The hope being I have mix problem and that will solve my not-passing-smog problems. From your description, it seems I whiffed this completely. I was testing voltage output from the two wires in the Bosch connector (disconnected from the harness) when I should've been testing this still connected to the harness. Obvious now that you said it. ;-)

I am following the Greg Gordon guide, but I have a version from 2003, so I'll check out his site to see if there is a newer version that clarifies even further for remedial electricity students like me.

Thanks for the help on this everyone!
 

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I was testing voltage output from the two wires in the Bosch connector (disconnected from the harness) when I should've been testing this still connected to the harness. Obvious now that you said it
I think you've still got it wrong. The Bosch connector is solely for the sensor heater. You don't need to do anything with that: leave it hooked up.

The third wire with the brownish connector is the sensor voltage output. That's where you measure. Leave it hooked up, connect your red probe to that, and your black probe to ground.
 

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Discussion Starter #18
Yeah - I didn't see that one at all. Will get out there again tomorrow and hunt it down. Thanks for the help here. Maybe I can make some better progress now, or at least no harm.
 

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My 85 GTV6 won't pass smog, so I have been running though various fuel injection diagnostics. Then I touched my multi-meter to this electrical connector (pictures below) while the car was running and it died and won't re-start. It'll turn over, but not start.

The connector is on the passenger side (US). I believe I was testing voltage from the O2 sensor, but certainly fried something when attempting to. This is my first go at L-Jetronic tuning. Seems I am learning the expensive way.

Any one know what I killed?
In regards to smog, you might want to check if the AFM spring tension has been messed with? It is a common modification that will almost always result in a smog "fail" (at least in California) I ended up tightening mine about 5 notches on the wheel before it passed. Good Luck!
 

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Discussion Starter #20
Thanks for the tip! My pecking order for working through what is causing the smog fail in particular (both at idle and cruise) is:

• Idle mix adjustment
• Timing (came from non-smog state, so someone may have advanced for performance)
• AFM settings
• O2 sensor
• Electrical
• Air leaks

Eventually I will make it through all of these just as a check of the system, but trying to get to passing smog as quickly as possible as I want to get the car registered.

If anyone has other/better ideas for prioritizing smog-related fixes, I am all ears.

Thanks!
 
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