13 replies to this topic

[ChrisA]

My ground to the PPF got gas soaked. The insulation has softened too. Knowing that gas (and probably it's residue) is a poor conductor of electricty, should I just strip the insulation and hose the wire down with brake clean or replace the ground wire? If I replace it where does it originate from? Is it the main ground from the battery or does it "T" off that line? This is on a '99.

[Tom Hampton]

Which wire are you talking about? The ground wire from the negative battery terminal that actually connects the PPF to chassis ground, or the ground wire that runs up to the engine compartment ALONG the PPF?

Maybe that doesn't really matter, though. Stripping the wire and cleaning it isn't useful, insulation exists for a reason...you can't adequately re-insulate (for underbody exposure) the wire once you're stripped it. Water will get in and the wire will corrode over time---eventually compromizing the electrical connection. Grounding problems are the bane of electrical engineers. Weird things happen when your ground is only mediocre.

Wire is pretty cheap.

PVC has decent chemical resistance to gasoline...so, I'm not sure how it would have softened unless it was soaked FOR A WHILE. If the insulation has softened, I would probably go ahead and replace the wire. Besides, the wire inside the insulation can't be affected unless the insulation is just melted away, anyway. The only wire that could have been affected is any exposed copper or terminals...which could be cleaned with some scotch brite. If you don't want to replace the wire, then you could just remove any discoloration back to shiny metal.

I don't really think that gasoline would leave a residue. Its a pretty good solvent, and the varnish it can leave is due to exposure over YEARS, not a single dousing. The bigger concern is the compromized insulation. Although, its a only ground wire; and nothing bad is going to happen immediately. For the price of a few feet of 4 AWG wire, why risk it?

[ChrisA]

I'm talking about the ground wire that is grounded to the PPF. Guess I will replace it. So does this wire T off the line from the battery and if so, where? Just want to figure out how much wire I'll need & what kind of connectors I'll need on hand before I start. The car lives outside and raining out, so can't really investigate.

[Tom Hampton]

I'm talking about the ground wire that is grounded to the PPF. Guess I will replace it. So does this wire T off the line from the battery and if so, where? Just want to figure out how much wire I'll need & what kind of connectors I'll need on hand before I start. The car lives outside and raining out, so can't really investigate.

I've got a '92, not a '99. But, the wire goes to a chassis ground stud in the trunk and then straight to the negative battery terminal on my '92. Probably, 6' of wire, total.

Plus a battery terminal connector, and then the PPF connector. My ground stud crimps onto a 3/4" section of stripped wire. It would be easy to pry off the crimped stud from the old wire and reuse it for the new wire.

I know autozone has a crimp on battery terminal set that I used to replace the PPF end of the connector for less than 10 bucks:

http://www.autozone....-Clamp/_/N-25nk

http://www.autozone....fier=95962_0_0_

Also, O'reilly may have an exact replacement cable complete with connectors.

[ChrisA]

Hum, that might be exactly the way the '99 is done..? So you're saying the negative line does not run all the way to the engine compartment, correct? That would make it easier. The major connections being: Battery > Chassis > PPF and then the engine bay Engine > Chassis braided connection.

[Tom Hampton]

Hum, that might be exactly the way the '99 is done..? So you're saying the negative line does not run all the way to the engine compartment, correct? That would make it easier. The major connections being: Battery > Chassis > PPF and then the engine bay Engine > Chassis braided connection.

That's the way the NA cars are wired. Can't speak for the 99/NB.

[ChrisA]

That's the way the NA cars are wired. Can't speak for the 99/NB.

I was able to take a look yesterday and the 99 has the same wiring set up. I did a continuity test & checked resistance, only 0.5-ohms, so I guess I'm okay..?

[Tom Hampton]

I was able to take a look yesterday and the 99 has the same wiring set up. I did a continuity test & checked resistance, only 0.5-ohms, so I guess I'm okay..?

I don't know what the FSM recommends, but 1/2 an ohm seems high. You can get the NB FSM from toe downloads section of my website.

Copper wire that thick should have a resistance so low you can't measure it over 6 feet (0.001 or so). Even allowing for crimp connections, it should only be 0.1 or so.

Does it matter? Dunno.

Its one of two conduction paths from the engine back to the battery. There's the engine ground strap, which goes straignt to the chassis. Then there is engine block, to tranny, to PPF, to this strap. I'd guess that starter current flows through the PPF, and ignition coil current probably passes through the engine ground strap. But, that's just a guess.

Starter current could be effected by 1/2 an ohm. I doubt the ingiter would be effected though. Again, though without knowing the design of the igniter that's another guess.

Best advice is check the FSM and replace as indicated. Yes, as little as 1/2 ohm could matter.

[Jim Boemler]

I agree with Tom that 1/2 ohm could really matter, but it's also likely that what you're seeing is a measurement problem rather than real resistance. As long as all your connections are clean and tight, you should be fine.

[Tom Hampton]

I agree with Tom that 1/2 ohm could really matter, but it's also likely that what you're seeing is a measurement problem rather than real resistance. As long as all your connections are clean and tight, you should be fine.

True. Make sure your contact points on your PPF wire are clean and shiny new metal (use sandpaper, schotchbrite, etc). Remeasure. Make this a habit before measuring resistance. Oh, don't forget to disconnect from the battery before you measure. Any current flow would skew the results (make it read HIGHER that reality).

If its still high....

To test your equipment: Touch the terminals of your ohmmeter together. What resistance do you get (X)? Should be 0.

Get a brand new length of 18 AWG wire, 10 feet long is a good number (longer is better though). But whatever you use, the result should be 0.0064 ohms per foot. Clean the copper with sandpaper, scotchbrite, etc...nice and shiny. what do you get? 10 feet should be 0.064+X. If its still high...your multimeter is out of calibration, or more likley low on batteries.

Its very unlikely that any gasoline would have caused any CHANGE. So, if it is bad now, it most likely was bad before. You would have had issues starting the car, and possible misfirings...particularly at higher RPM.

[dstevens]

I just measured mine, trunk cable, stock clamp through PPF (no braided cable or connection to trans), it's so low it only reads 0. I used a Fluke 177 and the manual says the minimum reading for resistance is 0.1 ohm. After that threshold it will read to 100ths.

[ChrisA]

True. Make sure your contact points on your PPF wire are clean and shiny new metal (use sandpaper, schotchbrite, etc). Remeasure. Make this a habit before measuring resistance. Oh, don't forget to disconnect from the battery before you measure. Any current flow would skew the results (make it read HIGHER that reality).

To test your equipment: Touch the terminals of your ohmmeter together. What resistance do you get (X)? Should be 0.

Its very unlikely that any gasoline would have caused any CHANGE. So, if it is bad now, it most likely was bad before. You would have had issues starting the car, and possible misfirings...particularly at higher RPM.

Okay, all ground contact points were cleaned through out the car last fall. Snugged down good and tight they should all be air tight, except the one that got gas soaked. As I mentioned the wire insulation has softened & loosened in that area and the wire is visibly contaminated. Since electricity flows on the surface of the wire, not through it, I don't think cleaning that contact point would do much. My tester is a Fluke multimeter and it tests okay. However, I did not disconnect the neg. terminal from the battery when I tested. Will re-test this coming weekend.

Bingo! I was having some Hi-RPM misfire, but it was not constant, as it would diminish after the first few laps. I wasn't sure if it was an ignition problem or bad gas. Coil pack, wires, fuel pump and filter are new so don't think they were the issue. Spotted the ground wire issue during my post event inspection.

[Keith Novak]

While you're at it, some people recommend adding the little star shaped washers between the contact points to get a reliable contact. I put them on just snug and wiggle the connection around to scrape the surfaces up a bit before tightening them down.

[Tom Hampton]

No. My point was to make sure the metal you are touching with the fluke probes is clean.

The skinning effect isn't really relevant in a car. It's a much higher frequency phenomenon. Surface corrosion doesn't have any impact on it anyway.

Star washer is a good idea.