View Full Version : What are the grounds on the valve cover for? (2000 B5 A4, ATW)

01-14-2015, 06:16 AM
I gave a few quick searches here and around the net but can't seem to find a solid thread or info that specifically says what the grounds that are bolted to the valve cover near the ignition coils are for.

I recently picked up a 2000 B5 A4 ATW for my wife to beat on while she learns to drive. I am slowly bringing it back to life after god knows how long she's been neglected. Currently, she runs good but occassionally at heavy throttle, she seems to cut out for a second. It's a tiptronic and I'm pretty sure that the trans mounts are shot and I likely need a good drain and fill on the trans fluid + a new trans filter.

It doesn't feel like a misfire or the trans slipping though. I did have a few misfires but I have been able to clear them up with new coils and plugs. I've also cleaned the MAF, cleaned the throttle body, all new vac lines, N249 delete, new SAIP, and cleaned the combi valve. After all of this, the car really got some pep back in its step but I am still fighting this occassional loss of power under heavy throttle. It usually occurs at about 4k rpms under hard acceleration like if I am attempting to pass on the highway. If I let off the gas then it all goes back to normal. I get no CEL and have no codes stored. I don't think it's the EPC because I did get the EPC error once at hard acceleration prior to deleting it. I've deleted the N249 by looping the vac line on the valve and running the DV straight to the manifold and since then, have not had any EPC issues indicated by an EPC dummy light.

This brings me to those grounds on the valve cover. They look pretty beat and I know that I need to replace them anyway, but what effect would a short to those grounds have on the car? It starts up great, idles fine, and seems to run without issue aside from that loss of power I've described. If these are for the coils then is it possible that the heavier loads are causing some type of short/arc at the grounds that is cutting power to the coils? Maybe I don't understand or know exactly what I'm talking about here, but at this point, I'm just making a wild guess and I'd love a bit of help/info on things.


01-14-2015, 06:29 AM
The problem you would have with the grounds would not be described as a "short circuit", but rather an "open circuit". In reality it wouldn't be fully open, but just poor continuity.

The wires are supposed to be grounded directly to the valve cover. They provide the ground for the ignition coil secondary windings. If the connection is not sufficient (ie: has too much resistance) then everything might work fine under normal operation, but when taxed to maximum (ie: high load and high rpm), there may be too much voltage drop. This would limit the attainable ignition output voltage. Possibly limiting it enough that the spark is no longer able to jump the spark plug gap, resulting in a hard misfire.

That's just one possibility. The same could be true of any of the wires to the ignition coils. They all get baked to death up there. If you suspect the grounds, check for visual problems (corrosion, frayed wires, etc) and check the resistance between the respective coil pack pins to the negative battery terminal. Should be less than 1 ohm.

01-14-2015, 02:25 PM
Thanks for the info. The ground wires look like some of the shielding is missing and the exposed wires are a bit frayed and corroded. I definitely need to repair them but wanted to know what effect these wires would have on my performance.

Sounds like it could be a culprit of my power loss.