4000cs quattro header pipe
 

What is the small tube that comes off the collector and goes back along the header to the engine compartment and is capped off with a couple of wires coming off the cap? Mine is broken at the connection at the collector and I would like to replace it or know if there is another fix.

Might be the E-Test sniffer pipe?
 

Comes from down on the exhaust somewhere, and is clamped to the intake, and has a grey cap on it?

If so, that pipe is there so it's easy to sample the exhaust gas ahead of the cat, for setting up the CO levels.

If the wires are brown, and bolted under the same clip as the end of the pipe, they are the ECU ground wires. VERY important that that ground connection be clean and good!

I've never seen one of those pipe assembliesthat was ever complete and working. The bottom connection usually gets dumped first time the exhaust gets replaced..

About those ground wires...
 

Yeah, definately make sure you keep them grounded to the side of the intake manifold. I was driving on the highway one day when the car would buck back and forth suddenly then completely shut off and die. I had no clue what it was, had to have it towed, woops!
But yeah, that pipe is useless, I wouldnt bother replacing it.

Those ground wires..
 

As insignificant as those grounds on the side of the intake seem to be, they are REALLY important.

As they are the ECU ground, it references all of the sensors the ECU sees, and also provides the ECU power ground.

When it comes off, or goes bad, you get the same symptoms as when the 'spare fuse' is missing.

A friend's 4kq was running really bad, and he couldn't figure it out. He brings it over to my place, and when he was in using the washroom, I noticed and fixed the bad ECU ground. Easy fix, *if you know about it*! Car ran way better.

He was amazed. (And I looked like a genius!). Sometimes, you just get lucky...!

Re: Those ground wires..
 

Thanks guys for the help!!!!!!!!!
This forum has been a great help to keep this fine auto on the highway!!!!!!!!!!!!!!!

Re: Might be the E-Test sniffer pipe?
 

WOW!

You just solved a small problem I had when I was testing my Fuel DPR when my 4000Q was on the fritz.

I posted your comments about it here:
http://www.quattro123.com/4000VacuumLeaksandWires.htm

It seems that during my repair I encountered a no start, which was the problem I was trying to solve. In doing two things at once I actually prolonged the no start condition even though my repair was done because I had undone the ECu ground and was just poorly grounding it back to the IM during some test starts.........

Now I know better............. Thanks for filling in the blanks....
-Scott by BOSTON<ul><li><a href="http://www.quattro123.com/4000VacuumLeaksandWires.htm">Shameless info plug</a></li></ul>

We all learn from each other..
 

That's why this forum is pretty good. We all learn from each other's pain!

(And are willing to share it!)

So how did we do it, before the interweb? :-)