Dwayne

THANKS for the comments. I definitely have a leak - significantly audible. I'm going to try the leak test with duct tape as Mrmerlin suggests - I expect to see water....will post again in a few with the result.......

Dwayne

OK....I tried the leak test and sure enough water came out....here's a pic of the duct tape on the ends of the "Y" pipe.


And when I filled it with water throught the O2 sensor opening, water came out both sides of the "Y".


So I decided I needed to dremel off the heat shield of one of the "Y" arms and see what was going on. After getting the shield off, I found some insulating wrap. Here's the pic:


After removing the soggy insulation, I could see no indication of a leak, the pipe looked solid.


However, it was still rotating at the junction of the "Y". So, I needed to remove a little more heat shield about the junction. The "Y" arms are fitted to the junction and welded all the way around for a sealed connection. My welds had completly broken off. Here's the pic:


At this point, I could simply remove the pipe. So, I guess the question is what to do now? I think it is repairable given the pipes are still in great shape, structurally. I would need to re-install the CAT and "Y" pipe to get the position correct, then spot weld the connections again to hold it in place. Then remove the CAT and "Y" pipe once again and re-weld a nice seal around it again. Then do the leak test again. Does this sound doable??

The other option I'm considering is doing the above fix to meet smog but also purchase the one piece aftermarket "Y" pipe without CAT for daily driving and switch it out when it comes time for smog. Has anyone tried this....is it worth the trouble? THANKS for the help!

Dwayne

Oh, I guess this answers the question, "Is the 'Y' pipe supposed to rotate/move?" I'd say "NO" given mine looked like they were originally welded solid - if they move, I don't think it's by design.

Bill Ball

Right. The insulation sleeve can break free, but the underlying pipe should be solid. That later H-shaped dual exhausts do not have this sleeve, and the arms are definitely not movable. It looks like the sleeve trapped water and rusted out the exhaust pipe.

Garth S

Dwayne,
You are on the correct R&R tract - the weld needs to be repaired (fit/tack/remove & weld). The piping is very sturdy stuff and normally a stainless alloy, like SS 409 .... rust errosion should not be an issue.

Aspiration of air into the O2 sensor location, if it occurs at all, should only be an issue when the exhaust is at some negative pressure - like over run with the throttles closed and clutch engaged: this is a more common cause of burbling and even backfiring in the exhaust .... but not surging at part throttle running conditions. Anyway, at normal operating speeds, there is adequate positive pressure such that the exhaust leaks outwards from the crack ( or missing cap).

As to the elusive surging .... have you adjusted the MAF mixture screw to get the correct CO? If slightly on the lean side, my car will surge: Not having a CO meter, I monitored the O2 sensor output while adjusting the MAF .... plus some 'feels good' tweaks to get it running right. This might be a place to look if not already done so.

EDIT: AFM .... not MAF, my freudian slip ... the AFM bypass passage of unmetered air controlled by the 2.5mm allan screw is the adjustment in question ....

Imo000

I don't know, it sure looks like a stress fracture to me. My first 928, an '83 has a re-welded Y and it kept on cracking. So I guess once it's cracked it probalby will crack again. I just replaced mine with a Y cat bypass pipe. I don't know if they are still available but when I bought mine, (almost 8 years ago) it was supposed to be the last one avaiable at the time. Later on I installed a regular. off the shelf, cat on it to pass the emission test.

blown 87

You would think that would be the case, but it is my understanding that the pressure waves will suck air into the pipes.
There are a bunch of factory trouble shooting guides from MB and others that point to exhaust leaks as problems with getting correct O2 sensor signals.
It may not be the problem here, but It always helps to start with the problems that you know you have and correct them before you go looking for other problems.

Greg

shmark

Whaddaya know, I'm guessing this is a common failure since I've seen it on two different cars - that's why I assumed it was right. And mine doesn't seem to leak at all. I'll be going in for an emissions test soon and then I'm going to throw it away since GA has a rolling 25yr exemption. So I ain't fixin' it, time for an upgrade!

Dwayne

THANKS all for the posts/information. I plan to fix the stock exhaust but also am looking at options for an upgrade to performance "Y" pipe and maybe keep both sets. I've posted another thread looking for some feedback on experience with the aftermarket "Y" pipes and vendor sources. THANKS again!

Dwayne

After I get the fixed stock system back on, I'll post again as to whether this fixed the surging. If it doesn't, I'll look into the MAF adjustment as Garth suggests. THANKS!

Dennis Wilson

The earlier Lambda systems cut off the ECU A/F adjustment when the throttle position switch was at idle. That stopped the idle hunting during A/F adjustment. Is the LH system supposed to work the same way? If so, could the switch be out of position or bad?

Dennis

Bill Ball

Yes, since he didn't report a rot spot, it probably is a broken weld. The later Hs don't do this AFAIK.

shmark

Let me know Dwayne. I was out driving today and while mine surges a little at idle (sounds cool, and my former 83 sounded the same), I noticed that the acceleration is a little ragged. It seems to smooth out above 4500rpm but below that isn't as smooth as I would expect.

Dwayne

Hello Dennis,
I may have forgot to mention that this work is being done on the '84. I don't think I have an LH. On my L-jet system, I have a WOT micro switch and an idle microswitch. Are you saying the computer is supposed to ignore inputs from the O2 sensor when at idle?? I know it does ignore O2 sensor at WOT. I'm still a newbie - not sure what a lambda system is.

Dwayne

Will do....probably this weekend (Saturday)....