So I was driving around this afternoon with a boost gage (vac hose strung through the pass. window) checking the boost pattern. Boost pattern is 10-4-5. I knew it wasn't running strong enough when I bought it, but the compression was good.

I get home, pop the hood and poke around looking and listening for vacuum leaks when I see something bright orange behind the intake! The stock downpipe is glowing orange and the heat shields were a nice shade of red. Fortunately, I have a new downpipe in the garage ready to go on the car. Looks like i'll be wrenching on this thing again...

Any advice on replacing the downpipe? Seems pretty straightforward to me with the possible exception on removing the old rusted bolts.

Also going to be looking at the boost issue (once the downpipe is in). Could the clogged pre-cat be contribting to the boost issue? I'm leaning toward NO because I see 10 PSI on the primary turbo then it drops to 4 at 4k rpm and goes back up to 5 at ~4500 rpm. Any ideas?

 

Almost forgot:

The car is a bone stock 93 auto. Just finished replacing FPD, injector O-rings, hose job, and quick check of all solenoids and check valves this weekend. Car runs EXACTLY the same as it did before the hose job.

 

clogged pre-cat gives you lower boost because the turbochargers can't spool up properly due to exhaust gas buildup... mine wouldn't boost at all anymore... chances are you're problem will solve itself when u install yur downpipe.

 

I hope so. I'm just skeptical because it hits the full 10 PSI and then drops to 5 PSI immediately.

I do think the clogged pre-cat is hosing my idle though. Idles at about 600 RPM, kinda rough and only 10-12 inHg.

 

Exhaust restriction after the Turbocharger will show up as boost pressure drop-off at higher RPMs, (i.e. roll off after 6,000 RPM) the most common failure part here is the pre-cat, (sits between the turbos and the main catalytic converter). Due to the high exhaust temperatures, the pre-cats can start to fail in a plugged manner after about 50,000 miles. The common fix here is to replace the pre-cat with a down-pipe or have the pre-cat gutted.

This is from a troubleshooting guide...

 

Your new DP may also glow orange when it's hot. It's the nature of the beast!

 

I would highly recommend getting a decent thread solvent like PB Blaster or Liquid Wrench, and thoroughly spraying the DP bolts the night before you begin work to allow time for the solvent to soak in. I would also recommend calling Malloy Mazda and getting some spare DP studs and nuts, as there's a good chance that instead of the nut coming loose, the complete stud will come out instead.

EDIT: Oh yeah, your turbo system probably has other issues besides a clogged pre-cat, judgiing by the boost pattern you described...

 

I can understand the downpipe glowing during WOT conditions, but I had just idled around the neighborhood for 2-3 minutes after a drive. The car was just idling in the garage (and had been sitting there for a minute or two. I dont think this is normal.

 

It is normal. My DP was glowing at a smog check. No hard acceleration there. It was not a dyno smog.

 

It can be, actually. There are times when even just "idling around the neighborhood for 2-3 minutes after a drive" won't be enough to let your DP (especially the stock cast steel unit) cool down enough to keep from glowing.

 

With my downpipe, I've seen glowing just when I cold-start the engine. But it was a faint-reddish glow, and probably caused by the dripping injector that was creating a very rich idle condition.

After WOT runs, some glowing is normal, but certainly not enough to redden your heat shields. When you get the downpipe in, expect better boost.

I agree with the penetrating solvent - PB Blaster is my choice. As for studs and nuts, it's normal for them to come out together like a bolt. You can use them again if they look good.

Although it's not as bad as pulling the turbos, you could break one or two of them, so have some spares on hand. Do NOT use a regular bolt as a replacement - use only Mazda hardware or some other special manifold bolt. If any of the studs that come out look like the threads are rounded or damaged, get a plug tap in M10x1.5 and chase the threads in the manifold before putting in the new stud.

Dave

 

I had the opposite situation. It would glow the longer you let it sit and idle. But if you drove around it would be perfectly fine.

 

The downpipe istall on a nearly stock car is probably one of the most frustrating things you'll ever do on your FD. You'll have to get all the intake system out of the way, and if you want to make life really easy on yourself you can remove the Y-pipe. But to do that you'll also have to remove the air pump. Whether you do that is up to you, but if you try to put the DP in without removing the Y-pipe, you'll be cursing a lot more than if you had taken it all out in the first place.

Also, if you have a tap and die kit, make sure to run it in the bolt holes to clean them out once you get the studs out and the precat off. I'd also reccomend using new studs and locking nuts if you can get them from your mazda dealer, those old studs should be replaced.

And remember, when you put the DP in, do NOT tighten the bolts connecting it to the main cat until after you have tightened up the DP to the motor. You will need to wiggle the DP around to get the studs in and you cant if you have it tight to the main cat.

 

Yes what they said and by the way you can use the 7 to PRE-Heat food at any time winter or summer.. My personel fav is to POP popcorn. Drive for five minutes add the bag wait 3 minutes then serve.

Doc

 

I can't imagine it being any worse than replacing the FPD and injector O-rings!

 

WORD!
every 3rd gen needs a dp anyways.