Catconverter burn-up..

[fixkick]

lets start over, who said the burned up 2 Catconverters now. by what measure, P0421 codes, or smog man or?

The P0400 means the EGR fails.....  in some way , if the cat broke up in pieces and went byebye EGR then fails too.  the cat must be there and must have normal back pressure or the EGR MODulatopr FAILs to work. (goes offline)

did you fail a smog test or something, please advice  here.
thanks for posting !

first one was obvious.  header turned dark from over-heat, lost all power slowly and dramatically, pulled the cat and it was melted to a rock.  I'm getting same subtle indicators now again. mostly progressive vibration from the cat as it sounds audibly to be deteriorating.  I'm in Minnesota so no smog test. 

no P0421, only P0400 that is incessant.  I clear the code, drive for a bit comes back, but no clear circumstance.   Sometimes first drive, sometimes second.  sometimes on first start up, sometimes at random while driving.  

New EGR, tested ISC good.  decent gas milage so not in limp, ego exhaust port should be open as the engine/header only has about 8000 miles on it after total rebuild.

only other bit of information I left out of original post is recently it has started to hiccup a bit.  at cold idle worst, or low throttle, not with open throttle.  not a full misfire, seemed almost like it had bad gasoline, but I'm on tank 3 from different locations and same issue.

fuel pressure is stable and good.

the first cat did burn up,  from engine super rich, that is what cause burn up , the CEL lamp also flashes when the ECU knows it is rich, the flash means ( go  slow or cat burns up)
the 2nd cat IDK,  why , same reasons? who knows.
but lets talk 2 things here, first off there are 2 causes of rich, (gross rich and simple rules)
it is in limphome ,  for many reasons, even 02 front dead,
or the ECU is lost.
lets do lost,  (02 dead,front means injection rates are now lost,  no real controls only the MAF output, and is purposefully rich, so you dont burn up exhaust valves from too lean.

Injectors can leak, or fuel pressure way too high, FPR bad and causes this, or 02 sensors is bad or reads wrong (exh. leaks near it)

the only way to prove closed loop is to see the scan tool show CL, for closed loop ,noT OL open loop cruising. (and at idle hot)
or scan the 02 and plot it. it must swing and swing on a 0.45v center. 
the can be no exhaust leaks near the front 02 or it goes rich, AFR super rich, max.

if the new cat broke up  EGR is not the worry, the CAT must be good to get EGR working, EGR uses that CAT to gauge full engine load, and run EGR flows based off of that.
The cat is part of EGR, (backpressure)
if the CAT melts, (engine goes weak cant pump air) then EGR overflows wrong, due to huge CAT back pressure and causes even more power loss...
maybe the second cat got hit by road debris.  or vibrated too hard and broke up, had a jeep do that 3 times,  (made a mount for the cat to keep it from vibrating and was cure.

is there not a frame mount for the cat? on this car, IRRC.  I forget, but will  look that up in the AM.

Seen one china clone maf used that run way too high and the eCu could not trim it down so high and ran rich, full time. o2 could not correct this error.

mGP on my 96 5sp was 28mpg, that is possible. tad less in town.

if the O2 hunts at light cruise say 40 MPH, the ECU and 02 are ok,  it must hunt around 0.45volts just like the scope views show.  no stuck high ,low or offset.
this and short turn true at same time also tells me what is up,

do the EGR stall test, and live test yet? 1996, up, the live test is rear wheels off the ground and 1mph or faster, no 0mph,
per my gen2, EGR page. and FSM rules on same.
my guess is the stall test passes, (exh paths all good)  and is vacuum issue, CAT blown out is top of list. for EGR death.

I'm mostly city driving, getting around 26mpg which is why all the CAT results are a little odd.  I can't do the live test because I have GPS vss., also I don't have all of the "idiot" lights (original gauge indicator lights worked out yet) so CEL is always on.. maybe because of this, maybe because of all kinds of craziness.  Long story short all of the dash is missing, including gauge cluster.  (flooded in Florida hurricane and then abandoned outside for 11 years, everything destroyed)  info Im getting is from scanner and aftermarket gauges (high quality).  I'll attach picture so you can see the extent of this project.  

you are just like me at 15.5years old building cars from the dead . (best way to learn is this, no better hands on why) cheers to you brother !

seems with that custom car, not having  real scan  tool,, is the problem. (partly sure)
a real scan tool can log data,  as you drive on any USA made,  (market) 1996 or newer card.  by law, OBD2, rules.
see the other persons post here with logs, for 2.3L engine in sidekick and overheats(cure custom radiator) he post huge log files in CSV  format.  (Using Excel from MS office)
The logs show what happens as you cruise. (but  will not show what CAT does, unless code p0421 pops)

if you did that we'd see how it  messes up. as  it surely   does.  

the cat needs to be close to the exhaust manifold , what manifold is there stock or not stock.(photo?) love photos... very helpful and thanks.
the now cat close to the exhaust header, keeps it LIT OFF. and working. 
and the cat must not bounce and beat itself to death. (if it rattles, IT DID)

if not kept lit off, the Cat acts as huge HC sponge, (raw fuel) and then when car goes fast or up hills the CAT wakes up and lights off, and overheats.
HC= hydrocarbons.
we know this too because one guy in LA, calif, failed smog endlessly, and exhaust was all custom, not one suzuki part there. and failed.
it failed for 1 reason, NO LIGHT OFF. CAT.  (or too big cat) in his case the cat had to be moved closer to the exhaust header end.

what suzuki did back then in the 16valve, G16b, was they had cat front neck pipe that is double walled, this helped get hotter HC gases hitting the cat, the inner wall glowing red.
The problem was, that wall, inside, melts twists and plugs the walled pipe, and kills the engine dead or near. (blocking exhaust) and SUZUKI had to recall the PIPE with TSB (have it do)

This car has complex EGR3 class setup, it has extra VSV valves, for extra EGR testing.  seen here. vsv 1 and vsv2 is gen3, 1996 added vsv 2, vacuum solenoid valve.
the new valve helps see if EGR is suck on or off.






The new EGR on this car does 2 EGR tests, (and failures tests) the 2 P0400A and P0400B tests are cruise test, and cut fuel (like going fast and foot of throttle to say stop sign test)
the system can also flag errors or dead or stuck EGR, using vsv2

i still have to look up your cat mounts... next (so it can not beat it self to death)