Catconverter burn-up..

[fixkick]

part 1 is 92-93 fed car only e3 (not calif E33) cars.
but parts do get mixed up. for sure on old cars and engine swaps, and us, wrecking yard scroungers.
The cal cars and 96 all have long exhaust manifolds (stock) see my chart here on the many manifolds used. by year.

best is the cat mounted close to here as possible, and pellet cat better. (I bought this new, 2007) for sure , other aftermarket manifolds can work too. (with EGR port)
One other trick (like race cars do but not for CAT)  for custom manifolds is that high temp exhaust pipe wrap tape, that will send more heat to the CAT.

[TomPrestin]

Quick response before I have to step into work- did a lot of reading through the the site yesterday, noticed that standard plenum vacuum at hot idle should be 20 inHg, mine is stable at 8.. so I may have a vac leak somewhere, probably contributing. I have a new VSV2, and nothing under the hood is "custom" I've gone to great lengths to make all the mechanical components as original as possible. Header was cracked bad, currently running a dougthorley, no funky tube, goes directly to Cat inlet. Cat hangs from rubber grommets so I'm sure it is bouncing around a bit, also maybe contributing. my scanner will log/save so I'll pull down the info and post. thank you!! I'll update again asap

[fixkick]

Quick response before I have to step into work-  did a lot of reading through the the site yesterday, noticed that standard plenum vacuum at hot idle should be 20 inHg, mine is stable at 8..  so I may have a vac leak somewhere, probably contributing.  I have a new VSV2, and nothing under the hood is "custom" I've gone to great lengths to make all the mechanical components as original as possible.  Header was cracked bad, currently running a doug thorley, no funky tube, goes directly to Cat inlet.  Cat hangs from rubber grommets so I'm sure it is bouncing around a bit, also maybe contributing.  my scanner will log/save so I'll pull down the info and post.  thank you!!  I'll update again asap

19 OR 20" IS HOT IDLE,  800RPM AND NOTHING ELSE , not cold ,  not 8. SO RPM IS important here.
the engine cam must timed correctly and compression near 180 PSI, all 4,
then no melted cats, if melted the engine can not pump air, and can not have normal  vacuum.
the header can not be cracked or it sucks in air, and makes the 02 front go NUTS.
the Exhaust pressure pulse,  goes Positive then goes to slight vacuum  each PUTT . (AND CRACKS ARE NO GOOD HERE, NO CAR WITH EFI GOOD with cracks near O2)
was cracked, or is?.  so the Thorney has no EGR #4 port?  You say?, if yes, no port EGR will never work, ever. ((ahh funky means 90deg suzuki front tube, sure)

you  should do photos of what you  have so wild questions end ,  old cars, have wrong parts and bad parts and missing parts, endless , but yours is not. got it.


8" inches HG vacuum is NO GOOD ever,  (unless EGR sticks open or what told above)
vacuum wrong is big time serious.

on an normal engine, we see about 19" hot 800 idle
then blip the throttle and vacuum drops fast and recovers fast when released.
with a melted cat if car runs at all, some do not ( the vacuum acts very odd and very slow to recover,  unlike any good engine behaves.

is the cat sized for 1.6L or 3L/?  sizes matters, to get it lit off and keeping that  way, only correct sized cats work. 

ECT read 300 ohms hot engine, if not burn up cat you will, (ECU sees below 150f water temp for actual hot engine goes rich and is very bad. 180F is correct or more, 195f are sold.
some folks in EU have like 3 types of ECT and buy the wrong own, and pure hell ensues.

when p0400 pops we scan and get the freeze frame so we can see if EGR A or B test failed. one is cruise and other us cut fuel test. ( we see this with vacuum readings in the freeze frame)
but with 8HG vacuum the tests have no change for sure the cut fuel mode, EGR B test. hopeless....

cam timed right. (not using the 16v cam cog wheel false marks !!!)
spark timed right
compression at spec, 180psi at sea level, my compression page covers correction rules for folks at height altitude.
the vacuum at 19" HG hot. engine 800 rpm.

those are the basics on the engine, if not right, EFI can and will go nuts, the EFI adjusts for normal engine wear and 8" Vacuum is not normal at all, not even 1/2.

[TomPrestin]

todays information- then questions. fyi I'm getting paranoid that I'm destroying an engine I spent the last 2 years hunting down parts for.

old header was cracked, thrown out. new thorley header does have EGR port. looked extensively tonight at all vac hoses/connections, and header, all are connected correctly and don't see any leak points.

Scanner does freeze-frame when coded- freeze frame from today says:
DTC Code: P0400
Fuel System1 status: CL
Fuel System2 status: ... (not sure if this is applicable or not, but its listed in the frame)
Calculated LOAD Value: 19.6%
Engine Coolant Temp: 177f
Short Term Fuel Trim - Bank1: -1.6%
Long Term Fuel Trim - Bank1: 1.6%
Intake Manifold Absolute Pressure: 8.7 inHg
Engine RPM: 2547
Vehicle Speed: 49mph

Doesn't say anything about EGR A or B. seems like something is missing.. you and me both.

I took multiple other snapshots tonight while driving and then arrived home basic info listed here. not sure if it will offer any insight but I'm at a loss on it. especially the low vac pressure:

DRIVING
SnapShot1:
Long Term Fuel Trim - Bank1: 0.8%
Intake Manifold Absolute Pressure: 15.6 inHg
Engine RPM: 3030
Vehicle Speed: 75mph
Ignition Timing Advance @Cylinder #1: 33.5degrees

Snapshot2:
Long Term Fuel Trim - Bank1: 1.6%
Intake Manifold Absolute Pressure: 12.9 inHg
Engine RPM: 2585
Vehicle Speed: 66mph
Ignition Timing Advance @Cylinder #1: 30.5degrees


Home, Idle hot1 (no accessories on):
Long Term Fuel Trim - Bank1: 2.3%
Intake Manifold Absolute Pressure: 8.1 inHg
Engine RPM: 787
Vehicle Speed: 0mph
Ignition Timing Advance @Cylinder #1: 10.0degrees

Home, Idle hot2 (no accessories on):
Long Term Fuel Trim - Bank1: 3.1%
Intake Manifold Absolute Pressure: 8.1 inHg
Engine RPM: 803
Vehicle Speed: 0mph
Ignition Timing Advance @Cylinder #1: 9.0degrees

To add to the confusion cold idle is now very high. Upon beginning of cold temps here it would run 1500(ish)rpm when cold, then settle right down when warm. Now running 2500-3000 cold, settles down as normal when warm. Simply a change I thought might add insight to this conundrum. Still doing newly revealed mild hiccup also, mostly at cold idle and also at barely open throttle- cruising.

I'll send pictures of engine bay tomorrow when sun is up.

My paranoia and lack of experience leaves me with these questions (in response to your check list) tonight:
1. Is is even possible for the engine to run as well as mind is with incorrectly timed cam? Been my daily driver since I got it all put back together in April. My assumption (very possibly wrong) is incorrectly timed cam would result in pretty dramatic loss of power and awful gas milage?
2. Upon more reading on the site today, says cam is timed at #4, but then in instructions for setting timing say to connect timing strobe to #1 SparkHV lead. Is that correct? I followed those instructions at original reassembly, so not questioning, just confirming to eliminate variables for my own piece of mind.
3. I'm just plain baffled. Trying to keep an eye on O2 graph readings while driving, both seem to be swinging as if working correctly, but I am sure no expert. Only time no swing is closed throttle while moving (hard deceleration) all O2 values drop to bottom until throttle is reopened. I'll download that info and post as soon as possible also.
4. Paranoia says I timed something wildly incorrectly, but its hard to believe that's the case as its capable of running stably, consistently, been my daily driver since the early spring, with no obvious signs of problems other than this CAT burnup ordeal.

Thank you for all of your input, knowledge and suggestions.

[fixkick]

todays information- then questions.  fyi I'm getting paranoid that I'm destroying an engine I spent the last 2 years hunting down parts for.

old header was cracked, thrown out. new thorley header does have EGR port.  looked extensively tonight at all vac hoses/connections, and header, all are connected correctly and don't see any leak points.  

Scanner does freeze-frame when coded-  freeze frame from today says:
DTC Code: P0400
Fuel System1 status: CL
Fuel System2 status: ...      (not sure if this is applicable or not, but its listed in the frame)
Calculated LOAD Value: 19.6%
Engine Coolant Temp: 177f
Short Term Fuel Trim - Bank1: -1.6%
Long Term Fuel Trim - Bank1: 1.6%
Intake Manifold Absolute Pressure: 8.7 inHg   (this is the EGR BARO RELATIVE sensor, NOT A MAP and NOT ABSOLUTE BARO at all. ) same as  hand tool gauge does!
throttle is open (too bad freeze frames do not show all sensors. sadly)
Test B needs at least 22"HG vacuum (rel) 0.75bar so the above is TEST A.  the above  is the  cruise test. failing. (it commanded the VSV valve open and closed and the change on BAR failed (differential test it ) it tells us only 2 things EGR main is dead, or the Exh path is blocked. (we do more tests to learn which of the 2 it is.
the only clues as to TEST A or B are the vacuum readings, high vacuum is B , lower is A, cruise.

Engine RPM: 2547
Vehicle Speed: 49mph

---

Doesn't say anything about EGR A or B.  seems like something is missing.. you and me both.  (that is correct only the numbers give it away)
yes the factory dealer scan tool has button to press to get A or B cause we dont have  that in OBD2 tool land, so vacuum it the KEY to what  is UP.

I took multiple other snapshots tonight while driving and then arrived home basic info listed here.  not sure if it will offer any insight but I'm at a loss on it.  especially the low vac pressure:

 DRIVING
SnapShot1:
Long Term Fuel Trim - Bank1: 0.8%
Intake Manifold Absolute Pressure:  15.6 inHg 
(this is  not normal MAP sensor it is EGR MDP sensor and uses relative reading) noW I Know you dont own a vacuum tool (first time)
Here is the true output MDP,     https://fixkick.com/sensors/EGR/EGR-map-test.html
At WOT, (or just keyon) Absolute pressure is~ 29" HG or 1 BAR  (sea level all) ( this is normal at sea level , air pressing down on you an car and MDP)
At idle , Absolute, is at 19" or 0.64bar
now we do , relative pressure, is against , actual atmospheric pressure. of 1bar.  R = 1Bar Absolute(now) minus reading) this is what a hand tool does, this.Relative.

so WOT is 0BAR  (1 minus 1 = 0) math. very different readings.  for sure. than above.
idle is  1bar minus,  .64bar and = .36 bar,  and .36 is 10.6"HG,  this IS HOW THE MDP works on this car, and is only  and EGR sensor,  just for it alone.
MDP does this, and your  tool LIES (marked as Absolute is the lie only, not the data) and told you it was 8.  if you had used hand vacuum gauge you see 19"HG. it idle.
the hand tool is 0bar disconnected, Relative.  Just like the MDP. so is NOT a MAP sensors  it is  Relative BARO sensor.  MAP means manifold absolute pressure, and MDP is NOT That.

the MDP uses these spec, rules. https://fixkick.com/sensors/EGR/EGR-map-test.html


Engine RPM: 3030

Vehicle Speed: 75mph
Ignition Timing Advance @Cylinder #1: 33.5degrees

Snapshot2:
Long Term Fuel Trim - Bank1: 1.6%
Intake Manifold Absolute Pressure:  12.9 inHg (relative MDP and is not a MAP)
Engine RPM: 2585
Vehicle Speed: 66mph
Ignition Timing Advance @Cylinder #1: 30.5degrees


Home, Idle hot1 (no accessories on):
Long Term Fuel Trim - Bank1: +2.3% (o2 reads -2% lean ECU goes +2% rich) all normal.
Intake Manifold Absolute Pressure:  8.1 inHg  (not this is 8, MDP relative pressure not absolute,  tool lies on name.  a hand tool shows 1 (relative MDP and is not a MAP)
Engine RPM: 787 (idle)
Vehicle Speed: 0mph (parked)
Ignition Timing Advance @Cylinder #1: 10.0degrees

Home, Idle hot2 (no accessories on):
Long Term Fuel Trim - Bank1: 3.1%
Intake Manifold Absolute Pressure:  8.1 inHg
Engine RPM: 803
Vehicle Speed: 0mph
Ignition Timing Advance @Cylinder #1: 9.0degrees (all above is normal, only the word absolute is dead wrong "name".  (relative MDP and is not a MAP)

---

To add to the confusion cold idle is now very high.  (this is all very normal the IAC open more if the air temps are colder, all fully normal. (well depends on how high.)
when talking about cars and UEFI TELL THE Helper out door temps,  and altitude,  (for the latter, in feet or say near sea port or, some clue, ok>?
I guess not really cold and in florida?  (where the grow oranges or KEY Limes (yum)
too high idle means vacuum leaks, (cold)the ISC and the IAC are the only normal leaks by design)
any leak from intake valves to MAF is a leak. (no that maf is not a leak ) The TV is closed at idle.
There are some tests to do to find leaks, (air) unplugging the ISC connector,  makes it close 100%.  (if not stuck open) 
The ISC has 3 hoses,(2 are water) 1 is air you can pinch the air hose and if idle drops to the good zone say 1500.. cold the ISC IS STUCK open.
testing the IAC is super hard. (the 8valve G16a is vastly more easy to test.) not to mention, pinching all air hoses. small.
The IAC is bolted below the TB, and the bolts love to seize making it damn hard to do that hot water pan on stove tests, I like to do.
On can starve it from all air inputted to see its CONTRIBUTION to air. (rpm drop actual) IAC is closed 100% at 150F temp, water, so its colder we want to test it at.  The  hole is in the TB front air  horn bell. HERE. (have you found the TB air bleed screw yet and it not missing?)
that is just 2 sources for leaks there are vast more.
all vacuum lines
all diaphragms even that brake booster)
the injector cushions leak, if not new. sure they are I think. new.
cracked or bad VSV (all)
the main air pipe huge up top can crack,  anywhere there cracks (even mounts broken off and leaks air)  and the large rubber connector  fittings to same  bad.
That is  about it, but sure gaskets too.
finding vacuum leaks is skill set,,, using propane gas trick, pinching lines, vacuum leak down testing hand tool,  sonic leak detectors (a tool) and the SMOKE machine. One guy here (he was at wits end) 8v,  we found after doing all tests,  every single one to no avail the smoke machine nailed this.
the silly car at one time was parked in 0F degree weather with only water as coolant (in FLORIDA) the water now pure deep inside the TB IAC, forze
and ICE expands when frozen and this cracked deep inside the TB cause and air leak, in the IAC, and high IDLE.  where no human can ever go, by the way.
yes vacuum leaks can be a HUGE HORROR. (some are easy some are a horror)
one guy even put his hand over the air horn (do not do that) and he found his engine runs with no air there,  OOPS ,  deep deep damaged.
even intake manifold leaks in very hard to find places...
hope my vacuum stories help you.





Upon beginning of cold temps (how cold?) here it would run 1500(ish)rpm when cold, then settle right down when warm.   common in temperate climates.
Now running 2500-3000 cold, settles down as normal when warm. 3000 is too high, for sure in Florida. (im in TX, was 78F yesterday see? )
  ( ok in maybe Alaska 3000? IDK, but never been there, ,  but for sure more RPM THERE, maybe 2000 max is my guess.)

The 16valve engine only races too fast or only 2 reasons. (throttle cable not set too tight, will do it, 10mm slack is FSM spec on TV cable and cruise cable)
1: the 2 air acutators
2: Vacuum leaks, other.
IAC messing up or ISC sticking. both add air (metered air ) the engine, and do stick when old.  car is old,
IAC is cold engine fast idle device.
If engine is rich, as it sure is cold for fact, any #2 vacuum leaks of any kind will cause HUGE IDLE speeds cold.  (fuel + Air = fast idle)

Simply a change I thought might add insight to this conundrum.  (and is correct, all evidence good bad or ugly helps Diagnosis. for SURE.

Still doing newly revealed mild hiccup also, mostly at cold idle and also at barely open throttle- cruising.  (if you have vacuum leaks, hiccups are common)

I'll send pictures of engine bay tomorrow when sun is up.  (no hurry but I know what belongs there and not, so showing me can help)

First off my comments are for all G16b and all things that can cause problems, I can not discount things, I can't see or know or, any of that , so I show all things for cause. I did not see you set belt tensions all wrong, see? (the belt must never be set to 100lbs tension ever , it fits loose using  tiny spring or it will fail)
but did not , as say car runs great, mostly. do you have the crank pulley 17mm head bolt set to 94ft/lbs as the FSM and TSB DEMAND, (this is  a day 1 fix on all G16)(retroactive to 1989 up)


My paranoia and lack of experience leaves me with these questions (in response to your check list) tonight:  
1.  Is is even possible for the engine to run as well as mind is with incorrectly timed cam? (not it can't run right like that)
 Been my daily driver since I got it all put back together in April.  
My assumption (very possibly wrong) is incorrectly timed cam would result in pretty dramatic loss of power (so true) and awful gas mileage? (see green line above)

2.  Upon more reading on the site today, says cam is timed at #4, but then in instructions for setting timing say to connect timing strobe to #1 SparkHV lead.  Is that correct?
NO spark is set at #1 wireHV TDC firing,  the CAM is timed at #4 firing, period. the 1996 FSM is free and linked in the sticky first post here on this BBS.
The cam cog on this car has 2 false marks, are you aware of that.?
The engine after full assembly and good shop does compression test, to see if all that hard work paid off.  did you? this is first step, then top end oil checked , just cranking a cold new engine, with spark  or better FI fuse pulled so fuel stops flowing, we check that the cam gets OIL, if not stop do not run any new engine every , skipping these first steps.
the make sure oil gallery pressure is good, on a cold engine it is near 50PSI, (cold cranked only , no fuel) then I attempt to start the engine)
I never just throw and engine together and start it up. not me, seem so my do that and wreck a good engine. sad to watch.
The next step is get the vacuum tool off the shelf or tool box, and check vacuum at idle 800rpm hot.  see 19 or 20 " easy.  HG inches, Relative vacuum is 0 HG key off.
Once you get this far, you know that Vacuum is AOK.   and that he scan too lied to you (vast do this) at (relative MDP and is not a MAP)
You need to know that,for EGR , the EGR MDP sensor , work in RELATIVE mode not ABSOLUTE mode..  



 I followed those instructions at original reassembly, so not questioning, just confirming to eliminate variables for my own piece of mind. I'm sure you did but my posts are for
all things that can be wrong, seen Timing belts done wrong vast times or belt too tight and it shreds.... keep and open mind and win., things can fail even new things.

3.  I'm just plain baffled. ( don't be we are collecting Evidence,  and you did GREAT !!!!!
 Trying to keep an eye on O2 graph readings while driving, both seem to be swinging as if working correctly, but I am sure no expert.  (get a helper to drive and you look)
No need every to work alone if doing dangerous tests, use 2 persons, my Laptop has record mode,  and can log live data (and filtered) all day long. no hands
how you log , can be easy or hard or dangerous.  (see my photo above with tons of wiggly lines, that was recorded, all that was)scantool.net. _+Palmer scan software.
I own this software called Palmer. (nothing Ive seen is better or for sure more safe to use (hand free logging) (push record, drive, stop , push play back,.)


the O2 sensors, are not static, at all, they measure 02 and the ECU hunts the mixtures constantly never ending (hot engine) and those readings you see are like scope
each time the voltage crosses 0.45 (center) (called cross counts) that is the ECU doing that with fuel mix, trim,  it is a dynamic ECU servo action, no different than idle speed ISC or cruise controls all are servos.... they hunt to attain perfect, all do. but the O2, hunts deeper on purpose to keep that CAT hot (by law, and by Physics of the cat)

So if it is cross counting like my  photo clearly show, and the swing go near 0v and near .9v   then all is  well in trim land and 02 land.  sees so to me.
The swings end at WOT< and if you move the throttle fast.  the come back as you cruise steady or just idle (hot engine )




 Only time no swing, is at closed throttle while moving (hard deceleration or WOT) all O2 values drop to bottom until throttle is reopened.  
I download that info and post as soon as possible also.
4.  Paranoia says I timed something wildly incorrectly, but its hard to believe that's the case as its capable of running stably, consistently, been my daily driver since the early spring, with no obvious signs of problems other than this CAT burnup or  deal.

Thank you for all of your input, knowledge and suggestions.

The engine is running ok,  I see that in the data so far.
the EGR is dead, but we can fix that,
(so far we have cat melts, cat breakup inside, and EGR dead, and bad cold idle and hiccups,  any more?) evidence.?

Let me explain limphome and only for EGR.
some of these cars (and by law) if the EGR fails, that means the car is NOX polluter, for sure. (driven hard)

the ECU seeing EGR 400 fail, may in fact go rich NOW, and this can and will overheat some CATS. (depends on maker of cat and mode)
if you have NOX, the best solution of all to ending NOX is to go rich,  Rich cools combustion and NOX ends NOW.
this is in fact mandated on some cars then and now. dealing with NOX is serious  (acid rain and burned lungs ,etc)
so the car may run perfectly until 400 sets, and then goes rich, not saying yours does, but many cars do.
It may also flash the CEL lamp (missing on your car) and the flashing CEL means CAT burn up , is soon, the operators guide tells you to not pull a trailer and drive slow and fix car.

I'd say all is good, but EGR failing and CATs melting, only why remains.
The cat some sold new are what I call weak cats, unlike the 1996 robust cat, the new cats do not last  long of fuel mix goes out of control and for long time (weeks)
By the way thanks for sharing your data.  (data is king)

The EGR test #1 is first.
at the MAIN< and is behind the exhaust manifold #4 runner rear, and very hard to see much less touch. so we use hand vacuum tool like the video shows.
and see RPM fall from hot 800 to 400 or stalls, end test.
we do that first.
then check the bark tube for barking pulled, I call that the bark test, (putt putt putt) keyoff, tube pulled (below MOD) and start engine hear the tube port  bark. loud.


if not there are 4 places this blocks, EGR main (bark port)packed in carbon, intake  mAN- S bend packed, head tunnel packed and the Thorney tube packed in carbon.
if bark passes. last is the live test all this in covered on my EGR page, step by step

next is LIVE test but your car has no real speedo,  VSS must work or the EGR will be dead,, on all these cars. (1993 and newer, approx but 1996 up for SURE)
the EGR will never open at 0MPH ever,by hard coded ECU internal firmware logic.

also clean the MDP, just get its port on the bottom clean, no gunk there,  so it can work right, (note I assumed it is 1996 old , here)
the plenum on theses cars are a mess,  (the EGR cloud hits the  PCV valve, could and forms GUNK, this gun lands all to easy on the MDP port) making read wrong or go slow.

The ECU is lame, the OBD2 should check the MDP 3times, by it self but does not,  keyon, idle and cruise test.
but no it does not it just does the 2 EGR tests. and one fails.

Im not sure (im not firmware genius) but if EGR test A fails, test B may be aborted, A = Cruise test, B= moving fast cut fuel tests.(throttle at 0)

test A proves EGR main opens, 
test B proves EGR main closes.

it does differential MPD readings to do that,  (it does test A valve closed then opens it and gets 2 readings from MPD, and the difference in  MPD pressure, is checked, (pass/fail)


MDP page.


the GM EGR truth page, A and B. (hard to find but I have it)    PAGE1   and  PAGE2

cheers and good day.

[fixkick]

if the live test fails then we test the vacuum devices, many.
the live test, kicks off with.
hot engine,
idle normal to start.
1mph or faster (rear tires off ground VSS clicking away. factor stock Care, VSS in speedo head stock) transmissions are in GEAR, to spin rear drive shaft.
then VSV1 opens, and then you open the throttle and vacuum hits the VSV1 and VSV opens now and vacuum hits the MOD port.
if cat back pressure is not 0 or not 10psi,(melted) the MOD sends the correct vacuum to the EGR main and it opens and flows exh gasses to the intake EGR mono port.
as you increase RPM (and mph) the flow increases in direct proportions to cat back pressure,

this is how EGR works LIVE
in the old days 1993? or 92, no need to spin real wheels at all. and EGR opens even parked in neutral. seeing it open may take a MIRROR on any 16v.
As you can see most of this takes 2 men ( or Gal) one to drive jacked up in the air,and one to use a mirror to watch the DIAPHRAGM move inward.
Not a very safe test, but taking off rear tires would make this saver. the rear axle turns and the speedo cable spins and the speed clicks VSS and EGR opens.
the rear axle drive prop shaft must turn even gently so.... be safe ok?

[fixkick]

one more just a photos to show all places vacuum air leaks can happen and do.  All engines want to leak , a vacuum loves to fail , even sucking in gaskets and more.

I added what I think (crib note comments) all possible failure paths. on normal engine cold air supply is  only IAC. (and the bleed ,tiny air)

my first 96, had broken mount, at Red #3 and suck air like mad  and crazy symptoms,

[fixkick]

i have used clay to block the IAC input port, put back the air horn so MAF is working
then start the engine, it may take right foot action to keep cold engine running with Dead IAC>
but what the engine does now tells you if the IAC is bad, or there is this other leak. of air.
The IAC closes 100% hot, and must, if someone tuned duty cycle to 50% with the bleed screw and there are leaks, then when the engine is cold the air leaks add to the IAC normal flow.
my point here is sometimes, folks adjust the bleed and used that to hide air leaks, hot. by screwing the bleed screw in 100% CW clock wise turned.
see? Duty cycle is set on hot engine only, using bleed so the ISC is in the middle of its dynamic rage, and done only if no illegal air leaks are present.
if the bleed is bottomed out, that is a RED FLAG.

[TomPrestin]

fixkick pid='12318' dateline='1574168998']CAT 101 : basics (then covering beat to death CAT last)
when you start a cold engine the CAT gets a load of unburned fuel (HC) dead cold, and ECU is in cold start rich burn mode and the cat gets light off fast. (and must stay so)

then ECU goes to hot engine mode, and goes to STOICH,  14.7:1 AFR, and if the cat is too far from the exhaust header it can now go DEAD< a dead cat. (means not lit off)
then it sucks up fuel cold , and overheats at some point , mostly going fast. after the fuel soak up. (dead) (suckup , fry , suckup , fry repeat)

The goal is , A hot engine, and at every stop signal, (stop light /sign) the CAT stays LIT off, or it can overheat later, (imagine this endless cat torture if not working right)

The cure is get the cat close to the header. close as possible. IF You do the CAT can list 100,000 miles, even more. mine had 150k on it.
looking at examples:
see Modern V6 engines with 2 cats mounted at 45degree angle dead close, this is THAT and WHY. faster light off and stays so, is the reason.

one thing great on this Suzuki Drive line , no extra wasted parts, all parts on topic have  PURPOSE,  so here I will exhibit what parts do DOWN UNDER,

this was your car, before the hurricane. (stock car)

I pasted this photo of the SUZ EPC, parts cat, (official dwg)

parts 7 must be there.  if a custom cat , one must design there own mounts. if not? the cat beats it self to death from the  nasty 4cyclinder  huge vibrations.  and the monolith element inside cracks then breaks up to chucks then dust, (my jeep 88' did the same. and I made a custom mount, to replace the jeep mount that broke, every 10,000  miles (fixed and drove 250k more and I had 2 of those cars, one Pickup and one 4door SUV both failed. both cured.)


part 17 is to body frame rail, mount.
part #1 is what I call the funky tube. (some are double walled) if are and not upgraded it insides collapses.   <<<the TSB is here)

if your part 1:   can be missing, or not a 1996+ (Good one)  or 1992-95 bad one, then all this matters,  what matters is the the insides of pipe 1 is not collapsed.
other cards CAT's  are  with a pelleted  cat guts do not fail shook hard, (James Bond, shaken but not stirred)

now some more news.
SOME OBD2 DTC tests are skipped, if some tests before it failed. P0421 is that, if the 02 front fails it can not test the rear 421 test. so skips this.
that means fix 1 thing and 2nd error happens, see why? (called unmasking) OBD2 joys.

NO lie this cat is fragile,  that is a fact, some make huge rattling sound inside (the doomed sound) 
or buy a pellet cat,  for 1.6 to 2.0L and use that, end the pain of weak CATS.

TSB = suzuki technical service bulletins. ( on all cars read these first then turn the wrench)

and last good luck with your custom Kick,  and please put a human protect on that side crash bar mounts. (foam? wrapped?) IDK but a for sure knee killer.

Took pictures under the hood today- will post tomorrow after converting.  Did EGR test, seems good, does as your test suggest when opened, recovers quickly when released (closed).  

Considering how many times I've had this thing in pieces I am certain there is/never was (possibly removed by PO) the #17 body to frame rail mount for CAT, so something to look in to.  

I actually have a boost/vac gauge of the same set as currently installed, but not hooked up yet. I'll try to get that accomplished this weekend also and have constant eyes on actual VAC levels now that you've informed me scanner is not accurate direct vac reading.  (thank you)

Both 02 sensors seem to be doing what they should as I observe during regular driving, will still pull down info and post when I have time.  

forgive my ignorance, but I'm lost on the CAT "LIT" subject.  mostly because I don't know definition of LIT.  Searched site and couldn't find it in the jargon area.  

On the high idle-  Apologies for the location confusion, I'm in Minnesota.  vehicle was originally a Florida car (where I found it) but now resides in MN, so winters are cold.  first cold was 10-20 overnight, a few weeks ago.  Started as expected ran 1600rpm until warm then dropped to 800.  recently warmer (last week and this in the 40's) but idle surging on start up to 2800rpm, holding there until warmup then dropping down to 800.  possible IAC or ISC just need cleaning?  or indicator of vacuum issues waiting to be tested/visualized.  Again- I don't see any places with cracks or damage that could be causing the vac leak, but certainly not going to stop looking.  

On the subject of headers-  as stated I have the Thorley, which you are correct the EGR port is not well designed.  Alternately the gasket they send for mounting is a softer compression gasket which I have to imagine could EASILY press into the machined EGR passage and block it partially or completely simply with installation.  IF I'm following correctly- EGR test good suggests all EGR passageways operating reasonably?  For sake of convo; if the EGR exhaust port were blocked, could it be a contributor to the CAT burnup issue?

More to come when I can make time!   Thank you!!

Pictures finally