Poor mileage and running rich

[Clint09]

First ever post for me here. I’ve been struggling to get my USA 97 16v running properly. The most obvious symptoms are poor mileage (18-21), very rich exhaust at idle, a code for bad catalytic converter, and an occasional misfire. The previous owner told me the catalytic converter was al busted up inside so he hammered it all out and it is now gutted. I Have been testing different things and it seems that the EGR doesn’t work properly. The EGR passes the stall test but when I rev the engine (with rear wheels turning) doesn’t seem to move the EGR diaphragm at all. After more research I learned that the EGR needs the CAT in place to function properly. So I have plans to reinstall a CAT but I am wondering if this could also be the source of my rich exhaust issue or is that being caused by something else? According to a scan tool all other sensors are reading fine. Also what would be a good option for a replacement CAT?

[fixkick]

First ever post for me here. I’ve been struggling to get my USA 97 16v running properly. The most obvious symptoms are poor mileage (18-21), very rich exhaust at idle, a code for bad catalytic converter, and an occasional misfire. The previous owner told me the catalytic converter was al busted up inside so he hammered it all out and it is now gutted. I Have been testing different things and it seems that the EGR doesn’t work properly. The EGR passes the stall test but when I rev the engine (with rear wheels turning) doesn’t seem to move the EGR diaphragm at all. After more research I learned that the EGR needs the CAT in place to function properly. So I have plans to reinstall a CAT but I am wondering if this could also be the source of my rich exhaust issue or is that being caused by something else? According to a scan tool all other sensors are reading fine. Also what would be a good option for a replacement CAT?

OBD2 USA rule #1 (mine) is dot not worry P0421 cat codes, until the engine is fixed (EFI and all)  CAT errors are normal if the engine is sick, and is.
18mpg is horrid.
ok gutted, and break ups are common and so is that act, if not in smog testing state no worries there.
The P0400 error (DTC) will be endless as will the cat error P0420 , P04xx errors endless all, no Cat,
the cat missing on these cars, kills dead EGR so EGR errors P04xx hit. all 100% normal for missing cat or rodded out.
EGR uses cat back pressure to measure engine loads,  to inject EGR Gasses at the correct rate
The Cat misssing means the EGR mode will be dead, how can it not be dead. in this case.
but lets forget all the above for now... focus on spark and fueling, if compression is 180psi all 4 cylinders, done WOT.


The scan tool is handy but you need to look more carefully.
Rich means, 2 things, (besides gross misfiring bad spark, parts, ever do full spark tune up?)
1: fuel pressure is too high. (FPR dead as most are this old) (need keyon pressure  and idle pressures to know) no fuel leaks out vacuum nipple FPR.?
2: 02 sensor fibbing, or just the #4 exhaust tube heater crack sucking in air making the o2 lie all the time.
QOD:
1: is the o2 in closed loop at HOT idle.
2: is the O2 sensor scanned, swinging at hot idle.
3: is coolant at 180F for sure in scans of ECT at 180f or above?
4: drive car lots with O2 unplugged, Ignore DTC, errors, and get better MPG and end black exhaust smoke and raw fuel stink?

lots more but this is a good start.

[Clint09]

First ever post for me here. I’ve been struggling to get my USA 97 16v running properly. The most obvious symptoms are poor mileage (18-21), very rich exhaust at idle, a code for bad catalytic converter, and an occasional misfire. The previous owner told me the catalytic converter was al busted up inside so he hammered it all out and it is now gutted. I Have been testing different things and it seems that the EGR doesn’t work properly. The EGR passes the stall test but when I rev the engine (with rear wheels turning) doesn’t seem to move the EGR diaphragm at all. After more research I learned that the EGR needs the CAT in place to function properly. So I have plans to reinstall a CAT but I am wondering if this could also be the source of my rich exhaust issue or is that being caused by something else? According to a scan tool all other sensors are reading fine. Also what would be a good option for a replacement CAT?

OBD2 USA rule #1 (mine) is dot not worry P0421 cat codes, until the engine is fixed (EFI and all)  CAT errors are normal if the engine is sick, and is.
18mpg is horrid.
ok gutted, and break ups are common and so is that act, if not in smog testing state no worries there.
The P0400 error (DTC) will be endless as will the cat error P0420 , P04xx errors endless all, no Cat,
the cat missing on these cars, kills dead EGR so EGR errors P04xx hit. all 100% normal for missing cat or rodded out.
EGR uses cat back pressure to measure engine loads,  to inject EGR Gasses at the correct rate
The Cat misssing means the EGR mode will be dead, how can it not be dead. in this case.
but lets forget all the above for now... focus on spark and fueling, if compression is 180psi all 4 cylinders, done WOT.


The scan tool is handy but you need to look more carefully.
Rich means, 2 things, (besides gross misfiring bad spark, parts, ever do full spark tune up?)
1: fuel pressure is too high. (FPR dead as most are this old) (need keyon pressure  and idle pressures to know) no fuel leaks out vacuum nipple FPR.?
2: 02 sensor fibbing, or just the #4 exhaust tube heater crack sucking in air making the o2 lie all the time.
QOD:
1: is the o2 in closed loop at HOT idle.
2: is the O2 sensor scanned, swinging at hot idle.
3: is coolant at 180F for sure in scans of ECT at 180f or above?
4: drive car lots with O2 unplugged, Ignore DTC, errors, and get better MPG and end black exhaust smoke and raw fuel stink?

lots more but this is a good start.

It has new plugs, wires, cap and rotor within the last year. fuel pressure is around 45psi, compression is mid 170s on all cylinders, Fuel pressure reg is new and tested working and not sucking fuel through the vacuum line into the intake, I did notice the #4 manifold pipe is cracked. I didn’t realize the cracked manifold would suck in air and mess up the o2 sensor. I’ve unplugged the o2 sensor and drive for a while but didn’t notice much difference. Maybe I’ll try that for a full tank of fuel and see if the mileage changes.

[fixkick]

It has new plugs, wires, cap and rotor within the last year. fuel pressure is around 45psi,
compression is mid 170s on all cylinders,
Fuel pressure reg is new and tested working and not sucking fuel through the vacuum line into the intake, I did notice the #4 manifold pipe is cracked. I didn’t realize the cracked manifold would suck in air and mess up the o2 sensor. I’ve unplugged the o2 sensor and drive for a while but didn’t notice much difference. Maybe I’ll try that for a full tank of fuel and see if the mileage changes.

the the scan tool will show closed loop at idle
and same at steady right foot cruise say 45mph.
must do that O2 present sure. and O2 must swing or it will suck fuel.

the Exhaust PUTT sends out a huge pressure putt this hot gas cools fast and goes to a vacuum just after the putt.
and sucks in 20 % AIR O2 gase from air and hits the o2 sensor and it goes mad, to 0v. and can change at the crack gets larger and smaller as you drive.

45psi, keyon only or at idle.

[fixkick]

keyon pressure is 36 and drops to 30psi on mine,

43 is max no matter what.
what matters most is the 6 PSI change from keyon to idle.
that matters big time if you go to full throttle the PSI will to down to near keyon pressure as low as 30

why is your pressure so high?
is the return line partially blocked/ or pinched, but what matters first is the 6PSI above,

good report so far, you have handle on what was done and what might be wrong still.

Not sure me if this year has limphome for P04xx codes, I do think not, but.... nobody knows all ECU that well.

[Clint09]

keyon pressure is 36 and drops to 30psi on mine,

43 is max no matter what.
what matters most is the 6 PSI change from keyon to idle.
that matters big time if you go to full throttle the PSI will to down to near keyon pressure  as low as 30

why is your pressure so high?
is the return line partially blocked/ or pinched, but what matters first is the 6PSI above,

good report  so far, you have handle on what was done and what might be wrong still.

Not sure me if this year has limphome for P04xx codes, I do think not, but.... nobody knows all ECU that well.

I rechecked fuel pressure it’s at 42psi with key on and 35psi at idle. I took the entire return side of the fuel system apart and could blow air through it so that’s not restricted. I put about 40 miles on it with the o2 unplugged and it still runs super rich at idle possibly even worse than before. Just got done running a NOID llight test on the injector wiring connectors and they all blink and seem to be working normal. Also I forgot to add that when I started trying to figure out this issue about 6 months ago the EGR passages were plugged and the intake manifold was caked with black sludge inside so I took it off and ran it through a parts washer until it was spotless inside. I noticed today looking through the throttle body that it is starting to build up black grime inside it again.

[fixkick]

keyon pressure is 36 and drops to 30psi on mine,

43 is max no matter what.
what matters most is the 6 PSI change from keyon to idle.
that matters big time if you go to full throttle the PSI will to down to near keyon pressure  as low as 30

why is your pressure so high?
is the return line partially blocked/ or pinched, but what matters first is the 6PSI above,

good report  so far, you have handle on what was done and what might be wrong still.

Not sure me if this year has limphome for P04xx codes, I do think not, but.... nobody knows all ECU that well.

I rechecked fuel pressure it’s at 42psi with key on and 35psi at idle. (good)
I took the entire return side of the fuel system apart and could blow air through it so that’s not restricted. 
I put about 40 miles on it with the o2 unplugged and it still runs super rich at idle possibly even worse than before. (ECU  sees that and punishes us)
Just got done running a NOID light test on the injector wiring connectors and they all blink and seem to be working normal.
Also I forgot to add that when I started trying to figure out this issue about 6 months ago the EGR passages were plugged and the intake manifold was caked with black sludge inside so I took it off and ran it through a parts washer until it was spotless inside.
I noticed today looking through the throttle body that it is starting to build up black grime inside it again. (all normal for EGR + PCV cloud of death)
EGR is dead now so is just rich fuel cloud and PCV cloud there making carbon.  The EGR main can be defeated with vacuum nipple to it unplugged and Golf tee the free hose end so it can not suck air.
I presume the injector leak down test passes?

ok FPR is ok, and no return line issues.
It is rich,
what is your OBD2 data look like, hot engine fully , a hot idle 800RPM , does 800 work and hold with head lamps on and heater blower turned on and off?
OBD2 scans.
1: closed loop. true not false.
2: LTFT?  (fuel trim)
3: ECT at 180f? or more? 300 ohms hot. (see my ect page)
4: MAF flow.    1.5–4.0 grams per second  idle hot, 800rpm,  and gunned to 2500 goes to 10-GPS. parked ,  driving looks like this (real and hills)
will your scan tool do at least this below?  (simple code readers are mostly useless) real scan tools are very useful.
5: O2 scans. below.

the engine is running rich,  I bet the scans show that too.. but I can not see them.
The fuel pressure is ok;. engine OK, exhaust man NOT OK.
O2 can fail at any time in road trip as that crack widens, then shrinks and very odd thermal dynamic actions of any crack here.

this is the super cheap scan tool (hand held) that can do even this.... act.

this is the O2 swinging, fast.  and not stuck high , not stuck low and the heater in the O2 is not dead. (sure plugged back in)
B1S1 is bank1 , s1 is front sensor, the rear is useless for fuel trim.  note the deep and full swings here and  not offset high or low. centered it is.
when the #4 exh crack widens it sucks are and this signal slams to 0v and ECU goes full on rich( LTFT way off the scale)


EGR flow, dead parked,  only moving and the large hump is the barkpressure from the cat , causing more flow via Modulator.

see this. this a PUTT,  note the negative pressure "B" a vacuum and at this point  , any crack sucks in 20 % oxygen in to said cracks, never good.



The O2 front fails for many reasons, not just bad O2, or Bad dead 02 heater

1. wrong 02 used? not the Bosch correct 4 wire? (ask)
   
2. bad wires to the 02, heater or the CELL (+-) inside. they love to burn as they hit
   
3. exhaust cracks. near front sensor 02 putt fail put fail. (luck)
   
4. the gasket at end of header, missing cracked or loose sucking in air at PUTT + B.
   
5. engine not at 180f but cold. (ECT 300 ohms hot or scan shows 180f+)
   
6. injectors leaking or   1 dead as it mindlessly pumps fresh are (engine is air pump) to 02. and it fail. (each misfire is wasted fuel)
   
7. Gross misfire, some cheap carbon spark wires even new are bad, use only MAG wires on this car and gain even better spark than stock. spark gap 0.028"
   
8. ECU stuck in limp-home mode and suspends closed loop. and runs rich; all do that. only scans find this.
   
9. MAF gone wild (rare, most go lean never seen one ever stick high) see live maf PLOTS on these post. from me. 2nd post same thread.
   

what is injector pulse widths at hot idle? 800rpm parked.  2.5 mS.

what can happen on any exhaust system not new, is cracks, come and go , some even open wider hot or hotter or fail at idle or only driving  fast.
this makes diagnosis very hard this thermal dynamic nature.

if rich at idle what is PW at injector. about 2 mS is par. 800rpm;. hot.



Make sure to use  the scan tool and click on Pending codes. for sure. see if any P03xx codes pop all are misfire.
the DTCs (many) do not set until 2 driving key off cycles pendings do not lie.
the other factoid is the DOME fuse  is blown the ECU will NOT STORE DTCs  that would be tragic here, if true.  never run with a bad DOME fuse.


now OBD2 top  #1 weakness. Misfiring.
OBD2 has only 1 O2 sensor not 4, that means if one cylinder misfires the 02 lies and the other 3 suffer.
this is #1 in my mind all the time, working OBD2. 

there are other causes,  not sure history of  any car this old.
is wrong injectors stuffed in this car, or  bought from china, junk class crap injectors, from H3LL.  
(ask  your injector pro sonic cleaning shop how they like this, (they can not use them and cores worth $0)

if ecu is  in closed loop now, at 800rpm fast idle , the exhaust  will not be black smoke but what you smell is horrible NOX gas , eats lungs up NOX.
rat nasty smell that. like back in pre 1975 cars. (epa mandated)

[fixkick]

we know it is not the engine, with good compression, not head valves leaking. +

The maf goes dirt 99% of the time and goes lean not rich. if factory maf Mitsubishi still there, china mafs who knows, what.

most of these cars set P0171/172 if fuel trim falls off the map (scale)



A good  scan tool can do this too,  shows if the EPA monitors are all run out. means complete, and if complete you get to see all DTC  errors NOW.
that dead cat will DTC 420 wwhen cat montor finishes, but know this,  if the ECU does no like the front 02 sensor it never runs the 420 monitor (hides it)
evap takes ton of driving over 30min to complete, failing man smog tests just for this one fact.



Just to show off what can really be done with OBD2 (1996 and 97 G16 sidekicks both)

here is what my fancy tool can do.
on Laptop, with USB dongle OBD2.
I logged all this data,
the MPG is computed, the ECU never knows this. (from maf readings and speed =vss)
0 MPG not driving. at red stop signals..
note the sweet spot,
so owners of cars only see average MPG, (measured at the gas island pump, odometer read)
this below is reality,  so if you  drive 40mph in top gear 18mpg is 1/2 normal.

note how coasting saves fuel, (fast moving and no fuel to burn cut fuel mode in ECU)

[fixkick]

as you can see driving and plotting any errant OBD2 car can be really revealing. above software is. Palmer scan software


https://www.palmerperformance.com/store/...ucts_id=36


even log CVS files and import them into Exel. and graph anything you what, even hours of data.

[Clint09]

as you can see driving and plotting any errant OBD2 car can be really revealing. above software is. Palmer scan software


https://www.palmerperformance.com/store/...ucts_id=36


even log CVS files and import them into Exel. and graph anything you what, even hours of data.

I don’t currently have a scan tool that can read o2 sensor data just a code reader but I had it at a shop that pretty much gave up on figuring it out. They told me that both o2 sensors were reading fine. The injectors passed the leak down test and and are all flowing the same according to my fuel pressure drop on my cheapo flow tester.  Since my last post I replaced the cracked exhaust manifold with a stainless header and seems to run just as rich as before. Looking at the spark plugs they don’t seem to be wet or look as wet as I would think they should for running rich. Also the misfire on cylinder #3 is becoming more consistent but the only way to make it do it is driving at top speed for a few miles with my foot to the floor then the light continues to flash even after decelerating but I still can’t feel a change I how it drives while it’s flashing. Could it be possible that I am mistaking rich exhaust for coolant in the exhaust? The engine has new cap, rotor, plugs, and wires about a year ago. In the next couple days I’m going to borrow a friends fancy snapon scan tool to get better data.