97 Tracker - Poor Idle, Hesitation

[Mike8500]

Ok, new FPR in place. Has improved but still getting the hesitation, miss, bucking just off idle. Seems to run slightly better with the MAP sensor unplugged. Manifold vacuum at idle is about 20in-hg.

Do you think it is worth disconnecting the battery for a while and let it start relearning out from scratch? Not sure what my next move is yet. I think I'm going to purchase either Scan XL soon.

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So I guess the next things I need to do are to check timing, and make sure EGR is fully closed at idle. I may try and swap some sensors from a friends 95 parts vehicle (mine is a 97.) I am also going to do a TPS calibration although it appears to be working perfectly.

I think the FPR was a problem, but not the main problem. I'm wondering if after I cleaned out the EGR, if somehow a piece of carbon fell into the valve and is keeping it partially open.

Can you clarify a few thins with this EGR test. So I disconnect the vauum line from the intake, then I start the engine and "blip the EGR main" (does this mean press on the diaphragm?)

egr trick if needed, make sure its closed, parked, engine off
take off top egr hose, top of rear plenum at TB.
off it and plug it with golf tee, end EGR not wanting to close. as a test. parked blip the EGR main 3 times, 1,2,3 (for luck) hear it go thump, thump , that is full closed.
with EGR out of picture can help testing. for sure if likes to stick. some do , but only real hot.


I will check the crank pulley bolt torque when I am checking the timing.

[fixkick]

wow 2 problems, no wonder its pistol to fix.
you can pull the dome fuse, and it forgets everything, and DTC'S STORED
The learn time is just minutes... driving.
if the idle switch is set wrong. it will buck you, against your right foot, during then 1st 5% of throttle.
this is way i asked for, tip-in bogs, at other throttle angles, if they bog ,that is no TPS related
see? the carbon usually wears out, in only one spot, once discovered
yes, diaphram blip, sorry ......
17mm pulley bolt, if 5 speed, use 5th gear to do it.

13420-58B10
narrow base TPS , part,number

can you tip in , the throttle at other speeds ? with no hesitation or bog,
the tps is not easy to calibrate on any MPI, 16v
the path is mostly blocked on car.
the ecu watches the rapid movement of throttle angle, to enable enrich mode.
rate of change.
if worn out, the spot the wears can be totally different city car and highway.. later might bad at 60mph angles/.. on cruiser.
the city car will wear out at stop lights. low angle.

yes , I just make sure EGR IS CLOSED, and defeat it , the best way is at the egr main vac hose. , so it cant suck air.
once closed it stays closed, for fixing other issues,
then later put it back in service.
can save alot of grief.
had one that works perfect but sticks hot, no mater how many times cleaned.
cheers.

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if going say 20mph
moving in any gear
can moving the right foot cause this bog or hesitation?

[Mike8500]

So I'm back, I was away on Vacation and the poor Tracker just got left out in the rain. After driving it some more, I've determined that the idle quality and hesitation are worst when it is cold. The idle is quite erratic as I posted in the video earlier, sometimes even stalling at stoplights. Now even after the engine is up to temp, the idle is still wacky and it hesitates randomly under half throttle. BUT after driving for about 25min or more, the symptoms are significantly reduced. Idle is fairly good, no major dips and it won't stall. The problem never completely goes away, but after a good long highway drive, it clears up some.

I was watching a few things on the way home from work today. MAF readings are stable, ECT is accurate and stable, Air Intake Temp is stable and correct. TPS reads smooth and follows the input from my foot seamlessly.

I was just using a free app on my phone (Torque Free) but the STFT was -25% at idle, and would jump to right around zero when cruising. Still running rich it seems. The next time I'm working on it, I'm going to pull the newish plugs that are in it and see if one cylinder is drastically different than the other.

can you tip in , the throttle at other speeds ? with no hesitation or bog, Speed doesn't seemt o factor in, only throttle position, fine over 50% throttle.
the tps is not easy to calibrate on any MPI, 16v
the path is mostly blocked on car.
the ecu watches the rapid movement of throttle angle, to enable enrich mode.
rate of change.
if worn out, the spot the wears can be totally different city car and highway.. later might bad at 60mph angles/.. on cruiser.
the city car will wear out at stop lights. low angle.

yes , I just make sure EGR IS CLOSED, and defeat it , the best way is at the egr main vac hose. , so it cant suck air. Still have to check this.
once closed it stays closed, for fixing other issues,
then later put it back in service.
can save alot of grief.
had one that works perfect but sticks hot, no mater how many times cleaned.
cheers.
if going say 20mph
moving in any gear
can moving the right foot cause this bog or hesitation?

It (never really bogs - i consider a bog a continuous loss of power, vs a hesitation is like a hiccup. If I'm going 20 and hit the gas to more than 1/2 throttle it accelerates fine.

[fixkick]

welcome bad from road trip..
-25% means the ECU is removing 25% fuel from a gross over rich mixture.
if it misfires, at all at idle, this sends, excess oxygen air slugs to the exhaust ports, and 02 sees that as lean , oxy lean. and goes huge Plus percent to correct it.
same with exhaust leaks near 02. huge oxy (air 20%) land there and huge + percent LTFT.
so what on earth causes -25%
too high fuel pressure tops my list
leaking injectors. (1 or more)
MAF stuck high,(but under the DTC error stuck high point, nah)
not clogged injectors as LTFT goes +25% to compensate.

its nice having scan tool data, no?
see whats going on with fuel trim... is a very good thing.
so you have zero DTC errors.

[Mike8500]

welcome bad from road trip..
-25% means the ECU is removing 25% fuel from a gross over rich mixture.
if it misfires, at all at idle, this sends, excess oxygen air slugs to the exhaust ports, and 02 sees that as lean , oxy lean. and goes huge Plus percent to correct it.
same with exhaust leaks near 02. huge oxy (air 20%) land there and huge + percent LTFT.
so what on earth causes -25%
too high fuel pressure tops my list
leaking injectors. (1 or more)
MAF stuck high,(but under the DTC error stuck high point, nah)
not clogged injectors as LTFT goes +25% to compensate.

its nice having scan tool data, no?
see whats going on with fuel trim... is a very good thing.
so you have zero DTC errors.

Yes so another day driving home from work I monitored some PIDs.

Today it started running properly much more quickly than the previous trip. Idle still started out shaky but it started running fine almost as soon as it warmed up. No DTCs present. STFT and LTFT were both a lot more normal today (0-6%).

I didn't change anything from yesterday to today. When I parked it, it was running perfectly normal. Strange beast this is. I considered a leaking injector, but that wouldn't fix itself after 20min of driving. Brand new FPR although I haven't actually put a gauge on it. I'm going to continue driving it and see if the problem continues to clear up (wouldn't that be nice).

I'm trying to think of what would cause horrible idle when cold with hesitation, and wouldn't cause a problem when warm. Dark and rainy out tonight so I'm not pulling the plugs just yet, but I will do it sometime this week. I still have my suspicions about the EGR valve aybe sometime being sticky. That should make it read lean, but maybe when it misfires, the raw fuel gets dumped and burned one the next ignition event (in the exhaust manifold). Possible?

I really need to get a proper datalogging software so I can datalog when it's running weird.

[fixkick]

hello
so hot suddenly goes good. odd that.

I still have my suspicions about the EGR valve maybe sometime being sticky. (get it cleaned, and closed then defeat if (temporary) by pulling hose to it and using golf Tee to plug hose)
now its out of the picture, (could ping, on a real hot day so, use gentle right foot)
The EGR loves to stick as you come to a stop sign. (its commanded closed then( and ported vacuum too) , and rpm will be as low (egr stuck open) as 400 rpm and engine shakes and ISC can not correct this.


Misfire (hot)

yes, each intake stroke pulls in clean fresh 20% air slug and some fuel , the if it fails to fire, (misfire) the oxygen rich air slug, goes to the exhaust, and 02 sensor (hot engine) sees that slug of air. (02 sensor reads lean and ECU closed loop matches that with rich fuel) or +25% (guessing %)
-25% (means low oxygen was detected) the -25 means ecu removed 25% fuel, due to low oxy readings.
keep in mind, 1 misfire, can send 20% oxy rich air, (and fuel) to the exhaust port.
The O2 RAILS to 0vdc, even with 1% oxy seen. so is 20x leaner in truth. and and ecu goes richer, to cure, that +40%. (1/2 time the wrong way,OBD1/2 sickness i call it.)
---------------------------------------------------------------------------------
now cold , that is different, totally , no 02.
open loop cold start works from tables.
phases...
(IAC+ISC +bleed screw = air supply) and then the ecu assumes these air paths all work , to crank start with this air supply, if not , bad deal. flooding.
The ECT is now the major player, here, if read wrong say too low, it goes rich and misfires. (the ECT allows colds starts even in Alaska)
The MAF comes on line as it starts. (and is not very accurate at idle. kinda crude there. at low idle speeds, very good at 1500 rpm)
what is your cold start RPM, 700, 1200 1500s? ,usually its around 1500, and winds down to 800 hot and then regulates (ISC servo action) at 800 solid.
ECT:
The ECT needs to read near 3000 ohms (50F) on cool day to start engine. or 6000 ohms, 32f freezing morning , then go to 300 ohm hot. this is a key sensor.
http://www.fixkick.com/ECU/temp-sensors.html
check out my Exel plots too.above.

the one thing we dont know (weakness in OBD2 designs) is are all 4 cylinder working same way, all misfiring, or all 4 lean? hot. or all 4 doing same thing cold..
this is the weakness. we all face, and the ECU's bad act of adding fuel on a rich engine, during gross misfire, takes the cake on dumb ECU (measuring oxy instead of fuel is reason...)

HOT running, issues. (common)
I'd run Bosch mag wires on this engine, it has weak spark, (by today's standards) so mag wire is best. or NGK mag (pricey)
make sure spark TIMING is dead on, with timing freeze jumper set.

compression over 150PSI on all 4 at sea-level. (mine did 180psi warm)
my 2: (bench marks)
"My 1996 Geo Tracker 1.6Liter 16valve. , pulls 183-185 PSI on all 4 cylinders. (warm not fully hot. )
My 97' pulls 185 PSI min. dead cold. (a new head) later and hot it does 195 PSI. Old 100k mile engine, now with new oil rings, new crank and new head."
altitude 500ft.above.s

Leaks, on 16v MPI are all bad, unless very tiny. (even injector base cushions can leak air, causing one cylinder to go super lean,)
no induction air leaks, as they can cause maf to read too low, and under-report air flows , engine goes rich and if 02 is working, goes -25% (possible)
that huge big pipe on top , no cracks allowed. no cracked, big pipe seals there. from TB to MAF. some have accordion flex pipes that love to crack there.
This leaks cause a physical lean, stated, that the ECU Closed loop servo will go +25 or more, not -25% so is not it.



COMMON fails:
No crack? at #4 header tube (cast iron) this causes oxy leak and 0xy sensor to rail lean (0v) and trim goes rich. +40% Fuel (so is not this)
I'm listing super common failures here. for this old car. and symptoms.
FPR is new. and most are failing now. So fuel pressure i bet is ok, 36to 43psi, (at idle) and rises 6psi(about) up to WOT. (not this i bet)
bad spark at anytime will cause the 02 (hot) to read lean. and ECU to go rich. (to a large + number) on pre 96s far worse rich, it can go.

what if only 1 cylinder misfired?, same results on last line above, but may then cause all cylinders to go rich and misfire. (like lemmings) +25% or more.
(not your cause this)

high fuel pressure (probably not. with new FPR) will cause your -25% or more.(goes super rich but ecu corrects it)
Induction leaks (large) will cause +25% or more LTFT
MAF reads low all the time. (causing physically lean AFR, then (un-metered air cause lean burn ) , but closed loop the ecu is correcting it to +25%)
unmetered air is same effect at air leaks. (but is not -25% , so is not it either.)

welcome bad from road trip..
-25% means the ECU is removing 25% fuel from a gross over rich mixture. (-5% is normal because MAF is 5% naturally rich on purpose)
The MAF is designed (or ECU tuned) to be always on rich side (safe side, because lean burns valves) so the closed loop corrects this, error.
then when you go wide open throttle and he 02 closed loop shuts down, it must not go lean, every, and this is the MAF air flows, that prevent lean, WOT or just accelerating.

if it misfires, at all at idle, this sends, excess oxygen air slugs to the exhaust ports, and 02 sees that as lean , oxy lean. and goes huge Plus percent to correct it. (so is not it)
same with exhaust leaks near 02. huge oxy (air 20%) land there and huge + percent LTFT. ( so is NOT IT)
so what on earth causes -25%

too high fuel pressure tops my list
leaking injectors. (1 or more)
MAF stuck high,(but under the DTC error stuck high point, nah) very rare for MAFs to stick high say 1volt more than REAL air flow) seen 1 china clone maf do that , magic.
not clogged injectors as LTFT goes +25% to compensate.

its nice having scan tool data, no?
see whats going on with fuel trim... is a very good thing.
so you have zero DTC errors.

Yes so another day driving home from work I monitored some PIDs.

Today it started running properly much more quickly than the previous trip. Idle still started out shaky but it started running fine almost as soon as it warmed up. No DTCs present. STFT and LTFT were both a lot more normal today (0-6%).

I didn't change anything from yesterday to today. When I parked it, it was running perfectly normal. Strange beast this is. I considered a leaking injector, but that wouldn't fix itself after 20min of driving. Brand new FPR although I haven't actually put a gauge on it. I'm going to continue driving it and see if the problem continues to clear up (wouldn't that be nice).

I'm trying to think of what would cause horrible idle when cold with hesitation, and wouldn't cause a problem when warm. Dark and rainy out tonight so I'm not pulling the plugs just yet, but I will do it sometime this week. I still have my suspicions about the EGR valve maybe sometime being sticky.
That should make it read lean, but maybe when it misfires, the raw fuel gets dumped and burned one the next ignition event (in the exhaust manifold). Possible?
EGR open at idle, makes it do gross misfire and 02 will read lean. (air slugs) +20% (my theory)

I really need to get a proper datalogging software so I can datalog when it's running weird.

keep in mind a hot engine can stick a head valve.
check vacuum is about 20 "hg at idle and no bouncing vacuum allowed.

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-25% (raw causes)************************************
means 02 reads too low oxy. "0v lean, 1v rich, rules."
means 02 reads high voltage, for too rich. (means low oxy)
means ECU closed loop servo, action sucks fuel out of mix by -25% (all injectors go lean by -25% , shorter pulses)
that is not misfire.
injector leaks., yes.,
HIgh fuel pressure,yes.
maf over reporting air flows. (reads too high volts for reality) (a very rare failure mode this) yes, with me skeptical.
its all things that can cause gross rich conditions.

usually 02 sensors never stick high (Bosch says, designed to not ever do that) (seen some cracked inside)
but if the heater inside fails and leaks to the +CELL side, it will in fact stick +voltage. (crying wolf for rich, fibbing link a mad dog.) how old is your 02./?

one more 02 oddity, told by Bosch, (great white papers there )
is the carbon blanket effect (short list) (lets say FPR jammed to 55psi.)

engine goes rich, then the ECU sees, what, sees, 02 lean? due to gross misfiring (air slugs)
so the ECU adds fuel to rich misfiring engine, (silly huh?)
then the 02 sensor is covered in a carbon blanket.
the 02 sensor is now dead (for a time) and reads 0v. lean now. stuck at 0vdc.
this causes ECU to cut fuel. (closed loop actions) and this carbon burns off... then,. goes rich again.
and the cycle repeats.

[Mike8500]

SOLVED!!!

So after reading all sorts of info from your site, pondering it over in my mind for hours at night, contemplating what could cause the problem I finally got it fixed.

I decided to throw away the idea that I could solve the problem looking at it from a hot engine vs cold engine stance. It may have ran better when hot, but as longas the ECT reading was correct, there's not much else that changes with how the system runs when it's hot.

After doing some research i realized that MAF sensors interchange all the way back to 92-98 and TPS were specific to 97-98 Trackers and 96-98 Sidekicks. Well I didn't have access to a TPS other than buying one brand new. I did however, have a coworker that had a 93 4dr sidekick in his yard that I could swipe the MAF from just to eliminate it.

A couple bolts and a hose clamp and I had them swapped out. Fired up the Tracker with the "new" MAF. Ran and idled perfect. In fact, the low speed driveability has improved so much, I didn't realize how bad it had gotten. It cruises better on the highway, idles smooth as butter and I'm hoping to get some significant MPG gains.

I noticed that when it's idling now, it reads about 2.7-3.3g/s. The old sensor was reading anywhere from 3.7-4.3g/s. That's 27% difference!

Now interestingly enough, the old sensor gave out a nice smooth signal, with no jumps or spikes except when the engine was idling rough (as expected since sometimes it would almost stall.) A smooth, WRONG signal.

I'm going to continue driving it and see what kind of MPG I get on this tank. Between a proper MAF reading and a new FPR that doesn't leak through the vacuum line into the intake i'm guessing it should be quite a bit better.

All that being said, I thought the MAF was fine because I read somewhere that around 3-4g/s was fine. At that low of engine speed, even being off by 1g/s is a big difference. If it's off by 1g/s at WOT, you would never know. I think that's why it drove fine from 1/2 Throttle and up.

Thanks for all your help, dedication to this site and tireless answering of questions.

[fixkick]

congrats !
yes, it's a very hard sensor to test.
near impossible. if its not dead.
one test is the rap test, hit it gently at idle and if idle changes, it's bad.
sounds liker yours might fail that.
nice work, and such good luck finding a test subject.

Cardone does sell rebuilds... if that helps


happy trails!