2002 Trailblazer stalling - stumped on why

evoblazer

Original poster
Member
Dec 7, 2011
32
hey guys..

so after a lengthy battle my trail blazer still stalls after high way speeds and comign to a stop.
it also surges at highway speeds... so say going 120km/h constant it will slow down to 100km/h then surge back up

I have done the following:

New CPAS/Crank sensor/cam sensor
Case relearn
check fuel pressure - 55psi
ran live diagnositics with a Mac scan tool while driving and stalling
TB cleaned
Maf Cleaned

i really have no other ideas what can be causing it.

There are no codes which makes it even more difficult to find!!!
 

mika

Member
Dec 6, 2011
82
Do you have any aftermarket remote starter or antitheft devises installed? May not be related but I had a aftermarket antitheft device on one of my vehicles, when it malfuction I had the same symptoms as you are describing, it's worth a shot to check it out.
 

RayVoy

Member
Nov 20, 2011
939
You got 55 psi of fuel, but, at idle, maybe not at 70mph.

Sounds like a fuel starvation problem, or plugs failing, or not sufficient air getting to engine.

I'm betting on fuel, change the fuel filter.

And, check the air filter while your at it.
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
jham said:
just throwing this out there what about your tps
There are two sensors (potentiometers) in the TPS, and the same in the APP. A fault in any of those four sensors or the wiring would both throw a code and light up the REP light, and the limp-home behavior would start.
 

Chickenhawk

Member
Dec 6, 2011
782
Old school diagnostics - back in the days they used the seat of their pants instead seating a plug into a socket - says that misses at high RPMs are usually spark related; misses at low RPMs are usually fuel related.

I would still be suspicious of that fuel pump or the fuel pump wiring. Fuel pumps do not exhibit early signs of failure at high demand levels, they usually exhibit early signs of failure at low demand levels such as steady highway cruising.

While that seems the opposite of what one would think, old school diagnosticians would argue it is perfectly logical because fuel pumps have bearings and as they start to wear, they run okay when you push them hard (for a while) but those worn bearings will slow the pump at low flow levels, firstly only occasionally, then more and more until one day it gets hard to start after you get a tankful of gas.

Good luck and keep us informed.
 

evoblazer

Original poster
Member
Dec 7, 2011
32
nope no dice.

changed fuel pump and filter.
reads fine and stalls out stiil.

the light does pop but jsut before stall looks like an rpm thing? or maybe cruise control?
 

evoblazer

Original poster
Member
Dec 7, 2011
32
change my cat too and still stalls out..
water pump is leaking a bit.. could that stall out?
 

RayVoy

Member
Nov 20, 2011
939
Hmmmm, may be time to spend $75, or $100, to have it properly diagnosed
 

evoblazer

Original poster
Member
Dec 7, 2011
32
Joe D 04 said:
How does your voltage gauge look during these surges?

voltages are fine before surges and during.
it keeps stalling at highway speeds.

also i get a tick noise now where the crank case is.. so i am dreading timing chain but i would suspect this to be at all gears not just when vvt is activated.
 

evoblazer

Original poster
Member
Dec 7, 2011
32
its gotta be the VVT...
today i had time to do this..
gun it from a stop or going with the pedal all the way down to kick in VVT.

from there it would be able to exhibit the same symptoms of rough idle and stalling.

and thats not reaching 120km/hour constant cruising.

could it still be gummed up? or do you think the chain is stretched? what are these symptoms?

what about the phazer going bad?
 

RayVoy

Member
Nov 20, 2011
939
I doubt if the timing chain is stretched; but, who knows. You've thrown a piss pot full of money at this problem, with no fix in sight.

Ya know, sometimes we just need to seek professional help -------

RayVoy said:
may be time to spend $75, or $100, to have it properly diagnosed
 

CaptainXL

Member
Dec 4, 2011
2,445
evoblazer said:
hey guys..

so after a lengthy battle my trail blazer still stalls after high way speeds and comign to a stop.

Aren't those the two instances when the purge valve for the evap canister activates?

I would also check your fuel pressure regulator and see if it's leaking. You are gonna want to take some STFT and LTFT readings as well with the scan tool in the vehicle while driving. Sounds like you might have enough cash for a good scan tool.
 

evoblazer

Original poster
Member
Dec 7, 2011
32
well i ran a live scan with a launch scan tool.
then coil 5 went bad lol.. and thats the new coil put in about 3 months ago... so gonna get my money back on that.

so i changed the coil and off i went to scan again.

I can make her stall out at anytime now by gunning her hard so the tool shows no issues for purge or evap ony that vvt is activated and it wont go back.

that leads me to beleive the duty cycles show that its getting stuck somehow.

i am gonna run the car with 1 L of ATF and gun the shit outta her to activate VVT constantly to see if i can free up the phaser.

if not its coming apart.

CaptainXL said:
Aren't those the two instances when the purge valve for the evap canister activates?

I would also check your fuel pressure regulator and see if it's leaking. You are gonna want to take some STFT and LTFT readings as well with the scan tool in the vehicle while driving. Sounds like you might have enough cash for a good scan tool.
 

evoblazer

Original poster
Member
Dec 7, 2011
32
got my hands on the latest snap on tool..

did a live scan> NO CEL (but scan tool shows P0130)

idle

TPS 5%
TPS voltage greater than 4V
RPM 0 ( WTH)
MAF not working
o2 both not registring
OPEN loop mode

When holding throttle all the way down the most i get with TPS is 40%...

i dont even know how this car is running.. best part no CEL

So tried a CKP relearn. - fuel cut off is between 4-5k rpm

would not fuel cut off

then finally rpm started to register

Dunno thinking ECU or TPS or MAF or electrical somewhere looks like i will back probe the shit outta everything.
 

CaptainXL

Member
Dec 4, 2011
2,445
evoblazer said:
got my hands on the latest snap on tool..

did a live scan> NO CEL (but scan tool shows P0130)

idle

TPS 5%
TPS voltage greater than 4V
RPM 0 ( WTH)
MAF not working
o2 both not registring
OPEN loop mode

When holding throttle all the way down the most i get with TPS is 40%...

i dont even know how this car is running.. best part no CEL

So tried a CKP relearn. - fuel cut off is between 4-5k rpm

would not fuel cut off

then finally rpm started to register

Dunno thinking ECU or TPS or MAF or electrical somewhere looks like i will back probe the shit outta everything.

That's f'd up man...

Just an observation. For all the money your spending on high end scan tools and such don't you think it would be a better idea to cut your losses and get a newer/better working SUV? Or is this some type of reverse engineering exercise for a diagnostics class in school? I might be way off here but just pointing out what seems to be the case.
 

evoblazer

Original poster
Member
Dec 7, 2011
32
I am reverse engineering it.. back probing all sensors to see if there is a faulty sensor not throwing a DTC.

As for the boat load of money? what money?

I can borrow tools all day from anyone to do this stuff as i have alot of hook ups on it.

Plus all parts i have bought have been at cost.. i maybe dumped 400 into it..

Cat was the blunt of it at 250 for the replacement pipe.

I am gonna borrow the scan tool all weekend and run a diagnostics to check each sensor to ensure its reading right. so i will compare each voltage to each reading.

My guess is that the scan tool needed to be configed for the correct bus as there is no way RPM reads zero lol... it reads off crank sensor. if tach works - sensor works

Plus having shopkey and alldata to my disposal helps too.
 

evoblazer

Original poster
Member
Dec 7, 2011
32
so after configuring the tool this is what i get.

IAT fine
IAC fine
TPS fine
TPS voltage fine
Fuel pressure fine
EVAP fine and solenoid i can purge 10% to 100% all day
Cam phaser i can activate from 10 to 100% all day and back
Cam solenoid as well can be activated
A/F 14.5
ECU diagnostics fine
02 post cat fine fluctuates only 200mv

now... 02 pre cat flutates from 100mv to 900mv.. that thing is screwed but i dont see how that could cause it to stall.

i moved the phaers to 100% duty on at idle it does not stall.. but doesnt run perfect.. but cannot stall out

I am gonna change the 02 and see whats up tomorrow.

i also checked MAF and thats fine too lol

I love these tools.. and i have it all week!
 

christo829

Member
Dec 7, 2011
509
Fairfax, Virginia
Rapid fluctuations of the pre-cat O2 sensor are good, as well as the lack of fluctuations post-cat.
If the pre-cat O2 readings are slow or stable, then there's a problem with that upstream sensor.
I need to find the post or the manual sheet that lists the appropriate range, though. Got it on
the computer someplace.....

In theory it *could* cause stalling due to the PCM adjusting the mixture incorrectly to compensate
for incorrect readings, but you'd probably notice other driveability symptoms as well.

You can command the cam phaser and solenoid but can you see if they are reacting properly
to the cam sensor readings? I'm wondering if it's not so much a non-functional component
but one that's responding incorrectly to a sensor or one that's getting the wrong information
from a sensor.

Good Luck!

Chris
 

evoblazer

Original poster
Member
Dec 7, 2011
32
yes fluctuation on precat is fine but not that high a of mV range and taht fast.

it also finally started to throw P0130 codes all day lol.

as for the cam to crank i can graph.. but i cannot get it to read cam to camphaser.

christo829 said:
Rapid fluctuations of the pre-cat O2 sensor are good, as well as the lack of fluctuations post-cat.
If the pre-cat O2 readings are slow or stable, then there's a problem with that upstream sensor.
I need to find the post or the manual sheet that lists the appropriate range, though. Got it on
the computer someplace.....

In theory it *could* cause stalling due to the PCM adjusting the mixture incorrectly to compensate
for incorrect readings, but you'd probably notice other driveability symptoms as well.

You can command the cam phaser and solenoid but can you see if they are reacting properly
to the cam sensor readings? I'm wondering if it's not so much a non-functional component
but one that's responding incorrectly to a sensor or one that's getting the wrong information
from a sensor.

Good Luck!

Chris
 

christo829

Member
Dec 7, 2011
509
Fairfax, Virginia
evoblazer said:
yes fluctuation on precat is fine but not that high a of mV range and taht fast.

it also finally started to throw P0130 codes all day lol.

as for the cam to crank i can graph.. but i cannot get it to read cam to camphaser.

Actually, 100mv to 900mv is normal for zirconia type sensors (OXYGEN SENSORS),
but I don't have my manual handy to see if that matches the suggested readings for our trucks. The fluctuations should
be about 2-3 times per second.

The P0130 sure sounds like it's gone, though. Any idea whether that's the original sensor or replacement?
Some members have had problems with non-OEM sensors, but that seemed to be mainly heater element codes
with Bosch O2 sensors.

Sounds like you're not going to be bothered by replacing it, regardless, so it'll be interesting to see if it solves
the problem or not!

Cheers-

Chris
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
christo829 said:
Actually, 100mv to 900mv is normal for zirconia type sensors (OXYGEN SENSORS),
but I don't have my manual handy to see if that matches the suggested readings for our trucks. The fluctuations should
be about 2-3 times per second.
That's exactly what I see on live data. The fluctuations mean that the PCM is working well in closed-loop mode, and succeeding in varying the mixture slightly above and below its target.
 

evoblazer

Original poster
Member
Dec 7, 2011
32
currently it fluctuates way more then 2-3 times per second. it goes from 900 to 100 mV constantly as if it was shorting. i get way more than 6 a second
the roadie said:
That's exactly what I see on live data. The fluctuations mean that the PCM is working well in closed-loop mode, and succeeding in varying the mixture slightly above and below its target.
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
evoblazer said:
currently it fluctuates way more then 2-3 times per second. it goes from 900 to 100 mV constantly as if it was shorting. i get way more than 6 a second
Are you looking with eyeballs on that data fluctuation, or a datalogged frame data list with time stamps? Or a pseudo oscilloscope display? I don't see the mixture control loop capable of being faster than 3 Hz. But if it's wiggling at all between those numbers, I bet the sensor is OK.
 

evoblazer

Original poster
Member
Dec 7, 2011
32
a data logged frame data list with time stamp.
also throwing p0130 dtc with pending p0130 lol so its done.. gonna change it today.
the roadie said:
Are you looking with eyeballs on that data fluctuation, or a datalogged frame data list with time stamps? Or a pseudo oscilloscope display? I don't see the mixture control loop capable of being faster than 3 Hz. But if it's wiggling at all between those numbers, I bet the sensor is OK.
 

Flyersguy

Member
Nov 21, 2011
28
buy a new tranny and your problem will go away. This issue has been brought up many many times, by many different people (including myself) nobody not even the dealerships or other mechanics i took it to knew what was going on. the only thing they could tell me was to get the tranny looked at. so i did. and i no longer have the stalling out problem i had.
 

evoblazer

Original poster
Member
Dec 7, 2011
32
and this is why you are not a mechanic... lol
Flyersguy said:
buy a new tranny and your problem will go away. This issue has been brought up many many times, by many different people (including myself) nobody not even the dealerships or other mechanics i took it to knew what was going on. the only thing they could tell me was to get the tranny looked at. so i did. and i no longer have the stalling out problem i had.

i fixed my car by replacing the wiring on the o2 sensor and running an AC DELCO o2 sensor.. amazing what some real engineering can do once i got my hands on a live scan tool with gm diagnostics.

The only reason dealerships will tell you what they think it is is because most dealers hire idiots as mechanics.. i know this as i work in the auto industry as an engineer. you need the R&D engineers and mechanics to do real work.

Anyways the fix is 02 wiring to the PCM and a new sensor. The wiring was faulty inside the insulation as there was fluctuations in the readings that were too fast per the type of sensor.

its all good now and she runs like a dream.
 

Flyersguy

Member
Nov 21, 2011
28
evoblazer said:
and this is why you are not a mechanic... lol


i fixed my car by replacing the wiring on the o2 sensor and running an AC DELCO o2 sensor.. amazing what some real engineering can do once i got my hands on a live scan tool with gm diagnostics.

The only reason dealerships will tell you what they think it is is because most dealers hire idiots as mechanics.. i know this as i work in the auto industry as an engineer. you need the R&D engineers and mechanics to do real work.

Anyways the fix is 02 wiring to the PCM and a new sensor. The wiring was faulty inside the insulation as there was fluctuations in the readings that were too fast per the type of sensor.

its all good now and she runs like a dream.

nor have i ever claimed to be. maybe you shouldnt be one either. I did replace to o2. did it work. NOPE! i know of several people that tried the same thing on the old dite and it didnt work for them either. a few people did say it seemed to change for a little once the o2 was changed but it went back to doing the same thing. :raspberry:
 

Gevans17

Member
Jan 8, 2012
63
evoblazer said:
hey guys..

so after a lengthy battle my trail blazer still stalls after high way speeds and comign to a stop.
it also surges at highway speeds... so say going 120km/h constant it will slow down to 100km/h then surge back up

I have done the following:

New CPAS/Crank sensor/cam sensor
Case relearn
check fuel pressure - 55psi
ran live diagnositics with a Mac scan tool while driving and stalling
TB cleaned
Maf Cleaned

i really have no other ideas what can be causing it.

There are no codes which makes it even more difficult to find!!!


Why not try a bottle of Techron fuel injector cleaner and a good tank of gas? Worked for me.
 

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