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2003 chevy trailblazer_ls
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Discussion Starter #1
Hello Everyone!

I am having a nightmare with my 2003 Chevy Trailblazer. Here is the history of the current repair so I can get some advice from you FINE GENTS hopefully.

OK, so I had the fuel pump bust a sending line the other day which dumped all the gas out and noticed it in a parking lot where it finally ran outta gas just as I was about to turn it off (idling).

So I replaced the fuel pump with a new one from advanced auto (Aftermarket) and then when I started it there was a slight knocking sound coming from the vehicle. I traced the sound and it didnt really seem to be coming from motor but instead from the exhaust and there was no physical pounding vibration being put out from the knocking through the motor I could feel with my hand. Then I was getting a P0300 or random misfire...so I drove it for a few miles and it finally registered a P0306 or cylinder 6 misfire. So, I swapped the ignition coils and spark plug from cylinder 6 to cylinder 2 and drove a min and the misfire migrated to cylinder 2.

I replaced the ignition coil and spark plug on the now misfiring cylinder #2 and no more misfire! So, I figured it was just happenstance that had a ignition coil went at same time as the fuel pump.

Well...then I drove the car about 30 miles after this repair and noticed a reduction in power gradually and at same time the SES light came on now kicking out a P0172 code or SYSTEM TOO RICH (Bank 1).

Figuring the system was just catching up I reset the code and carried on, well got halfway home from family on christmas and lost almost all power on highway dropping down to about 20 mph on expressway and had to take back roads home rest of the way. Basically it didnt have enough power to maintain speed above 30mph and if u lightly touched the gas it would speed up, but if you went any more then lightly feathering the gas pedal it would bog down and loose speed.

I drove next day and seems like it is running better when cold and when it warms up it looses even more power and runs even worse.

Freeze Frame INFO Data:

Calc Load% 95.7%
ECT(c) 91
STFT B1% 0.0
LTFT B1% -11.7
MAP(kPa) 74
Eng RPM 1461
Veh Speed (km/h) 7
fuel sys CL
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Concerning Live Data Info

02S B1 S1(V) .765
STFT B1 S1(%) -19.5
O2S B1 S2(V) .785
STFT B1 S2(%) 99.2 <------ (This Seems Wrong To ME) ???

Also running LTFT numbers are regularly showing anywere from -5 to -15 or so while under load while STFT are holding steady between +5 - -5 depending on loads while runing. but LTFT seems to always go into the -15 or so anytime load is put on...NEVER to POSITIVE numbers side.

My concern is that all this is happening right after installing this new fuel pump...I dont wanna keep chasing down problems if the fuel pump has something wrong with it and seems odd that all this happens after I swaped out the fuel pump but not before...However, the vehicle did run outta gas at a stop and this might have had an effect on the systems.

Please, any advice will be hugely appreciated and I WILL CHECK this forum regularly for any questions or updates any places here.

Thanks.

Brad!
 

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2003 gmc envoy_slt
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628 Posts
I've not done much on the 4.2 but a few things I would check.

How does it do power wise? Does it pull strong or fall on it's face at full throttle?

How do the MAF readings look when you jump on the throttle at idle in neutral? Do the readings jump up a lot?

Do you have a fuel pressure gauge to confirm that your fuel pressure is correct?
 

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2003 chevy trailblazer_ls
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Discussion Starter #3
Map sensor reading jumps with the throttle depression like it should and the power falls off when I push down the accelerator. If I push down on the throttle while at speed I sputters and decelerates but lite feathering of the throttle and will pick up speed.

No I dont have a pressure tester for the gas pressure but thinking I might need to get one. Pisses me off cause just put new fuel pump in there but thats how it goes.
 

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2003 gmc envoy_slt
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What brand of pump? I've seen new pumps that can't make spec pressure.

One method of checking if you are low on fuel delivery is monitoring the O2 voltage at WOT. You MUST have. 9 volts if you are not running lean. It should change from the usual up/down swing to a steady line maxing out at. 9 volts. Graphing the voltage is the best.

B1S1 and B2S2 on a V engine.

 

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Discussion Starter #5 (Edited)
Ok...so I have a Matco MD1052 Scanner and I know it does some graphing but unsure if it does o2 graphing...I will check when I run it next...should be a few hrs and will check with WOT but if memery servs correctly it did go up to 9 volts with WOT.

Does anyone think these problems or numbers could result from a bad rear O2 sensor? I dont think so myself cause I never seen a bad O2 Sensor cause the power to fall flat on its face when u accelerate but just had to ask cause not a full mechanic...I am a Auto Body guy that does light mechanical when asked and on personal vehicles which this is my personal vehicle.

Will check and post info here when it is done.
 

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The rear O2 does not affect running. It is only there to monitor the cat's efficiency.

Rarely will a bad O2 upset the running much.

A scanner will show fuel trims and the O2 voltage will show lean or rich.
 

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Discussion Starter #7
Here are all the Scanner Graphs that I have taken...Please keep in mind I have only driven this about 10 minutes since manually resetting the computer and I have not driven it enough yet to get the P0172 code to kick off yet...I figure another 10 - 20 minutes of driving will get the code and a freeze frame to be generated....till then this is what I have.

Please offer any suggestions or thoughts you might have with this live data info added into the infomation now provided...

My concerns... Is the rear O2 Sensor bad causing the loss of power...or would it be more likely for a bad catalytic converter to be causing this, or could this possibly be an injector problem or something else??? Please, any input is helpful!!!

Thanks,







 

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2003 chevy trailblazer_ls
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9 Posts
Discussion Starter #8
ANYONE know how to interpret these Live Data Graphs??? Please let me know ur thoughts???
 

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gmc envoy_sle
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so before fuel pump went bad/replaced you had no problems? if you had none of these symptoms before would wonder if you got the right pump, too little pressure or too much not sure why all this would happen but ive had horrible luck with aftermarket fuel pumps for me usually lasting weeks or months not causing crazy symptoms but its just an idea
 
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