No Power After Fuel Pump Replacement - Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum



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Go Back   Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum > 2002 - 2009 TrailBlazer/Envoy Tech > 02-09 Vortec 4.2L I-6 Engine and Drivetrain > OEM Issues

OEM Issues Original Equipment Repairs and/or Problems

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  #1  
Old 05-14-2017, 04:02 PM
jneub60 jneub60 is offline
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2004 Chevy TrailBlazer LS
Steel Gray Metallic 4.2L I6 4X4
Join Date: Dec 2016
Location: Knoxville, Tennessee
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No Power After Fuel Pump Replacement

I have a 2004 TB 4X4 I6 with 196,000 miles. I have had it for about 5 months and have no information on previous work or maintenance. I pulled up to a stop sign and the engine died. It would restart and immediately die. So I had it towed home and after a search through the forums determined it was probably the fuel pump. I pulled the tank and replaced the pump and reinstalled everything. Now, the truck will not climb a hill. I live in east Tennessee, a very hilly area. The truck runs fine on flat areas but doesn't have the power to go up a moderate hill. The truck just bogs down and sounds like it's choking.

At first I thought the transmission was slipping badly but the more I thought about it and the more I read, it sounded more like the TB needed cleaning. So I pulled the TB and it was bad dirty and I cleaned it but it made no difference when I reinstalled. I then suspected a clogged CAT so I pulled the O2 sensor to see if it helped and it did not.

I am running out of ideas of things to try. I can't figure out why it ran fine before the fuel pump went out and then after the repair it runs this bad. That is why I started to discount the transmission but now I am 2nd guessing that. The only thing left I can think of to check is the fuel pressure. Maybe the new pump isn't working properly? That would explain why the problem didn't show up until after the pump replacement. It idles ok, it just doesn't seem to have much power.

I have had CEL codes that I checked. Mostly a 303 indicating a miss in #3 but nothing is showing right now. Any ideas what to check next? Or how can I determine if it's the transmission or something in the engine? Thanks for any thoughts.

Jim
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  #2  
Old 05-14-2017, 04:12 PM
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AWD V8 AWD V8 is offline
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So you didn't confirm that fuel pressure was your problem in the beginning?

So it could just be the same issue has gotten worse.

I'd check out the cat, possibly clogged. You could do this first if you don't have a fuel pressure gauge.

Unscrew the O2 sensor before the cat. Leave it connected, just unscrew it and tie it up out of the way. Drive the truck now, it will be noisy. If the power has returned the cat is clogged. If you still don't have power then you need to check the fuel pressure.

To reinstall the O2 sensor just wind the sensor backwards about 3 turns before you screw it in, that way the harness won't get wound up.
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Old 05-14-2017, 05:17 PM
jneub60 jneub60 is offline
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Thanks for the idea but as I posted, I have already tried removing the O2 sensor. The reason I didn't test the fuel pressure before removing the fuel tank and pump was because the pump made no noise so I knew it wasn't functioning. I checked the electrical connection to the pump and got voltage when I should have. But thanks again.
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Old 05-15-2017, 01:44 AM
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AWD V8 AWD V8 is offline
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Well I'd check the fuel pressure to be able to eliminate that as a possibility. I only trust Bosch, AC Delco & Delphie pumps. All others are possible poor quality. I seen new pumps that were worse than the old pumps.

Do you have a scanner that can read live data?
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Old 05-16-2017, 11:36 AM
jneub60 jneub60 is offline
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Thank you for your reply and ideas. I will check the fuel pressure Friday and post my findings. And yes, I do have a scanner capable of reading live data.
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Old 05-16-2017, 12:22 PM
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Quote:
Originally Posted by jneub60 View Post
And yes, I do have a scanner capable of reading live data.
One test you can do to see if the engine is running lean,

Graphing Oxygen Sensor Bank1Sensor1
At WOT you MUST be seeing .9 volts or the engine is starving for fuel. This could indicate a weak fuel pump.

You should see the voltage go up and stay there while you are WOT
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Old 05-17-2017, 11:03 AM
jneub60 jneub60 is offline
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That is very helpful information. I will let you know what I find tomorrow or Friday when I get a chance to get back under it. Thank you.
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Old 05-18-2017, 09:44 PM
jneub60 jneub60 is offline
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2004 Chevy TrailBlazer LS
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Location: Knoxville, Tennessee
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Just as an update, I checked the fuel pressure this evening and it was around 15 in the "on" position, then off, back on and it rose to over 30 and then the 3rd time it was a solid 50 without starting the engine. Then I started the engine and the needle stayed around 59 in all throttle positions. I will check the oxygen sensor per your directions tomorrow or Saturday and report back.
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