SOLVED! P0171 Driving me insane - Totally

yyz

Original poster
Member
Feb 18, 2014
7
Guys, need some help with this as I have run out of options. 04 Envoy with a 4.2 is what I have.
Since late summer the truck has been really hard to cold start, rough idle, hesitation, loss of power. Once she warms up idle is not too bad, a bit high at times. Sometimes takes 5-10 tries to get a cold start. Also, you kind of have to leave the gas pedal alone. As soon as you hit the gas the engine will stall out during cold starts.
So far these are the part I have changed.
New SAIP solenoid, new front O2 sensor, new spark plugs, new coils, new MAP sensor, new intake manifold gaskets. I also changed the valve cover gasket since I was already halfway there.
I also cleaned the throttle body as well as swapped out to another TB just as a test.
Tested the air injection pump as well. I have good suction as well as it's blowing hard thru the pipe.
Also checked out the fuse that powers the SAIP solenoid.
Any help would be appreciated, as this is my winter truck and really want to get her back on the road.
Thanks.
 

yyz

Original poster
Member
Feb 18, 2014
7
Only the P0171. After clearing the code it will come back after the second startup.
 

xavierny25

Member
Mar 16, 2014
6,323
Staten Island, N.Y
I've got the same code a few weeks back and the engine shut off while my wife was driving. She was in traffic at the time. She was able to get it running again after throwing it into park and starting it again.
This morning the truck would not start,tried switching the fuel pump relay and no dice I thought it maybe a battery issue so I got it jumped and still nada.

I'm picking up a fuel pump tomorrow morning since everything else seem to check out. Throttle body is clean and not sticking, maf sensor is clean and no air leaks. This is where I am at with my diagnosis.
 

yyz

Original poster
Member
Feb 18, 2014
7
I changed the fuel pump a couple of years back as the lines were all corroded on the old pump. I would be surprised if that were the culprit. To change it is a huge PITA.
 

Capote

Supporting Donor
Member
Jul 14, 2014
24,227
Atlanta, GA
Try replacing the Camshaft Position Sensor, then doing a CASE Relearn. I swapped mine out after a long time of troubleshooting issues with high idle and lean problems. That solved everything.
 

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON

yyz

Original poster
Member
Feb 18, 2014
7
So this past week I replaced the fuel filter. Made no difference in startup behavior.
Last night replaced the cam sensor and the valve timing solenoid. No luck, same issues.
I will order a new fuel pressure regulator, see if that makes a difference.
 

yyz

Original poster
Member
Feb 18, 2014
7
Well, here is what went down the last couple of weeks.
To follow up after replacing the fuel filter and other cam related items without having any luck I decided to check the fuel pressure as the last resort.
I was reading 10 PSI instead of the 50 or so PSI. What a drag!
After all this, the culprit WAS the FUEL PUMP!
The fuel pump was replaced less than 2 years ago, so this was the last thing I suspected. When I dropped the tank last week, I found the old pump had fallen apart and it was in pieces inside the gas tank. Unreal.
The moral of this is that I should have tested fuel pressure a long time ago!
I'm not sure how to mark this SOLVED, but please do if you can.
Thanks for any input - again!
 

Capote

Supporting Donor
Member
Jul 14, 2014
24,227
Atlanta, GA
Well, here is what went down the last couple of weeks.
To follow up after replacing the fuel filter and other cam related items without having any luck I decided to check the fuel pressure as the last resort.
I was reading 10 PSI instead of the 50 or so PSI. What a drag!
After all this, the culprit WAS the FUEL PUMP!
The fuel pump was replaced less than 2 years ago, so this was the last thing I suspected. When I dropped the tank last week, I found the old pump had fallen apart and it was in pieces inside the gas tank. Unreal.
The moral of this is that I should have tested fuel pressure a long time ago!
I'm not sure how to mark this SOLVED, but please do if you can.
Thanks for any input - again!
Glad you got it solved brother. What brand fuel pump was it by the way? Would be good to let others know to be wary of it, when looking for a replacement themselves.
 
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yyz

Original poster
Member
Feb 18, 2014
7
Good point. The crappy one was I believe Autobest brand. Rockauto does not carry them anymore. The new one I put in is Bosch.
I had replaces two other fuel pumps in my other Envoys years ago and always used Bosch with no problems whatsoever. Since this truck was only a winter use vehicle I put in a cheapo pump and it backfired on me.
Get what you pay for was true this time.
The positive takeaway is that my kids get to keep the Blue Beast for a few more years with all these new parts installed. Haha
 
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