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1996 Chevy Blazer wants to die at a stop light

Tiny
ITALY426
  • MEMBER
  • 1996 CHEVROLET BLAZER
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 145,000 MILES
Ive been trying to diagnose this problem for a while now and havent figured it out yet. When comming to a stop light or any other time the vehicle slows down to a stop when the accelerator is pressed again the engine almost dies. It requires the accerator to be tapped then normal acceraration can resume. This does not happen every time however. It currently has a p0446 code for the evap system malfunciton, but I dont believe that has any effect on this. Ive replaced fuel pump, fule filter, wires, cap rotor, and coil. The plugs were also replace about 10,000 miles ago. Any help would be appreciated.
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Thursday, May 13th, 2010 AT 6:15 AM

6 Replies

Tiny
PEAR69
  • MECHANIC
  • 1,482 POSTS
Check for vacuum leaks. The p0446 code can mean that there is a short in the evap vent valve voltage or ground -- or that there is a problem the vacuum that the valve is supposed to create. Check for blocked evap system lines (or cracked lines). Check for blocked evap vent valve.
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Sunday, May 16th, 2010 AT 11:01 AM
Tiny
ITALY426
  • MEMBER
  • 3 POSTS
I checked for vaccum leaks. Replaced some hoses and orings on the intake. It does not seem to have any other vaccum leaks. The truck still has a problem at stop lights, but only when your sitting still for and extended amount of time and not every time either. Any thoughts?
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Wednesday, May 26th, 2010 AT 6:17 AM
Tiny
CONSAKA
  • MEMBER
  • 31 POSTS
I would have a tendency to immediatly suspect the TPS in a situation like that. If the mixtures were off say because of o2 sensors or something like that it would be consistent. But a throttle position sensor has moving parts that can get contaminated with dust when they wear out. That makes an intermitant problem. Replace that bugger and see if it doesnt solve your problem.
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Wednesday, May 26th, 2010 AT 10:11 AM
Tiny
ITALY426
  • MEMBER
  • 3 POSTS
I agree. I had already replace that a few months ago. That did fix the throttle responce from stop. It no longer jerked from a stand still to 1/4 throttle. However, it did not fix this part of the problem. I just took a look at the evap vent valve last night. The valve filter was clogged with what looks like dried salt. The truck came from PA so that seems reasonable from winter driving. The whole bottom and acctuator was filled with poweder. I had another unit and replaced the whole thing. I had noticed a lot of air flow when I fill the truck with gas. I had already replaced the cap but after driving this morning I took the cap off and there was no air flow sound. Im not sure if that may have had an effect on this. I also reset the check engine light to see if that clears the p0446 code. From what I can gather the evap vent valve lets air into the fuel system so as the fuel is used in the tank it doesnt create a vacuum. Because that wasnt letting air in I think it was harder for the fuel pump to pump fuel to the intake. Does that sound right?
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Thursday, May 27th, 2010 AT 5:56 AM
Tiny
CONSAKA
  • MEMBER
  • 31 POSTS
Well yeah I suppose enough to throw a code but that being said it would not take much vacuum to totally collapse your fuel tank.
Did it fix the runnability problem? I still think you should reset the computer by unplugging the battery for a few hours.
It would run like crap for a little bit but then should smooth out.
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Thursday, May 27th, 2010 AT 9:40 AM
Tiny
PEAR69
  • MECHANIC
  • 1,482 POSTS
Being that this truck has been through some harsh and corrosive conditions -- Follow the evap line from the fuel tank module to the evap canister. This line can rust and corrode. Closely check for rot and/or cracked fittings and hoses in the evap line from the fuel tank. MAKE SURE this line is not blocked or broken in any way. This code is a code set for a blocked or failed evap vent line.
Also, check the fuel inlet hose and vent hose for any issues. If all this fails, have the computer reflashed -- if that fails then it is probably a computer issue.

BTW -- Test things before you go changing them. The TPS signal voltage should go from (approx).4 volts and increase to around 5 volts when you open the throttle. It should do this smoothly -- If it doesn't then (and only then) change it. Just throwing parts at it will cost you in the long run. Test - Confirm Condition - Replace or Look elsewhere for problem.
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Thursday, May 27th, 2010 AT 9:27 PM

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