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Discussion Starter #1
Just purchased a 2008 Trailblazer LT w/ the 4.2L i6. It has 113,000 miles on it.

About 1 week after purchasing the TB we began to have an issue with the car stalling while driving. The problem became worse and worse until it would stall everytime it would run.

Took the TB into a trusted local shop. They got a code for an issue with the throttle body so we had it replaced.

2 days later the issue came back. They dropped the fuel tank after receiving codes for a fuel tank pressure sensor, an evap canister and an evap solenoid. We replaced those.

This seemed to fix the problem as far as it stalling while driving, but now another issue has come up.

Now the TB will start up from a cold engine fine, but after running for an hour or two if you shut the TB off it won't start back up.

After this problem came up it dropped a code for a crankshaft sensor. We replaced it. Still didn't solve the issue.

We took it back to the shop and they have noticed that after the car is shut off that the fuel pressure will drop to almost nothing & sometimes 0.

We then replaced the fuel pump. Still no luck. It continues to have an issue starting after the engine is shut off. Still having the fuel pressure drop to nothing.

Our local shop vows to get it running and they have been going above & beyond to get it running, but our level of frustration is at a breaking point.

Could it be the fuel pressure regulator? Or does it have to do with the ignition modulator? Or could it be a fuel injector leak? I'm really hoping we can get an idea of what is going on.

Thanks in advance for any help!
Derek
 

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First, your repair shop has "ZERO" diagnostic capabilities!!!!!!!! Can't even get close to them being qualified in repairing any driveability issues.
You haven't given any diagnostic format whatsoever.

Going to the repair shop multiple times tells me they don't function 3 dimensionally in the diagnostic process. Professionals don't replace
Throttle Bodies (TB's), they diagnose the systems within the throttle body. Throwing multiple parts at a EVAP problem reaffirms they are way less than diagnostic capacity.

All the parts replaced in the fuel / EVAP system prove to me they we guessing.
No mention of fuel pressure readings, fuel samples or even hooking up a scan tool to "graphing" sensor data. etc.

Since "THEY" can't figure it out the problem(s) effectively, some of here will walk you through the "proper" diagnostic procedure.

First, hook up a fuel pressure gauge. key up the ignition, … but do not crank the motor.

Did the fuel pressure reach 55 to 62 pounds in 2 seconds or less? Did the fuel pressure drop off super quick???
Fuel pressure regulator is in the fuel pump / gas level sending unit. 2005+ Trailblazers used a pulse-width modulated fuel pump to regulate fuel pressure. It doesn't have a fuel rail mounted press regulator with a return to the tank.

Ask your repair shop to identify what kind of fuel pressure regulator / fuel pump you have. If they can't repeat that above underline designation, get the hell out of that shop!!!

If and when this fuel pump / regulator has to be changed, use only a "factory OEM Delco" unit along with a fuel filter change to avoid future driveability problems.

Second, road test the vehicle and "induce" the vehicle's driveability problems while "graphing" the sensor data. This shop hat to determine is it a fuel issue or an electrical issue at this point.
 

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Discussion Starter #3
They found a burnt wire running from the fuel pump relay to the PCM... seems to have fixed it so far. We got the car back yesterday afternoon. We'll see
 
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