Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum banner

1 - 20 of 25 Posts

·
Registered
Joined
·
12 Posts
Discussion Starter #1
Hi everyone! This is my first post here, so forgive me if this the wrong section.

I have a somewhat bizarre issue and thought I would see if anyone has any ideas. I have a 06' LS 4wd with the 4.2.

A few months back, I replaced the fuel pump as the sender unit went out, and after about a week with the new pump, the car began to not want to start until the second crank. With the pump being a Delphi, I doubted that it was the issue, but I decided to replace it with another unit anyways. Same issue. While I did the spark plugs at the same time as the fuel pump, I believe this is a fuel issue, but I don't know what else the issue could be at this point unless I just somehow managed to get two dud units in a row.

I should mention that after the car starts, it runs great. No CEL, either.

If anyone has any ideas, it is greatly appreciated!

Thanks!
 

·
Registered
2002 chevy trailblazer_lt
Joined
·
676 Posts
Is 06 a returnless type? I can't remember what year they changed. Anyway, I would look to 2 things. Firstly, do you hear the pump run for a couple of seconds when the key is first turned to run and before you turn to crank position? Second, have you thought about maybe checking the fuel pressure for possible loss of holding pressure after the initial pump prime?
 

·
Registered
Joined
·
12 Posts
Discussion Starter #3
Is 06 a returnless type? I can't remember what year they changed. Anyway, I would look to 2 things. Firstly, do you hear the pump run for a couple of seconds when the key is first turned to run and before you turn to crank position? Second, have you thought about maybe checking the fuel pressure for possible loss of holding pressure after the initial pump prime?
Thanks for the response! I believe it returnless as I was looking online earlier and saw something that said 06+ doesn't have a regulator. I tried listening for the pump awhile ago and thought I heard it but my hearing isn't the best. Will get a pressure gauge this weekend. Any specific numbers I should look out for? Thanks!
 

·
Registered
2006 Trailblazer EXT LS 4.2L
Joined
·
7 Posts
Thanks for the response! I believe it returnless as I was looking online earlier and saw something that said 06+ doesn't have a regulator. I tried listening for the pump awhile ago and thought I heard it but my hearing isn't the best. Will get a pressure gauge this weekend. Any specific numbers I should look out for? Thanks!
i had similar issue with my 06 TB 4.2i had to crank it twice after fueling, replacing the vapor purge valve by the engine block fixed my issue
 

·
Registered
Joined
·
12 Posts
Discussion Starter #5
i had similar issue with my 06 TB 4.2i had to crank it twice after fueling, replacing the vapor purge valve by the engine block fixed my issue
Interesting. Did you have a check engine light? Also, looking at the parts here I see two different ones. Do you happen to recall the part no.? Thank you!
 

·
Registered
2006 Trailblazer EXT LS 4.2L
Joined
·
7 Posts
Interesting. Did you have a check engine light? Also, looking at the parts here I see two different ones. Do you happen to recall the part no.? Thank you!
Yes engine light was on, this is the part "ACDelco 214-1680 vapor canister purge valve". I bought it off amazon for $25, i replace it couple years ago and still good
 

·
Registered
Joined
·
12 Posts
Discussion Starter #7
Yes engine light was on, this is the part "ACDelco 214-1680 vapor canister purge valve". I bought it off amazon for $25, i replace it couple years ago and still good
I will have to look into that, I am not sure that is the culprit cause I don't notice the issue to be related to filling up the tank. Thanks for the part no.
 

·
Registered
2006 Trailblazer EXT LS 4.2L
Joined
·
7 Posts
I will have to look into that, I am not sure that is the culprit cause I don't notice the issue to be related to filling up the tank. Thanks for the part no.
I never had trouble filling up the tank, my issue was i had to crank it more than normal to get it to start
 

·
Registered
2007 chevy trailblazer_ls
Joined
·
5 Posts
One thing you might want to investigate is the possibility that one (or more) injectors has a tiny leak which after on hour or perhaps overnight will drop the holding fuel pressure. That tiny leak won't show up during operation or throw a code.
As TJ Baker said, listen for the pump, or you can just turn the key to ignition and wait a few seconds before cranking as a workaround. If it starts on the first crank, there is a tiny leak somewhere.
 

·
Registered
Joined
·
12 Posts
Discussion Starter #10
One thing you might want to investigate is the possibility that one (or more) injectors has a tiny leak which after on hour or perhaps overnight will drop the holding fuel pressure. That tiny leak won't show up during operation or throw a code.
As TJ Baker said, listen for the pump, or you can just turn the key to ignition and wait a few seconds before cranking as a workaround. If it starts on the first crank, there is a tiny leak somewhere.
Thank you for the response. I got a helper to listen for the pump and I found that it indeed does not prime all the time. Even when it does prime, it seems a touch slow to start. BUT here is where it got interesting, while I was messing around with all of this, a CEL popped up! Which...is odd. I have had this issue for 2 months and drive 300 miles a week and never got one but anyways, it's a P0451. I can't find much online other than its probably the tank pressure sensor.

Do you guys think that will be the end-all solution? It seems odd to me that it is just now recognizing an issue and I wonder if it's a combination of issues and I am unsure if that senor can cause the pump, not to prime causing the slow starts.
 

·
Registered
2007 chevy trailblazer_ls
Joined
·
5 Posts
Think about the procedure this way when you turn on to ignition only - If the pump does not prime (turn on), it "should" mean the fuel lines pressure is nominal to operate the injectors. If it primes it means the fuel lines pressure was low or zero and the ECM signals the pump to turn on immediately. It takes some time - a second or two or three, for the pressure to build up to nominal. That is why there is a delay in starting the engine if you turn on to crank immediately (normal). It is waiting for the fuel pressure and will eventually start.
 

·
Registered
Joined
·
12 Posts
Discussion Starter #12
Think about the procedure this way when you turn on to ignition only - If the pump does not prime (turn on), it "should" mean the fuel lines pressure is nominal to operate the injectors. If it primes it means the fuel lines pressure was low or zero and the ECM signals the pump to turn on immediately. It takes some time - a second or two or three, for the pressure to build up to nominal. That is why there is a delay in starting the engine if you turn on to crank immediately (normal). It is waiting for the fuel pressure and will eventually start.
Put that way, I would think another bad fuel pump?
 

·
Registered
Joined
·
1 Posts
Put that way, I would think another bad fuel pump?
I interpret that to mean there is a small leak in the system. As it sits for a period of time the fuel pressure drops to near zero. The next time you turn on the key, it takes that 2, 3, seconds to get back to nominal pressure. Once it is at pressure, an immediate retry of the key won't need to prime it again. A bad/worn injector could be why it loses pressure and why its slow to start.
 

·
Registered
2004 chevy trailblazer_lt
Joined
·
628 Posts
Definitely test your fuel pressure. Be sure to leave the pressure gauge on for a few hours to see if the pressure holds or drops. If it drops, then you might have a leaky injector. Also, fuel pressure spec is 50 - 57 PSI.
 

·
Registered
2002 chevy trailblazer_lt
Joined
·
676 Posts
Be aware that the fuel tank pressure sensor has absolutely zero to do with the fuel pressure to the engine. The fuel tank pressure sensor is there for the EVAP system. This system traps the fuel vapors that would otherwise escape to the atmosphere. That sensor actually measures vacuum in the fuel tank while the PCM tests for leaks. Has nothing to do with fuel line pressure to the engine.
 

·
Registered
Joined
·
12 Posts
Discussion Starter #16
Thanks, everyone for the valuable insight. I had figured it was a pump issue since it wasn't priming every time but I will try to get a pressure gauge over the weekend. I am assuming that I need to hook up the gauge and put the car in the on position and just monitor the pressure for a few hours? Also, which port would it be? I see a green cap and a black one.
 

·
Registered
Joined
·
12 Posts
Discussion Starter #17
Be aware that the fuel tank pressure sensor has absolutely zero to do with the fuel pressure to the engine. The fuel tank pressure sensor is there for the EVAP system. This system traps the fuel vapors that would otherwise escape to the atmosphere. That sensor actually measures vacuum in the fuel tank while the PCM tests for leaks. Has nothing to do with fuel line pressure to the engine.
Thanks for the info. So I probably have two separate issues then. Any idea what else that code could be on our cars?
 

·
Registered
2004 chevy trailblazer_lt
Joined
·
628 Posts
Green cap is for EVAP system testing. Black cap is for fuel pressure gauge. I would test the fuel pressure this way:

1) Key on, Engine OFF - see what pressure is and write it down

2) Key ON Engine ON - see what pressure is and write it down

3) Key OFF Engine OFF - leave pressure gauge connected and then check it every 30 minutes for 2 hours, write down pressure reading each time
 

·
Registered
Joined
·
12 Posts
Discussion Starter #19
Green cap is for EVAP system testing. Black cap is for fuel pressure gauge. I would test the fuel pressure this way:

1) Key on, Engine OFF - see what pressure is and write it down

2) Key ON Engine ON - see what pressure is and write it down

3) Key OFF Engine OFF - leave pressure gauge connected and then check it every 30 minutes for 2 hours, write down pressure reading each time
Awesome, thanks for the steps. I will give it a shot this weekend and report the results.
 

·
Registered
2004 chevy trailblazer_lt
Joined
·
628 Posts
Good luck!
 
  • Like
Reactions: kstripe
1 - 20 of 25 Posts
Top