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Discussion Starter · #1 ·
Okay so I've read I don't know how many threads on this issue and I'm seeing if anyone has any fresh input. I have a 2009 GMC Envoy Denali with the 5.3 around 75k miles, it randomly will either not start but cranks fine, or will stall while driving. At first I thought it was a fuel pump going out bit after some reading it seemed the issue was in the fuse box under the hood. If it was having the problem I would pull the fuel pump relay out and reinstall it and 9 times out of 10 the car would start up fine. When the car was having the issue the fuel pump wasn't priming, it was dead. Once I pulled the relay and put it back in and put the key to "on" then it would prime. Finally got it to a mechanic and he said the pump has good pressure when priming, he changed the ignition switch, no fix. He said he thought it was the fuse box under the hood cause it looked like it had gotten hot enough to discolor a bit. He changed it and the people went away for 2 weeks now it's doing it again, worse now. The fuel pump relay gets hot (hotter than it seems like it should) while driving. Could it be the fuel pump pulling too many amps overheating the circuit? Any help would be great.
 

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Could it be the fuel pump pulling too many amps overheating the circuit?
Given any thoughts to measuring the current draw of the fuel pump?? My 2002 TrailBlazer 4.2 fuel pump draws about 4.2 amps as measured at the PCM B fuse (with the 0.4 amps of the PCM itself subtracted from the gross reading).
 

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Discussion Starter · #3 ·
I haven't tried that but I will look into it and see what how many amps it's pulling.
 

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Has the relay been changed? Worn contacts could make it generate heat. Have a look at the relay terminals that insert into the fuseblock. Are they all the same color or do some look like they ha e been getting too hot?
 

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Discussion Starter · #5 ·
Has the relay been changed? Worn contacts could make it generate heat. Have a look at the relay terminals that insert into the fuseblock. Are they all the same color or do some look like they ha e been getting too hot?
They're all the same color no signs of heat damage on the relays themselves. None of the relays have actually failed if you move them they work in other areas too. The new fuse box came with all new fuses and relays also.
Given any thoughts to measuring the current draw of the fuel pump?? My 2002 TrailBlazer 4.2 fuel pump draws about 4.2 amps as measured at the PCM B fuse (with the 0.4 amps of the PCM itself subtracted from the gross reading).
The fuel pump is pulling 6.96-7 amps through the fuel pump relay in the fuse box. Is this high for that fuel pump, does anyone know? I've read that depending on the type of fuel injection that pumps can pull up to 9-10 amps. After I checked it with the multimeter I got a p0320 code (fuel pump primary circuit malfunction) but I plugged the relay back in and it was running with this code.
 

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The new fuse box came with all new fuses and relays
OK, didn't know that. Thought maybe you had the same old relay in there . The replacement was a new part, yes? Not used?


The fuel pump is pulling 6.96-7 amps through the fuel pump relay in the fuse box. Is this high for that fuel pump, does anyone know?
I didn't know so I just tested my 05 Yukon with 5.3 LM7 and got a little more than you did, 7.5 amps. So you appear good there.

When the fault happens, have you ever noted if when the key is turned to run the fuel pump relay clicks but the fuel pump doesn't prime? Or does the relay remain silent? It might require a finger on the relay to confirm the click, which might require a helper even. This would serve to narrow down the location of the fault to either the control circuit or the power circuit. If the relay clicks but the pump does not run then it is the power circuit. If no click then look into the control circuit.
 

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Discussion Starter · #7 ·
OK, didn't know that. Thought maybe you had the same old relay in there . The replacement was a new part, yes? Not used?




I didn't know so I just tested my 05 Yukon with 5.3 LM7 and got a little more than you did, 7.5 amps. So you appear good there.

When the fault happens, have you ever noted if when the key is turned to run the fuel pump relay clicks but the fuel pump doesn't prime? Or does the relay remain silent? It might require a finger on the relay to confirm the click, which might require a helper even. This would serve to narrow down the location of the fault to either the control circuit or the power circuit. If the relay clicks but the pump does not run then it is the power circuit. If no click then look into the control circuit.
When it happens and the fuel pump doesn't run I have not checked to see if the relay clicks when the key is in the "on" position. I will see if I can get it to fail and check that.
 

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Discussion Starter · #8 ·
When it happens and the fuel pump doesn't run I have not checked to see if the relay clicks when the key is in the "on" position. I will see if I can get it to fail and check that.
And yes the fuse box that was installed is a brand new part, not used.
 

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Discussion Starter · #9 ·
OK, didn't know that. Thought maybe you had the same old relay in there . The replacement was a new part, yes? Not used?




I didn't know so I just tested my 05 Yukon with 5.3 LM7 and got a little more than you did, 7.5 amps. So you appear good there.

When the fault happens, have you ever noted if when the key is turned to run the fuel pump relay clicks but the fuel pump doesn't prime? Or does the relay remain silent? It might require a finger on the relay to confirm the click, which might require a helper even. This would serve to narrow down the location of the fault to either the control circuit or the power circuit. If the relay clicks but the pump does not run then it is the power circuit. If no click then look into the control circuit.
Sorry it took me a while to get back to you, kinda let the car sit for a while. So I got it to fail and the relay clicks when the pump doesn't prime. I had talked to my mechanic before I got it to fail and he said he'd try the fuel pump. So I did, I put in a Delphi premium fuel pump and it's still giving me this issue. So you say of it clicks it's the power circuit, where do I go from here?
 

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Sorry it took me a while to get back to you, kinda let the car sit for a while. So I got it to fail and the relay clicks when the pump doesn't prime. I had talked to my mechanic before I got it to fail and he said he'd try the fuel pump. So I did, I put in a Delphi premium fuel pump and it's still giving me this issue. So you say of it clicks it's the power circuit, where do I go from here?
So here is what I mean by the "power circuit". Battery 12 volts positive goes directly to the underhood fuseblock and provides power through fuse 10 to the fuel pump relay (and also a bunch of other stuff as well). When the fuel pump relay clicks closed that power should flow through the relay (diagonal terminal pins) to a gray wire that runs all the way back to the fuel pump. To complete the circuit back to the battery negative the fuel pump is grounded to the frame through splice S306 and on to ground G305 on the frame. Up at the front there are a few grounds from engine and frame to the battery negative. I will post a couple of different wiring diagrams of the same circuitry but do note that these are for an 07. I do not have 09 diagrams but other than possible wire color changes I suspect it will be the same.

So since your relay clicks that pretty much proves the control circuits of the ignition switch and wiring/operations of the PCM and BCM look to be doing what they should. That leaves this power circuitry described above. There can be a fault anywhere along that whole circuit.

Often we will jump on the most likely spot(s) for trouble. Since you have already replaced a lot the choices are narrowed. For an intermittent issue grounds are frequently suspect. One could start by servicing the ground point G305 seen as point #20 in the last picture I will post here. Don't confuse this point with the very similar G304 that is further forward on the frame. Remove the wire terminal from frame, clean everything and reassemble.

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