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8th Gen Antagonist
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Discussion Starter · #1 ·
So this same 02 3.4 that I have been having trouble with for awhile, replaced the FPR a few times, but now it will start and run a few seconds and stumble then die, sometimes doesn't start, but just sputters. I noticed that with the key on the IAC sits there and makes a loud clicking noise, I know its the IAC because I can feel it and it stops when I unplug it. Resistance check shows 58 ohms across the bottom 2 terminals and 55 across the top 2. Manual didn't say what it should be, only that they should be close to each other.

I don't have a lot of experience with IAC valves, the guy at the parts store said he believes it can cause these symptoms, and it should not be clicking. And I believe him to be right on both counts. But, how do I know if this is the problem? I checked the fuel pump circuit, everything is good there, and it spits gas out when the key is turned on and when cranking. There are no codes, and the I/M monitors are all reset even though I did not reset the computer or disconnect the battery. Could the ECM be bad?

I would really appreciate as much help as quickly as anyone can manage, I need to get this thing fixed.
 

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8th Gen Antagonist
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Discussion Starter · #2 ·
Crap, well I went ahead and swapped the IAC with one from another running vehicle. The clicking went away, but the symptoms remain. And the other vehicle starts and runs with the IAC from the problem car. Symptoms do not change if I unplug the MAF, if anything it just dies quicker.
 

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8th Gen Antagonist
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Discussion Starter · #4 ·
Not sure what you mean by datastream, I can read live data, but that only does so much good when the car won't stay running.
 

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no but you can red things like FP, voltage to sensors etc and see if anything looks out of ordinary
MOST of the engine sensors are 5v, cam pos sens demands fuel, maybe there?
pcm could be bad too tho
Check the gound wire coming off the coil pack make sure it isnt broken/loose
Does it run for a few secs then die out? u swapped ecm, check to see if the bcm/pcm VINs still match each other (should be able to pull that info w/ a MAC Mentor or similar)
IAC shouldnt click, but IDK about it cutting off the engine, the newer EVAPS click, LOUD for some reason though
Massive Vac leak will kill the engine like this
forgot to hook brake booster line up on this vid :p
 

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8th Gen Antagonist
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Discussion Starter · #6 ·
Well for the short time I can get it to run, I don't show anything out of the norm on load values or fuel trim, FT is actually 0. I have not touched the ECM, I did swap the BCM awhile back, but swapped it back and it wasn't an issue after that.

I can tell it's fuel and not ignition though, it doesn't start every time, but when it does it will run for as short of time as yours in the video, to as long as 30 seconds or so. It will idle very low, and stalls with any throttle. I still need to get a fuel pressure gauge, I'm thinking maybe the pump is weak.
 

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Possible causes:
Weak fuel pump
MAF
IAC

At the moment I would look more at the fuel pressure since it will stall even at part throttle. IAC is more of a concern when the engine is at idle. Not sure how to rule out the MAF sensor in this case.
 

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8th Gen Antagonist
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Discussion Starter · #8 ·
I could try another swap with the MAF, that'll have to wait till Tuesday which is the next time I'll have the other car at the shop. And since I already swapped the IAC with a known good one, I guess that will tell me whether or not it's the pump, which is out of warranty by like 7 months yay!
 

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8th Gen Antagonist
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Discussion Starter · #10 ·
Yeah, I did when I replaced one on one of our 8th gens though. GM bastard engineers...
 

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8th Gen Antagonist
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Discussion Starter · #12 ·
I'd probably miss the first time, or cut through one of the lines.
 

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I just reread this thread and you said that you had tried to unplug the MAF sensor and the car just died quicker. With that I would rule out the PCM and MAF for now since you put the car into open loop by unplugging the MAF, that should have caused the engine to run. IMO you are down to the fuel pump being the issue. Really need to get a fuel pressure gage and see what its output is.
 

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8th Gen Antagonist
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Discussion Starter · #14 ·
Kinda what I was thinking, I'll have to get a gauge Monday or Tuesday and get this figured out.
 

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8th Gen Antagonist
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Discussion Starter · #15 ·
Ok, fuel pressure is 50 key on engine off, maintains 50 at idle, jumps to 59-60 if I touch the throttle, but still stalls out. So it's not the pump, not the FPR, not the IAC, wtf?
 

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8th Gen Antagonist
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Discussion Starter · #16 ·
Just now I tried swapping the MAF, no change. Checked for vacuum leaks, none. It starts pretty consistently now, and seems to idle ok, but still doesn't respond to throttle, and will die on it's own after a bit regardless.
 

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8th Gen Antagonist
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Discussion Starter · #18 ·

 

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8th Gen Antagonist
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Discussion Starter · #20 ·
Not sure atm, haven't found the appropriate wires to check. However, as I was checking the cam position sensor input voltage, it was just a little over 8v, it's supposed to be 12. All of a sudden it spiked to almost 10v, and I heard a couple clicks from the fuse block. I checked battery voltage, it was down to 10v, so I threw the charger on for a minute. I then started the car, and it's running fine. Took the charger off, checked alternator output, it's fine. Car has been running for 20 minutes now absolutely perfect, idle is good, throttle response is good, even with A/C on. Now I'm really confused, I certainly can't send the car back into service, what the hell is going on?
 
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