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2006 STS4 4.6L
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Discussion Starter #1
Driving home this evening after work, had been driving for about 10 minutes. Pulled up to a stop light, car shut off/stalled suddenly, I shifted to park and started it back up (started fine) stalled again, restarted car once again. Drove car all the way home without any other detectable issue.
In the past I have seen the rpm's dip a bit while at idle from about 600 to 450-500 or less, seeming like it is going to stall then recovering.
I'm leaning towards fuel pump (fun LoL). In the past my mechanic told me that the fuel volume was borderline (close to being less than ideal).
Anyone else experience this? No engine codes for it yet, I'll check again tomorrow.
 

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08 STS 1SG HUD ACC F55 AWD, 08 STS 1SG Platinum HUD ACC F55 RWD
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Before you start on the fuel pump, change the fuel filter. I was told by a knowledgeable mechanic that there was not one except in the fuel tank. Wrong. Follow the fuel lines from engine toward the rear fuel tank. From memory - within 6 inches of the bottom edge of the doors. Lots cheaper and easier and it MAY fix your problem. Good luck.
 

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Discussion Starter #3
Thanks, I had it changed about 1.5 years ago so it hasn't been way too long, but I suppose it's getting up there.
 

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Discussion Starter #4
Now it's stalling even while driving, definitely leaning towards fuel pump.
 

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96 FWB
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I've never heard a mechanic describe fuel in terms of volume, always pressure. Quite a bit faster, easier and cheaper is do a fuel pressure test, and check function of fuel pressure regulator.
Add some background:
How many miles on engine?
What ALL work done in the past month?
Just when cold starting the day or thoroughly warmed up. Or only when running unusually hot?
Have you already thoroughly inspected all hoses and fittings for cracks, collapse, holes (vacuum leaks)?

It could be just bad gas. Have you done any search yourself and eliminated anything from checks so far?
 

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2006 STS4 4.6L
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Discussion Starter #6
Let me correct myself, I had the mechanic tell me a long ago that the fuel volume was reading zero (during a system lean code diagnosis, ended up being the MAF). Recently he told me the fuel pressure was just below normal but still relatively acceptable. It's at about 146k miles. Had a smoke test performed recently with no detectable leaks, checking it today it appears to have no vacuum leaks.
Had the alternator replaced a few weeks ago, I changed the oil the other day.
Cleaned the throttle body a little while ago, maybe 2 months.
It stalled when thoroughly warmed up yesterday, stalled while just warming up and after fully warmed up today. Started it and let it idle a few minutes ago and has been idling normally for about 15 minutes.
Bizarre.
Getting a P0300 Random multiple misfire code.
 

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Discussion Starter #7 (Edited)
Update, when the accelerator is given basically a small "tap" to rev the engine to about 1k, a small hissing type pop is heard from the power steering pump area. Related? Unsure. Might have to let my mechanic mess with it.
Edit: Took it over there to let him look at it, I'll keep you guys posted.
 

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Discussion Starter #8
Still waiting to hear back from my mechanic. Been brainstorming about a couple issues my vehicle was experiencing on the way to his show.
While I was driving the car stalled at least 7 times on the 5 minute drive to the shop, as I was nearing his shop I got a "check oil level" message on the DIC. I changed the oil a couple days ago, and checked the level to ensure it was good, everything looks good to go. 2 things which really make me wonder; firstly, the recent replacement of the alternator, perhaps the vehicle is experiencing some electrical issues due to a bad replacement alternator, or maybe a ground or other wiring was not fastened well enough (or a short) is causing the stalling.
We all know how bad batteries and/or alternators can act on the way out.
My other thought is that the oil pressure sensor, or maybe the oil level sensor is malfunctioning. Of the two oil sensors, I would lean towards it being the pressure sensor, as I have heard about stalling due to bad oil pressure sensors, can't say the same for the level sensor.
Thoughts?
I know I should chill and let the shop sort it out, but I have seen misdiagnoses more often than I would like.
 

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[Snipped]

........
Had the alternator replaced a few weeks ago, I changed the oil the other day.
Cleaned the throttle body a little while ago, maybe 2 months.
It stalled when thoroughly warmed up yesterday, stalled while just warming up and after fully warmed up today. Started it and let it idle a few minutes ago and has been idling normally for about 15 minutes.
Bizarre.
Getting a P0300 Random multiple misfire code.
Well, what are you doing to run down all the potentials with that code? Do you have a FSM?

....as I was nearing his shop I got a "check oil level" message on the DIC. I changed the oil a couple days ago, and checked the level to ensure it was good, everything looks good to go.

2 things which really make me wonder; firstly, the recent replacement of the alternator, perhaps the vehicle is experiencing some electrical issues due to a bad replacement alternator, or maybe a ground or other wiring was not fastened well enough (or a short) is causing the stalling.
Defective electrical parts right out of the box is all-too-common nowadays. Get VOM to run all output function tests. Don't let the mech. do it. High prob. that you'll end up with a new alt.

My other thought is that the oil pressure sensor, or maybe the oil level sensor is malfunctioning. Of the two oil sensors, I would lean towards it being the pressure sensor, as I have heard about stalling due to bad oil pressure sensors, can't say the same for the level sensor.
For safety, I believe both can affect the engine operation. See if there's a VOM reading to check whether good/bad.
Thoughts?

I know I should chill and let the shop sort it out, but I have seen misdiagnoses more often than I would like.
Talk like that makes me flinch. At $125+/hr. those 'misdiagnoses' sprout big bills, not to mention lotsa parts (at full msrp retail price) that you didn't need.
Sounds like looking into what things operate open v. closed loop.
I heard enough messing around with stuff on and near the intake just wondering if the IAC and/or TPS needs a check and/or adjustment procedure.
 

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05 Stealth Gray CTS-V, 08 Light Platinum SRX V8, 05 White Diamond STS4 V8 1SG
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Ruling out a fuel supply issue should be relatively easy. You can check fuel pressure at the rail at idle and under load (depending on how long the hose is). I think spec is 60 psi but I'd have to double check. Maybe 55-60 or something.

Also, you can check fuel trims. With a good scan tool I think there are some historicals you can check, not just current. Heavy positive correction on both banks points to fuel supply issue (especially when combined with suspect pressure behavior).
 

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2006 STS4 4.6L
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Discussion Starter #12
Yeah I'm just having my mechanic diagnose the problem, I'll fix it up after he lets me know what's going on
 

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Discussion Starter #13
So, it appears that the main wiring harness (or at least part of it) was dragging on one of the driveshafts (passenger side CV I believe), a bit difficult to visualize without actually seeing the problem so maybe I can get pictures when I'm under it next. The dragging wore through to some of the wires and basically rubbed the insulation off and into the wires, causing something of a short. My mechanic said he moved the harness out of the way and fastened it so it wouldn't be rubbing again, only assuming he covered it with some tape or something but I'll check to be sure. He stated that one of the engine mounts is done for and caused enough movement that as it was driving forward the harness rubbed, whilst in reverse or park the rubbing didn't happen. I had a feeling that at least one of the engine mounts was at least worn but didn't realize it was quite as extensive. So for now it operates normally but I'll be needing to get the exposed wires cleaned up/soldered, and I'll have both engine mounts replaced with poly mounts at the same time.
 

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Geez, that's a little concerning. I'll have to inspect mine - curious exactly where it rubbed. My mounts are pretty shot....
 

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Discussion Starter #15
I honestly don't think it's due solely to the mounts, I think the issue is mostly due to an old harness clip or something which had previously held the harness in place, no longer holding it in place. I'm going to jack the car up and take a gander, soon enough.
 
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