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Discussion Starter #1
Hey guy all of a sudden my 07 GXP started having this weird problem where hitting decent sized bumps in the road (like the lip where a road meets a bridge, or where there's a lot of cracks in the road) my turbo will cut off. I can mash the throttle as hard as I want and get the RPMs up to 5500 and there's still no turbo.

But if I let off the accelerator completely, the turbo comes back.

This happens every single time I hit a bump. Sometimes the car backfires, just one quiet pop, sometimes it doesn't. Sometimes if it's a particularly bad road with really rough conditions it feels like the engine is about to stall, again, it all goes away when I take my foot off the accelerator and put it back on.

What's going on? Grounding issue? There's no codes for anything yet, and it's been about 140 miles since this started.
 

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Starting with the obvious...is there a "low traction" warning on the dash? Or a flashing stability control sign? They may be hard to see if it's sunny out.
 

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Discussion Starter #3
No there are no dash lights whatsoever. No lights, no dinging sounds, no flashing. But now that you mention that, on the way home today I'll run it with all that turned off and see if it makes a difference.

I should probably add that this happens when I'm just at cruising speed, ~2100 RPM so I'm not beating the hell out of it going over these bumps
 

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Discussion Starter #4
Well, I think I know what's up.
Came out of work and the car wouldn't stay running. It would crank and start then sputter and die out.

So I poured in a bottle of octane boost, topped off the tank with 3 gallons of fresh gas and let it run for ten minutes.

And what do you know, the whole way home, no problems.

I bet it's that God dang 7-11 I stopped at to get 4 gallons of gas the day before these problems because I forgot to get it when I left work. Probably got myself a nice tank of water.

We'll see what happens
 

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I go some crappy gas myself a few years ago and the car ran like crap for 3 or 4 tanks after. Hopefully that IS your issue and it straightens itself out.
 

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Are you tuned? If not, are you using premium or regular? The turbo cars require premium. My car requires pure 93 octane, or else it sputters and backfires because I'm dyno tuned to the edge. There are only 2 gas stations within 5 miles of my house that I trust, the other 10 I've gotten bad gas on more then one occasion from...and they're name brand stations like BP and MOBIL.... Believe it or not the Kroger station is one of the 2 that I trust!
 

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It seems odd to me that a fuel-related problem would occur specifically when hitting bumps. I would be looking for loose electrical connections.
 

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Discussion Starter #8
Got fed up with the problem going home yesterday so I decided to floor the hell out of it until it gave me some codes. I got
P0463 - Fuel level sensor circuit
P0089 - Fuel pressure regulator performance
P0455 - EVAP leak large

So I'm thinking the in tank fuel pump may be failing. But after beating it, parking it, clearing the codes and running it again I didn't seem to have any problems even over bumps in the road.

One other thing that came to mind when I searched the forum for those codes was my last oil change. I got a faint whiff of gasoline from the oil. The engine was brand new with only 500 miles on it at the time so I just figured it was some contaminant left over from the whole swapping process. I don't have the car with me right now but I'll check that smell again when I get home.

The car has about 154k original miles, is it reasonable to think it might be the in tank fuel pump and not immediately jump to the HPFP? Especially since it's giving me codes for everything on the in tank pump?
I don't have anything to test fuel pressures myself but that memory of the gas smell is haunting me now and I don't want to ruin this brand new engine
 

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The in-tank pump is not going to put fuel in the oil, but the HPFP will. Finding out what is in your oil is a key item, I think. It may be time for an oil analysis.
 

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Discussion Starter #10
The in-tank pump is not going to put fuel in the oil, but the HPFP will. Finding out what is in your oil is a key item, I think. It may be time for an oil analysis.
yeah I wasn't really making a connection between my current problem and the gas smell from 5 months ago until I started doing some reading here on the HPFP. I went ahead and placed the order for the in tank pump after the codes came back because it was only $200, and I got the email that it had shipped right as i was going to cancel, so I guess I'm replacing the in tank pump just for fun. My fuel level sensor has been dead for almost 2 years now anyway so it's not a *total* waste. And that evap leak is definitely somewhere in the tank because it doesn't hold pressure (no *whoosh* sound when i take the cap off) so I'm crossing my fingers it might fix that, too.

I'm also gonna go ahead and order the HPFP since it's also only $200 on ZZP and give that a go since the car is gonna be down anyway. After the two pumps, the only mechanical parts that won't be brand new are the alternator and transmission. Everything else from the intercooler to the cat are all <5,000 miles. I had set aside $600 when I changed all those specifically for fuel pump problems because really, that's all I had to worry about. Just didn't think it would be so soon

Will update in a couple days with results
 

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HPFP is extremely easy to replace. Time consuming part is removing the vent cowl.... Otherwise it's a 30 minute job.
 

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Discussion Starter #12 (Edited)
Update

Replaced in tank fuel pump, car started up beautifully! No more random misfires, no shuddering, no hesitation when accelerating. It definitely had a completely different feel to it! I put a brand new engine in it about 5000 miles ago and it finally FEELS like it's a new engine!

Got it home after a 50 mile drive and let it sit. HPFP came in yesterday so I went about doing that. Once I started wrenching on it I could clearly see oil leaking all around the old gasket for the HPFP, so that was replaced as well.

Fuel gauge, sadly, still does not work. It began to fall to E intermittently about two years ago, did that for a week then just quit but the "distance to empty" display still worked correctly. About a week after THAT, it went too. I always figured it was the level sensor/sending unit since that's what I read about. I guess it's not.

Parts list
in tank fuel pump - # 19168738
includes level sensor and gasket
https://www.rockauto.com/en/moreinfo.php?pk=1022681&cc=1433710&jsn=401

High Pressure Fuel Pump - # 12629135
https://zzperformance.com/collections/ecotec/products/direct-injection-high-pressure-fuel-pump
High Pressure Fuel Pump Gasket - # 12595951
https://zzperformance.com/products/di-mechanical-fuel-pump-gasket
 

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Discussion Starter #13
Well, that didn't last long. Went to leave 2 mornings ago and the car won't start again. Starter goes, engine starts to turn over, sputters and chugs for a few seconds then dies.
Tried again that night, same problem.
Went out the next day at 2pm, car started right up, but was backfiring like crazy when I rev it and let off the throttle
Tried again the same night, back to sputtering and cutting off.
Tried this morning, no start, but code P0089
 

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A bad EVAP solenoid can cause the sputtering, hard starting and stalling. It's located on the intake manifold. There's a DDM video on how to test it.
 

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Discussion Starter #15
A bad EVAP solenoid can cause the sputtering, hard starting and stalling.
I had just tested it three months ago when I replaced the manifold pressure sensor because I kept getting a code for evap leak, alternating between large and small, and it was tight as a tiger.
But it never hurts to check again
 

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Check the video. It's a one way valve that can leak internally even if it's tight. I've been lucky enough to have replaced 3. I got them at my local auto parts and I'm guessing the quality isn't as good as a GM part.
 

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Discussion Starter #17
Tried it again when I got home at 4:30pm and again, it starts. It seems like it's not wanting to start when the ambient temperature is below 80 degrees.

Bought the purge valve too. Replaced the old one. Started, but no different than it did before replacing it. Still a ton of backfiring when in park after giving it gas and letting my foot off. Still a slight stumble at idle. I'll wait until night and see if it starts again or if the pattern persists.
 

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I'm pretty certain it's your HPFP.
 

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Discussion Starter #19 (Edited)
HPFP was replaced 5 days ago when I replaced the in tank pump.

This slight misfire and backfiring has been an issue I've had since 500 miles after putting in a brand new engine. First 500 miles it was perfect. After that, started having trouble finding an idle rpm at a cold start, but if you shift out of park it immediately smoothed out and drove fine, just an occasional miss.

I did change the IC out somewhere around the 500 mile mark because I was in an accident before the engine swap and the IC got a pretty nice dent in it. Didn't affect the performance of the car very much so I left it that way for over a year. Once I put a new engine in I figured it was time to fix that.

There's no obvious signs of damage to the new IC, and everything is hooked tight. Unless there's some internal problem with it I would hesitate to think it's related and just coincidental with the timing. It is an OEM IC, nothing cheap and nothing performance.

Update
Tried to start the car again at 10pm and just like before, sputtered and stalled out

Got it to start on the second try and stood outside while it idled. I noticed a lot clattering I've never heard before. It actually kind of sounds like the noise a starter makes when the car is already running. Like a rapid fire sparking. That noise would coincide with an audible change (decrease) in engine RPM but no change on the dash. After about a minute of idle, the sparking sound was happening very regularly like clockwork, and the car sputtered and stalled.

Restarted it a third time. That sparking noise happened twice after the engine turned over at regular intervals. The ticking of the HPFP would speed up and slow down for the first thirty seconds before settling in to a nice lazy pace. I let it run for ten more minutes and there was no additional noise and the car continued to idle without stalling.
 

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Discussion Starter #20
Update after taking it to the mechanic.

Mechanic said same as you guys, all signs point to low pressure fuel pump not providing enough volume or HPFP intermittent failure. Recommended replacing both pumps (again) as well as barometric pressure sensor.

I asked him to check the gas for contaminants.

Test came back positive for water, a significant amount.

I guess my original guess was the correct one
 
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