Engine backfires, turbo cuts off when hitting bumps - Page 2 - Pontiac Solstice Forum
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post #16 of 23 (permalink) Old 06-14-2019, 08:00 AM
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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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post #17 of 23 (permalink) Old 06-14-2019, 03:44 PM Thread Starter
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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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post #18 of 23 (permalink) Old 06-14-2019, 03:57 PM
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I'm pretty certain it's your HPFP.

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post #19 of 23 (permalink) Old 06-14-2019, 04:32 PM Thread Starter
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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.

Last edited by Zanepaul; 06-14-2019 at 09:16 PM.
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post #20 of 23 (permalink) Old 06-25-2019, 08:45 AM Thread Starter
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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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post #21 of 23 (permalink) Old 07-18-2019, 05:23 PM Thread Starter
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Last update. It wasn't the gas. Or the fuel pumps.

It was a damaged pigtail on the fuel injector harness paired with a failed fuel rail pressure sensor.

Official diagnosis was pigtail had been damaged (i.e. Pulled out by the wires) previously and degraded overtime (years) to the point of failure.

Fuel pressure sensor failed due to constant cycling of rich/lean commands over time.

Everything is perfect now. Even the slight stumble I was getting at idle is gone, which is something I've seen mentioned a lot as being diagnosed as bad injectors only to reappear again after replacement. Might be worth checking the harness if anyone else has that issue.

Repair cost at a pricey (but flawless) service center was $1100, haggle down to $632. $300 for parts, $300 for labor
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post #22 of 23 (permalink) Old 07-18-2019, 07:22 PM
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Glad you found it, and were able to work a deal.

John
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post #23 of 23 (permalink) Old 07-20-2019, 10:10 AM
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Just for future reference, your HPFP is not the same as your in-tank fuel pump.... Your HPFP sits up on the motor and pressurizes the fuel to, at times, 1500psi. It is also about the only item that will put raw fuel in your oil...usually.

____________________________________________

Solo Street Race exhaust
Fujita CAI
ASAP T2 stripes and badging
Windrestrictor V2 lighted in white
Windrestrictor lighted door sills lighted in white
DDM Works IC Piping
Undercar LEDs in white to match Windrestrictor

ZZPerformance dyno tuned - 286HP, 317ft/lbs of torque at 23psi of boost.
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