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Troubleshooting Mileage and hot start surge, on 3.8L V6

 
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Quasi-Traction
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Joined: 24 Oct 2005
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Location: stumptown

1986 Chevrolet Camaro Berlinetta

PostPosted: Sun Dec 14, 2014 12:35 pm    Post subject: Troubleshooting Mileage and hot start surge, on 3.8L V6 Reply with quote

recently my Daily has been giving me a weird condition when starting the motor after a lot of stop and Go traffic. After starting, the idle will feel kind of rough and serge between about 700-800rpm and 1000rpm and feel like its misfiring a bit, then after about a minute, idles smoothly. Mileage has gone down a bit too.

Did plugs/wires and coil packs back in August. Checked a couple times for a loose plug wire, no problems. No SES light. Plugs looked ok.

I read that the inline fuel filter is supposed to be changed aprox every 30K miles, and I think the last time I did it was when the fuel pump failed, at 94K and it has 132K on it now. Should I replace or check other places first to find what the cause of this is?

Aaron, Brandon? do you guys know the fuel pressure I should be seeing with key on, and FP primed on the check valve on the fuel rail? I have the gauge to check it. A quick google search didn't bring up what the spec should be. Motor is a 01 series II Buick 3.8L

Anything else I should be checking out? Thanks, crew.
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aaron_sK
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Joined: 23 Jan 2006
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1987 Chevrolet Camaro IROC-Z

PostPosted: Sun Dec 14, 2014 3:25 pm    Post subject: Reply with quote

KOEO 53-59psi
KOER 3-10psi drop

I'd guess fuel injector leaking down, which would be pretty easy to test for with your pressure gauge.

Also check the regulator. The diaphragm can get weepy and bypass fuel into the vacuum line. I doubt that is the issue since it clears up quickly, but it's a common issue and easy to check.
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Twilightoptics
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1987 Chevrolet Camaro IROC-Z

PostPosted: Sun Dec 14, 2014 5:02 pm    Post subject: Reply with quote

Sticky IAC maybe.
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aaron_sK
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Joined: 23 Jan 2006
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Location: Back in beautiful Tacompton

1987 Chevrolet Camaro IROC-Z

PostPosted: Sun Dec 14, 2014 5:30 pm    Post subject: Reply with quote

It's been awhile since I have one of the drive-by-wire intakes, but I don't think they have an IAC.
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Twilightoptics
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1987 Chevrolet Camaro IROC-Z

PostPosted: Sun Dec 14, 2014 5:56 pm    Post subject: Reply with quote

'01 was DBW? Gross.
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Quasi-Traction
"I have petals"


Joined: 24 Oct 2005
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Location: stumptown

1986 Chevrolet Camaro Berlinetta

PostPosted: Sun Dec 14, 2014 7:24 pm    Post subject: Reply with quote

yeah, its Drive By wire, and no IAC. FP seems to be within spec when checked on the rail, primed and "key off". Maybe poor spray pattern? AFAIK they're the factory injectors.

Check resistance on the injectors? check the terminal w/ "Key on" power to each one?

Aaron, where's the regulator you're talking about?

I'm still wondering if I shouldn't just do fuel filter, but that's a bitch and fuel is a precious commodity Laughing
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aaron_sK
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1987 Chevrolet Camaro IROC-Z

PostPosted: Sun Dec 14, 2014 8:54 pm    Post subject: Reply with quote

Regulator is on the passenger side of the rail towards the back. Probably buried under the cowl in that chassis. A quick check is to pull the vacuum line and smell for fuel. If you have a MityVac you can use that to test it.

A quick and dirty check for injector leakdown is to do the KOEO test and then check the gauge after a few minutes.

FWIW I doubt it is the filter.
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Twilightoptics
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PostPosted: Sun Dec 14, 2014 8:56 pm    Post subject: Reply with quote

Not a legit check. Pump will bleed down. Also most regulators will bleed down too.
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Twilightoptics
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1987 Chevrolet Camaro IROC-Z

PostPosted: Sun Dec 14, 2014 9:09 pm    Post subject: Reply with quote

Similar issue I had fixed with fresh plugs. They "looked" ok too. It's my opinion that with cheaper plugs, if you pull them out, put new ones in.
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Quasi-Traction
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1986 Chevrolet Camaro Berlinetta

PostPosted: Mon Dec 15, 2014 4:58 pm    Post subject: Reply with quote

So Consensus is to leave the filter as is, R & R the plugs, and see if the condition improves or goes away?

I'll have to save checking the regulator for next weekend. Its dark when I leave for work and Dark when I get home and they won't let me work on my car @ my storage unit.
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Twilightoptics
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PostPosted: Mon Dec 15, 2014 5:26 pm    Post subject: Reply with quote

I don't see the filter being an issue with low flow operation but okay under load.
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aaron_sK
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PostPosted: Mon Dec 15, 2014 5:47 pm    Post subject: Reply with quote

Pull the plugs hot if you can and smell them for gas.
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