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PostPosted: Mon Jan 18, 2016 6:40 pm 
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Joined: Mon Mar 25, 2013 8:49 pm
Posts: 23
Location: Columbia, MD
Year and Trim: 1998 SSEI
The Original Problem was intermittent stalling while coasting to a stop. Stalling was not bad, only happened twice, but wanted to clear it up.

Prior to troubleshooting Engine and Supercharger WERE working great, no misfires.

Troubleshooting: FPR had minor fuel moisture and vacuum lines were dried and brittle. Changed the Crank shaft Sensor which appeared to be the original. Swapped out FPR and Crankshaft Sensor with ACdelco parts, and all new Vacuum lines bought from reputable eBay source.

After Changes==> The dreaded "P0300 Random - Multiple Misfire Detected." All seemed good after changing parts, until I punched it hard. At about 4500 Rpms, started getting the poppoppop misfiring, and code appeared. Car runs well at low Rpms, but misfires when pressed.

I have searched this forum, and found long dreadful threads on P0300. Hopefully I did not interject weirdness

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1992 SE, bought new in '92, (RIP)
1998 SSEi (81k miles)
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PostPosted: Mon Jan 18, 2016 8:07 pm 
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Joined: Thu May 01, 2014 9:37 pm
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Year and Trim: 1993 SLE
1998 SE
2001 SSEI
2002 SSEI
When a new problem crops up after installing new parts, it makes the new parts likely suspects.
It could also be that whatever was failing that caused the original issue was not replaced and is now getting worse.

You might not be aware that there are 3 different quality levels of ACDelco parts.
ACDelco OE grade parts are the top grade.
ACDelco Advantage is their lowest grade of parts.
Middle range is ACDelco Professional.

It's never a bad idea to begin with a basic "tune up" to ensure that there is nothing simple, easily fixed and inexpensive causing the troubles.
A basic tune up is to install a new air filter, gap and replace the spark plugs, pcv valve and replace the fuel filter.
If the spark plug wires are old, a new set of ACDelco OE wires shouldn't set you back much from RockAuto or even Amazon and might be all of or part of what's needed solve the problem..
Checking the fuel pressure can eliminate or pinpoint fuel pressure as a problem.
A brand new fuel pressure regulator can't possibly allow the fuel pump to deliver enough fuel if the fuel pump is bad and/or the fuel filter is clogged.
A fuel pressure gauge is relatively inexpensive and some parts stores even loan them out for free.
That should eliminate the fuel pressure as the culprit.
To check fuel pressures, here's what you do:

There is a valve, covered by a plastic cap on the metal fuel rail that feeds the fuel injectors, that you connect the gauge to.
1.Turn OFF the ignition.
2.Turn OFF the air conditioning system.

Wrap a shop towel around the fuel pressure connection when connecting or disconnecting the gauge in order to reduce the risk of fire.
The towel will absorb any fuel leakage that occurs.

3.Thread the fitting on the pressure gauge hose onto the fuel pressure fitting.
4.Place the bleed hose of the fuel pressure gauge into an approved gasoline container .
5.Turn ON the ignition.
6.Bleed the air out of the fuel pressure gauge into an approved gasoline container.
7.Turn OFF the ignition for 10 seconds.
8.Turn ON the ignition.


Take the following 3 readings and write them down
A) Read fuel pressure Key On /engine OFF (KOEO) should be above 50
B)Key On /engine running (KOER ) mid to upper 40's is typical running fuel pressure
C)Key on/ engine running -- disconnect vacuum hose to fuel pressure regulator and then reconnect it
When you do this there should be approximately a 10 psi increase in fuel pressure until the vacuum hose is reconnected.
If pressure does not increase, you have a faulty FPR.
There should not be any gasoline in the FPR vacuum hose.

Service manual lists normal fuel pressures as:
2001 - 2004 VIN 1 & K KOEO 53-59 psi
2001 - 2004 VIN 1 & K KOER 3-10 psi less than above

Here's a helpful video by a mechanic on troubleshooting a P0300 code https://www.youtube.com/watch?v=OyvdWeyDHf4


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PostPosted: Tue Jan 19, 2016 6:48 am 
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Joined: Mon Mar 25, 2013 8:49 pm
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Location: Columbia, MD
Year and Trim: 1998 SSEI
Thanks for the advice.

One question: does the fact that the misfiring only happens at high RPMs point toward any particular cause? The idle is smooth and firing performance under 4500 Rpms is good.

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-- Kevin
1992 SE, bought new in '92, (RIP)
1998 SSEi (81k miles)
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PostPosted: Thu Jan 21, 2016 7:55 am 
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Joined: Mon Mar 25, 2013 8:49 pm
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Location: Columbia, MD
Year and Trim: 1998 SSEI
Cased closed (for now). The misfiring gradually improved with driving. After about 30 miles on the highway, punching it a few times, the P0300 cleared, and no more misfiring. Maybe the new FPR was sticky? In any case I'll be watching it.

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1992 SE, bought new in '92, (RIP)
1998 SSEi (81k miles)
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