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DLC360 · Joined: 18 Sep 2012 Posts: 76 Location: Parma Hts Ohio

1987 924S with 146000 miles. I have been chasing a sputtering / stumble issue and I need a little help.

Under acceleration the car will stumble, like its not getting fuel, around 3000 to 4000 RPM. If I got full throttle, this doesn't happen. Also when driving on the highway, again at 3000 to 4000 RPM, it will start to tumble, again like its not getting enough fuel.

I have already changed, New strainer at the tank, new fuel pump, new fuel filter, cleaned flow tested and installed new O rings on the injectors and cleaned and adjusted the air flow meter on the air box. The only parts I have not changed are the fuel dampener or the fuel pressure regulator. I have read that a bad regulator may cause this problem. Is there a way to check the fuel pressure regulator under driving conditions?? The car idles and drives fine, as long as I keep it under 3000rpm or at full throttle.

jason c · Joined: 13 Jan 2014 Posts: 1018 Location: Nwi

You can hook up a fuel pressure tester and either mount the gauge in the cockpit or on the windshield using the wiper to hold it down to test while driving. You can restrict the return line or pinch it shut (with pinch pliers) to raise the fuel pressure or deadhead the pump, respectively, for the test.

If it runs well under full throttle, its likely that the fpr is not the problem. I'd look at the ignition system (plugs, wires, rotor & cap) and the tps (for a dead spot) next.

DLC360 · Joined: 18 Sep 2012 Posts: 76 Location: Parma Hts Ohio

THANKS, I did forget to include that I did change the plugs (NGK standard) wires, cap, rotor and coil as well.

Its really stumped me. If I roll into the throttle, it stumbles between 3k and 4k. If I jump on it, it goes past 3k - 4k with no problem. Then while cruising at 3200 / 3500 rpm it will run and then start to stumble like its not getting fuel.

When I changed the fuel filter and dumped out the old fuel, it was black. The fuel pump, filter and strainer were all the original equipment. The air flow meter had 2 very deep groves so I bent the tab to move the pick up off the groves, I also cleaned all the contacts as shown in the Clarks garage write up. Every time I change something, it gets a little better, but it still has the stumble.

!tom · Posted: Sat Jul 12, 2014 1:39 pm Post subject:

Sounds like fuel filter.

Is the new one clogged?

Is the new one installed backwards?
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78 924 NA
5-lug

DLC360 · Joined: 18 Sep 2012 Posts: 76 Location: Parma Hts Ohio

Paul · Posted: Sun Jul 13, 2014 10:07 am Post subject:

If the damper and regulator are also original parts, they are over due for replacement.
_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy.

Rasta Monsta · Joined: 12 Jul 2006 Posts: 11733 Location: PacNW

You need to have your AFM rebuilt.
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Toofah King Bad

WeiBe (1987 924S 2.5t) - 931 S3

DLC360 · Joined: 18 Sep 2012 Posts: 76 Location: Parma Hts Ohio

Rasta Monsta · Joined: 12 Jul 2006 Posts: 11733 Location: PacNW

More to the rebuild process than that but OK
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Toofah King Bad

WeiBe (1987 924S 2.5t) - 931 S3

Paul · Posted: Tue Jul 15, 2014 2:25 am Post subject:

Have you checked the cap and rotor?
_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy.

DLC360 · Joined: 18 Sep 2012 Posts: 76 Location: Parma Hts Ohio

Rasta Monsta · Joined: 12 Jul 2006 Posts: 11733 Location: PacNW

DLC360 · Joined: 18 Sep 2012 Posts: 76 Location: Parma Hts Ohio

ThomasJoseph315 · Guest

EGR valve sticking?

DLC360 · Joined: 18 Sep 2012 Posts: 76 Location: Parma Hts Ohio