924Board.org

Maybe924 · Joined: 14 Aug 2007 Posts: 412 Location: New London, CT

Hello my 924 bretheren,
Over the past few months I have been sorting various running issues plaguing my 931.

1. Tracked down and fixed vacuum leak causing erratic performance, boost bleed off, hesitation during no boost/boost transition and poor idle.
Solution: Replaced lower charge tube (she was leaking between this and the intercooler.)

2. Intermittent misfiring under load and an occasional backfire.
Solution: Replaced distributor, rotor, airfilter, new spark plugs and wires.
(carbon buildup on both rotor and dizzy, hole in one of the spark plug wires, plugs and filter just because.)

3. Severe hesistation under load, no power above 2000 rpm and a lean running condition.
Solution: Replaced fuel pump. (Pump stopped making any noise, it use to sing a bit. I was surprised the car ran at all, it idled just fine even with the dead pump.)

I'm batting 3 for 3 as far as diagnosis goes but I've got one more thing to sort before she'll be running perfect.

The car hard starts both cold or hot. Essentially the car needs to turn over 3 or 4 times before it catches. Even if I start it and immediately shut it down, then start it again... it always takes 3-4 turns. It used to start quicker in 1 turn usually. I've ruled out spark as an issue and low compression seems unlikely since the car runs very well besides this.

With the help of the search button the mostly likely culprits are:

1. Fuel Accumulator
2. WUR
3. Pressure Control Valve

I'm leaning towards the accumulator but its a pricey guess especially after the recent install of the new fuel pump.

Any thoughts?
_________________
1981 931 GT (CGT Intercooled)
1985 911 Targa Carrera (Sold)

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

Mine did the same before/after the addition of the intercooler. It used to start with a "bump" of the starter, now you have to crank it for 2-3 secs hot or cold. Could be due to intake restriction created between throtle body and afm, don't know.
_________________
Toofah King Bad

WeiBe (1987 924S 2.5t) - 931 S3

Buwani 931 · Joined: 31 May 2004 Posts: 308 Location: Napa California

The accumulator is easy to check. Take the little screw out the bottom, run pump, look for leakage. A bad accumulator would effect hot starting much more than cold, does not sound like your problem.
Timing correct?

Shawn
_________________
1980 931
That's thirty minutes away. I'll be there in ten.

Paul · Posted: Mon Aug 11, 2008 9:35 am Post subject:

When the underhood temperature is more than 95 degrees, the thermotime switch does not activate the cold start valve. This is often the cause of delayed starting in the summer as cranking has to occur long enough to move the plate in the metering unit. Adding an I/C adds length and volume to the intake tract, so yes an I/C can make it worse.
_________________
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.

Maybe924 · Joined: 14 Aug 2007 Posts: 412 Location: New London, CT

I very much appreciate the replies.

The confusing part about this is its the same with both cold and hot starts. No difference... 4 turns before she fires. The only time it'll turn quicker is if I immediately restart after shutdown. Even then its still 2 turns. She used to start in 1 turn, this was even after I installed the CGT intercooler. The hardstarting problem is a recent thing. In fact, I stalled it really badly one day, foot was firm on the brake and I let out the clutch thinking it was in neutral, the car shuttered badly and stalled. Ever since that incident I've had a hard start problem. That was the defining moment.

I'll give the accumulator the test and go from there. So I loosen the screw after its be running? Or do I loosen the screw then start it?
_________________
1981 931 GT (CGT Intercooled)
1985 911 Targa Carrera (Sold)

Smoothie · Posted: Mon Aug 11, 2008 10:31 am Post subject:

Loosen the screw at any time. There's a rubber bladder inside the accumulator - if it's torn fuel will drip out when you loosen the screw. That'd indicate it's time for a new accumulator.

You could also try turning on just the ignition a few times before activating the starter. This'll prime the fuel system. See if it starts quicker after doing this..
_________________
"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

Maybe924 · Joined: 14 Aug 2007 Posts: 412 Location: New London, CT

Update:
I checked the accumulator this evening. No gas leaked out of the screw hole, so looks like its still good. Also, checked the lines to fuel pump and accumulator, all had no leaks.

A curious thing is that the fuel pump does not run when the key is in the on position and the car is not started. I thought it used to run for a few seconds to pressurize the system???

It does however run when the car is started.

Could this point to a voltage issue? Maybe a bad ground somewhere?
_________________
1981 931 GT (CGT Intercooled)
1985 911 Targa Carrera (Sold)

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

If you haven't tested your pressures, you might want to do that. You may also want to look at your primary pressure regulator. . .failure there can bleed pressure out of the system making starting take longer.
_________________
Toofah King Bad

WeiBe (1987 924S 2.5t) - 931 S3

Smoothie · Posted: Tue Aug 12, 2008 11:58 am Post subject:

Buwani 931 · Joined: 31 May 2004 Posts: 308 Location: Napa California

Maybe924 · Joined: 14 Aug 2007 Posts: 412 Location: New London, CT

The fuel pump relay is new, just got it a couple of weeks ago. It was in fact the cause of the no-start condition I had at the time. I feel like I may have shorted something out when I stalled the car... it was a violent stall and as I said, it has hard started ever since. I know it doesn't make a whole lotta sense but it was the defining moment for this particular problem.

I'm also feeling like its running a little bit lean. Not sure if this is possible to "feel" but I get the sense through feel and sound that its lean. It has a distinct (to the trained 931 owner's ear) sound when its running perfect and its not sounding this way. When its going perfect its kinda more throaty and deeper than it currently sounds. The best way to describe its current running condition is that its running the way it would on a 95 degree day... full power just ain't there and spinning up the rpms sounds a bit shrill.

I guess the next step is a control pressure test but I'm still baffled on the lack of pre-ignition priming.
_________________
1981 931 GT (CGT Intercooled)
1985 911 Targa Carrera (Sold)

Maybe924 · Joined: 14 Aug 2007 Posts: 412 Location: New London, CT

Update:

I jumpered the fuel pump from plug 87 to 30 and the pump ran with the ignition in the on position and the car started immediately. I guess I got a bum replacement relay.

Or... it still may be the ground
_________________
1981 931 GT (CGT Intercooled)
1985 911 Targa Carrera (Sold)

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

Maybe924 · Joined: 14 Aug 2007 Posts: 412 Location: New London, CT

ideola · Joined: 01 Oct 2004 Posts: 15550 Location: Spring Lake MI

Hmmm...on my NA, the pump always primes when the key is put to the on position (before cranking). On the 931, it never does. Maybe you had an incorrect (NA) relay in the 931 previously?

Also, NONE of my cars fire on the first turnover of the motor. They ALL take about 2-4 revolutions to fire up when cold. When warm, it's a different story, usually fire right up. Don't know what that means, but consider it anecdotal.
_________________
erstwhile owner of just about every 924 variant ever made