ScootCherHienie

So our 957, most of the time, needs two to 5 twists of the key to get it started. Each time you turn the key, the motor DOES turn over so it's not like there's a dead-spot in the starter motor. It just doesn't turn over LONG ENOUGH to start the engine. It will be a very brief rotation of the engine when it doesn't start, so it's not surprising that it doesn't start. The thing is, how do I stop the engine/ecu from stopping the starter motor before the engine is running? The engine ALWAYS starts, just not on the first twist of the key. Holding the key "twisted" (rather than releasing the key quickly) does not change the odds of the engine starting on any given twist of the key.

State of charge of the battery doesn't change the outcome... a heavily discharged battery (from running errands all day with very short drives between stops and lots of opening and closing the hatch) doesn't make the issue worse (or better).

100,000 miles, 2008 model year, "S" model, auto-trans, owned since it had 80,000 miles on it. No idea about age or condition of spark plugs, spark plug wires, and coils -- but the engine doesn't miss or shudder, ever. This has not changed in the 3 years we have owned this Cayenne.

deilenberger

I'd actually be looking at the fuel pressure. Especially if this happens more frequently when the car has been sitting for a while. A Cayenne V8 should start almost instantly. The starter motor shutoff only happens as a time out when the engine hasn't started in a reasonable time. On my '06 S - this was caused by fuel pressure leaking down when the pumps weren't running. What fixed it was replacing the entire pumping system in the tank.. in your case - since I believe your 957 is HPFI - it may involve the high-pressure-fuel-pump.

ScootCherHienie

Is there anything else that would be going on if the fuel pump is marginal? There's no loss of power at high RPMs and I've had it up to 150 mph (indicated, but relatively accurate) for 10 or 12 minutes with no issues.

I will try to keep tabs on whether it is harder to start after sitting a while... it can, indeed, sit for 2 or 3 or even 4 days without being driven.

If I was to turn the key to the right "RUN" position and leave it there for 5-10 seconds before turning it farther to engage the starter, would fuel pressure build up before turning the key to start the motor?

deilenberger

The electric pumps in the fuel tank are "primed" when you open the door the first time after it's been sitting (you can hear them..) but not on subsequent openings unless the car has sat stationary for XX minutes (I forget what XX is..) BUT - the high-pressure-fuel-pump is driven off the port side camshaft (at the rear of the engine) - and that won't bring pressure up to the injectors until the engine actually turns over. That's the more critical circuit for pressure retention - between the HPFP and injectors. A leaking injector can cause loss of pressure, or a bad HPFP (and that's not unknown, particularly on the early direct-injection motors.)

oldskewel

No disagreement with the other advice. A fuel pressure issue makes sense, whether it is a pump, internal leak, or some other issue.

I will add that the starter cutoff is exactly like that on my 2004 S. My car never fails to start right away when I want it to. But when I did the compression test for my PPI on it, I removed the fuel pump fuses and DME relay (I think, maybe that was my BMW). During the compression test, you crank the engine, and it was nice that the starter cranking would cut itself off automatically after the same amount of time. Seemed to be about 8-10 seconds, very reliably. That probably led to more consistent pressure readings for the tests.

The other general comment is that if your car is having trouble starting, you probably want to get that fixed to avoid later having to replace the starter. Starting on the second try is not a big deal. But if it gets worse and multiple tries are needed, you might be cooking your starter, causing it to fail due to the heat.

Wisconsin Joe

You say it cranks, but very briefly. Do you mean like 1/4 crank of the engine? Instead of Ruhr, ruhr, rurh. vroom; it goes ruh and that's it?

Your starter is on the way out.

I don't understand why it does this. I've never found a good explanation.

But it's a symptom of a failing starter.

Mine did it and when I did the cooling pipes, I did the starter at the same time.

It hasn't done it since.

ScootCherHienie

So when I started it this afternoon, it had been sitting at least 3 days without being started, maybe 4 days. It took 7 attempts to start.

Each failed attempt sounds like maybe 1-3 engine revolutions (so probably not even an entire 4-stroke cycle) before the engine stops cranking.

After driving 1/2 mile to Costco, the next start only took 2 tries. Another half mile drive to the grocery store and again, 2 tries to start. So it IS beginning to look like the high-pressure pump. I feel like the engine is VERY CLOSE to starting on the failed attempts and if the engine would just spin for 1 or 2 more rotations it would start every time on the first try.

I'm having a hard time blaming the starter motor since it never seems to miss a beat, but SOMETHING makes the engine stop turning too soon to start. I'm used to damaged electric motors (i.e. starter motors) developing dead spots or loss of torque/power/speed. But the starter SOUNDS stout when the engine is cranking. This is sounding more like the HPFP issue to me. Presumably a shop will be able to test for leaking injectors and for proper fuel line pressure at startup. And this has been pretty much the same situation for 3 years and 20,000 miles. It hasn't gotten worse or better in that time.

Petza914

When you open the driver's door, do you hear the fuel pump prime as Don wrote? You can only test this once as multiple openings within 10 or 15 minutes won't cause it to reprime a second time so do the test in a quiet place and listen carefully.

JAGMAN1

As mentioned, if it cranks only for a split second and stops it is probably your starter failing. If it cranks normally and takes a while to start it is something else (probably fuel related)

ScootCherHienie

I forgot to listen for the fuel pumps when I opened the door, will look into that. All I've noticed so far is the CD changer cycling through to see if there are any discs inserted.

I didn't mention before, this car has spent it's whole life between San Francisco and LA (first owner was in the central valley closer to LA than SF, where it is a bit hotter than here in summer but about the same in winter. We are 25 miles east of San Francisco. The garage is between 40 and 100 degrees inside depending on outside temperature and sun.

How long the engine cranks before giving up is random. Sometimes it is a brief/interrupted crank with the engine making no more than 1 or 2 revolutions before stopping...so maybe 3/4 to 1 second. Other times it will crank 3 or 4 revolutions and ALMOST start. I get those conditions in random sequence... it could be a long one, then 2 short one, or 2 short ones and a longer one... doesn't seem to be anything consistent. It WILL start with 1 turn at times. After a rest stop on the freeway, for example.... stop for gas or restroom, get back in and it almost always starts on 1 turn (as I think about the history of this, I remember more of the car's behavior over time). My wife uses the car too, but less often than I do. So she sees things that change over time perhaps a little better than I do because slow changes can go unnoticed. She thinks the requirement for more key turns to start has gotten worse over time, where it would take at most 2-3 key turns early after we got the 08-S. Now we are as high as the 7 turns required the other day. So while the frequency if needing 1 turn to start the car hasn't gotten worse, the number of key turns to get a start has increased very slowly. 2-3 turns didn't bug me much, but now that it is up to 6 to 7 turns... that's getting annoying.

If it is the high pressure fuel pump, and it is mounted at the back of the cylinder head on the passemger side, it must be very close to the firewall? If it does end up needing replacement, how difficult is replacing that pump?

If it is the starter motor, I'll probably take it to the shop (not dealer).

Wisconsin Joe

If it's making a complete revolution of the motor (not very brief cranks - 1/2 second or so) or more than one, then I'm less inclined to diagnose it as the starter.

What is the cranking speed like? Has it slowed down any? That goes along with the 'brief crank and stop' that indicates a failing starter.

ScootCherHienie

Drove it again today after sitting for for 3 days. 2 twists to start, 8 miles on the freeway, 2 twists to start after parking for 10 minutes. Stopped for gas after 8 freeway miles. 1 turn to start after filling with 22 gallons. Not much of a pattern developing.

J'sWorld

The ecu controls the relay and the relay provides power to the starter. Either the ecu is stopping the start signal tithe relay or the relay is playing up. Doesn' t sound like an ability to crank, cranking speed, ability to run, or running issue to me.

oldskewel

Above, I said: "But when I did the compression test for my PPI on it, I removed the fuel pump fuses and DME relay (I think, maybe that was my BMW). During the compression test, you crank the engine, and it was nice that the starter cranking would cut itself off automatically after the same amount of time. Seemed to be about 8-10 seconds, very reliably."

Based on my own 2004 S, which was and is working with no problems, the starter would crank for a full 10 seconds (or whatever exactly it is) every single time. That's what it did on probably 2-3 dozen "starts" during the compression testing (I did some multiple tests to confirm the numbers, making sure it was a good test).

If it is randomly cutting out before that, it is not normal, and it probably points to the things J mentions. Doing tests that bypass anything that might be wrong with the ECU and/or relay will help isolate the problem. E.g., jumper the relay, power the relay independent from the ECU.

For now, I would forget about actually starting the engine, and try to figure out only why you are not getting full 10-second cranks. I'd pull the fuel pump fuses, etc. to simplify things. Hook up a battery charger to the jump ports in the engine bay to remove that variable.

iamjpad

I had an issue with mine like 2 year ago, I thought it was the starter going out, I had already had HPFP replacement.
I even bought the damn starter to be replaced.
I get to my local indie, we crank it like multiple i.e 3-5 times to start.
He walks of and comes back with a jump starter and hooks up to the car.
Car started every time multiple times.
Check the voltmeter on your car what it is reading. It has to be at least marginally above 12 otherwise no dice.
The issue came back again 4 months ago. I just changed the battery myself and carried on.
This is the most battery sensitive car I've ever driven.