Kazual99

Need a little help figuring out a starting point for chasing a starting problem. The problem is the car cranks but doesn’t start. This happens randomly and can occur with the car hot, cold, first starting of the day or after several starts with minutes or hours in between running. The cranking cycle is strong and does not spin slowly.

Okay the next description is strange but it is what happens….
The engine cranks and eventually will start but it sounds like it is not getting fuel, but then gradually starts. Is reminds you an old carbureted car that you pump the gas and it finally “catches” and starts.

First thoughts point me to the crank position sensor, but the way the car starts could point to a fuel issues. One more fact, when first starting after a failed crank cycle, the car hesitates when the pedal is depressed.

1999
No CEL, no codes on the Durametric, and some days it starts right up and drives fine.

Chuck

Ahsai

Did you notice if the tach needle bounces when the no start happened? If it does not, it points to the crank position sensor. If it does, it's not conclusive.

My next guess is the fuel pump and fuel filter. You may need to check the fuel pressure when it doesn't start up. Do you hear the fuel bump priming at all when no start happened?

Also have you cleaned the idle stabilizer and throttle body?

Kazual99

The tach needle only bounces when the cranking results in starting. There are moments when the car initially cranks and almost starts, the tach will move slightly then not move until the car starts.


I recently moved and no longer have access to my tools and garage, this greatly hinders my ability to troubleshoot. I will pay attention to the fuel pump priming during the next startind cycle.....I didn't think of that...Thanks



Nope, and that needs to be done. I will do that tomorrow..

Ahsai

Sounds like a bad crank sensor to me because a healthy one will bounce noticeably until the engine starts, at which point it just shoots up to 1k+ rpm then settle back down to 900 or so.

When you turn the key to the last position before crank, you should hear a brief a ~2s fuel pump priming. If you don't, you will need to check the fuel pump relay and fuel pump itself.

Youri Ko

What if you just let it crank? Say 10-20 seconds, would it catch up and start in the end?
Mine was acting like this

DBJoe996

9/10 times for this scenario it is the CPS....crankshaft position sensor. Have to agree with Ahsai. If it is running fine otherwise, CPS.

Ahsai

Please try not to do that as it may overheat and destroy the starter.

fsixaa

I agree, CPS. I had a similar thing happen with my Infiniti G35. The sensor took a beating from a large rock or something that was thrown under the carriage. If the car was exposed to water at all it would not want to start or would take considerable amounts of cranking.

It actually shut itself down in a rainstorm while I was on the interstate doing 70mph! In my case it was the wiring that was smashed and I was actually able to save the sensor. Very similar symptoms...

speed rII

I had similar symptoms in my car. When stopped after short drive, engine needed long crank before it started. Pushing the throtle to the floor helped, so I think that plugs were wet.
I have new crank sensor, but it did not fix the problem.
I now use plugs with only one ground electrode and had no probles after that.

My coilpacks are old and cracked, and needs to be replaced. I think that this is the reason why the engine had starting broblems with stock plugs with larger gap. (more resistance to get stromg spark)

Youri Ko

So, two theories now - Crank Sensor or Plugs.
My initial thoughts were on plugs too - see my other post.
Jake Ruby once replied suggesting Camshaft Hall sensor , saying that when they fail, engine does not go into "fast start" mode - I've no idea what it means though.

Is there a way to test one of those sensor without PIWIS ? And if they "fail" - I suppose a CEL or Freeze Frame of some sort would be registered, I had none. Which leads me to spark plugs, in many cars I had, sparkplugs were always the issue.

Macster

A failing crank shaft sensor does not affect emissions so there is no OBD2 error code/freeze frame data available. There may be a Porsche proprietary error code logged but to obtain this would require PIWIS or perhaps a Durametric.

Plugs would have to be pretty bad to cause a crank but no start problem.

How many miles on the plugs? Stock plugs IIRC are good for 60K maybe longer I forgot the change interval. Keep in mind non-stock plugs may not have nearly the same service life.

No need to over analyze this I guess. If you believe plugs are at the root cause of the symptom then replace the plugs. If the coils show signs of deterioration it is best to replace them too.

If the symptom was from the plugs (and possibly coils) you'll know soon enough as of course the symptom will be gone.

If the symptom persists afterwards well, you can then replace the crankshaft position sensor unless a more likely explanation comes to mind in the meantime.

Ahsai

I'm with Macster on this one. Based on my own experience, in general marginal spark plugs should give you a lot of trouble (misfires) under load way before they could stall the car or cause a no start situation.

To check the crank position sensor and cam position sensor, ideally you want to use an oscilloscope https://rennlist.com/forums/996-foru...l#post11469612

Kazual99

Thanks Macster. The plugs and coil packs were replaced 40K ago and I used OEM replacement parts from Pelican. I'm leaning more and more towards the CPS and will have the indy replace it as well as clean the IAC and throttle body.

Chuck

Kazual99

Macster and everyone,
Aside for the CPS could it be a failing fuel pump? I’ve reached out to a local indy and the logic that I'm following/applying to this scenario is the car cranks and "catches" but fails to start because the pump has lost its prime.

The tach does move when cranking, which I misreported before.

Is it possible that pump must generate enough fuel pressure to eventually start if the pump loses its prime? Is it possible for the pump to behave in this manner? I tell you what; it sure reminds me an old car that you must pump the gas pedal to get enough fuel to start.

Thoughts?

5CHN3LL

The pump is in the tank, so it shouldn't ever need to be primed, but a failing pump can result in low fuel pressure.

How old is your fuel filter?

The ground strap issue that has been reported in various threads may also result in an occasional hard start.