Man in a Garage

Porsche Puzzle Anyone?



If anyone is willing to try to solve this one I promise to share the answers. Hopefully, it’s something common we can all learn from.





This 2001 Carrera 3.4 was my first engine rebuild and a great education in the magical world of mechanics.



Here is a link to the video in question:




The problem the car is having is the slow-to-fire and slow-to-idle issues shown in the video. To give you an idea of how common the issue is, out of 30 starts at various times over a few days the car said tarted normally 20 times, was slow to start 5 times, and was slow to idle 5 times.



It rarely does it on the first start of the day, it rarely does it if previously started within the last 20 minutes.



If it has ran already and then sat for 1-3 hours, it’s more likely to have the starting problem.





So far I have tried a few things in an attempt to resolve or diagnose the issue.





What I have tried already:





1. I threw a new Crankshaft Sensor at it, no improvement.





2. I threw a new Duralast Gold 730 CCA battery at it, slight improvement, maybe.





3. Vacuum System tested with smoke, no leaks.





4. Purge valve disconnected from intake (Holes Plugged). No Improvement.





(what I’ve learned is that it can be possible for the purge valve to get stuck open causing excess gasoline vapors into the mix on startup)





5. Activated Secondary Air Blower using a Durametric, sounds like a hair dryer on high. I think that means it’s good?





6. Using a cable clamp meter I did a “Starter Current Draw Test” across the positive cable in the frunk with the Fuel Relay Removed. The result was 160 amps with the new battery.







What I have not Tried:



I have not done a voltage drop test to check the Y-Cable, does anyone know how to do that??





What I think it might be:





1. The Y-Cable that connects between the B+ junction box, Alternator, and starter seems to be a common issue due to voltage drop as a result of inner corrosion.



I feel this cable or some other grounding/electrical issue might cause the starting issue and possibly the faults.





2. Fuel Pump or Relay - Prior to install the tank was drained using the car's own pump, the rate was within spec though I have not tested the Fuel Pressure while functioning?





3. Perhaps there is no electrical gremlin and the codes are accurate, throwing a new secondary air blower and bank 1 variocam solenoid might fix it?





Other things that may not be related:





Other electrical issues that make me suspicious of some rogue grounding point are as follows.





1. The rear Engine Hatch button always works, the frunk button sometimes does nothing, if it doesn’t work, pressing the button will cause the interior lights to shut off?





2. The door locks behave strangely? When I first put the engine in and powered the car up the door lock button (Dash) would not do anything plus there was an error code in the durametric. Now, for no real reason the error code is gone and the button on the dash kinda does something (Clicks and lights)



3. The blower fan for the heat and ac does not run. the fuse is ok, the screen and dash button work but no fan.





Just for clarification, this car was non running when I purchased it. I don’t know if these problems have any history prior to the engine rebuild.



Wow! thank you for reading to the end 🙌 I appreciate any insight you can provide to solve this issue, You Rock🤘😎

JohnCA58

one question, slow cranking ? or normal cranking ?

Dr_Strangelove

Very recent thread with similar symptoms - applying gas helps the car start: https://rennlist.com/forums/996-foru...ard-start.html

I think it's time for you to start monitoring your fuel pressures.

Man in a Garage

Thank you for your help 🙌

The cranking is generally a decent speed even when it does not fire up.

here is a video that shows the good the bad and the ugly.

dsbl

Yea sounds like that other thread. Since its cranking strongly I'd not suspect the Y cable or ground strap or other major electrical things, that should give you a slow crank that isn't fast enough to start the engine.

Man in a Garage

Awesome Thank you!! That was a great threat. I rented a fuel pressure tester from Autozone this morning, I'm hoping to play with it tonight 🥳

zbomb

Y cable and starter, the other guy hasn't replaced his starter yet either and I am yet to be proven wrong that is not the problem.

DBJoe996

Starter...do it first.

Porschetech3

I'll take that bet and give 10 to 1 odds...

hardtailer

Leaking injectors I think (as I did in the other thread). I base this on the observation that A little gas (=more air into the cilinders) helps. It gets the mixture less rich just enough for the fuel that has dribbled into the intake from bad injectors to burn together with the injected fuel.

In case of a bad fpr that no longer holds pressure after engine shut-off, then the pressure is built back up during cranking but during that time the injectors (also in-spec ones) will inject too little fuel to ignite. This fuel overrichens the mixture just like the droplets from leaking Injectors do. A little gas in this latter case has the same effect as described above.

Of course it could be more than 1 thing wrong but based on the speed the engine is turned over I see no symptoms of bad starter or voltage drop due to a corroded y-cable.

Mike Murphy

+1.

ltusler

Had a similar issue, turned out to be the coolant sensor.

Porschetech3

Interesting and very plausible. Any details on the before and after test data??

Or was this a SWAG method that worked..lol

ltusler

After much troubleshooting, Jake mentioned it as a possibility.

cdk4219

Fuel pump check valve, leaking injectors, or coolant sensor come to mind. You can put to rest the leaking injectors or check valve with a simple fuel rail pressure check, turning the key on it should prime to 60psi and hold. If it drops quickly either the check valve in the pump is bad, or possibly the in tank feed line is partially ruptured. If it drops slowly a leaky injector may be the culprit, although the car may run rather rough in the first few seconds of operation with too much fuel in the cylinders affected.

Coolant temp sensors are relatively inexpensive and probably not a bad idea to replace if that is a concern. When I have a temp sensor failure it seems to flash a red light in the temp gauge and starting is difficult when warm.