Hard Start After Sitting (Cold Start)

[R996]

My 99 996 for the last couple of months has been starting hard when it's cold or I haven't driven it in a week. Once it's warmed up, it starts fine. I did see on a post on here about a fuel pump going bad. I have just replaced my battery and my starter was replaced last year, along with the wire that runs from the starter to alternator, just so everyone knows those issues have been fixed for the warm starts I have had before.  The car runs great once it's running, no rough idle or anything. Any ideas would help.

Edited September 14, 2019 by R996

[dwtaylorpdx]

Most common fails on electric pumps.... In no particular order. (Based on general cars not just porsche... )
Fuel Pump - Basically they wear out.

Fuel Pump relay - Same,, sometimes they can get sticky from age and with enough attempts they will work but its a warning.

Check valve in Fuel pump. - Still have to replace the pump to fix problem, but I have gotten them to work by removing the pump and soaking the internals down with seafoam ,, they varnish up with age and seafoam will desolve it.. Its a fussy job ,, good for a winter weekend and a good beer..

 

If you have a scanner hooked up (Durametric or PST ) You  might catch a code if you dont keep trying just try once and stop..

Weak sensor like CPS/TPS/IAT etc.. can cause this symptom..

If Equipped,, It can also be the e-throttle needs to re-sync,, just start cold, turn the ignition on and let sit for a few minutes, you should here the throttle cycle..

If its a mechanical version the TPS can cause a slow start ..

 

Cheers!

[hardtailer]

It sounds more like the fuel pressure regulator to me than fuel pump or relais.

Apart from controlling the pressure it also keeps the fuel rail under pressure to avoid fuel vapour forming in the rail when the car is parked up with a warm/hot engine.

In your scenario the pressure in the rail is not maintained but instead bleeds away through the FPR into the return line back to the tank.

Next time before a cold start run the fuel pump by bridging/shorting terminal 30 and 87 of the fuel pump relais. As soon as the sound of the running pump remains the same, start the car.

If it starts normally then it's the FPR.

Another test for this would be to clamp the fuel return hose shut next time you park the car for the period of time that would lead to difficult starting. After that time has passed, remove the clamp and start the car. If it starts normally then it's the FPR.

 

Another reason could be leaking injectors that bleed off the fuel into the cilinder

Edited November 4, 2019 by hardtailer
added hint regarding injectors