EVVRJB

Have what I believe to be a ground problem but my mechanic cannot locate the spec ground causing issues.

Occasionally the int lights do not come on when I open the door or they are very dim & the elect seat motor will run slower than norm. Both issues go away if I immediately start the car - lights will go to full brightness and seat will move at normal spd. On the rare occasion, starting is difficult.

Some issues show up during actual driving, for example, the defrost fan will vary speeds from normal to much slower as I drive and headights will dim, sometimes in conjunction w/ switching on defroster sometimes not. Also, engine will "stumble" or hesitate - this typ occurs during very wet/damp periods or heavy rain.

Any thoughts on which grounds I should check? Other possible causes besides faulty ground??

All responses are greatly appreciated!!

Thanks

grmnxtc

Faulty alternator??? Suspect battery??? (internal cell fault)

Intermittent alternator would lead to battery not charging properly (low on volts = slow crank, seat slow, dim lights....)
Could cause dropouts during driving (especially if the regulator in the alternator is dropping out and effectively shorting out the battery!).

Is your mechanic a good one? That sounds like a no-brainer alternator/regulator issue to me. That or the battery has an internal cell fault.

kkim

what year is your car... has the wiring harness been updated?

KASH '95 993

Sounds like a faulty alternator (assuming that you checked the connections to the battery terminals)...

JasonAndreas

Does the stumble/hesitation only happen when its wet out?

EVVRJB

Tahnks for all the feedback. My mech is the best "local" mechanic for Porshe and has always treated me well and done good work. This issues seems to have him stumped though which is why I came here.

To answer some of your questions:

Yes, hesitation/stumbling seems to occur only while driving during heavy rain and/or over very wet roadways where there is a great deal of water on the road surface. It is a 1995 model and the wiring harness has been updated. Mech has "checked all connections & grounds" and they were "fine" at that time. SInce problem comes & goes sporadically though, it has been tough to nail down. What is approx cost to replace alt?

Thanks to all for your feedback. I would really love to get rid of this gremlin!

User 4221

If it were a ground problem then the issue would be present no matter if the car were running or not.

Without knowing the voltage levels and conditions, it's a little hard to diagnose.

chris walrod

Try cleaning the ground connection from the chassis to the lower starter bolt. Sometimes when this heavy guage ground wire (or cable) is tightened up, it swings or winds the cable connection clockwise when the barrel nut is tightened. At this time, the cable is somewhat preloaded and with engine movements, vibration etc., this connection can loosen up.

A good friend of mine found this nut to be VERY loose when he dropped his engine/trans for a LWF change. Just a thought..

JasonAndreas

Was your O2 sensor ever replaced with an aftermarket, i.e. non OE sensor? The factory sensors for the 993 are plunge-proof and the regular Bosch O2 sensor for the 993 is not.