Hard start when warm Tach all over the range
 

New to this forum. I have a 1989 930 29.5K miles. All was wonderful until the warm weather hit here in northern California. Starts and runs as it should when cold. When I try to restart when warm the car may or may not start. If it starts on first crank all is well. If it requires more than two cranks it may take up to 6 or 7 short cranks to start. When it does start the tach will swing from one extreme to the other and may or may not calm down after a minute or two. Fuel check valves were replaced at 28K during 30K checkup as was fuel filter.

I'm not an expert, but have read enough posts on erradic tach action to think it's all electrical and usually related to bad ground and/or a problem with the alternator/voltage regulator. But it does also sound like hot engine vapor lock or loss of fuel reserve due to a faulty fuel accumultor. If it wasn't for the tach as you've described, I would be looking for fuel related issues only.

A few things to look at: the ground strap from the frame to the transmission (crawl under the car), as well as the ground connection from the battery to the frame. Make sure they're clean and tight. And, while under the car, look at all the wire connections to the starter for cleanliness/tightness. Finally, put a voltmeter on your battery when the car is running to see what voltage it is charging at. Should be at least 13.5 I think to show that the regulator is working properly.

You'll have other folks chime in here shortly, I'm certain.

I'm just waiting for the barrage of "show us some pics" posts :D

Thanks for the pointers, pictures to follow shortly. Measured the voltage at the battery when running @ 2500RPM, 14.55 volts, rock solid, with and without headlight and AirCon load. Been under the car, connections at starter were tight but removed, cleaned, and re-tightened. Could not locate a ground strap, at least not in the same location as the one on my 87 930, possibly a new hiding place?? Problem of hard start and bouncing tach when hot still exists. Any other thoughts?

Hmmm.....CDI, or whatever ignition source you're using? Sounds like it may be getting heat soaked and failing sporadically. In instances when she fails to start up when hot, how's your spark looking? Constant or erratic? Pop the coil wire, hang on and have your closest friend and paramedic crank the engine. If it doesn't rythmically bounce you off the ceiling of your garage, then it's suspect.

Do a search and you'll probably find info on how to trouble shoot and/or test it. An inexpensive (relative to a new or rebuild Porsche CDI) would be to convert to MSD6AL. Mine performs like a champ.

When the tach is swinging all over the place, is the engine also running like crap...or just the tach bouncing for no apparent reason? Just trying to sort out whether you've got a fuel or electrical problem. A bad fuel accumulator, for example, will result in hard start but things should settle down to normal once she gets running.

When the tach bounces engine is running fine, if the tach stays at zero for more than a few seconds engine dies within 5 seconds and may or may not restart. Have never seen this problem with my 87 930.

Strange, sounds almost time delay related or fuel starvation, regardless of what the tach is doing. One more stretch here, and one of my least favorite topics: Could it be related to the ignition delay cutoff relay (I presume the '89 has one just as does my '87)? It should shut the fuel pumps off a few seconds before shutting power off to the ignition when turning off the key. Might somehow be related. $55 fixes it.

Or, how about the infamous overboost relay (yellow, in my case). Notorious for fuel pump issues. $150 for a replacement. Unfortunately there isn't any way to test these relays, but you can bypass the overboost by shorting across pins 87 and 87A in the socket (try that next time she won't start; at least you'll know the fuel pumps are running anyway). Read the following for some more insight if you're not up to speed on these relays:
http://forums.pelicanparts.com/911-930-turbo-super-charging-forum/470196-my-turn-barrel-stranded.html
http://forums.pelicanparts.com/911-930-turbo-super-charging-forum/470389-relay-id-engine-compartment.html

You need to do some diagnostics next time this happens. Can you force the fuel pumps to run by pulling the connector at the back of the fuel distributor? If yes, then focus on ignition.

Nothing like having spare parts, side by side. Pulled the yellow relay out of the 87 and put it in the 89, off for a test drive.

Def. no expert, but thought I'd share my starting 'trick'.

My '87 likely needs an accumulator, I ran into the same thing after I got it a couple years ago where warm / hot starts were a PITA.

Now, I simply mash the accelerator to the floor then turn the key. As soon as it catches lift foot. Sometimes I only need to mash the pedal during the very first second of turnover, and it catches great. It's worked for me 100% since I started doing it, FWIW. Accumulator can wait 8-).

But your swinging tach is odd. Good luck.


ps. PICS! 8-)

Soooo.....you made it home ok? Is she still being difficult?

Made it home via CSAA flat bed, not the ignition delay or overboost relays. Got my work cut out for me this long weekend.

Damn, this is getting frustrating if not expensive. The only consolation would be that if your car now refuses to run at all, at least you may eventually find the culprit. Nothing frustrates me more than intermittent problems; sometimes it's best that whatever is failing has finally failed completely.

Gotta love it, started on first crank this morning, run over Hwy 9 to coast and back with out a hiccup.

Man, you've got the attitude of a saint!!! Take off on a Sunday (or any day) drive, come back on a trailer...sometimes. I would be going bannanas by now. Have you been able to diagnose/narrow down if this is fuel or ignition related yet?

Looks like both or common cause, so a non 930 porsche buddy from Monterey pointed me to the DME relay. OK, I look under the drivers seat where it is in the 87 and it is not there. The DME controller, and 2 factory alarm units are there but no DME relay!! ANYONE have a clue where it could be hiding?

There is no DME on CIS 930's. Normally aspirated 911'...yes. But not the 930. DME is for electronic fuel injection.
What's under the seat is the control unit for the emissions, the Lambda freqency valve/O2 sensor, stuff like that.

Fair enough, so then the question is what is the mystery relay part number 911-618-154-00 under the 87 drivers seat connected to the large controller and the same controller under the 89 drivers seat has no relay next to it but the wires go into the channel on the drivers side of the car.

On my 87, I've removed all that electrical dead weight from under the drivers seat. Car runs like a champ!

Ditched all the extra stuff in the engine compartment as well.

Looking more and more like common cause, had a friend ride navigator this morning on drive over hwy 9. We stopped just to test the restart issue. Sure enough to 7 cranks to restart and tach bounces from zero to upper limit, but idle was steady at ~800. Continued on the drive and when the tach dropped to zero there is a noticeable loss of HP, no missing. What he also noticed was the factory alarm chirped. 30 minutes of driving and every time the same 3 symptoms. Now all I need to find is what is common to all three circuits. Any thoughts? got the workshop manual open now.

I think you can rule out fueling, and it still seems like you've got an intermittent electrical power issue....especially with the new clue of the factory alarm chirping. I know you've cleaned all your ground points and your alternator appears to be sending the proper voltage to the battery...at least when you've checked it anyway.

Experts out there....isn't there a diode back behind the tach that has something to do with voltage regulator function? I'm out of fresh ideas...