924Board.org

[austinporsche]

Hi all.

I have a 1988 924S that I've owned for several years and recently have been getting more familiar with.

For the past 6-12 months it's become increasingly harder to start.  When I attempted to crank, it would present a combination of low current (the dash lights indicative of cranking would not be dim) and weak or no solenoid action.

Battery is strong, so as a throw-part-at-it type of mechanic, I first replaced the starter.  No change.

The past week, I replaced the ignition switch (including the plastic sleeves).  Now the cranking indicator lights on the dash are very bright when the key is in the start position, and the solenoid engagement is loud and (presumably) strong, but it still has issues actually cranking.

Sometimes it will crank right over, other times it will engage the solenoid but not the starter motor itself until I work the key on and off several times (I think that the key barrel itself is good as I checked that).  I understand that the key barrel "tongue" that goes into the plastic ignition switch has three (3) distinct prongs/steps on it that not only turns the ignition switch itself but is also somehow directly involved in completing the starter circuit?

The 924 doesn't appear to have any starter relay, so I am trying to figure out the circuit issue I might have (maybe a bad ground?).

I thought that the starter itself always had current to it from the positive terminal and that the ground return path was thru the body starter casing into the bell housing and engine and to the ground strap, and only when the solenoid is engaged.was this ground opened.

FYI, I also have issues with the interior light, the sunroof lift and the radio.  Could they be interrelated (I think the radio is a speaker wire short issue as the radio will power up for a few seconds, then power off).

Any advice on what to do next would be most appreciated.

[924RACR]

Yeah, that has to be a straight up issue with the circuits to/from the starter. You've already knocked out a number of the possible issues.

But I don't think you've checked any of the heavy leads? Ground of battery to body, ground of engine to body, and main power lead from battery to starter could all be issues.

The first two can be potentially shunted around (for testing purposes) by using a jumper cable lead from the block directly to the battery negative terminal. Indeed, if you try to jump-start it, grounding to the engine block vs. the battery negative terminal should produce identical results - but may not.

Obviously check for corrosion on the connections of both ground straps to the body, engine, and (presumably already dealt with) to the battery.

It is possible that either one (or both) of the ground straps, or equally the large positive cable to the starter are bad, internally corroded and need replacing. But to check on the positive cable, you essentially have to replace it... so try the grounds first.
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[austinporsche]

wow, that is a great, simple way to determine whether the engine-to-body or battery-to-body ground path has an issue. Thanks for that advice.

FYI, I have cleaned the battery-to-body ground point but never tested the actual resistance of the cable itself, and same with the engine-to-body ground strap (not even sure where it is, but guessing it's one of those braided style straps rather than a cable).

I'll try bypassing/improving the ground path first, then the positive path using jumper cables.

Also a friend with half a dozen Porsches says that the Bosch starters tend to be POS so it could also well be that my "newish" starter could be bad.