Do you own a first-gen 997? Are you experiencing hot start issues? Chances are, the wiring harness linking the alternator and starter motor has failed. It's a common complaint caused by exposure to repeated heat cycles in the engine bay. PIE Performance shows us the fix...
997 owners may suffer a slow crank when their car's flat-six is hot. Worst case, the engine won't turn over until the temperature has dropped. The problem was addressed in time for the second-gen 997, but owners of earlier models may run into the issue, often misdiagnosed as a faulty battery. We visited PIE Performance Porsche (pieperformance.co.uk) for the fix. 1
The problem stems from the alternator/starter cable being routed in such a way it is exposed to repeated heat cycles in the engine bay, causing deterioration. A new genuine cable (pictured left) costs less than £90 and the fix should take you no more than three hours, though allow extra time if working with a Tiptronic-equipped 997 (due to more compact packaging). 2
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Wiggle while you work and lift the airbox free of its locating pins. Make sure the loose jubilee clip doesn't fall into the engine bay and be careful not to cause damage to the oil filler neck.
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With the two wiring harness plugs disconnected and the jubilee clip fastening the airbox trunking to the throttle body loosened, it will now be possible to pull the airbox free.
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To begin with, raise the car on a ramp or axle stands. Remove the scuttle covers and disconnect the battery. Then, remove the airbox. Begin by loosening the jubilee clip fastened to the throttle body.
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The main body of the airbox is held firm by locating pins. You will require no tools to pull the part free, but exercise care and be sure the following steps are observed beforehand.
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There are two wiring harness plugs attached to the airbox. Both need to be disconnected and pulled to one side. The first is clearly visible on the back of the housing. Carefully pull it free.
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There is a mounting support bracket attached to the throttle body. It needs to be removed, but undo the bottom bolt with care — it is pressed against a bolt with an integrated rubber collar prone to splitting.
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Undo the wiring harness plug attached to the throttle body and pull the part clear. Now is the perfect time to clean it free of any contaminants, such as build-up of sticky oil between the housing and butterfly valve.
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The harness we're replacing is attached to the rear of the alternator. We need to pull the unit forward to get access, which means removing the auxiliary belt. Using a socket, loosen the idler pulley.
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If you've excessively loosened the jubilee clips attaching the plenum to the main inlet pipework, put them to one side or re-tighten them to ensure they don't drop down the back of the engine bay.
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Next up, you need to remove the plenum behind the throttle body. Unclip the breather hose and then loosen the jubilee clips attaching the part to the main intake pipework. When loose, pull free.
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The second plug is less obvious, hidden behind the airbox body, but easily accessible. Pince the locking pin and disconnect the plug. Pull it to one side.
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With the airbox removed, you can now remove the throttle body. Four bolts hold the part in place. Using a ratchet and socket, free all of them.
This is the connector linking the wiring harness to the starter (refer to step 2 of this guide for clarification). The heat of the engine bay can cause the rubber boot to melt, leading to problems. 18
Here is the same connector, as viewed from within the engine bay, and with the harness attached to the starter. Access is limited, so unscrew using a 13mm socket on the end of a universal joint. 19
There is only one fastener to unscrew, but much like the jubilee clips mentioned earlier, be sure not to drop the nut down the back of the engine bay. You're now halfway through the job. 20
This end of the alternator/starter harness attaches to the gearbox. It is hidden from view, and the plastic cover hides a fastening nut, which must be removed to allow the old loom to be pulled free. 24
With undertrays removed, this image shows you where the harness attaches to the gearbox. If working with a Tiptronic, the transmission will need to be slightly lowered to allow enough room to work. 25
Start by removing the 15mm bolt at each end of the rear chassis brace. As you can see, PIE Performance technician, Billy Mclean, finds this part of the job immensely satisfying. Probably. 26
With the clips successfully prized free, you now need to work underneath the car. Using a 10mm socket, undo the plastic nuts holding the protective undertrays in place and pull them free. 23
You will almost certainly need to use a flashlight to catch a glimpse of the clips. If you find yourself getting nowhere fast, it may be useful to unbolt the aircon compressor, allowing more room to work. 22
The alternator/starter wiring harness is held firmly in place by a pair of clips attached to engine bay hardware. These are notoriously difficult to see, but need to be unfastened to allow removal of the cable. 21
With the idler pulley allowing you to pull the belt free, unscrew the alternator's fastening bolts and pull the unit forward, to allow access to the rear. You may need a pry bar if the part puts up a fight. 15
And here is where the connector attaches to the back of the alternator. With the part pulled forward, access should be easy enough, but you will need to get a ratchet and 13mm socket in there. 17
This is the wiring harness connector attached to the rear of the alternator. It can be a pig to get at unless you have sufficient lighting and nimble wrists, but removal is a simple case of unscrewing a nut. 16
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Put the chassis brace safely to one side. As mentioned earlier, the 997's smaller manual gearbox provides enough room to work without having to remove the brace or lower the transmission.
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This picture illustrates the mounting bracket attached to our Tiptronic S-equipped 997's gearbox. Undo the six 16mm bolts holding it in place and the transmission will drop a few millimetres.
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The gearbox will have lowered sufficiently for the next phase of work to begin. Return to the cover hiding the connector attaching the wiring loom to the side of the gearbox. Undo the two 10mm bolts.
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The harness we are removing (and the one were are installing) features plastic cowling to force routing, protect the cable from corrosion and to hold it firm. This locating lug is pushed into the gearbox housing.
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At this point, the alternator/starter harness joins a second loom linking all the way along the car to the battery. In some cases, this loom will also need to be replaced, but can be treated as a separate job.
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With the plastic cover free, you can now undo the 13mm nut holding the wiring harness in place. The position of this nut makes it susceptible to corrosion. Renew the part, rather than reinstalling.
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Shine a light where the alternator/starter harness lives and you will see the plastic cowling. Its rigidity can make moving through the engine bay tricky. Removal allows easy extraction of the wiring.
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The removed plastic cowling. As previously noted, the smaller dimensions of the 997's manual transmission allows for easier harness removal and installation, meaning this step may not be required.
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The removed alternator/starter harness. At first glance, there doesn't seem to be much wrong — the rubber boot is in tact and no sign of cable damage — but heat can deteriorate wiring hidden from view.
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As the late, great John Haynes so often said, refitting is the reversal of removal. When done, reconnect the battery and enjoy driving your 997 without fear of being stranded with hot start issues.
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The new wiring harness ready for installation. You may find it useful to have a friend help route the cable around the oil cooler and down the side of the gearbox while you feed it through from the top.
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The connectors previously attached to the back of the alternator and the starter. Yours may show serious corrosion or melted rubber. Signs of failure, however, aren't always so obvious.