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brokenporker

Intermittent Issue - Cranks but Won't Start...

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Hi

First post from me so be gentle, but to be fair, first issue with our 987 in nearly 3 years of ownership... :)

My wife's 2005 S has developed an intermittent starting problem - every now and then it just won't start. It cranks and cranks but doesn't even try to go. If you leave it a few mins it will do the same thing, leave it a few hours and then it will start first turn of the key, within a few cranks as normal.

Battery is good, it turns over at normal speed when it's cranking. Using an OBD-II reader no current or stored faults are shown. I've checked the carpets under the seats and they seem dry, the fuse box seems dry, pulled the battery and the fuel pump cover and the connections are all clean etc. Doing a search suggested that the 986's suffered with relay issues, but the 987 has everything controlled by the ECU.

I've run out of things to check now - any more suggestions? I'm thinking potentially either the fuel pump (although normally these normally fail completely, not randomly stop working then start again later), ECU issue or an immobiliser issue. What happens if the transponder in the key is failing - will it still crank or do nothing when you turn the key?

Any help much appreciated - my wife is paranoid about driving it now as she's had to be recovered on a flatbed once due to it already! If I take it to Porsche it will end up very expensive as it's an intermittent fault which will no doubt take them forever to recreate...

Thanks!

Jon

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987 use mini relays for fuel pump etc., located in the relay box under the dash, driver side LHD cars. The TDC sensor also will cause some starting problems once in a while, usual with warm/hot engine.

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Thanks for the reply. It's a RHD car, and the only relay listed in the fuse box on the drivers side is 'Relais' (top right) as follows:

fusebox.jpg

Is there another fusebox hidden somewhere else that the owners manual helpfully doesn't mention! :)

Edited by brokenporker

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OK, it appears that there's a relay board above the fuse box (which isn't mentioned in the owners manual at all!), which contains the mythical DME relay.. The next question is how the .... do you get at it??

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RFM is on the money with this one, this sounds like a Crank Position Sensor which turns off the fuel pump when it acts up because the DME cannot see the engine turning over. Not uncommon, easily fixed.

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OK - so I can see the underside of the relay board looking above the fusebox - it looks like it unclips somehow to drop down to give access to the relays, but I can't figure it out, any pointers?

I've got a new DME relay so I may as well fit it, then look at the crank sensor... :)

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If you're working with the car on the ground or stands, put a thick towel over the door sill and lay flat on the door sill with your head in the footwell. Get a good bright light and you will be able to access/see all of the relays.

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OK - so I can see the underside of the relay board looking above the fusebox - it looks like it unclips somehow to drop down to give access to the relays, but I can't figure it out, any pointers?

I've got a new DME relay so I may as well fit it, then look at the crank sensor... :)

Not to rain on your parade, but you are looking at relay panel #1, and the DME relay is not in that panel, it is in panel #2 in the rear boot. :eek:

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Oh for a decent workshop manual....

Where's the relay panel in the rear boot then? :)

Facing into the trunk from the rear of the car, pull down the inside trim liner at the front of the trunk area.

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Sorry, I gave some incorrect info, it is not in the front of the trunk, but on the drivers side (behind a removable panel) on your car. :huh:

relay1.pngrelay2.png1. Open luggage−compartment lid, turn the two fixing clips at the side by 90° and fold down the luggage compartment cover.2. Pull relay carrier forward on the two supports.relay3.png

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Perfect - many thanks.

Any chance of the instructions to extricate the relay board #1 - on my back looking up at it from the footwell I can see the underside of it, and reaching up I can feel the relays on the top (with a cover for the connections below) - there looks to be clips to release it somehow, but I can't get it to release..

I've found some pics on here for the 986 which shows the board mounted vertically with lots better access, but none for the 987 which seems to have been designed by Houdini - there's no way I could get at the relays without dropping it down somehow...

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Perfect - many thanks.

Any chance of the instructions to extricate the relay board #1 - on my back looking up at it from the footwell I can see the underside of it, and reaching up I can feel the relays on the top (with a cover for the connections below) - there looks to be clips to release it somehow, but I can't get it to release..

I've found some pics on here for the 986 which shows the board mounted vertically with lots better access, but none for the 987 which seems to have been designed by Houdini - there's no way I could get at the relays without dropping it down somehow...

Being double jointed definitely helps; we have never tried to pull one down, preferring to work upside down with my head under the dash using a small mirror and light. Not comfortable, but it is quick. The front relay panel may be mounted on a similar set of arms that the rear one is.

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At least on an older 996, it makes it much easier to access the relays in the footwell if you remove the large piece of trim that covers the fuse box and kick area. It is not that hard to remove after you take out the 4 screws under the fuse panel cover.

Also, having removed the fuse/relay holder (again on my older model), I can tell you it was not designed to "swing down" for easy access... so don't be tempted to break something by yanking on it.

You really do need to wedge yourself up in that area to get better access to it.

I'm 6' tall and am able to get my head right where the pedals are, then reach up with one or two arms and access any of the relays.

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On the 997/987 cars, Porsche changed the design of the relay banks, apparently for space reasons. The one in the rear boot on a 987/Cayman now flips somewhat and slides out on arms unlike the early ones that are bolted to the firewall under the trunk carpeting on a 986, and the one up under the dash appears to be a similar design, although I have never tried to move it as it is in a very confined space so something has to move out of the way to make room for it (when you look up under the dash, you are looking at the bottom cover of the relay bank, so you need a small telescoping mirror to extend above it to see what you need to do). While it may represent progress, it is a bit peculiar. In any case, relay changes are not a daily occurrence, and remain possible if a bit arduous.

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I truly, truly hate this car sometimes. Took everyone's advice and bought a new crank sensor. Through a combination of gymnastics through the top access hatch and underneath, I got it unplugged and got the torx bolt out. Crank sensor was stuck fast though.

After approx 3 hours of persuasion with screwdrivers, wiggling it back and forth I finally get the old on out (well, the remains of it!). It was in there very, very tightly. Offer up the new one, and it won't fit in the hole - it's slightly, slightly too large. It probably explains why the old one was such a PITA to get out! I guess it was installed on the bench when the engine was built and pushed / tapped in. There's no way I could get (or want to get!) the new sensor in...

So now I'm left with a non functional car, a sensor that doesn't fit and very, very sore arms :(

What do you think the best option is - try and sand down the new sensor to get it to fit? Guess I'll have to chop the old one up to see how much plastic there is around the innards...

Cheers

Jon

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There's plenty of plastic around the metal core... Have sanded the new sensor down a bit and it is now fitted. Just need to connect it up and hope it still works (and fixes the intermittent starting issue!)

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Back to square one...

Got it all back together, car fired up, idled fine. Put the cover back on, carpets etc, fired it up again, it ran for a second then died.

It just turns over now, tacho readout shows it turning over so I guess that rules out the new crank sensor? No fuel smell when it's turning over...

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Have you already, as requested, replaced the fuel pump relay or at least the relay bridged?

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Yep - I managed to get access to the relay panel, which is different to the layout shown on Pelican Parts (http://www.pelicanparts.com/techarticles/Boxster_Tech/22-FUEL-Fuel_Pump/22-FUEL-Fuel_Pump.htm). I'll add some details as it might help someone figure it out in the future!

On ours it's above the drivers side fuse panel, but 'upside down' with a cover on the bottom:

fusebox-relays.jpg

You can unclip the wiring cover underneath, then towards the wing of the car you can lift and unclip the relay board, and it will just about twist upwards and drop down through the gap. There's no way you could change the relays in situ..

relays.jpg

The parts supplier sent me a screengrab of the Porsche parts system for our car - S11 is listed as the DME relay, S8 is the fuel pump relay.

I've put a new DME relay in, and swapped the fuel pump relay for the one next to it (mini relays, not the full size) and it still won't start...

At least now the problem isn't intermittent, so hopefully it'll make diagnosis easier!

Edited by brokenporker

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Did some more testing today..

Took the battery out, and the fuel pump cover. Bridging the fuel pump relay causes the pump to run as soon as the battery is connected (seems to be different to a 986 which only runs when the ignition is on? Apparently the cayman also runs the fuel pump all the time when bridged too). You can hear the pump running (faintly).

With the pump bridged, it still cranks but doesn't start. Pulled the fuel feed pipe from the pump, it was full of fuel. Fuel return appeared to be dry though. Put a pipe from the feed to a petrol container, fired the pump up and got a healthy flow of petrol into the container. Put it all back together, refitted the fuel pump relay, refitted the battery, turned the key and it fired up and ran perfectly... Stopped it and started it another 5 or so times with no issues..

Really not sure what to check next - unless removing the battery has reset something in the DME / immobiliser? Which I really don't want to be the case as it's going to get expensive to get that fixed :(

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Did some more testing today.. Took the battery out, and the fuel pump cover. Bridging the fuel pump relay causes the pump to run as soon as the battery is connected (seems to be different to a 986 which only runs when the ignition is on? Apparently the cayman also runs the fuel pump all the time when bridged too). You can hear the pump running (faintly). With the pump bridged, it still cranks but doesn't start. Pulled the fuel feed pipe from the pump, it was full of fuel. Fuel return appeared to be dry though. Put a pipe from the feed to a petrol container, fired the pump up and got a healthy flow of petrol into the container. Put it all back together, refitted the fuel pump relay, refitted the battery, turned the key and it fired up and ran perfectly... Stopped it and started it another 5 or so times with no issues.. Really not sure what to check next - unless removing the battery has reset something in the DME / immobiliser? Which I really don't want to be the case as it's going to get expensive to get that fixed :(

If the battery disconnect were to "reset something", there should be a code stored in the system.What fuel pressure are you seeing at idle?

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I couldn't see any codes stored via my OBD-II reader when I tried before - I'll check again later on.

I've not put a pressure gauge on the system (I don't have a mechanical one) - can you read the pressure via diagnostics?

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No, you need to connect a pressure gauge to the test port on the fuel rail.

I would also strongly suggest scanning the car with a Porsche specific system ( PIWIS, PST II, Durametric system).

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I'm pretty sure the recovery guy put a gauge on the fuel rail when my OH was recovered a week back - although I wasn't there to confirm... I'll see if I can borrow a gauge and check myself...

One of the next steps is to take it to the local recommended indy and ask them nicely to plug it into the 'proper' systems rather than a generic code reader...

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