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986 3.2s wont start

Stoo.c

Well-known member
Joined
7 Apr 2014
Messages
205
Afternoon guys. I'm aware this question has been asked a million times and believe me I have read and researched absolutely everything regarding this issue and have my own ideas but I'm keen to see the view of the collective.

So I bought a 986 which needed a bit of work as it was running hot. I was aware of this which is why I bought it in the first place so other than a few test drives I haven't actually used it - the hot running is an aside to this issue and not really relevant given it hasn't actually over heated. The day I test drove it, it took quite a bit of cranking to start but it was on a steep slope and the fuel was below empty so I put this down to low fuel. Once it started it ran brilliantly and then stopped/started again several times with no problem.

Likewise once it arrived at my place off of the low loader it started and ran fine - few jerry cans of fuel in it by now. However over the next few months (when I actually got a chance to look at it) it progressively got harder and harder to start i.e. cranking for ages, bit of gas and finally it would kick in to life - not happy about doing it though. Once started it would run absolutely fine and would happily then start again from hot so the opposite of the usual crank sensor issue.

Now however it wont start at all and shows no sign of wanting to. Not battery related at all - battery is strong and I have made sure it was fully charged every time. It cranks the starter over very well and the engine is spinning as I've removed the inside access panel to check.

I thought fuel pump or relay so I jumped the terminals and the pump is running yet car still wont start and shows no sign of doing so. Whilst its possible the pump could be weak, it seems unlikely to be the problem as I would expect it to at least cough and fire a bit. I would test the pressure at the rail but don't have the required fittings. Again it could be the fuel filter but I think this is incredibly unlikely.

Now would be a good time to say I'm in no rush for this car and am not interested in having the car recovered somewhere to be diagnosed as firstly I don't really trust anywhere (and don't want to pay them for it) and secondly I do all of my car work myself down to engine building (as a hobby but I am an engineer).

So at the moment I'm still feeling that this sounds like a crank position sensor issue as its clearly something that has got progressively worse and appears to be affecting spark rather than fuel (no I haven't checked yet). Ive just fitted another engine to my 996 C4S after a rather painful failure so have removed the known working crank sensor from the old engine that I took out and will swap it over to see if it gives any joy. I also need to check if its sparking however the freezing weather put pay to me doing much over the last few weekends as the Boxster is outside.

Are there any other theories out there that could fit my description? I dont get much time to work on my cars and even less to put aside for the Boxster so anything else I can test at the same time would be great or is the collective in agreement that this sounds like a crank position sensor issue?

Thanks for reading.
 
Normal way forward would be to put a tester on it .. a code or lack of a code will help point you in the right direction .

Usual things first though .. has it got spark .. has it got fuel ..

You can use a Noid light to check injector switch or pull a plug and see if its damp if you want old school :)

What im basically saying is if you dont have fuel or spark then its the crank sensor .. if you have both then maf sensor , fuel pressure springs to mind .

Crank sensor can be scoped but it depends on what equipment you have .

For fuel pressure then you would need a gauge on the rail to confirm .. Boxster pumps are pretty good though .. rare to fail .

As its a Boxster then check under the passenger seat .. alarm cu is there and if it gets wet then all sorts of strange problems will happen .


From your description though it does sound like a classic crank sensor failure .. nice to prove it first though .. i hate just throwing parts at a car as a guess !

EDIT .

Overheating .. check the fans are working .. there are fan resistors in each fan which can fail .

Thermostate failure .. air lock if its been worked on previously , they are the more obvious ones to look for .
 
In my amateur opinion you've got it all covered. I would bow to Demort's expertise here but my first thought was either an immobiliser issue (ie wet ecu) or the good old CPS.

Let us know how you get on!

PS I love a guy who does his own stuff, there's a good few of us on here who like to have a go. I keep thinking about getting a knackered 3.8 M97 unit and rebuilding it as a learning exercise and then putting it in the Boxster, but i've got far too much other stuff going on and only ever seem to half finish projects like that!

:thumb:
 
Thanks guys. No codes showing on my code reader which is better than a cheapy one but isn't Porsche specific. I'm also against just throwing parts at a car (couldn't agree more) however as I have a spare known working CPS I figured I'd give it a go. I also have a spare MAF from my old 996 engine which I can try.

If the weather doesnt defeat me this weekend, I will do the old fashioned spark and fuel tests and at least I know I have both parts that it may well be.

Alarm appears to be doing its job and the car is dry inside so I'm hopeful this isn't the issue.

Regarding overheat - I started a little bit of diagnosis before the non start issue kicked in. Fans work fine and there are no leaks based on me pressure testing the system. Water pump appears fairly new (year or so) and is in great shape and somebody had removed the thermostat - tell tale bodge trying to fix an overheat from someone who doesn't understand these cars). It was a bodge job - no new gaskets - just instant stuff. I replaced the stat with my spare known working 996 one and used new gaskets on both the stat and waterpump. I also replaced the expansion tank cap as it was original and for the sake of about £3, replaced the seals on the bleeder valve as well. I figured these were worthwhile preventative measures regardless. Somebody has mixed coolants in the past so its a bit messy. I now need to flush it fully and carefully fill and bleed. My hopeful money is on an air lock - certainly feels like it. Very similar to my 996 when I put the new engine in as it air locked at the first fill and exhibited near identical characteristics. I then drained it fully from every pipe and very slowly refilled and its been brilliant ever since - perfect running and no change to the coolant level.

I will need to do this to the Boxster once its running again and hope for the best. The only other possibility there is pressurisation from exhaust gases which I really hope it isnt. I did a block test and it came up negative but I'm not overly confident with the quality of the kit I used. It does smell a little fuelly in the coolant when its got hot but that may just be me being paranoid. When it gets hot (not even overheating), it will spew out coolant at the tank which again feels very much like an air lock particularly as the heaters then went totally cold.

There is no intermix at all which seems to be fairly common if there is a cracked head and from what I've read its pretty unlikely for the HG to go on these.
 
ragpicker said:
In my amateur opinion you've got it all covered. I would bow to Demort's expertise here but my first thought was either an immobiliser issue (ie wet ecu) or the good old CPS.

We think alike :)

CPS .. i just call it a crank sensor .
Imobiliser and i just call it the alarm cu .

CPS is the most obvious even if there isnt a code .. it still generates a signal but its too weak for the dme to act on .. as its not open circuit which is the only check the dme can do then it doesn,t generate a fault code.

1 other thing to note .. a fuel pump failure will also not generate a fault code , thats what i meant by lack of codes being helpfull .. fuel pressure .

EDIT ..

If the engine gets hot with no hot air from the interior heater then you have an airlock.

If a head gasket had failed and pressurised the coolant system then you would know all about it after 5 mins running and removeing the coolant cap .. headgasket will REALLY pressurise a system to the point of water pouring out as you try to undo the cap.

usual chemical / sniffer test would prove it and i dont think its that .

Head cracked and you get a oil / coolant mix .. not overheating .

There are suction tools available to get coolant into the car without an airlock .. Porsches do tend to benifit from them due to rads at the front and so many places to get an airlock.

First one on google ..


http://www.ebay.co.uk/itm/like/2223...=9045811&device=c&campaignid=738217568&crdt=0
 
Thanks again for another response. I have a pressure/vacuum bleeder tool which I will use when I get round to it. I bottled it with the weather again this weekend unfortunately - I have plenty of other jobs to be getting on with so the Boxster will have to wait until a mild weekend.

You and I are in complete agreement on both the non-starting issue and the overheat issue so I'm keeping my fingers crossed as it would mean getting it back up and running for the cost of some new coolant.

I'm hopeful as its a really nice car with decent mileage and in very good condition.
 
Drain the coolant into a 25 ltr drum , check antifreeze strength , top up if needed and reuse i would say .. large funnel required .

Drain from a pipe on the engine and also from pipes comeing from radiators just in front of the engine.

You will get max out that way and the coolant " sucker " will do a better job .
 
Hi again. Same as when I fitted the new engine to the 996 - I drained from every pipe I possibly could to get as much coolant out as possible and it really worked well. I'm going to get rid of the coolant thats in the boxster - somebody has previously mixed different types so I'm going to fully flush the system and fill with fresh stuff.
 
So the weather was on my side on saturday but I couldnt get the crank sensor out - totally stuck in the block still. The bolt came out no problem at all but I just cant shift the sensor out of its hole. Removing the 911 one was tight but as the block was out of the car I was able to simply push it from the inside.

Any tips at all?

I gave up pretty quickly and fitted some new front droplinks to the C4S instead.
 
Ive not had one stick on a Boxster .. but its not very accessable at the best of times so this doesn,t sound good .

Twist side to side is the usual way with anything you can get on it .

With wheel speed sensors and one mare of a job i had with a 928 crank sensor then i started by drilling but as soon as you reach the magnet the drill snaps .. it was a case of drilling down the side and digging bits out .

Its about 3 inches long .. 928 must have taken me 3 hours and i could get at that .. sorry :(

Worst possible way would be box out , flywheel off and do it from inside the houseing.

Might be best to confirm its actually faulty before continueing as this is sounding like a big job :(
 
You can test the crank sensor in situ with either VCDS (Is there anybody near you that's got this?) or an old school oscilloscope where you can look at and count the spikes in voltage as it cranks.

If you are trying to take it out then I can only assume you intend to replace it (a visual inspection isn't likely to show up much) in that case a bit of heat to the case around the sensor, from something akin to a hot air gun, along with a spray of some penetrating fluid will assist.

:)
 
I'm thinking the same guys - worth confirming its actually faulty before I worry about getting it out. Battery was flat so couldn't try much at the weekend - its on charge so will try and confirm what it wrong this saturday. If indeed it is the sensor and I cant get it out, I'll just take the box off. Its not the worst job in the world and from being underneath I can see the CV boots are starting to perish so an excuse to do them with the shafts out as well. Clutch is probably original too and the rms weeps a bit so an excuse to do all sorts of things.

Duffy - reason for taking it out was not to 'see' if it was faulty - more the fact that I have a known working one from my old 911 engine so I though (wrongly clearly) that it would be a nice easy swap :grin:

If indeed I can confirm that its the crank sensor, then I like your heat idea actually as that may well work. If I have to replace it anyway then I'll just hit it with a blow torch and try and expand the crank case enough for it to come out easier.
 
That makes sense, it needs to either be checked in situ or replaced to rule it out so that would cover that and as you've got one it's cost free!

:)
 
So today I bolted the existing crank sensor back up and plugged it in and would you believe it the damn car started. I hate intermittent faults like this as it was definitely plugged in properly before. So by unplugging and plugging back in or by jacking up the rear of the car it seems to want to start again. I turned it off and on a few times and it started every time although it took a bit of cranking. Something is definitely not quite right.

I then decided to pull the plugs and see if there was any sign of 'steam cleaning' from coolant leaking into the cylinders (back to my overheat issue now). Certainly no sign of that as they were all pretty murky - nothing particularly out of the ordinary - just a little old. Oddly enough there were 5 beru plugs and one NGK - why would you change 1 plug? That coil pack had also been replaced as it was a Bosch where all the others were original Beru ones.

I decided to compression test as well whilst taking the plugs out which was a right pain on my own so couldnt do it with the throttle open which is how I normally do. The readings seemed very low but then again im used to testing vtec engines with silly compression.

Both cylinder 2 and 5 were showing 75 psi or so (engine was slightly warm, throttle closed) then ranging up to 3 cylinders showing 90 and one at 110. Again no 1 cylinder really stands out and I'm not overly confident in the compression tester at this point.

I'm still convinced there is some exhaust gas getting into the coolant though - it really stinks in the reservoir of fuel when its running with the lid off or when you take the lid of any relieve pressure.

Really dont have the time at the moment to do a great deal.

Anyone want to buy a cheap Boxster S :D
 
They've been chasing a fault on that cylinder I'd think which is a sign in itself that there's been something up that they've fixed on the cheap. One coil pack I can understand but one plug is a bit rubbish.

The compression test on the Boxster is a PITA to do but you are looking for consistency of result if nothing else. Did you repeat the test or just do it once?
If you do it again do it in reverse order and see what your figures are.

Running VCDS would be well worthwhile as low compression on one cylinder will not prevent it starting.

Don't write it off yet

:)
 

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