Porsche Enthusiasts Club Forum

Hi, got the dreaded no start on my 2.5na last week so been reading the forums and trying stuff out.
it was fine one day , then parked up left it a week and then no dice, not playing.

Situation is as this....
it turns over well, starter motor sounds good but wont fire....battery ok.
tested coil, 12v to ground both terminals , resistance readings 6000ohms( within range) and 1.2ohms( slightly high as 0.4-0.6ohm given in spec...would this cause a failure?)
used a spark test light on plugs and distributor nothing showed
got a new dme relay ( should have had a spare anyway i know!) didnt help any, had them tested and both are fine..
jumpered the relay as per clarks and fuel pump ran ok ( i put a new one and filter while its been static) and put a gauge on the fuel rail. showed about 38psi . didnt check exact flow rate as it said to do from pressure reg output and didnt want to remove as of the time but it looked to be flowing pretty well .
I got a replacement dme ecu correct model but still no start.

At this point youre all saying its the speed and reference sensors and im thinking youre all right but i cant get them to budge from their housing.
I have tested the resistances in situ to the sockets and theyre ok 973ohms and >1Mo and also checked them down to the ecu connector ok....i cant do the oscilloscope thing as i aint got one and wouldnt know how to use one if i did!
Any specific removal advice would be welcome as no-one seems to specify a technique in what ive read around., just twist and remove.......yeah simple till they dont . Do they snap off in place easily , can you pry them or get clamps on to hoik em out or are they like faberge eggs in plastic and tin foil...

My issue is i dont want to force them out and bust the housing or break em off in place until absolutely neccessary as there is one discrepancy i have found elsewhere which id like opinion on from you more knowledgable peeps.
So, I found this checklist , part of it below, on 944online site in the USA so followed it. ( My results are stated after each)

12v at the battery with adequate cranking voltage when I turn the key. Yes
12v from battery to ignition switch YES
12v from pin 50 on switch to pin 4 on dme plug (start signal) � NO
12v on pins 1 (ignition pulse to ign. coil) and 18 (to G5 dme relay power supply) � YES
12v pin 30 at dme relay (fuel pump power supply) � YES
12v to pin 86 at dme relay in the run position (primary coil voltage) � YES
12v to coil + black wire to ground 12v to - (green wire) to ground � YES
12v to one side of the injectors � YES
All ground contacts are clean � >>>>erm Yes
Fuel pump will run if dme relay is jumpered 30/87/87b � YES
Fuel pressure at the rail is 29psig +/- 3 (jumpered 36 psig) � YES
20 minute leakdown not under 14.5 psig � YES OK
Fuel flow rate is 28oz after 30 seconds � Not Sure
Ignition coil primary resistance across + and - is between .4 and .6 ohms � 1.2ohm
Secondary resistance is between 5000 and 7200 ohms � 6000ohm
Ignition wires are good no cracks or splits including coil wire and seated � yes
Plugs are properly gapped � YES


So, im not seeing 12v from the ignition switch pin 50 to ecu plug pin 4 .
It says this is a start signal to the dme yet the starter motor is turning fine.
I tested resistance between pin 30 and 50 on the switch and got this;

a/ max ohms at key insert pos 1,
b/ max ohm at pos 2 ( ?accessories?) ,
c/ zero ohms at start pos3, ( at this point i presume this is where it should be sending 12v
to the ecu pin 4 or should it be when cranking it only?)
d/ zero ohms at turning over.

I checked continuity between pin 50 ignition and pin 4 dme and its ok.

Im wondering if this shows possibly a switch failure which is not sending the signal to the dme ecu ?
would this cause these symptoms?
I dont know how the switch works and it looks a pain to remove unless necessary but it might be easier than bashing sh1t out of the ref/speed sensors when they could be ok.

Can you jump the switch terminals to simulate a start without using the key to see if that will bypass a faulty switch and allow the dme to see what it needs? if so how? im no 15 yr old carjacker so i dont know where to start...lol
I can see 6 terminals in the ignition switch plug / socket so if anyone has a method i could try it.

any comments helpful or not would be most welcome as im tearing my hair out here.
its my birthday tomorrow so i could do with some good news to compensate!

cheers

Andy

hi Andy feel your pain have you got an immobilisers on it
for the like of me i cant find how to build a little tester to check your pulse on my bookmarks
see if its in my post here
viewtopic.php?f=25&t=17069
it will cost less than a pound tgo make from maplins or similar and will tell you if you have a pulse when cranking
your right about them not just pulling out mine dident bought two new in end from gsf about £70 for the two i think
dont rule out a bad earth too as i think thats what mine was in end as shes still running .
found it
http://forums.pelicanparts.com/porsche-924-944-968-technical-forum/343212-hiow-test-crank-sensor.html
woops on early 5 oclock start bye

You seem to have covered quite a bit but wondered if youve missed something simpler
You dont mention fuses, have you checked connectors both sides of fuses while turning over ?
Especially fuse 2

thanks for that, i'll give it a go tomorrow as im going near Leeds maplins anyway.
I'd read your thread as it was the nearest to my issue but missed the link to the led tester .
Can you give me a bit more description about your sensor removal efforts as for £75 i might as well get a couple new ready to go if no.one has any suggestions re my switch theory.
I've got an old mount with sensors also unmovable as a spare
so might practice on that before attacking the ones in situ.


oh what a learning curve!

Thanks again

Andy

hi jason,

fuse 2? whats that then? lol
sorry, im in bed typing no access to fusebox!

i checked the fuel pump fuse 34? but tbh no others....gonna be a happy mupppett if its something as simple as a fuse that sorts it so cheers, ill look at that again in the morning.
which connectors are you meaning?

cheers for the input

Andy

hi jason,

fuse 2? whats that then? lol
sorry, im in bed typing no access to fusebox!

i checked the fuel pump fuse 34? but tbh no others....gonna be a happy mupppett if its something as simple as a fuse that sorts it so cheers, ill look at that again in the morning.
which connectors are you meaning?

cheers for the input

Andy

well there is a god and his name is jason..... i'll give you the credit for making me check relay g2 which i guess is what you meant by fuse 2 yesterday. Having cleaned up the earths and swapped relays round and jiggled sensor wires etc etc i gave it a go and hey presto it fired up runnig as normal.
One happpy muppet here overthinking stuff as you suggested but hey....i know a lot more about my car now than 2 weeks ago and it made me sort the fuel pump system out so nothing wasted in the end.

Thanks again to you 2 , campervan i needed a bit of moral support and encouragement last night , much appreciated guys.


thanks again


Andy

post closed

part num for led is n26fn and one resistor m220r they only work one way i think ( cant rem ) the tdc crank sensor will only flash once per revolution
dont do what i did and replace it caus it only flashed once
the other sensor will flash while its cranking over
you can also check the sensors at plug at end of sensor as well, so if it flashes there and not in foot well wiring plug off ecu you know its wiring issue .
while your at maplins get n78kg and m330r and build yourself a cheep noid light to check injector pulse or any thing else working off 12v
crank sensor is £37.74 from gsf but i would personally check them first as it might be a bad earth or somthing else as mine were a pig to get off and i broke bit of bracket getting it off the car as they would not budge ,
then spent best part of an hr getting them out the bracket in several pieces .
if there working i would leave them .
hope that helps and makes sense

whoops took me that long writing dident see post

This an interesting read.
I share your pain on a non start and boy do these cars seem to suffer more no starts than any car I have come across

Every so often my 2.5 lux refuses to start and the old tacho is bouncing fine.
I swear at it and use another car and then when I try at the end of the day it starts instantly
When its difficult to start but finally does start it does not like the throttle opened as it starts to die, then it picks up and behaves normally.
It never falters when running and has no misfire atall.
In fact it was at Silverstone with me today (Sat) while I watched my daughter race her Boxster (JMG built fine lusty engine ) and the drive home was great as its not the fastest of cars but it is a great tourer with sure footed road holding.

The trouble with a fault that occurs occasionally but then clears is that you cannot sort it but I suspect the fuel pump sometimes falters.