944 Turbo Headache odd...No spark

[peanut]

could you just give us all an update where things are at the moment re trying to start the engine .

If you remove the HT lead to the distributor Is there a spark on the HT lead ?
When you try start the engine are you pumping the throttle ? it should be started with zero throttle.
Have you checked that you have 12v+ at one of the injector connectors with ignition on ?
Have you tried starting the engine using easystart yet ? what happened ?
Is the engine trying to start at all ie coughs splutters etc ?

I'm trying to build a picture of an engine that none of us can see or test.

 

[Sweeney2255]

Hi

No spark at king lead, power to the coil however.

No power at maf sensor on any connection.

Power to injector fine.

Signal coming from Crank and speed sensors ok.

No attempt to start just winds over. If you try it lots of start stop cranking, you may just get one tiny cough.

using a spare plug, it sometimes flashes a weak spark as thekey is returned from crank to pos 1

??

Will try easy start, tommorow.

 

[944Turbo]

There is a range of resistance values for testing the coil in the workshop manuals - sorry haven't got time to dig through them now but they are usually available for free download.
Worth a check if there is power and signal getting to the coil, but no sparks coming out. You haven't got that far as you will need sparks but the fuel could well be past its best if the car has been standing a while.
Tony

 

[peanut]

so you have 12v+ at the coil primary but no HT spark from the secondary .

Its essential to understand that the way the Bosch fuel and ignition system works is that the ECU initiates the spark NOT the coil
If the ECU doesn't pulse the ignition system you'll not get a HT spark anywhere even though your coil is ok and you have 12v+ and ground at the coil

Do you have 12v+ at terminal 30 on the base of the DME relay with the ignition switched off ? this is the only power supply to the entire fuel delivery and ignition system and all its components including the ECU and all its sensors.

 

[blade7]

I've known briefly shorting the king lead to earth to cure starting issues in the past. Try at your own risk, I take no responsibility.

 

[Sweeney2255]

You guys are so helpful, its v appreciated.

Ok i have checked again, its completely no spark whatsoever now, tried the easy start, not even a cough.

12v at the coil,
8 and 9 ohms from the speed and ref sensors,
getting power to the injectors on cranking, about 2volts i think..
There is 12volts at the dme relay although there is now no click or anything when you pop the dme relay in with ignition on. Previously it would click.
I have sent the KLR and ECU off for testing today to see if that is the issue, as am running out of ideas, thanks to the chap who recommended a place to send it earlier in this thread, shall
see what they say.
I have checked the connections and earths also.
The DME and KLR look like they have already been fixed before, so obvs has been an issue in the past???????

 

[Waylander]

the ref sensors should be 900 ohms if memory serves

https://www.bosch-automotive-catalog.com/en/product-detail/-/product/0261210003?returnPage=https%3A%2F%2Fwww.bosch-automotive-catalog.com%2Fen%2Fproduct-search%3Fp_p_id%3Depdssearchresult_WAR_aaecatportlet%26p_p_lifecycle%3D0%26p_p_state%3Dnormal%26p_p_mode%3Dview%26p_p_col_id%3Dcolumn-2%26p_p_col_count%3D1%26autoLoad%3D1

https://www.opieoils.co.uk/p-122074-bosch-crankshaft-sensor-0261210003.aspx

.86 Kohms

 

[Sweeney2255]

I better recheck that other one, and one was 9 and a bit i think the other was like 8.1

 

[Waylander]

Anywhere near is good enough,

 

[peanut]

you say that you have 12v+ at the DME relay but you haven't stated which terminal so that information is completely useless ....there are 6x terminals all with a different function. For an auto electrician I have to say you sure are careless with your answers considering we are trying to diagnose the problem over the internet!..

I have been diagnosing and fixing these non start hard start issues for 944 owners around the World on 3 Porsche forums for the past 15 years and I can see where this story is heading so I'm going to take a back seat and wish you the best of luck .

 

[Sweeney2255]

Im not an auto electrician? Dont know what gave you that idea..Someone said have I got 12 volts at the terminal they specified, which I answered yes ???????
Im just answering questions as a low skilled porsche owner, trying to get his Porsche going.
I bow to your knowledge, but not everyone has your experience.

 

[jonnyporsche]

Just skip read this and I have it in mind that if the fuel pump doesn't deliver enough pressure the ECU doesn't fire up the electrics, I could be wrong someone will correct me. Good luck with it.

 

[Sweeney2255]

Cheers Jonny, yes I am fairly low skilled so my knowledge is a little scant. Hence me asking for assistance ?? No idea about that fuel pressure, but have 12 volts to term 30 under the dme relay

 

[peanut]

Just skip read this and I have it in mind that if the fuel pump doesn't deliver enough pressure the ECU doesn't fire up the electrics, I could be wrong someone will correct me. Good luck with it.

no that is not the case .
The ECU relies on numerous sensors supplying the correct data in order to function but fuel pressure is not one of them johnny

 

[944Turbo]

Found it .......

ignition coil
primary resistance term 1 to term 15 =0.4 to 0.6 ohms

secondary term 1 against 4= 5 to 7.2 k-ohms

Also it says checking term 8 and 27 of dme plug the sine wave should be 2.5V pk to pk if not then check distance of starter ring gear and sensor so I am guessing with a scop on the flywheel sensors you should see 2.5v.

It is also worth noting that the leads can look pretty good and be terrible! the first time I looked at my 944 engine (which was running quite well) on a dark night there were sparks 'leaking' out all over the place from otherwise reasonable looking leads.

It is also worth checking all the engine grounds - the handbook lists 2 beside the (speed and ref) sensors onto the engine and one from engine to body at rear of engine.

Tony

 

[peanut]

Im not an auto electrician? Dont know what gave you that idea..Someone said have I got 12 volts at the terminal they specified, which I answered yes ???????
Im just answering questions as a low skilled porsche owner, trying to get his Porsche going.
I bow to your knowledge, but not everyone has your experience.

Ok apologies I must have misunderstood your first post about auto electrician .That would be a complete waste of money and time because you need someone familiar with Bosch fuel injection and engine management systems not car electrical systems.

Its really important to be specific in your answers to questions . We cannot see your car or apply any tests ourselves so we are utterly dependent on your full and accurate reporting .

We know that there is a history of this engine not running for many years and its reasonable to assume that the previous owners and others , have replaced parts adjusted settings and possibly introduced further issues we are unaware of. Its absolutely the worst case scenario .

To diagnose fault or faults it is essential to follow a logical troubleshooting sequence based on the observed issue . The more things we alter ,change, adjust and fiddle with at random, the more difficult it is to troubleshoot an issue .

Ok we have established that there is 12v+ at term 30 on the base of the DME relay good! .......thats a crucial first step.
The 12v+ at Terminal 30 ultimately supplies the ECU , injectors, fuel pump, sensors and ignition pulsing etc but all of that is controlled by the DME relay and ECU in conjunction with the engine sensors

Second test (with the DME relay removed ),is terminal 86 on the DME relay base . It should show 12v+ when the ignition is switched on. ....yes/no?

The third test for now is to do a continuity test with your multimeter between a clean ground point on the chassis and terminal 85 on the DME relay base . You should see continuity showing that the the first DME relay coil is being grounded ...yes/no ?

 

[944Turbo]

there is a simple diagram that shows
Coil term 4 is the centre for the king lead term 1 comes from ecu pin 1 and 15 from the battery via the ignition key. Terms 4 and 1 are shown as being potential danger spots.

Again not an issue if the king lead isn't sparking but when thats sorted - getting thie distributor cap on correctly can be tricky manual says 'turn both clamping hooks against the left stop then push in and turn counterclockwise 1/4 turn. check the cap fits tightly and hooks are firmly engaged.

plugs 25-30 Nm give threads a light coat of graphite grease

skipping back
plug for DME ahould have batteyr volatge between terms 35 and 5 and 18 and 5 (plug disconnected from DME and ignition switch on)

then check speed and ref sensors (it does mention checking they are plugged into correct sockets in engine bay)
speed using pins 8 and 27 (2.5V sine wave and if not measure resistance 0.6 to 1.6K)
term 8 to term 5 should be more than 1M-ohm

(try0 to start engine
ref term 25 and term 26 a single sine oscillation of a =ve slope of more than 2v with a starter speed of at least 200rpm (signal smplitude depends on starter speed)

if no signal same specs apply as speed sensor

then goes on to checking coil specs as earlier - checking rotor arm and cap for burns rotor arm has 1k resistance plug caps 3k

ignition timing at idle (operating temp) 800rpm +-50rpm 5 to 15 degrees



with airflow sensor connected push back sleeve voltmeter on 9 and 6 should show more than 8V

term 7 and ground 150 to 250mV remove airfilter and push open sensor plate voltage rises above 8Vwith plate fully open

check on intake air temp - turn off ignition and pull off air flow sensor plug connect ohmeter between term 6 and 22 on the AFM (both outer flat plugs) 15C to 30C 1.45 to 3.3K ohms

 

[Sweeney2255]

Thanks P and 944, i shall carry out the dme volt test today. Does it matter that my DME and Other box is off being tested?

 

[peanut]

. Does it matter that my DME and Other box is off being tested?

No they are not needed for the 2x tests on the DME relay base that I requested.
Make sure that you test the correct DME relay sockets as per the diagram on the DME relay can .

It is much less confusing for everyone if the Engine Control Unit is referred to as ECU which is how BOSCH and Charles O Probst refer to it in their manuals .

Calling the ECU a 'DME' frequently leads to confusion because half the time nobody is certain if its the ECU or the DME relay that is being referred to. and many novices refer to both units as DME because they are unclear of the difference or too lazy to attach the word relay .

 

[944Scott]

I know your diagnosis is further down the line now but I have some spare leads,dizzy caps, rotor arm and dme relay if you want/need to borrow them.