Another "no start post"

[byron911]

Hi

sorry this lengthy question is my first tech post....but help would be most appreciated.



Firstly the car:

1978 SC with an '84 3.2 fitted (wired by a 5 year old I'm thinking)

The said wiring is a nightmare that I'm going to tidy up and re-label as I work through the mess, this I suspect is the basis of the problem.



Secondly, the problem:

The car has started and run well since purchasing it a few months back, however a few times it wouldn't start (It turned over ok) but with persistence and fiddling with the poorly wired aftermarket immobiliser and central locking, it eventually would go. Symptoms included turning the key to 'on' and or start and the door locks would lock after unlocking with the remote key fob.

Anyway, a few weeks back I drove it a few km into town, shut it off and returned a few minutes later and no start. It coughed and ran for a few seconds then died..it's been comatose since.



What I've done to try and fix it:

I firstly removed the immobiliser and central locking including all metres of crappy wiring. It was only connected to the fuel pump circuit

Still no start

I've chased the DME wiring harness and tested the relay, they seem Ok. Power to the fuel pump, earths good, injectors clicking.

I removed the ECU and discovered a blown resistor on the board which is connected to #4 pin on the connector. This is 12v start supply direct from the ignition switch. I removed and replaced the resistor with a newy. I've limited knowledge of electronics, but figured that with a replacement ECU @ $700.00, I may as well try to fix it myself. I cant test the ECU, however I've tested every terminal in the ECU harness connector according to Bentley and all the parameters are OK.

I've removed, cleaned and reconnected grounds

Still no start, however it coughs a little, like it just may run...

I've worked thru the Bentley manual troubleshooting guides thoroughly

Spark....OK. Shorted a good plug to ground and it fires so I suspect a fuel problem

I've squirted carby cleaner into the air intake and it runs for a couple of seconds...it's gotta be fuel right!? I can smell fuel and suspected flooding initially, I've replaced the spark plugs just in case.

But the injectors fire (they were recently serviced) I've tested fuel volume which is spot on, I haven't a coupler the correct size to connect my pressure gauge though so pressure not known. I jumped the pump to 12v to run it without the DME relay and tried to start but still no good.

So, I'm stumped..

maybe there's still a fault in the ECU, maybe a dodgy ignition switch, wiring not earthed or connected to supply properly??

I've ordered a replacement DME relay, although it tests OK

any other ideas please

Greg

[universeman]

you can test pressure by calculating fuel volume expelled over time (such as into a jar or beaker) it does sound like a fuel delivery problem have you checked to ensure the gas is good? maybe someone sold you bad gas?

[75 911s]

I suspect wiring issues remain. I had a kill switch on mine and when it's engaged it gave similar symptoms. Double check the area around the ignition switch. You mentioned you removed the 'imobiliser' I assume you rechecked spark after doing so right?

[byron911]

thankyou for the responses

I did do a volume check as per Bentley, ie 30 seconds produced pretty close to .85 litres. Not sure how to extrapolate that to pressure...I can grab a coupler on Monday when the local parts store reopens and stick a gauge on it.

When you say bad gas, do you mean dirty? the filter is new and flow is there. Water perhaps?

Yeah wiring is decidedly dodgy but I've rectified a lot and checked power and earth paths to the major circuits. There is spark no probs with 12v feed to coil Ok.

I've read about worn ignition switches giving some wierd symptoms too.

I was reading on IB forum last night a guy with similar symptoms and it turned out to be the fuel pressure regulator. The main suggestion from others was check the TDC sensor as well so I'll readdress that (it checks out ok from the ECU connector end)

I'll keep at it and let you know

Thanks again

[88911coupe]

Definitely sounds like its related to the immobilizer however, my 3.2 was having random no start condition and thanks to Ingo,i I finally determined it was one of the speed or reference sensors that was failing intermittently. I incorrectly thought they either worked or DIDN'T work however I found they tested good on occasion and band on others. Replaced the buggy one and no problem since.

[ischmitz]

Greg, let me try to summarize:

- This is an engine transplant into an earlier car. So it's not entirely clear if/how the DME relay is wired. On a stock 3.2 the DME relay's first stage switches on when the key is turned to RUN. That powers the DME. The second stage of the DME relay is controlled by the DME and powers the fuel pump and the O2 sensor heater. It gets turned on when the FW is rotating >200RPM or when cranking (+12V to pin 4)

- You found a damaged resistor inside the DME related to pin 4. Pin 4 is the input that senses when the engine cranks (key in START) and then turns the 2nd stage of the DME relay on.

The fact that that resistor is damaged means there is most likely more damage related to the DME relay control. The resistor itself won't burn unless the driver is also damaged. A non-working DME relay could explain why your fuel pump isn't running and you have issues.

- You get spark when cranking (tested by grounding a spark plug to the engine
- You get some running when spraying starter fluid into the intake

My advice:

Verify that the ICV is vibrating when the key in RUN or START position. This tells you the DME has power and there is nothing wrong with the aftermarket alarm/immobilizer unit.

Check for fuel pulses with a NOID light while cranking

Check that the fuel pump is running when cranking. The best method is to measure voltage drop across the fuel pump fuse. Alternatively, you can measure voltage directly at the fuel pump. If all else fails check for fuel pressure. My guess is the fuel pump isn't running and that's why your car doesn't start.

BTW, the DME can be checked and repaired - let me know if you need help.

Cheers,
Ingo

[mysocal911]

Originally Posted by byron911

Spark....OK. Shorted a good plug to ground and it fires so I suspect a fuel problem

I've squirted carby cleaner into the air intake and it runs for a couple of seconds...it's gotta be fuel right!? I can smell fuel and suspected flooding initially, I've replaced the spark plugs just in case.

I've ordered a replacement DME relay, although it tests OK

any other ideas please

Greg

It appears your problem is fuel related since fuel into the intake starts the engine
momentarily. If the DME relay doesn't solve the running problem and:
1. The fuel pressure is not O.K. Then you can try to ground pin 20 of the DME ECU
which should cause the pump to run for checking the pressure. If still no pressure
then the pump is possibly bad.
2. The fuel pressure is O.K. Then there is a injector driver problem possibly caused
by an over-voltaging alternator or possibly other ECU circuitry problems.

If the DME ECU is the problem, Pelican Parts does provide a rebuilding service.

[byron911]

Greg, let me try to summarize:

- This is an engine transplant into an earlier car. So it's not entirely clear if/how the DME relay is wired. On a stock 3.2 the DME relay's first stage switches on when the key is turned to RUN. That powers the DME. The second stage of the DME relay is controlled by the DME and powers the fuel pump and the O2 sensor heater. It gets turned on when the FW is rotating >200RPM or when cranking (+12V to pin 4

I've chased the wiring and believe that the DME relay is connected as per a stock 3.2.
All the Bentley DME troubleshooting checks are OK

- You found a damaged resistor inside the DME related to pin 4. Pin 4 is the input that senses when the engine cranks (key in START) and then turns the 2nd stage of the DME relay on.

The fact that that resistor is damaged means there is most likely more damage related to the DME relay control. The resistor itself won't burn unless the driver is also damaged. A non-working DME relay could explain why your fuel pump isn't running and you have issues.

mmm ok, bad news! But when i jump the fuel pump to a direct 12v supply it runs however I try to start the engine it still won't fire

- You get spark when cranking (tested by grounding a spark plug to the engine
- You get some running when spraying starter fluid into the intake

yep

My advice:

Verify that the ICV is vibrating when the key in RUN or START position. This tells you the DME has power and there is nothing wrong with the aftermarket alarm/immobilizer unit.

Yes, it vibrates. I have removed the immobilizer

Check for fuel pulses with a NOID light while cranking

I don't have a noid light. I've made a test light with a small 3 amp bulb which I'm told should work....it does flash during cranking

Check that the fuel pump is running when cranking. The best method is to measure voltage drop across the fuel pump fuse. Alternatively, you can measure voltage directly at the fuel pump. If all else fails check for fuel pressure. My guess is the fuel pump isn't running and that's why your car doesn't start.

I haven't checked voltage drop, so will do so. I can check pressure tomorrow when i grab an adapter

BTW, the DME can be checked and repaired - let me know if you need help.

Thanks Ingo

[byron911]

Dave
Thanks for your advice too.
No one has bought up the voltage regulator issue...sheez another thing to check!
I've done the shorting trick for the pump to check volume and this is good
I'll let you know how tomorrows pressure tests go
Greg

[ischmitz]

Greg,

From your response it wasn't entirely clear so I'll ask:

You tested the fuel pump by jumpering it. Good.

Did you also crank while the jumper was in place?

And another question just to be sure: If the jumper was in the DME relay socket did you make sure that you powered both stages of the DME relay (ICV was vibrating & you verified fuel pulses)?

I'm still trying to unify all your observations with one failure. And so far it points to your fuel pump (controlled by the DME relay) not running. This would also be in line with the damage inside the DME.

Of course you could have more than one failure at the same time but most times one component failed.

Ingo

[kidrock]

FWIW, I once had a no-start issue and proceeded through all the tests and swore that my fuel pump was "running", which it was...but not actually sending fuel. Replaced pump, car started.

Sometimes it's the simple stuff. Hopefully, this is your case as well. Good luck, you have a lot of experienced contributors giving you great advice.

[byron911]

Greg,

From your response it wasn't entirely clear so I'll ask:

You tested the fuel pump by jumpering it. Good.

Did you also crank while the jumper was in place? No

And another question just to be sure: If the jumper was in the DME relay socket did you make sure that you powered both stages of the DME relay (ICV was vibrating & you verified fuel pulses)?
No, I just jumped the pump to verify that it was running. I see my mistake....without the relay plugged in there's no pulse only fuel pumping...

I'm still trying to unify all your observations with one failure. And so far it points to your fuel pump (controlled by the DME relay) not running. This would also be in line with the damage inside the DME.

Of course you could have more than one failure at the same time but most times one component failed.

Ingo

To summarise todays checks...

I tested the fuel pressure. Is was 35psi during cranking and held 15psi 15 mins after, so that's a tick. This was done with the key start ie no jumping at the DME terminal

A new DME relay arrived in the post, so I plugged it in (I was pretty confident the old one is ok)

I tried to start the car again and same as yesterday, it's coughing trying to start but no cigar....

I noticed a small fuel leak around #3 injector, it looks like fuel is getting past the O rings, buy the injectors were tested and had new o rings fitted a few weeks back.

I also tried the timing light to confirm spark is good and it is firing at TDC #1 ok

I now need to check that the pump is running whilst cranking!!

this is pointing to the ECU as you suggest....

[mysocal911]

Originally Posted by byron911

I tried to start the car again and same as yesterday, it's coughing trying to start but no cigar....
I now need to check that the pump is running whilst cranking!!

You might try jumping the temp sensor connector with a paperclip to eliminate an open
sensor causing a flooded engine, i.e. after all testing that's been done to this point.
You can also use a noid light to check the injectors' firing with & without the temp
sensor plugged in, i.e. the noid light should get brighter with the temp sensor disconnected.

Originally Posted by byron911

this is pointing to the ECU as you suggest....

Not yet.

[ischmitz]

Greg,

I'm still puzzled by your data. You say fuel pressure was 35 psi during cranking. That sounds about right (spec is 36 psi, engine off, fuel pump jumpered). It wasn't clear whether this was due to residual pressure from jumpering the pump prior or because the pump ran during cranking. Further you say you are going to check if the pump is running while cranking.... so you are not sure either?

FYI, the Porsche WSM calls for several checks for the fuel system:

- static fuel pressure with engine off: 36psi
- residual pressure: >14.5psi after 20 minutes
- fuel delivery rate 0.85 liter in 30 seconds


Sounds like you have done (1) and (2). Maybe check (3) delivery rate while you are at it.

I'd still be curious to verify that the DME relay is switching correctly. For the first stage it is easy to just listen to the relay while turning the key to RUN. Every time you turn the key to RUN you will hear it click. I believe that is working as your ICV comes on fine.

For the second stage the check is a little more difficult because of the noise from the starter. The Porsche WSM suggests an assistant listening to the pump while cranking the engine. Alternatively, you could try to place your hand on the DME relay and see if you can feel it click while cranking. Or you could temporarily disconnect the yellow spade connector at the starter relay. This will prevent the starter solenoid from kicking in.

As a matter of fact you can turn the key to RUN, disconnect the yellow spade connector from its terminal at the starter and then momentarily touch it to the big red wire on the starter relay. This is equivalent to putting the key in START (energizing terminal 50). You should hear the fuel pump running right there.

A little safer: Get back up and turn the key to START and you will hear the second click of the relay and the whirr of the fuel pump coming on. If one or both don't happen you found a critical issue: Its either the DME relay (not very likely as you tested two, but not unheard of either) or the DME itself because you have tested the fuel pump can run.

On a side note: Rather than shifting towards other tests now I'd follow one lead to the end first. Keep in mind you found damage on the PCB inside the DME and it's highly questionable that replacing R750 is a sufficient repair. Once you confirm that you have the fuel pump running while cranking and decent fuel pressure it's time to move to the next set of tests.

Ingo

[silverc4s]

Would be good to either: try your ecu in a running car, or : try a known good ecu in your car. Of course you need a friend with a ecu or a car to loan to do this, where are you?

[silverc4s]

I'm guessing somewhere in Canada...

[ischmitz]

Originally Posted by silverc4s

Would be good to either: try your ecu in a running car, or : try a known good ecu in your car. Of course you need a friend with a ecu or a car to loan to do this, where are you?

hm - this will trigger a lengthy discussion as to whether swapping one into the other is safe. Bottom line, depending on the fault both can potentially cause more damage. In this case I would be a little concerned that the car in question doesn't have the original wiring. So 'd probably try the DME in question in a good car rather than the other way around.

But before that there are more tests that the OP can do to narrow it down.

ingo

[byron911]

Ingo

I'm still puzzled by your data. You say fuel pressure was 35 psi during cranking. That sounds about right (spec is 36 psi, engine off, fuel pump jumpered). It wasn't clear whether this was due to residual pressure from jumpering the pump prior or because the pump ran during cranking. Further you say you are going to check if the pump is running while cranking.... so you are not sure either?

FYI, the Porsche WSM calls for several checks for the fuel system:

- static fuel pressure with engine off: 36psi
- residual pressure: >14.5psi after 20 minutes
- fuel delivery rate 0.85 liter in 30 seconds


Sounds like you have done (1) and (2). Maybe check (3) delivery rate while you are at it

I initially wasn't sure about pump running during cranking because of noise from the starter. I was working alone so no-one was around to get under the car and listen to the pump. I can get a helper to check today, but that's unnecessary now as the pressure gauge is registering 36psi during cranking...it MUST be running?

The pressure was in spec during both jumping AND cranking. Also I did a delivery volume check and it was OK too.


I'd still be curious to verify that the DME relay is switching correctly. For the first stage it is easy to just listen to the relay while turning the key to RUN. Every time you turn the key to RUN you will hear it click. I believe that is working as your ICV comes on fine.

Yes it's clicking

For the second stage the check is a little more difficult because of the noise from the starter. The Porsche WSM suggests an assistant listening to the pump while cranking the engine. Alternatively, you could try to place your hand on the DME relay and see if you can feel it click while cranking. Or you could temporarily disconnect the yellow spade connector at the starter relay. This will prevent the starter solenoid from kicking in.

The Bentley manual also suggests back probing the relay whilst it's plugged in and ignition is on:
a. batt voltage at terminal 87...YES, first relay has energised
b. whilst cranking test for ground at 85b...YES
c. whilst cranking test for batt voltage at 87b....YES (this seems unnecessary as we know pump is switching on)



As a matter of fact you can turn the key to RUN, disconnect the yellow spade connector from its terminal at the starter and then momentarily touch it to the big red wire on the starter relay. This is equivalent to putting the key in START (energizing terminal 50). You should hear the fuel pump running right there.

A little safer: Get back up and turn the key to START and you will hear the second click of the relay and the whirr of the fuel pump coming on. If one or both don't happen you found a critical issue: Its either the DME relay (not very likely as you tested two, but not unheard of either) or the DME itself because you have tested the fuel pump can run.

On a side note: Rather than shifting towards other tests now I'd follow one lead to the end first. Keep in mind you found damage on the PCB inside the DME and it's highly questionable that replacing R750 is a sufficient repair. Once you confirm that you have the fuel pump running while cranking and decent fuel pressure it's time to move to the next set of tests.

Yes, I get it thankyou. I'm pretty confidant that the pump is OK and DME relay. I'll go back and triple check as you suggest.

I want to make sure that it's definitely the ECU as it is a pretty expensive replacement with only one place here in Australia that offers an exchange/repair service. Unfortunately mine has a 911chips chip fitted and the company here won't refit this it and give a warranty on the new refurbished unit. The current ECU originally came from the USA as its got a "specialized ECU repair" sticker on it

I still may send it to the US even with our sinking dollar!


Get back to you later...

[byron911]

Bill
I'm a long way from Canada mate....Australia

[silverc4s]

Greg,
Yes, and your DME is on the wrong side of the car too...

I think trying your DME in another car is not very likely to harm any of the rest of that car, and will tell you very quickly of your DME is good or bad.
I agree with Ingo, if you found and replaced a bad resistor, well that was a symptom, not a cause of your troubles. Resistors burn because too much current is forced thru for some reason...
Hope you get to the root cause soon.