HELP! car won’t start

[Ian Comerford]

I do still love my car thought….

[carrpet]

On 10/04/2022 at 18:34, PeterK said:

How fast does the starter spin ?

Could there be so much current draw that the starting voltage is being dragged down too far ?  Unlikely, as I assume the CDI will still spark at 10-11 volts,  whereas the starter might be suffering by then

 

Good luck Ian,

I think there may be something to think about here. Ian has the Brise uprated 2kw starter installed and an Odyssey battery with a CCA (Cold Cranking Current) of 170A.

Jonny Hart's work has shown that even with a standard 1.5kW starter motor the cranking current will be 380A dropping to 180A (ignition disconnected). During cranking the voltage may drop significantly even though the starter is turning the engine over acceptably. The CCA specification is based on a voltage drop to 7.2v although at sub zero temperatures. So there is a possibility that a combination of

1) Brise Starter Motor (30% higher power than standard)

2) A smaller than specification battery (although high quality and well tried) but with CCA significantly exceeded = unknown voltage drop

3) A CR CDI+ box.

may push beyond workable limits with a cold engine.  I wonder how many of us have tested that combination ?

The car bump starts easily, possibly because there is no starter motor load to drop the battery voltage and the ignition is very happy !

I agree with all of the comments on the CSV. I have permanently disconnected mine !

I hope that helps and get back in one piece

Peter

Edited April 12, 2022 by carrpet

[Ian Comerford]

Thanks Peter, useful analysis and worth maybe asking Jonny for some real subject knowledge comment.  Another thing that confuses slightly is when it first exhibited this non-start scenario shortly before leaving for France I swapped out the red fuel pump relay for the electric window one and it fired several times but wouldn’t run.  Any thoughts on what this means?

[proporsche]

any chance that the cold start valve is plug with an emergency plug which goes on the sensor plate? Also the fuel pump relay should really be red..

[carrpet]

51 minutes ago, Ian Comerford said:

Thanks Peter, useful analysis and worth maybe asking Jonny for some real subject knowledge comment.  Another thing that confuses slightly is when it first exhibited this non-start scenario shortly before leaving for France I swapped out the red fuel pump relay for the electric window one and it fired several times but wouldn’t run.  Any thoughts on what this means?

Did you swap it back Ian ?

All I can say is that between the two of us we have enough relays to nail this one. We could insert a suspect relay into my car and see if this creates a similar issue ?

[Chris T]

The emergency plug Ivan refers to is a micro switch on the airflow plate designed to stop fuel flowing if the sensor plate does not move. Mine was faulty and they are NLA from Porsche although I’m sure they are a standard Bosch part back in the day. I simply disconnected mine and it now starts reliably. It’s on the firewall side of the airflow sensor, blue plug.

[carrpet]

5 minutes ago, Chris T said:

The emergency plug Ivan refers to is a micro switch on the airflow plate designed to stop fuel flowing if the sensor plate does not move. Mine was faulty and they are NLA from Porsche although I’m sure they are a standard Bosch part back in the day. I simply disconnected mine and it now starts reliably. It’s on the firewall side of the airflow sensor, blue plug.

Its in the fuel pump circuit

[Ian Comerford]

9 minutes ago, carrpet said:

Its in the fuel pump circuit

This is what I thought and does lead to the conclusion that the CSV is part of the problem as the car nearly started with the window relay in place.  

[carrpet]

36 minutes ago, Ian Comerford said:

This is what I thought and does lead to the conclusion that the CSV is part of the problem as the car nearly started with the window relay in place.  

The CSV is not in the fuel pump circuit though it is driven via the starter yellow wire from the ignition switch which David Moss referred to so not sure I follow your logic about the fuel pump relay ?

[Jon Miller]

Regarding the relays, as far as I know the only difference between the red and black relays is that the red ones are designed to take a higher load for an extended period of time.

I've only speed read this thread so apologies if I've missed something, but if the car starts easily with a bump start then it suggests to me that the problem is a low voltage or bad earth problem, The starter will draw a lot of current and if you have electrical problems somewhere then the starter takes power away from the ignition and leaves you with a weak spark and no start, yet a bump start will work every time as the ignition etc gets all the available battery power.

Have you checked your battery voltage in the mornings?

Bad ignition electrics could also give you the stuttering you are experiencing, normally at lower revs under load, (trying to accelerate from lower revs in a higher gear for example, yet when you drop a gear it's fine)

Cheers

Jon

 

[PeterK]

Just fyi 😇 and in my totally non-technical way, the red relays have a diode on them to prevent back emf or chatter when the power is removed.  It reduces the risk of the ‘safety switch’ burning out, as any back emf can apparently reach a couple of hundred volts.

[Jonny Hart]

^ No and kinda.  Yes, the red relay has a flyback diode to prevent voltage spikes caused by the relay coil when deactivated.   But why?     Well, it is to protect a sensitive device like a transistor that might be activating the relay.    But there are no transistors operating the fuel pump relay?  Not on a U.K. car but on a car with emissions equipment there is a primitive ECU which can switch off the fuel pump.   I believe that is the only reason for the red relay and Porsche just made it standard as there is no harm in having the diode on a non ECU car. 
 

——

 

Ok, here is a possibility.    On an original Bosch CDI unit, the spark output is proportional to the battery voltage.    So if the battery dips, the spark is weaker. 
 

We didn’t like that so with CDI+ we designed a circuit that produces a constant output at all battery voltages down to around 8v.   This wasn’t an easy thing to do and some of the early units had to use a very specific ceramic resistor in the circuit.  I do remember that a few of these units did get returned and we found that the mounting screws for the resistor were overtightened and had cracked it which caused the low voltage circuit not to work.   This would result in no spark below 10v instead of 8v.   
 

Ian’s CDI+ is a early unit bought used.  We did go through it but there is a possibility that the component has cracked after we tested it.  In later versions we designed out the troublesome device. 
 

Bear in mind though that I ran my own car for a year prior to the low voltage mod and only discovered the issue after the cad had sat for 3 or 4 weeks and the battery was quite low. 
 

 

 

[World Citizen]

Four engineers get into a car. The car won’t start.

The mechanical engineer says:
“It’s a broken starter”

The electrical engineer says:
“Dead battery”

The chemical engineer says:
“Impurities in the gasoline”

The IT engineer says:
“Hey guys, I have an idea, how about we all get out of the car and get back in”

[GaryH]

2 hours ago, World Citizen said:

The IT engineer says:

“Hey guys, I have an idea, how about we all get out of the car and get back in”

Fifth guy: Software Engineer (no such thing as an IT 'engineer')  says:

"Bet it's the hardware guy's fault !"

Edited April 13, 2022 by GaryH

[GaryH]

Talking of mechanics....

A puffin was driving home, when smoke starts pouring out of his exhaust, so he pulls in at a garage in Seahouses. The mechanic says he can take a look, but it will take a couple of hours.
The puffin takes a walk along the harbour and down to the beach, buys a 99, looks in a couple of shops, then heads back to check on his car.
The mechanic says "looks like you've blown a seal".
The puffin wipes his beak and and answers "no, it's just ice cream".

[Bugs 77]

Boom boom.

[Ian Comerford]

11 hours ago, carrpet said:

The CSV is not in the fuel pump circuit though it is driven via the starter yellow wire from the ignition switch which David Moss referred to so not sure I follow your logic about the fuel pump relay ?

The logic, if indeed that’s the right word, was in the difference(s) between the two relays and  fuel pump relay was causing a problem with the CSV that the window relay could not because it wasn’t wired/designed that way.  So maybe it’s not that.

10 hours ago, Jon Miller said:

Regarding the relays, as far as I know the only difference between the red and black relays is that the red ones are designed to take a higher load for an extended period of time.

I've only speed read this thread so apologies if I've missed something, but if the car starts easily with a bump start then it suggests to me that the problem is a low voltage or bad earth problem, The starter will draw a lot of current and if you have electrical problems somewhere then the starter takes power away from the ignition and leaves you with a weak spark and no start, yet a bump start will work every time as the ignition etc gets all the available battery power.

Have you checked your battery voltage in the mornings?

Bad ignition electrics could also give you the stuttering you are experiencing, normally at lower revs under load, (trying to accelerate from lower revs in a higher gear for example, yet when you drop a gear it's fine)

Cheers

Jon

 

Thanks for the input Jon, I thought we had something until I read Jonny's reply.  The battery doesn’t seem weak though, it feels like it is turning over the starter quite well.  Guess I may have to rely on bump starts to get home, which isn’t actually that bad, just involves a bit of planning when parking for the night.  It always starts when warm.

9 hours ago, Jonny Hart said:

^ No and kinda.  Yes, the red relay has a flyback diode to prevent voltage spikes caused by the relay coil when deactivated.   But why?     Well, it is to protect a sensitive device like a transistor that might be activating the relay.    But there are no transistors operating the fuel pump relay?  Not on a U.K. car but on a car with emissions equipment there is a primitive ECU which can switch off the fuel pump.   I believe that is the only reason for the red relay and Porsche just made it standard as there is no harm in having the diode on a non ECU car. 
 

——

 

Ok, here is a possibility.    On an original Bosch CDI unit, the spark output is proportional to the battery voltage.    So if the battery dips, the spark is weaker. 
 

We didn’t like that so with CDI+ we designed a circuit that produces a constant output at all battery voltages down to around 8v.   This wasn’t an easy thing to do and some of the early units had to use a very specific ceramic resistor in the circuit.  I do remember that a few of these units did get returned and we found that the mounting screws for the resistor were overtightened and had cracked it which caused the low voltage circuit not to work.   This would result in no spark below 10v instead of 8v.   
 

Ian’s CDI+ is a early unit bought used.  We did go through it but there is a possibility that the component has cracked after we tested it.  In later versions we designed out the troublesome device. 
 

Bear in mind though that I ran my own car for a year prior to the low voltage mod and only discovered the issue after the cad had sat for 3 or 4 weeks and the battery was quite low. 
 

 

 

Thanks Jonny, appreciate the feedback.  I assume it’s best to return the CDI+box to you when I get back and ask you to check it out for this potential fault.  It would be good to know one way or the other.  Thank you

[SilverWT]

11 hours ago, Jonny Hart said:

and the battery was quite low. 

As the original user/tester of "CDI+ unit No 1" I can corroborate the battery needing to be low to get this effect.

During the testing phase I noticed some hesitancy starting a couple of times, but it was only when the starter sounded sluggish due to a low battery (the car had developed an alternator issue).

Jonny investigated and made a mod in the unit and it has been perfect in all the years since, regardless of battery condition.

 

Mark

[Ian Comerford]

Thanks Mark, the battery doesn’t seem to be low but I can’t test to confirm.  I do carry some spare parts on trips like this, things such as a spare coil, a set of relays etc and I also have my old CDI unit in the car just in case.  I guess I could swap it out and see what happens, but would need Jonny to confirm I don’t need to do anything with the timing?  Thank you

[carrpet]

3 hours ago, Ian Comerford said:

Thanks Mark, the battery doesn’t seem to be low but I can’t test to confirm.  I do carry some spare parts on trips like this, things such as a spare coil, a set of relays etc and I also have my old CDI unit in the car just in case.  I guess I could swap it out and see what happens, but would need Jonny to confirm I don’t need to do anything with the timing?  Thank you

Hi Ian,

The timing shift (4-5 degrees) on the CDI+ occurs when you change the CDI+ mode to incorporate the in-built "programmable advance curve" even if the curve is flat zeros. I have done this under Jonny's guidance in the last 3 months. Your unit is not set to do this at the moment and you are using mechanical centrifugal advance so it should not be an issue.

Clearly I am sure you will want Jonny to corroborate this !

However you should bare in mind that as the original CDI unit's spark quality is proportional to voltage,  if the voltage is dropping to say 9.0V during cranking you will get a spark but it may be a weak spark ?

When are you back in Blighty ?

Peter

[Jonny Hart]

No changes to timing needed unless you locked the dizzy.   Pretty sure you didn’t.  

[carrpet]

Ian,

For a reference point,  I have just done a cranking test on my 930 which hasn't been started for over a week. it is 12C in my garage. Cranking voltage dropped from 13.5 v to 12.17 volts (Lithium Polymer battery) car started normally (no CSV connected).

General wisdom seems to be that 9.5V - 10V is normal for a healthy lead acid battery during cranking from cold. CCA limit not exceeded.

Peter

Edited April 13, 2022 by carrpet

[Lesworth]

18 minutes ago, carrpet said:

Ian,

For a reference point,  I have just done a cranking test on my 930 which hasn't been started for over a week. it is 12C in my garage. Cranking voltage dropped from 13.5 v to 12.17 volts car started normally (no CSV connected).

General wisdom seems to be that 9.5V - 10V is normal for a healthy lead acid battery during cranking from cold. CCA limit not exceeded.

Peter

What app are you using for that test, Peter?

[carrpet]

1 minute ago, Lesworth said:

What app are you using for that test, Peter?

I am using a BM2 battery monitor with bluetooth which talks to an App called BM2 Battery Monitor (IOS and Android).

You can buy the BM2 on Amazon for £27

Battery Monitor BM2 device for Cars & Campervans 12V Battery/leisure battery tester Compatible with Android iOS and Ipad with bluetooth 4.0 and above. : Amazon.co.uk: Automotive

or directly from China

12V Car Battery Monitor Tester Bluetooth for iOS & Android BM2 Battery Tester | eBay

for £18.64

[Lesworth]

Thanks, that looks very useful!