Memorial Day diagnosis

[RDM]

I was on my way to a Memorial Day service at a US cemetery not far across the border in France when my engine just died. Instantaneous complete power loss, three times accompanied by a very loud backfire.

The car would always restart and run for a few seconds to a few minutes after each episode. By experimenting I found that turning the key off, then on while still rolling (no need to run the starter or take it out of gear) would make the engine run again.

The day was very hot for here, 90 or so.

I headed for home as the problem got worse. I finally stopped at a different US cemetery to pay my respects, let the car cool off, and pick my friend Jόrgen's brain by telephone. I thought electrical part of the ignition switch, as turning the key off and on fixed the problem and the backfiring indicated there was lots of gas available. Or maybe the CDI box. Jόrgen suggested the fuel pump relay, and since I had a door-pocket full of relays I purchased from a fellow Pelican, I swapped that out.

The car took me home without further incident. Two questions:

1. IT seems like there are two possible explanations for the problem, the fuel pump relay or heat causing some other electrical problem. Have you seen these symptoms before? If so, what was it?

2. On the way back, I drove about 100, and it was a very hot day. Would an oil temperature close to 250 be normal? I've got the 28 tube brass cooler.

Thanks, and some pictures to say thanks for those who gave all.




King David, Charlemagne, King Arthur, and George Washington

[JJ 911SC]

Originally Posted by RDM

... or heat causing some other electrical problem. Have you seen these symptoms before? If so, what was it?...

Starter.

WR1-INT - Hot Starter Relay Kit;Pelican Parts - European Automotive Parts and Accessories - Porsche • BMW • Mercedes • Volkswagen • Audi • Saab • Volvo • MINI

[RDM]

Originally Posted by JJ 911SC

Starter.

WR1-INT - Hot Starter Relay Kit;Pelican Parts - European Automotive Parts and Accessories - Porsche • BMW • Mercedes • Volkswagen • Audi • Saab • Volvo • MINI

How would the starter make the motor die?

[JJ 911SC]

Originally Posted by RDM

How would the starter make the motor die?

Mis read your problem but its a good Mod to do

[Nick Triesch]

I was on a trip a few years ago in our local mountains. A very hot day. Car would not start at a road side stand. I push started it home and took a rubber mallet to the starter and smacked it a few times. and took off and cleaned all my wires to the starter. Really dirty. Anyway, has been fine years later.

[Bob Kontak]

Originally Posted by RDM

The day was very hot for here, 90 or so.

Beautiful pictures.

The only time my relay failed was on the expressway on a miserably hot day in Charlotte, North Carolina.

Sometimes my relay would wiggle out enough to break the connection so that was my first check. Had not backed out. I put a black one in, stolen from another spot and it ran fine for the 150 miles to my pals house. He has a newer 930 and had a stash of backup red ones and gave me one.

I put the black one back and tried the red "failed" one and could not get it to fail but replaced anyways.

[RDM]

I spread the contacts on the red one and put it back in when I got home. I still worry that it's a spark problem caused by heat. Maybe the spare CDI box goes with me when I travel now....

We're definitely very blessed to live where we do.

I just had a close friend move to Tipp City OH. How far is that from you, Bob?

Originally Posted by Bob Kontak

Beautiful pictures.

The only time my relay failed was on the expressway on a miserably hot day in Charlotte, North Carolina.

Sometimes my relay would wiggle out enough to break the connection so that was my first check. Had not backed out. I put a black one in, stolen from another spot and it ran fine for the 150 miles to my pals house. He has a newer 930 and had a stash of backup red ones and gave me one.

I put the black one back and tried the red "failed" one and could not get it to fail but replaced anyways.

[rwest]

I'm hardly an expert, but the backfires and hot issues sure point to ignition to me.

250 degrees on a car with an oil cooler is pretty hot even in ninety degree temps. I believe improper ignition settings can lead to hot running- not positive and hopefully the more knowledgeable folks will chime in.

How are the condition of your wires, rotor, cap and plugs? I don't think you have points in yours.

What brand CDI box do you have? I chased intermittent starting/ running issues on a Permatune box that was extremely frustrating. Soon as you got equipment hooked up to test, it would start! I was driving around with a timing light and oscilloscope wires attached and tucked safely in the compartment so I could hook up fast and anywhere.

[Bob Kontak]

Originally Posted by RDM

I just had a close friend move to Tipp City OH. How far is that from you, Bob?

Tipp City is about three hours away. Southwest. That's near where Dave Chappelle lives. Close to Cincinnatti.

[GothingNC]

Coil going bad?

[sugarwood]

Can you drive around the block?
Why not put your old relay back in and see if the problem comes back.

[ischmitz]

Bosch CDI have a known failure mode that could do what you describe. When they get very hot they lock up and you loose all spark. Power-cycling (turn ignition key off, then back to ON) will reset this and they become operational again) Depending on the temperature the box will lock up shortly thereafter again. And this behavior is temperature-dependent. If you let it cool off for 30 minutes or ambient is not too high it might run like a champ for a long time. But if it's hot outside it might happen as early as 30 minutes into your drive and then every minute.

Here is how to diagnose it: You need two people or a perfect ear:

Get the car into a condition where it looses all power. Coast to a stop and do not turn the ignition off. Open the rear hood and listen to the whine of the CDI box. You will hear a tone with about 4.5kHz. While you listen have a second person turn the ignition off and right back on. If the note (tone) of the whine changes to a lower tone (~ 3.6kHz) you have identified a lock-up condition. In locked up condition the note is higher in pitch because the DC/DC converter works against a shorted SCR and once you power-cycle the pitch changes back to a lower note because the SCR is turned off again.

If you confirm this your CDI box needs repair.
Ingo

[RDM]

Originally Posted by sugarwood

Can you drive around the block?
Why not put your old relay back in and see if the problem comes back.

I did and it does drive around the block. So the problem is heat. The question is which electrical component is affected?

Originally Posted by ischmitz

Bosch CDI have a known failure mode that could do what you describe. When they get very hot they lock up and you loose all spark. Power-cycling (turn ignition key off, then back to ON) will reset this and they become operational again) Depending on the temperature the box will lock up shortly thereafter again. And this behavior is temperature-dependent. If you let it cool off for 30 minutes or ambient is not too high it might run like a champ for a long time. But if it's hot outside it might happen as early as 30 minutes into your drive and then every minute.

Here is how to diagnose it: You need two people or a perfect ear:

Get the car into a condition where it looses all power. Coast to a stop and do not turn the ignition off. Open the rear hood and listen to the whine of the CDI box. You will hear a tone with about 4.5kHz. While you listen have a second person turn the ignition off and right back on. If the note (tone) of the whine changes to a lower tone (~ 3.6kHz) you have identified a lock-up condition. In locked up condition the note is higher in pitch because the DC/DC converter works against a shorted SCR and once you power-cycle the pitch changes back to a lower note because the SCR is turned off again.

If you confirm this your CDI box needs repair.
Ingo

Thank you. This is extremely helpful. What you describe was exactly my car's behavior. Fortunately for the car and unfortunately for the diagnosis, it sounds like our hot weather is done for a while.

[steely]

Awesome pics - thanks for them btw

[boyt911sc]

Dru,

What is the ID number of your ECU? I could lend you one of my ECU's if you decide to send your ECU to Ingo so you could still drive the car while the ECU is being tested and evaluated here in the USA.



PM me whenever you would need one. I have about a dozen of these ECU's and I don't even own a car with a lambda system.

Tony

[RDM]

Tony,

Thank you for your generous offer. Do you think it's the Lambda box? Ingo wrote about the CDI, not the ECU. Fortunately I have a spare CDI, and fortunately we don't get that hot that often.

If it turns out that I need an ECU I will be in touch.

[boyt911sc]

Originally Posted by RDM

Tony,

Thank you for your generous offer. Do you think it's the Lambda box? Ingo wrote about the CDI, not the ECU. Fortunately I have a spare CDI, and fortunately we don't get that hot that often.

If it turns out that I need an ECU I will be in touch.

Dru,

That's my mistake. I remember Ingo mentioned about the CDI but for some strange reason, I offered you my ECU. Anyway, my offer still stands.



I have more of these ECU's and CDI's if you would ever need to borrow one.

Tony

[RDM]

Originally Posted by rwest

I'm hardly an expert, but the backfires and hot issues sure point to ignition to me.

250 degrees on a car with an oil cooler is pretty hot even in ninety degree temps. I believe improper ignition settings can lead to hot running- not positive and hopefully the more knowledgeable folks will chime in.

How are the condition of your wires, rotor, cap and plugs? I don't think you have points in yours.

What brand CDI box do you have? I chased intermittent starting/ running issues on a Permatune box that was extremely frustrating. Soon as you got equipment hooked up to test, it would start! I was driving around with a timing light and oscilloscope wires attached and tucked safely in the compartment so I could hook up fast and anywhere.

I'd be interested in more input on the temperature issue. Would lean running due to an air leak cause this?

The CDI is a Bosch OEM box. I've heard too many stories. The rest of the ignition system is under 10,000 miles.

[Bob Kontak]

Dru,

Is yours a US or ROW car? Asking O2 sensor or not.

GothingNC asks about coil. Replace yours even if you can't prove it is bad.

[rwest]

Originally Posted by RDM

I'd be interested in more input on the temperature issue. Would lean running due to an air leak cause this?

The CDI is a Bosch OEM box. I've heard too many stories. The rest of the ignition system is under 10,000 miles.

Yes, a lean engine runs hotter, you might want to look into that as well.