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> Understanding Bosch Jetronic Fuel Injection, (and some other questions)
IanMan
post Nov 11 2017, 09:51 AM
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Hello all. I enjoy spending my time reading about how things work and I'm kind of confused on the Jetronic fuel injection system in the Countach as well as ignition. Mostly everything I read about it says that it is an electronic system, but I've read other people saying it's technically a mechanical system.

First off, let me say this, what a complicated design, lol. It did it's job but it seems like so much could go wrong with it. What I'm having trouble understanding is does the system constantly spray into each cylinder, or did it have a way of knowing which cylinder to inject to before it is ignited? Since there is not crank position sensor, how does the car know which cylinder to ignite in what order?

Thanks.

Ian


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QUOTE (capt_chaos @ May 19 2017, 12:59 PM) *
That said I seen some pictures of people on this website and they do not look like they have evolved properly.
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abolfaz
post Nov 11 2017, 10:45 AM
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Jettronic is mechanical with a few electronic bits for cold start and warm up regulating.


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Jalpa_Mike
post Nov 11 2017, 02:50 PM
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K-Jetronic is a mechanical fuel injection. It was a big thing back in the day.... it was used on Saab, Volvo, Mercedes, Porsche, DeLorean, BMW, Ferrari and many other cars during the 70’s and 80’s.

The only electrical elements in the system are:

1. Cold Start injectors which are operated via a thermo-time switch located in the thermostat housing. When the engine is cold, the thermo-time switch sends a signal to a relay with opens and allows the cold start injectors to operate. Once the engine is warmed, the thermo-time switch closes, the relay shuts off the power to the cold start injectors.

2. The O2 sensors in the exhaust send a signal to the respective computer box (behind the right rear trunk panel) which causes the frequency valves (basically an additional fuel injector) to open or close depending on whether the mixture is too rich or lean.

The fuel injectors on the Countach have a spring inside them and are fopened by fuel pressure. This is one of the main reasons fuel pressure is so important on K-Jetronic cars.

Attached is a photo from the K-Jetronic service manual describing the fuel injector with a nice diagram.

Mike
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Attached File  EE988AB5_E5FE_4F15_AEA0_5EE6B471DA99.jpeg ( 714.83K ) Number of downloads: 0
 


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'86 Lamborghini Countach 5000QV #GLA12002
'05 Maserati Quattroporte "Sport"
'16 Mazda CX-5 Grand Touring
'10 Jeep Wrangler "Sahara"
'83 Lamborghini Jalpa #DLA12071 (Sold 10-22-09, but not forgotten)

Aerodynamics are for people who can't build engines. -- Enzo Ferrari
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IanMan
post Nov 11 2017, 08:41 PM
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That actually clears up a lot. I remember working on my Porsche 924 (just barely) when I was a teenager. Some of the parts seem very familiar when looking at the Countach.

Thank you for the very detailed explanation Mike! I really appreciate it.

Is the engine run 100% off the cold start injectors until up to temp?

Would it be possible to remove the entire Jetronic injection system and instead install modern Bosch fuel injectors where the cold start fuel injectors go? I understand that multiple people have built modified injection systems, but I wonder if this would would work. A throttle body would have to be added at the beginning of the plenums to control air flow of course. I know this would have to be paired up with an electronic ignition system, but is there enough room for an adequate amount of fuel to travel through the passages where the cold start injectors go? If not, I wonder if they could be bored out.


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QUOTE (capt_chaos @ May 19 2017, 12:59 PM) *
That said I seen some pictures of people on this website and they do not look like they have evolved properly.
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Jalpa_Mike
post Nov 11 2017, 09:14 PM
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QUOTE (IanMan @ Nov 11 2017, 08:41 PM) *
That actually clears up a lot. I remember working on my Porsche 924 (just barely) when I was a teenager. Some of the parts seem very familiar when looking at the Countach.

Thank you for the very detailed explanation Mike! I really appreciate it.

Is the engine run 100% off the cold start injectors until up to temp?

Would it be possible to remove the entire Jetronic injection system and instead install modern Bosch fuel injectors where the cold start fuel injectors go? I understand that multiple people have built modified injection systems, but I wonder if this would would work. A throttle body would have to be added at the beginning of the plenums to control air flow of course. I know this would have to be paired up with an electronic ignition system, but is there enough room for an adequate amount of fuel to travel through the passages where the cold start injectors go? If not, I wonder if they could be bored out.


No, the cold start injectors just dump more fuel into the intake manifolds along with the fuel from the injectors. So, it just runs rich until the car starts getting warm. Funny thing, I know several owners who just unplug the connectors and not use the cold start injectors and the car starts and runs just fine.

Just as a test one time, I pulled one of mine off and put a glass bottle under it. I started the car and it was pretty interesting to see the fuel coming out of it. It was a nice atomized spray pattern, so I knew it was OK. After the car warmed up I started the car again and no fuel came out of the cold start injector, so I knew everything with the thermo-time switch was OK.

BTW, if your Thermo-Time switch ever goes bad. You don’t have to pay Lamborghini the outrageous $600+, its the same switch used on the Alfa Romeo GTV6 and can be purchased for around $130.

Mike


--------------------

'86 Lamborghini Countach 5000QV #GLA12002
'05 Maserati Quattroporte "Sport"
'16 Mazda CX-5 Grand Touring
'10 Jeep Wrangler "Sahara"
'83 Lamborghini Jalpa #DLA12071 (Sold 10-22-09, but not forgotten)

Aerodynamics are for people who can't build engines. -- Enzo Ferrari
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IanMan
post Nov 11 2017, 09:35 PM
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QUOTE (Jalpa_Mike @ Nov 11 2017, 09:14 PM) *
No, the cold start injectors just dump more fuel into the intake manifolds along with the fuel from the injectors. So, it just runs rich until the car starts getting warm. Funny thing, I know several owners who just unplug the connectors and not use the cold start injectors and the car starts and runs just fine.

Just as a test one time, I pulled one of mine off and put a glass bottle under it. I started the car and it was pretty interesting to see the fuel coming out of it. It was a nice atomized spray pattern, so I knew it was OK. After the car warmed up I started the car again and no fuel came out of the cold start injector, so I knew everything with the thermo-time switch was OK.

BTW, if your Thermo-Time switch ever goes bad. You don’t have to pay Lamborghini the outrageous $600+, its the same switch used on the Alfa Romeo GTV6 and can be purchased for around $130.

Mike


Seems like a waste of fuel!

Back to my question though, do you not think modern injectors could be fitted in place of the cold starts with some modification or is it not in an ideal position?


Thanks for the tip! I've been reading up on replacement parts and are finding quite a few better if not cheaper replacements. Jason blog on his Countach restoration has a lot of good data!


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QUOTE (capt_chaos @ May 19 2017, 12:59 PM) *
That said I seen some pictures of people on this website and they do not look like they have evolved properly.
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Jalpa_Mike
post Nov 12 2017, 09:22 AM
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I have no idea..... I suppose anything is possible. With the introduction of the Diablo, they moved over to electronic fuel injection, so I wonder if someone could retrofit the Diablo system onto a Countach? Might be possibble......

Mike


--------------------

'86 Lamborghini Countach 5000QV #GLA12002
'05 Maserati Quattroporte "Sport"
'16 Mazda CX-5 Grand Touring
'10 Jeep Wrangler "Sahara"
'83 Lamborghini Jalpa #DLA12071 (Sold 10-22-09, but not forgotten)

Aerodynamics are for people who can't build engines. -- Enzo Ferrari
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IanMan
post Nov 12 2017, 10:30 AM
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QUOTE (Jalpa_Mike @ Nov 12 2017, 09:22 AM) *
I have no idea..... I suppose anything is possible. With the introduction of the Diablo, they moved over to electronic fuel injection, so I wonder if someone could retrofit the Diablo system onto a Countach? Might be possibble......

Mike


That would be really interesting to see.

I've been trying to find a webpage I saw a little while ago, but I can't find it. This guy was installing the modern BMW fuel injection system and ignition and coil packs from a 760LI V12 on a fuel injected Countach. I think he had to make modified plenums but I never saw the end result.


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QUOTE (capt_chaos @ May 19 2017, 12:59 PM) *
That said I seen some pictures of people on this website and they do not look like they have evolved properly.
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emilio
post Nov 13 2017, 03:03 PM
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QUOTE (Jalpa_Mike @ Nov 12 2017, 09:22 AM) *
I have no idea..... I suppose anything is possible. With the introduction of the Diablo, they moved over to electronic fuel injection, so I wonder if someone could retrofit the Diablo system onto a Countach? Might be possibble......

Mike


it has been done
there is a yellow qv FI in Italy running with diablo system since years


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IanMan
post Nov 13 2017, 03:25 PM
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QUOTE (emilio @ Nov 13 2017, 03:03 PM) *
it has been done
there is a yellow qv FI in Italy running with diablo system since years


Oh wow! Is it more powerful? Did they completely remove the K-Jetronic system?


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QUOTE (capt_chaos @ May 19 2017, 12:59 PM) *
That said I seen some pictures of people on this website and they do not look like they have evolved properly.
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Allan-Herbie
post Nov 13 2017, 03:46 PM
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QUOTE(emilio @ Nov 13 2017, 11:03 PM) *
it has been done
there is a yellow qv FI in Italy running with diablo system since years

No.. the yellow q.v. has a motec system. My first countach I converted to electromotive electronic fuel injection and distributorless ignition.


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IanMan
post Nov 13 2017, 03:52 PM
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QUOTE (Allan-Herbie @ Nov 13 2017, 03:46 PM) *
No.. the yellow q.v. has a motec system. My first countach I converted to electromotive electronic fuel injection and distributorless ignition.


I think the Electromotive system is pretty neat since you don't have to permanently afix anything to the motor like a crank position sensor.


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QUOTE (capt_chaos @ May 19 2017, 12:59 PM) *
That said I seen some pictures of people on this website and they do not look like they have evolved properly.
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Allan-Herbie
post Nov 13 2017, 06:42 PM
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QUOTE(IanMan @ Nov 14 2017, 12:52 AM) *
I think the Electromotive system is pretty neat since you don't have to permanently afix anything to the motor like a crank position sensor.

My first Countach with EFI would eat any Countach for lunch.


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emilio
post Yesterday, 01:05 AM
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QUOTE (Allan-Herbie @ Nov 13 2017, 04:46 PM) *
No.. the yellow q.v. has a motec system. My first countach I converted to electromotive electronic fuel injection and distributorless ignition.


the one in Italy has diablo plenums and trottle bodies
i seen yesterday owner and he confirmed that
it is a lamborghini mecanic since 25 years, his car is in Italy since 20 years or so

is not the same car as the yellow QV in the STates


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IanMan
post Yesterday, 10:01 AM
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QUOTE (emilio @ Nov 19 2017, 01:05 AM) *
the one in Italy has diablo plenums and trottle bodies
i seen yesterday owner and he confirmed that
it is a lamborghini mecanic since 25 years, his car is in Italy since 20 years or so

is not the same car as the yellow QV in the STates



That's awesome to hear! I take it the plenums just bolt right up? Do you have any photos? I'd love to see!


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QUOTE (capt_chaos @ May 19 2017, 12:59 PM) *
That said I seen some pictures of people on this website and they do not look like they have evolved properly.
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emilio
post Yesterday, 10:48 AM
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QUOTE (IanMan @ Nov 19 2017, 10:01 AM) *
That's awesome to hear! I take it the plenums just bolt right up? Do you have any photos? I'd love to see!


i have to ask him for pics - will try to have him send me by phone
otherwise i will do them personally, next time i am at his shop...i ususally go there once a month or so

he told me the car runs very well, really smooth and faster than stock. he was very happy with the results
he did not mention lot of worcks to adapt it to QV engine...so you probably are right is "bolt on" or almost (i think i can supply all parts if you want to go this route...plenums and trotthle bodies)

he did it thinking it would be a plus for strict emission rules coming but in reality the classic cars never went to pass strict emission tests in Italy


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IanMan
post Yesterday, 12:13 PM
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QUOTE (emilio @ Nov 19 2017, 11:48 AM) *
i have to ask him for pics - will try to have him send me by phone
otherwise i will do them personally, next time i am at his shop...i ususally go there once a month or so

he told me the car runs very well, really smooth and faster than stock. he was very happy with the results
he did not mention lot of worcks to adapt it to QV engine...so you probably are right is "bolt on" or almost (i think i can supply all parts if you want to go this route...plenums and trotthle bodies)

he did it thinking it would be a plus for strict emission rules coming but in reality the classic cars never went to pass strict emission tests in Italy


Thanks Emilio! smile.gif


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QUOTE (capt_chaos @ May 19 2017, 12:59 PM) *
That said I seen some pictures of people on this website and they do not look like they have evolved properly.
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