JetTronic
11-15-2002, 01:29 PM
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JetTronic
Can anyone tell me what the JetTronic does and what it might cost for a good used one? My 84 928S Euro has not been starting well lately and the technician diagnosed it as a bad JetTronic. Does 650 dollars seem like a fair price to pay for it?
11-15-2002, 09:47 PM
#2
Jetronic is the Bosch brand name for their CIS injection system. There are many components which can go bad but it is doubtful that the whole system would need replaced. I would ask your mechanic which component was bad and if he couldn't tell me I would get a new mechanic.
Dennis
Dennis
11-16-2002, 01:34 AM
#3
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Also verify of which jettronic system. K or Lh.
Check out this link for more info...
<a href="http://www.netopsys.com/928/troubles.htm" target="_blank">www.netopsys.com/928/troubles.htm</a> for more info on CIS systems...
Check out this link for more info...
<a href="http://www.netopsys.com/928/troubles.htm" target="_blank">www.netopsys.com/928/troubles.htm</a> for more info on CIS systems...
11-16-2002, 01:51 AM
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Further clarification to the previous post:
"Jetronic" is a trade name of Robert Bosch for their "stand alone" fuel injection system. There are several generations of Bosch fuel injection.
The K-Jetronic was used in the first generation of injection used in 928s (along with many other autos around the world). It is a mechanical continues injection system (CIS) that meters fuel to all cylinders in a manner like a garden hoses ... opening and closing the faucet is the metering to increase and decrease fluid flow. The 928 used CIS in the U.S. up to Model Year 1979, where the ROW 928s used it up to MY 1983.
Bosch "fine-tuned" the CIS system with their KE-Jetronic injection, which was used by Mercedes Benz. This system used a closed loop electronic circuit to “fine tune” the CIS idle mixture along with a catalyst and O2 sensor to meet the first round of emissions reduction requirements. This system didn't find its way to Porsches.
Porsche moved from "K-Jetronic" injection to a pulse-injection system called "L-Jetronic" where L stands for "luft," the German word for air. L-Jetronic uses a "spring loaded flap" mass air flow (MAF) sensor to measure the mass of air entering into the engine. You can think of pulse-fuel injection as turning a water hose on all the way at the faucet and then stopping the flow by bending it to quickly stop the flow 100%. If you start and stop the flow fast enough the fuel is metered as is necessary. Pulsed flow is more accurate then the CIS system. The U.S. 928s used L-Jetronic injection from 1980 to 1984. It is crude in the standpoint that analog computers were used to calculate fuel flow, so there is no Read Only Memory (ROM) to remove and reprogram to change operating parameters.
The next and final fuel injection technology for the 928 was LH-Jetronic, where the H stands for heiß (hot in German). The L-Jetronic’s spring loaded flap MAF sensor was replaced by a hot wire. As air flows past the hot wire, it loses heat in direct proportion to the mass of air flowing across it. An electronic circuit maintains a constant temperature at the wire and the amount of current needed to keep the temperature constant is what the electronic brain uses as a value to calculate the necessary fuel flow. The LH-Jetronic injection uses the same pulsed fuel flow at the injectors as L-Jetronic. The LH-Jetronic "brain" used a small digital 8-bit microcontroller to do the math. Therefore this system has a ROM chip that can be changed to modify how the system works and to modify the internal maps. The LH-Jetronic was used by ROW 928s from MY 1984 onwards, where the US didn’t see it until MY 1985.
You might ask about spark, don’t fuel and spark go hand-in-hand? Correct. The CIS and L-Jetronic systems worked with a simple "old style" transistorized ignition. The LH-Jetronic injection was teamed with a digital controlled spark system called EZK to improved ignition spark timing (spark plugs are called Zündkerze in German). The non-US cars had EZK in MY 1984. The US cars were upgraded to EZK spark control with the 32-valve engine in MY 1985.
One other bit of trivia. Bosch also made a combined fuel injection and spark control system called Motronic engine control. The 928 never saw this system, however most of the other Porsches as well as BMWs used and still use integrated fuel and spark control.
"Jetronic" is a trade name of Robert Bosch for their "stand alone" fuel injection system. There are several generations of Bosch fuel injection.
The K-Jetronic was used in the first generation of injection used in 928s (along with many other autos around the world). It is a mechanical continues injection system (CIS) that meters fuel to all cylinders in a manner like a garden hoses ... opening and closing the faucet is the metering to increase and decrease fluid flow. The 928 used CIS in the U.S. up to Model Year 1979, where the ROW 928s used it up to MY 1983.
Bosch "fine-tuned" the CIS system with their KE-Jetronic injection, which was used by Mercedes Benz. This system used a closed loop electronic circuit to “fine tune” the CIS idle mixture along with a catalyst and O2 sensor to meet the first round of emissions reduction requirements. This system didn't find its way to Porsches.
Porsche moved from "K-Jetronic" injection to a pulse-injection system called "L-Jetronic" where L stands for "luft," the German word for air. L-Jetronic uses a "spring loaded flap" mass air flow (MAF) sensor to measure the mass of air entering into the engine. You can think of pulse-fuel injection as turning a water hose on all the way at the faucet and then stopping the flow by bending it to quickly stop the flow 100%. If you start and stop the flow fast enough the fuel is metered as is necessary. Pulsed flow is more accurate then the CIS system. The U.S. 928s used L-Jetronic injection from 1980 to 1984. It is crude in the standpoint that analog computers were used to calculate fuel flow, so there is no Read Only Memory (ROM) to remove and reprogram to change operating parameters.
The next and final fuel injection technology for the 928 was LH-Jetronic, where the H stands for heiß (hot in German). The L-Jetronic’s spring loaded flap MAF sensor was replaced by a hot wire. As air flows past the hot wire, it loses heat in direct proportion to the mass of air flowing across it. An electronic circuit maintains a constant temperature at the wire and the amount of current needed to keep the temperature constant is what the electronic brain uses as a value to calculate the necessary fuel flow. The LH-Jetronic injection uses the same pulsed fuel flow at the injectors as L-Jetronic. The LH-Jetronic "brain" used a small digital 8-bit microcontroller to do the math. Therefore this system has a ROM chip that can be changed to modify how the system works and to modify the internal maps. The LH-Jetronic was used by ROW 928s from MY 1984 onwards, where the US didn’t see it until MY 1985.
You might ask about spark, don’t fuel and spark go hand-in-hand? Correct. The CIS and L-Jetronic systems worked with a simple "old style" transistorized ignition. The LH-Jetronic injection was teamed with a digital controlled spark system called EZK to improved ignition spark timing (spark plugs are called Zündkerze in German). The non-US cars had EZK in MY 1984. The US cars were upgraded to EZK spark control with the 32-valve engine in MY 1985.
One other bit of trivia. Bosch also made a combined fuel injection and spark control system called Motronic engine control. The 928 never saw this system, however most of the other Porsches as well as BMWs used and still use integrated fuel and spark control.
11-16-2002, 02:09 AM
#5
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Jon,
Sorry for being so verbose in the last post, I'll address your question directly now ....
Can anyone tell me what the JetTronic does and what it might cost for a good used one?
>> I hope I answer the what it does question. The how much cost question depends upon what is wrong! It is a system that is made out of many bits. It depends which part failed.
My 84 928S Euro has not been starting well lately and the technician diagnosed it as a bad JetTronic. Does 650 dollars seem like a fair price to pay for it?
>> Your '84 Euro should have LH-Jetronic Injection. Hard starting can be caused by many things. However, a defective ECU (controller brain) is sadly a possibility. This sounds like what was diagnosed as failing. I cannot speak to the cost of parts in Europe. In the US these brains are listed at EXACTLY $650 for a rebuilt unit at one of the big-three suppliers. Is that a fair price, I guess it is if you cannot find one for a lower price.
>> I suggest that you verify exactly what was diagnosed by your mechanic as being bad and then you contact all the potential sources of replacement parts and determine what is fair or not.
Sorry for being so verbose in the last post, I'll address your question directly now ....
Can anyone tell me what the JetTronic does and what it might cost for a good used one?
>> I hope I answer the what it does question. The how much cost question depends upon what is wrong! It is a system that is made out of many bits. It depends which part failed.
My 84 928S Euro has not been starting well lately and the technician diagnosed it as a bad JetTronic. Does 650 dollars seem like a fair price to pay for it?
>> Your '84 Euro should have LH-Jetronic Injection. Hard starting can be caused by many things. However, a defective ECU (controller brain) is sadly a possibility. This sounds like what was diagnosed as failing. I cannot speak to the cost of parts in Europe. In the US these brains are listed at EXACTLY $650 for a rebuilt unit at one of the big-three suppliers. Is that a fair price, I guess it is if you cannot find one for a lower price.
>> I suggest that you verify exactly what was diagnosed by your mechanic as being bad and then you contact all the potential sources of replacement parts and determine what is fair or not.
11-16-2002, 02:36 PM
#6
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Probably the most concise, comprehensive description of the evolution of the 928 Bosch fuel delivery system I've seen.
Well done Rich.
Well done Rich.
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01-02-2004, 12:58 AM
#9
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The air flow sensor for USA engines has an anti-tamper plug for the idle mixture control screw. Legislation in the USA requires that the bore in the air flow sensor housing providing access to the mixture screw be plugged in a manner that a certain minimum time would be required to make the screw accessible. This is intended to prevent tampering or unauthorized changing of the CO level adjustment. Consequently the bore providing access to the mixture control screw has a plug. Should the idle speed/CO level have to be adjusted, the air flow sensor must be removed to remove the plug.
Last edited by Steve J.; 01-02-2004 at 03:32 AM.
01-02-2004, 02:12 PM
#10
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Jon,
I would ask some serious questions of yoyur mechanic before agreeing to part with your money.
What does he mean by "jetronic" - the fuel injection ECU ?
How does he know that this is the problem ?
Can he guarantee that if you have this unit replaced, "another" faulty component won't also need replacing ?
Poor cold starting is rarely caused by an LH2.2 fuel ECU.
The problem could well be elsewhere.
I would ask some serious questions of yoyur mechanic before agreeing to part with your money.
What does he mean by "jetronic" - the fuel injection ECU ?
How does he know that this is the problem ?
Can he guarantee that if you have this unit replaced, "another" faulty component won't also need replacing ?
Poor cold starting is rarely caused by an LH2.2 fuel ECU.
The problem could well be elsewhere.
01-02-2004, 03:14 PM
#11
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Where's the screw?
BigWebb: I'll take a stab. I don't have a 16v engine, therefore use with 2 grains of salt. From page 24-24 in the WSM. On the air flow sensor is a flat structural rib. From context, I believe it is on the passenger side, lower portion of the meter, facing front of engine where the neck descends into the throttle body. There is a flat, round indentation about 1 cm in diameter. This the anti-temper plug you must drill out (and replace after adjusting) in order to access the screw. Apparently, you cannot access the plug or screw as mounted on the engine b/c the instructions are to "1) Remove air flow sensor. 2) Drill hole in plug with a 2 mm dia. drill bit (up to stop on steel insert). 3) Pull out plug with a left-turning drill. " You then reinstall in order to perform adjustment on running engine "Turning clockwise = richer; counter clkw = leaner... install new plug, push flush. Never reuse a drilled plug!" HTH.
