So I've grown tired of the poor and stinky driveability of my carbs and have decided to return to fuel injection. I have a 1975 1.8L, but I purchased another engine for it that was said to be a '75 1.8L as well, but I'm not entirely sure (hence the question mark next to L-Jet in my title). Based off of what I am finding online, it looks to be that it is indeed an L-Jet system. I am new to this system as I got rid of it immediately when I bought the car and haven't seen or touched it since, which was over 7 years ago. I understand how it all works, but I'm having trouble with the connectors, where some things go, and vacuum hoses.
I found a .pdf of a 912 with L-Jet for the vacuum diagram, but it has some smog equipment on it such as an EGR valve and EVAP Charcoal Canister, which I do not have. In this .pdf it also contains a component list of all the things that are used in this system and I think I have all of them. I just dug the whole setup out today so I will have to check on exactly what I have tomorrow, but I'm specifically wondering about where a few things go/are such as the cold start valve (I assume this is attached to the TB or the intake plenum?), thermo time switch (I know I have this but I don't know where it goes), auxiliary air valve (I also know I have this but don't know where it goes), the "temperature sensor II (I have no idea where this is and whether or not my engine has it), and the dual relay which has its own harness (I'm pretty sure the relay I have is junk--the cover is missing and things look tweaked).
Next thing I am looking to find is a vacuum diagram for this engine/fuel injection. I have lots of pieces of vacuum line, lots of nipples, and no idea what goes where. I did search on here to find some already posted, but I could only find one for the 1.7/2.0L D-Jet system. Also, is there a simple way to figure out which connectors go where? More specifically, the male and female spade connectors... I can pretty much figure out where most of the connectors go based off of the number of pins and color/shape. I also found a wiring diagram in that 912 .pdf but I am not sure if the wire colors will match to my engine so that's another concern of mine.
I greatly appreciate the help and thanks in advance for all information!
-Chris
Full Version: 1975 1.8 (L-Jet?) Help!
Try this
75 vaccum Diagram
75 vaccum Diagram
QUOTE(914itis @ Nov 13 2013, 08:55 PM) 
That's definitely a great start, thanks!
For the vacuum advance on the dizzy, it looks as though one line goes to ported vacuum and the other one goes to man vac, which nipple on the vacuum diaphragm goes where? Looks like purple is man vac and yellow is ported? And what is the decel valve? I don't remember seeing one in my box of parts, but I'm not 100% sure...
On the 75, only one Vacuum port is connected from the dizzy, most of us removed the decal valve, it is possible that the previous owner may have done the same.
If the throttle body has two fittings, then hook both up. It if only has one fitting, it will be manifold vacuum and get hooked to the retard fitting on the distributor dashpot. That's the fitting that points back toward the distributor body.
The decel valve lets (metered) air into the manifold at very high manifold vacuum--basically, while the car is on overrun, at higher RPMs with the throttle closed.
Temp Sensor II is in the right-side cylinder head, near the #3 spark plug.
The CSV goes into the manifold. The thermo-time switch (or thermo-switch) goes into a bracket sticking up from one of the mounting legs of the manifold, I think. (That's where it is on the 2.0 cars, at least.)
The Aux Air Valve (AKA "AAR") goes on another bracket near the manifold, but I don't remember the details.
The dual relay hangs off of the battery tray, as does the resistor pack for the injectors.
--DD
The decel valve lets (metered) air into the manifold at very high manifold vacuum--basically, while the car is on overrun, at higher RPMs with the throttle closed.
Temp Sensor II is in the right-side cylinder head, near the #3 spark plug.
The CSV goes into the manifold. The thermo-time switch (or thermo-switch) goes into a bracket sticking up from one of the mounting legs of the manifold, I think. (That's where it is on the 2.0 cars, at least.)
The Aux Air Valve (AKA "AAR") goes on another bracket near the manifold, but I don't remember the details.
The dual relay hangs off of the battery tray, as does the resistor pack for the injectors.
--DD
Chris
I have a 75 1.8 with fuel injection and extra parts. I would be happy to help. Send me a pm.
Regards
James
I have a 75 1.8 with fuel injection and extra parts. I would be happy to help. Send me a pm.
Regards
James
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I also had another thought about using a different type of air filter setup. For those of you who are running a cone type filter instead of the big box setup, did you remove the MAF? If so, is there anything that needs to be done on the PCM side after removing it? Please let me know. Thanks!
QUOTE(914itis @ Nov 13 2013, 09:22 PM)
On the 75, only one Vacuum port is connected from the dizzy, most of us removed the decal valve, it is possible that the previous owner may have done the same.
Ok cool, thank you! So if I remove the decel valve it looks like I might have to plug up one port on the plenum... Easy enough! Thanks!
QUOTE(Dave_Darling @ Nov 14 2013, 07:56 AM)
If the throttle body has two fittings, then hook both up. It if only has one fitting, it will be manifold vacuum and get hooked to the retard fitting on the distributor dashpot. That's the fitting that points back toward the distributor body.
The decel valve lets (metered) air into the manifold at very high manifold vacuum--basically, while the car is on overrun, at higher RPMs with the throttle closed.
Temp Sensor II is in the right-side cylinder head, near the #3 spark plug.
The CSV goes into the manifold. The thermo-time switch (or thermo-switch) goes into a bracket sticking up from one of the mounting legs of the manifold, I think. (That's where it is on the 2.0 cars, at least.)
The Aux Air Valve (AKA "AAR") goes on another bracket near the manifold, but I don't remember the details.
The dual relay hangs off of the battery tray, as does the resistor pack for the injectors.
--DD
What does the resistor pack for the injectors look like? Is it connected on the same harness for the dual relay? Only pics I have of this setup shows the dual relay next to the voltage regulator, but that's from the 912 .pdf not a 914. Please let me know. Thanks!
QUOTE(jesiv @ Nov 14 2013, 12:51 PM)
Chris
I have a 75 1.8 with fuel injection and extra parts. I would be happy to help. Send me a pm.
Regards
James
Will do, thank you! I think I will be ok on everything except maybe the harness part, so I will let you know. Thanks!
The resistor pack looks like these:
Taken from this post: http://www.914world.com/bbs2/index.php?sho...p;#entry1243325
Look through the "parts vault" forum for images of more stuff; it could be quite helpful.
--DD
Taken from this post: http://www.914world.com/bbs2/index.php?sho...p;#entry1243325
Look through the "parts vault" forum for images of more stuff; it could be quite helpful.
--DD
QUOTE(Dave_Darling @ Nov 14 2013, 10:25 PM)
The resistor pack looks like these:
Taken from this post: http://www.914world.com/bbs2/index.php?sho...p;#entry1243325
Look through the "parts vault" forum for images of more stuff; it could be quite helpful.
--DD
Wow, I've definitely never even seen these before! Looks like something else I'm going to have to buy!
Any input on removing the MAF?
I'm also having a hard time figuring out where the thermo time switch goes, I can't find any sort of bracket or mounting point to use to install it so I'm a bit lost. Does anyone have any pics of it installed? Also, in terms of the temperature sensor II, I know where it is supposed to be, but it has either been broken off or removed. What is the purpose of it and how necessary is it to have it connected? Please let me know. Thanks!
-Chris
The car will NOT run without thew MAF sensor, AKA the airbox. Cone filters aren't good enough to qualify as junk. Temperature sensor 2 is inboard of the 3/4 intake manifold, beneath the tin. There's a hole in the tin for the wire, and the sensor can be accessed through that hole. The car will NOT run without it, and it has to be properly installed to ensure a good ground. There are used resistor packs available. I have a couple. The most common failure is broken wires. It is worth noting that L-jet as installed on a 914 will NOT run with vacuum leaks. There are 2 very specific rubber gaskets in the oil filler cap that must be there and intact, as well as the cork gasket under the filler assembly and the valve cover gaskets. The rubber intake boot must be free of cracks, too. Timing is set in a manner different from all other Porsches. I probably wrote that up in the classic threads.
Good luck! The Cap'n
Good luck! The Cap'n
QUOTE(Cap'n Krusty @ Nov 15 2013, 04:49 PM)
The car will NOT run without thew MAF sensor, AKA the airbox. Cone filters aren't good enough to qualify as junk. Temperature sensor 2 is inboard of the 3/4 intake manifold, beneath the tin. There's a hole in the tin for the wire, and the sensor can be accessed through that hole. The car will NOT run without it, and it has to be properly installed to ensure a good ground. There are used resistor packs available. I have a couple. The most common failure is broken wires. It is worth noting that L-jet as installed on a 914 will NOT run with vacuum leaks. There are 2 very specific rubber gaskets in the oil filler cap that must be there and intact, as well as the cork gasket under the filler assembly and the valve cover gaskets. The rubber intake boot must be free of cracks, too. Timing is set in a manner different from all other Porsches. I probably wrote that up in the classic threads.
Good luck! The Cap'n
I know that disabling the MAF will stall an engine so my mistake, what I should've said was is there a way to relocate the MAF or use a MAF from a different car that is something like a 3" housing with a MAF, for example? Are there any cars that use a MAF that will work with these systems? I have other plans for the future that will require removing the air box, if it is possible. I'm pretty sure the temp sensor II is broken then because I was looking through the hole in the tin and could not see/feel anything in there. Is timing set differently than it is with carbs? Please let me know. Thanks!
-Chris
Another member has found both the Dual Relay and Temp Sensor II for me, but they are from a '74 L-Jet. The part number for the relay is 332.514.121 and the part number for the temp sensor is 280.130.012. Are these parts compatible with the '75 L-Jet system? Please let me know. Thanks!
-Chris
-Chris
QUOTE(Nor.Cal.914 @ Nov 15 2013, 07:09 PM)
I know that disabling the MAF will stall an engine so my mistake, what I should've said was is there a way to relocate the MAF or use a MAF from a different car that is something like a 3" housing with a MAF, for example? Are there any cars that use a MAF that will work with these systems? I have other plans for the future that will require removing the air box, if it is possible. I'm pretty sure the temp sensor II is broken then because I was looking through the hole in the tin and could not see/feel anything in there. Is timing set differently than it is with carbs? Please let me know. Thanks!
-Chris
Chris,
It is not really a MAF (Mass Airflow Sensor), it is a VAM (Vane Air Meter), but that is just me being picky about the nomenclature.
You have to understand that the L-Jet fuel injection is very primitive in comparison with a current FI system. This even applies to the Motronic on a 911, which is the direct decedent of the L-Jet system. Modern FI you can reprogram the computer for the replacement MAF, and it will work. There is no way to reprogram an L-Jet ECU to accept a different Air Flow Meter. The innards are just discrete transistors, and everything is done with hardware. You would have to know what resistors and capacitors to replace, and then you would have to experiment with the values until you found the one that gave you the correct mixture.
My suggestion is to use the Vane Air Meter that came with the L-Jet. It is correctly calibrated for the engine already, and it is very reliable. My wife's 74 914 1.8L has 350,000 miles on it, and she drives it to work every day. It starts and runs in any weather, and other than the old age of the parts causing failure, I don't worry about it.
Oh, and don't put one of the crappy K&N rock stopper cone filters on it. They let too much crud into the engine for what you get.
Hope that helps.
QUOTE(ClayPerrine @ Nov 18 2013, 05:51 PM)
Chris,
It is not really a MAF (Mass Airflow Sensor), it is a VAM (Vane Air Meter), but that is just me being picky about the nomenclature.
You have to understand that the L-Jet fuel injection is very primitive in comparison with a current FI system. This even applies to the Motronic on a 911, which is the direct decedent of the L-Jet system. Modern FI you can reprogram the computer for the replacement MAF, and it will work. There is no way to reprogram an L-Jet ECU to accept a different Air Flow Meter. The innards are just discrete transistors, and everything is done with hardware. You would have to know what resistors and capacitors to replace, and then you would have to experiment with the values until you found the one that gave you the correct mixture.
My suggestion is to use the Vane Air Meter that came with the L-Jet. It is correctly calibrated for the engine already, and it is very reliable. My wife's 74 914 1.8L has 350,000 miles on it, and she drives it to work every day. It starts and runs in any weather, and other than the old age of the parts causing failure, I don't worry about it.
Oh, and don't put one of the crappy K&N rock stopper cone filters on it. They let too much crud into the engine for what you get.
Hope that helps.
It is not really a MAF (Mass Airflow Sensor), it is a VAM (Vane Air Meter), but that is just me being picky about the nomenclature.
You have to understand that the L-Jet fuel injection is very primitive in comparison with a current FI system. This even applies to the Motronic on a 911, which is the direct decedent of the L-Jet system. Modern FI you can reprogram the computer for the replacement MAF, and it will work. There is no way to reprogram an L-Jet ECU to accept a different Air Flow Meter. The innards are just discrete transistors, and everything is done with hardware. You would have to know what resistors and capacitors to replace, and then you would have to experiment with the values until you found the one that gave you the correct mixture.
My suggestion is to use the Vane Air Meter that came with the L-Jet. It is correctly calibrated for the engine already, and it is very reliable. My wife's 74 914 1.8L has 350,000 miles on it, and she drives it to work every day. It starts and runs in any weather, and other than the old age of the parts causing failure, I don't worry about it.
Oh, and don't put one of the crappy K&N rock stopper cone filters on it. They let too much crud into the engine for what you get.
Hope that helps.
Thank you for the insight, it definitely does help! I guess I've spent too much time around the new FI systems to be able to understand how complex these older ones are. I'm thinking standalone may be in the future, but I'm intrigued enough already to figure out the L-Jet system first. I appreciate the advice, thank you again!
-Chris
***Does anyone know about the part numbers I listed for the dual relay and temp sensor being compatible with the '75 L-Jet? Please let me know!***
Chris
Call Rich at HPH he can tell you
Regards
James
Call Rich at HPH he can tell you
Regards
James
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