TPS Rotate for 240sx 60mm TB & General Info

[Headstrong280z]

So I picked up a 1990 KA24E throttle body and TPS (TPS basically brand new) for $50 on craigslist for my 76 280z. I plan on going megasquirt and turbo, so I figured this is a step in the right direction, and something to keep me busy. I did a ton of searching and found a bunch of info scattered around about 240sx TB/TPS but figured I would try to combine some of the info here, as well as present a work-around for repositioning the TPS. This way, the stock wiring does not have to be extended or modified.

 

- From what I found, the 280z uses a two switch TPS that has idle, off, and full throttle (white TPS below). At idle and full throttle, the computer adjusts gas flow accordingly. In the off position, (when neither switch is closed) no gas is flowing. If I understand the 280z EFI theory manual correctly, the gas is only turned off after the full throttle switch has been closed, and is then opened (as if the car is decelerating from full throttle to coasting). I dont think it would make much sense to turn off the fuel if you go directly from idle to coast, never touching the full throttle switch. Maybe somebody can clarify this part for me.

 

- The automatic 240sx TPS only has one switch, the idle switch, you are either idling or you are not (red TPS below). The pigtail hanging off is a different signal than what Z cars use and is useful for megasquirt and other aftermarket EFI systems as it continuously varies resistance (voltage) with throttle position using a potentiometer. 280zx (only turbo I believe) also uses a two position switch, so the auto 240zx TPS can be used as a replacement. However, it seems some 280z owners have managed to use the 240sx TPS with varying degrees of success.

 

It appears to be well known that the 60mm TB by itself does basically nothing for performance, however it MAY increase throttle response. It will definitely help if you plan on doing forced induction, stand-alone EFI with MAP (eliminating the z's restrictive AFM), porting head/intake, or any combination of these. It makes sense to start from intake/filter and work your way toward the head to gain the most performance for your money.

 

One issue with using the 60mm 240sx TB is that it rotates the TPS 180 degrees, so that the plug is now facing the front of the car when it is mounted in a Z. If you are still using the stock EFI, this forces you to extend or somehow modify your TPS wiring. Looking at the throttle body itself, I found away around this issue. It may be debatable as to which is more work, but since I hate messing with wires, and stock wiring, I decided to give this a shot.

 

I first followed the disassembly on Gray's Garage http://www.graytechsoftware.com/garage/tbs_linkage.asp

 

Basically once you remove all the springs and linkages from the 240sx TB, there is a "metal stopper" as he calls it at the end/bottom. This is the part of the TB that actually limits the rotation travel. By removing this (somewhat difficult and tedious because it is wedged onto the shaft) and rotating the spring/linkage shaft, you can effectively rotate the TPS sensor shaft on the other side 180 degrees (Sweetness).

 

1. First picture shows the orientation of the TPS shaft before modification, it is facing primarily towards the outlet side of the TB.

 

2. Carefully slide the metal stop plate up the spring/linkage shaft using whatever tools you have (I used a flat head screw driver, hammer claw, and then my fingers). It gets easier as you go, but the key is to be very careful and not damage anything. ROTATE the SPRING / LINKAGE SHAFT (NOT the stop plate) 180 degrees and put it back on, DO NOT FLIP the stop plate. Before you press the stop plate back on, make sure it will end up between the stops of the throttle body that the stop plate hits. Also make sure that the TPS shaft is primarily oriented toward the inlet of the TB. Press the stop plate back down to the bottom using a metal tube (or improvise with something else) and hammer. It may be wise to do this before cutting and tapping the shaft as directed on Gray's page, this way if you damage the threads you dont have to worry about it. DO NOT HAMMER TOO HARD, as there are bearings in this assembly. You may damage the bearing balls, races, or retainer by hammering with too much force. It is better to hammer with less force, and do it more often. Once the stop plate is back down to the bottom, verify again that everything is in the right position.

 

3. Notice that you now have a stop plate that rotates between the stops on the TB, and a TPS shaft that is oriented toward the inlet of the TB.

 

4. Whatever TPS you decide to use (280z, 280zx, 240sx) when it is mounted, the plug should now be facing the rear of the car. Modifying the wires is no longer needed!

Edited May 15, 2011 by Headstrong280z

[Tony D]

Replies/Comments below:

So I picked up a 1990 KA24E throttle body and TPS (TPS basically brand new) for $50 on craigslist for my 76 280z. I plan on going megasquirt and turbo, so I figured this is a step in the right direction, and something to keep me busy. I did a ton of searching and found a bunch of info scattered around about 240sx TB/TPS but figured I would try to combine some of the info here, as well as present a work-around for repositioning the TPS. This way, the stock wiring does not have to be extended or modified. The only KA24 Switch that will do that is the one with the pigtail on it from the first couple of years---the Transmission used the two-position switch same as the previous models, while the potentiometer SENSOR is used for fuel control on the ECCS. You can then hook the SWITCH to the stock ECU in the car, while datalogging with the Megasquirt hooked to the potentiometer sensor.

 

- From what I found, the 280z uses a two switch TPS that has idle, off, and full throttle (white TPS below). At idle and full throttle, the computer adjusts gas flow accordingly. Not really, at idle it enriches the fuel curve, at WOT (above 35% throttle position) it enriches the fuel curve by putting it on a pre-programmed 'WOT' map... In the off position, (when neither switch is closed) no gas is flowing.No If I understand the 280z EFI theory manual correctly, the gas is only turned off after the full throttle switch has been closed, and is then opened (as if the car is decelerating from full throttle to coasting).You are describing fuel-cut, and that is in operation when the IDLE contact closes above XXXX Rpms, which then allows the reduction of emissions and a GREAT bump in fuel economy. At XXXX rpms, it starts the injectors working again. I dont think it would make much sense to turn off the fuel if you go directly from idle to coast, never touching the full throttle switch. Maybe somebody can clarify this part for me.Above, hopefully. Use the 'EFI Bible' for more in-depth explanations than what are in the later manuals. This book was designed to introduce 'carburettor generation mechanics' to the basics of the Bosch EFI system (it is very similar to the original 68 VW Training Materials...)

 

- The automatic 240sx TPS only has one switch, the idle switch, you are either idling or you are not (red TPS below). The pigtail hanging off is a different signal than what Z cars use and is useful for megasquirt and other aftermarket EFI systems as it continuously varies resistance (voltage) with throttle position using a potentiometer. Explained above, if you want to run the stock ECU while working on the MS, you have to use one of those dual TPS units. The SWITCH section goes to the stock ECU or ECCS, while the potentiometer SENSOR goes to the Megasquirt. 280zx (only turbo I believe) also uses a two position switch, so the auto 240zx TPS can be used as a replacement. However, it seems some 280z owners have managed to use the 240sx TPS with varying degrees of success. They replace the KA24 TPS (which is usually NOT the pigtail-type, and replace the Throttle Position SENSOR assembly with the existing Throttle Position SWITCH off their current T/B.

 

It appears to be well known that the 60mm TB by itself does basically nothing for performance, however it MAY increase throttle response. No 'may', the relative flow increase relative to tip-in throttle angle change is greater, giving the impression of a larger throttle movement in a 50mm body. Same 'tuning' is why an Explorer has a humongo TB and the Mustang with the same engine has a MUCH smaller T/B---in the heavy Explorer, you get a FEELING that the engine has a LOT more power, but if you had the Mustang Throttle Body on it, if you just mashed the throttle to 3/4 it woiuld feel like the Explorer T/B moving from idle to 1/4...after that the physics of flow take over, and the engine only flows what it can flow, so the great tip-in jump quickly falls flat on it's face relative to an engine with REAL power behind it! It will definitely help if you plan on doing forced induction, stand-alone EFI with MAP (eliminating the z's restrictive AFM), porting head/intake, or any combination of these.I'd question 'definately'---the 50mm T/B will flow more than enough CFM to supply even pretty high performance engines. It's all butt-dyno impressions for the most part... It makes sense to start from intake/filter and work your way toward the head to gain the most performance for your money.

 

One issue with using the 60mm 240sx TB is that it rotates the TPS 180 degrees, so that the plug is now facing the front of the car when it is mounted in a Z. If you are still using the stock EFI, this forces you to extend or somehow modify your TPS wiring. Hmmmm, this was not an issue on my car... I will have to go back and see, maybe I cut the pigtail for the T/B off the harness at the clamp at the middle of the plenum to gain more distance...I don't recall having to add any wires... Looking at the throttle body itself, I found away around this issue. It may be debatable as to which is more work, but since I hate messing with wires, and stock wiring, I decided to give this a shot.

 

Sounds like a lot of work compared to at most adding a pigtail (which likely is required on most stock harnesses anyway!)

[Headstrong280z]

Replies/Comments below:

So I picked up a 1990 KA24E throttle body and TPS (TPS basically brand new) for $50 on craigslist for my 76 280z. I plan on going megasquirt and turbo, so I figured this is a step in the right direction, and something to keep me busy. I did a ton of searching and found a bunch of info scattered around about 240sx TB/TPS but figured I would try to combine some of the info here, as well as present a work-around for repositioning the TPS. This way, the stock wiring does not have to be extended or modified. The only KA24 Switch that will do that is the one with the pigtail on it from the first couple of years---the Transmission used the two-position switch same as the previous models, while the potentiometer SENSOR is used for fuel control on the ECCS. You can then hook the SWITCH to the stock ECU in the car, while datalogging with the Megasquirt hooked to the potentiometer sensor. OK good to know for those that want to run the stock ECU and MS.

 

- From what I found, the 280z uses a two switch TPS that has idle, off, and full throttle (white TPS below). At idle and full throttle, the computer adjusts gas flow accordingly. Not really, at idle it enriches the fuel curve, at WOT (above 35% throttle position) it enriches the fuel curve by putting it on a pre-programmed 'WOT' map... Exactly, computer adjusts flow accordingly (by enriching) In the off position, (when neither switch is closed) no gas is flowing.No If I understand the 280z EFI theory manual correctly, the gas is only turned off after the full throttle switch has been closed, and is then opened (as if the car is decelerating from full throttle to coasting).You are describing fuel-cut, and that is in operation when the IDLE contact closes above XXXX Rpms, which then allows the reduction of emissions and a GREAT bump in fuel economy. At XXXX rpms, it starts the injectors working again. I dont think it would make much sense to turn off the fuel if you go directly from idle to coast, never touching the full throttle switch. Maybe somebody can clarify this part for me.Above, hopefully. Use the 'EFI Bible' for more in-depth explanations than what are in the later manuals. This book was designed to introduce 'carburettor generation mechanics' to the basics of the Bosch EFI system (it is very similar to the original 68 VW Training Materials...) Thanks for the correction, forgot about the EFI bible

 

- The automatic 240sx TPS only has one switch, the idle switch, you are either idling or you are not (red TPS below). The pigtail hanging off is a different signal than what Z cars use and is useful for megasquirt and other aftermarket EFI systems as it continuously varies resistance (voltage) with throttle position using a potentiometer. Explained above, if you want to run the stock ECU while working on the MS, you have to use one of those dual TPS units. The SWITCH section goes to the stock ECU or ECCS, while the potentiometer SENSOR goes to the Megasquirt. I agree, thanks for the additional info. I do not want to run the stock ECU and MS, I am only using the stock ECU in the meantime. 280zx (only turbo I believe) also uses a two position switch, so the auto 240zx TPS can be used as a replacement. However, it seems some 280z owners have managed to use the 240sx TPS with varying degrees of success. They replace the KA24 TPS (which is usually NOT the pigtail-type, and replace the Throttle Position SENSOR assembly with the existing Throttle Position SWITCH off their current T/B. I agree this is what they SHOULD do, but like I stated, I have read on numerous posts where people have ran and have suggested running the 240sx throttle position switch (and ignoring the pigtail) instead of the 3 position 280z TPS. I cant see how this would work very well if the computer is made to run with a full-throttle switch.

 

It appears to be well known that the 60mm TB by itself does basically nothing for performance, however it MAY increase throttle response. No 'may', the relative flow increase relative to tip-in throttle angle change is greater, giving the impression of a larger throttle movement in a 50mm body. Same 'tuning' is why an Explorer has a humongo TB and the Mustang with the same engine has a MUCH smaller T/B---in the heavy Explorer, you get a FEELING that the engine has a LOT more power, but if you had the Mustang Throttle Body on it, if you just mashed the throttle to 3/4 it woiuld feel like the Explorer T/B moving from idle to 1/4...after that the physics of flow take over, and the engine only flows what it can flow, so the great tip-in jump quickly falls flat on it's face relative to an engine with REAL power behind it! You are right, 'may' was used because I have yet to experience this myself, but that makes perfect sense. It will definitely help if you plan on doing forced induction, stand-alone EFI with MAP (eliminating the z's restrictive AFM), porting head/intake, or any combination of these.I'd question 'definately'---the 50mm T/B will flow more than enough CFM to supply even pretty high performance engines. It's all butt-dyno impressions for the most part... It makes sense to start from intake/filter and work your way toward the head to gain the most performance for your money.

 

One issue with using the 60mm 240sx TB is that it rotates the TPS 180 degrees, so that the plug is now facing the front of the car when it is mounted in a Z. If you are still using the stock EFI, this forces you to extend or somehow modify your TPS wiring. Hmmmm, this was not an issue on my car... I will have to go back and see, maybe I cut the pigtail for the T/B off the harness at the clamp at the middle of the plenum to gain more distance...I don't recall having to add any wires... Like I said, I did not feel like modifying the existing harness. It looks like you could probably remove some sleeving from the bundle to gain the necessary cable length. Looking at the throttle body itself, I found away around this issue. It may be debatable as to which is more work, but since I hate messing with wires, and stock wiring, I decided to give this a shot.

 

Sounds like a lot of work compared to at most adding a pigtail (which likely is required on most stock harnesses anyway!) No pigtail is required if you are connecting your stock TPS to your stock wiring harness(if you rotate the TPS). I would much rather do what I did, than add a pigtail or cut and splice. Again, its debatable. Both options are now on the table.

Edited May 17, 2011 by Headstrong280z

[Tony D]

I can't recall which switch is in the TPS for the KA engine---it's either idle or WOT. It really is meant for the Transmission in the KA Application, and I believe that means "WOT"...

 

How it would work in the stock application is that the "Idle" enrichment is not as critical to 'smooth running and transition' as WOT contacts are. If your idle contact isn't getting a contact signal, and doesn't enrich then it's not a big deal, the car will still idle.

 

But if you don't have WOT, and go WOT significantly before 3500rpms, you will have a significant delay in throttle response, and experience lean surging sometimes---more acute when it's cold.

 

I can't recall offhand if the idle switch is opened or closed at idle either, which would add another dimension.

 

But that is the general idea how the KA TP Switch with one contact works in place of the stock ECCS or EFI TP Switch with TWO sets of contacts (while there may indeed be three sets of contacts, only two of them are used: idle and WOT)

[Headstrong280z]

I can't recall which switch is in the TPS for the KA engine---it's either idle or WOT. It really is meant for the Transmission in the KA Application, and I believe that means "WOT"...

 

How it would work in the stock application is that the "Idle" enrichment is not as critical to 'smooth running and transition' as WOT contacts are. If your idle contact isn't getting a contact signal, and doesn't enrich then it's not a big deal, the car will still idle.

 

But if you don't have WOT, and go WOT significantly before 3500rpms, you will have a significant delay in throttle response, and experience lean surging sometimes---more acute when it's cold.

 

I can't recall offhand if the idle switch is opened or closed at idle either, which would add another dimension.

 

But that is the general idea how the KA TP Switch with one contact works in place of the stock ECCS or EFI TP Switch with TWO sets of contacts (while there may indeed be three sets of contacts, only two of them are used: idle and WOT)

 

Yea, the KA switch is idle only, not WOT. The idle switch is closed when when idling, at any other position, all three pins are open. Based on this, one has to conclude that using the KA tps with a 280z or N/A 280zx ECU would be a bad idea.....thanks Tony

Edited May 17, 2011 by Headstrong280z