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Discussion Starter #1 (Edited)
Update with pictures.

I ran into a snag trying to get a B21 engine wire harness to work with the B20a5 engine I just rebuilt.

First of all, the TPS. There were no CEL codes in regards to the TPS. However, the car would not idle right, and full throttle would cause the car to almost stall out. What I found was the TPS wires for the B21 harness were backwards compared to the B20a5 harness. Of the three wires, the two outside wires were reversed. It's a simple fix. Cut those two wires and wire them back up in the correct order for the B20a5 TPS.

Second of all, the O2 sensors on the B20a5 do not plug into the harness because the B21 has a single, four wire O2 sensor. I addressed this by running two wires from the O2 sensors up to where the engine wire harness plugs into the car near the firewall.

So basically, the effective differences are:
1) TPS connector
2) O2 sensors

I will try to get some pictures of this maybe tomorrow after I get the car through emissions.

The TPS


Reversed the yellow and green wires. Left the red alone.




O2 sensors need to be wired in. The easiest thing to do is run new wires. As you can see, I ran a red wire and a blue wire into the engine wire harness when I re-loomed it.


O2 sensors can be wired directly to where the engine wire harness goes into the car.


The green O2 sensor plug goes to the stock red wire w/ blue stripe. I wired that to the red wire, then back to the red w/ blue near the firewall. The O2 sensor with the white/tan plug uses the white wire. I connected that to the blue wire and then back to the white wire at the firewall connector. On the connector, both O2 sensor wires are right next to each other. Take a close look at the picture to get an idea of where they are located on the plug.
 

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Discussion Starter #3
what did you end up doing with the small plug by the underhood fuse box?
I didn't do anything with it. I believe that is used for the heated O2 sensor on the B21. Not 100%, but that is my best guess.
 

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hey fyi on the tps when you switch the wires you more than likely can just remove the wire all together from the connector and switch spots. theres a way to back probe so you dont have to cut wires. but i wouldn't suggest anyone do this who has never done it, if you could get someone who knows how to, have them show you. overall it would look cleaner, but good job on picking up that the wires needed switched!
 

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Discussion Starter #6
hey fyi on the tps when you switch the wires you more than likely can just remove the wire all together from the connector and switch spots. theres a way to back probe so you dont have to cut wires. but i wouldn't suggest anyone do this who has never done it, if you could get someone who knows how to, have them show you. overall it would look cleaner, but good job on picking up that the wires needed switched!
Yea my uncle has a tool for doing that. He lives in Florida though and we aren't on the best terms anymore. I've done this exact procedure with similar wiring projects.
 

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straight pick is what i used to depin mine. you just made a discovery though. b21 and b20 throttle position sensors are pinned backwards.
 

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are you using b20a5 ecu?
 

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I figured you would be but thought I would ask. Didn't think it would run right if you didn't because of the secondaries. I knew the plugs are different at the ecu. I guess I just didn't understand why you were doing it this way. But I guess its because you only had access to b21 engine harness?
 

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Discussion Starter #11
Pretty much yea. I have a B20a5 harness but the wire insulation is cracking and separating. Some wires are broken too. The secondaries are controlled by the vacuum box. Did I miss something for that function to work?

I mean, it seems like the secondaries work. I only tested them briefly while seating the rings. At about 4200 RPMs in third gear the tires were trying to break loose. Ground was wet and it was pretty obvious. It seemed like an indication of a sudden power spike. That's about all the testing I did for it. Still needs 750-800 miles before I will rev it above 4000 RPMs.
 

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I was out having a sig in my garage, my last one for the night, and looked over at my b20a5 turbo prepped engine IM and tb and thought I don't ever recall the wires being bipolar in the old ass schamm toofast IM and throttle body bore thread. I recall the coolant lines underneath it pointing at different directions between it and b21a1. I also remember something about the tps being riveted on. I do know however that I have read onhere recently about people replacing the throttle body tps. I remember from back then you had to buy the whole throttle body to get a new good tps sensor. So what am I missing somebody school me! Where are people getting good tp"s" "sensors" and from what honda or part number are they getting them from?? and are they drilling out the rivets to replace? Thanks, Kevin!
 

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Discussion Starter #13
Search motoxxxmans "started threads" (under 'Statistics' in his profile). He posted the TPS part numbers and all that good stuff. You can cut slits into the TPS rivets and remove them just like screws. Flat tip screw driver.
 

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i turned out the breakaway bolts on mine with a pair of straight cutters while the throttle body was off of my car. they come out really easy. hard part is cleaning the throttlebody without damaging the seals. i didn't know any better, so i threw it in a gallon can of carb cleaning solution for a few days. came out spottless, but the seals were wasted in the process. that one is gonna go to maxbore for an overbore and new seals. with any luck all of the port and polish work i did on the intake will pay off and the opened up throttle body will allow the motor to breath easier.
 

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Update with pictures.

I ran into a snag trying to get a B21 engine wire harness to work with the B20a5 engine I just rebuilt.

First of all, the TPS. There were no CEL codes in regards to the TPS. However, the car would not idle right, and full throttle would cause the car to almost stall out. What I found was the TPS wires for the B21 harness were backwards compared to the B20a5 harness. Of the three wires, the two outside wires were reversed. It's a simple fix. Cut those two wires and wire them back up in the correct order for the B20a5 TPS.

Second of all, the O2 sensors on the B20a5 do not plug into the harness because the B21 has a single, four wire O2 sensor. I addressed this by running two wires from the O2 sensors up to where the engine wire harness plugs into the car near the firewall.

So basically, the effective differences are:
1) TPS connector
2) O2 sensors
man I would have wired the 4 wire o2 to work and used B21 exhaust manifold/mid pipe.
also, its SO easy to depin honda connectors...why did you ruin the wire harness by cutting into it to swap wires?
either swap the pins or swap the TPS. Neither is hard and you wouldn't have had to cut into the harness.
bah...


came out spottless, but the seals were wasted in the process.
what seals!?
There's a paper gasket on the TPS and a paper gasket between the throttle body and the intake manifold.

I was out having a sig in my garage, my last one for the night, and looked over at my b20a5 turbo prepped engine IM and tb and thought I don't ever recall the wires being bipolar in the old ass schamm toofast IM and throttle body bore thread. I recall the coolant lines underneath it pointing at different directions between it and b21a1. I also remember something about the tps being riveted on. I do know however that I have read onhere recently about people replacing the throttle body tps. I remember from back then you had to buy the whole throttle body to get a new good tps sensor. So what am I missing somebody school me! Where are people getting good tp"s" "sensors" and from what honda or part number are they getting them from?? and are they drilling out the rivets to replace? Thanks, Kevin!
you can get a TPS from another car (AFAIK it has to be a prelude. I have a throttle body off a 2.5 vigor on my 3rd gen but I had to use the vigor TPS because it turns opposite of the prelude TPS) by cutting a notch in the head of the sheer bolts that hold it on, then use a flat screw driver to remove the bolts and replace them with some small (4mm I think) allen head bolts. then it's super easy to adjust on the car :)
 

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Discussion Starter #16
I did what I did to the harness so I can easily take measurements when adjusting. Also, I'll be replacing the TB with something bigger. Probably Vigor TB and max bored. So not sure if the TPS will be backwards or not on that too.

And I will use a 4-wire O2 sensor one day. Currently, I just wanted to get the car running again without spending several hundreds of $$. Don't worry, it will have a B21a1 header and downpipe w/ heated O2 soon.
 

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I did what I did to the harness so I can easily take measurements when adjusting. Also, I'll be replacing the TB with something bigger. Probably Vigor TB and max bored. So not sure if the TPS will be backwards or not on that too.

And I will use a 4-wire O2 sensor one day. Currently, I just wanted to get the car running again without spending several hundreds of $$. Don't worry, it will have a B21a1 header and downpipe w/ heated O2 soon.
A heated O2 can be picked up for less than $100 from places online. I bought my NTK sensor for $82.

taking measurements is cake...get some t-pins (you can find em at craft stores) back probe your connector (slide the pin in next to the wire...don't shove it through the wire or the seal) voila.

IIRC, the vigor TPS doesn't require any wires to be moved.

tsiah, the seals i was talking about are the shaft seals in the throttlebody for the throttle plate.
ah.
aren't they just o-rings?
is it causing problems?
if they aren't binding up or causing weird idle issues, I'd let it go.
 

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the issue after cleaning it was the idle was unstable. i would rather have the seals done anyway though, since the throttlebody will be opened up. and this is gonna be a daily so it needs to be reliable for me.

re the harness though, you got the car to run on the stock ecu. do you have a plan for another ecu or conversion harness and ecu? pretty sure you do, but i am just about to start assembly on the same build, and was curious. that is my plan, just a bit lost on who to go through at the moment.
 

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Discussion Starter #20
Soon I will buy another ECU and OBD1 conversion harness. I was going to buy from motoxxxman, but I heard he doesn't have internet. Right now, that's ok. Some dude still owes me tons of money I was counting on having by now. I just picked up another entrepreneurial job that will be worth 5x's as much and pays in bulk. So, money will not be an issue soon... except LowJack is still like $500 for the base install.
 
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