91 2.0 o2 sensor issue

[tjonesnc]

I am new to the boards, sorry to hit you with such a pain in the butt question from the start.

I just bought a 91 SI 4WS with a B20A5 swapped into it (the B21 was blown) and it was nearly finished when I bought it, it had been sitting for a year.

I did all the regular maintenance, spark plugs, plug wires, valve cover gasket, about to do the cv joints etc etc. I was driving one day and was losing power through any part of the rpm range when I hit the gas, just losing throttle power. I changed the fuel filter thinking all the gunk is being forced through causing this backup. Come to find out when I was looking around I noticed an o2 sensor was not hooked up. It is a 2 wire sensor with the barrel type connector. There is no other open plug for connection even hanging with the exception of a 3 wire rectangle harness which is about 18 inches away on the left side near the distributor cap. The upstream o2 sensor is a 4 wire that is just hard wired in. I have been trying to look for some assistance with this or even a schematic and/or electrical diagram so I can hard wire it myself if need be. Or is there a barrel connector to rectangle connector adapter? I am lost and even people at advanced auto and carquest cant help...Thanks for your time

[spiffyguido]

First of all, welcome to PreludeDriver.com.

Don't worry about your question. We love the hard ones here.

You may find this helpful:
http://media.honda.co.uk/car/owner/medi ... 0/5-58.pdf

Are you sure that the oxygen sensor is the cause of your problems? Is your ECU throwing a code?

[tjonesnc]

I am getting 1 blink on the indicator, but it isnt all the time. I saw it quite a bit and after I started looking into what all is wrong with the car, and find out, now when I run it to try and get the light to come on it won't. The problem comes and goes and typically doesn't happen until about 45 mins of driving.

[tjonesnc]

I appreciate the pdf also, unfortunately it is a page in the manual I have looked at quite a few times, I downloaded the service manual and have looked through everything, about 12 hours worth of it and found nothing.

[spiffyguido]

Would you be able to post a picture of the wires in question? I think we'd be able to help you better if we could see the types of plugs that you are referring to.

[tjonesnc]

Yep, here they are. I don't have a digital so phone quality pics are going to have to do! Thanks again

[spiffyguido]

Those plugs definitely don't match up. I am having some new thoughts though.

First of all, I think it's important to know that there are some electrical differences between B21A1s and B20A5s that might be causing some of your loose wires.

First is, a B21A1 only has 1 4-wire O2 sensor whereas the B20A5 has 2 1-wire O2 sensors. This is because the B21A1 is a OBD1 engine and the B20A5 is an OBD0 engine. This may explain the extra wire you have, as I'm wondering if whoever did the engine swap didn't swap the main wire harness with the engine. Your wire harness may be the one from the B21A1, which means it won't have 2 O2 wires.

Second is that the B21A1 has a different wiring setup on the distributor. The extra square plug you have may be a left over from the more complex distributor setup on the B21. I've attached a picture of a B21 setup. Can you identify which plug might be the one that you have loose?

Other question are. What ECU is the car running off? Is the B20A5 using the B21A1 ECU, or was that swapped?

B21GenDistributor.jpg (70.68 KiB) Viewed 13486 times

[tjonesnc]

In reguards to your picture, I do not see the exact wire in the picture. It looks like if it were anywhere, within relevance to the positioning of mine, it would be under your intake. Now, you enlightened me to an entire new spectrum of possibilities. Just by feeling, I believe I have the ODB1 ECU, since the 1 hooked up O2 sensor is a 4 wire. Which, I may be wrong because you are a lot more experienced in this filed than I am, but I think that would rule out the disconnected O2 sensor, due to the ECU only needing to read one. I didn't see any ODB0 or ODB1 on the ECU, but I took some pictures here:







The numbers on this last picture are 37820-PK3-A00, 530-319297, 3L20

Which would this be? Or am I looking in the wrong spots for the numbers? Although my dashboard indicator is speratic so I can never really tell, the ECU showed 7 flashes which is the Throttle Angel Sensor. The only thing with that, is I reconnected it having it disconnected just before I started the car to check the ECU LED indicator. I don't know if you have to let it sit for a few minutes before that to "re-configure", but would a bad throttle angle sensor give me my original issues? Which was..hitting the gas and getting hung up in any part of the RPM range, typically above 3000 RPM, and it jerks like it catches than will be fine for a minute. Thanks again for all your help!

[spiffyguido]

The 'PK3' on your ECU means that it is the B21A1 ECU. If it were for the B20A5, it would say 'PK2'. This is definitely something we'll want to keep in mind as we diagnose your problems. Whatever sensors, etc that you have need to be able to talk to the OBD1 ECU. Since your O2 sensor is a 4-wire, you have the right sensor. Ignore the other one. If you don't like it there, just yank it out and plug the whole with a bolt or something.

Now that we're getting a code 7 of your ECU, I'm going to propose that this is probably your actual problem. O2 sensors can cause idle problems, but I've never heard of them causing issues as violent as what you seem to be experiencing. Throttle Position Sensors (Throttle Angle Sensors) on the other hand CAN produce such results. I recall one TPS sensor that went bad in a car I was driving; the car would drive fine till about 1800 rpm or so and then the engine would fall flat on its face.

The unfortunate thing about TPS sensors is that they are often riveted to the Throttle body. If this is the case, you're going to have to get creative with removing it, or just go to a wrecker and pick up another throttle body. Check the wiring as well. Since the TPS sensor is highly embedded in the Throttle Body, it's unlikely that you will be able to clean it to make it work, but try anything you can.

[tjonesnc]

I tell you what dude, you have helped me greatly. Also, along with this whole situation finding out that the ECU is the B21A1 ECU, I figured out why the throttle body and Intake Manifold are completely different than the diagram, all from the old motor. I called to try and get a TPS sensor and did find out that I did have to order a throttle body to get it. Now....the question is, do I have to get the 2.1 throttle body just to make sure it all fits to the current application or should it really matter? I am still having a rouge vacuum hose problem due to a different setup than OEM. And ya, you explained it exactly, above 2000 RPM it wants nothing to do with the gas pedal. No wonder I couldn't find anyone to give me a solid answer on this problem, using 2 different model parts on one car can really mess things up. I maybe could have caught this about 6 years ago when I was working with a Honda a lot! Thanks again.

[spiffyguido]

You should probably get the B21 throttle body.

I'll check at home to make sure that the B21 throttle body correctly matchs up to the b20A5 intake plenum.

[tjonesnc]

Currently there I think there is a B21 throttle body on there, due to the bolts going in the opposite side and also the placement of the vacuum tube hoses. No parts stores had the B20 TB so I called Honda and they want $478 for a throttle body, I guess I should try calling them tomorrow to see how much cheaper a B21 TB is. Also, I lost my pdf manuals for the B20 and B21 engines, anyone have a link for them? I have one vacuum line that I have no clue what it connects to and hadn't had time to check through the B21 manual before my computer crashed. I appreciate it.

[spiffyguido]

Looking at my throttle bodies, it looks as though the vacuum setup to the B21 TB is different from the B20. I wasn't able to see if they match up as one of my TBs is on my car right now.

You can get manuals at: http://hondatech.info/downloads/Auto/Ma ... elude%203/

[team123luder]

The problem is you have a B21 engine harness and a B20A5 engine. The header is also from a B20A5 which uses 2 single wire O2 sensors on runner 2 and 4 I believe.

The B21 uses 1 4 wire heated O2 sensor near the last merge collector on the down pipe.

The fix????

Use a B21 header, EGR pipe and B21 intake manifold. Then use your standard 4 wire O2