B18A1 engine swap questions

i have a 1990 acura integra gs with a stock 1.8 B18A1 engine with a 5 speed manual transmission. the engine died, so we are replacing it with an engine from a 92 LS automatic. there are a couple problems we ran into.

one, we took off the auto trans and put the manual on and found that there are two extra vaccuum tubes. one goes to the egr valve and the other goes to the auto trans. both come from the intake manifold, the black tubes on the passenger side. there are 4 tubes total there. one goes to the charcoal canister, the other to something on the intake. one goes to the egr valve and the other to the auto trans, but which goes where? AND since we dont have the auto trans on anymore, can we just plug that tube somehow? will there be any other problems?

two, i assumed the engines were the same since they had the same numbers on them. i was wrong. the wiring harness on the manual has two small plugs that plug in near the alternator from the old engine, but those two plugs arent on the new engine at all. what are they for? how do we bypass them?

three, on the other end of the wiring harness is the plug for the O2 sensor. there are two small plugs there also. cant remember where they went.

please let me know if we are going to run into any other problems using this setup. sorry i didnt do a more thorough search as i didnt find anything related to what i was looking for.

the newer b18a is obd-1, while your older b18a was non-obd…u should use an obd-1 wiring harness

I can help with the plugs back by the alternator/ near the oil filter.
On my 91 motor I had three plugs in a triangle shape. Looking at the back of the motor (looking toward the front of the car) The lowest of the three plugs and closest to the oil filter is the Oil pressure switch. This one is most likely already hooked up as it is the same between the two years.
The highest of the three plugs on the 91 motor is the thermosensor. This operates your electric fans so you obviously need this one as well. However in 92 this switch was relocated to the thermostat housing. If you compare the housings…not the cover but the housing itself… then it will be obvious what is different. If I remember correctly they use different plug styles so you will need to extend your wires from behind the alternator to the thermostat housing and change the plug style to the 92 to hook it up. On the 91 the plug was extremely hard to unplug and I tore the boot up real bad trying to get it off. Under the boot was two single prong bullet style plugs. The males were on the sensor side. On the new motor the plug on the thermostat housing used the same style connection as the map sensor on the firewall.
The third plug is not on all motors. I believe it is used on A/C cars only but this is only speculation. This plug is green in color and sits between the other two plugs in hight on the 91 motor however it is offset towards the alternator thus creating the triangle I was speaking of. If your old motor had this switch then you will need to move it to the new motor. There will be a plug where the switch goes in the same location as the old motor.

Hope this helps as far as it went.

yeah, thanks!

i found out that i am trying to plug an obd2 harness into an obd1 engine. sorry guys. i tried searching, but wasnt looking under the right things.

so, all i have to do is rewire those plugs? i looked up obd1 conversions and it looked HORRIBLE!!! all i want to do (if possible) is hook it up so that it will run properly. im not looking for anything special.


what about the two small plugs on the old (obd1) harness that come off right at where the old harness’ O2 sensor comes off? down by the transmission… we cant find on either the old OR new engine where they came from.

You really should be using the wiring harness from the car not the one from the motor. There is no need to convert OBD0 (your car) to OBD1 (new motor) just to swap the motors. If you use the original wiring harness you know that you have a working electrical system.
There is a difference in the fuel injector design so you will need to use the OBD0 injectors as well. Also you will need to use the Exhaust manifold from the old motor because I think the new motor has the O2 sensor in a diff location. To use the new setup you would have to use the 92 exhaust back to and including the cat. to match the 92 manifold. And you will need the OBD0 dist from the old motor as well. Changing these few items is much easier than rewireing your car for the OBD1 conversion.

Using the original wiring harness everything will reattatch in there proper places except the wire for the thermosensor as mentioned before.

I believe that the wire by the O2 sensor wire goes to the backup light switch on the tranny.

Again… from the old motor you need:
Fuel injectors
Exhaust manifold
Wiring harness
Using the intake would make all the hoses the same but you may be able to just change the items the hoses run to. Some of the extra hp some believe come from the intake being a better flow design but I think it is actually from better cams. If you do change the intake match the port sizes to be sure. You are using an automatic motor so it may not have better cams.

Using the right parts makes this a plug and play swap exept for the thermosensor.

Good luck.

thanks for all your help!

yeah, everything went in fine except for that one set of plugs not being the same. we had to change the driver’s side motor mount too, but that wasnt a big deal.

i just wanted to make sure that the engine was going to run fine and we got everything hooked up, etc, since it was different. this is my first engine swap ever and so im kind of ignorant and anal about doing right. its also for my girlfriend’s car, so…

thanks for your help though! if i have any more questions, i know where to go:)

I did the same exact swap, here’s what I did, use the engine harness from the CAR, you can do this. Use the distributor from the (90) car. Everything else bolts up.

thanks for all the help guys! i do have another question though.

this is what we did. we got everything hooked up. everything was the same on the wiring harness except the injectors which we changed AND the two plugs (for obd 0) spliced into the one plug (for obd 1). we also switched the distributor.

we also used the exhaust manifold and downpipe from the 92 automatic (which seemed larger and to have better flow) and replaced the 4 wire O2 sensor with the one wire one and rewired it back into the same plug location. as you probably know, the 4 wire O2 sensor is located in the downpipe towards the end whereas the one wire one was closer to the manifold.

anyway, its running although not as well as it should AND the check engine light is on. any ideas on what might be wrong? there is a space in the exhaust that we are going to get fixed tomorrow.

my friend who helped me thought it could be insuffiecient back pressure because of the gap in the exhaust. i wondered if it might be the o2 sensor location change. what do you guys think? any ideas? otherwise, everything sounds and looks good. the fan turned on when it should, so our rewire job seemed to work. and its no missing any cylinders, just seems to sputter more than it should.


Ok sounds alot like my situation with a B20Z install. Now about this third switch. Do you know what it its called? Because it is not on my new engine and I would like to be able to hook it up what ever it is so that I don’t get any cel or other errors.

The third plug is an oil temp switch. I simply moved it from the old engine to the new one. The new engine had a plug where the switch went.

did you figure it out?

on my car, we replaced a b18a1 engine with the same engine only the new one was an obd-1 whereas my original was an obd-0. SO, i cant speak for how your engine hookups may be.

my originial harness had two small indvidually wired clips that plugged into the rear of the engine kind of near the alternator. on the new engine, those plugs werent there, but a new gray plug replaced them. it is kind of under the distributor right under where the wiring harness branches into like 3 or 4 branches. we had to splice in an obd-1 plug for this plug. it was easy though as the wires are the same color as the obd-0 harness. everything worked fine and my coolant fan came on, so i assume it worked fine.

pretty easy swap overall. this was the only wiring difference and we swapped everthing else from the obd-0 to the obd-1 (exhaust manifold, downpipe, driver side motor mount, etc).

So there is an oil temp and pressure switch?:think:

The temp switch is only on A/C cars. I do not know what it controls. I was told that it was an oil temp switch. I do know from experience that the extra switch is in the oil system not in the water system. And that the oil pressure switch is the same in all B series that I have seen.


I had my timing belt go last febuary and i had to pay someone to do the swap, out of it i too got the 92 motor in my 90 integra. There was no switching of motor mounts(maybe due to the manual b18 to manual b18 swap) but we did have to change the exhaust manifold Becauase the obd0 uses a heated O2 sensor where as tha obd1 does not. We also switched the distributors and the fuel injector wiring harness. But the guys who did the swap never rehooked up the thermostatic switch and my car almost overheated one day funny cause its never been hooked up for like 2 monthes and i never had a problem exept when i was waiting in line for the car wash. But i HAVE found that my car is not getting the gas milage it should be getting, my old motor w/ 340000 kilometers ( something like 200000 miles) got close to 450 every tank now this motor is only getting like 350, now does any one have any ideas about this, i was thinking its because of the computers. Let me know im kindof desperate to know.


im pplannin on doin the same swap…

is there a reliable source for the switch over for the vaccumm lines…harnesses…parts etcetc…i dont wanna get into this half a$$…i wanna be prepared :manual:

New B18a1 cylinder heads

Anyone have any recommendations of where to purchase a new b18a1 cylinder head?

Ebay has very scarce info.

Do I have to stick with a B181a head?

As to where to get one I would have no clue.

Any non-vtec B-series head will bolt to your block with the possible exception of the old Prelude B20a motor as that motor is in a class by itself. That means any head from a B18a/b or B20b/z will bolt to your block with no mods other than external like needing the right intake manifold.

As for what to use if you have to buy a new head then my recommendation would be to upgrade to the P-75 head from the later B18b and B20 motors. It is the best flowing stock of the non-vtec heads. But to get those benefits you will also need to use a decent intake manifold. Either the P-75 manifold or an aftermarket manifold. Of course there are likely some vacuum hose diff and I know the map sensor is diff between the two as well. That head with some decent cams will really wake up a B18a motor.

The reason I specify the P-75 instead of just saying B18b head is that it is often talked about on this board and others that the B18b head is better than the B18a head but that has yet to be proven. The biggest diff seems to be in the cams. However there is a visible diff between the p-75 head and the PR-4 (I think that is the right number?) head. It has also been believed in the past that the B18b '94 and up automatically had the P-75 head however there are many examples of the PR4 head on B18b motors up til 95 so I think the P-75 may be '96 and later as I know of no examles of a PR4 head after '95.

Next question would be why do you want new? There are many examples of used heads avail and the newer the donor car the fewer miles it will likely have on it.

The response to this one should be interesting…

I was estimated 700-1000 for new valve seals. I was told by a few people that I could get a nice used clean head for that price and bolt it on myself. I was told not to attempt changing the valve seals since I’m not familar with the head work internals, so changing the head would be easier.

She’s blue blowin smoke at start ups…

You could go for a replacement head or just swap engines from something with less milage on it.