I've got a 1990 Prelude Si (originally had a B21A1), automatic. About a year ago a replacement engine was put in -- a B20A3 block with a fuel injected head (not the head from my B21A1; rather, the mechanic put in an engine he had that had already been modified).

This engine is less powerful than my original engine. Also, its power curve doesn't match my transmission settings, so my transmission no longer shifts at the proper points.

The biggest issue I've had with the replacement engine is that it dies while idling. The bigger the load, the more likely it is to stall out. Typically, if I have it in park, it won't die (but there are exceptions). However, if I'm waiting at a light, with the headlights on, the brake pedal depressed, and the AC on, it will usually die before the light turns (thus I'll typically shift into park at lights). Also, I need to press the brake pedal gently when approaching the light. If I press to hard, that puts too much load on the engine, and it dies.

The idle in park is about 800 RPM, which is what it's supposed to be. So it's possible this is an idle compensation problem--that it is not compensating for the increased load.

When one swaps to a less powerful engine, is one supposed to change the computer that controls that engine? I'm wondering if the less powerful engine needs a stronger idle compensation algorithm than what my stock engine had.

 

If you dont have right ecu how do you think your engine would work properly?

 

I came here to get substantive answers, not for childish snark. Of course I know that not having the right ecu has the potential to compromise functionality, since I raised that issue myself. What I'm wondering if the specific issue I'm seeing could be due to a possible ecu mismatch.

Here's more background: My purpose is not to get this car to optimum functionality, it's just to keep it running for another year or so at minimal expense, since I can't afford a replacement at this time. 18 months ago it couldn't pass smog with the current engine, so the engine had to be replaced. Standard cost for that in my area (I did shop around) is $4000 ($3000 for rebuilt engine+$1000 for installation) (I live in Los Angeles, and car work is expensive here). I found a mechanic that was willing to put in another engine that would pass smog for $1000. So I got another 18 months of use for $1K, which was a lot cheaper than replacing the car. The tradeoff for such a low price, which I accept, is that I'm now encountering other problems for which I need a fix. I'm just trying to keep the car functional enough to use.

 

Thats where i would start. Youll find very little information on 3rd gen ludes when it comes to things like this. PreludePower is where you want to be if youre dealing with a 3rd gen. Theres a large community of 3rd gens there (at least there used to be). Are there any check engine lights? any other symptoms?

 

The check engine and battery lights come on occasionally. But they're not on continuously--in cases when the do come on, they'll typically disappear if I turn the car off and restart it (this was the case with the stock engine as well). I'm sure the current mechanic will also check the error codes (this car is so old you can't plug a computer into it to read codes; rather, there are flashing lights under the carpeting in the passenger footwell).

I did also posted about this on the 3rd generation Prelude Power forums, but I noticed this forum has some technically astute answers, so I decided to post on here as well. My plan is to collect all the ideas and run them by the electrical specialist who is working on it now.

 

I'm assuming your setup consists of a b20a3 block (which is actually exactly the same as a b20a5 block), and a pk2 head (b20a5). Can you verify whether the head is pk2 or pk3? it should say on the front of it somewhere between the exhaust manifold and valve cover.
Also, there is nothing wrong with this setup, and it actually makes very similar power to the b21 that originally came in your car. the question is; which intake manifold is on this engine?
Next, is the cel on? have you checked for any stored trouble codes? Have you done any basic maintenance, like plugs, wires, cap, rotor, valve lash adjustment, ignition timing adjustment? All of these things will have a huge impact on how the engine runs.

post back answering the above questions and I'll move on to what to do next to get your power back to where it should be

 

Tried posting this once before, several hours ago. Hasn't appeared yet, so I'll try again:
Check engine light comes on occasionally, goes off when I restart the car. But this precedes the installation of the replacement engine. There are error codes (series of flashing lights; car is too old to talk directly to a computer). I'll ask the electrical specialist if any are still lighting up when I pick up the car tomorrow.
Symptoms are the three I mentioned: stalling during idling, lack of power, and transmission shifts no longer sync well w/ engine RPM, plus one other: an odd engine noise I have trouble describing.
I did also post on PreludePower, but I noticed there are some very technically astute people here, so I thought I'd try this forum as well. No response yet to my post on PreludePower.

 

no, you do your MAINTENANCE - theres absolutely no point of getting new engine for that. Unless your piston rings are gone and it burns oil a lot or theres some valve damage etc

and even if you get another engine there it would be wise to rebuild it to make sure thay its healthy


" quick what to do list

usually these things fix bad idle or/and hesitations:

- new spark plugs & wires
- new distributor cap & rotor
- new air/fuel filters
- clean injectors/iacv/egr/fitv
- bleed the coolant
- new pcv
- adjust valves and ignition
- adjust idle from tb's screw and throttle cable
- check does sensors work properly: map, iat and tps (and try calibrating tps)
- then check wires, connectors and hoses

check o2 sensors and vacuum/exhaust leaks (check all the seals - IM/header/TB gaskets, injector seals, maybe even buy valve cover gasket set...)
check timing. after that: double check timing

clogged cat might you give some trouble as well (usually when driving) - check cats condition

those are basic maintenance as well. "

but since you dont have correct ecu there and you engine is making noises.... it could be ruined already - do compression and leak tests

 

scroll up and read my comment, I'm awaiting your reply.
not to toot my own horn, but I'm a 3g guru. you'll probably see me all over preludpower, but I can't reply there anymore because I was banned for consistently talking smack about one of the douchey moderators lol

 

I wasn't able to answer until I got the car back from the mechanic. So here's the story:

HEAD DESIGNATION. Not sure where the stamp is supposed to be. I did see an "F9K" on the front right of the head. Could that be it? See pic below.




Also, for good measure, here's a pic of the engine as a whole (the red arrow shows where the "F9K" stamp appears)"


STATUS OF CAR:
After I picked it up from the electrical specialist (who fixed the starting problem by adding a booster and an additional ground wire), I swung by a Honda specialist he recommended. Here's what he said:

ERROR LIGHTS/CODES: None were on.

PLUGS/WIRES/DISTRIBUTOR CAP/ROTOR: The guy who installed the engine 10 months ago put in new sparks and Denso wires. Nevertheless, it now needs new spark plugs again. And one spark plug wire is bad, causing misfire (and the odd noise I was hearing). He wants me to pick up new wires (Denso or NGK), plugs (NGK), and, for good measure, a distributor cap and rotor (any brand), since the latter are cheap, so might as well replace them along with the sparks and wires. [Know a good online source for these items?] After I get them I'll swing by and he'll install them. [He could order them, but then I'd need to leave the car.] The misfire might explain some of the power issue, but probably not the stalling at idle (though it might be contributing to the problem). Also, he said the distributor/rotor was unlikely to be contributing to my stalling at idle, since if those were bad enough to cause the car to stall at idle they'd also cause the car to stall while driving. And while driving, I never have a stalling issue.

STALLING AT IDLE: He noticed the problem right away--the idle was dropping while I sat in drive. He initially thought it was the ICV, but wasn't so sure when he noticed no error lights were on (says when the ICV is bad there's almost always an error code). I told him it didn't make sense to me it would be the ICV, b/c I never had an idle issue until the new engine was installed. He said the guy that installed the new engine might have been lazy, and didn't bother to disconnect the ICV attached to the new engine and swap in my old ICV. I.e., when I got the new engine, I might have gotten a new (bad) ICV along with it. He bumped the idle up by 50 RPM, but it wasn't enough to prevent the stalling. It's now set to 1000/750 (park/drive w/ brake on).

ECU: He doesn't think this is involved in the stalling; he says the ECU mostly comes into play when the engine is cold, and my stalling problem gets worse the hotter the engine is.

TIMING AND COMPRESSION: The guy who installed the engine checked the timing and compression and said both were within spec.

PISTON RINGS: I get some white smoke, but not as much as with my old engine, which definitely had bad rings (which is why it wouldn't pass smog). Need to put in 1 qt of oil every other fill-up.

HEAD COVER BOLTS: You'll notice the center bolt is missing! But the mechanic told me I can get by with just the remaining four.

AUTOMATIC TRANSMISSION SHIFT POINTS: I can give you a more specific description of the problem. The issue is the car delays downshifting. So say I need some power on the highway and floor it. The car stays in high gear, and thus struggles. By the time it downshifts I'm going too fast for the lower gear, and the car actually suddenly slows a bit (due to engine braking) when the downshift occurs. I've noticed that putting it in sport mode (which forces lower shift points) helps a lot (at least in city driving; haven't tried it at highway speeds), but I don't like using this routinely b/c of gas consumption.

 

that engine bay pic helps a ton. the head that's on it really doesn't matter. the important thing is that the original intake manifold was used, which it was. that is the b21 intake manifold. reason being that the b20 intake manifold is drastically different, and you want the manifold to match the ecu, both of which are pk3 (b21). It's near impossible to have put the wrong ecu in the car because they have totally different plugs. so you're good there.

yes definitely replace the plugs (NGK only), wires (NGK only, do not use denso or any other brand), cap and rotor (any brand). all of these you will find the cheapest on rockauto.com. look everything up for the b21. you can search under the b20 as well, but make sure you're under the 2.0 dohc, not the sohc.

the first thing I see in the above pic is that the distributor is fully advanced. between that, and your lack of power and stalling issue, it makes me wonder if the timing belt is off a tooth or more. First thing I'd do once the new above parts are installed is get it fully warmed up, jump the service connector (left side of black vacuum box in back left corner of engine bay, it's a two wire connector stuck in a yellow rubber boot), unplug iacv, adjust idle screw to idle at 600-650, then run the timing light on the flywheel by removing the black rubber plug on the bell housing. the pointer should point at the middle of the 3 marks on the flex plate. adjust the distributor until it does. if you max out the distributor before it lines up, that means the timing belt is off, and that could be the entire reason for your issues. this procedure should be done every time plugs/wires/cap/rotor are changed.

Next thing I'd do is a valve lash adjustment. I'm assuming this has not been done in a while, if at all. It's supposed to be done every 20k miles or less, definitely much less after an engine rebuild. If it's off, this too can be the entire reason for your issue. And while the valve cover is removed for the valve lash adjustment, check to make sure the timing belt is installed correctly. if it's off a tooth or more on either cam, this needs to be corrected asap. As for the bolts missing from the valve cover, it's temporarily ok, but I highly seuggest replacing them asap because if any are missing it can cause oil to leak into the spark plug wells, causing heavy misfires and loss of power. You will also want to get a new valve cover gasket set to install when putting the valve cover back on to ensure these leaks don't occur. The missing bolts... they may just be missing, or they may be broken. if they are broken, the threaded part is actually a replaceable stud in the top of the head, so no thread repairs are needed, just replace the studs. you can usually order these at a dealer, or you can buy used ones from fellow 3g owners, we like to hoard piles of spares haha. I personally have a ziplock full of them haha.

lastly, the tranny issues. There is a kickdown cable attached to the throttlebody. that probably needs adjustment. This is part of how the tranny knows when to downshift. I forget how to adjust that though, I can report back later after I take a look at the service manual for a reminder. The shifter cable has an adjustment as well, which requires removing the center console to be able to see the shift cable. in a nutshell, the shifter needs to be put in neutral, and theres a couple scribe marks on the shifter housing base that are supposed to line up with a notch in the shift cable. if that is not adjusted correctly, the tranny will do all sorts of weird things. the cable has adjustment nuts to be able to slide it back and forth til it lines up.
One other thing to check too as for the tranny shifting wrong is the tps (throttle position sensor). backprobing the signal wire with ignition on should show 0.48-0.50 volts at full closed throttle, and 4.2-4.8 volts at wide open throttle. if the tps is not adjusted correctly, or is installed wrong, or is broken, the tranny will shift terribly.

 

If there is a bad spark plug wire causing a misfire, you are really only running on 3 out of 4 cylinders, so that will make any issue with power or any load on the engine much worse. For the 40 dollars or so it will be, get that taken care of right away, and see how the car does. In L.A. you should be able to find what you need just about anywhere, or have it within 24 hours with Ebay or Amazon.

Aside from that, motoxxxman has given you lots of more technical advice that is relevant to your car, and he is probably going to be the best source of information for a car of that age, that you will see on here.

 

Don't know why my big post with the engine pics disappeared. Sent a message to the site to ask if they could retrieve it, so I don't have to reconstruct it.

 

My last post still hasn't appeared, even after several hours. Damn, that was a long one--not happy about having to reconstruct it. Hopefully the admin can fix the issue. Going to copy and paste before posting this time. Anyways, here it is again:

Wow, that was extraordinary! Thanks for taking the time to write such an informative and detailed repair strategy!
May I ask your guidance on some of the part purchases?

SPARKS: There are several NGK options, which would you recommend as the best for my particular situation?:
Std/Copper: NGK 2262 {#ZFR5F11} V-Power, Gap 0.044"; Actual OE Part, $1.73
Platinum: NGK 7098 {#ZFR5FGP} G-Power, Gap 0.044", $2.17
Double Platinum: NGK 4363 {#PZFR5F11} Laser Platinum,Gap 0.044", $8,47
Iridium: NGK 2477 {#ZFR5FIX11} Iridium IX,Gap 0.044", $5.67

VALVE COVER GASKET: Does it make sense to get this one vs. the others specifically b/c it comes with new spark plug tube seals (which I assume are needed b/c I figure my current ones are contaminated with oil)?
FEL-PRO VS50391R w/Grommets & Spark plug tube seals; molded rubber Gasket. incl.; PermaDry® w/Grommets & Spark plug tube seals; PermaDry® molded rubber Gasket. incl. [[url=http://www.rockauto.com/lang/en/answersTab2.html#closeout]Wholesaler Closeout -- 30 Day Warranty] ($12.30)

DISTRIBUTOR CAP AND ROTOR: Sorry to bother you, but can you just tell me which ones to get? I was thinking maybe the AIRTEX/WELLS 3D1143, since it says it's the OEM replacement, and it has both the cap and rotor together. The reason I ask is the site seems to have some compatibility errors in it. For instance, this is the cheapest cap listed for the 2.1L w/ fuel injection, but it says "w/o FUEL INJ", and its picture looks different from that of all the others, since it has one port facing at a R angle:
AUTO-TUNE PT1519 w/TEC DIST., w/o FUEL INJ

Also, for the VALVE COVER BOLT, that's no longer available from my dealer or Majestic (or rockauto), so I'd be happy to purchase one used from you (along with the corresponding stud, just in case it's needed). So I sent you a PM. But you mentioned missing "bolts" (plural). Am I missing more than just the one in the center? I think I have all the rest -- the two in front, two in back, and the ones on each side. Here's an overhead pic, showing all the bolts, in case that helps:

 

I replied to your pm. it looks like the driver side rear VC nut is incorrect, I'll throw one of those in the package for the hell of it lol. but yeah, the middle is the only one missing.

for the plugs, the copper vpower zfr5f11 will make a little better power for the first 5k miles or so, but you'll want to check and adjust the gap on them at every oil change, and replace them every 15k miles or so. After the first 5k miles of use, they'll drop a little bit of power.
Don't bother with platinum plugs.
zfr5fix11 irridium plugs are good for 50k-100k miles (I recommend changing at 50k, or anytime they ever get fouled with soot or oil). they will make a hair less power when brand new compared to brand new copper plugs, but their power production doesn't fade over time like the copper plugs. so the choice is yours there.

VC gasket set, yes, that felpro set that includes grommets and seals is what I always use too. and it can be reused several times for up to a year since first installed in most cases. just clean any and all liquid gasket off the head surface, and clean all oil off the surface where the gasket touches too. And put a tiny dab of liquid gasket ONLY in the corners of the cam caps, where the curve sticks up from the head surface.

The airtex wells cap with rotor is good. I usually use beck arnley, but they should be about equal. It's funny actually, the airtex cap with rotor is only 19 cents more than just the airtex cap haha.
the autotune cap is wrong, I don't know why it shows up in that list.