Major accelerations issues - Honda Prelude Forum

AngryTaco · 03-29-2011, 11:15 AM

I have an 89 si Dohc 2.0. I just swapped in another si engine out of a 91. It idles fine and has no problem warming up and idles at about 750. Problem is..... Even when Im in neutral, the engine bogs like crazy when I open it up. After about 1-2 seconds of bogging itll pick up the rpms but my top speed was about 70mph after flooring it for a good 1/2 mile. It will not stall even though the rpms dropped to around 200 after stopping. (5speed btw). O2 sensor maybe? Im losing my mind over this.

Colfax · 03-29-2011, 01:41 PM

Was the engine in the 91 an Si or a 2.0Si model? If it was an Si, it most likely contained a b21a1. If this is the case, did you use the intake and exhaust manifolds from that engine, or did you use your manifolds from the 89?

You didn't really say what you've done to fix it, so here's a few things to check if you haven't already...First of all, are there any trouble codes stored? You need to make sure and take care of those if there are. Can I assume that you used new spark plugs, distributor cap, and rotor when you changed engines? Did you replace the timing belt when you changed engines? If so, make sure your crank to cam timing is spot on. Then check your ignition timing to make sure it's also correct. Be sure to jumper the connector with the yellow cover while you adjust timing. Have you replaced the fuel filter? You could also have dirty injectors. that should keep you busy for a little while.

AngryTaco · 03-29-2011, 02:34 PM

Yes it is an si engine. I did not swap the intake or exhaust manifolds (i did however swap the throttle body as the sensor was broken on it). The timing belt looked fresh as well as the rear main seal. I did not change anything other than swapping the alt, ac, ps, etc over. I did swap the distrib and cam sensor over from the old engine. Plugs are new, wires are fresh and there is spark. Also, whether or not its a B21a1, IDK, but I do know B20A5 is stamped on the block

AngryTaco · 03-29-2011, 02:37 PM

I also see that you are in eastern washington. Im in spokane, where might you be? Colfax judging by your name?

Colfax · 03-30-2011, 08:40 AM

Lol, was it that obvious? Yes I'm in Colfax.

It's a b20a5 then if that's what the stamp says. Just a little information for you...The 90/91 3rd gens came with one of two engines if they were fuel injected. The 90/91 Si had a b21a1 and the 90/91 2.0Si had the b20a5. The b20a1 is OBD1 and the b20a5 is OBD0.

Now, as for your problem...have you checked for any engine codes? This is the first thing you should do. I'm suspecting you may be having issues with the throttle body you are using, specifically the throttle position sensor (tps). It's kind of important to know what model the donor car is that you pulled the engine out of. Even though the engine is a b20a5, it's very possible that the car may have had a b20a1 in it originally. It's common for people to swap from the b21 to a b20. If the original engine was a b21, then the wires going to the tps will need to be modified to work with the new tps mounted on your throttle new body.

So please check for trouble codes first, but also post up what model the donor car is.

AngryTaco · 03-30-2011, 09:17 AM

Well unfortunately, I did not do the pulling myself as I had it shipped out of california. From what they told me, it came out of an Si model but they werent specific as to the 2.0Si or just Si.

Edit: I just realized I didnt make myself clear; the TB is from my oringinal '89 engine as the donor engine's TB's sensor was hacked off by someone a little to eager to destroy things. But I am using the cars original obd0 TB

Colfax · 03-30-2011, 09:58 AM

In that case it doesn't matter, at least as far as the throttle body goes. But that brings up another question then. You said did not swap the intake and exhaust manifolds. Does that mean you are using the manifolds that came with the engine? You don't happen to have a picture of it do you? I can tell at a glance if it's a b21 or b20 intake manifold if the picture is clear.

Check for trouble codes then. Here is a link describing how in case you don't know...

ECU Error Codes

AngryTaco · 03-30-2011, 12:05 PM

I swapped the exhaust manifolds but that was it. From what I saw they were the same other than how the exhaust pipe bolted up to the manifold (newer one had studs and I didnt have the proper nuts so I put the original one on). Ill try and get a picture up later. I workin airway heights and the car is in my dads shop up in Athol

Also, from what I could tell, they looked the same; all the vacuum lines hooked right up and everything is where the original one is. What are the differences?

Colfax · 03-30-2011, 01:06 PM

There are several small differences, but mainly the b20 IM has two sets of runners and a set of valves that divert the air into the proper runners depending on rpm. The b21 IM does not have this, and has fewer vacuum lines. As long as everything was the same as far as vacuum lines go, it's a b20 IM.

So we're back to pretty much first doing what I've already recommended. Check the trouble codes, distributor cap and rotor, and make absolutely sure that the crank to cam shaft timing is perfect, and then make sure the ignition timing is right. Then replace the fuel filter. It's mounted on the firewall in case you were wondering. Then, if you have any codes stored, we'll have a better idea of where to go from there.

AngryTaco · 03-30-2011, 09:00 PM

Appreciate the help. I'm a Dodge and VW guy, hondas are a mystery to me right now. I'll be getting to it Friday night and should have it figured out Saturday. I'll get back to you after I change what was suggested.

Ive never owned a car with so many damn vacuum lines running around

Colfax · 03-30-2011, 10:49 PM

Lol, I know what you mean. Until 2006 I was strictly a Chevy guy. But these engines are pretty easy to figure out. And if you think your b20a5 had a lot of vacuum lines, you don't even want to look under the hood of an 88-90 Prelude S model (dual carb'd). At least three times as many vacuum lines as you see under your hood.

AngryTaco · 04-11-2011, 09:05 PM

Just thought I'd give an update.

The problem was a combo of 2 things. The ignition was too retarded so I put it on full advance and run mid-grade 89.

One of the temp sensors harness on the thermostat housing had a broken wire.

Thanks for the help again man. Now to sell it....as my friend wants to sell me his 86 Audi Quattro 4000 CS

Colfax · 04-13-2011, 11:10 AM

Glad to hear you fixed it. So that's your 89 lude for sale on the Spokane craigslist. Congrats on the Audi, but you're gonna miss the lude once it's gone.