90 prelude with 88 motor transplant, random start problem - Honda Prelude Forum

dynabill · 09-10-2011, 08:15 PM

Hi all, My son has a 90 SI fws we bought the car with an 88 motor installed,2.0l it ran good on the test ride (don't they all) after a few malfunctions, ie.. clutch master cylinder, alternator replace. the car would fail to start occasionally. PO said we may have to replace computer because of older motor with new technology. was wondering if there was any truth to this. (I was on a trcker forum for 3 months trouble shooting one I had, so i am thinking that this may hold water.) We took it to the shop that my buddy owns eventually he came to the conclusion that it was the disty. So it has a new disty. still same problem. I was home, and car failed to start one night. neighbor had spark tester, and all four cylinders were firing, we could smell gas, (didn't have time to test fuel pressure) finally i had him roll all windows up and close sunroof. all electric. car started. He has been pop starting car lately when car wont start. so my thoughts are, possible computer problems, because of 2.0 motor in a 2.1 electrical system, some sort of short, loose wire, or fuel pump problems. Any help, would be appreciated. I will gather info about car as needed. I can give vin numbers if this will help with car identification. thanks Bill
also CEL comes on with key in on position, intially it wasn't on, but now it is. son hasn't had it checked yet. maybe tomorrow. will advise when i know what it is. Cheers

S-LudeDan · 09-10-2011, 08:31 PM

when the PO swapped in the 88 motor, did he also swap in the 88 ecu? or he left the same ecu that was already there?

dynabill · 09-10-2011, 08:34 PM

yes the original ECU was left in the car. thanks was calling it computer, couldnt think of ecu. cheers bill

S-LudeDan · 09-10-2011, 09:08 PM

that might be your problem. But like I said, might be. I think you need the original ecu compatible with that motor.

dynabill · 09-10-2011, 09:37 PM

hey dan, thanks for quick replies. that is the way I was kind of leaning.I will check codes in the a.m. what am i looking for, is there oem, numbers i need. there has been no mods to car other than air intake. Another thing I didn't mention. when i go WOT the motor will hit a certain point and loose all power until I release gas pedal. Than rpms will come back up and run normal. This only happens when I slam gas pedal to the floor. normal acceleration this doesnt happen. I am thinking that this is connected to the ecu also. Cheers bill

Colfax · 09-12-2011, 12:05 PM

I'm pretty sure you have two unrelated problems. First of all, if when you swap a b20a into a 3rd gen than originally had a b21a1, as long as you retain the intake and exhaust manifolds from the b21a1 you will have no ecu issues running the b20a. Don't attempt to use a pk2 (b20a5) ecu in place of a pk3 (b21a1). It won't plug into the harness anyway so it's useless unless you swap the harness and a few other things as well.

Problem 1. I suspect that your first problem is the main fuel relay. You can try this fix Main Relay Fix

or just buy a new one.

Problem 2. Your second problem sounds like it's the tps (throttle position sensor). I had this issue on my 91. If someone has replaced it they may not have adjusted it properly. What I did was replace the throttle body (with tps) from a junkyard pull I had. I didn't have to adjust anything.

dynabill · 09-13-2011, 11:33 AM

Hi col thanks for the reply. I did fuel pressure test and saw that pressure was low. I did find main relay fix and did tests on it it was bad so I have a new ordered. I have adjusted gps before was wondering if u had a link for specs on it thanks for reply. Cheers. Bill

Colfax · 09-14-2011, 09:54 AM

Here is a link from an online factory service manual for troubleshooting the tps (referred to as throttle angle sensor in the manual). Remember that when it says to open the throttle body fully, use the gas pedal and don't manually open the throttle body with your hand. You may be able to actually open it a slight amount farther with your hand than you can with the pedal, and it may throw off the adjustment.

http://media.honda.co.uk/car/owner/m...f121/6-138.pdf

dynabill · 10-16-2011, 08:09 AM

Hi all, colfax I hope you are reading this. we are still having problems with sons 3rd gen prelude. I have been through the fuel supply system starting on page 6-188. the only thing I really havent done is check injectors for clicking, I have done injector resistor test, pressure regulator test, main relay test, main relay harness test. So far this is what I have replaced,New distributor, fuel filter, main relay, and recently fuel pump,
First time through, I missed the main relay test, so we bought one on line, both are testing out perfect now. before I commited to new fuel pump, didn't want to throw money away, but did, i resoldered old main relay, and tested main relay on page with pump replacement ( i only found this after printing out replacement page.
At any rate, car is still doing same thing, random "no starts" If you wait long enough and crank engine occasionally, the car will eventually start on its own. It will always pop start, and run. It never dies while running either. I had fuel pressure gauge on it once when it wouldn't start, and gauge would slowly climb to recommended pressure and than start.
I found this page Honda Acura Essential Electrical Repair Website. Troubleshooting Main Relay, Coil, Igniter, etc. and saw where I should check grounds on the ECU, we havent done that yet, it is on the list as is aligning fuel injectors with hash mark on head, ( not sure if the 88 engine in the 90 lude has these, but next work session I will check it. also, I want to make sure ECU is correct for year and model lude.
So I am now leaning toward ECU probs, for some reason ECU may not be sending enough voltage, or weak signal to main relay. and possible injector problems. if anyone has other thoughts, please throw some ideas out.
I did go through the grounds in engine compartment and sanded and retightend them.
I was wondering if perhaps ignition switch could be failing to?
anyway thats all I have for now, thanks in advance for any help.
Cheers Bill

Colfax · 10-17-2011, 11:16 AM

There are a couple things you said that kind of stand out to me. You can bump start the car and it always starts this way? That could just be coincidence, but it also leads me to suspect the ignition switch. I know that they are a common problem on 3rd gens. I had to replace mine a couple years ago. But the symptoms were that the radio and heater blower would stop working. I didn't have any troubles starting the car.

The other thing that stands out is your description of the fuel pressure. Maybe your fuel pressure regulator is malfunctioning.

As far as the ecu goes, it would be good if you could look at it and post up if it's marked PK2 or PK3. I'm suspecting it's a PK3, which is what your 90 Si would have come from the factory with. An 88 Si would have come with a PK2 ecu. As long as you are using the stock intake and exhaust manifolds, you want to use a PK3. Maybe post a quality pic of your engine bay so we can see which intake manifold you are using.

dynabill · 10-21-2011, 09:17 AM

Ok I have some pics, ready to post. ecu is a pk3, , cheers Bill

dynabill · 10-21-2011, 09:28 AM

I forgot exhaust pics here they are. cheers Bill

Colfax · 10-21-2011, 11:18 PM

What you have there is kind of an anomaly. That's a b20a5 intake manifold (pk2), and the ecu is pk3. I can't tell about the exhaust because that's an aftermarket header, and your pic doesn't show the lower end of the header. Look and see if the header has two O2 sensors in it. They would be located just below where the pic cuts off, lol.

Whoever swapped that b20a5 in there made it more work than they needed to. It would have been easier to use the original intake manifold that came with the car instead of using the one that came with the b20a5. I don't know if that combination is causing any problems. I don't know anyone who's running that combination. Although I'm sure there are some.

BTW, just so you know. That transmission (D2J5) is also from an 88. Your 90 would have come with a D2A4. So if you ever need to replace the clutch, be sure to buy a clutch kit for an 88 2.0 Si.

dynabill · 10-22-2011, 09:44 AM

Hi colfax, thanks for all the info. I checked o2 sensors there is only one, before cat, none after. Not sure if I posted this but, Cel operates normallyon for two seconds and audible clicks, i hear fuel pump. I am showing code 6, intake air temp. I did ohm test and it is in specs. I gues i am gonna have to back probe ecu to see if it is showing correct amps. I don't know if this is my problem, although, it wasn't showing when we bought car. I also checked coil and it is within specs too.
Are you thinking that I need to use pk2 ecu? My gut told me not to get this car, should have listened to it. Oh well! thanks for your help. I don't give up too easy on these things Cheers, Bill

Colfax · 10-22-2011, 10:36 PM

Quote:

Originally Posted by dynabill

Hi colfax, thanks for all the info. I checked o2 sensors there is only one, before cat, none after. Not sure if I posted this but, Cel operates normallyon for two seconds and audible clicks, i hear fuel pump. I am showing code 6, intake air temp. I did ohm test and it is in specs. I gues i am gonna have to back probe ecu to see if it is showing correct amps. I don't know if this is my problem, although, it wasn't showing when we bought car. I also checked coil and it is within specs too.
Are you thinking that I need to use pk2 ecu? My gut told me not to get this car, should have listened to it. Oh well! thanks for your help. I don't give up too easy on these things Cheers, Bill

Code 6 is for coolant temperature. Use this link for reading the trouble codes on 3rd gens...
ECU Error Codes

Your setup surprises me. You have the b20a5 intake manifold, but everything else is from the b21a1 that used to be in the car. I'm kind of curious as to why they didn't retain the original intake manifold. You won't be able to switch to the pk2 ecu without a conversion harness. Besides, you'd be going from OBD1 to OBD0. What you probably need to do is to switch the intake manifold. But I'm not sure what they did to make that intake manifold work. The vacuum lines are a bit different and so is the control box.

If it was me, I'd hit my local junkyard and grab an intake manifold and vacuum control box off a 90/91 Si. Put it back to a known condition and then troubleshoot from there. With what you have now you might just be chasing your tail. Maybe it has nothing to do with your problem, but even it not it's not the way it should be.

dynabill · 10-23-2011, 08:22 AM

Hi thanks for info, not really what I wanted tohear, but... is the way things go. On vac control box, just to be sure, that is the black plastic box in upper left hand corner of 2nd motor pic?

I did the check on water coolant temp http://www.1funryd.com/hondapreludemanual1988.pdf fromthis page. Only as far as checking the .TW sensor. It was within specs. Im not sure if I need to finish, this test and back probe ECU to check voltage.since I have a bastard mix on this car. what are your thoughts, it all kind of leads to ecu problems. which could be because of wrong parts on car sending bad info to ecu. guess i am chasing my tail either way. lol

Am i locked in to only using prelude motor parts or is there other models, such as civic or accord I can rob parts from? thanks
Cheers Bill

Colfax · 10-23-2011, 11:02 PM

Quote:

Originally Posted by dynabill

Hi thanks for info, not really what I wanted tohear, but... is the way things go. On vac control box, just to be sure, that is the black plastic box in upper left hand corner of 2nd motor pic?

I did the check on water coolant temp http://www.1funryd.com/hondapreludemanual1988.pdf fromthis page. Only as far as checking the .TW sensor. It was within specs. Im not sure if I need to finish, this test and back probe ECU to check voltage.since I have a bastard mix on this car. what are your thoughts, it all kind of leads to ecu problems. which could be because of wrong parts on car sending bad info to ecu. guess i am chasing my tail either way. lol

Am i locked in to only using prelude motor parts or is there other models, such as civic or accord I can rob parts from? thanks
Cheers Bill

Yes, that's the vacuum control box. Here is what a b21a1 intake manifold looks like. It's not a detailed pic, but you can see the differences in the vacuum tube routing.

You could try another pk3 ecu. I've read that there are other Honda ecu's that will work with an OBD1 system like yours. But I'm not sure on that and you would want to do some research before trying it.

I wish I could be more help on this, but I have no real experience with the combination you have. If it was me I'd probably try to find the original b21 parts and change out what you have that is from the b20a5. But I'm not sure if you want to do that.

dynabill · 10-24-2011, 07:10 AM

Hi colfax, I checked ebay for intake manifold and found this , 90-91 honda prelude OEM intake manifold injectors si | eBay saying is for a 91 prelude. this is the one that is on the car. So I am assumeing that I am ok with what is on there. also, vaccuum control box looks the same as yours , it has four tubes coming out, not 5 like it show in the manual, but that could be because of different models,ex. ky, kx, etc. I checked vacuum lines from map that is on the hood and compared to one from online manual and they are the same. I did find that the moron PO had one wrong and fixed that too. I did find that hose that comes from vacuum advance,(next to fuel regulator) was stuck in a hole, not a fitting or tit, but kind of stuck in plastic connector after the 90 degree turn for filter on the intake.. I will get pic and show later
I did find a vacuum leak, it was over by the cruise control actuator, front right side. repaired that and it helped lower idle speed, which is expected. for some reason, there where two check valves on it. still doesnt work, but that's not an issue now.
when i verified pk3 ecu, i also looked at ignition switch, droped lower steering wheel cover and pulled 3 prong connector apart and replaced. I didn't do much but nose around a bit. I also removed the ICU aand reinstalled. I put it all back together and took neighbor for test drive. The radio, kept shutting off but would turnback on ocasionally while driving. If i took key to acc position, the radio would power back up. this is leading me to think that the problem may be in the key switch. When the car starts and runs, it runs great, idles nice, no noticeable rough idles or anything to point out. other than when I go WOT it has that dead spot. I don't notice any power failures, all accesories work. I Only thing is the radio. I am going to go back and check all of the connections i took a part and verify that they are tight and making contact. Than I am going to take back side of ignition apart and see if there is any pitting on contacts . reason i am leaning this way is I went from key in and slowly turned to make the starter crank, Other than doing a fast turn to where it ends). what i heard was almost like electric arcing, almost sounds like main relay clicking off and on fast. but really didn't sound like it was coming from there. More like under steering column where elec connections are made. I am going to use this link http://techauto.te.funpic.org/ignitionswitch.php as my guide. I'm not sure if the ignition will be the same, but will find out. I hope you can follow some of my explanations, if not I will try and make clearer with pics and answers. thanks for your help. Cheers Bill

Colfax · 10-24-2011, 07:40 AM

The intake manifold in the pic is from a b20a5. The seller has is listing it wrong. It very well could be from a 90/91. But it's from a 2.0 Si (b20a5), not an Si (b21a1). Look at the end of the plenum and you'll see that there are several small vacuum lines on your intake. Then look at the pic I posted and see that there is a single large line for the b21a1 intake. There are other differences in the intakes, but that's an obvious indicator for me. The b20a5 was available all fours years that the 3rd gen was produced. But the b21a1 was only available in 90 and 91. Here are the models that were available, at least in the US...

88 and 89
Prelude 2.0 S (b20a3)
Prelude 2.0 Si (b20a5)
Prelude 2.0 Si 4WS (b20a5)

90
Prelude 2.0 S (b20a3)
Prelude 2.0 Si (b20a5)
Prelude Si (b21a1)
Prelude Si ALB (b21a1)
Prelude Si 4WS (b21a1)

91
Prelude 2.0 Si (b20a5)
Prelude Si (b21a1)
Prelude Si ALB (b21a1)
Prelude Si 4WS (b21a1)

The symptom you described about the radio turning off and on is classic for a bad ignition switch. It's not the key section, it's the electrical part that the key section is connected to. You can try cleaning the contacts on the switch, but your best bet is to replace it while you can still buy one. It's #12 in this link...
Part Detail

dynabill · 11-03-2011, 03:35 PM

I replaced ignition wiring and car is still acting up. I am thinking fuel regulator, will that work intermitently>? Radio problem was bad wiring behind it. I guess if its not fuel regulator I'll have to get intake for it. Another thing, is there a certain ecu that is needed for that car, if so can you advise.
One other thing when car is not starting, you can really smell gas in engine compartment. That isn't normal for a fuel injection system. Any thoughts on that? Perhaps rubber seals on injectors? IDK. One other thing will there be any issues bolting up the b21a1 to the existing block on ?

any way thanks for the help. ?Bill