Engine problem driving me crazy... please help! - Honda Prelude Forum

devtec · 10-04-2008, 05:42 PM

Hey all,

My engine is just making me really depressed, and I'm about to go crazy so would appreciate any help.

Here's the deal: got an S Spec engine (235psi across the board) swapped into my 97 SH exactly 1 year ago, and it has just never been right. Soon as the swap was done, problems started with a severe stuttering/stumbling/misfiring during acceleration from 2000-3200 rpm (such that my car would be jolting down the road looking like I couldn't drive a stick), and I was getting about 15-16mpg city. Also when cruising at these low rpms, I'd intermittently feel just a blip when the engine wasn't firing. Needless to say, low end power was also very poor.

After about 8months of troubleshooting, finally replaced the TPS, and the stuttering disappeared immediately. Engine came to life, got 24mpg city, and the car felt like a beast! I was a happy man. What vindication.

Well, this lasted for a week. One day it was raining heavily and I felt a very distinct moment when the engine just bogged down and power disappeared. Thought I had a flat at first. But I didn't, and since then the engine has remained weak and loud. It has gotten a little better, but still feels off: low end power is terrible, sounds louder like the engine is struggling or like the ignition timing is off, and I'm back to getting about 16mpg. I do not have a CAI (have a Type S), so I don't think it was hydrolock by any means. I replaced the TPS again, but it made no difference.

Funny thing, also when it was raining my horns pretty much stopped working, got really quiet, made maybe 5% of their normal sound. After a few weeks, their sound returned to normal. Don't know if this is related, but it made me suspect some sort of electrical problem (main relay?).

I get totally down every time I drive the car now. I've spent all this money, and have never been able to enjoy the car except that one week when it was driving beautifully.

Here's what I've done so far, and whatever else I can think of to check:

ELECTRICAL
- replaced ECU with a known good SH ECU, JDM S Spec ECU, and got tuned with a P72/Hondata S200; none of them solved problem
- Poor ground somewhere?
- Main relay?

IGNITION
- replaced spark plugs (tried iridium, platinum, copper), wires, distributor, distributor cap & rotor; none solved problem
- Ignition coil?

AIR
- replaced PCV valve
- cleaned EGR valve, EGR intake ports, throttle body, IACV

FUEL
- replaced fuel filter
- tried fuel injector cleaners multiple times
- Fuel pressure regulator?
- Fuel injectors?
- Fuel pump?

SENSORS
- replaced knock sensor
- tried a known good MAP sensor, made no difference
- O2 sensors are new from the swap
- replaced TPS twice, eliminated stuttering, but now back to poor power and fuel economy

So if you guys can think of anything else I can do, please let me know. I don't think its a fuel problem. Right now I'm thinking it's some sort of electrical problem, since the new problems started in the rain, and I had some other funnry electrical stuff happen. But really I'm at a loss and don't know what to do next. The shop that did the swap won't help me, they think I'm crazy. Well, I have the 16mpg and resulting depleted bank account to prove it. I've never had a CEL throughout any of this.

Thanks in advance for your help.

h22aluder · 10-08-2008, 10:58 AM

hey I actually have the same problem with my lude. misfiring bucking stutering in low rpm does it do it more in uphill driving or fast acelleration? well mine does and i still have not diagnosed it. All I have tried doing is changing the fuel filter. yeah I'm broke and really strapped for time, but I think I have a fuel or spark problem. next thing i'm gonna do is get the injectors cleaned. well let me now if you find a diagnosis caz it's a real pain in the ass driving a car that eats gas and doesn't act right.

98auto · 10-12-2008, 09:37 PM

mine does it too. it does it from 1000rpms to about 2200 rpms. If I drive with light load in this range, the car bucks and feels like every other cylinder is misfiring. no codes. Im guessing tps. Since Honda has decided that I must replace the entire throttle body, Im not fixing it.

devtec · 10-12-2008, 09:41 PM

98, you can find an OEM replacement omnipower TPS on ebay for $29. Look for my writeup on how to replace it. Very easy, takes about 20 minutes.

How to replace and adjust Throttle Position Sensor (TPS)

My problem now though is no longer bucking, but low power and fuel economy. I think I'm going to try replacing the ignition coil next... how much money will this take.......

prepreludesh · 10-12-2008, 10:04 PM

That's a tough one man!

Wow, you did everything I could think of and still I see you're having trouble. My first thing i would've gone for is the MAP sensor after you said you replaced the TPS Sensor. I believe they both have the exact same connector, and I remember after my supercharger got bolted up, the very first problem I had and couldn't figure out was why the engine sputtered while giving it gas, turns out I had the MAP sensor plug plugged into the TPS (I had an aftermarket MAP sensor so I really didn't need it) but after switching it, it ran right.

The second thing I would've guessed was a fuel pump failing due to your lack of power (meaning not enough fuel is getting to your injectors) but that wouldn't make sense if you had previously replaced your TPS and everything worked well. Also, the fact you said your horns are very weak make me wonder what is going on electrically in your car...

Have you tried a very simple ground wire strap kit? It's a simple and effective way to troubleshoot the idea of a poor ground in your car. Hell, you might just want to strip a really thick wire or two and start by grounding one from the battery terminal to the car and then one from the terminal to the engine/trans.

Also, have you tried switching out batteries? Maybe this battery you have in is going to fail? Or do you have an aftermarket radiator with stock fans? I know when I put my Koyo Radiator in with stock fans, the metal fan shroud of the drivers side fan cut into my alternator power cable and shorted out my whole car.

Have you tried replacing the fuses? Or at least checking them? Granted fuses either work or they don't in my opinion, but it never hurts...

If you don't know how to do a compression test, why not go get one? It might not be that expensive and could show you if you are losing compression in one of your cylinders?

Have you noticed any increase of black soot coming out of your tailpipe? I'm sure you would throw a CEL if you were, but you made no mention of any CEL coming on.

I'm interested to see what this turns out to be! Keep us informed!

vinuneuro · 10-12-2008, 10:42 PM

Dev, you can test all the ignition components. Look in helms. Definitely test whatever you plan on replacing first. All you need is a multimeter.

devtec · 10-13-2008, 04:56 AM

thanks for all your suggestions preprelude.

TPS vs MAP: you say the connectors are the same? not getting any CELs, but will double check if the connectors are swapped.

Fuel pump: will get my fuel pressure checked somewhere.

Ground wires: will be purchasing materials to make my own ground wire kit. I have a big 6 channel amp anyway, so this will probably help irrespective of the engine problem.

Battery: it's an optima yellow top deep cycle battery, so strong and damn near indestructible. Don't think it's a prob, but will test voltage to make sure.

Radiator: don't have an aftermarket one.

Fuses: guess I can check these...

Compression: recently tested, all numbers good.

Soot: some around exhaust tip, none on bumper, seems about normal.

Timing: according to shop that did the swap, they adamantly say it's fine.

Vignesh, yes, will break out the multimeter and test what I can. thanks as always.

98auto · 10-13-2008, 11:11 AM

You can check the timing with a timing light to be sure, but the ecu controls the timing unless the timing belt is off a tooth.