I've owned my 95 prelude vtec 5 speed for 1 year. In the past 3 - 4 months, I've noticed my RPM has decreased when at my usual cruising speed. At 80mph, my RPM is at approx. 3000 (whereas it used to be a normal 3500, easy). Even pushing the speed limit to 90+ mph only increases my top RPM to barely 3300? I can't reach 4000 - 5000 RPM without feeling like I'm really "pushing" my engine to its limits...! My car "feels" normal -- no pinging, knocking, tranny feels smooth and by all other interpretation, my engine feels "strong". I just don't understand why the sudden loss of power?

even out of 1st gear, i can't rev my car past 3000 RPM. I usually go to 2800-2900 RPM before having to shift to 2nd gear... and every gear is the same -- my RPM does not spike past 3000 unless I press the pedal to the floor (which I am reluctanct to do, since I do not wish to stress the car; plus it used to drive normally before).

I've taken it to a Honda dealership where they ran diagnostics and they told me the computer chip did not return any errors with the car. They did find a crack in my header.

In the past month - I've replaced my cracked exhaust manifold. It did not increase my RPM. I also replaced my catalytic converter (it wasn't clogged like I expected, but I put in a new one anyway hoping it would help). Nope, it didn't help. I've even replaced the clutch (which just happened to go out). That didn't improve the RPM problem either...

Another weird thing is: about 2 months ago (before i fixed anything), I was driving to work and the problem miraculously CORRECTED itself! For my entire 15 minute drive to work that morning, my RPM was back to normal -- i could accelerate quick, punch my gas and see my RPM needle easily spike past 3000 - 4000, EASY. Then when I hopped back into my car later during my lunchbreak, it went back to being all f*cked up again! It's never improved since... what' sup wit dat?? I'm so confused... My resting (idle) RPM also seems a bit high (at 1500). It used to be 500 or so before all this began...

What could be the problem? Is it the O2 sensor? Is it my aftermarket cold air intake? my timing belt? I don't know where to look next -- running out of patience and money!

it says I CAN'T POST MORE THAN 5 MSG PER 24hr period??? how do i change my member settings? do i have to pay or something? i'm getting helpful IM's and replies... unfortunately, I'm unable to respond??!


also - what are the known symptoms of an old timing belt? could i possibly be a case study? (i've yet replaced mine in the year i've had it. it's got 150k miles on it)


Modified by pkprelude at 4:05 PM 5/8/2003

 

First things first:
There is a Honda God, and he doesn't like Preludes. He has cursed us all.

I would start with the timing belt.

Make sure that the hydraulic tensioner is still holding STRONG. Do this ASAP.

I'm assuming you've changed plugs, wires, rotor and cap etc.

 

I have a factory Honda Manual at home i will look tonite to see if there is a troubleshooting process.

 

I've not changed plugs, wires, cap/rotor, etc. I've had the cap/rotor visually inspected and was told they were in good condition about 2 months ago. Otherwise, I suppose it is time for a tune up (over 1 year). Could it be that simple?

As for the timing belt -- I am aware of the infamous reputation that all Honda owners need be aware of this golden rule (of changing every 90K miles). I bought mine at 135K. Previous owner had no record of timing belt change, but said the work was done when he purchased the car himself at 90K. I've yet replaced the timing belt myself, and my car is now at 150K.

Regardless, my question is: What are the known symptoms of a bad (worn out, soon-to-be-going-out) timing belt?

 

Symptoms of bad timing belt:
1. Belt snaps
2. Engine stops
3. Valves bend

You can check it visually, but old timing belts don't always show wear. I had a 60k old belt on my previous car changed that could have been confused for the new replacement one.
The timing belt is an interval peice no matter what. Cams reduce the operating life, btw.

 

An easy check would be to remove the valve cover to access the top of the timing belt and check for slack or worn ribs.I dont think the rpm problem is related though.It sounds more like a voltage problem to the tach.Have you tried hooking up a tach under the hood.On the pass side strut tower there is a blue wire in a connector usually in blue tape.That is the tach wire.You could either get a tach from someone to borrow and connect power and that wire and then check the rpm's or some voltage meters have a tach function on them also.

 

visual inspection sometimes means jack.
Replace all of the above.

And TIMING belt isn't your issue. It's the SLACK in the belt that will cause it to bog etc.

I KNOW about that. Pull the valve cover off, and the cover for the timing belt off and check to make sure it's tight. Make sure you cant slide it back and forth easily on the cam sprockets.

If the tensioner is gone/going out, then it'll cause slack in the belt, and the cams retard themselves because they're running behind the crank. It's a VERY deffinate possibility. I had the problem three times in my car, and just had it in Mikes. The very same symptoms.

I'd do plugs, wires, and cap. Just suck it up and replace them.

 

actually, it sorta sounds like an intake problem. This happened with my AEM when the extention tube was inside the filter leaving a 1/2" ring around the top of the filter for air to come in... tromping it let it revv to barely 3700 rpm, and it revved really slow. You might want to check your intake track and make sure nothing got sucked up somehow, and that your filter is good. maybe the intake tubing collapsed (dont' know how but who knows). It could be alot of things but this is a pretty easy and cheap thing to check out...

 

It's got to be the tach. Sounds like your engine is getting up there on the RPM's, but your tach isn't displaying it. At 90 in fifth your RPM's should be around 5000.

 

ahh you mean the engine is revving insainly but the tach is reading really low? If that's the case, the tach coil is most likely burned out... and IIRC they aren't cheap, something in the ballpark of $200