1992 Honda Prelude Running Rough

1992 HONDA PRELUDE
175,000 MILES • 4 CYL • FWD • MANUAL
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DAVID-B
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The 2.3L was running smooth a week ago, then suddenly started running as if one cyl. wasn't firing. Still runs smooth for the first minute after startup, then starts running rough (a very consistent rough though), and you notice it at idle and acceleration, not when slowing down. After stopping and getting out of the car, there's an unusual burning smell.

Since then, I've replaced plugs and distributor, and run some injector cleaner through it but that hasn't helped. The code from engine light is 23, which means Knock Sensor, but that's been intermittent for 2 years and think that's unrelated. So, it seems the remaining possibilities are these three and look for your comment on A) which is most likely, and B) how to isolate in the most effective way...

1. Dirty injector, or failing injector (meaning the solenoid plunger inside the injector).
2. Intake or Exhaust valve that seats when engine is cold, but then doesn't after running a minute.
3. Manifold Actual Pressure (MAP) Sensor (see this in the manual's troubleshooting chart. Expensive part.

Regards, David
Nov 28, 2008 at 8:03 AM
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KHLOW2008
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Hi David,

Thank you for the donation.

What is the idling rpm, at cold start, after 1 min of cold start and warmed up?
At idle, rev up engine to 3000 rpm and release accelerator, does the engine rpm drop to below 700 and then rise again?
Did you test the resistance of all the plug wires?

Honda seldom have problems with the MAP and injectors and the most likely cause would be tight valve clearance.
Nov 28, 2008 at 9:02 AM
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F4I_GUY
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Sorry but I disagree. I have seen quite a few injectors fail on hondas. I am not sure if it's the weather up here (in canada) but I have seen honda injectors fail and not fire whatsoever.

Anyways, do a cylinder balance test, unplug each injector one at a time, if you unplug an injector and the engine note/ idle doesn't change whatsoever then you have isolated that cylinder to be faulty. I would then go into tests for STRONG spark, fuel and compression.

A quick test for injectors is to use a stethoscope or just a long screwdriver and have a listen to each injector. This is not an accurate way by any means, but this tells you if the injector is atleast firing or not.
Nov 29, 2008 at 1:05 AM
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KHLOW2008
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Hi,

I did not say they won't fail, just that they seldom fail. Plug cables failures are common and that should be the first test. If those are positive, then we should proceed with the next.

Thank you for the input. It does provide more options.
Nov 29, 2008 at 6:27 AM
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DAVID-B
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First, to your questions:
- When starting the engine cold, it goes to 1,650 rpm on its own.
- Over the course of a few minutes of warm-up, idle drops to 1,000 rpm.
- If then taken to 3,000rpm and then foot taken off gas pedal, rpm drops to 1,100 then back 1,000 idle.
- I tried unplugging one spark plug wire at a time, and the same thing happened each time, which is momentary drop in rpm, almost to stall point, then it recovered back to 1,000 rpm on 3 cylinders...smart car;) So this test didn't reveal anything.
- Haven't measured resistance on plug wires, but will look that up given it's faster and cheaper than replacing them. I'll let you know what I find. If I can't find resistance values in the manual I'll revert back. Question though - can the problem even be a plug wire, given the engine runs great during the first (cold) minute? Meaning, if a plug wire is bad, wouldn't it be bad at all times and temps? I wouldn't think temp would affect this engine part.
- I tried the stethescope on injectors and, not being skilled with that one, found it difficult to place the stethoscope in a telling position given the tight quarters. I picked up what I thought to be firing on a couple of them, but I don't put a lot of faith in my doing this check because I don't have a trained ear for it.
> By 'unplugging each injector' one at a time, I assume you mean unplug the electric wires from it, so the solenoid stops working?
Regards, David
Nov 30, 2008 at 3:19 PM
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KHLOW2008
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Hi David,

The cold start and warming up cycle seems correct but the idling speed is too high. Idling speed should be 700 - 800 rpm.

Without load, a bad plug wire would not show and during cold start, the idling speed is highewr so it ouwld be even less noticeable.

Plug wire resistance should be between 6k ohms to 15 k ohm depending on the length and type of wire. Anything more than 25 k ohm is bad and continuity must be present.

Yes, you need to unplug the injector wire one by one if you want to test if they are working.
Dec 1, 2008 at 6:40 AM
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DAVID-B
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The symptom was solved by replacing the spark plug wires. It still idles a little high but that's easy to fix;) and it cranks for some time before starting when below 30 degees or so outside, but those days aren't common in our vicinity, so really wouldn't have to solve that one (may be due to declining compression on a high mileage engine).

Regards and thanks for advice. David
Dec 12, 2008 at 6:44 AM
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KHLOW2008
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Hi David,

The idling speed can be adjusted by turning the idle adjust screw on the upper portion of the throttle body. Some of these idle adjust screw would work themselves loose, ( if they had been adjusted previously and the O ring had hardened)

If the idle adjust screw does not help, you need to check fopr vacumn leakages, the EACV and coolant level and clogging of the EACV bypass hoses.
Dec 12, 2008 at 7:45 AM