Engine misfire / sanity check

[redaztec]

Hey all,

The engine in my 89 LX-i has been misfiring, and I'm trying to figure out what might be causing it. Here are the things I've already tried:

-Gone through several tanks of gas in case it was bad gas
-Run fuel injector cleaner
-Changed the plugs (twice)
-New wires, cap, and rotor
-Checked resistance of the ignition coil
-New TW sensor
-Adjusted the timing and idle speed
-Checked the air filter

While these things helped a little, the engine still misfires. It's fine over 2000 RPMs but under that it stumbles a lot.

I changed the plugs again today and noticed that they were all extremely fouled with dry carbon-type deposits, and they smelled strongly of gasoline. The old plugs were cheap Bosch copper-core plugs that had been in for about 500 miles, and I replaced them with NGK V-power plugs.

Because of the deposits on the plugs, it seems to me that the engine is running rich. Does that sound reasonable? Either way, any advice on how to proceed would be greatly appreciated. Thanks in advance!

Edit: By the way, I have searched a lot - however I've seen so many similar problems with different suggestions of which expensive part to replace that I don't want to go spending hundreds of dollars without a little advice first. :)

[russiankid]

Sounds like the car is running rich. Could be the O2 sensor. Also did you check the timing belt? It could be off a tooth.

[2oodoor]

change fuel filter?
sounds like coil output, but hard to say
what kind of fuel injection cleaner did you use?

[redaztec]

I'll see if I can check that timing belt soon. Truth be told I probably should change it soon.

I forgot to mention it above - I have already replaced the fuel filter.

I used Lucas fuel system treatment. I ran two tanks of gas with that since I'm sure the last owner never did.

I checked the resistance of the coil with a multimeter as described in my haynes manual, and all values were well within specs. Is it possible the coil is going bad even so?

Is there any way I can check the O2 sensors to see if they're working right other than just replacing them?

Thanks for the help so far!

[AccordEpicenter]

any check engine lights? Id check vaccuum hoses esp for map sensor

[coope]

mine did that it was the wire and check the rotor button that might be it and check the ground on ur injector wires its on the fuel rail

[redaztec]

Well unfortunately I've not had a chance to pull open the timing belt cover to check that. Hopefully next week. There's no check engine light, and the light on the ECU doesn't light up or flash a code. All electrical connections seem fine.

I also cleaned and tested the TA sensor and it seemed to be within specifications.

I have been paying even closer attention to it, and I've noticed that for the first couple of minutes the car runs, it's almost fine. A bit of misfire on idle but that's it. The engine pulls strongly, revs freely, etc. Of course I'm not revving it hard when it's cold, just a little. Once it gets a bit warm it stops responding so well - it stumbles upon revving or acceleration, and it bucks a little when cruising at about 25 in 3rd (just under 2K RPMs).

So it seems that at least one piece of this puzzle is related to engine temperature. I noticed that the O2 sensors are not heated. I'm wondering if what is happening is that the O2 sensors are bad and therefore the ECU is enriching or leaning out the fuel mixture too much only when the O2 sensors warm up and activate. Does this sound reasonable?

[shepherd79]

it is your distributor. the vacuum adavance is not working and little springs inside the distributor worn out.
My car did the same thing. I rebuild distributor with new springs and found good working vacuum controller (dealer is the only place that sells them for our cars, i tried advance auto parts and they had wrong parts).

[redaztec]

I'll check the springs, thanks! The vacuum advance is fine though - in fact I just replaced that a couple months ago.

[88Accord-DX]

I find a lot of mis-fire issues are from carbon deposits on the valve seats, not letting the valve seat good. Which leads to leaking air past either the intake or exhaust valve.

[redaztec]

Thanks, I picked up some seafoam this afternoon so I'll let you know how that goes.

Between dealing with finals (over now and none failed!) and a bunch of other stuff, I haven't gotten to work on the car much. I did put in some new O2 sensors though, and that helped a bit.