Misfire at low revs

[arsenalgirl]

Hello

I wonder if anyone can help. My little beat has never given me any trouble, but it is now doing something odd! It misfires / stutters at low revs. Increasing the revs clears the issue but as soon as the revs drop, it stutters. It also sounds a little 'off' at idle.

the rotar arm has been changed, new plugs put in and the timing all checked out. I gave it nice new super fuel but still the same. Does anyone have any other ideas as I've run out...

Thanks.

[old'uns]

mines doing the same at moment, feels like mixture too low, i think i unscrewed the idle mixture out too much to get the timing right.
must get round to looking at it one day :rolleyes:

[Steve_M]

Id look in two areas if you have covered the ignition side of things

1) ECU capacitor causing fueling issues. Carry out a diagnostic check to see if there are any DTC stored. Do you know the history of the ECU? Capacitors replaced before? Worth having ECU cover off to see if there are any capacitors blown and board corroded.

2) Burning / burnt out inlet valve. Carry out a Compression check. Slight leakage on a valve causes a missfire at idle and if the leakage is low will clear as revs rise. If this is the case, dont leave it as damage to the valve and valve seat could turn out expensive e.g. New head

HTH

[old'uns]

well finally had time to have a look.
nothing obvious, fast idled OK then to 1200, revved off idle OK until hot.
at idle you can hear the slight splutter or miss, then when opening throttle it mis-fires until approx 2k then is fine. also seems to be a little smokey, light greyish? as you get in winter time with cold air temps. smells rich as well

compression test next on list, X fingers :awwww:
also got old ECU to try.
worst case scenario, head off, engine in or out?

[Steve_M]

head off, engine in or out?

I would not bother taking the engine out to take the Head off, not unless your going to do other stuff to it e.g. Piston rings/bearings.

Just Head off is easyly do-able with the engine in.

[old'uns]

cheers Steve.

worst case scenario, is there anything worth replacing/needed if head is off?
gaskets, rubber seals etc. valve obviously if damaged.

may need to enquire @ dealer re. stock availability as i'd like to get to Belgium/France late June

[Steve_M]

I would not pull the head off just yet, get all the other bases covered first.

ECU
Distributor cap, plugs leads etc.

Compression check.

Fuel Pressure check (If you can)

A mechanical missfire e.g valves/rings etc. it will normally be a permant missfire (Always apparant at the same engine speed)
Burnt/burning out valve can cause missfire at idle only and seem to clear at higher revs, thats just because they are only a slight leak.

ECU capacitor failure can really affect the engine Mixture as this is totally controlled by the ECU, even miss reading of the O2 sensor can cause bad running like that and make the engine faulter which you could feel is a missfire.

[LawrenceHarding]

To digress a little could capacitors be an issue in an early 90's Prelude?

[old'uns]

right then.....

leads, plugs etc checked, all seem OK
ECU swapped back to original one, no misfire/stutter, EML permanently on which i knew about
http://i66.photobucket.com/albums/h276/old-uns/Honda%20Beat/ecu.jpg

bit hard to see but the area in the circle is a bit 'crusty' so i'm assuming this is why light is on?

took the cover off other ECU & found this...

http://i66.photobucket.com/albums/h276/old-uns/Honda%20Beat/DSCF0100.jpg

even when warmed up, i can still smell fuel as though it's still 'choke' mode, what's the sensor screwed into inlet manifold as i have a spare one of these also to try after ECU's get repaired

[beatbythesea]

Hi,

I think I just solved a similar problem on my Wifes Honda Beat which was running fine when cold but when hot misfired at low revs and eventually stalls. Runs fine when she thrashed the engine above 2000rpm, but was a problem keeping it running at traffic lights. Also really hard to restart once it stalled, had to let it cool down.

I checked Valves-Timing-Fuel-ECU-HT Leads-Plugs-compression-Air intakes -Idle air valve etc all seemed ok. But I changed out the distributor with one I purchased a long time ago of ebay, from my "just in case" collection of parts, and seems to have solved the problem.

The car is left standing over the winter and due to the location of the Distributor on the engine, the air/drain vent does not allow the condensation to run out of the Distributor cap. So in the past we have had issues with condensation in the distributor cap stopping the engine. The Distributor I removed looked a little rusty inside and I think the High Voltage may have been arcing around inside to the electronic sensors maybe damaging them.

Anyway ours is now running better than ever. I have modified my distributor with a air vent part that has a gortex filter in the hope that it will stop moisture getting in and damaging this one.

Hope this info helps as much as all the other posts have helped me.