Civic VX miss under load

[GasSavers_95civicvx]

It seems several folks were having this issue...and although this is an old question I thought I'd querry to see if anyone had ever sorted out out a solution.

Mine feels like an ignition miss, but ignition seems to check out. I bypassed the egr valve by attaching another one to the hose and plug and no dif. in running, so not the EGR. The next step is replacing the o2 sensor...but from what I'm reading, that does not seem to be a good fix.

Any help here would be a great plus. the car starts, idles and runs great before it warms up...after that, lots of stumbles at low rpm between moderate and high load. 95 Civic VX (non CA) has 175k miles alsways averaging 41mpg over that last 5 years.

This has been getting progressively more noticeable over that last 3 mos. Valves are adjusted, and plugs are new. I'd start replacing everything, piece by piece, but so far that does not seem to have worked for some of the posters here.

Any help would be well appreciated. Thanks in Advance

[jadziasman]

1) Rough idle at all when warmed up?

2) When coming to a stop after traveling at 70 mph with a warmed up engine, do you have a rough, low idle that increases to 600-700 rpm after a few seconds?

3) Any CEL's in the past year? Specifically code 48 - LAF sensor?

I have been experiencing some of the above and have not decided yet what is causing the problem. I just tried cleaning the throttle body today with a can of Gumout air intake and throttle body cleaner. I used about half the can and sprayed it through the pcv inlet in the air intake hose (I didn't need to take the hose off of the throttle body bore). I revved the engine to 3000 rpm while spraying in the cleaner in small bursts. No harm done since this cleaner only has acetone and xylene in it. Turns out these two solvents are put in gasoline in small quantities anyway. After spraying the cleaner, I took my VX for a ten mile drive with the speed up to 85 mph at one point.

I noticed an immediate improvement in the second symptom above when getting off the interstate. But, this might just be a temporary improvement.

In your case, I would take the air intake hose off the throttle body and check the throttle plate for carbon and oil lacquer. You might have deposits that are blocking air from getting into the intake manifold when the throttle is slightly open. You could have a rich mixture that won't ignite and subquently misfires when you are "lugging" the engine with high load, low rpm cruising or accelerating.

Misfires can cause the LAF sensor to send the ECM a signal that trips a CEL code 48 because the oxygen in the charge that did not burn goes into the exhaust manifold and gets read by the LAF as way too lean (too much oxygen).

Running rich would also mean your mpg should have dropped recently too.

I have averaged 43 to 44 mpg with my VX year round. I usually get 40 to 42 in cold weather (sub freezing) since it takes five minutes to reach operating temperature if I don't get on the highway in the first mile or two. My VX has 168K miles now.

[GasSavers_95civicvx]

I think I have run across the same issue on my vx. crack in the radiatior neck seems to have fouled the O2 sensor. putting on a new one will be worthless until I replace the radiator...any possibilities any other chemicals are coming into contact with your O2 sensor?

[jadziasman]

My mechanic's instinct tells me my VX is periodically misfiring - and I have not found the cause yet. There are so many things that could be causing it and I have just started looking at them. The ECU has all it can handle to control combustion and emissions under these conditions. I wish I had the proper diagnostic tools to find out if the engine is running too rich or too lean. Either one will cause a misfire. I find it hard to believe that a malfunction in the LAF would cause the misfire. So, it could be the EGR, PCV system, fuel injector, etc, etc. I've already checked the ignition side of the equation and am convinced this is not causing the problem.

[oh95vx]

Hi, I'm the wacko who started this thread way back in the spring. Interesting to see the thread has come back to life. I'm not the only one with this problem, which means there might be enough of us to actually figure out what causes it.

No success so far on this end.

Veronica VX can't go anywhere since her registration expired and (though I haven't tried) I doubt that she'll pass smog. She's currently sitting beside the garage (too many projects inside it to fit her in too), gradually filling up with rain water from the bog-standard Honda window leaks and no doubt hosting a few happy families of mice thanks to the bog-standard Honda quarter panel rot. Not to mention the bog-standard Honda brake rotors that start returning to the iron oxide from whence they came if you don't drive the car for about 2 days.

Ahem. Yes, I still like Hondas. There is a term for people like me.

Never mind. Back to business.

I just can't get past the weird ignition timing. Ladies and gentleman, your humble correspondent here has been bumping his head on hoods and grimy chassis for 35 years. I have *never* seen timing that didn't advance. But that is what Veronica's timing does. Or, rather, doesn't.

Back in the day when computers took up an entire room, yea verily an entire half an office building, and telephones had dials and were tethered to the wall, ignition advance worked like this. You opened the throttle and carb vacuum pulled on a diaphragm on the distributor. This moved the breaker plate inside, on which the points (!) were mounted, advancing the timing so the car could get out of its own way until the RPM built up.

Now, with increasing RPM came centrifugal advance. Deep in the nether regions of the distributor was a set of weights which swung out as the distributor shaft rotated faster. These also nudged the breaker plate, advancing the timing.

Later in the wild west days of emission controls (1970s), the engineers added another diaphragm, to retard the ignition when the throttle was closed for deceleration.

Bottom line was that timing *always* advanced with increasing RPM, and also when the throttle was opened to accelerate.

I realize that engine control is a different critter today, but I just can't believe that ignition timing that changes no more than a couple of degrees as RPM increases is working right. And for it to RETARD for a second when the throttle is opened - well, by gum, that's just plain unnatural.

Now, the question is - is this the CAUSE of the problem, or is it a SYMPTOM?

I say it has to be a symptom. Ignition timing is under the sole control of the ECU. It looks at what the alphabet soup of sensors are saying and says, Spark! Spark! Spark! over and over again, always (when all is right with the world) at exactly the right microsecond. If any of those alphabet soup messages stop coming in or don't make sense, that ECU is supposed to set a trouble code, and temporarily replace the sensor's data with its internal close-enough tables.

Well, mine hasn't said a word. No CEL. So, if some sensor is returning wrong information, it has to be just close enough to right info to make sense to the ECU.

What else can go wrong? Unlike the old days, there's no breaker plate in the distributor to get stuck, no centrifugal weights to gum up, no vacuum diaphragm to bust. So *something* being reported by one or more of those sensors has to be bogus. Whatever it is, it's causing the ECU to think it should keep the timing at initial, and even retard it for a second when the throttle is snapped open.

But what?

No sense in reiterating what I've tried so far. You can read that all above. Others now have listed some stuff they've tried. None of us seems to have quite found it yet. (BTW, how many of you ever got the EPA 56mpg out of this car? Even close? Yeah, that's what I thought.)

So, short of stripping the engine down to a short block and cleaning and/or replacing everything, what can you other parents of these troubled children think of? If you find something that makes your VX run like new, please for goodness sake post it here, and I'll do the same. But don't hold your breath. Spring's a few months away yet.

[rlprlp1]

Not sure if this will help u or not, but i didnt see it mentioned in the thread. I pulled the back up fuse out and i started getting better gas mileage, dont know why, since i didnt have any cels. Im sure its not as easy as this, but its worth a try.

[oh95vx]

I've rebooted the ECU dozens of times with no improvement I can detect. The ignition timing still acts weird. I even tried a different ECU. Same song, still off-key.

Might work for somebody else, though.

[mrmad]

Here's a complete guess as to what could be causing your timing issues. Could your timing belt either have skipped a tooth or be so loose that the cam is not keeping in sync with the crank? If so, maybe the TDC signals are confusing the heck out of the ECU.

[GasSavers_MarkW]

My 1992 Civic VX has the same symptoms, only my car's symptoms seem a little worse and give off a check engine light code that may help you.

Gives off CEL code 4 for a defaulty CKP sensor or wiring(crankshaft position sensor)

my engine misses and stumbles enough sometimes that the ECU shuts off the engine. The rpm will be erratic, set off the CEL which you can feel the engine slightly improve as it retards the timing to correct and make the fuel ignite easier, then the engine will start missing again. Your problem sounds like mine, just not extreme enough to trip the CEL yet. My problem started off mild like yours (no CEL), but I've kept driving it and its gotton worse

[edgolla]

I have had an intermittent miss in my VX for some months now. I tried various things to fix it, such as Oxygen sensor, distribuator, fuel filter etc. and nothing seemed to help except that the problem only seem to occur after the engine was warm, so I sent the ECU false information by replaceing the temperature sensor with a 1 k ohm resistor. This helped a great deal but I didn't know why. I also found that if I removed the lead from the throttle angle sensor the miss would go away. I have finally discovered the source of the problem. There was an arc occuring across the end of the rubber boot that extends the plug wire down through the head. This happened on two of my boots. You could just barely see a very faint light gray trace across the bottom of the boot. I scraped this trace clean and then coated the end of the boot with a light coating of silicone grease. This complete eliminated the miss that I was having. It only seemed to happened when the engine was warm, because the car goes into lean burn only when it is heated up to operating temperature and I believe that under the lean burn condition the plug is harder to fire and that causes the spark to bypass the plug and arc to the metal wall by way of the rubber boot. Disconnecting the throttle angle sensor gave a CEL and also kept the ECU from going into lean burn. Let me know if this helps you. egolla@airtesting.com