old97civic

Recently started experiencing some hesitation on acceleration with my 97 Civic. It is a DX coupe, everything is stock.

The hesitation is not when moving off the line, it's in the mid range usually going from 30 to 60 km/h. If I hold the throttle position steady with my foot, I would get a "sawtooth" type of acceleration, ie it would go up for a bit, then ease off for a couple of seconds, then speed up some more, then ease off for a few seconds, and so on. It would do this about 3 or 4 times until at around 60-70 km/h. After that there would not be hesitation.

What I've observed so far is that the hesitation only occurs when the engine is fully warmed up.

Some background and recent maintenance: About a year ago I had noticed some oil spots on the ground and realized I had leaks from my oil pan and valve cover gaskets. I changed the valve cover gasket at that time including the spark plug tube seals, and changed the oil pan gasket in June this year. In June I did a tune up. Changed the distributor rotor and cap, plugs (don't remember if it was V or G power, but they were NGK), and plug wires. I changed the oil seal O-ring between the distributor and engine. (I marked the position of the distributor on the engine before removing it to not affect timing). To not overlook the basics, I pulled the spark plug wires and saw a bit of oil in the spark plug tubes. Not a lot, just a bit on the side near the top, but I think the tube seals were cut a bit when I put the cover back on. These were the new seals I had just put in too. I will have to change these out again and be more careful.

Because of the symptom only showing up when the engine is warm, I suspected the O2 sensor. The CEL is not on. I don't know if there are any stored codes, but I have a code reader coming soon. I disconnected the primary O2 sensor to see how it would run. It idled a bit rougher and would seem like it would bog down when maneuvering in a parking lot (eg moving off in reverse), but never stalled. Drove around like this for a few days and didn't get hesitation. Now I've reconnected the O2 sensor and cleared the CEL (it came on when I disconnected it). I've only driven it a bit since and haven't seen the hesitation yet but it's only been a day.

Before looking into the O2 sensor I replaced the fuel filter (in the engine bay), as I thought maybe it was a fuel pressure issue. I have not looked at the pump or the strainer. The filter AFAIK had never been replaced so it was a good idea to change it anyway.

It was weird how the hesitation started showing up just a few weeks ago in September. It wasn't every time, but was getting more frequent.

Anyway, I'm wondering if any of you have experienced anything like this, and what you ultimately found to be the problem? I've searched quite a bit and most posts refer to O2 sensor or throttle position sensor.

ezone

I cannot tell you if this is or isn't your problem:
I've witnessed O2 sensor problems that cause the symptom you described, and the problem can be very random and intermittent.

A scanner that gives a good datalist could help identify if one knows what to look for:
Primary O2 sensor voltage sticks high or low, then fuel trim numbers climb or fall off the scale in response to the stuck sensor. Bucking or hesitation comes as the engine is trying to run either "pig rich" or as it's starving for fuel.

old97civic

Thanks for the info. I will drive it as is for a bit and see if the hesitation comes back. Didn't get any today. Intermittent problems are a pain... I can get a Denso O2 sensor for $30 (+$15 for shipping ) which isn't bad (except for the shipping) so it might not be a bad idea to change it anyway. All the sensors are original, odometer is at 270 000 km (about 169 000 miles)

ezone

See what brand is in there now and replace with the exact same, it will be either DENSO or NTK.

(You may need to remove it and use a wire brush or wire wheel to read the name and numbers)

Look up the right part number on the manufacturers (NTK or DENSO) website.
I don't trust much, I like to look up and confirm numbers on my own most of the time.

old97civic

Agreed. Whenever I look up a part on the parts supplier's site, once it gives me the part number that corresponds to the car, I check it on the part manufacturer's site. This double checks the fitment but also it allows you to shop around more. For example a while back I looked up Monroe Econo-matic shocks and once I had the numbers and checked them on Monroe's site I found that getting them through Amazon was by far the cheapest. (I ended up not changing them though. At 17 years old(the car that is), I may not get much life out of them)

About the O2 sensor, is it actually written somewhere on the body of the sensor?

ezone

If it's original, then I expect it to be stamped somewhere. Here's an example pic from a completely unrelated job:

old97civic

Many thanks for ezone, it doesn't get any clearer than that!

Update on my intermittent hesitation issue. Well, it's not back. After driving around with the O2 sensor disconnected, the only thing I had done was to disconnect some of the spark plug wires as I was going to look at the plugs. That's when I discovered a bit of oil in the tubes. Not much, but the boot had an oil film on the outside at the top and bottom. I found your thread in which you had excellent photos showing the spark plug tube seal and what it looks like if not properly seated. That's exactly how some of mine looked. When I took the cover off they looked much worse, they were torn right through. So I changed those today and was much more careful reseating the cover (the cover gasket itself is about 1 year old so I knew I could reuse it). I wiggled the cover a bit to get the seals over the ends of the tubes. I lubed them a bit with some fresh oil to help with this. Once the tube seals were properly slipped around the tubes, the cover sat itself right down.

Anyway, as far as the hesitation is concerned, I wonder if maybe the connection between the wire and the plug might have been a tad loose, and that would have caused some hesitation? Just weird that it was under specific conditions that it occurred. Aren't intermittent problems fun.

I still need to pull the plugs themselves,to see if there is oil in the combustion chamber. I haven't seen smoky exhaust and all the previous times I pulled the plugs, they always looked good, never fouled.

Also, BTW, I got my OBD2/CAN code reader and as expected, no codes.

I will post again when I pull the spark plugs

ezone

As soon as you unscrew the plugs, any oil that was standing in the tubes will go into the combustion chambers.
And coat the ends of the plugs, so you may not be able to tell much.
And then you will screw the plugs back in and there will be a huge cloud of smoke when you get the engine fired up again.


Also, (IF it's the engine version I'm thinking of) it uses O rings between the halves of the plug tubes. They tend to harden and allow oil to enter the tubes. At work we call them 'rocker stand seals'.
I can link a parts diagram if you want.
Hard to say, and I'd guess probably not. Ignition related high voltage leakage problems are usually fairly easy to duplicate and are usually demand/load dependent.

Some of the O2 sensor issues I have seen over the years seem to be related to the temperature of the sensor itself, as in they fail in a rather specific temperature range... say for example shortly after a cold start and before the exhaust manifold has reached its normal temp.

old97civic

There wasn't much oil, just a bit on the outside of the boot, which is surprising given how torn some of the seals were. Then again they may have torn when I pulled the cover off, because of the way they were not evenly seated on the tubes. Either way I'll shine a light in the tubes and clean up with a rag and screwdriver if need be.

Engine is D16Y7, which I don't think has seals at the bottom of the tubes. I think these are pressed in but I'm not 100% certain.

I kind of regret not having done it the other day when I had the cover off, but I'm thinking I should check/adjust the valve clearances. I know it hasn't been done in a long time. What's a symptom of worn cam lobes? Generally poor performance? I'm visualizing that the valves wouldn't open as fully, which could restrict air/exhaust flows in and out. The car is definitely not as peppy as it used to be. When it was new, you really had to keep your foot on the brakes at a stop. As soon as you let off the car would take off. Now it more or less sits there and you need to give it a bit of throttle to get it going.

ezone

Finally got a minute to look at the parts diagram. You're right, this is not the engine I was thinking of earlier. No rocker stand seals on this engine.Probably, but I've never seen it happen on one of these. You might be able to hear noise, see serious lobe wear with a visual check and notice the rocker and valve don't open as far as the others, maybe notice the roller ate off of the rocker arm(s) on the affected parts.

That just sounds like the idle speed used to be far too fast, now it's either normal or low.

When you floor the gas pedal -- does it have full power, or is it anemic?

old97civic

I wouldn't call it anemic, but the acceleration isn't as quick as it used to be. Or maybe I just remember it being better than it actually was.

I would say fuel economy isn't as good either. This Civic gets 24-26 mpg. Yet it has never had issues passing the emissions every 2 years. Never had to do repairs to pass. Had the car since new so we know its history.

I wish I'd held off on getting my code reader, as I'm looking at getting ScanTool's Elm5 USB tool as it's only a bit more money and it does a lot more like looking at live data. I might get it anyway as even with getting this one in addition to the other reader I just got, it's still cheaper than getting any scan tool from any local store

ezone

How about maybe the trans isn't backshifting to first gear at stops?

old97civic

I'll listen for it but I don't think that's it.

Anyway, I was all set to check the valve clearances today and I'd have to pull the plugs to do that to make it easier to turn the engine over, but I wanted to remove any oil that was in the tubes first. Well, it wasn't much in cylinders 2, 3 and 4, but 1 had more than the others. Looking through my toolbox I didn't have anything long enough and slender enough to get to the narrow areas between the flats on the plugs and the inside of the tube, so I have to leave it for now. But on the other 3, I pulled the plugs and the electrode tips were dry. And I got a bit of smoky exhaust when I started it up. It lasted only for a couple of seconds.

Also, I got my set of feeler gauges and discovered that my 0.007" gauge is way off. I measured it with a 0-1" micrometer and found it was actually 0.014" thick! The 0.008" one is ok, can I just use that for the intake valves? I know the published range is 0.007-0.009 for intake (and 0.009-0.011 for exhaust) but what does experience say to aim for?

ezone

I woulda pulled the plug out anyway, let it drink the oil.
Stick a towel over the open plug hole to catch any that spits out....
Crank the engine over with the plug(s) out so it doesn't hydrolock, then reinstall plug (cleaned the wet oil off first). Fire it up, let the blue smoke burn out.

My personal preference on customers Hondas is to set at the loose end of the spec range.
I do this because so many of Hondas engines tend to tighten the valves over time and miles, instead of getting looser over time.

Someone who does their own and does them frequently and wants every last ounce of pep might go for tighter clearances.

Anywhere within the printed spec range should keep them quiet.




Old timer taught me:
I'd rather hear some valve noise than none at all.
Loose valves just make noise. (too loose)
Tight valves burn. (too tight) That's very bad.

Tight valves also can cause manifold vacuum to be lower than normal, and can cause rich codes, low compression, and misfire codes... depending on just how much too tight they are.


Not good.

old97civic

Well guess what? The hesitation problem went away on its own, but showed up again once yesterday. Again it was when the engine was relatively warm; I had gone somewhere for an errand and the hesitation happened on the way back.

I'm thinking of going ahead and replacing the O2 sensor. I would like to identify the sensor before getting the replacement one, so I'm thinking I should remove the heat shield to be able to get a better look at it. Problem is the bolts that hold the heat shield on the exhaust manifold look very rusty. Specially now that it is cold, I'm afraid my impact wrench will just break the heads off. They don't look big, 10 mm head or so.

I have some Liquid Wrench, so I can apply some of that a couple of times before attempting to remove, but would it be better to attempt removing the bolts after having driven the car?

ezone

9 out of 10 seen to just snap off.

You're much better off to get the correct tool for removing the sensor.

Here's a couple examples

old97civic

Oh for the sensor yeah I will get the socket with the gap, but I was referring to the 2 bolts that hold the heat shield, they look real rusty. The sensor itself looks fine.

Edit: Yeah I guess once I have the sensor socket I won't need to remove the heat shield in order to look at the numbers on the sensor , I can just remove the sensor to examine it.

ezone

NOW you're catching on.


Breaking off the heat shield bolts is just gonna give you a headache.

old97civic

Finally got around to removing it to check for marks. Was kind of anti climactic actually. Came off very easily, like a spark plug. It is a NTK type. It says NTK Japan on the crimped part just like in your pic ezone. On the flats it read 4E31 but this doesn't cross reference to anything. Best as I can tell I need NTK 24542 (my engine is D16Y7). On the other hand, Denso also has one and it goes for about $12 less. What's the harm in going with the Denso vs the NTK?

ezone

My first choice is exactly what the factory put in there.

Price is not part of the equation.

old97civic

I know everyone's just eagerly anticipating the results....

Just waiting for the sensor to arrive.

old97civic

The sensor arrived on the 23rd but had company over and things going on...

All the hesitation issues were always when the car had warmed up, so that's why I always suspected the O2 sensor. In the past few weeks the hesitation had been getting worse. Would happen more often and the bouts of hesitation were getting longer. Never got a check engine light and it was intermittent so it was rather frustrating...

The new primary O2 sensor (NTK) is in. Been driving it for a few days now. Definitely much better throttle response now. It's only been a few days, but so far so good, no hesitation. I've topped up the fuel tank and reset the trip meter so I can work out the fuel consumption at the next refill.

Thanks ezone for all the help and tips. I will monitor mileage and keep an eye out to see if anything happens over the next few weeks and report back.

old97civic

Update...

No hesitation since putting in the new O2 sensor, so that's good. Fuel mileage, meh. Not driving the car much these days, and only used up half a tank since swapping out the sensor, so maybe it's a case of not enough data but somehow I doubt it. But at least the driveability issue is taken care of.

old97civic

Update re: fuel mileage....

New NTK O2 sensor put in in January. Driveability issue disappeared.

Fuel mileage now observed to be better, due to different driving pattern. Earlier in the year, the car stayed put most of the time and was essentially only being driven on the weekends, and for short trip local driving. When I calculated fuel economy it was always really bad. On some short trips, I estimate half of the time was spent idling at a red light.

Now I am in a different situation and drive about 100 km/day (60 miles) on the highway. Fuel consumption is now 7.2 L/100 km (32.6 mpg). This is with speeds anywhere from 100-120 km/h (62 to 75 mph). This is good news, so the engine is still doing pretty good for its age and mileage. (just turned 274,000 km) (about 170,000 miles)

ezone

Good to hear, thanks for the update!

old97civic

Another update on fuel mileage...

Got 6.6 L/100 km on one tank (35.6 mpg)
6.0 L/100 km on another (39.2 mpg)

Leads me to believe I don't have any major issues with the engine. I believe I will hang on to this car for a few more years!