Hi and thanks in advance for any help and sorry for the long post. I am a new member here, but have been lurking for a while. I have a 1993 Civic EX Coupe that is experiencing a weird issue upon acceleration. At times the car drives normally and runs great, but at other times, it is really hard to start from a stop because the revs won't come up when I give it gas, or cruising along at steady throttle, it feels like all of the sudden the butterfly closes, and the car bucks until I give it a lot more throttle. The trouble spot seems to be right at throttle tip in. I have been chasing this gremlin for a while now. Been to several forums including this one, tested, swapped parts, cleaned connections, etc. No luck.

As I said, car is a 1993 EX Coupe which my dad bought new in 1993. The car has had an easy life, other than sitting idle for an extended period a few years ago, and only has 61,000 miles on it. Overall, the car is in good condition. No wrecks, no rust, no major mechanicals. After my dad retired, he only drove it once every couple of weeks and then about 7 years ago, he let it sit in the garage for three years without starting it. I needed a second car, so I asked my dad if I could borrow his Honda for a while. We put a little oil down the spark plug holes, put in a new battery, and it fired on the first crank. It ran ok, but It never seemed to be as strong as it was before the down time, but it drove well enough to get me through until I got my current car.

Here's what was done to the car immediately after getting it running again:

New Spark Plugs
New Rotor and Distributor Cap
New Plug Wires
Timing Belt Service
New Water Pump
New Tires
Brake System Flush
Fuel System Clean and new Fuel Filter

After that, the car had a noticeable vibration until about 4k RPM, but other than that ran ok. The intermittent bucking/rough running started shortly after. Chasing this problem led to:

Tested old TPS with multimeter
New TPS
Cleaning all grounds including one on Thermostat housing and replaced two ground wires
Cleaning Electronic Air Control valve
Testing wiring to new TPS, both signal wires have continuity to ECU
Visual inspection of ECU, no visible damage or leaking caps
Symptoms are there whether the TPS is plugged in or not (found someone with similar issue, but his car ran better with TPS unplugged)
Fuel System pressure tested
Throttle body cleaned
New drive axels (fixed the vibration before 4k RPM)
New struts

The symptoms make it feel like it is the TPS, and it could be that my replacement was bad, but I calibrated it and it tests normally with a multimeter. I don't have an oscilloscope to verify there aren't any dead spots. I'm at a loss.

I feel like this should be an easy fix since the car has so few miles and is mechanically sound. I feel like I'm overlooking something obvious but I'm just not sure what to look at next. ECU? Injectors? Some other sensor?

I'm going to try to test to see if it is getting spark during one of the "events."

Anyway, sorry for the long post, but I wanted to let you know what I've already tried. I appreciate any help I can get. This forum has been a useful resource as I've tried to figure this out, but I'm not sure where to look next.

Thanks!

 

Two things I forgot to add:

Verified Mechanical timing after Timing belt replacement
Timing advance checked when drive axels installed

Car is almost entirely stock. I would like to use this as my daily driver if I can get it sorted.

 

Also checked the coil and values were within spec. Don't remember what they were, but I can test again if needed.

 

I had this hesitation upon acceleration and was quite head scratching. I started to wonder whether it was my fuel pump having dead spot or ignition related. I had a misfire on one cylinder and turned out that it was a spark plug wire....better acceleration but still had hesitation then one day it run just like doo and my flashing cel light immediately told me to check my distributor--coil or ignitor at fault.Bottom line was that my coil was good but ignitor was faulty--It would act just like you described better some days worse others

 

I read another thread that was saying their ignitor was being intermittent...

 

I'll add my own experience.. I had an aftermarket distributor (honda doesn't sell the hitachi for the hx anymore) go bad on me. The ignitor died while I was on the highway, boom! Nothing.. No rpms. coast to the shoulder. Starter worked of course, but engine not firing, towed back home. The tests that Honda has for the ignitor (brains of the distributor) will leave you laughing. It basically checks to see if there is voltage to the ignitor but doesn't do any real tests to the component itself!

There were dead spots in my acceleration before the ignitor died.. More like spots where it was flat accelrration. I did replace the distributor with another aftermarket after I checked the resistance of each of the 3 sensors built into the housing. Then I replaced the ignitor with a Honda (not cheap, ouch) one, as well as a Honda coil. been working well for a couple of years now. The acceleration now.. is pulling throughout the rpm band, like it should be.

 

I totally agree. If I were to buy a new ignitor/coil, it would have to be from the honda dealer. The manual is just testing inputs and outputs (voltage)of the ignitor and resistance test on coil they do not actually tell you their condition except for secondary igniton forms on an osciloscope. And of course there is the "take the ignitor to autobone and get it tested: the only time I did that they told me the ignitor tested bad and it was not

 

autobone.. lol.. sorry I haven't heard that before now! love it!

I have learned my lesson on some aftermarket parts (especially ignition parts of no-name brands), there's a reason they're cheaper priced! I'm not endorsing Honda, their prices for some things are insane.. but when it came to the ignitor, being stranded on the side of the road was enough for me to pay more for the Honda part. I did take my chances on SMP branded new fuel injectors instead of honda, that turned out well.. anyway.. yep most people would need an oscilloscope to diagnose the ignitor..

 

Thanks for the suggestions. Next plan of attack:

O2 sensor - drive car until it exhibits symptoms, usually once the car warms up. Unplug O2 sensor and see if it still happens. This should force it into open loop, and if the O2 sensor is bad and it is unplugged, the car should run better. Am I correct in my thinking?
igniter - buy an inexpensive (ish) igniter and swap for the original, test drive. If symptoms go away, I'd be willing to buy a quality igniter, but I don't know if I want to make another $150 gamble. I'll gladly pay for a quality part if I can be sure it will fix the issue.
Test injectors for cycle operation and spray pattern.

Anything else I should be looking for?

One other bit of info. Got a CEL way back when this started happening that pointed to TPS, so that's why I went that route first. Have not had a CEL in some time, but to be fair, I don't drive the car much right now since it isn't really running well.

 

Close. Since you are not getting an O2 sensor code, a "wacky" O2 sensor will provide the ECU with faulty readings during closed loop operation. This causes your short-term and long-term fuel trims to grow to really big numbers... either too rich or too lean. Unplugging the O2 at that point doesn't change the fuel trim values... it just stops increasing or decreasing from that point, so the engine may still run poorly. Unplugging the ECU or removing the ECU and back-up fuses under hood for 30 seconds will reset the ECU and your fuel trims will return to zero. Unplug the O2 and then drive. If the car doesn't exhibit the issue then... I would say you are on to something. Now, TYPICALLY, a wacky O2 sensor will drive your long term fuel trim to the limit one way or another, and then you get a 43 code. Since you are not getting this code, there is a good chance that you do not have a bad O2 or an exhaust leak causing improper readings being taken by the O2 sensor itself.

Your "cheap" igniter and then quality igniter idea... sounds like a waste of money. How about trying a "known good" distributor from one of your friends or neighbors first and if the car runs properly, then you can just buy a quality igniter. Rarely do igniters perform poorly after warm up... usually they perform bad all the time... and it is load sensitive. The more throttle angle you give it, the worse the engine stutters. If your TPS has been properly set at .490-.500 v with the key on and engine off... this should not be an issue at all.

 

Thank you, that helps a lot. I'll try the O2 sensor first. I agree that the purchasing the igniter without knowing that it is the issue is not the best plan, but I don't have anyone I can borrow a working one from. Problem really only manifests at really low throttle input, tip-in, steady highway, etc. I calibrated the TPS to ^ specs when I swapped it, but I have heard that the aftermarket TPSs are kind of a mixed bag, some work well, some not so much.

I've read through every thread I could find here with cars exhibiting similar symptoms, but they all seem to have a different root cause. I'm not a tech, but I'm reasonably good with a wrench, but this one has me completely baffled. I don't want to keep throwing money and parts at it, so I'm doing my best to diagnose. This forum has really helped me cross things off the list. I really don't want to give up on this because the rest of the car is so good. I feel like this is something minor, I just have to figure out what it is.

 

Ok, so just tested the O2 sensor as outlined above. Reset ECU, disconnected O2 sensor, drove car. Car did not act up at first. Went home, reset ECU, reconnected O2 sensor, drove car and experienced intermittent hesitation/bucking. Reset ECU again, disconnected O2 sensor again, drove car, and experience intermittent hesitation and bucking again. Car showed CELs when O2 sensor was unplugged, as expected, but not when everything was connected, as expected again.

Going to try bleeding the cooling system, even though I think it is probably good. Then I'll test injectors. I don't have another dizzy/igniter to test with, but trying to track something down.

What else am I missing?

 

Outstanding first post!

When you checked the fuel pressure, did you also check for proper functioning of the fuel pressure regulator?

Have you inspected the filter sock on the fuel pump? It can cause the problem you are experiencing, especially when the fuel level is at 1/4 tank or below?

 

Are you saying that you used a timing gun to verify the ignition timing of the warm, properly idling engine when the service connector was jumped?

Did you subtract the internal resistance of the multimeter from the primary coil reading?

Internal resistance of multimeter = Ohm reading with two probes touched together

 

The fuel pressure was tested at a shop when I had the drive axles replaced. Same for timing advance, and it was done with the connector jumped. I don't have a timing light anymore. Resistance of Ohm meter was factored into coil readings, but I'm willing to test it again and post numbers.

 

So it's unclear whether the FPR was tested, correct?

If the FPR is fine, check the fuel pump sock.

 

Correct. Just told me "fuel system is ok." As for the sock, It happens at all tank levels, but might be worth a look. Car has about 1/3 tank right now.

 

Ok, didn't have time to run tests until today. Here's what I checked and rechecked:

1. Bled cooling system. Used a spill proof funnel and let the car come up to temp until fan kicked on. Got a few small bubbles, but not much.
2. Coil test
   1. A to B terminal 0.8 Ohms (corrected for multimeter resistance)
   2. A to Secondary 15200 Ohms
3. Fuel Pressure test
   1. Car running vacuum off of fuel pressure regulator 44psi
   2. Car running vacuum on fuel pressure regulator 35psi
4. Fuel Injectors
   1. Injector 1, 12.0 Ohms
   2. Injector 2, 12.0 Ohms
   3. Injector 3, 12.0 Ohms
   4. Injector 4, 11.9 Ohms

One new development. Car seems to idle fine, but if I give it steady throttle above 1750 RPM the engine surges. Revs to whatever I'm holding at and drops back to idle and repeats. I am uploading a video to youtube and linking below.

https://www.youtube.com/watch?v=5FMa...ature=youtu.be

Going to check on the fuel pump in the tank next, but may not get to it today.

Any other suggestions?

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Check TPS output.

 

TPS has been tested and retested. Calibrated and within spec. Doesn't appear to have any dead spots but I don't have an oscilloscope to test with.

 

Interesting and very informative video.

The problem shown in the video should be very helpful in diagnosing the problem.

Hook up an inductive timing light to check whether the drop in engine rpm correlates with a loss of spark. If so, buy a new igniter unit from AutoZone, and install it in your car. Does the problem go away? If not, return igniter unit for a refund. If so, rejoice.

 

Two new videos I made tonight. It's hard to tell what's going on because the light flashes are sometimes being canceled by the shutter speed, but it seems like when I try to hold steady throttle and it drops RPM, the light is going out. That would lead me to believe spark is absent. What's weird is that it seems that RPM drops before I am seeing an interruption in spark, but that may just be how I am seeing it. Going to try a new ignitor tomorrow and cross my fingers that it will fix the issue.

https://www.youtube.com/watch?v=HQA3...ature=youtu.be

https://www.youtube.com/watch?v=GQ_B...ature=youtu.be

 

Good luck.

Just an FYI: The inductive timing light can only see spark at one plug at a time. If you were able see the loss of spark at all 4 plugs simultaneously, the effect would be ~4 times more dramatic.

 

Tried it on #1 and #4 and saw the same behavior. We'll see what tomorrow brings. Thanks for your input!

 

So, here's a preliminary update. I switched out the ignitor, and...

...the car ran fine on the test drive! The last few times I took it out, the problem occurred right away, this time, no sign of the hesitation, bucking, or anything else. The surging RPM are gone as well. Thank you to fonkernuckle, oneheadlight, JRCivic1, 94 Civic Si, and muellersfan for the help.

I still need to do more of a test drive to be sure, but I am cautiously optimistic. During the course of all of the testing, I realized that the distributor on the car is not the OEM Dizzy. My dad never said anything about ignition issues with the car, so I know it never had a reason to have it replaced. The only thing I can think is that at some point when it was being serviced, someone saw an opportunity to get their hands on a very low mile OEM piece and swapped it out. I hate to think that, but I don't see another explanation. This is one of the reasons I try to do as much of my own car maintenance as I can.

I'll be on the lookout for another OEM distributor as I don't have a lot of faith in this one lasting long term. Are there any safe bets in the aftermarket world for this car?

Thanks again to everyone who chimed in and offered help and advice. I couldn't have done this without you all.