xtrattitude4u

My little brother's car has got me stumped.
97 Civic DX automatic. 170k miles.

The car runs normally from a cold start until it is almost fully warm.
As it warms up, it will start to miss at idle and at lower rpms while accelerating. After 2500 rpm or so the problem disappears.
The longer the car is driven, the worse it will get until it is almost constantly missing and has no acceleration.

I shook the CAT around to make sure it wasn't going bad/ getting clogged.
Not a sound.

No trouble codes are stored.

We changed the plugs first, then wires, cap and rotor and fuel filter.
The plugs solved rough running conditions, but the miss is still there.

Yesterday I tested the ignition coil and it read out of spec (1.1ohms)
Got a new one that read about .7 ohms, within spec.
Hooray! I was convinced that would solve the problem.
But life is not fair, and it didn't.

I watched live data using Torque and saw the system is in closed loop, but the O2 sensor drop to 0 volts when the engine misses.
Is that just reading like it should?
I replaced the O2 sensor about a year ago.

Long term fuel trim stays at -1.6%. Short term is about -3 to +3.

I noticed the data showed coolant temp dropping to 170 while driving, then rose all the way to 210 when parked at the light,
but the dash gauge didn't seem to move at all.
Coolant temp sensor bad?

The distributor is the last piece of the ignition I haven't replaced.
Can I test it myself, or can the the parts guys test these?

Thanks for any help guys.

Buckshot870

Have you checked your O2 sensor wires for damage / loose wiring?

xtrattitude4u

Not really . . .
I will have to perform a continuity test on the harness side.
But wouldn't an open circuit on the O2 sensor throw a code?

xtrattitude4u

I had my brother disconnect the O2 sensor and drive around for a day.
The problem remains.
He did say it ran noticeably better without the O2 sensor plugged in though.

grumblemarc

iTrader: (4)

How is this not throwing any CELs? Has the timing been verified?

xtrattitude4u

Well, it probably has a code for the O2 sensor now that we unplugged it,
but Iv'e scanned it several times and there were no other codes.
The CEL bulb is burnt out so I don't know if it flashes when the car misses.

I haven't really listened to a lot of engine problems.
It starts going Puff . . . . puff puff . . . . puff. . . . . puff puff puff when it gets warm.
Doesn't sound like a backfire. Gets really bad at low RPM acceleration. This is "missing" right?

Anyway, timing check/adjustment is next on my list.

xtrattitude4u

I'll have the car again today.
I plan on thoroughly checking the plugs and wires despite having replaced them recently.
Then I'll check the timing.
If that doesn't reveal anything, I plan on testing the dizzy. This is where I need advice.

Since it is an intermittent problem, I'm thinking about how to test this.
The test procedure I found for the dizzy is for when there is no spark at all.
The car seems to only miss on one cylinder at a time.
Is it possible for the dizzy to have an intermittent fault like that?

I'll have the timing light, so I'm thinking of connecting it to the different spark plug wires and see if I can visually detect a lapse in the spark to see if it is just one cylinder.
Any advice on testing the dizzy for an intermittent fault would be very helpful.

Thanks!

xtrattitude4u

Timing looked 4-5 degrees off.
I jumped the blue 2-pin connector, set to factory red mark, tightened dizzy.
Verified timing again, shut off vehicle and removed the jumper.

It runs smoother now, and misfire did not happen, at first.
Test drove it and it started again. The worst at low rpm acceleration.

Parked it and it seemed to be much better, only once or twice a minute.

I examined the plugs, and they looked all the same, and good.
I tested all the injectors, resistance was identical across the board.
Tested the coolant temp sensor, 200 ohms at running temp.
Sprayed carb cleaner everywhere, and checked for leaks, none found.
Removed brake booster hose and plugged it, still misfires.

Is there a way to test the distributor for a very intermittent fault like this?
I don't want to throw money at the problem if there is another option.

xtrattitude4u

I guess we'll never know.
Selling the car now.
Thanks for the help anyway, guys.