1994 Honda Civic Stumbling

I have a Honda Civic LX 1994 that stumbles on acceleration. It seems
to be worse when it is warm. It feels like only one of the cylinders
misfires while accelerating, making the car lack power and vibrate, and
once the RPMS get high enough, at around 3000RPMS, the misfiring
dissapears. Nonetheless, it is a combination of the engine load versus
the RPMs, I can get it to stuble at any given RPM setting, if I press
on the throttle pedal too hard. Here are the parts I have now replaced:

Entire distributor, including the cap and rotor.
Spark Plug Wires
Spark Plugs
Fuel Pump and fuel strainer
Fuel Filter
Fuel Rail
All 4 Injectors
Fuel Regulator
Air filter

I have checked the TPS with a multimeter, 0.5V at closed throttle and
4.5V at full throttle smooth transition in between.
I have tested the MAP sensor with a hand vacumm gauge and a multimeter,
sensor is all nominal but here is the chart if anyone cares to look at
it:
0psi 2.80V
5psi 2.34V
10psi 1.86V
15psi 1.39V
20psi 0.96V
25psi 0.52V
I have tested the fuel pressure, pressure is normal.
I have tested the O2 sensor with a multimeter and propane torch. Again
it seems to be normal. I have also disconnected it from the car and
driven it without the lambda sensor, still the car behaves the same and
stumbles.
I have checked the timing with a timing light, and the timing is right
on according to specification.
The ECM reports no trouble codes. The ECM reports no "Check Engine"
light while driving, although the car stumbles wildly.
I am running out of ideas... can anyone think of anything else I should
check or that could possibly be the reason for the car stumbling.

- JR

 

A few more basics to check or do:

-- Dump a bottle of Chevron Techron fuel system cleaner into
the car's near empty fuel tank. Fill with gas.

-- Check the ignition timing.

-- A bad O2 sensor will not necessarily set off a CEL on a
1994 Honda (pre-OBD2). Since the problem occurs after
warmup, that makes me especially suspicious of the O2
sensor. https://www.automedicsupply.com/ has the best
prices I've seen for OEM O2 sensors: About $69 altogether. I
have used them. Good, prompt service. Maybe not a bad
investment for a car this old.

-- Purge cooling system thoroughly of air. Follow the
manual's instructions. Getting the fan to come on may take
as much as 40 minutes of idling. If various ECM sensors
aren't cooled properly, then this may cause erratic
behavior.

Are all the ignition parts (plugs, wires, distributor etc.)
OEM?

 

You haven't indicated your transmission. Auto or manual?

Might be an EGR valve sticking partly open. Have you checked for this?

 

The car has no EGR system. The car has a manual 5 speed transmission.

- JR

 

Like I said, the O2 sensors tests OK. I have unplugged the sensor and
driven without it, only to experience the same problem. The O2 sensor
has only 20,000 miles on it. It was put in six months ago; Bosh made.
All other replaced parts are OEM.

- JR

 

------------------------------

What's the mileage on the vehicle? Did this problem show up after your
last Timing Belt replacement? Were the valves adjusted at the same time?

P.S. Almost everybody agrees that Bosch O2 sensors shouldn't be used on
Hondas :-( Same for their plugs.

'Curly'

 

I have personally rebuilt the engine... the problem did not show up
after the timing belt replacement, which happened at the time the
engine was replaced. All of the major compenents in the car were
changed in 20,000 miles ago, along with the entire motor. The car has
been running just great until now.

Even then, unplugging the 02 sensor, the car experiences exactly the
same problem I have described.

 

The problem occurs at all times, it just happens to be MORE pronounced
when warm than cold.
As I have said before, I have cheked the timing and it is right on the
spot.
Following your suggestion I have gone through the air purging on the
coolings system (which did not need to be purged by the way). No
change.
Thank you for your suggestions.

- JR

 

-----------------------------

How far back (days / months/ miles) does the term "running just great
until now" go back? Last fill of gas?

After you got the engine re-installed, did you find that you had to move
the distributor about 10 degrees to get the ignition timing correct? If
so, I'd guess that the cam timing is out, but the ignition timing is
correct(ed). Do you have to put the jumper on the ECM connection when
you time a '94, like you do for the newer (OBDII) ones?

Is the new engine an exact match to the car, or did you import the ECM
as well?

'Curly'

 

Running great until 100 miles ago. Running well for 20,000 miles after
rebuild.
I didn't have to do anything special except point the gun and align the
lines on the crank pulley with the alignment mark on the timing cover.
You DO have to jumper the connections with a a jumper wire, and you
have to wait until the engine has come to normal temperature to do the
timing.
The engine is an exact match to the car.

- JR

 

How about a compression test?

 

Interesting answer... I never thought the problem could be mechanical.
I will run a compression test. I will let you guys know.

 

i second that. unless this is something really rudimentary like a
vacuum hose has fallen off, a burnt inlet valve is a good candidate for
the symptoms described. it should be very distinctive on cold cranking
though - instead of 4 even compression cycles, one will "wow" much
faster than the rest.

 

That's not dispositive.

I personally would not yet eliminate the O2 sensor. That
it's Bosch certainly makes me suspicious.

Two cents.

 

I don't know if a bad ring would do that or not.

 

I've got a '90 Civic doing the same thing. I was thinking that my
timing wasn't advancing right.
Anybody know what makes the timing advance?
Did you try running the car with a jumper wire in the connector for
testing the timing? Would that show anything?

-supa

 

I doubt a ring would cause the problem; though I will certainly check.
The car does not burn any oil.

 

What causes an inlet valve to burn? I am at work now, but I will run a
compression test later this evening. I will let you guys know the
results. All of you have been very useful... at least I feel I am
going somewhere trying to diagnose the problem.

 

The usual cause is inadequate valve lash. If the rockers are too tight the
valve will leak and the combustion gasses will torch a channel in the valve.
That should show up on the compression test, although it may not be shocking
yet.

Mike

 

I am curious as to whether he has gauged the voltage from the coils at
the spark plugs.
If I've read correctly, he can get the misfire to occur at will by
increasing throttle pressure relative to extant engine RPM--in other
words, putting enough load on the engine--to the point of the voltage
being insufficient to ignite charge.
For what it's worth, it is also within the realm of possibility that
the engine controller itself it the culprit, hence no MIL (check engine
light).
Note that I'm not experienced with Hondas in particular, I'm just
throwing this out as my 2ç.
New to this group (looking at a Honda in a car lot)! :0)