Misfire w/o CEL?
 

Is it possible to have a misfire w/o triggering a CEL?

RE: Misfire w/o CEL?
 

Apparently the answer is yes. See picture taken from 96-98 Civic service manual.

[IMG]local://upfiles/25538/5ADD47ECD93B4543858FA76FE946884C.jpg[/IMG]

RE: Misfire w/o CEL?
 

Damn, RonJ, you're fast. I've got one more question...The cylinder #s are 4-3-2-1 from left to right, right?

RE: Misfire w/o CEL?
 

I don't know if it matters, but what year and model Civic do you have?

RE: Misfire w/o CEL?
 

98 HX. D16Y5

RE: Misfire w/o CEL?
 

Yes, when you are standing in front of the car.

The picture also may be helpful to you.

[IMG]local://upfiles/25538/2A1088DB692A4F7E8A3EB5F9B43EB233.jpg[/IMG]

RE: Misfire w/o CEL?
 

I'm assuming the problem I'm experiencing is misfiring. I'm hearing a rough idle/popping noise coming from the exhaust.

RE: Misfire w/o CEL?
 

Sounds misfire-like to me. Can you categorize the problem using the chart in the picture?



[IMG]local://upfiles/25538/5C238F8893DD455B8AC24ECBD8BD9137.jpg[/IMG]

RE: Misfire w/o CEL?
 

Hehe. I was just looking at the same chart trying to figure it out. Here's the deal: I converted my CVT (which uses a standard narrow-band primary O2 sensor) to A 5-speed (which uses a wideband primary O2 sensor). I just put in the wideband O2 sensor today (which got rid of the CEL I had for several months) and I replaced my ignition wires w/ NGK wires today too. Since I'm not getting a CEL, I'm assuming my new O2 sensor is functioning properly.

So, that means it's probably the ignition wires, right? Should I pull them one at a time while running and see if the idle changes?

RE: Misfire w/o CEL?
 

I think that's a good idea. Could you also verify by showing a lack of spark from the suspect wire?

RE: Misfire w/o CEL?
 

By having the spark plug in the ignition wire w/ the car running, but the wire/plug out of the cylinder?

RE: Misfire w/o CEL?
 

Sorry. Disregard my last comment. I wasn't thinking clearly. The picture shows a way to test the wires with a multimeter, if you have one.

[IMG]local://upfiles/25538/1A6D70ECC82F44FCA9B7FC68C1D6DD0B.jpg[/IMG]

RE: Misfire w/o CEL?
 

I don't have a multimeter (but I could get one). Will my method work instead?

RE: Misfire w/o CEL?
 

I think your method may work. I was trying to provide you with an alternative if your test led to an ambiguous outcome.

RE: Misfire w/o CEL?
 

I'll give it a shot tomorrow and see what happens.

RE: Misfire w/o CEL?
 

I wonder whether disconnecting a good plugwire will trigger the CEL to turn ON. If so, would that say that your misfire problem isn't due to a faulty plugwire?

RE: Misfire w/o CEL?
 

Okay, I checked my ignition wires w/ multimeter...no problems. I also replace my new wires w/ the old ones I was using previously...same symptoms. So, I'm ruling out ignition wires as a possible cause.

Since it's not the wires, it's gotta be the new O2 sensor I put it. So, I unplugged the sensor (which triggered a CEL) and the misfiring got better. I could still here it popping a little, but the engine wasn't shuddering like it was w/ the sensor still plugged in.

As I mentioned before, my old CVT setup used a standard 4-pin narrowband O2 sensor. Since I converted it to a 5-speed, I had to use a new wideband O2 sensor (8-pin/7-wire; D16Y5 5-speed is the only model that uses an OEM wideband O2 sensor).

Now, I assumed I wired the new sensor into the wire harness/ECU correctly since I didn't throw a CEL. Is it possible a bad wire splice on my part would cause the sensor to read incorrectly, but not throw a CEL?

RE: Misfire w/o CEL?
 

I'll look at the ECM/O2 circuit and see if I can come up with an answer (unfortunately not guaranteed). Is it the primary O2 sensor?

In the meanwhile, even though it seems like the problem is coming from the O2 sensor, maybe you should also check whether some of plugs may be fouled.

RE: Misfire w/o CEL?
 

Yes, it's the primary O2 sensor. And I just replaced the plugs last week (made sure they were properly gapped, too). Here are the page numbers from the manual that I used as a guide for the re-wiring:

Electrical Section - 202-5 - Plug C123
" " - 202-26 - Connector A
" " - 202-27 - Connector C & D

RE: Misfire w/o CEL?
 

Just a thought. Do CVT and 5-speed Civics have the same ECU? If not, could this be the problem?

RE: Misfire w/o CEL?
 

No, they have different ECU. I replaced it when I did the swap.

RE: Misfire w/o CEL?
 

Yeah, now I better understand your focus on the wiring.

RE: Misfire w/o CEL?
 

Can you tell me how you rewired the O2 sensor to the ECU. Also, where did you find the pin out for the original O2 sensor 4-pin connector?

RE: Misfire w/o CEL?
 

Okay, the number on the left corresponds to the plug C123 on pg 202-5 and the number on the right corresponds to the pins/connectors (pg 202-26) that plug into the ECU.

#1 Blk/Wht > #6 on Connector A
#2 Blk > I gounded it in the engine bay
#3 Grn/Blk > Grounded in the engine bay
#4 Wht > #7 Connector D
#5 Empy
#6 Wht > #25 Connector C
#7 Blk > #23 Connector C
#8 Red > #24 Connector C

RE: Misfire w/o CEL?
 

Ok, what about this...I grounded wires #2 & #3 in the engine bay (I figured grounded was grounded), but if you look at the top-right diagram on pg 11-147 it says that that wire #3 (Grn/Blk) is supposed to be plugged into #11 on Connector D. Might that cause a problem?

RE: Misfire w/o CEL?
 

Yes, definitely rewire #3 to ECU D11. Otherwise, I agree with your wiring. See Page 23-13 of Electrical Index section (actual page 1891 of 96-00 manual) for additional confirmation of your wiring. I expect that the #3/D11 change will resolve your problem. Good luck.

RE: Misfire w/o CEL?
 

Well, I wired #3 into #11 on Connector C...no dice. Still having problems. I guess the next step is to pull out the O2 sensor plug/wires and start testing continuity, voltage, etc. as per the instructions on pg 1891. I'll try and get to it sometime this week. I'm burned out and frustrated right now...bah!

RE: Misfire w/o CEL?
 

Dang! You probably just made a typo, but the #3 wire goes to terminal 11 of the ECU D connector not the ECU C connector.

Just a thought: It may be important for wire #2 to be grounded to the specific location indicated in the manual. This is the only other possibility that I can think of to explain the sensor not working.

Don't worry. After your get some rest, you'll figure it out.

RE: Misfire w/o CEL?
 

Is it possible my timing's off, RonJ?

RE: Misfire w/o CEL?
 

Yeah, given that the CEL is OFF with the O2 sensor connected, checking the timing seems like a good idea. Also, how you categorize the misfiring in the chart (see post #8 of this thread) might suggest additional components to troubleshoot if the timing were fine.

I guess the dilemma is that disconnection of the O2 sensor lessens your misfire problem. This observation may indicate that the sensor is making O2 readings but they are incorrect. Maybe the #2 wire needs to be attached to the specific ground location shown in the manual to make proper readings? Alternatively, maybe the new O2 sensor is defective? Are you able to use a scan tool to test whether the O2 readings make sense?

RE: Misfire w/o CEL?
 

I'm gonna check the timing, go down the misfire diagnosis list/chart, and then try and get my hands on a scanner. I recently replaced my IACV w/ a used one I purchased. I'm not sure how clean it was, so I'll start there. What should I use to clean it? Brake cleaner?

RE: Misfire w/o CEL?
 

Sounds like a good plan. I've heard carburetor cleaner is the way to go for the IACV.

RE: Misfire w/o CEL?
 

Alright, here's my plan for the weekend:

Replace Dizzy cap and rotor
Clean TB and IACV
Seafoam that bitch

RE: Misfire w/o CEL?
 

Update

1.) Replaced cap and rotor; Cap had what appeared to be grit/build-up on one of the four terminals. And the rotor appeared brown and discolored (burned?).

2.) Cleaned out IACV w/ carb cleaner (alot of black **** came flying out).

3.) Seafoamed it.


Car seems to be running much better now. Popping/shuddering is 90% gone...but it's not 100% yet. Now the car seems to idle a little too low <500 rpm (which I assume is the cause of the occasional shudder/near stall). Hopefully today I'll be able to tweak the idle so it runs a little higher. Gas mileage seems much improved and the new wideband O2 hasn't thrown any CELs yet. I'm crossing my fingers adjusting the idle screw will fix my problem. Thanks again for your input, RonJ!

RE: Misfire w/o CEL?
 

That's great news! I look forward to hearing that the engine's running 100% when the idle is adjusted.

RE: Misfire w/o CEL?
 

Got another question...what's the name of the goop used to keep the idle screw from coming out? I'm assuming once I adjust it I'll need to re-goop it, right?

RE: Misfire w/o CEL?
 

Not sure. The idle screw for my 97 Civic is simply protected by a plastic cap insert.

RE: Misfire w/o CEL?
 

The idle screw for my 87 (carbed) civic is unprotected under the air cleaner box (which is on top of the carb). I guess the air cleaner box keeps most stuff from touching it.

The idle screw on my 86 (FI) crx is unprotected. It's pretty exposed on the side of the throttle body. If you're worried about vibration loosening the screw, you could buy some threadlocker and apply it to the screw. I'd first drive for a week or two just to see if vibration (or anything else) would offset the screw.