1997 Accord EX 2dr 5spd - CEL code 71 - Misfire

Greetings,
Ok, this is driving me crazy.
I'm getting CEL code 71 (paper clip in blue connector under passenger side)
Misfire or Random misfire on Cylinder 1.

I've changed:
Rotor button, distributor cap, Plug wires, and Plugs.
No oil or anything noticable on the old plugs.

Runs perfect, does not hesistate, sputter, miss, etc.
As a matter of fact, it ran fine before I changed all of the above.

The CEL only comes on when I let off the gas pedal, ie deceleration.
Clear ECU, comes back 2 or 4 days later while decelerating.
Same code, 71.

I've been told this could be:
1) Clogged EGR ports
2) Crank angle sensor going bad

Is this correct? Any other possible causes of this code 71?
Any way to verify whether or not the crank angle sensor is going bad?
Any way to clean the EGR ports with fuel additives?

Because the car has 156K miles, runs freakin great, still gets good gas mileage too.
I don't baby the car either, it gets a good running day in and day out.
Practically everything is stock, except for the removal of the scoop on the air box intake, which has been off for over 100K miles.

Any help would be appreciated cause I don't want to spend any more money until I know the exact source of the problem.

Do car shops with code readers provide more detail as to the source of CEL codes?

Thanks

Greetings,
Any help would be appreciated cause I don't want to spend any more money until I know the exact source of the problem.

Do car shops with code readers provide more detail as to the source of CEL codes?

Thanks

Not with this code and not on your car. A scope would rule out any ignition cause for it, but it's probably safe to assume it's not gonna be an ignition issue, based on what you've said.

I think I'd look for a vacuum leak localized around the #1 cylinder. If your EGR resides close to #1, then yeah, it might be suspect, but usually when they hang open with closed throttle (which causes lean misfire) that causes idle instability, i.e. when you drop the throttle and come to a stop, it wants to idle rough or even die, and this isn't the case here.

But if it feeds closest to #1 and it was stuttering instead of snapping shut instantly like it's supposed to when the throttle is dropped, I could see where it could cause a lean misfire momentarily on one cylinder. It wouldn't be the passage crud doing it, but the valve itself. You can remove the EGR and clean it up and rod out the passages (suck the crud you bust loose out with a shop vac), make sure the pintle moves smoothly and seats straight...etc. Might get lucky and that's all you gotta do..

Crank sensor is at the heart of how it detects misfire...it reads crank position and as it does the PCM anticipates how long it should take for the next angle to be sensed...a misfire causes a slight discrepancy in the time it takes for the crank to rotate through that cylinder's firing stroke, and the PCM calls foul if it sees over a preset amount (don't know how many on yours, but usually 20 or more) of crank decelleration at one angle.

But in general crank sensors are either bad or they are not. They are just a simple inductive coil, and if the winding breaks, the sensor fails. They will sometimes fail when hot and the winding is broken, only to make contact again after cooling down. I can't see any way one could fail where it was indicating a misfire in one cylinder...if it was coding for multiple random misfire/all cylinders or something yeah, then I might suspect it if the car ran perfect.

Hey. I just realized. You said 1997. That should be an OBD II system, and you can't do the jumper wire trick on those, doesn't work.

So either you have a late 1996 (OBD I) model, or you are doing something meaningless with the jumper trick....

OBD II codes have to be extracted with a scan tool, and are formatted as "PO171" or similar...

Hi jeffcoslacker,
Many thanks for the detailed response pertaining to the EGR and crank angle sensor.
That's the details I needed to know.

So, it's got to be something related to the EGR, moreso the EGR valving. Right?
Cause it runs great, might idle rough every now and then, but very rare, and it never acts like it's going to die.

What parts do I need (gaskets?, etc?) to remove, clean EGR system, and re-install?

Some more detail:
MFG Date: 9/96 - 97 Accord EX

There is an ODB connector behind the ashtray. I have no clue if it's OBD-I or II. Plus, there is a 2-wire blue connector under the passenger side dash. I have used the paper clip jumper trick with this 2 wire plug to fix a faulty O2 sensor in the past. I found the CEL list for my model a couple years ago and have kept the printout in my toolbox in the garage. :)

Insert jumper, turn key to ON, CEL blinked the proper morse code for faulty secondary O2 sensor, bought a new one, replaced it, cleared ECU, and the O2 sensor has not given me a problem since. This was back around 120K miles. So I know I can use this method for 'quick' diagnostics, and that's how I know I'm getting 71 - Cylinder 1 misfire, CEL blinks 1-1-1-1-1-1-1:1 constantly with the jumper in place.

Yet for more detailed diagnostics, I'd need to get my mechanic buddy to hook into the OBD connector behind the ashtray, right?

Either way, I'll see what I can do about cleaning the EGR system this weekend. Especially if you can clue me in as to what parts I need and any other pointers on the matter of cleaning the EGR system. Again, many thanks for the info. I appreciate it. (and yeah, I've got a shopvac :)

I do not know if you have Autozone in Alabama. But if you do just go there. They will give you a code reader and that will be it. I did it two days ago.
Good luck!

Sam

Hi jeffcoslacker,
Many thanks for the detailed response pertaining to the EGR and crank angle sensor.
That's the details I needed to know.

So, it's got to be something related to the EGR, moreso the EGR valving. Right?
Cause it runs great, might idle rough every now and then, but very rare, and it never acts like it's going to die.

What parts do I need (gaskets?, etc?) to remove, clean EGR system, and re-install?

Some more detail:
MFG Date: 9/96 - 97 Accord EX

There is an ODB connector behind the ashtray. I have no clue if it's OBD-I or II. Plus, there is a 2-wire blue connector under the passenger side dash. I have used the paper clip jumper trick with this 2 wire plug to fix a faulty O2 sensor in the past. I found the CEL list for my model a couple years ago and have kept the printout in my toolbox in the garage. :)

Insert jumper, turn key to ON, CEL blinked the proper morse code for faulty secondary O2 sensor, bought a new one, replaced it, cleared ECU, and the O2 sensor has not given me a problem since. This was back around 120K miles. So I know I can use this method for 'quick' diagnostics, and that's how I know I'm getting 71 - Cylinder 1 misfire, CEL blinks 1-1-1-1-1-1-1:1 constantly with the jumper in place.

Yet for more detailed diagnostics, I'd need to get my mechanic buddy to hook into the OBD connector behind the ashtray, right?

Either way, I'll see what I can do about cleaning the EGR system this weekend. Especially if you can clue me in as to what parts I need and any other pointers on the matter of cleaning the EGR system. Again, many thanks for the info. I appreciate it. (and yeah, I've got a shopvac :)

That's what I was thinking...it had to be a late '96 sold as a '97 model because all cars here (unless you aren't in the US) had to be OBD II by 1997 model year. That's why you are able to do that...it's still OBD I.

The OBD connector allows you to access the streaming signals from the sensors on the fly, yes...but unless you could see a dropout in CPS signal or something it probably wouldn't be much use for this problem.

You did seem to say that it might idle a bit rough at times? That could also be consistant with a minor EGR leak from sticking or not seating fully intermittantly, correct. I didn't mean to imply that EGR problems would always cause harsh idle and stalling, just that's the point where most people get to before they bother to have it looked at.

You'll need a new EGR gasket and you can clean the pintle and seat with a toothbrush and some carb cleaner or something along those lines...don't use a wire brush or anything like that could scratch the seat or bore and cause sticking or sealing trouble....and I think yours will have a pipe that comes up to the EGR from the exhaust that you just wanna use caution not to break or twist...if that is a position sensing EGR (has electrical wiring) be sure the small metering ports are clean and clear...

And before you do any of this take a quick look around the #1 cylinder to verify there's no other sources of a vacuum leak that could exist...like sometimes there will be vacuum ports coming off the underside of an intake runner that you don't even see if the hose fell off of it, so run your hand around or stick a small mirror under and look around...

Just for a little more info, the reason I'm liking the EGR theory is this:

Like I said, when you drop the throttle while the car is moving, intake vacuum level rises to the highest it ever gets (motor with momentum acting against a closed throttle plate...lotta suction), and when the MAP sensor tells the PCM that the vac level is that high, and it sees the Throttle Position Sensor reporting a closed throttle, it cuts injector dwell back to a minimum, otherwise, you'd have the big blast of unburned fuel that you got with carbed engines on throttle cut.

So as the motor is spooling down to idle, the PCM is only allowing the injection to meter out just enough fuel to keep the motor running, until it settles back to idle, then it has to fatten it back up a bit for a stable idle. With it running at the leanest it ever does at that moment, it will be suceptible to extra air being pulled in by the high vacuum levels, and cause a mixture just beyond the threshold of ignition, and you get a lean misfire condition until the vacuum level stabilizes or the injector dwell changes, which both happens as the car comes to a stop.

If that isn't it, I might start wondering if that injector was a bit plugged or sticky...something like that. At the miles you have it's very possible...

I do not know if you have Autozone in Alabama. But if you do just go there. They will give you a code reader and that will be it. I did it two days ago.
Good luck!

Yeah, there's Autozone, Napa, AdvanceAuto, etc around here.
Long story short, I do computer work for my mechanic, and he gives me car freebies in return. He's already told me to stop by next time the CEL comes on and he'll hook in the diag reader. He's also mentioned he'd charge me $140 for a full induction + EGR cleaning. I've worked on my own vehicles for +15 years, just never had to deal with 'misfires' caused by the EGR system. :)

That's what I was thinking...it had to be a late '96 sold as a '97 model because all cars here (unless you aren't in the US) had to be OBD II by 1997 model year. That's why you are able to do that...it's still OBD I.

The OBD connector allows you to access the streaming signals from the sensors on the fly, yes...but unless you could see a dropout in CPS signal or something it probably wouldn't be much use for this problem.

You did seem to say that it might idle a bit rough at times? That could also be consistant with a minor EGR leak from sticking or not seating fully intermittantly, correct. I didn't mean to imply that EGR problems would always cause harsh idle and stalling, just that's the point where most people get to before they bother to have it looked at.

You'll need a new EGR gasket and you can clean the pintle and seat with a toothbrush and some carb cleaner or something along those lines...don't use a wire brush or anything like that could scratch the seat or bore and cause sticking or sealing trouble....and I think yours will have a pipe that comes up to the EGR from the exhaust that you just wanna use caution not to break or twist...if that is a position sensing EGR (has electrical wiring) be sure the small metering ports are clean and clear...

And before you do any of this take a quick look around the #1 cylinder to verify there's no other sources of a vacuum leak that could exist...like sometimes there will be vacuum ports coming off the underside of an intake runner that you don't even see if the hose fell off of it, so run your hand around or stick a small mirror under and look around...

Man, you know Honda's, that's for sure. :)
I hear you about it being OBD-I and a diag reader probably won't reveal anymore helpful details. Yet, never hurts to give it a shot. Thanks for the part and cleaning info. Very valuable info. I can't thank you enough for your help. It seems like there isn't much involved with manually cleaning the EGR system on this vehicle based on your description. Also, I'll check around CYL #1 intake for disconnected/broken vacuum hoses and such before I start taking things apart. Appreciate the tips..

Just for a little more info, the reason I'm liking the EGR theory is this:

Like I said, when you drop the throttle while the car is moving, intake vacuum level rises to the highest it ever gets (motor with momentum acting against a closed throttle plate...lotta suction), and when the MAP sensor tells the PCM that the vac level is that high, and it sees the Throttle Position Sensor reporting a closed throttle, it cuts injector dwell back to a minimum, otherwise, you'd have the big blast of unburned fuel that you got with carbed engines on throttle cut.

So as the motor is spooling down to idle, the PCM is only allowing the injection to meter out just enough fuel to keep the motor running, until it settles back to idle, then it has to fatten it back up a bit for a stable idle. With it running at the leanest it ever does at that moment, it will be suceptible to extra air being pulled in by the high vacuum levels, and cause a mixture just beyond the threshold of ignition, and you get a lean misfire condition until the vacuum level stabilizes or the injector dwell changes, which both happens as the car comes to a stop.

If that isn't it, I might start wondering if that injector was a bit plugged or sticky...something like that. At the miles you have it's very possible...

Wow, very detailed description of the 'behind the scenes' deceleration process going on with the engine, components, and electronics. All makes sense to me as to why the ECU thinks it's misfiring when the throttle is fully closed. It's got to be the EGR. Although, good point about the injector. Yet, I don't think it's the injector. Wouldn't the ECU detect this? Or I should be able to notice a performance degradation if the injector was acting up, right? This CEL #71 problem started 3 weeks ago. 1st week, change parts. 2nd week, run out a full tank with fuel system cleaner. 3rd week, post here for more details from the Honda experts. :)

I am very appreciative for all of your help, tips, and suggestions. I'll look for vacuum leaks and etc before I start taking the EGR system apart to clean it.
Thanks man

I was just thinking that the closed throttle, decel fuel management strategy calls for very short injector dwell....so if you had one that was having a bit of trouble with a very fine metering like called for in this situation, it could cause a lean condition for a few revolutions....and since idle under load or acceleration/cold start all call for wide dwell patterns with comparitively more fuel delivered, you wouldn't notice an injector just beginning to have trouble with delivering a very fine, low volume spray pattern, see what I'm saying?

It's possible for it to be a bit clogged or sticky to where it has trouble with very quick duty cycles with light spray, but still blows mid to full flow with authority. Sometimes if sticky, with quick dwell commanded they just dribble fuel rather than spray, because the pintle doesn't act fast enough during the short duty cycle...

And thanks for the vote of confidence, but I know JACK about Hondas in particular, that's just typical feedback fuel loop common to all cars...they have there differences, but when you get down to it, they all do most things the same way....

jeffcoslacker,
LOL, I hear you..
Here's an update.
Ok, didn't get to work on it this past weekend. Wife reminded me of certain pressure washing duties I had to perform around the outside of our house all weekend long..

I took the car by my mechanic yesterday afternoon (Monday).
Sure enough, it is OBD-II, and gave us a code 401 - Insufficent EGR flow.
So, that settles it...

I could do the cleaning myself this coming weekend.
Yet, I've got a little extra $$$, and I'm going to get my mechanic to do their 'BG chemical EGR+Intake cleaning'. They've got a kit that pressure cleans (60 psi?) the EGR valve, ports, and full intake cleaning from throttle to intake valves. Said he'd even run an extra can of the cleaner thru it for free. I figure why not, car has 156k and might as well do a professional full on induction cleaning. That way it should be good for another 150K miles.
:)