rtstephn

Just yesterday at a stop light, my EX v6 started missing. I put a obd code scanner on it when I got home, and it read a P1399, which is a random misfire code. Took it by the Honda dealership, and, after the mechanic ran diagnostic on it, came back and said that all cylanders were misfiring! he had no idea why it was misfiring, could be any number of a dozen things, and said he wanted to put it on the clock, and just start working. I asked for an estimate, he said could be $600 to $1,000 just to diagnose it.

Took it to a second dealer (first one didn't charge me for the initial test), and he said just to change my plugs (the car has 70,000 miles on it). I took it home and changed my plugs, but still misfires with same code (I earlier cleared the codes).

Does anyone have any ideas on what this might be? Any help would be very much appreciated.

sonnieeeeboi

do you feel the car misfiring? That is odd that all your cylinders would be misfiring even after changing out the plugs. What kind of plugs did you use?
Chances of all the coils going bad at the same time is highly unlikely.
Another thing could be dirty fuel injectors. Try running some injector cleaner in it.

rtstephn

Yes, I can feel the car misfire. The idle is very rough, like it's skipping or misfiring.
I used NGK plugs in it, the Iridium set. Supposed to be good plugs, from what I am told...were about $9/piece. AFter changing plugs, I could feel it was idling better.

I went ahead and put fuel injector cleaner in the tank, as you recommended. Definately helped, but it still idles rough, and the P1399 "misfire" code still comes up. Could it be a dirty fuel filter in the tank? Or should I try more fuel injector cleaner?

Other ideas? The plugs and injector cleaner has helped quite a bit, but still misfires. Could it be timing related? Or would that be a different error code?

Ross 2.0

Troubleshooting Multiple
Misfire DTCs
NOTE: This article applies to ’98–02 Accord L4s,
’95–02 Accord V6s, ’98–01 Preludes, and ’99–02
Odysseys.
When troubleshooting misfire DTCs (P0301 thru
P0306) with the PGM Tester, look at the freeze
data values for the throttle position (TP) sensor
and the exhaust gas recirculation valve lift sensor
(EGR VLS).
If the EGR VLS value is more than 1.25 volts, and
the TP sensor value is 0.5 volt (closed throttle), the
EGR valve opened when it should have been
closed, and is defective. Replace the EGR valve.
If the TP sensor value is more than 0.5 volt, and
the vehicle speed sensor (VSS) and RPM values
indicate that the DTC was set while the vehicle
was moving, write down or print out the EGR VLS
value. Then, drive the vehicle at the same VSS and
RPM as shown in the freeze data, and note the
EGR VLS value:
• If the freeze data EGR VLS value is more than
1.25 volts, but the EGR VLS value from the test
drive is less than 1.25 volts, the EGR valve was
stuck open, and is defective. Replace the EGR
valve.
• If the EGR VLS value from the test drive is
similar to the EGR VLS value on the freeze
data, the EGR valve is OK and isn’t the cause
of your misfire DTC problem. Look for other
possible causes.

rtstephn

Thanks for the detailed reply! Since I don't have immediate access to a PGM tester, should I just replace the EGR valve regardless? What would you recommend?

rtstephn

One thing I forgot to mention is that, with the car in park, if I raise the RPM to above 2500, the engine smooths right out, and feels just as it did before the problem started, running very solid. However, when I am driving the car, and the engine is under load, it seems that regardless of RPM, it idles rough.

Ross 2.0

i bet you have a clogged EGR valve, you would need to replace the EGR valve and clean the egr port in the plentum and install a Stainless pipe. to "prevent" further clogging.

rtstephn

I will definately do that. Any how-to on cleaning the plenum? Should I just use gas to clean the area, or other specific cleaner.

What do you mean by a stainless pipe extension? Ideas on where to buy this?

Thanks for the heads up.

swayzeesd

You should have a distributor-less ignition system meaning no distributor or plug wires if so here you go

1.Check the spark plugs 1st of all

2.Check compression on the cylinders and make sure they are within specs

3.find out if you have any other codes besides 1399 bcuz you should have a P0300 witch is random misfire... along with that you should have p0301-p0306 not all of them but a few... p0301 is cylinder 1 missfire and 302 is cylinder 2 and so on....if you can narrow it down to a few cylinders try switching the coils of known good cylinders not missing with the ones that are,then clear the codes and re-scan the car, if you are getting diff cylinder misses now then you know the coil packs are bad....check the wiring harness for power to the coils

4.check the Cam Positioning Sensors and wiring around them make sure they are not loose or corroded along with the Crank Positioning sensor i think Honda calls them something different but yea those tell the PCM where the cylinders are located and when to give what cylinder fuel and when to give it SPARK, check the wiring harness for resistance to ground and for power that will tell you if you have a short to ground or no power going to the injectors

5.with a noid light check your fuel injectors and make sure they are firing, if you dont have on use a DMM(digital multimeter) to check resistance in the injector i believe thats what you need to check for at the same time check the wiring harness for power to the injectors

5. if your coils are good and the crank and cam pos sensors are fine and compression is checking out ok then you might have a faulty PCM(ECU,Computer) whatever you want to call it but yea hope this helps

swayzeesd

o yea try taking a can of brake cleaner and spraying it around the INTAKE MANIFOLD where it meets with the head where the gasket is and if the rpm's come up and the miss starts to go away then you have a leak in the plentium or intake manifold gasket

natheath

I have the same problem on my 2000 accord EX with 98k. I've tried almost everything except replacing the ECM/PCM. Since I have two 2000 Accords (one with a f23a1 engine and the other with an f23a4 engine) can I swap ECM/PCM's to tell if that is a problem? I would have access to a honda PGM tester if the key code needs to be set.

natheath

Problem Solved! After replacing the spark plug wires originally I tested the resistance according to specs. The wires were suppose to be less than 25k ohms. The old ones were around 8k ohms. These were 0 ohms. However, I never took into account that the insulation might be defective, and that one of the wires were grounding out. Consequently, my short wire (#4 plug) was defective. When I added an additional component to the wire (an inline spark signal tester) the engine was back to normal. It's a good thing no one pays me to diagnose their vehicle, for it would cost them a fortune.

Alo Lo

PROBLEM SOLVED!

The problem was the ignition coil!

The obd tool showed multiple misfires, but after watching this video I found ONLY ONE to be defective


Had it replaced, no more blinking check engine, no more rough idle, stuttering, its running better than ever!

Dont go by the obd tool for which cylinder is misfiring, you have to check them all to see which one is bad

Could also be related to spark plugs, but I had the iridium by ngk and checked them and they were all like new

Could also be the spark plug wire!

But for me this one coil was defective!