'95, 64k miles, (driven only 400 miles in past three months) has been idling rough for several months. in city gas mileage seems to be down to 14.5 ish MPG (avg 18MPG three months ago). OBD codes have shown 0304 knock sensor, and after reset, 0604 misfire cyl#5. Calif emissions are passing at 15mph, however, at 25mph the NOx reading 750 FAILS--above limit. Tech examined EGR with a vacuum gage and concluded he wants to clean the EGR system.

Regarding the onboard diagnostic computer code 0604, placed a test object between the #5 ignition module and #5 spark plug--the test object did light up as the ignition module delivered its pulse. Therefore, assumes fuel injector #5 is defective. Spark plug is clean but the tip seems to be shaped like a cone rather than a 'cylinder shape'.

I am hoping to fix this misfire issue by pouring some cleaner into the gas tank in effort to clean the injector#5. Assuming the misfire continues, I suppose removing the intake manifold will be necessary to enable replacement of fuel injector#5. Tech says removal of intake manifold is necessary to clean EGR system. At this point, I am feeling EGR cleaning will not be necessary and the defective fuel injector #5 is causing the high NOx at 25 MPH. He estimates $350 (remove manifold and replace one fuel injector) +$100 to clean EGR system as manifold is removed anyway.

Please comment regarding whether fuel additive cleaner might correct the misfire which seems to be caused by defective fuel injector, and whether a misfire of cyl#5 might cause high NOx at 25MPH, and whether further EGR cleaning might also be needed to reduce NOx at 25MPH.

 

0604 points to a misfire caused by a coil pack, not a fuel injector.

1) Replace the coil pack on Cylinder #5
2) Put a new set of NGK plugs in the car
3) Clean the throttle body
4) Put a bottle of fuel injector cleaner in the gas tank and go for a nice long ride on the highway. Open it up good a few times!

Your idle should be smooth and you should pass emissions inspection after performing the above steps.

 

>>0604 points to a misfire caused by a coil pack, not a fuel injector.

1) Replace the coil pack on Cylinder #5<<

I referred to one of the ignition coil packs as an 'ignition module'... although the tech's test object did light when it was placed between the coil and the spark plug of cyl#5 (which indicated the coil was ok), I should have asked him to swap that coil with a diff cyl's coil. I will try the swap to see if the misfire follows that coil to another cyl.

 

having swapped #5 coil with #3 coil, the misfire code 0604 leads me to feel the problem is with #5 fuel injector. will try using retail fuel system conditioner to clean possibly dirty fuel injector. any other ideas about whether the misfire in cyl#5 would cause the NOx level to be too high at 25MPH emissions test? reading was 750 which is above limit. reading at 15MPH test was passing.

 

The exact same thing happened to me, and it was neither. What really happened was one of my NGK's actually fell apart into the valve. Yeah, the actually diode was in the valve clinging around, the only way my cylinder was firing was from arching to the cylinder wall. Might want to check your plugs.

 

when the tech tested coil#5, he pulled out the spark plug and felt it looked good. I am trying to understand whether the misfire code in cyl #5 0604, which is the same as before I swapped coil#5 and coil#3 (the car runs rough) is likely the same condition which is causing the NOx failure at 25MPH. I am hopeful that fuel system conditioner added to the gas will clean and correct any problem I might have with injector#5. If the fuel sys conditioner does not correct the misfire in cyl#5, I will replace injector#5. The tech feels the EGR needs cleaning--the reason for the NOx failing at 25MPH.

Did you get a misfire from the broken spark plug in the valve? or did you get a failing NOx emissions test? Thx.

 

the misfire in cyl #5 ... i have tested resistance on injectors #5, #3, #1, but I cannot see a difference. swapped the coils between #5 and #3, no change to misfire in cyl#5. placed fuel system cleaning additive in gas tank, but still misfire #5. wondering if the signal to the injector might be cause of misfire... would hate to replace injector and still have misfire problem. i get code 06-04 each time after i clear the onboard diagnostic. any other ways to test the injector without the hassle and cost of simply replacing the injector?

 

If you are already in there, try swapping injectors like you did with the coilpacks. If the problem follows, then its injectors. If not, probably the connector or harness. If you have any EGR issues, believe me it'll set the CEL and you will pull codes like 0302, 0305, 0306, 1005 from the ECU.

 

0604 Should Be A Cylinder 4 Misfire. P0600=general Misfire...p0601=cyl 1 Mis
P0602=cyl 2 Mis...p0603=cyl 3 Mis...p0604= Cyl 4 Mis...p0605= Cyl 5 Mis And So On. You Get The Point. I Think You Are Working On The Wrong Hole So To Speak.

 

the possiblilty of code 06-04 being a misfire in cyl#4 had not occurred to me! The reference for codes seemed to be 06-004 is cyl#5, but i will check further to see if my problem is misfire in another cyl.

 

after 1996 all codes must be the same in every car unless it is a manufacter specific code. so any time you pull a code from a car like a P0600...P0604...its going to be the same whether you drive a honda, chevy,nissan whatever it is. a P0604 is always a cyl. 4 misfire after 1996.

 

The ECU DECODER shows 0604 (6 long pulses & 4 short pulses of the CEL) as Cylinder 5 Misfire.

 

i dont know what long pulses and short pulses are. i work on cars for a living and when we pull codes from an ecu we use a scanner and it shows up like this

P0604:cylinder 4 misfire detected

perhaps you are pulling the codes in a diffrent manner...in that case then i dont know if you actually have a P0604. if you pull the codes w/ a scantool though then i can help you out.

 

Most of us, who can't afford a scan tool, are pulling codes via the diag **** on the side of the ECU. Go to this link. I would assume that whatever the scanner pulls is most accurate than the other method.

 

Both methods are equally accurate as long as you read them correctly. A scan tool is easier but you either have to buy one or get a place/someone who has one to pull them. Autozone will do it for free but the blinking CEL method is not that hard.

If you are reading from a scan tool please use the P#### format. If you are using the blinking CEL method then just post the numbers in #### format. That tends to keep things clearer.

 

three months after getting the diagnosis of code 06-04, paid a mechanic to replace injector in cyl #5. He showed me the old injector and its resistance was wrong...the injector was not working. the new injector fixed the problem. no more codes! car runs well.