misfire on cylinder 4 & 6

[jrobie79]

background: explorer ran fine for a year or so after I bought it, however would notice sometimes at WOT the CEL would flash briefly till I let off the gas, and it would accelerate and run fine

fast forward to a week ago, I finally got a CEL that was constant...ran the code and got p0306...misfire cylinder 6...I knew the wires needed changing, so I swapped those out, seemed to work for a bit but then it came back.

check the codes again and I'm getting p0306 and p0304, seems to have grown to cylinder 4 as well. The CEL flashes while driving, but remains solid if I roll for a bit and am at a stoplight, until I accelerate again, then in blinks.

I checked the coil pack via some method I found on here, it seems in spec, the secondary readings were all pretty much identical, and the primary one gave me 1.1-1.3 ohms on all 3 pins.

the fuel filter was replaced less than 15K ago...along with the plugs. the 6th cylinder plug didn't look that different either, I was going to swap the plugs from bank 1 to bank 2 and vice versa to see if that helps, but I'm kinda stumped now? I was reading that vacuum leaks could cause that, but I took starting fluid and sprayed it around connections with no noticeable engine revving. I cleaned the MAF tonight and it didnt help.

possibly the intake manifold gaskets? it just seems weird to me that its only cylinder 4 and 6 but skips 5, so its not that whole bank...I'm starting a new job in a month or so, but i commute like 110 miles a day and I need this to last me another month or two (it has 255K on it, so a new vehicle is in the cards)

 

[rb142]

First of all, you shouldn't be driving it with the CEL flashing. That means you have a damaging level of misfire happening, and you are slowly destroying your catalyst, which will end up being a much more expensive repair.

Just because you have misfire codes for cylinders 4 and 6, don't trust that too completely. You probably do have problems on those cylinders, but it is not impossible to have problems on other cylinders too. The system, especially back then, is not perfect.

There are lots of things that could be causing the misfires ... especially at your mileage. How is the compression on those cylinders? Could be spark, injectors, air leaks, etc. Those cylinders aren't coil pairs, so it's probably not spark. A fuel pump or filter would affect all cylinders. A vacuum leak should be worse at idle than under load. I'd be leaning toward an injector problem in this case, assuming there isn't some mechanical (compression, head gasket) problem in those cylinders. If you have access to a scan tool, check the fuel trim values. That will give you a big pointer in the right direction.

 

[jrobie79]

First of all, you shouldn't be driving it with the CEL flashing. That means you have a damaging level of misfire happening, and you are slowly destroying your catalyst, which will end up being a much more expensive repair.

Just because you have misfire codes for cylinders 4 and 6, don't trust that too completely. You probably do have problems on those cylinders, but it is not impossible to have problems on other cylinders too. The system, especially back then, is not perfect.

There are lots of things that could be causing the misfires ... especially at your mileage. How is the compression on those cylinders? Could be spark, injectors, air leaks, etc. Those cylinders aren't coil pairs, so it's probably not spark. A fuel pump or filter would affect all cylinders. A vacuum leak should be worse at idle than under load. I'd be leaning toward an injector problem in this case, assuming there isn't some mechanical (compression, head gasket) problem in those cylinders. If you have access to a scan tool, check the fuel trim values. That will give you a big pointer in the right direction.

my car will be 15 yrs old when its due for its next inspection so if the cat is damaged, I'll just replace it with a resonator, no emissions testing after 15 years in mass...not that I'm advocating on driving my truck while its in this condition...I am going to check the compression this weekend, and see what I get. Also when you say a scan tool, you are talking about something more advanced than a bluetooth piece that is read via the "Torque" App on smart phones?

I was thinking it was possibly the injectors as well because if I clear the codes and let it idle for awhile, while the idle is kind of erratic, the CEL light never comes on, and nothing gets stored until I put the truck under load.

 

[rb142]

If you have Torque and a bluetooth adapter, that will work just fine. It will read live data. The short term and long term fuel trims (stft, ltft) on each bank will indicate if it is trying to add fuel or remove fuel to compensate for a condition that is leaner or richer than expected.

Listen to the injectors with a stethoscope. If you hear the clicking, you will know the injector is being commanded and is at least activating. There may still be a fuel problem though. If you don't hear the clicking, check the wires with a noid light or voltmeter to see if the injector is even getting a signal.

 

[2000StreetRod]

Sohc v6

I searched back to your new member post and learned that you have the SOHC V6. rb142 is giving you good advice. This thread may also help: Engine misfire procedure

 

[jrobie79]

well i figured I'd check the codes again this morning, and I realized I never checked the pending codes...I'm getting P0174 as a pending code now...so it looks like thats pcv related? would that be a trigger to the misfire codes? The Pcv valve is cheap and I've never changed it since I've owned the car so I'll probably do that this weekend too.

 

[2000StreetRod]

Why PCV valve related?

P0174 System too Lean (Bank 2)

Why do you think replacing the PCV valve will fix your lean condition?

Lean condition procedure

 

[BrooklynBay]

Compare the spark voltage in each cable with the tools in this link: http://www.explorerforum.com/forums/showpost.php?p=3009013&postcount=16

 

[2000StreetRod]

Otc 3141

That looked like a desirable tool so I searched the internet for one and apparently none are still available. Did it plot the voltage or just display a digital readout of the max and min voltages? I'd like something that plots the voltage for my future dual fire ignition experiments.

 

[BrooklynBay]

It records the minimum & maximum voltage, and displays the current voltage. It was an expensive tool, but came in handly numerous times. It even works on high voltage transformers in CRT monitors, television sets, and microwave ovens.

 

[rb142]

If you have a lean code then you should focus on looking for an air leak. Check the injector seals, intake gaskets, etc.

 

[Turdle]

misfires on 4&6 (bank 2)
Lean condition bank 2

Could be fuel injector related.

Do yourself a favor though and double check the bank 2 spark plug wiring order. I can't tell you how often I have mixed them up. It is a very common mistake. We won't laugh at ya--


PS

long shot but it only costs a time, no money:

I believe the 02 sensor is used to detect a misfire. Since the Lean and misfire codes are both on the same bank, swapping the bank one and bank 2 02 sensors just might "move" the codes to bank 1. You will need to swap the connections also. (duh)

 

[rb142]

You're right. An injector problem could make it go either rich or lean. Definitely need to check those. You could even swap a couple injectors and see if the problem follows the injector (assuming you already found the signals to them to be OK). If you swap it with one on the other bank, you will be verifying the O2 sensors at the same time.

The O2 sensors are not used at all for detecting misfire. That IS where the lean code comes from though.

 

[jrobie79]

so I did the codes again, and I'm getting p1151 and p0174 as the pending codes, the misfires on cylinder 4 and 6 as the stored fault codes.

places I've read said the culprit for a host of these codes is the 90 degree elbow for the pcv valve...that'll be the first thing I check, see if its cracked and creating a vacuum leak. After that I was gonna swap the intake gaskets to new ones as preventative maintenance, and use the stethoscope to check the injectors and go from there.

 

[rb142]

Checking the elbow is a good thing to do anyway, but if that was the problem it should affect all of the cylinders, not just 4 & 6. You need something that just feeds those cylinders.

 

[jrobie79]

sealed up the garage with some tarps (its still under construction) and its freezing outside...gonna fire up the heater tomorrow and dig into it...will report back

 

[2000StreetRod]

two problems?

I'm beginning to suspect there were/are two problems. Fuel trims and O2 sensor outputs are irrelevent at WOT when factory programmed data tables are used to determine injector pulse width (air/fuel ratio). Small vacuum leaks that the PCM adjusts the fuel trim for have the most effect on air/fuel ratio at idle when mass airflow is minimum. Engine misfire at WOT (flashing CEL) indicates the PCM measured power pulses for cylinder 4 & 6 were significantly less than the other cylinders. My engine at 150K miles had significant upper and lower intake manifold gasket leaks (cold start engine flare, P0171, P0174) but I never detected a misfire at WOT and the PCM never reported any for all my driving conditions.

Do you still have misfires at WOT or was that corrected by the ignition wire replacement?

I agree with rb142 that a compression check is warranted.

 

[jrobie79]

its still there, its a bit of a struggle to get up to highway speed on an onramp, because it chugs while accelerating...if i let off the gas a little and get back on it it does better and finally i dont notice any chugging or surging once i've been goign 65

 

[RomeovilleIL]

What type of plugs were installed? Have you actually pulled them and inspected yet?

 

[jrobie79]

looks like it was the injectors...took my dmm and got a reading of between 13.9-14.8 on all the injectors except #4 and #6 which were like 8.2 ohms and 6.4 ohms respectively. went to the JY pulled two that were at 14.1 ohms and will be installing them tomorrow along with the new PCV valve, new plugs (because why not at this point), new upper and lower intake manifold gaskets and we'll see where that gets me