codes 302 and 306

[hgsmith]

I have a 1999 ranger, 4.0. I have changed the fuel filter, changed the idle sensor, cleaned the maf.I have put in new autolight spark plugs, new spark plug wires and a new coil pack. The gas milage has gotten worse. It use to just have the 302 code, now it also has the 306. I know it is a missfire on cylinder 2 and 6.The exhaust is starting to smell. Well what next ? 02 sensor.....new maf....new catalytic converter....new injectors..... Any help would be appreciative.....Thanks

 

[LittleBigFoot]

Hook up a fuel pressure tester and see if it's fluttering.

When I was diagnosing some issues with my 3.0, I rigged up some fittings to use an oil pressure guage off one of the fuel rails.

Fuel delivery and return issues can cause motors to act really weird. Don't go just throwing money at it till you're 100% sure what it is.

 

[modelageek]

I have a 1999 ranger, 4.0. I have changed the fuel filter, changed the idle sensor, cleaned the maf.I have put in new autolight spark plugs, new spark plug wires and a new coil pack. The gas milage has gotten worse. It use to just have the 302 code, now it also has the 306. I know it is a missfire on cylinder 2 and 6.The exhaust is starting to smell. Well what next ? 02 sensor.....new maf....new catalytic converter....new injectors..... Any help would be appreciative.....Thanks

just some thoughts! the chances of 2 injectors going bad at the same time is less likely. the misfires are on 2 different heads so the chances of both o2 sensors and both cats going bad at the same time not likely. the maf is a possibility. I would do a fuel pressure test and check out the egr valve.

 

[modelageek]

I just noticed that littlebigfoot and I posted at the exact same time and gave you the same suggestion. definitely do the fuel pressure test. You can borrow/loan one from the autoparts stores. if you live near a harbor freight they have one for $20. I am having a similar issue with my 4 banger p0303. I did the test and i get koer 64 i get 62 koeo, however it takes 8 cycles of the key to go from 0 to 62. I am getting missed opinions about my results. I think it is my issue but I am not positive.

 

[Xandor]

Don't chnage em. I have the same problem and changed them and It did help but didnt fix.

 

[modelageek]

Don't change what? Injectors, o2 sensors, cat's?

 

[hgsmith]

Thanks for the replies. My truck is a stock 1999 4.0 , just like it rolled off the assembly line. I have not done anything to it. How do you check the egr valve?

 

[dbp]

Pull out the plugs and look for any signs of a misfire on those two cylinders. It's strange that it's only 2 and 6...if it were any of the things you mentioned, normally it would just be a bank or a random cylinder misfire. It almost has to be two plugs, two wires, two injectors, etc. I mean I've seen weirder things, make sure none of your plugs are cracked...try swapping 2 with 4 and 6 with 1 or something, see if your codes change.

 

[adsm08]

To HG, first thing's first. Stop. Breath. Think. We're here to help and teach you.

Your coil pack ignition system uses a waste spark system with paired cylinders. So for every time the coil fires 2 plugs go off.

The pairing goes:
3|4
2|6
1|5

So the misfires on 2 and 6 are probably related. The advantage of the waste spark system is that you can get the wires mixed up for paired cylinders (IE have terminal 4 connected to cylinder 6) and it will still work right. But sometimes the coil won't fire out one side for some reason. I'd guess this isn't your problem since both are missing.

One of the 4 wires going into the coil should be brighter than the others, ignore that one and check the middle one of the other 3 for ground with the key on.

You can also check the continuity of the coil by putting your ohm meter on the two terminals for 4 and 6.

 

[modelageek]

Adsm. That is good logical thinking. HG said he replaced the plugs wires and coilpack. I assume that the issue was there before he replaced those items. That being said most likely the wires are on correct but still worth checking. Intially that is why I was thinking fuel presure or egr valve. What instructs the injectors to fire?

 

[adsm08]

You are right, up to this point he has been thinking clearly logically. But at the end of the original post its starts to sound like he's his a desperation point. A bad O2 or cat is highly unlikely to cause a miss in only 2 cylinders. Far more likely those would either cause it to run poorly on all cylinders, or make it not run at all.

I'm a professional, and sometimes I still need that reminder to stop and think a bit more when the usual suspects aren't working.

Cam position sensor tells the PCM when to fire the injectors and the coil, but if that was an issue I'd guess that it wouldn't run at all, or it would be a more random miss.

I'm assuming that his wires are good, but wondering if he may have gotten a bad coil out of the box, or if there may be some problem in the control circuit since it seems the center coil just isn't firing.

 

[modelageek]

I'm assuming that his wires are good, but wondering if he may have gotten a bad coil out of the box, or if there may be some problem in the control circuit since it seems the center coil just isn't firing.

interesting thought. I am assuming the OP had the issue with #2 AND #6 before doing the work. That being the case the chances of getting a new coil with the same issue would be slight.

 

[adsm08]

interesting thought. I am assuming the OP had the issue with #2 AND #6 before doing the work. That being the case the chances of getting a new coil with the same issue would be slight.

Original post said initially the problem was only #2 cylinder, then it showed up in on 6 later. My experience with Ford 6 cyl coil packs is that the center one (the one in question here) is the most common one to fail (I think its because it heats up more being in the middle).

But you are right, its not that likely (but not unheard of) to have the same problem with two parts like that. That's why I also had him check the ground circuit. Seeing if it shorted to ground (the test I asked him to do) is easier than seeing if it gets a good signal. It also can't hurt to check it and see. Worst case scenario is he wastes 5 minutes ruling out something that isn't the problem.

 

[hgsmith]

Hey guys, thanks for the replies. I replaced the old coil with the new one and still had the same problem. I used the jab blue wires which are numbered and replaced one spark plug and one wire at a time. However I did check a diagram and they are on there in the right order. Checked the grounding and every thing is grounded.I am not sure how to check the egr valve. From the day I got the truck it always had a hiccup in the idle but now it is really rough. It is ok at first start but as it warms up and the rpms go below 1000, it gets rough. And the emission light comes on after a drive cycle is completed. It has plenty of power at any speed. But the gas milage is very poor. It use to get 19 mpg now it gets 16 mpg. I thank every one for all of your help.

 

[kimcrwbr1]

a compression check and check the vacuum will give you a good idea on the engines health and eliminate two variables if it checks out good. if the compression is good but the vacuum jumps or is low check for leaks. I dont know much about FI but cant you check each wire for spark first with a light unplug injectors while the engine is running and watch a tach for rpm drop then work your way back to the computer. and does the computer tell the coil when to fire. also is the EGR controlled by vacuum if so connect vacuum to the egr at an idle the engine should die right. my guess it is below the throttle body if it has one. I find that focusing on the obvious first take your time change the oil and filters check all connectors vacuum lines put a wrench on nuts and bolts and get to know it first ask questions it is funny how the obvious is so easy to overlook.