misfire prob! help

02gtpony · Mar 13, 2006

i have a misfire problem, engine light is throwing P0308, P0174, P0316 codes, 0174 is lean on bank 2, 0308 is misfire in 8 cylinder, but what the hell does P0316 mean, its an unknown code in my manual, so i put new plugs in it and changed the eighth cylinder coil pack and it still misses, someone told me it could be a burnt valve, is this true? my mods are K&N cold air and mac off road H pipe, any info on this subject would help, thanks

MyEarsHurt · Mar 13, 2006

Well I googled that other code and it says this... P0316 Misfire Detected On Startup (First 1000 Revolutions). How old are the plugs and the plug wires? How many miles on the car? My stang was misfiring for a long time and I couldnt figure it out cause I had just replaced the plugs and plug wires, well I had a bad set of plug wires, got a new set installed and everything was perfect

Kilgore Trout · Mar 13, 2006

He does not have plug wires.

Could you have forgotten to connect plug the wire harness into the new coil? Go check the plug connection to the coil #8.

stangGT97 · Mar 13, 2006

MyEarsHurt said:
Well I googled that other code and it says this... P0316 Misfire Detected On Startup (First 1000 Revolutions). How old are the plugs and the plug wires? How many miles on the car? My stang was misfiring for a long time and I couldnt figure it out cause I had just replaced the plugs and plug wires, well I had a bad set of plug wires, got a new set installed and everything was perfect

unfortunately, being that he has an 02 GT, he wouldn't have wires to replace. The coil was going to be my suggestion, but that has been replaced already. If you are running lean on bank 2, cylinder 8, perhaps you should check that injector for clogs. Did it somehow get unplugged or unseated? Run some injector cleaner through the gas, or have them cleaned. The fact that the coil and plugs are brand new make me think it may be a fuel pressure problem for that cylinder. Others may know better, but it wouldnt hurt to check what I said

MyEarsHurt · Mar 13, 2006

stangGT97 said:
unfortunately, being that he has an 02 GT, he wouldn't have wires to replace.

news to me but okay, just trying to help...

Mike97gt · Mar 13, 2006

well the po174 lean bank 2 code is caused by the misfire. what happens is the 02 sensor picks up the unburned oxygen from the misfire, since it never sees the extra fuel ( it's a oxygen sensor DUH!! it don't sense unburned fuel) it assumes that bank is lean due to the extra oxygen

now what you need to do is check your oil. does it smell like fuel???

what happens a lot on a bad misfire is the unburned fuel makes it's way into the crankcase and these fuel vapors are sucked back into the intake by the pcv system, that causes a rich mixture and more misfires due to the rich mixture caused by the fuel vapors.

so change your oil and remove all the plugs and clean them well with brake clean if you don't have a spark plug cleaner.

another reason you could still have a misfire on cyl 8 is also related to oil.

sometiems when you have a misfire the unburned fuel washes the rings down so you will have a temporary drop in compression in that cylinder.

I hae seen as much as a 30 percent compression drop and thats enough to cause a misfire.

to fix this again change the oil and filter and clean the plugs and run it untill it goes away. don't worry if it's reason #2 the compression will return to normal.

and please remember to post back when you find the problem.

stangGT97 · Mar 13, 2006

MyEarsHurt said:
news to me but okay, just trying to help...

oh hey, I wasn't trying to be a jerk or anything! just saying for your own knowledge (and for anyone else who may not know) that in 99 Ford switched to coil on plug in the mustang... certainly does make locating the root of a misfire a lot easier

MaxedGT · Mar 14, 2006

02gtpony said:
i have a misfire problem, engine light is throwing P0308, P0174, P0316 codes, 0174 is lean on bank 2, 0308 is misfire in 8 cylinder, but what the hell does P0316 mean, its an unknown code in my manual, so i put new plugs in it and changed the eighth cylinder coil pack and it still misses, someone told me it could be a burnt valve, is this true? my mods are K&N cold air and mac off road H pipe, any info on this subject would help, thanks

On a GM vehicle code p0316, is an injector circuit fault on cylinder 6. Seeing as OBD2 is supposed to be universal, I'd say thats what the code means for Ford as well. That would explain the lean code on bank 2 as well. Code p0308 is probably a by product too. Swap #6 injector with another. clear the codes and see what codes set. My guess is the p031_ code will follow the #6 injector.

Mike97gt · Mar 14, 2006

MaxedGT said:
On a GM vehicle code p0316, is an injector circuit fault on cylinder 6. Seeing as OBD2 is supposed to be universal, I'd say thats what the code means for Ford as well. That would explain the lean code on bank 2 as well. Code p0308 is probably a by product too. Swap #6 injector with another. clear the codes and see what codes set. My guess is the p031_ code will follow the #6 injector.

NO... the codes do not interchange. please see the sticky at the top of the forum

po316 on a ford is: misfire detected in the first 1000 rpms's

po308 is: misfire cyl #8

po 174 is : lean bank 2 and is caused by the unburned oxygen from the misfire

the po174 being there tells me this is a constant missfire and was probally ran for a little while that way.

the po316 indicates the same. thats a constant miss if the pcm picks it up instantly.

without being there to diag the car myself it's hard to be 100 percent sure but I would be comfortable enough to place a bet on it being this

we run into this with new cars all the time. the sales people move them a few feet and shut them off, after awile the plugs foul and you get misses. after awile with misses unburned fuel gets into the oil.. unburned fuel make a poor lube and the missing cylinders rings get "washed down" and the results are a temporary loss of compression in that cylinder. PLUS the fuel in the oil gives of fuel vapors that richen the mixture making the problem worst.

I bet he has atleast one plug thats fuel soaked. and his oil probally is washed down with fuel.

to fix this.

1. change oil and fitler

2. remove plugs and clean them really well a plug cleaner would be ideal ( it's a mini sandblaster that cleans plugs) or clean them really well with brake clean.

another thing that could cause this problem is if a plug was damaged during install or a boot not seated right.

Mike97gt · Mar 15, 2006

OK any news???

it is very important to update ont he problem. if you don't the thread becomes just about usless to others.

Kilgore Trout · Mar 15, 2006

Rarely does anyone ever report back

Mike97gt · Mar 15, 2006

Kilgore Trout said:
Rarely does anyone ever report back

yeah I know ticks me off.

stangGT97 · Mar 15, 2006

Mike, what you described is exactly the condition I have been seeing in my car. I changed my oil and plugs at the same time, but didnt torque one plug down enough, so I had a pretty decent misfire and compression loss in cyl 8. After torquing the plug down, the misfire did not go away. I recently pulled my plugs to re-check the gaps, and 2/4 plugs on the driver side bank were soaked in gas. Do you think that perhaps my oil also got contaminated with gasoline, and now is dropping my compression? All I can tell you is my car is a dog lately and misfires @ 1400. I wish I had your knowledge of cars... thanks dude

Mike97gt · Mar 15, 2006

stangGT97 said:
Mike, what you described is exactly the condition I have been seeing in my car. I changed my oil and plugs at the same time, but didnt torque one plug down enough, so I had a pretty decent misfire and compression loss in cyl 8. After torquing the plug down, the misfire did not go away. I recently pulled my plugs to re-check the gaps, and 2/4 plugs on the driver side bank were soaked in gas. Do you think that perhaps my oil also got contaminated with gasoline, and now is dropping my compression? All I can tell you is my car is a dog lately and misfires @ 1400. I wish I had your knowledge of cars... thanks dude

well when you have a misfire that badly the unburned fuel ends up in the oil. as i described above this has 2 bad effects.

change the oil, pull all the plugs and clean them. you need to clean them really well, not just wipe them down. brake clean works in a pinch but a plug cleaner is what you really need.

02gtpony · Mar 15, 2006

sorry guys i havent replied back in a while i work full time and go to school so i havent had a chance to log on, so here is what i did, i changed spark plugs all of them are tight enough, none of the old ones had gas on them, i bought a new coil pack and replaced #8 cylinder and it didn't do anything, i switched the old coil to the other side and it worked fine so it wasn't the coil pack, did an oil changed not too long ago and filter and fuel filter the works, no gas in the oil, this whole ordeal has happened before in the past, even before i had any modifications, so what do you think it could be now?

Mike97gt · Mar 15, 2006

02gtpony said:
sorry guys i havent replied back in a while i work full time and go to school so i havent had a chance to log on, so here is what i did, i changed spark plugs all of them are tight enough, none of the old ones had gas on them, i bought a new coil pack and replaced #8 cylinder and it didn't do anything, i switched the old coil to the other side and it worked fine so it wasn't the coil pack, did an oil changed not too long ago and filter and fuel filter the works, no gas in the oil, this whole ordeal has happened before in the past, even before i had any modifications, so what do you think it could be now?

did you remove all the plugs like i told you and clean them. I don't care if they are brand new they can be fouled instantly and not even look wet.

so is this a second set of new plugs?

and as far as the oil how does it look and smell? if the oil has 1 mile on it but was driven with a bad misfire it could be contaminated and adding to your problem. we end up doing oil changes on brand new cars with less than 7 miles on them that were allowed to foul the plugs out.

if none of this works get a brand new plug to replace the #8 plug. plugs can have a crack in the insulator that can't be seen or other undetecable damage.

if you exhausted all of this you can try to swap the number 8 injector and see if the misfire moves.

02gtpony · Mar 15, 2006

oh and i forgot to ask, if i do change the oil and the filter and that happens to be the problem, how long will it take for it to take effect and the engine light go off,and the misfire go away, cause if it is a burnt valve i don't want to drive on that too long and mess something else up ya know?

02gtpony · Mar 15, 2006

oh and something else, when i did the plugs they were the exact same plugs as the old ones i took out but did not go in as easy as they should have, i could not get the threads to line up and it took forever what could that have been

Mike97gt · Mar 15, 2006

02gtpony said:
oh and something else, when i did the plugs they were the exact same plugs as the old ones i took out but did not go in as easy as they should have, i could not get the threads to line up and it took forever what could that have been

what kind of plugs are you using? do your self a favor and get some stock motorcrafts. i don't like the sound of this threading issue. if that plug is a tiny bit off and is not the correct height into the combustion chamber, then you have problems.

and when i say change the oil i mean after you clean the fouled plugs off. you have to do both at the same time to fix it if thats the problem. either way your new plugs have to come out

02gtpony · Mar 15, 2006

the plugs are the motorcraft plugs that ford uses, it took me 3 hours farting around trying to get the threads to line up, i'll change the oil and filter and clean the plugs and i will let you know how it goes, it won't be until friday cause im crammed pack the rest of the week, don't worry its retired until this problem is fixed, check back on sunday and i will post up how it goes, thanks for your help,

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