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what causes misfire code?

beakie

NAXJA Forum User
Location
Ontario, Canada
just like the title asks,
I have a misfire code (been asking a lot of question on this topic last 2 weeks)
Anyway, I have had it read and it says #1 and #2 cylinders Misfire. However the plugs are fine, the wires are new (and working) the injector plug is on the correct injector and neither I nor my buddy who is a mechanic can figure out why it is giving this code.
It idles rough, when cold its just below 750rpm, when hot its around 900rpm. The only thing I can think of that it sounds like, is a big block V8 that you'd see at a drag strip... the gurgling sound that they make, like they could die any second, thats what mine sounds like at idle.

The only thing we could think of would be a bad injector perhaps. The exhuast kinda smells like fuel, but it doesn't seem to be burning anymore than usual. Temps are good all the time.
A misfire I would feel, a bad CPS I would def feel (have before), and other than a rough idle it seems to be running fine.


So what could be causing this code to appear?

oh, 97, 4L, auto, recent head gasket job, new plugs, wires, rotor, dist.

thanks
 
A misfire code is set when the computer detects irregular crank speeds. If the computer detects the crank is slowing down while the combustion event should be occurring on a certain cylinder, it will set a misfire for that cylinder. You must be losing one of the key components for combustion---Proper fuel mixture, compression, or spark. I would suggest doing a compression check on all cylinders at this point. If that proves to be good, I suggest doing a block check (check for hydrocarbons in the cooling system)

I hope that helps.
 
Its a new direction, which is good.
I have just been going over the same things time and time again trying to figure out what could be wrong.
Unfortunately I won't be able to do that for 1week/1000km+ until I get it back home where my tools are.

Just to add, just went out for a beer run, noticed that when stopped in gear it idles rough and around 800rpm, shift into N and idle returns to normal, but still chug/gurgling sound.
At hiway speeds it has hardly any GO between 1500rpm and 2750rpm... I guess that could be from the gasket port matching of the head I did, maybe took away from bottom end, but I didn't take much material off for fear of taking too much. But when I hit the gas in that range it doesn't move like it used too, above 2750rpm it hauls again, but sounds like its bogging any lower.

After these holidays and all the driving is out of the way I am bringing it to my mech and telling him to make it proper again... or swap a lower milege engine in... this is getting silly.
 
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with the low rpm power loss, weird idle, and surging/misfiring it sounds like a timing event(s?) out of whack. distributor indexed incorrectly, misrouted plug wires, cam/crank synch off? just sort of thinking out loud here...maybe this helps?
 
what kind of plugs are you running?...........have you tried switching the plugs around to see if the miss folows the plugs?( put 1&2 in 3&4)......possible problem in the head between cyl 1&2?
 
distributor indexed incorrectly, misrouted plug wires, cam/crank synch off?

my mech and I went over those today, wires were good, dist indexed properly, as for the cam/crank out of synch, not sure how to check that, but will check it once I find out.

have you tried switching the plugs around to see if the miss folows the plugs?( put 1&2 in 3&4)......possible problem in the head between cyl 1&2?

tried switching plugs, than tried all new plugs, and the head was magnifluxed and checked out ok after .012" taken off.

I agree with timing, but everything seems to be fine, and once I give it gas I would not know anything was wrong (other than knowing something is wrong)
Is there a chance the timing chain has skipped a cog? or are there any other smalls teeth/cogs that could have slipped, that would cause this?

My mech wouldn't charge me for the time and effort he put into it because he had no idea what to do, after we tried what we did... and he wants to be told whats wrong if I ever do fix it so he will know for the future.
 
imo it sounds a lot like what would happen if the timing chain was very worn, or the cam/crank gear was indexed wrong upon reassembly. i've never known anyone with a 4.0 that had a chain jump. not impossible, but seems unlikely. maybe dr.dyno will chime in?
 
maybe try switching the injector's to different holes and see if it follows, timming or other mechanical error would affect more than cyl 1&2.
 
injector swap, I like it.
to be honest that has been the only thing I can think of left to do. I hadn't thought of how timing would mess with everything as opposed to just #1 & #2.
I have cleared the codes atleast 6 times in the last week, and everytime it comes back with a code '43' within a little while, followed by another not long after... once it got upto 3 misfire codes... but #1&2 are the standard.


as soon as I can I will try and switch the injectors to see.

on that, what are the chances the injector plugs/connections are messed up? I read about one guy who when reinstalling, pushed on male clip up into the plug so it couldn't make contact... I will have to check that aswell.
 
Did you ever check the compression? Misfire code can be caused by a difference in cylinder compression, i.e. a normal cylinder followed by a low compression cylinder shows up as slow crank speed to the computer via the CKP sensor. Too much, or too little fuel, i.e fuel injector, no spark or late spark, or low voltage spark, or bad spark plug, leaking valve or head gasket, or sticking valves or sticking piston rings, worn cylinders and or rings can cause the low compresion leading to a power imbalance between cylinders that triggers the slow down of the crankshaft rotation that triggers the computer misfire message. Note that an increase in crankshaft speed from a low compression cylinder followed by a normal compression cylinder does not throw a msfire code but will casue a rough engine idle.

Also note that once it throws a misfire code the computer will shut off fuel to that fuel injector periodically to keep excess unburned fuel from damaging the Cat converter, this increases the rough idle!!!!!

Why was the head gasket replaced????
 
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I replaced the head gasket after ai blew the old one (well I thought I did, turns out it could have been a leak from water pump area confused me) either way its done, this problem has been since its gone back together.

I haven't been home yet, and have been driving for the last 3 days, will be for another 5... rediculous I know but can't be helped for now.
I will check comp when I get home, and also move injectors around to see if the problem follows certain ones. Comp. late this last summer was fine when I gave it a tune up, but I should check again, once I am back home that is.

Having been hiway and city driving for the last few days... it must be on only 4-5 cyls, as it doesn't have the pull it used too, whether up a slight hill, or when needed for passing (mostly on hills tho) in city the idle is still rough, when hot its a little less rough, but still if left in D it rumbles much more than if put in N. After all our snow up here, its been rain for 2 days, so no chance or place to get under the hood and make sure injector connections are good.

My thoughts are focused on a bad injector, but I have a good list of possible problems from this thread. and my mech mentioned I could have torqued a rocker down too much and it could be too tight causeing problems, but I followed the FSM to a T, so that shouldn't be a problem...
can I run the engine with the valve cover off to see if all the rockers are moving freely????
 
just wanted to finish this off for anyone with a problem like this one.

after an overheating problem, and subsequant blown head gasket I replaced the gasket at home on my own (first time doing that job)
I had the head decked .012" and new valve stem seals installed. Put everything back together, started it up and thats when the misfire codes started.

Well after bringing it to my mech, and having him tear into it, it turns out that the original overheating caused a bit of warpage (heat discolouration of valve stem near valve cap) to the intake valve on cyl#1 leaving a tiny gap between valve and head . the result was low compression, and exhuast gases back firing out the intake port and causing problems with #2cyl aswell.
Brought the head back to the machinist, and he fixed the problem.
SO it turns out I did everything properly. But me without the knowledge of such a problem being a possibilty. And the machinists not taking a closer look at each valve didn't think to have the valves matched or 3 angle job done the first time around.
New gasket, new head bolts, valve job, and labour (which I could have done if I had know it was this simple) finally its all back together.


So, if you ever overheat the engine, be sure to check the valves before re-assembly.
 
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