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Discussion Starter #1 (Edited)
Howdy all! As a preemptive strike... I did a search on 'misfire' and didn't exactly find my car's issue... close, but not exactly. Some of the suggestions in those threads I have taken already, and some will be done soon... but I value your opinion if there is one on this. Let me set you up with details:

First, off, I have a 1997 HoopTBird LX 3.8L V6.

Yeah, the code is fairly obvious, misfire #6. The weird part is this:

Stone cold, start it, no misfire at all.

Drive it about for *hours* if I want... No misfire. All warmed up, temp gauge at middle of 'normal'. Never a problem.

However, this is the good part: Park it at a store, go in for about 15 minutes, come back out, start the car up... Misfire.

Temp gauge at this point says about 1/4 of the way up.

If I let it sit there like that... it'll be 10 minutes before I can stop it, then restart it, whereby the misfire goes away... and the temp gauge is back to the middle.

If I rev the engine to 3k and keep it there for about 1 minute, then turn off the car... wait about 20-30 seconds, then start it... It likely is now 'fixed'. It has taken up to 3 of these cycles before it goes away... so that'd be about 4-5 minutes tops.

Sometimes, I'll drive off with it acting this way, sputterin' on 5 cylinders... And at every stop light, I will shut it off... then when it's time to go, turn it back on and hope it's stopped.

I have replaced the following, and checked them out best as I can to ensure they're good:
Spark plugs
wires
coil pack
Cats have been replaced (clogged)
throttle body cleaned.

I have yet to try these:
MAF sensor cleaning (tomorrow morning)
Swapping the wires about. (we'll see...)
Fuel injector cleaning (next two tanks will happen though.)
Swap out the #6 injector.
O2 sensors

My confusion is this. Why is it this "not too hot, not too cold, JUUUUST right" Goldilocks type scenario? Why does it not do this cold, nor warmed up, just when it's... somewhere in the middle? Why is it always #6? If it were something more "generic" than "specific" would not other cylinders NOT fire as well?

And I can repeat it at will... unfortunately, I usually have to GO somewhere... and the A/C is a requirement here in Houston... Ugh.

Any and all help is appreciated. Even the obvious isn't in this case, to me anyway, so no stone is too unimportant to turn over on this... It's drivin' me nuts.

I thank you very much in advance!

Mikey
 

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Since you replaced the coil, wires and plugs, you've covered all the major bases with the ignition system. The fact that the misfire was consistent on cylinder #6 is actually helpful. The MAF sensor can be a big player in mysterious problems. I'd try cleaning that first, and don't forget to reset the computer. A bum injector is certainly not out of the question as well. I wouldn't look at the oxygen sensors as the cause of this problem, but if they've got more than 100k replace both front ones.

Also, how long was the engine run with the cats plugged? This is not good for head gaskets, especially on the 3.8L. This could have caused a problem if it wasn't addressed quickly.
 

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Discussion Starter #3
Firstly, thanks, master486, for the reply!

I've not yet done the MAF yet... I'll likely get to it tonight.

Resetting the computer... I seem to remember a help page 'round these parts... I'll do so. Gotta find it though...

The car does have 136.5+K on it. I *guess* I could replace those Oxys... if nothing else works I will.

The cats were plugged a total of 1 entire day. And I babied it home that night it happened. Of course, if they were plugged before then, I wouldn't know about it. It just sorta... *happened*. Car had never had a problem with power before until then.. and it all of a sudden, within about 10 minutes, it started this gradual power loss, then it (apparently) blew off one of the DPFI sensor hoses... and it ran like crap.

That hose was fun to figure out, BTW, never having to deal with it before... After I learned what a P1402 was... it was easily fixed with a new hose. Amazing how loud that little bitty pipe can be.. :)

Anyway, it sorta just all of a sudden did that... I got it home after about 40 minutes... It was strange... I had rememberences of my sister in law crunching hers on a parking stop she ran over (didn't know it was there and took off. Nice.) That was how it acted (88 cougar v6, btw) and that was how I immediately knew what it was.

Took it to an exhaust shop the very next morning and got that taken care of. So.. running time... maybe 2 hours, and as babied as I could.

(long story short.)
(too late.)

Currently, the car otherwise seems fine. Doesn't hurt the power any when it's not missing. It's only that "twilight time"... and it goes away, I can get it to stop it within 5 minutes now.

The CEL blinks sometimes... you know the computer's not happy when it blinks... :)
But after restarting it stays steady on... due to the P306.

I think it's the injector. I'll be replacing it/them (depending on how much is left in my pocketbook after all the adventures this car has put me into this month... Sigh) tonight. Gotta lift that dang plenum again... ugh.

The "going away" part has me thinking that's it... if it's leaking a little until the pressure's gone from fuel rails... that cylinder has a little liquid gas in it, right? Which means it either it has to evaporate (over the course of a couple of hours, not a problem, eh?) or it has to get gone somehow... Which is why it goes away if I get the engine warmed up a little... and then stop it... the heat causes it to evaporate quicker... and the car runs right!

<.<
>.>

Right? Or am I just drinking the wrong coffee?

o.0

Thanks again for the advice! I will let you know.

Mikey
 

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Discussion Starter #4
Well, today, in about 1.5 hours, I swapped the left side injectors...

Tada, as it were. Car's working right.

I cannot for the life of me explain how in the heck it did this:

Cold: Fine... Run all day without turning engine off, fine.
After all heated, turn off, wait 10-15 minutes, would misfire.
Anywhere from 5-10 minutes of running around like that, irritating the computer, shutting off, turning back on. etc... it'd go away and run all day until the next 10-15 minute break.

But it's fixed, it appears... Specifically made stops to check it.

Weird, weird, weird.

Now I need tires, struts, fix the pax window gear, and get the pax door handle surround and lock replaced due to some punk tryin' to break into her one day...

And it'll finally be worth about $500 less than what I just sunk into it... so with those it'll be, what about $1000 less? :p

Here's crossin' my fingers in the hopes it's done nickle and dimeing me...

Thanks again, Master, for pointin' me in the right direction.

Mikey
 

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Glad you got it worked out. Maybe it was something in the fuel rail like a particle that was making it mess up and switching around the injectors got the thing out. If the problem does come back (which hopefully it won't) and it switches sides, that would be a good thing, considering it would be a bad thing that the problem came back at all. Anyway, glad to help!
 

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Just to kinda add some addtional information, about two years ago, I had something like this happen. I managed to clog a couple of the injectors, replaced them, problem solved. Until, a few months later, it starts to randomly drop one of the cylinders, namely the #1 hole. I'm thinking something really weird is going on, thinking something expensive is going on. It turned out, the harness going to the injector had not gotten snaped on completely, over three or four months, it worked it's way to the point that only sometimes would it pulse the injector.

Just FYI
 

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Discussion Starter #7
Thanks, Kelsey, for that info... the injector harnesses all appear to be in good connection and working order, so unfortunately I don't think that's it...

And the car is back to doing that crap again.

I just DON'T get it... why!??! What else is cylinder related? I would think that if a MAF, Oxy, Temp, EGR or something non-cylinder specific was broken/borked, it wouldn't throw JUST the P306... and would run even worse than it does...

And I would expect it to be messed up when fully hot... or fully cold.. but not this weirdness.

I am now done with this car. I will just abuse the carp outta it. If the cats go... Oh well. If the cylinder dies... oops. The car's worth about $1200 if I'm lucky, and I fix the other stuff that needs fixing (all recent problems, btw. I don't usually let stuff go for long)

By the time I put the money into fixing all this stuff... and whatever money is needed to fix the misfire... I'm in the hole. I'm already there as it is... I'll NEVER get my money out of this pit...

"Better than a car payment..." - my dad.

Not at the expense of my sanity, Pops... or my hair.

Any advice... I will take any and all.

Besides dumping the car in a river or something... That I've got covered.

(Hey... I *could part it out... there's still great stuff on it...)
((where would I do that? 2 car car port.. and those pesky neighbors prolly wouldn't like it...)

Mikey
 

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The real question is: Is it doing it on the exact same cylinder? If so, then I would suspect the MAF sensor or even possibly (but less likely) the EGR valve/EGR vacuum regulator. The MAF sensor is critical for getting the A/F ratio just right and it can cause a lot of strange problems. If you haven't cleaned it yet, DO IT NOW and reset the computer and report back. If the misfire changed cylinders, it followed the injector and that's your problem.
 

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Discussion Starter #9
Now?!? I'm at work. I don't think they'd like it if I just jumped up all of a sudden and went to....

...

oh. I see. ASAP, as it were... Ok, that I can do. Tonight. Gotta get those goofy torx...
 

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Maybe I've missed something but did you change the fuel filter? Change an injector and things improve and then go back. EFI and carbs are not much different. The weakest cylinder fails 1st. MAF could exacerbate it if the computer thinks there is less air going through then is therefore leaning further but I doubt it is the source. I have seen no basic fuel system diagnosis done here yet. That may, and often does include a compression and leak down test. Cylinders need basic integrity to "suck" fuel but more probably to use what it gets effectively.

Quit chasing. Do a basic fuel sytem maintenance. Then start checking from there. Otherwise it is like farting in the wind. You see no results. :D

Brad
 

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Doesnt cylinder #6 get the fuel last?
 

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In terms of firing order, yes.
and position in the fuel system. I would be interested (learning) which headgasket pops most often or 1st on these engines. I was totally unaware as my brothers 89 3.8 went well over 300k with average idling time of 2.5 hours per day in Florida heat while he filled out his reports (retired to family). Before this board I thought it was a rock solid engine of reasonable performance. The 89 3.8 would cruise just as comfortably at 90mph as his next TBird, a 5.0 would cruise at 85mph (troopers became less tolerant). The '93 5.0 was retired to family at 285k with the same daily idling time and is still terrorizing roads to this day in the hands of his father-in law. Wonder if it had anything to do with his faithful 3k or less oil changes? 30k transmission fluid changes maybe the reason the original trans lived aswell?

Brad

ps. sorry, don't mean to steal the thread but I was thinking of picking up a 3.8 as a daily driver and then resell when when my mods are done.
 

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Discussion Starter #14
I have done the fuel filter and all that, brad, but thanks for the advice. New filter, and the injectors... what else is there?

I'm going to get the right side injectors today. Might as well make them all new. :p

I have a theory that perhaps it's the paired cylinder...#2? that is causing the issue with #6. I still have a rich condition at start when it's doin' this... you can smell that fuel...

And I'll do the MAF too. I've gotten the special tools for those dang screws now. :)

It is doing it on #6. Only code that shows up is P306.

As far as compression check... Hm. Well, the only question I have is this:

Cold: fine
Normal op temp: fine
Start cold, and run all day: fine
Somewhere in between cold and normal op temps... the misfire syndrome.

Wouldn't a head gasket cause an, if you will, extreme condition symptom? I.E. Only when it's cold or only when it's hot, but not this in between stuff?

I'm sure I'm not a know it all... just physics don't really say this is possible... Expansion doesn't work that way... does it?

(too much egghead there... my bad)

As far as quitting chasing... well... The last car that acted like this was my Mark VIII (glad that car is gone) and it had broken valve springs. But they went and did all THIS stuff first before getting there too... and they were professional mechanics. Damn them.

:)

I would go right for springs if it didn't run right 95% of the time...


So. MAF and injectors. Then I'm done. THe car dies now... I don't care. VOA gets it when I get my new 'Stang. :D
 

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Discussion Starter #15
Update:

Performed the MAF cleaning. No change. Misfire still happening as described. Ugh.

Going to install new right side injectors now. That'll be a complete set.

After this... I dunno what else there is. A sort of check list:



Fuel: Fuel filter and injectors replaced, new

Air: cleaned TB, MAB, Air charge temp sensor (just in case!)

Exhaust: EGR hose acquired and replaced, new cats, new left side manifold (cracked old one...)

Computer: Reset. Several times now. :) Also, redid the timing with the Spout (I think I did it right) and also the idle setting (again I think I did it right)

Spark: Coil pack is new. Wires are new. Plugs are new.

I haven't replaced the EGR and the DPFE yet. I haven't performed a compression check... and I'm real not happy about getting to that point. Bleh.

But I'll do it...

Oh, and it stopped the misfire after a bit, just like I says.

I'll let you know... prolly be later tonight. I like to try to kill things as fast as possible. :D
 

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Discussion Starter #16
Well... I've cried "fixed!" before and then proven wrong... so this time I really tried to make it misfire after doing the injectors on the right side.

Car now refuses to misfire.

So... it's fixed. I guess... Again, I've said that before...

What is confusing is... and please correct me if I'm wrong... the #6 cylinder is on the left side rear of that 3.8L v6, yeah?

So... what the heck does the right side injectors have to do with that? I mean... really.

I think I may have the reason behind the (what may or may not be) apparent temperature issue...

Taking out the left side injectors, I lost none of the top hats, if you will, of the injectors in the ports of the intake. I did have to fish out one O ring... but that's almost a given eh?

But on the right side (pax side) all three of the injectors came out of the car... and then I had to fish out the little plastic top hat caps... and two O rings.

I'm thinking there's the expansion/temp weirdness right there... maybe.

Only thing I can think of is that whatever cylinder the positive/negative sparking thing happens with #6 was messed up due to a fuel mixture problem?

Honestly, the *only* reason I even bothered to try to get it running right is, besides the "damn it all, it WILL work" attitude I sometimes cop, is the A/C stops working when the computer is pissed off. :) In Houston that's an issue...

Thanks to everyone who helped me with their suggestions... I'm sure they all contributed to the final solution overall!
 

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If your looking AT the engine, its the cylinder closest to the driver.
 

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Discussion Starter #18 (Edited)
So... #6 is the one nearest the driver on my V6 TBird, yeah?

And if that's the coil pack... then #2 and #6 are "married?"

And therefore if #2 is borked... then it can cause the #6 to misfire?

Is it a positve-negative issue? #2 is + and #6 is -?

Inquiring minds... well, my mind anyway... want(s) to know.

It seems to be very good now... has a little stumbling in it... dunno what's up wit that... but the computer's happy, the A/C works... I'm merely... Ok with it... to dang much money spent for a car worth about $1200 or so. (no way I get 2k for it. Too much has to be fixed. It is a work truck. :D )

But I can assure you all... the misfire is gone... unless that stumbling is part of it.

There's a strange whistling too... I dunno if the #3 (rear, pax side) injector is all the way down or it's coming from somewhere else... The car is running good enough for me not to really worry about it... but if anyone has a suggestion on that... Hey, I've got open ears.

Thanks again... and nice job on the pic! I totally get it now... the coilpack/distributors indicate front of the car. Sweet.
 

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Maybe the whistling is a vac. leak?? Might be the cause of the stumble, too.

Jay
 

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Discussion Starter #20
Where it is it's very hard to find... Not much vaccum over the #3 cylinder... Maybe it's the PCV valve or the intake manifold/injector port?

I probably wont worry about it... I'm just elated the dang thing is running... Now I have to pay for all that work and those parts over the next few months... I hate that. Oh well.

It's better that... scratch that.

It's about the same as a car payment. :rolleyes:

Well, for the next few months anyway... :tongue:
 
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