Puh-lease help me diagnose mystery misfire before I go crazy

[Bad Black 3.8]

My 1998 3.8 Camaro has a mystery misfire that comes and goes, and never throws a check engine light. It mainly does it when it's hot & humid outside. The problem will disappear for fall & winter, and the car runs very strong. As the weather warms up, the problem creeps back. It's 100* out and humid now, and the car is really stumbling on acceleration. (worse than when I burnt a plug wire) It also seems like it's using more gas. The strangest thing is that when it runs bad, the tachometer is dead, occasionally jumping around wildly, but when it runs good, the tach reads correctly. I've been throwing parts at it here and there as money allows, but nothing has fixed it yet. Has anyone had a misfire that only showed up in hot, humid weather? Here's the list of stuff I've replaced: plugs & wires, coils, ICM, air filter, water pump (car runs cool), pcv valve, catalytic convertor, plus cleaned the EGR (which didn't seem too dirty). At this point, I'm thinking a stuck fuel injector, but i don't know if that would throw a code or not. Please help me before I drive this thiing into a tree!

[kristen]

Re: Puh-lease help me diagnose mystery misfire before I go crazy

are you losing volts cause maybe your ac is on. could it be an air problem like a maf or iac?

[Frechles71]

Re: Puh-lease help me diagnose mystery misfire before I go crazy

My old mans 3.4 acted up like that last summer. But his did it a little bit in the winter too but it was much more intermittent. sort of the same problem... once the car heated up it would, it would miss and sputter and backfire a little... ended up being the crank sensor i do believe... hope that helps

[Bad Black 3.8]

Re: Puh-lease help me diagnose mystery misfire before I go crazy

Thanks for the replies. I'm not really thinking it's any of those, because I would assume I would be getting a code for those things with as bad as it's running. I mean, that's what the sensors are for, right? I'm also wondering if it could be the fuel pump... I've run the car down to empty several times out of stupidity.

[Frechles71]

Re: Puh-lease help me diagnose mystery misfire before I go crazy

Your welcome. just to let you know when my dads car was doing it, it wasnt throwing any codes either...

i dont think it would be the fuel pump bc normally when a fuel pump is starting go, you have a lot harder time gettin the car started bc the cold starting requires more fuel pressure... but its easy to check... go down to your local autoparts store and pick up a fuel pressure gage... the connection will be on the manifold on the drivers side i do believe... it will have a black cap over it... make sure the car is off, take the cap off and screw the fuel gage on... turn the key to the on position and check how much pressure the fuel gage has... should be between 55-60 psi (i think)... closer to 60psi the better...

goodluck!

[Harrison]

Re: Puh-lease help me diagnose mystery misfire before I go crazy

dude....sounds like we are in the same boat. i posted a thread a couple days ago, and havn't really gotten a response on it. mine comes and goes and does it when its hot. the car will actually run fine for a while, then heats up and it starts missing and wont go away. most of the parts on my car are new and are in great condition...makes no sense. im inclined to think its fuel injectors, or my fuel pump.

[Bad Black 3.8]

Re: Puh-lease help me diagnose mystery misfire before I go crazy

Yeah, I'm really thinking it's fuel related. My fuel filter is new, but I've run the car down to E a couple of times like I said. I just don't have the money to keep throwing parts at the thing. Is your tach acting up when it runs rough too? That's what gets me... the tach is electrical, why is that going crazy when it runs rough? My battery volts are good, I just don't get it...

[Harrison]

Re: Puh-lease help me diagnose mystery misfire before I go crazy

my tach is alright, but idles at 400-500 when its missing and the oil pressure drops to around 45ish.

[ILuvPizzaTimes10]

Re: Puh-lease help me diagnose mystery misfire before I go crazy

Hey have u had it scanned? alot of codes wont turn the SES light on that could potentially be your problem. if u can get your hands on a fuel pressure gauge do it. also make sure your fuel pressure regulator doesnt have fuel in the vaccuum line going to it if it does u may have found your problem. Hope any of this helps. and as far as the tach check all your grounds for your ecm if u have a haynes manual there all in there. a bad ground will cause all this **** too. good luck man

[Meatyshells]

Re: Puh-lease help me diagnose mystery misfire before I go crazy

i personally think it's the fuel pump. Test the fuel preasure and see if it's ip to par.

[lil' jon]

Re: Puh-lease help me diagnose mystery misfire before I go crazy

Well since it's really humid and your tach is off at the same time i'm kinda thinkin that moisture is getting beneath the coil packs causing a misfire. and i'm not sure but doesn't the tach run off the ignition? so that seems to explain both of those symptoms...but i'm only 17 so don't take my word for it haha

[speedyz]

Re: Puh-lease help me diagnose mystery misfire before I go crazy

dude....sounds like we are in the same boat. i posted a thread a couple days ago, and havn't really gotten a response on it. mine comes and goes and does it when its hot. the car will actually run fine for a while, then heats up and it starts missing and wont go away. most of the parts on my car are new and are in great condition...makes no sense. im inclined to think its fuel injectors, or my fuel pump.

My old engine would warm up and not really miss out, but completely lose power, and start backfiring really bad. Never figured it out since a few days later the motor got toasted. Rebuilt a firebird 3.8 and haven't had any problems

[Bad Black 3.8]

Re: Puh-lease help me diagnose mystery misfire before I go crazy

What should the fuel pressure be? I'm gonna pick up the gauge today.

[ILuvPizzaTimes10]

Re: Puh-lease help me diagnose mystery misfire before I go crazy

key on engine not running should read between 49-55 PSI and it should drop around 10 PSI while running.

[Disruptore4]

Re: Puh-lease help me diagnose mystery misfire before I go crazy

I'm having this problem, and I almost started a new thread, but I read this one first. Whenever I'm accelerating about 1/2 throttle or more, the car either falls flat on it's face, or is VERY inconsistent during the acceleration. I'm really disappointed about this because I was just getting into modding my car and all that. I'm thinking either ignition or fuel delivery, just not sure what's going on. Again, no SES light. I may run up to Auto Zone sometime this week and get it scanned. Anyone else have this problem before? Diagnosis? Remedy? I think it would make a few of us very happy.