95 Z28 Camaro. 14,000 origional miles. However not the origional Opti if that matters ...

I had a slight misfire, that was intermittant, would come and go, always only when the car was hot.

This misfire has gotten progressively worse and worse ... It will not miss for the first few minutes when its cool ( when its in open or closed loop , whatever it is when it dont read from the sensors and stuff rite away, Forget which one it is ) but once its warmed up it misses to a noticable degree driving on level ground, anytime its under a load ( EVERY fricking little hill ) It misses so bad that the RPM's will actually start to drop, I need to downshift so im at 3000RPM's and then it seems to stop missing but it is still underpowered. If it starts missing, and I totally let off the throttle, then ease back into it, it USED to stop missing for a few seconds, then come back again, but now under a load, no matter what it misses inless I'm up there in the RPM range.

Strangely, at idle, if I rev it, it sounds like normal ? Rev's pretty fast, has good throttle response ...

I jsut regreased the plugs/wires on both ends, there is NO arching, and I dont see how it could be the plugs or wires. It was fine 250 miles ago and is now getting worse EVERYTIME its drove.

Someone suggested that it could be the O2's maybe, how can I test these?

Also, if its of any importance ... The car was totalled in 1996, and had sat from 96 until this past year when I rebuilt the front end and got it running. It did have some ( Less then 1/4 tank of fuel in it, that didnt smell varnished. I filled it all the way with premium BEFORE I started it since it couldnt be siphoned.

Also I did run the tank pretty low ( Below 1/8 ) once or twice before the miss, usually I try to keep it above a 1/4.

None of the fuel injectors are clogged btw, I had them cleaned a few hundred miles ago.

To sum it all up:
Slight miss, intermittant, develops into MAJOR, undriveable miss that is apparent under any slight load at all, seems to NOT miss while the engine is cold, and possible not under WOT, I only floored it once to check because I dont want to damage anything ... Plugs and wires are good, new fuel filter, always run premium, car did sit though for 7 years. Injectors are OK as well.


Someone please help me out, point me in the rite direction, I was thinking Opti or maybe coil but I just dont know, nor do I know how to test either of them. Any suggestions from anyone, Also, someone want to tell me more on how it can be the O2's maybe and how I can test them?

This is on a OBD1 car btw.

 

Deja Vu...I swear I just answered this in another post somewhere....

 

Sorry ... I had that one up for 2 days now and the only suggestion was the O2's ... I really didnt think it was them, so I figured I'd just make a new thread .. Cause i NEED the car fixed ASAP and cant afford to take it somewhere to work on it. No one said anything, so i figured Id try a new title and get lucky cause no one even was viewing it ... As soon as I posted the new thread, you jsut replied to the old one I think ???

Thanks though ... Any way I can check the coil and Opti ?

 

if it only happens in closed loop (when your car reads sensors), then its gotta be a sensor. If its a sensor, there should be some code. Get the car scanned for codes. bad O2 sensors will make the car run like crap (shaking). Typically, the service engine light comes (code!!!) and the cars runs better cuz it switches back to open mode.

 

I know my car had all the symptoms that his is having, and it was the wires.

Up at the front of the car, the serpentine belt had cut into 3 of my wires. Under load, the car would buck and drive like s*$t, but gear it down and it would fly. There was no arching, because there was nothing of them to arc to.

Buy a hanes manual on your car, it will tell you how to check the coil. Hanes manual is about $13, and a ohm meter from radio shack (cheep) will put you in business.

Have a scanner look at you O2's, and see what they tell you. I'd be willing to be it is in the ignition portion of your car, not the fuel.

D Moss

 

Ok .. My belt didnt nick the wires ... I jsut checked all of them and theyre all fine, plugging on firmly, and are greased. It felt like a miss but possibly it is the O2's ... and it seems for sure to happen jsut in closed loop.

 

how do you know the problem is in closed loop? does it come on suddenly?

 

I am pretty sure its only closed loop because it only misses once its warmed up. About 200 yards from my house on my street is a GIGANTIC hill and it cruises up it fine no problem when its cold ... If its already wamred up though, I have to go in first gear at about 3000 RPMs maybe 3500 to make it up it ...

It wont miss at all for the first minute or two. Also, I floored it once, and it missed as I was laying into the gas but once it reached WOT it seemed to go away ... So I asummed it was only a closed loop problem.

And yes it comes and goes suddenly. One minute I could be driving fine, next thing I know the car bogs way down missing and almost bucking there is so much of a power loss. Im trying to get ahold of my cousin so he can scan it for me, he said He may be able to borrow the scanner for this weekend
Also, the car misses WAY worse when its under load.

 

Check fuel pressure, when the car heats up it will make the engine miss if it is not getting enough. Someone corect me if I'm wrong. I *BELIEVE* it is due to pre-detination.

 

But if it was fuel pressure, it wouldnt take off at WOT would it ? I checked the fuel pressure about 500 miles ago when I was having a slight injector problem, and it was fine, right around 46 or 47 PSI I think ... I forget now... but I know it was in specs where it should be.

 

when i had that similuar problem mine turned out to be plugs, one plug went bad after i just put new in and it still fired a little but was all gunked up cause my car was running rich for a while and it fired a tiny bit but when at high rpms the plug couldnt keep up, make sure your plugs are still good

 

oh btw, next time id empty all fuel, gas is only good 6 months, that probably didnt help any

 

Yea ... I should have hooked up to the fuel pump prime, but im young and stupid

I just checked my coil, its fine. Wires are all fine. Coil wire is fine. The 5 plugs I pulled during my long tube install ( Less then 100 miles ago ) had no carbon buildup on them, they are all fine as well.

Also if it was a plug/wire, why wouldnt it affect the car when its first started and still in Open Loop ? That was the other thing that made me rule out plugs and wires as it seems to only be apparent during Closed Loop. This is fricking driving me nuts ...

 

my plugs didnt show the mis fire till they were under alot of strain, it was mis firing a little but it wasnt until i went to the dealership and had my friend hook up the tester to my pcm and we were drivin till he told em what exactly happened

 

When you scan it, make sure to watch that knock sensor, and see if it is pulling a lot of timming.

Keep an eye out for opti codes. If you've changed your opti, was it new or did you get that rebuild kit from NAPA?

It it was used, what did it come off of?

Just trying to figure out why did the car only have 14000 miles with a different opti? Unless it went out in the crash, someone may have swaped it with a bad one.

Keep your eyes open and continue to let us know. The only time my car acted this bad was when my opti was almost dead, and when I spun a bearing and the knock was pulling time really bad. (ran worse with the bad opti)

I'm leaning towards the opti, esecially if it was rebuilt.

D Moss