FBodyPerformer

iTrader: (19)

So the last 3 times it's rained my car seems to develope misfire. I figured it was a fluke. Now this last time it started again, but it hasn't gone away. It idles bad and when driving missing like crazy until I put the throttle to a certaint point which is almost to the floor. Now that's weird because I can be in 3rd gear at 3000rpms or 5th at 1500rpms, until the throttle gets to a certaint point, it misses.

I pulled a couple plugs, they seemed fine, drove the car again, started missing then started running fine. Got lunch, went to drive home, started missing again. I went through, pulled the wires and plugs. And here's where it gets weirder. The #7 cylinder's plug ground was half melted on the back side, the back side of the electrode was burnt like it was sparking between the electrode and the back of the ground. Again I replaced the plugs, still missing.

Finally I brought it to a local shop today to see what the problem is beyond the broad codes of P0300 and P0301 (multiple misfires detected). Turns out the #6 cylinder isn't firing. Absolutely no clue why, never had a problem before. The shop wants to do a leakdown and compression test but due to holidays and school, i cant afford this. I tried doing some full throttle runs, car runs fine, and now it seems to be running fine....for the time being.

So please, does ANYONE think they have an idea of whythis could be happening?!? Neither me or any friends seem to be able to put any of this together to find a conclusion.

Intercooler2

iTrader: (24)

Try some good known coils and wires from a friend

jimmyblue

iTrader: (11)

Why pedal matters, is cylinder pressure. More pressure
makes more arc breakover voltage. More voltage needed,
gives any other insulation fault a chance to take the
current first. Water causing the problem, also indicates
an insulation fault (coil, wire, boot).

If it's a spark problem. Because you could also have O2
sensor problems which along with a cylinder fuel delivery
imbalance, puts some cylinder too lean or fat to fire
when the aggregate is balanced to center. A melted
electrode might be telling you about that.

AgentLS1Z

Check your 02 sensors...I had this exact problem and my driver side pre cat 02 sensor got wet. The prongs on the sensor connector got corroded and the car had a P0300 code and P0301 code randomly. It was running so bad. I spliced an old 02 sensor connector end to the one on the car and it runs perfect now. I also had to replace all my plugs and wires though.But this definitely sounds like a fault 02 sensor. Check em out first.

blk/slvr02ss

iTrader: (21)

I had a 98 Z that did that only when it rain and one of the plug wire were not on .

FBodyPerformer

iTrader: (19)

So eliminate plugs and wires. That leaves coil and O2

joecar

How much did it rain, was it a good downpour...?

Rain water can leak past the rubber seal at the rear of the hood (the plastic cover beneath the rubber seal has a convenient joint in the middle) and drip onto the injectors (probably #6)... if the injector o-rings are old they might allow water to drip past the o-ring and into the manifold... this would cause a misfire.

joecar

#7 is not getting the right amount of fuel (various reasons, maybe clogged injector screen) and was running lean enough to detonate/knock which is what burnt/melted off the ground strap.

FBodyPerformer

iTrader: (19)

So lucky me has 2 separate problems I have to deal with figuring they aren't related. But if there was water leaking into the cylinder when it was raining why hasn't it gone away 3 days later?

I'm wondering now though if the reason I've always had a slightly rough idle is b/c #7 has been having issues? Well I guess along with O2 sensor and coilpack I'll check the injectors.

FBodyPerformer

iTrader: (19)

Pic of the #7 plug

jimmyblue

iTrader: (11)

That's some wrong-looking crust. You might check for a
runner vacuum leak that could be sucking in water when
splashed. Any coolant loss, oil in the water, etc.?

FBodyPerformer

iTrader: (19)

So that pretty much confirms I have 2 separate problems. I have no water in the oil. I think I have a small coolant leak at the front of the engine, but a drip a day if that. I use to have a FAST intake so I have a solenoid at the back of the bank 1 valve cover that has a vacuum line not connected to anything?

It's weird though, I took the car WOT all the way to 6200rpms through a couple gears and afterwards the car runs perfect. I park it for a little then drive again, it misses for a min then starts running fine again? Is this some sign that helps point to what it could be? Like something getting clogged?

joecar

That points to a slow coolant leak into a cylinder or two... AutoZone has a cooling system pressure tester that they loan out, you use it to pressurize the cooling system to see if it leaks (internally or externally).

FBodyPerformer

iTrader: (19)

Is that the best or only way to check if that's the problem? My car has 150k mules on it with what should be original head gaskets. If I need to replace them to take care of the misfire (still trying to find what could be wrong with #7 cylinder) then I'm not worried about changing my gaskets.

joecar

Several ways:
- cooling system pressure tester (checks for internal/external leaks in cooling system).
- block leak tester (checks for combustion fumes/gases in coolant/cooling system).
- compression test.
- leakdown test.

The first two are simple/quick, the second two should be performed to confirm the first two.

FBodyPerformer

iTrader: (19)

Well went to get the cooling system pressure test and when I turned off the engine I got a big cloud of smoke come out my exhaust. Got a smell of it and smelt like coolant. Got the tester anyways (even though just about confirmed it) started it up and it was smoking a little out of the engine bay for a second and the exhaust. So again, I think that confirms it's the head gasket

2 hours later and it's all torn down to just block and heads. I'll finish pulling the heads off tom so Monday I can drop off the heads to be decked just incase. Now just to find out why I have this problem with the #7 cylinder....

Edit-did the pressure test when I got back home and it was dropping at a very slow but steady pace.

joecar

With no external leaks that points to internal leak... but make sure it's not leaking where the tester fits on the radiator neck.

FBodyPerformer

iTrader: (19)

Well I'm burning coolant. That pretty much garauntees that the head gasket is leaking. the tester wasn't leaking at the cap. I haven't noticed any other external leaks. Even if it is leaking somewhere else, that leak wouldn't cause the misfire.

jsmith564

i think we are in the same boat.. what head gaskets are you going to use?

btw did you ever open the coolent cap while the engine was hot and running? when i did this my coolent blew out and boiled at the top. the car neve ran hot so i'm pretty sure my gaskets need replaced.

i too had a misfire i could not figure out.. no codes, just felt like it was'nt runing 100% and that when i checked the cap..

LS6427

iTrader: (2)

Uh, the misfire you have is from the internal leak in the gasket.....no????

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