Misfire when hot, replaced everything I could think of... Options

[cv7713]

OK, been chasing a misfire for quite some time. The car runs great first thing in the AM but misfires once normal operating temp is reached. Misfires at idle and while driving. First, I have replaced all fuel and ignition components and all vacuum lines. I decarbonized the combustion chamber (MOPAR CC Cleaner, good stuff!). I have replaced the MAP sensor, O2 sensor, and some various wires that looked corroded. Stock 5s-fe.

The engine bay seems to be getting extremley hot! (but not overheating). Yesterday I pulled the plugs to see if they show any evident signs of wear and I was confused by what I saw. The firing end looked great (brown to grayish color), however the insulator on top of the plug was brown and blistered (burnt)?! Anyone ever see this? They are NGK plugs with the factory heat range. Also (not sure if this has to do with the misfire) but every now and then I hear a pop come from my gas tank. Is the "pop" just releasing pressure from the tank? Is it supposed to do that? Sorry so long, I am just truly stumped!!

List of parts replaced:
Fuel Pump, Filter, Pressure Reg, Charcoal Canister, EGR Valve, and injectors
Brand new distributor, wires, plugs, igniter, O2 sensor, MAP sensor, and even the ECU!

Could this be a bad cat causing the heat? Cracked head? Thanks for input...

This post has been edited by cv7713: Nov 9, 2007 - 11:21 AM

[cv7713]

any suggestions?

[Blakout16]

check your coolant thermister, see if its not opening (possible)
put higher-octane fuel in it.
any CEL's?
check your coolant - for any mixtures of oil.
also, the piston rings.... misfires tend to happen under higher temp due to piston rings going out the window.
mileage?
timing, some retarding could help.

[cv7713]

thanks for the reply. no CEL. tried 87, 89, and 93 octane with same issue. car has 150k. had the coolant system flushed today. looked fine just a little too much water. I will try the timing. it just may be time for a rebuild. I planned on changing the head and the head gasket, may just need to spend a little more time and do the rest... pistons, pumps, etc. anything else you could think of? also, getting VERY poor fuel economy (17-18mpg) thanks again

[Bitter]

could be a lean issue, sticking or dirty injectors. have it ran on an injector cleaner machine or send them out to a place like witch hunter performance for clean and balance.

[95CelicaST]

or buy new injectors.

[x_itchy_b_x]

you replaced everything that i would suspect to be causing the problem.
the only time i had horrible miss firing is when i had old plug wires. they would leak voltage to the head or any ground it could find but only under boost.

[cv7713]

ok, compression checks ok. 190 +/- on all cylinders. vacuum is ok, 21 psi. installed injectors from a vehicle with 60k miles, same problem. coolant temp sensor is functioning properly. .2-.3 volts when warm.

this is definately a heat related problem. misfire occurs more frequently during the day (south florida) with the hood closed. I just had the car idling with the hood open and the sun has long been down and it only misfired a hand full of times during the hour I was standing there.

is it possible that the dizzy and coil are getting so hot it is causing it to intermittently stop firing? the wrap around the wires next to the exhaust man (oil pres send, cool temp sens, etc) has melted!!!

could the exhaust be causing the excess heat (carbon buildup)?

would headers cool it down a bit?

This post has been edited by cv7713: Nov 9, 2007 - 11:34 AM

[95CelicaST]

headers would make the engine bay warmer... unless you heat wrapped them.

Could you post a picture of your engine bay? and the wire that is melted..

[supradog1]

THANK GOD!!! SOMEONE IS HAVING THE SAME PROBLEM!!!! I live in South FL also and i to have a low misfire when the car is hot!!! i realy sucks cause when im at a light with my foot on the brake the car will misfire and jump foward some times!!! it also misfires more offten i turn the system up in the car...
PLEASE HELP!!!!!!

This post has been edited by supradog1: Oct 21, 2007 - 11:45 AM

[lagos]

can you describe "missfire" in more detail?
when you replaced your plugwires, cap and rotor, what brand did you use?

[supradog1]

can you describe "missfire" in more detail?
when you replaced your plugwires, cap and rotor, what brand did you use?

OK... i start the car up first time that day and it drive about 10 to 20 min car runs perfect... after this time frame the car is at full working temp, any time you stop after this time frame the car misfires whille idleing and during the launch from the dead stop... after 2k rpm misfire is gone but power is is week and gas mileage is crappy... also if you turn the bass up on the system the car misfires eaven more than before while idling!!! i have done full tuneup on celi inclueding autozone timeing belt, cam and crank seals, water pump, cap & rotor, bosh 02, ngk plugs and wires, puroltor fule filter, 93 oct fule with lucas fule additive, cleand egr system and replaced pvc, reset ecu and no check engin light... after tune up car runs good for about 20 min then misfire returns!!! put new ngk plugs in 3 times and dose not fix the problem!!! i am lost on this one, but i have also been told it could be the igniter... but i dout that because its eletronic and woud just fail altogether... right???

[cv7713]

Misfires at idle, when accelerating, and when driving steady (cruise control). Pretty much any scenario but it only happens when the car has been at operation temp for awhile. Usually 30 minutes of driving.

The plug wires are from Toyota, the distibutor is Dorman (which i am not thrilled about), and the plugs are OEM spec NGK copper core V-Power. The ignition components are (or were) fine. I have tried 3 different dizzys and 2 different types of wires.

Been to the Toyota dealership 3 times who are worthless and also an individual mechanic. All unable to diagnose the problem.

Any suggestions are appreciated

This post has been edited by cv7713: Nov 9, 2007 - 11:35 AM

[supradog1]

i puled my distibutor cap off and every thing looks fine... what is the dizzys??? that black thing with 2 wires runing to it inside the distibutor??? i checked all conections and wires, everything is good... whats causing this misfire???!!!!

[cv7713]

dizzy is the distributor. the black thing inside the distributor is the coil. our problems sound identical! i replaced the igniter with one from a newer car in the local junk yard and still had the same problem. i am stumped

This post has been edited by cv7713: Oct 21, 2007 - 2:30 PM

[supradog1]

is the timing off??? if i ajust the timing a little would this help maybe???

[cv7713]

i've tried adjusting the timing. if you want, paint a mark on the distributor and the head where they meet, then loosen the two bolts that hold the distributor on enough so you can twist the distributor. start the car and twist the distributor slowly both ways to see if it helps you any. if not, line the original marks back up and tighten the distributor.

[lagos]

i've tried adjusting the timing. if you want, paint a mark on the distributor and the head where they meet, then loosen the two bolts that hold the distributor on enough so you can twist the distributor. start the car and twist the distributor slowly both ways to see if it helps you any. if not, line the original marks back up and tighten the distributor.

thats not how you set the timing. you have to use a timing light, and bridge the diagnostic box to set it at 10tdc.

if you guys can. try to make a video of your problem.

[cv7713]

that's what I did, bridged TE1 and E1 and set to 10 degrees. i was just suggesting to advance or retard the timing a bit and see if there is a difference. if not, the original timing marks will be there to return the timing to where it was (without a timing light)

I will try to make a video sometime tommorow.

[supradog1]

i think i know what the problem is!!!! "a failing altanator!!!" i will prove this theory tomarow when i can put the altanator on a test bench but i think its the cause of the misfire... reasons why: #1 when i have the car up to runing temp and have no a/c or radio on the car has no misfiring (or at least its very rare) then when i turn on all my goodes(a/c, radio) the car starts misfireing like a m/f!!! reason#2 driving in normal cool weather with no goodies on car is fine, i drove onto southbeach and got stuck in traffic to see what happens when it gets hot with no goodes on and as i thought, it started misfiring more and more the the hotter it got... because the alt is is old and week the hotter it gets along with all the extra current draw from a/c and radio is causing it to start to fail and the warning sighn must be this misfire!!!