Misfire!

[JesseH]

ok, so for about a week or so I have been getting odd misfires, they only happen every once and awhile. It mainly occurs during warm up and heavy accel, but yet doesnt happen every time. I have my timing set right, I just changed out the POS bosch plugs (I know shame on me for using them) to NGKs and it happens less now but occasionaly still get o few misses randomly. my plug wires are newer, ive got and msd coil. could it possibly be my rotor and cap? the rotor did look a little worn last time I checked but I didnt think it was that ctitical but Ill probably go get a new one tomorrow. thanks for your help!

 

[jetjock]

Well, you didn't misspell misfire until you spelled it missfire. (Btw "misspell" is one of the most commonly misspelled words in the language). I'm pretty sure you screwed "critical" up though .

The condition of the rotor and cap in a distributor based ignition system is important because they comprise another gap the spark must jump. Think of it as a 7th spark plug that fires every time the others do. It can plainly be seen on an ignition scope as opposed to a DLI system.

Btw, you'll likely find repairing a car presents more of a challenge than repairing a sticky keyboard.

 

[JesseH]

Well, you didn't misspell misfire until you spelled it missfire. (Btw "misspell" is one of the most commonly misspelled words in the language). I'm pretty sure you screwed "critical" up though .

The condition of the rotor and cap in a distributor based ignition system is important because they comprise another gap the spark must jump. Think of it as a 7th spark plug that fires every time the others do. It can plainly be seen on an ignition scope as opposed to a DLI system.

once again jj you correct me and give good advice:icon_bigg . Ill go out and buy a new rotor and cap tomorrow, I also just now replaced the resistor to the msd coil, it was looking a little burnt up....so I think that was my biggest problem, Ill find out tomorrow. thanks for your help, appreciate it.:icon_bigg

 

[JesseH]

ok, still getting a slight misfire on occasions...what else could I be missing?

 

[JesseH]

ok, still getting a slight misfire on occasions...what else could I be missing?

anyone? any help would be great
EDIT: it only misses on heavy acell.

 

[jetjock]

Sure it's an ignition miss and not a loss of fueling? Does it do it under mild boost? Say 1-3 psi or above? I recently encountered what sounds like a similar problem. Was driving the owner nuts. Turned out to be a fuel pump relay that'd failed internally a certain way. When the ECU switched the pump to high speed under moderate load or above the relay's contacts would float and cause erratic fuel pressure. I found it by monitoring fuel pressure and pump current together while doing snap throttle tests. Bugger as it would only happen once every 4 or 5 times. A quick way to test for something like this is to jumper the fuel pump terminals in the diag block and take a quick drive to see if the problem disappears.

 

[JesseH]

Sure it's an ignition miss and not a loss of fueling? Does it do it under mild boost? Say 1-3 psi or above? I recently encountered what sounds like a similar problem. Was driving the owner nuts. Turned out to be a fuel pump relay that'd failed internally a certain way. When the ECU switched the pump to high speed under moderate load or above the relay's contacts would float and cause erratic fuel pressure. I found it by monitoring fuel pressure and pump current together while doing snap throttle tests. Bugger as it would only happen once every 4 or 5 times. A quick way to test for something like this is to jumper the fuel pump terminals in the diag block and take a quick drive to see if the problem disappears.

yea, ive been begining to think about that. I was pretty sure that it was ignition because it didnt start happening till I messed with some of my ignition parts. Is it possible that the relay could go bad all of the sudden? oh and ive got a walbro fuel pump, bypassed j-tube, and a new fuel pressure relay. Could I get the fuel pump relay at advance auto or would I have to go to toyota? (oh and im N/A) lol..........once again, thanks for your help jj, this has been driving me nuts the past week lol.

 

[jetjock]

Doh! Of course you're N/A, we were talking about caps and rotors before. Never mind . Too bad you don't have ready access to an ignition scope. It'll instantly tell you if it was ignition and in what cylinder.

 

[JesseH]

Doh! Of course you're N/A, we were talking about caps and rotors before. Never mind . Too bad you don't have ready access to an ignition scope. It'll instantly tell you if it was ignition and in what cylinder.

lol well I check the fuel pump relay tomorrow, Im really running out of ideas....the rotors new, caps not too old, coil is about a year old, new plugs, wires are about a year old, fuel pump, fpr, etc.....almost everything is either new or fairly new....the only things I can think of that i havent replaced is the fuel pump relay, and the maf