cjeff

This problem is crazy bizzare. I'm working on a 4runner 3VZE and have bad intermitten spark on cylinder 3 and no spark on cylinder 5. THIS IS NOT THE DISTRIBUTOR. I have so far checked plugs, wires, distributor pick up coils, dizzy cap and rotor, ecm, mechanical and electrical timing. I swapped in a dist. and ecm I know are good just to be sure and completly re-aligned the dist. to make sure it was syched properly and at 10º btdc. I bought this car recently with the misfire and am pulling teeth trying to figure this out. I was an automotive tech for 2 years and now work as an automation tech so I know my way around cars and electrical systems very well. I should also mention I just did the timing belt but everthing went smooth, I have never set a bad belt and even pulled the upper tb cover to verify that with my crank at TDC the cams align perfectly on the timing marks, not a half tooth off, right on the mark. This is extremly bewildering and now becoming frustrating. outside of checking my dist. pickup coil grounds and signal wires back to the ecm does anyone have any idea?

snobdds

You want a guy by the name of MudHippy. A little ruff around the edges, but knows the 3.0.

cjeff

Thank you snobdds, ill PM him.

ksti

Uhh, Your probably just going to have to wait and see if he reads it.

TNRabbit

Don't want to sound like an @$$, but how did you check the plugs & wires? I mean, what you're experiencing has to be between the distributor & cylinder if you are SURE the problem isn't in the distributor...

cjeff

I agree, that seems like the most probable issue but they have been checked correctly. First I noticed this problem with a timing light on the wire not firing. The lighg will not fire if there is no spark/ark as there is no flow of free electrons to create an electromagnetic field for the magnet on the timing light to sense. Even if the dist. Is firing on that wire if there is no spark you get no light. So I ohmed the cables, checked gap, and even checked the backyard way of disengaging the fp pulling and grounding the plug and looking for spark. Also I replaced ghe plug on cyl 5 because it looked fouled and swapped good wires on 3 and 5 when I had the chance to swap the ecu and distributor.

Gamefreakgc

It's a circuit issue. Since there's no spark going to #5 and you already replaced the wires, it is most likely you've got a bad cap and rotor (since you said you only checked it, not replaced). It's a regular maintenance item, will only run you $20.

The rotor spins and delivers a spark every time it nears one of the six spark wires. If the cap (or rotor) is rusted, corroded, warped, etc. that gap can widen, causing intermittent or no spark. Replace the cap and rotor, it is cheap and will eliminate that being the issue. I've had the rotor go bad and only fire on certain cylinders.

Basically, you'll want to go through each part of the circuit from battery to spark plug to ensure each part is working correctly. The cap and rotor is my suggestion since it's cheap and you have to replace it soon anyway.

cjeff

Sorry I should have stated these have been replaced. As well as had continiuty checked on the cap.

snobdds

Don't overlook all the grounding straps. Toyotas are "switched ground", and a dirty ground can play havoc on the system.

Also check the ignitor and coil...

cjeff

I do however believe its a circuit issue But coming from the pickup coil to the ecm. Intermitten signal would explain the random fire on three but not 5 also I would imagine a cel for the distributor.

cjeff

Thank you snbodds I checked my main engine grounds, but was unaware of the switched grounds. Ill search on here for an ignition schematic.

cjeff

Also wouldnt the igniter and coil cause a random miss.

ksti

IIRC I believe there is also a ground wire under coil or ignitor.

scope103

A bad ground shouldn't cause a problem on a single cylinder. Same with the igniter or coil or timing. Using the timing light on the plug wire is the most reliable (and easiest) way to determine the plug is not firing. So the only place it could be is plug, wire, or cap (I doubt it's the rotor, but since it's new I rule that out anyway). Or the connections between them.

Any chance you could swap just the plug wire? Even though you've ohmed the wires, it could be a connection problem at either end. Or an internal crack in the wire that only opens when you move it around. You might be able to swap 3 and 5. If the miss follows the wire, that's your clue.

j2the-e

If you tested and swapped around and replaced the ignition components you said you did, then your problem is likely not the ignition system. Did you test for spark with an actual spark tester?
I would start looking somewhere else. Have you done a compression test? #3 and 5 are right next to each other and prone to leaky head gaskets.

cjeff

Thanks for the replies, I checked wiring tonight it was good. I had a buddy come over and as a last attempt I pulled the wires from 3 and 5 and checked for ark, it was there. I have a massive valve cover gasket leak above 3 and 5 that has created large carbon buildup around and in the plug threads. I believe that the buildup is creating a bad ground on the plugs. I have never seen/heard of this before but it makes sense. Looking back I checked for spark with a plug that had this buildup. Has anyone seen this problem? I plan on cleaning the threads tomorrow with sea foam ill let you akk know how it goes.

oldblue

if you were a tech and still have some tools i'd check two things before you go any farther. with a vacuum gauge, check the engine vacuum at idle. a bouncy gauge will indicate vavle issues which will cause a missfire . i'd also do a compression test on all cylinders to find out the condition of the engine.

Guardian_Saint

The last time I did mine and has weak spark or to no spark was a bad timing. Don't remember if I did adjust the dist.. to correct it or the timing belt... Check dist. gear and camshaft gear.

bone collector

If you have that much carbon buildup around your plugs then while your at it, might as well clean your egr system. or just delete it if you can get away with it

cjeff

Good call on the compression and vaccum gauge test oldblue. I've got 0 compression on 5 and only120 on 3. My vaccum is only at 12hg and bouncing like crazy. I'm moving to a garage today to do the valve job. Any recomendations on a good valve manufacturer outside Toyota?