98 4runner help, misfire help please

marty79

marty79

Well-Known Member
Joined
Nov 24, 2013
Location
Newton, NC
hello everyone, we have a 98 4 Runner 3.4L at work that I am stumped on. Misfiring on well..here it goes!
started out with cylinder 2 misfire when I first started working on it..
swapped coils with different cylinder and the misfire followed it ...to now #4 cylinder misfire.
Ok, so I put in another good known coil he has...still #4 misfire! WTH
pulled fuel rail and swapped injectors even though they are all brand new, still same result #4 missing.
swapped coil again with one that fires the other cylinder and still #4 misfire WTH
coils OHM out the same cold or hot so I know it's not the coil, Injectors all OHM out good since they are new, and plugs are new (yes they are the double ground plugs as required)
Compression on #4 cylinder is like all others 164psi
Dollar Bill on the tailpipe is "inconclusive" since at idle it stumbles so it seems to try and pull the dollar in but at the same time it doesn't so I can't rely on that test for any helpful data.

I'm really lost that it began with cylinder 2 misfire and moved to #4 misfire and now it's staying there and no matter what I do nothing changes. It's the bosses rig (LOL, I know I feel terrible). It runs and drives ok, but has that idle mis that you can feel and you can really feel it in OD with the slight throttle.

ANY AND ALL advise would be appreciated as I'm lost and apparently I'm either overlooking something or gonna have to get into the electrical stuff tomorrow. thank you for the help!!
 
Leak down test on the affected cylinder. Tdc, rad cap off, intake open... Engine hot preferably.... Feed shop air to the cylinder and see if it starts pushing coolant out or at intake or exhaust? Is it Pumping coolant into the overflow? Crud in the cooling system? You say "another known good coil" that means used. Did you inspect the plug for carbon tracks from the faulty coil? I've seen them transfer from rubber to porcelain and cause a new carbon track to form.

And for what it's worth I've seen the 3.4 warp heads Without showing overheating on the gauge. Missing impeller blades in that particular case.
 
pass side, 1, 3, 5 front to back, drivers side is 2, 4, 6. if you have a misfire on 4 (middle drivers side), you likely have a bad plug wire or boot, very common, replace wire set with new, pay attention to routing and placement. Replace wire set AND the boots on the coil packs, recommend plugs as well.

what spark plugs are in the engine ? this engine runs best on dual electrode plugs ( DENSO or NGK ) the coil fires both plugs connected to it at the same time every time its triggered (waste spark), so the side electrodes tend to wear faster on single electrode plugs ( the reason Toyota spec'ed dual ) Don't waste $$ on Platinum or Iridium, they don't run any better in this engine

at this point, its unlikely you have a head gasket issue as the compression numbers are same across board ( according to your info )
 
Ok, plug wires are new but swapped them too, no change!
Coil that I swapped are the other coils that run just fine for those cylinders!
It has new denso plugs (the right ones).
Runs good as no overheating or no coolant in oil, no mixing anywhere.
Will try the leak down test tomorrow I reckon..bout the last mechanical test to run before electrical crap.
(The #4 plug is pretty wet when I've removed it the few times so I'm thinking ECU is keeping that injector open too long?)
 
a_kelley said:
And for what it's worth I've seen the 3.4 warp heads Without showing overheating on the gauge. Missing impeller blades in that particular case.
Click to expand...
This motor ran perfect he says in the 98 runner he took it from so doubtful on any engine issues I would think
 
Are you hearing/feeling the misfire ?

Have you cleared the code and then driving ? or just hoping it goes away after changing parts around ?
 
I highly doubt the ecu hanging the injector open. I'd take a look at the plug again or just change it. And the coil (s) & wires. It is entirely possible you have two faulty coils arcing out. Especially since they're all used. Question everything you assume or think you know about the problem, even if it's something you've checked or replaced. Basically start out fresh at square one.

Plugs foul. They get carbon tracks. Arc through boots, etc. If the plug is wet, she isn't firing. Plugs get dropped or have weak spots sometimes.
 
Of course, your also taking his word it didn't have any misfire before also..... Question all assumptions. It's nearly always something stupid simple. Especially if it's overlooked once or five times and not resolved.
 
Thanks guys I will start simple tomorrow again and report back.
 
Blkvoodoo said:
Are you hearing/feeling the misfire ?

Have you cleared the code and then driving ? or just hoping it goes away after changing parts around ?
Click to expand...
Yes you can feel it and hear it, not like huge but its there
 
Update: leak down test passed very good!
Swapped 2more coils, same #4 misfire.
Swapped another new wire and plug, same.

Looks like tomorrow start tearing into ECU and harness going to that injector I reckon...I'm all out of ideas.
Any more thoughts?? Thank you
 
Did you leak down the motor while it was hot with 150# air without the Schrader valve in the plug hose?

Plug still wet?

If the wiring was bad, it'd have a code for open circuit I believe. Same goes for the coil (and it would have a miss on the corresponding cylinder as well if it was the coil low voltage wiring.

Check the fuel injector pulse with a noid light. You said you swapped that injector and no change so I'm thinking it's not the injector or injector wiring.
 
a_kelley said:
Did you leak down the motor while it was hot with 150# air without the Schrader valve in the plug hose?
Click to expand...
Yes I did it just like so, passed. Can't get noid light in there while running, have to remove whole upper. Will look at firing order again, thanks for all the pointers
 
1-2-3-4-5-6 yes, really but, also remember that the coils fire a pair of plugs 1-4, 5-2, 3-6
 
@Blkvoodoo that's what I was talking about, the plug wire/coil combinations.

@marty79 check over the maze of vacuum lines.. other than that, you've got me stumped from over here. Is it a hard miss or a subtle miss? Check fuel pressure? Fuel quality? (Those are long shots but not covered, and would generally cause random multiple than one specific cylinder). Try pulling wires while it's running to see if it's not a specific cylinder missing perhaps.

Did the truck have misfire issues prior to changing the motor? Some back info may help.
 
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What brand plugs? Ngk or denso I hope.

just because coils test good, doesn't mean they are not firing out the side of the coil or internally breaking down under high voltage.

Looking back at the first post, Since your problem moved from 2 to 4 with the coil and stayed there, you're missing something. You changed the coil and the miss moved. Any possibility that the wire didn't clip in well? Check resistance on the plug wires? Spring fall out of the coil? Did you try a NEW coil? I'm a stickler for new Ignition parts when chasing something like this. To much back tracking and doubting yourself using used parts. If you diagnose it, identify the problem, but put used part in and has the same issue that someone claims their part is good, do you have another issue or is it the same cause you identified and really the used part?... See what I mean?
 
Little update but didn't spend much time on it today.
While running, pull #4 plug nothing changes, pull any other plug (did #2 its up front), motor changes like should sooo...
It fires on that wire I could hear it arching inside the walls when unplugging it but obviously not enough?, that was all I had time for today..(rock sliders to build lol)
 
Inspect the plug boot for carbon tracks and insulator puncture. Also check that the wire is snapping down into the plug. And check the new plug to see if it's cracked on the base or carbon tracked. See if it's wet with fuel or whatever. If it is change it. It's possible a whole box got dropped & damaged. BTDT.
 
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