Engine missing not all cylinders firing?

[mikael11]

I have a 1991 Toyota 4runner V6 4x4, 186K mi. Timing belt replaced once, manuel transmission.

I have a problem that comes and goes. When idling or accelerating it feels like 1 or 2 cylinders are missing. It sounds rough and my horsepower significantly drops. I have changed the spark plug wires, spark plugs, distributer components, sprayed most electrical connections with an appropriate cleaner and used Seafoam several times. I seemed to have some success w/ the seafoam which makes me think its my injectors (it ran for 3 weeks perfectly, then problem returned). It runs great in the a.m. and is fickle at best when warm, sometimes fine sometimes really rough. ANY suggestions would be much appreciated.

 

[ultrabongo]

Look for vacaum leaks. Look especailly for leaking injector seals. You can spray a soapy water soloution on the injector seal area and see if it gets sucked in. Some people spray ether or starting fluid and listen for a spike in RPM- I wouldnt suggest it because of danger.
The fact that it seems to be temperature related suggests looking at the coolant temp sensor - the one that feeds signals to the ECU.
Put a vauam gauge on the engine- that might give you more info, too.

 

[mikael11]

Thank you ULTRABONGO, I will look into your suggestions. Can you recommend a website or particular manual for locating the vacuum lines I need to inspect? I am flying blind in that arena and my Hanes manuel is not the clearest guide I'm sure is out there. THANKS

 

[ultrabongo]

The best thing is the Factory Service Manual (FSM on this forum.) Search this forum for a link to download it free or try 4crawler.org for a place to download it. There may be a diagram of the vaumn lines under your hood. Basically, check all the rubber tubes that run to the throttle body and valve cover. Good luck.

 

[buievonbozo]

I have the same problem. I did the plugs, wires, coil packs, injectors and fuel filter. STill having the issue. The only thing that changed was when I changed the injectors. Then about a month later, it started again. I'm thinking the ECU is next.

 

[KidVermicious]

I have the same problem. I did the plugs, wires, coil packs, injectors and fuel filter. STill having the issue. The only thing that changed was when I changed the injectors. Then about a month later, it started again. I'm thinking the ECU is next.

Nope. Isolate your problem first - if you think you're missing on a cylinder, start pulling spark plug wires. When you pull one and the problem doesn't get worse you've found your trouble. If you can't pull any of them without it getting worse, then it's not related to any one cylinder.

Don't just throw parts at it though, that gets expensive quick. Troubleshoot and isolate, THEN repair.

 

[77'911]

You might consider checking and going through the fuel system completely(fuel pressures:rest /running). Ethanol , age, and miles have not been kind to them. When I replaced our fuel pump, regulator(see pic), injectors seals, fuel filter, relay, the truck ran like a new machine afterwards.
As others have suggested, vac leaks, faulty EGR valve, timing not set properly, can also be suspects. Start with basics(fuel, spark, charging) to cross them off the list, then work your way in. I find this gives you a good basis to work off from. Best of luck with it.
regards

 

[buievonbozo]

When it is plugged into a hand held, the hand held directs to #1 and #2 cylinder misfiring. I forgot the codes.

 

[KidVermicious]

When it is plugged into a hand held, the hand held directs to #1 and #2 cylinder misfiring. I forgot the codes.

So pull the plugs. They'll probably tell you why the cylinders aren't firing. Are they wet with fuel? Fouled with oil? Clean and just not firing? Lots of info hiding in there.

 

[buievonbozo]

Ok... here is what I found, and it's kinda confusing.
Plugged in to handheld that my mechanic loaned me, codes came up as follows;
p0300- generic multiple cylinders misfire
P0301- cylinder 1 misfire
P0302- cylinder 2 misfire
So I figured since these two are connected by the coil pack waste spark system, the problem would be the coil pack. I changed it. The truck was still running rough. So I plugged it back in to the hand held. Now the codes came up;
P0305- cylinder 5 misfire
So i pulled that pack off and swapped it with #3 cylinder and checked the plug which seemed fine. Put everything back together and started it up. Still rough. Plugged it back in and this came up;
P0300- generic, misfire on multiple cylinders
P0301- cylinder 1 misfire
P0305- cylinder 5 misfire
P0306- cylinder 6 misfire
Now, I checked these codes against a software program at my mechanics garage and it gave me a list of possibilities.
Cam shaft timing
fuel pressure
fuel injectors
multiple ignition issues (plugs, wires, coil)
So, I took a can of starting fluid and sprayed it everywhere to see if it changed anything, just incase, before i took everything apart again and nothing changed. Got everything off down to the injectors and fuel rails. Noticed that 3 plugs were a 1/2 turn loose. All plugs seemed equal in burn color. Boots all snapped on nicely with good connectivity. Checked the seating of the injector seals, seamed good and tight. Checked for breaks or wire disconnects on injector electronics, seemed good. Put everything back together, completely stumped. Started it back up and of course, still running rough. Plugged it back in and #1 and #5 came up again as well as another code (forgot it) for system coolant level being insufficient. I checked that and the level is fine. WTF!!?
Now 2 months ago, give or take, I changed the plugs, wires, packs and injectors and it ran fine, as stated before. Then everything went to hell. I don't think the timing would be off cause, though I changed all that stuff, it would not have made a difference. I have yet to check the fuel pressure. Can someone give me an idea on how to do this?
I got this truck for free, being that it did not run before, and I replaced everything and a few thousand dollars later is was fine for a couple years. Now this. I am ready to throw in the towel.

 

[hoe_nah]

So pull the plugs. They'll probably tell you why the cylinders aren't firing. Are they wet with fuel? Fouled with oil? Clean and just not firing? Lots of info hiding in there.

If its wet with fuel what does that mean?
Fouled with oil?

I ask cause my #5 smelt like fuel and oil

 

[buievonbozo]

you want it to smell like fuel. That means the injectors are working. So does wet with fuel but it could also mean that it is not firing.
Oil would be bad. Blown gasket, seal etc. I think anyway.

 

[mikebontoft]

have you really done anything other than keep checking codes?

what plugs did you use and have you actually pulled them yet as kid suggested?

double platinum plugs I hope. REQUIRED for waste spark ignition.

 

[KidVermicious]

If its wet with fuel what does that mean?
Fouled with oil?

I ask cause my #5 smelt like fuel and oil

Smells like fuel is fine, they're all going to smell like fuel and exhaust. Wet with fuel would indicate incomplete combustion.

Buievonbonzo, I'm not familiar with your wasted spark setup, but the truck still has a distributor, right? So here's some ideas, just what I'd be doing (keep in mind mikebontoft is the mechanic here ):

1) start yanking plug wires to verify that the trouble really is jumping around the way your meter says is it
2) check the timing one more time
3) remove, clean, and replace all your big grounds, especially the motor grounds.
4) verify good spark from the coil/igniter
5) bypass the wasted spark setup, go back to stock and see if that clears it
6) replace the rotor and cap

Another thought - you said the truck wasn't running when you got it? And when this trouble first started it went away when you changed the fuel filter and injectors? Any chance it started again when you ran the tank particularly low?

 

[buievonbozo]

Thank you all for the replies. I am not a mechanic though I am very capable when it comes to taking things apart replacing parts or not and putting them back together again. Diagnosing is not my strong point, though I am capable in some cases.

Mike, I did use the NGK double platinum plugs. I have been using the hand held, as well as my mechanic and you guys, just to help guide me. I pulled the even number wires off of the coil packs and the idle was more rough. Now, I'm not quite sure how to do that with the odd numbers being that I have to disconnect the electrical clip from the coil pack in order to pull that out. And just for good measure, I tried and the engine dies. I have also pulled each plug a couple times with mixed results. Sometimes random ones are dry and sometimes the same ones are wet. This is what is confusing me and also why I thought the ECU may be shot. I think it is why, when I changed the injectors everything was fine and over time, they short out. So lost here.

KidVermisious, A waste spark system is where, instead of a distributor, the motor has coil packs attached to the spark plug boot and the opposite cylinders plug wire is run from it. Now, in a waste spark system, the plug with the coil pack sparks twice as much, once for itself on combustion stroke and once off the combustion for it's opposite cylinders combustion stroke. Hence, wasting one spark. The plugs get a work out, which is why multi-point plugs are recommended.

 

[mikebontoft]

Part of what is confusing Kid here is that you've posted this in the classic section which covers up to the 95 model year and yours is a third gen 3.4. BUT no worries.

Unfortunately this is where it gets tricky... and where I wish I could be there to fix it because I love these kind of problems.

I do have one question first. In relation to replacing the fuel injectors, when was the fuel filter replaced? before or after?

It is a random multi misfire... and I find it hard to believe that all six injector or ignition circuits fail to ground alternately (note the computer controls the ground side of each injector).

Back to where it gets tricky. Aside from getting a screwdriver or stethoscope on each injector to verify that they are clicking without a break in pattern... there's not much more I can really have you test unless you have and know how to use an oscilloscope. With one, I could check to make sure the fuel injectors are working correctly, your ignition system is working orrectly and most importanly/most useful, if your engine sensors are reading correctly. Something like the cam sensor, for example, could be tested to see if it has the correct waveform pattern.

With that said... I can only suggest replacing the cheapest thing first (not sure what will be). Crank and/or cam sensors, potentially bad plugs or wires... even a professional fuel system maintenance may be required.

 

[buievonbozo]

Thank you Mike, for all of this. Now, this is where my stupidity comes in. I did replace the filter after the injectors. For some reason, I did not think of this first since it was replaced once before. Though I can see where you are going with it, I am still perplexed at the issue of random misfires.
I did just have the knock sensors replaced about 10,000 miles ago. Is that another term for cam sensor? And the only reason I ask is because of there placement on the head under the intake.
I am familiar with an oscilloscope though I do not think I could get my hands on one. But I do have some friends who may be able to.
What is the other back yard trick with the screwdriver and stethoscope? Would I hold the screwdriver to the injector and the stethoscope to the top of the screwdriver and listen. Kinda like cracking a safe?
Just noticed you're from Price. I use to live in Bountiful. Not that it matters.
And I understand that this is not the right forum place, but the subject matter was similar. I'm also in 3rd gen and as you know, problems and warranty issues. Trying to spread it out.