wellyman

Hello all:
(This is 3rd gen engine related)
I have a 93 4runner, with the 3.4L conversion. It's been about a year or so since I completed the project. I get this horrible stumble on occasion. It starts when I'm sitting at a stoplight, or pulling out of a gas station, or other times when I'm idling or starting to accelerate. When I'm stopped, it will start to lobe, rpm's fall to under 500, and I have to give it a little gas to keep it from dying. It remains very rough. Once I can start moving, I have learned to push the clutch in, rev the motor, and feather the clutch out. When I rev it, the motor is very rough, and after a few seconds, it will get smooth again. It's like clearing your throat. Highway cruising is fine, never any problems. It's always at either stop, or start and go (city) driving. Sometimes I don't feather the clutch at all. Light turns green, I start driving and the truck is bucking bad, and then it will smooth out, and all of my power is restored and the tires usually bark when this happens and I'm thrown back into my seat. Sometimes this happens frequently, and sometimes I have days when it doesn't occur. Rain and temperature don't seem to affect the matter. Only other thing I notice is strong exhaust odor, which I don't know if this is normal or not. When I pull the truck into the garage, it runs for a few seconds until the door closes and I smell it strongly, unlike my other cars. No codes from the computer. I put on another trottle body and it didn't affect it. I'm about to send in the injectors for ultrasonic cleaning as I'm out of ideas, but I'd like to get everyone's opinion here as to what it could be before I keep wasting money on fixing unbroken parts. Only thing I can think of is injectors, maybe coil? It's quite annoying when it happens, although I've driven it enough that I feel safe it won't break down on me. The motor has about 40K miles on it. It did sit for a short while exposed to the elements at the junkyard before I bought it. Any ideas or suggestions would help alot. Thanks all.

Jeff

rimpainter.com

Jeff -

What kind of plugs are in it and did you gap them with a wire-feeler guage?

MTL_4runner

I hope those are OEM Densos or NGKs too.

Could also be a coil pack or the TPS causing you fits.
....do you have the OBD hooked up on it so you can see sensor outputs or get a CEL?

wellyman

I've replaced the plugs twice, and I'm pretty sure I have denso's in it now. I'm gonna double check them tonight to verify though. I was wondering about the coil packs. Any good way to testing, or is replacement the only way to tell? I'm 99.9% sure it's not the TPS or the IAC, as I've replaced the entire throttle body assembly as a diagnostic to this very problem. OBII is hooked up and functioning fine. No cel on computer.

BajaRunner

What about the clutch? Any possibility it could be that?

noahrexion

If its a violent stumble or a very quick cut out then its most likely ignition related. This is assuming that you have replaced FF, dont have a clogged cat or air filter; but when its off and on like that and load related (yu say its from stops and what not as soon as you apply load to the motor) tat it is the ignition. If you know you have good wires and plugs (those can be tested easily) then get a multimeter and a FSM and check the resistance on the coils. Its not uncommon for them to go bad.

I have done a lot of engine swaps w/ DIS cars. It seems that a lot of cranking, revs without load or trying to get the car started after a swap (when its been a while) has a negative effect on DIS systems (even distributors atually).

Check out the coils, you don't have to replace them. Just make sure you have an FSM or proper instructions so you know you are checking the right terminals.

wellyman

Well here's an update. Plugs are Denso PK16TR11, although the crappy haynes manual says use K16TR11, I assume these are the same. They are double polled, so I don't think I gapped them as I don't think you do with the side polls. If I'm wrong, let me know. When I checked the plugs, they did look like they have carbon buildup, and reddish brown on the electrode and ceramic. Haynes says rich mixture or weak ignition, which seems likely. I've replaced the FF twice, and I'm sure it's not that. I pulled all three plugs on the passenger side, and all of them are look identical as far as deposits. I did notice that when I pulled the air box and hose to the TB, that there's a wet brownish residue on the bottom of the TB, hose, and there's visible residue in the intake when I open the trottle plate. I don't really smell fuel in this gunk, but I have horrible smell. I will check into testing the wires and coils now, and see what that gets me. I wonder if the MAF sensor can cause this, as I've had codes thrown in the past with this. I've cleaned it as per instructed and I haven't seen a cel regarding this since.

ricky

Funny, I was having almost the same problem for quite some time. Started as a minor stumble, turned into a major sputter on takeoff...

Turned out to be the plug wires. I was just about to go out and have the super injector clean done at the dealer... then I decided that I would try to replace the wires. I had repalced the TPS, cleaned the throttle body, put massive amounts of injector cleaner and good gas into teh engine, only to find the plug wires were the whole problem.

wellyman

I think I'll replace the wires, just in case. Thanks Ricky. I looked thru my online Toyota manual, and I can't find where or how you test the coils or the wires. I have a multimeter, but don't know what to do.

noahrexion

Primary Resistance: 0.6 - 1.05 ohms
Secondary Resistance: 9.3 - 16k ohms

Take off the coils and get your multimeter out and set it to ohms (resistance setting). Primary resistance is measured between the two terminals where you unplugged the connector from the coil (the plastic clip that you had to unplug to pull the coil out). Then for secondary you measure the resistance between the positive (from the same place) and the high tension terminal which is where the coil attaches to the actual plug (just jam the tester inside there).

If any of the coils you test are outside either of the ranges then replace it. But like ricky said it may be your wires. You can check those as well to make sure they are good. Sometimes you may get decent resistance testing cause when you test them there is no load. Occasionally there is a small break and only under good amount of load will the wire jump and shoot the spark outside the wire. If you haven't replaced teh wires its a great idea to anyway, they are only like $30-35 for some new NGK's.

Also if it were me I would ditch ANY other spark plug and stick with NGK's (BKR5EKB-11) that you should be able to get anywhere. Keep us posted!

MTL_4runner

and also the resistance between the primary and secondary should be infinite (ie no conductivity).

DENSO made K16TR11
NGK made BKR5EKB–11

.....either of these plugs will be fine.

wellyman

OK. New plugs and wires are on their way. Going to test the coils tonight and will post back the results.

Thanks all.

nfenwick

Sounds like maybe a vacume problem to me. I know that is not spelled correctly

midiwall

Side note...

Do you mean that the plugs have two electrodes? If so, then yes, you DO need to gap them. The spec is .038-.043".

noahrexion

aside from what I said earlier you should consider the MAF as well. If its a vacuum problem it would probably be constant and have to be quite a large leak.

MTL_4runner

The gaps are usually fine out of the box for me (never found one out of spec anyway). The biggest thing to look for would be an electrode that was bent/damaged or cracked ceramic (even the best mechanics can have damage plugs by accident during an install).

Also look at the boots on the coils to make sure it hasn't been arcing down the boot (I saw that once with similar symptoms, bucking etc).

Runner003

How about a new fuel filter while your at it? My father always told me "Cheap things first" Wires and plugs are included in that list...

noahrexion

wellyman

I sincerely doubt that it has anything to do with the plugs, as I'm sure I put autolites in it at first when I did the engine swap. I replaced all of them with the densos that are in it now as a result of this specific behavior. They had no effect. But new NGK plugs and wires are on their way just in case. I've always suspected the MAF, as these are such a common problem with Toyota. Just so costly to find out. I still have not had a chance to check the coils. I don't think vacuum leak is suspect either. I remember having a real hard time locating the correct routing/connections for hooking up the emissions/vsv's. I'm wondering if it's possible that somethings not right here if it could cause something like this. I also wonder why I have this dark brown wet residue inside the intake, TB. I don't think this is normal? I'm thinking either clogged injector(s), faulty wires or coils, or MAF. But with the swap of the 3.4L, a lot of things are possible. There's a lot of discrepancies in the years and models as far as o2 sensors, number of cats, etc...
I wish whatever was wrong would just break and send a code to the ECU...Wouldn't that be nice. Save me a lot of money. As I'm typing this, I have it in the stealership doing the 50N safety recall service. They already called once and said there's a stripped bolt that holds on the skid plate. They said they have to either cut it off or drill and tap it, costing 50 bucks. All I have to do is apply downward pressure to the bolt and it backs out fine. Sometimes I wonder if they're crooks or idiots...I'm definitely not the most inclined or knowledgable person, which makes me really scared when I know more than some....

midiwall

Ummm, but you did eventually find a good reference for hooking things up, right?

Like was said above, a vacuum issue would normally present itself as a more continuous problem, but if there's a line missing, and there's unmetered air getting into the intake, then all sorts of weird things can happen.

I did what we know as the "ISR Mod".. One day, driving along, the truck just started running like crap - very similar to what you're describing. I pulled into a parking lot and starting going through the normal checklist... plugs, fuel filter, etc. Long story short, it turns out that one of the plumbing caps used in the mod had come out. The truck was running crappy 'cause of the unmetered air flying in through the hole where the silencer used to be.


It's "normal" in the sense that what you're seeing is blowback from the PCV valve. It depends on how much you're seeing and how often it comes back after you wipe it out.


Most are both.