Hello all,

I am really hoping i can find help on this forum. I will try to keep it short.

As the title states my 4runner suddenly started misfiring one day when I was out on a logging road so bad that I could not make it up the hills to get home causing my to pay for a $400 tow home. Several mechanics have come by and put their 2 cents in.

Symptoms:

Extrememly rough idle (somtimes sill stall)
Smell of gas
occasional backfire
excessive shaking of the entire vehicle

What I have done:
Plugs,wires,rotor,cap
fuel filter
VAF sensor
battery

One thing that is blowing me away is that no matter what I do the car will not throw a CEL, I can disconnect my VAF sensor pull plug wires and no CEL.

I had suspected fuel as the culprit as I beilive there is rust in the gas tank but I want to be sure before I go down that road.

Does anyone know of a way to 100% throw a CEL so that I can confirm my ECU is working? I know that if I had a bad ECU if would cause my symptoms. On that note, the light illuminates when i turn the key and I can enter self diagostic mode by shorting the pins inside the diagnostic port and this still does not pick up any faults.

Any input would be much appreciated, i want to get this bad boy back on the road.

[QUOTE=93bushbeater;2063122]Hello all,

I am really hoping i can find help on this forum. I will try to keep it short.

As the title states my 4runner suddenly started misfiring one day when I was out on a logging road so bad that I could not make it up the hills to get home causing my to pay for a $400 tow home. Several mechanics have come by and put their 2 cents in.

Symptoms:

Extrememly rough idle (somtimes sill stall)
Smell of gas
occasional backfire
excessive shaking of the entire vehicle

What I have done:
Plugs,wires,rotor,cap
fuel filter
VAF sensor
battery


One thing that is blowing me away is that no matter what I do the car will not throw a CEL, I can disconnect my VAF sensor pull plug wires and no CEL.

I had suspected fuel as the culprit as I beilive there is rust in the gas tank but I want to be sure before I go down that road.

Does anyone know of a way to 100% throw a CEL so that I can confirm my ECU is working? I know that if I had a bad ECU if would cause my symptoms. On that note, the light illuminates when i turn the key and I can enter self diagostic mode by shorting the pins inside the diagnostic port and this still does not pick up any faults.

Any input would be much appreciated, i want to get this bad boy back on the road

One other thing to add, I have removed the CAT to see if there is any difference, but none.

Uh, what engine??

Ya the engine type would be a fantastic additional piece of info...
But to answer your question about setting a code: having a 93 means OBD I. Even if you were to induce a code, it would be exceptionally vague and essentially useless. Something like "EGR Problem" or "02 malfunction" which may lead you in the right direction, but it may mislead you as well.
If it's misfiring you know one thing is missing of fuel, spark, air or compression. It's doubtful air or compression vanished out of nowhere and it seems like your spark/ignition system has been completely replaced. If it were me, I would try and find which cyclinder it is.
Simple enough, have all spark plug wires loose-ish on the cap and while its idling like garbage, pull one off at a time and place it back on to see which one does NOT change and that's your missing cylinder. I would be guessing that an injector just stuck open and is flooding that cylinder. An ECU issue is much less common, however anything is possible.
After finding which cylinder you then need to check the injector a couple different ways to determine why it's bad. I actually have a 93 Infinit in my shop right now that has an injector commanded fully on 100% of the time, even key off and sitting on the passenger floor. Turns out this one IS the ECU but like I said, it requires systematic testing to rule things out. (Plus this is a Nissan product...those aren't the soundest machines from and engineering standpoint)
There are lots of other things to check but this is the simplest. For example if you have the 3.0 those have the cold start injector which wouldn't necessarily affect a single cylinder but would still enrichen the engine to the point of misfiring potentially. Also if it has EGR that could be stuck open with carbon or something which would give you a crummy idle but you wouldn't feel it at higher RPMs (2-3K).
Good luck and let us know what you find.

Thanks for the reply, I guess I should have mentioned it is the 3vZe. 350 000 kms when I bought it, the lady that sold it to me told me that the top end was rebuilt 20 000km ago due to low compression on 2 cyl, service records I obtained from toyota confirm this.

I like the direction of pulling wires to find out which one does not make a difference I will give that a try tonight for sure. One thing I did try ref fuel injectors was a trick I read about using a flat head screwdriver as a stethascope to listen to the injectors open and closing. If you put your ear to the end of the handle you can hear clicking, which I did hear on all 6. is it possible an injector is bad but still open/closing?

On the EGR thought, when I bought the vehicle there was a CEL, it was for EGR I was told, I found the 2 wires for the EGR temp sensor hanging and made a make shift connection with crimp connectors which actually turned my CEL off never to come on again even after I have unplugged those wires since for testing purposes. Currently when I can rev up the engine to 2-3K RPM the roughness and shaking settles down but it is definitly noticlable still and 4runner sounds like death.

Is there an easy way to inspect/test EGR to rule it out?

I will keep you guys posted, thanks again.

As far as injectors clicking and not physically opening this is very possible. Also possibly it's clicking but not fully sealing when it's off. Hence the fuel smell due to cylinder flooding.

I believe you can take some larger wrenches, like 22 or 24mm (15/16" may work as well if you use standard sizes) and remove the EGR from the engine and cap off where it flows into the intake plenum. That's a relatively easy way to eliminate it and see what happens. It would be stuck open to cause the rough running. Also be warned when the EGR is removed there is a port coming directly off of the exhaust so it will make a horrendously loud lawn mower type noise which is normal since you're created an exhaust leak. No harm will come but it will be loud. You'd have to feel the steering wheel or look at the engine while its idling to see if the misfire goes away when removed.

Ok 4Reak Show, I tried what you suggested and pulled all ignition wires until I noticed changes. It seems like I have 2 bad cylinders #3 and #4. I am not sure what they have in common with each other but pulling them made no difference and it wasn't due to lack of spark. The spark was jumping out from the distributor a few inches on both #3 and 4. Would you suspect bad injectors on both? How could I narrow things down from here?

Again all help is appreciated!

Hey at least you narrowed it down a bit eh? Hmmmm well to start with, they come in order of firing sequence 1-2-3-4-5-6 if I'm not mistaken. That may even make it possible for incorrect wire routing? I believe bank 1 is on the right hand side of the engine when looking OUT the windshield, making those cylinders #1,3,5 starting from the front of the engine and of course the other side is #2,4,6 from the front. (I will confirm this when I get to work tmrw and can check my factory service manual). Just triple check you didn't accidentally switch those wires. It's easy to do and the cap should be labeled.
If that doesn't work I would try possibly moving one of those spark plugs from 3 or 4 and see if it follows that. Not sure if you had replaced plugs before or after this all occurred.
Otherwise the only Thing I can think of besides injectors is like a weird intake leak or something between the 2 cylinders since their respective intake runners are so close together.
Worst case scenario is 2 cylinders dropped a valve somehow simultaneously which would require a compression test to confirm.
Start with wire routing, then move a spark plug and recheck with removing wires to see if it follows the suspected plug, then rent/acquire a compression tester.
Good luck and keep us posted

Sorry forgot to mention, if the misfire stays on those cylinders, I can try and walk you thru testing of the electrical command portion of the injectors. Those aren't incredibly fun to change or even access for that matter so I just want to fully rule out anything super invasive before proceeding to the not so fun stuff.

Yes at least I did narrow it down a bit. I've had several mechanics come over to look at the 4runner and none of them suggested this easy test, it is a good one i will remember for sure.

You are right about the firing order and the cyliner arrangement. facing windshield from outside left is 1-3-5 and right 2-4-6 meaning both "middle" cylinders are not firing. I have double checked my wire routing and the plugs are new since my problems started which did not make any difference from the old ones.

I guess that leaves out the easy fix. . Do you think this could be a timing issue? I mean I really hope it isn't there is a decent amount of work involved in getting a the T-belt.

As I said before I did suspect fuel an an issue just becuase I know my gas tank has rust in it but to what extent I do not know. I would need to drop the tank to get a better idea, and judging by how rusty the bolts look it may be a frustrating job.

I would be open to checking injectors if that is the route you you think i need to take.

Thanks again.

Clogged injectors.

I think we can safely rule out timing at this point since it appears that only 2 cylinders are affected. I would also bet that the rusty gas theory isn't valid at this time because, again only 2 cylinders are affected. BUT it could be injectors. They are a simple "on-off" circuit. Now what I'm about to tell you is super simple IN THEORY but I remember those engines don't make accessing the injector very friendly. What needs to be done is to check that the injectors are getting commanded to turn on AND off. What I can do is look at the wiring diagram for you and perhaps the easiest location for this is at the computer itself. Normally I would suggest to remove the suspected injector electrical connector and wire in a light bulb in its place. While running, the bulb should turn on and off rapidly. Should flash pretty fast. They actually make special lights called Noid Lights just for this but I'm not sure if you have access to professional tools.

What I would say to do is to just replace the injectors in all honesty. It take a bunch of time to pull the intake off to even gain access to the actual connectors, then reinstall it and run it to check operation. Makes little sense to do the job twice really. The only reason I'm hesitant to run a light bulb that's wired in and backprobed into the ECU connector is that there have been cases where somehow the circuit can back feed ground and fry your ECU. I don't know that it's worth the risk.
The only safe way I know for sure to do the backprobe test is with a tool called a PowerProbe. It essentially is a circuit protected test light that allows you to harmlessly check when a circuit is getting power or ground. If one of your mechanic buddies has access to this tool then I can certainly give you the needed wiring info to tap into and access the injectors in question. Otherwise, it may be time for injectors. And perhaps all of them(?) since they are all the same age.
Let me know what you find out about the special tool. Good luck

Says he smells gas. Perhaps not fully sealing.

Also check the PCV hoses. They tend to get brittle and crack.
I had all the same symptoms and smells back in January. It ended up being 3 clogged injectors and a couple hoses.
You can find my photo documentary on here.
Just take lots of photos of the 8 zillion hoses coming off the intake plenum. I didn't take enough.

Hello again!!

So.....I found out injectors 1,3,5, are inaccessible without removing intake manifold but i was able to get a noid test light on the wiring harness for #4 and it had a steady pulse, also compression was good in all cylinders. Note, when I pulled the plugs for compression test 3 and 4 were full of gas, with good spark it is hard for me to fathom how there isn't combustion? too much fuel perhaps. At this point I will inspect the vacuum hoses but I suspect bad/dirty injectors on 3 and 4. Is there a way to clean then without removing them? ie. tap into the fuel system somehow? Do you know how big of a job it is to remove the intake and get at the injectors? Could there be anything else I am missing? If I am going to be doing the injectors common sense leads me to think I should pull the tank and clean or replace it as well so i don't foul up new ones. and, if I am doing the injectors I would suspect it is best to do them all?

Hopefully this 4runner isn't leading me into jobs I fear are over my head, I hope I can get some 4x4ing in this summer!