98 4runner runs rough.... sometimes

[ekgguy]

New to the forum, I have been reading a lot though, and I still have a question.

My daughter has a 98 4runner that she has been driving for almost 2 years now. About 4 months ago, it developed a miss and runs really rough, sometimes. So, she is now driving my truck and I am driving the 4runner until i can get this straightened out.

Here is what I have noticed.

Sometimes when I start the truck, it runs just fine. No miss, no rough idle or running. Works like it is supposed to. However, if I drive to the store (less than a mile), shut it off, come back and start it to leave, it has the miss again and runs rough. Sometimes after I drive it at speed, it will clear up and runs smooth.

Sometimes when I start the truck, it runs rough, has the miss and no matter how many times I shut it off and restart it, it doesnt help.

Sometimes the check engine light is on, sometimes it is not, sometimes it flashes intermittently. I did manage to catch the light with a code reader and received a P0306 code (cylinder 6 misfire)

There is no rhyme-nor-reason that I can correlate to when it runs rough or when it runs good. It doenst matter if it is cold out or warm out, if it is the first start up of the day or other.

After reading on this forum and another Toyota forum, I had decided that it was pretty much either a coil, spark plug or spark plug wires. However, I read a post where someone was experiencing kind of the same issues as me, but not exact, and they had changed the spark plugs, coil and wires with no resolution. It turned out to be the fuel injector.

So, armed with that, I changed the fuel injector for cylinder 6 and the truck ran great for about 2 days, then started doing the same thing all over again. Sometimes rough and sometimes good.

That is where I am currently at. I drove the truck to work tonight. When I started it to leave, it ran fine, with the check engine light on. On my way to work, I stopped at a store. Came back out and started it and it started running rough. Total mileage from my house to work is 1.6 miles.

My question after all of that is, since it is such an intermittent issue, could it be the coil pack, wires and plugs?

I apologize for such a long first post, but I wanted to give as much information as I could. I belong to another forum about 67-72 Chevy Trucks and I know the experts on there are a wealth of information and I am sure that they are on here as well.

Thanks in advance

Matt

 

[Squirt]

you were right to look to the fuel injector as the issue. However replacing one in the series doesn't always resolve the issue. if you are going to replace one injector it is smart to replace all 6 instead. you want the flow rate to be the same through the series of injectors and throwing one new one into the series definitely solve the problem on that cylinder however it is being partnered with 5 injectors that are considerably older and starting to perform poorly themselves.

 

[bama16]

you were right to look to the fuel injector as the issue. However replacing one in the series doesn't always resolve the issue. if you are going to replace one injector it is smart to replace all 6 instead. you want the flow rate to be the same through the series of injectors and throwing one new one into the series definitely solve the problem on that cylinder however it is being partnered with 5 injectors that are considerably older and starting to perform poorly themselves.

squirt and i have been chasing the same issues, but i can't get a CEL to pop. I have injectors on the way and will be replace those this weekend. I have replaced the fuel filter, wires, plugs, and test the coil packs (within spec) and nothings changed. I have 3 new coil packs ready to go in if the injectors don't fix it. I have been getting a pop out of the the intake lately when it starts sputtering and i leave my foot in it. Leads me to believe i'm running lean. let us know if you find a fix.

 

[Squirt]

I replaced plug wires, TPS, MAF, with no resolution.pulled the plenum and found that the upper plenum gasket was getting some blow by and had separated.replace the upper and lower plenum gasket at that point.they are cheap and easy to replace and definitely resolved some of the issue but it still remained at highway speeds.ended up replacing the upstream o2 sensor and got much better performance but again the underlying issue was still there.I have injectors on the way also and hope to replace them this weekend. replacing the plenum gasket and o2 sensor definitely fixed the air ratio problem caused by the fuel injectors performing poorly. the injectors starting to go bad can definitely calls trickle-down problems..so definitely test your o2 sensors MAF and check your plenum gaskets also.

 

[Squirt]

not sure where you purchased the one injector but you can get reman Denso injectors off Amazon for around $40ish a piece. pretty much puts you in an entire set of injectors for the parts house price of two.

 

[drallan]

I had a very similar situation. Didn't happen when truck was cold starting (like sitting overnight), but if I ran into the store for 10 min it would run like s*** and sometimes clear up. Didn't throw a code at first, but after about a month it progressively got worse and threw a code (don't remember what it was off hand) and eventually threw a code. Ended up being #4cyl injector. I replaced the 3 on drivers side and problem went away, even gained about 1mpg. This was about 5 months ago, I plan on doing all 3 passenger side ones this spring. I got mine Beck/Arnleys from AdvanceAuto using some $50 off coupon code (made 3 separate purchases), so the came out to only like $75 a piece.

I had recently (within last year) replaced plugs, wires, filter, cleaned TB and MAF, so I was pretty sure it wasn't those. Once it started consistently throwing codes I was able to eliminate a lot of things by moving parts around and seeing if the coded followed. For example, rotate your 3 coil packs, if the code changes from Cyl X misfire to Cyl Y you have a good idea that it is something you moved. If it stays w/ the same cyl it's not that part. After moving plugs, wires, and coils around I kept getting Cyl 4 misfire so decided to dive in.

One thing if you end up doing the injectors. Be very careful w/ all the plastic parts. By now they are very brittle and will break off. I even had one of the injectors break off a little bit inside the engine port. Had to rig up a shopvac w/ long skinny straw to suck everything out. I must have gotten everything as it is now 5-6 months and she runs great.

 

[ekgguy]

Thanks for the replies. Seems like this is a pretty common issue, but not a common fix.

The truck sat for 13 hours last night while I was at work. I started it this morning and it ran like ****. About halfway home, everything smoothed out, ran fine the rest of the way. CEL is still on.

I will definitely check the sensors and clean everything this weekend, but it sounds like the only answer is to throw parts at it until it is fixed.

 

[Squirt]

it's not really that it's a different fix for everyone.. overall issue is that the injectors going bad can affect any of your fuel/air related sensors and parts. that's why everyone ends up replacing o2 sensors MAF etcetera when this happens.

 

[angus]

In my 99 3.4 I too have had an intermittent misfire in the last few days showing a code for misfire on cyl #3. Since the truck has new plugs, wires and coils within the last week or so I suspected a defective part so I decided to check for spark while it was running (while missing) I pulled cyl #3 off and it sparks no problem.

I then pulled the plug and rechecked the plug fires.

I should mention that the problem is (so far) isolated to hot re-starts and never on a cold start.

Even from the start, a bad injector was in the back of my mind so my next step will be to swap the injector to a different hole and see if the misfire follows it.

With all the threads I have read on injectors failing in these motors I will not be surprised.

I'll most likely order a set of remans that has been flow tested/cleaned etc.

 

[Squirt]

In my 99 3.4 I too have had an intermittent misfire in the last few days showing a code for misfire on cyl #3. Since the truck has new plugs, wires and coils within the last week or so I suspected a defective part so I decided to check for spark while it was running (while missing) I pulled cyl #3 off and it sparks no problem.

I then pulled the plug and rechecked the plug fires.

I should mention that the problem is (so far) isolated to hot re-starts and never on a cold start.

Even from the start, a bad injector was in the back of my mind so my next step will be to swap the injector to a different hole and see if the misfire follows it.

With all the threads I have read on injectors failing in these motors I will not be surprised.

I'll most likely order a set of remans that has been flow tested/cleaned etc.

yeah I drive mine between 150/200 miles per day 4 or 5 days a week, and with over 260K on poor little Squirt I'm not surprised she's decided to cough up an injector.

 

[angus]

OK, so I just changed the injector and then I ran it around the block a few times.

Shut it off for about 10 min and restarted it - no problem.

I'll keep an eye on it over the next few days and see if it moves to cyl #1 (I swapped #1 and #3)

 

[rocyizhen]

I will definitely check the sensors and clean everything this weekend

 

[mako88sb]

I've been having a somewhat similar situation with my 97 4Runner except it only happens at start-up when we get some rain or wet snow. It doesn't happen every time either. When it does, it runs pretty rough until it's warmed up considerably. Any help would be greatly appreciated.

 

[bama16]

I put new injectors in and replaced my valve cover gaskets while in there.... My issue is fixed with new injectors.... Never did throw a CEL...... Glad it's finally fixed though!

 

[Squirt]

awesome man...!
glad you got it taken care of...

 

[angus]

I've been having a somewhat similar situation with my 97 4Runner except it only happens at start-up when we get some rain or wet snow. It doesn't happen every time either. When it does, it runs pretty rough until it's warmed up considerably. Any help would be greatly appreciated.

First thing would be to isolate it to the cyl or cyls. (OBDII scanner is handy here) and then you can diagnose from there.

So say it's #3 - you can then check for spark at the wire first then at the plug (only WHILE it's misfiring).

If you have established that it is not the spark, you can then swap the injector with another cylinder that is not misfiring. If the problem then goes to that cylinder you then know it's the injector.

This is what I have done but the problem had not happened again (yet) - the thing is I already determined that it has a good spark so I am going to replace my injectors with a set that has been cleaned and balanced anyway.

 

[ekgguy]

I am going to work on it this weekend, and I will change the coils to see if that makes a difference.

 

[Jhelms]

With injectors, when they get old and or dirty - they can get sticky causing the issue you had. When you flow test them, at idle / low flow it is amazing how far off they can be from one another. Generally as flow rate goes up - they average out better and the miss or rough running goes away.

An example - subaru's with side feeds like my outback xt - they generally do not have a fuel filter (piss poor design). Just a fuel sock in the tank so by 100K miles, the injectors are a nasty mess. Get them tested and serviced / back flushed and refurbed. Usually costs about $15-$20 per injector. It can take an ugly idle / missing engine to running like glass. Mine were off over 10.5% at idle between each-other. Was like 13.5 vs. 15cc. After service they all measured 15cc and idle was perfect.

I have a spare set of injectors coming in Monday or Tuesday that I am going to have AUS injectors here in Tempe Az service. They have done great work for me before. I have to replace valve cover gaskets, check clearances, timing belt and loads of other maintenance so figure while I am in there, will get them done. Will also have the spare set serviced so may toss them for sale on here if all is good with them.

 

[mako88sb]

First thing would be to isolate it to the cyl or cyls. (OBDII scanner is handy here) and then you can diagnose from there.

So say it's #3 - you can then check for spark at the wire first then at the plug (only WHILE it's misfiring).

If you have established that it is not the spark, you can then swap the injector with another cylinder that is not misfiring. If the problem then goes to that cylinder you then know it's the injector.

This is what I have done but the problem had not happened again (yet) - the thing is I already determined that it has a good spark so I am going to replace my injectors with a set that has been cleaned and balanced anyway.

Thanks for the help. I'll have to pick up a scanner today and see whats up. I've been checking some videos on fuel injectors and found this:

https://www.youtube.com/watch?v=rUUgR94drxg

Seems like a great idea. I'm not sure what you mean about balanced?

 

[angus]

Well today my problem got a whole lot worse.

Went out to buy a new phone and my friend (also an experienced mechanic) came along for the ride, along the way we chatted about my supercharger and tuning it etc. and I also mentioned that I have a bad injector...

Wouldn't you know it, when we got back to the truck after buying the phone the thing fired up and was missing.

Since I told him about what was going on with it (it was only on hot re-start) and that I'd swapped coils and plugs from one hole to the other and the problem stayed with the same cylinder - he suggested we tap on the injector to see if it would go - so we went back to my shop and I tapped with a screwdriver - no luck.

Then I had an idea - if it only misfires on a hot restart - HOW ABOUT SOME COLD SPRAY???

Well I got a can of duster spray out of the office and gave it a good (upside down) shot - about a 5-10 second burst.

You wouldn't believe the look on his face when it fired up smooth as silk!!

So I guess until I get my injectors in the next couple days, I'll be riding around with the can of air on the truck...

We also debated about why it does it hot and came up with a few theories.