Sure hope you guys can help. I’ve got a ’91 4Runner V6 auto that has developed a bad miss that I can’t find. I have changed the plugs and plug wires, distributor cap and tried several other attempts but can’t find the cause. It has very low power, but when run about 1500 RPM with no load it runs smooth with no miss. This 4Runner has a lot of miles on it but it has been well maintained. With this limited information I’ve given you, you guys got any suggestions what could be the cause. Thanks for any help……….

 

Wheeler....
Try replacing the fuel filter. I here its a pain to change out.
My Gmc Yukon was doing the same thing until i replaced the fuel filter and it made a huge difference.

Also think about having your injectors cleaned.
I think the dealer charges around $125. I'm going to have mine cleaned next week on my '88. A friend has his own kit which we can take our time and do it right.

 

Welcome to the forum Wheeler.
As Todd mentioned, the injectors could be very dirty.

Sometimes they get to the point where injector cleaner you put in the tank will not help.
Then you have to get it done professionally.

As Todd stated, some dealers can do the method where they disconnect the fuel line and run the rig on the cleaner solution.

Also some carb/injector shops have a better service that uses a machine by Snap On tools that also runs the rig on a solution for 30 minutes.
It cleans the fuel rails, upper chamber, and the injectors of carbon buildup.
It also goes for around $125 at shops.

Either way is worth looking into.
Mine where done the very expensive way.
The dealer pulled my injectors and sent them out to a shop to be ultrasound cleaned and tested.

That is the ultimate way to have the injectors cleaned as they also inspect the casings on them, and current test them.
But it also runs about $500 :eek:

Here is my flow test chart from the
job.

It clearly shows I had trouble in a few injectors.
My rig was running very bad at the time.

 

Dont forget the possible bad cylinder or valve. Run a compression check on it before you do the other things. I got a compression guage from sears for about 20 to 30 bucks, pulled the plugs and tried it out. I tested the one I suspected first and that was it. Normal should be about 160 to 170. My bad one was 30. I found the suspect one by pulling the plug wires one at a time. If it idled worse than before, then Id put that wire back on and go to the next. I would shut the engine off, pull the wire, then crank it up again. did not want to get bit. I finally found one that did not make any difference at idle if it was plugged up or not. that was the bad cylinder. valve job fixed it.

 

Looks like this one is ready for a major rebuild as the problem seems to be a serious one. Thanks to you all you have been much help..............great forum.........

 

That also sounds like a vacuum leak, check your hoses. My 90 4Runner had a cracked intake hose to the throttle body. Gave me erratic idle and a miss. The crack was on the underside of the hose too, so it wasn't readily visible.
One other suggestion is to have a trusted mechanic look at it. Could be a relatively simple repair.
Good luck

 

You are right. We did find the the intake tube cracked on the bottom side were the clamp attaches it to the intake. It has been cracked for a long time as the inside of the intake is really coated bad with oil and dirt were it entered thru the cracked tube. It don't look good. Thanks much for the reply..........

 

Thought you guys might be interested in knowing what we found. We run a compression check and the results were:
No. 1 cyl.=80 psi, #2=60psi, #3=80psi, #4=60psi, #5=85psi, #6=zero. The cause was the cracked air intake tube which allowed dirt and oil in. The air intake housing and manifold was coated with oil and gum. We have parked it in the garage til we decide what to do with it.........thanks again..........

Check your air intake tube if you haven't already...........

 

Whole new engine for sure. With the dirt getting in that far I bet its toasted most all the bearings and journals. Sorry to hear it.

 

We checked your pics out on webshots you got a real good looking runner there. Wish I could say the same about ours. Looks like we will make a winter project out of it.....


://community.webshots.com/user/matt2799 take a look at a few four wheeler pics..........