I have a 1999 Tacoma 3.4l that has had a miss for quite awhile now. Plugs and wires have been replaced with no change. Just went for a ride with the local mechanic who hooked up with an anylizer and found that one bank of cylinders is the source of misfire, Cylinders 1,3,5 with number 3 being a little worse than the others. No check engine light has ever come on.
It is worse after startup but will still miss on occasion when completly warm. Idles fine and cruises generally OK, but under heavy load or a little behind the power curve it breaks down badly.
Anyone else with similiar problems or solutions.
Thanks Dave

 

The 3.4 has a nasty flat spot in the power band between 2800 and 3200 rpm, very noticable under load. A clean MAF reduces this flat spot, but its still there.

That being said, the OBDII ECU will detect real misses and light the CEL. Perhaps you CEL lamp is burned out. You should plug in an OBDII scanner and see if any codes are being thrown.

 

Sounds like a bad coil pack to me...

 

Hi
Thanks for the responses,
The cel works when starting so it should work during a malfunction. And if it were a coil pack, then I wouldn't think that I would get a miss in cylinders 1 and 5 along with 3.
Dave

 

Test the coil packs and let me know what you get.

 

Hi Christian
Finally able to check the coil packs
#1 Prim 1.2 ohms
#1 Sec 12.9 K ohms

#3 Prim 1.1 ohms
#3 Sec. 12.9 k ohms

#5 Prim 1.1 ohms
#5 Sec 12.5 k ohms
All are original Densos.
I did notice thou that other than the resistence of the rubber boot going on and off there is no definitive snap or click as the coil is put back on the spark plug. This is the same for the wires running to the other side. There is the little springs inside the boot in all.
Just an observation.
On other systems there has always been a nice snap telling you that the boot was firmly contacting the plug.
Dave

 

Off the top of my head, that looks normal. However, I do not have the FSM in front of me. Let me FW this to Jamie. I bet he would know.

As for the "snap," I know what you are talking about. And to be honest, I don't get a defined snap either.

Let's see what Jamie says...

 

I don't have the FSM in front of but those look fine to me.
You need the resistance to be significantly out of whack (in relation to the others) for it to be defective that way.
Usually this does not mean that it can't be defective from grounding out and should be check as well.
Bad plug wires can also look like a bad coil (a look at the spark plugs will tell you it is the coil...ie both plugs on the same coil look bad).

Be sure to test the coil packs to ensure there is no grounding between the primary and secondary.

 

Have you had your timing belt done lately?
If an entire bank of cylinders is misfiring I doubt it is the coils....look for something else. Make sure to do a compression check, also check the Cam and Crank sensors to be sure the magnets are still there (sometimes the magnet can crack and cause a misfire). I would check the timing belt for alignment first because that would certainly cause a misfire and loss of power if the cam gear for that bank was off (3 cylinders in a row should tell you something about where to look).

 

Hi everyone
Looks like I have found the problem that has been plaguing me for over a year. Just to recap, the reason that I replaced the spark plugs and then wires was because of the misfire that I was experiencing. Then recently because it was getting worse I decided to make a greater effort to find the source. I followed all the sugestions posted to my original posting.
Coil resistence, coil grounding, compression checking, engine scanning, MAF sensor cleanig, throttle body cleaning, all came up with no signs of trouble. So before I took it into Toyota I figured that I might aswell start from the very beginning and put back in brand new OEM Denso spark plugs. I had put in Bosch Platinum plugs after the original plugs.
Well, it was obvious just from the start up that something was different, then after the drive up and down hills and highway, I was convinced that I had found the problem. It pulled perfectly with no miss or hesitation all the way through the power band,which it hadn't done for a long time.
I never would have thought that after putting in new plugs and then experiencing the same misfire that the plugs were faulty or incompatible.
Something to be said for OEM parts I guess.
I would like to thank all of those that responed.
Cheers
Dave

 

Did not know you had the Bosch Platinums (I assumed you had the NGK's or Denso's). Those plugs are definately a no,no for Toyota engines (and for most Jap engines for that matter).....although some have had luck with them. I am not surprised in the least if it was the plugs. Lesson is to always use OEM parts (I have learned this myself the hard way too!). Glad to hear you got it fixed.

 

I have a 96 4runner v6 3.4l... I've been having a miss when I get around 55mph and it seems to be getting worse. I put new plugs and wires about 4 months ago. new fuel filter, cleaned the air filter. .. Still missing. If I remember correctly my plugs are bosch also. Could this be my problem? There is no codes popping up and I'm just not sure cause it mainly happens around 55-60mph. I dont understand why it would happen the most at that speed. Any advice whatsoever would be extremely helpful because I'm lost. Thank you

 

Welcome to YT! Thanks for searching.

You should definitely take out the Bosch plugs, and replace them with OEM Denso, or NGK plugs. You can get the NGK's at most any parts store. Part # 3967 (BKR5EKB-11). These plugs should be replaced about every 30k miles. Don't waste your money on any other plugs, like iridium. laser platinum, etc. The stock resistor plug will work the best for your engine.

Also, what kind of plug wires do you have now?

Other simple maintenance items would be... Cleaning your MAF sensor, throttle body, and using some good fuel additive (I prefer Lucas).

Good luck.

 

I also was told a K&n air filter could foul up the air flow sensor? Any thoughts? Btw, this site is amazing. I'm no mechanic but this site had answered so many questions I've had and been so helpful. So far I've done rear axle seals, bearings, valve cover gaskets, tie rods and tune up. All with no knowledge or experience thanks to this site. I've never found anything so helpful. Thank you all very much

 

is a fuel additive safe to use on a old engine? Mine has 253000 on it.

 

I have NGK plugs but my wires are "belden" Idk?

 

Yes...too much oil on the K&N can cause the MAF to get coated with the filter oil. There are threads here on cleaning the MAF....

 

Ive also heard that extended use could foul it up so swap to aem dry glow cone if u have there a k&n intake system

 

I had a burnt plug, I looked it up and it says there could have been a crack in the ceramic and messed it up. Also I was told could be a bad injector that burnt it.... Changed the plugs and running great. thank you for the help :-)