1997 Toyota Avalon noise, slight misfire, and fuel economy problem

[jremboldt]

Could replacing 120,000 mile old Toyota spark plugs with BOSCH Part # 4301 PLATINUM+2 dual ground spark plugs cause a slight misfire?

I took my 1997 Toyota Avalon XLS to the dealer the other day because it was losing lots of fuel economy, sounded and smelled like it was running rich, and made a considerable amount of noise above 2500 rpm. It was not giving any check engine light or codes.

What their diagnosis was: noise is due to faulty harmonic balancer. Solution: replace entire center pipe for $500, just to get rid of noise. (I don't think I will be having that done ANY time soon)
As to the poor fuel economy, they said it had a slight misfire. They said this was probably because of the Bosch spark-plugs I put in 2000 miles ago, or the plug wires. Not wanting to spend $350 to have them put in new plugs and wires, I bought and installed the wires since they thought that was important after 123K miles. Since I don't know how to detect this "misfire", I can't tell if the wires helped. Any advice on how to detect this myself instead of going 50 miles to the dealer would be appreciated.
They also suggested "top engine cleaning" and "fuel system cleaning" for about $200. I did briefly do some of this myself about a month ago with some cheap fuel system cleaner and a spray can of intake cleaner.
My plan is to run a bunch of seafoam through the intake, and another can through the fuel system.
Any advice/suggestions would be appreciated as I have lost about 25% fuel economy over the past few weeks.

[robcam13]

misfire could be a coil going bad. do you have a check engine light?. did you have the fuel economy problem before the plug and wire change. if not maybe you got a bad set wires. i have run into bad new wires before.

[fourwheeler]

I would replace your plugs with OEM plugs. I have heard of problems using the Bosch plugs in Toyota engines.

[bbenson831]

I'm not too sure of the engine noise without hearing or seeing it myself, but it sounds like you need to do a full tune-up. Start with the cheap fixes first like new plugs, new plug wires, etc. I doubt, but it is very possible, that the coils would be bad. If so try pick n pulls or ebay because for just one of those coils its roughly $120(per coil). Next I would check out your sensors as bad readings from them can bring you down. however, the sensors are also as much as one of the coils as well. If your throwing codes go to a parts house and get a free OBDII reading from them. That should help clarify things a little bit for you. If you want a more pin pointed diagnostic you can pay $70 to have a shop read the code(s).

Let us know how it turns out.

[bbenson831]

sorry didn't fully read your post =x. If you are strapped for cash all that they told you that you needed can be done by yourself.

These are parts house estimated prices:
*do it yourself and save $60-90 per hour in labor fees
*Bosch or NGK plugs are roughly $8-11 per plug for the best ones at a part house and $2-5 per plug for the cheapest
*A nice decent set of plug wires can run you at roughly $35-45(Borg Warner brand)
*Harmonic balancer can run you a nice lump sum of over $100 but still cheaper than the shops prices
* $11 or so can have you throw in some good octane boosters or cleaners to clear up your fuel system also you can take out your injectors yourself and replace the o-rings and clean the injector for chump change and an hour or so of your time.

[pmesfun]

Start with replacing the Bosch plugs with OEM NGK(BKR6EKPB-11)/Denso(PK20TR11) plugs. What brand is the wireset you installed? A NGK wireset is $37.67 @ Amazon.

Amazon

Amazon

[jremboldt]

OK so I took out the spark plugs today and found varying wear on each one, but some of them were noticeably more worn than the Toyota plugs which had served FAR longer. One of them had a bent tip part. I still had one Toyota plug for some reason so I replaced the worst one with that and rotated the others based on wear. The slight misfire (which I had learned to detect) was better when I drove it after that.
I will probably be getting new Toyota spark plugs, since the Bosch ones are dying so quickly. My new Toyota wireset made no noticeable difference, but the old one really looked 14 years old.

I also ran seafoam through the intake system, and insured cleanliness of the MAF sensor. The clean intake system made a little difference, but not the difference I'm looking for.
My fuel economy now is still down quite a bit, but we'll see how the new plugs affect it. Considering that I was still getting good gas mileage when I put in the Bosch plugs, and how it steadily got worse after that, I am guessing it will make a large difference.
I don't know how to reach the coils to check them, but I doubt they are the problem.
If new plugs (and wires and seafoam etc.) don't fix my problem, than I don't know what I'll do, so I'm hoping for the best...

[bbenson831]

Most people do not know or look for it but when you buy spark plugs take some time to look at the way the tips are. Champion brands are notorious for this but it can happen to any of them. By looking at the tips you can see if the area where its gaped is slanted and not straight. That can also mess with the firing of your plugs.

[lubwiz]

In Feb, I changed all spark plugs to denso stuffs. I have a few mechanic friends, they say don't use bosch stuffs for spark plugs. It causes misfire. Anyway, you can see a sticker under the hood. Toyota recommends dual electrode spark plugs for 1MZ-FE engine. I bought denso dual electrode spark plugs at the rockauto site. Also you can change cable for them. I think I paid for $80 for both six spark plugs and distribution cable kit around $100. Denso plugs + NGK cable kit. The pickiest job is taking out the intake manifold. I didn't take out while I change firewall side plugs. I just believed my sense. The car still works fine. Make sure you use some glue for the spark plugs which prevents from leaking vacuum in cylinders. It the vacuum leaking happens your engine will shake a little then the vibration will transfer to handle. The glue is just less than $10 in autozone, advance auto parts, or pepboy. I hope you do it well. Good luck.

[jremboldt]

Well I got the spark plugs replaced with denso plugs from the dealer, and replaced the wiring with whatever brand the dealer uses. While I was at it I replaced the valve cover gaskets, which had been leaking pretty badly. I haven't driven it enough yet to make sure everything is working like new yet, but it seems to be better.

[bob2]

wellll i'm used to being the odd man out. lol

i used bosh irridium (4 electrode) plugs in mine, and it screams! no misfire at all

sea foam is good. lucas oil works better for me in the avvy

[bbenson831]

My god you paid $80 for six denso plugs and $100 for the NGK wires?! You got ripped off! Plugs average around $2-no more than 10 at a parts house per plug and $35-50 for a decent set of nice wires. If you were buying performance I could believe that but you didn't.

[HATEnFATE]

Originally Posted by lubwiz

Make sure you use some glue for the spark plugs which prevents from leaking vacuum in cylinders. It the vacuum leaking happens your engine will shake a little then the vibration will transfer to handle. The glue is just less than $10 in autozone, advance auto parts, or pepboy. I hope you do it well. Good luck.

Glue???

[bob2]

Originally Posted by HATEnFATE

Glue???

yeah - anti-sieze compound .)

[jremboldt]

Yesterday I changed the front valve cover gasket, since I didn't actually have time on Thursday. It ran fine aside from a check engine light caused by my forgetting to plug in an O2 sensor which was hard to see/reach. That was taken car of and then I set about changing the valve cover gasket.

There was quite a bit of sludge, which I scraped out of the valve cover, and I also managed to remove a lot from around the valve system. after cleaning the involved surfaces, I put in the new gasket and put everything back together. It should also be noted that I added a quart of Marvel Mystery oil (oil cleaning treatment).

After about a mile of driving the oil light came on, and when I checked the oil it was still at the same level. I figured it must be an effect of the Marvel Mystery oil. I continued driving and after 5 miles or so the oil light had gone to just a flicker and then was completely gone. As I continued driving the oil light came back, and within 5 more miles I started noticing some hesitation. This quickly got worse until the hesitation was really bad, the check engine light came on and the battery light. At this point I stopped at the side of the interstate, let the engine rest, and checked the oil and coolant (which were fine). I started it up and it seemed fine, except the oil light and check engine light were still on. At this point I just needed to get back home so I drove it at about 50 MPH with my hazard lights on. 5 miles or so later, hesitation returns, joined by a thump/knock in the engine. So I stopped again and turned it off. After letting it set 10 minutes or so and checking the fluid levels again, I turned it back on. The knocking was still there, and seemed to come from the front center of the engine. After checking the spark plug (seemed fine) and a bunch of wiring, I remembered I had another can of seafoam in the trunk. I put in 4-5 fl oz. of this and started it up. withing 15 seconds the check engine light was gone and the knocking as well. the oil light was still there. I drove it home (maybe about 8 miles or so) no more hesitation or sounds until I am almost in the driveway. So for the last 1/4 mile or so the knocking had returned, but no check engine light.

At this point I am not sure what the problem is, but I am guessing it involves sludge in the front side of the engine. Any advice or suggestions are welcome.

Thank God for seafoam!