Bad misfire after tune up
 

I had spent the last three weeks preparing the truck (84 4runner , 22r with an upgraded cam, 38 weber, exhaust mods) for a trip to Big Bend. Most of my time was spent upgrading the brakes and putting a new steering gearbox in. When I was finished with the brakes and gearbox, I changed the oil and spark plugs, and then my real problems began. It went from running like a bat out of hell to barely starting, missing and couldn't idle.
I checked all the plug wires, rechecked the gaps, and still the same. It was cylinder #4 that was almost dead. If I pulled the plug at the distributor, it ran the same. On close inspection of the wires, #4 was burnt and the resistance was low, so I ordered a new set of NGK wires just to be sure. Oh, and I am using the NGK Vpower plugs. Put the new wires on, there was a slight improvement, but you could still hear the miss. My truck sounds like chitty chitty bang bang:(
I went to a trusted mechanic, to have a compression test done and have a trained set of eyes on it. Here are the results:
#1-140, #2 & #3-120, #4-100.
I was shocked. They adjusted the timing and it runs now and idles, but its like night and day compared to how it ran before my tune up.
When I changed the oil, the oil looked dark, but not milk shake like. The coolant looks clean, but under the oil cap there was a whitish residue(Head gasket or just condensation?)

Any thoughts on what could have caused the loss of performance/compression?
I can hear the miss at idle and while driving.

I was hoping that it was some dumb rookie mistake on my part, but I am fearing the worst.
Chime in if anyone has some ideas.

Thanks !

Did you check your coolant level? I killed my head after doing a flush. It seems that the PO never really changed the coolant and when it was low he would add the green stuff. My head has major issues - unusable. It was #4 where the head failed causing the HG leak. I could really smell it in my exhaust and the truck was drinking coolant.

I hope it is something simple... the pic of your Runner looks nice. I like that color and that is one of my favorite years.

oil cap is mostly condensation, i see this all the time with new cars that dont get driven much.

might just need a valve adjustment but if it ran good before and all you did was a simple tune up. i dont see what could have gone wrong. unless you done something else even if its something small or big but you think its not related. it might be the cause. you sure u havent done anything else.

also make sure your wires are not touching anything that gets super hot. check them again and make sure none of the are arcing. have you tired to pull the plug wires to see if #4 is still not working?

CGeorge,
The coolant level is good, and I use the red stuff. I had mild overheating problems when I bought the truck back 2.5 years ago. It ended up being the fan clutch and I flushed the system them.
Toyotech,
Your line of reasoning is what I have been dealing with and running through my head. The only other thing I did that morning was clean the carb with carb cleaner and clean out the PVC filter( the po just has a small K&N filter on the valve cover).
I am going to look at the old plugs and see if I can maybe see a pattern in how they look.
Is it possible that I knocked a piece of crud into the spark plug hole and that started all of my problems and the burnt wire was just coincidental to the actual cause? Would a piece of dirt cause a valve to be stuck?

Yeah I have the wires running so that none of them touch either other or anything except the wire guides.

New info...thoughts
 

OK yota mechanics, does this sound feasible?:
Question: Will a bad vacuum leak affect all cylinders or will it affect the one closest to the leak?
Info:
Before doing the plugs and oil, and then noticing the problems, I did upgrade the brake system. In doing so, I swapped in a brake booster and MC as well. The booster had to be ground down to stop rubbing the steering shaft.
In working on the brakes, I obviously had to disconnect and reconnect the old and new booster vac lines. This is right next to the bad cylinder. If I have a damaged booster from modifying it, would that cause a vac leak that would affect #4 more than the others? Remember, my compression numbers were 140, 120, 120, and 100.

Thanks again!

If you have a vacuum leak, I am sure it isn't helping anything.

+1 if you have vacuum leak, get that fixed 1st. compression test isnt affect from a vacuum leak (i dont think)
the vacuum leak is gonna effect how the entire engine runs not just one.
might do a leak down test and see if its leaking past the intake valves, exhaust valves, rings, or head gasket.

you can clamp or plug the hose from the booster to engine and see if it gets better. if so they you have a leak

Yeah, I spent some time doing all of the minimally invasive diagnostic tests I could and learned a butt load on how vacuum/compression/and misfires are related.

I found this to be helpful for any novices like me that are reading:
http://www.aa1car.com/library/vacleak.htm
and this one:
http://dodgeram.org/tech/gas/Trouble/miss_diagnosis.htm

I found a few small vac leaks, but I think the booster and the vac line to it are fine. I had some leaks around the base of the carb so I tightened those bolts up. I replaced one section of vac line that was brittle, and it's idling much better, but something is still wrong.

In that second link, the writer mentions taking off the air cleaner and manually choking the carb by covering the throat with your gloved hand to see if the throttle increases or decreases. When I do that, my engine speed increases, so according to that link, I still have a vac leak.

I am going to try a few more things tomorrow, but its freaking cold for TX right now. Its 26 degrees! I know its nothing for you Northern guys, but I can't work outside for that long even with my Mr. Heater next to me..I am wuss when it comes to cold.

26 degrees is the perfect working temp! I was out working on my little Mazda today when it was -43 degrees. Now that's fun!

brrrrrrrrrrrrrrrrrr. Actually, the weather might have something to do with it running like poop. The last time it had problems was a year ago when we had a cold snap and the misfiring came on during the cold also.

You are a brave man for working on your truck in sub zero.

I dug out some old notes on what the previous owner did when he put in a rebuilt engine. I know that the engine is an ATK and has less than 30K on it now and that he put a performance cam, headers and 2 1/4" or 2 1/2" exhaust with no cat in when he did the rebuild. As stated earlier, its fed by a Weber 38 through fuel filter and regulator. It was a very strong engine until recently.

After researching some rebuilds, I am reading about valves and valve springs going bad prematurely if they are not matched to the cam so I emailed him to see if he remembers what he did and didn't do.

Any experience with ATK engines? quality stuff? Will valves fail early if they are not upgraded with the cam?

Thanks again. I am going back out tonight to mess with some vac tubes.

have you checked your valves to see if they need to be adjusted? Doesn't take to long to adjust them, 30 minute job :)

No, I haven't but its probably my next step in the my wrenching progression.

I am going to try and clean up the weber and at the same time get into the valves since that seems like a definite possibility.

I have been running it how the PO owner had it setup and have only tweaked a few things under the hood. I either have a fuel leak with the fuel pump (its a 22r so its not in the tank) or a fuel line coming from it. I found that before I went to work so something to look into tomorrow.

I am going to replace:
cap and rotor, even though they only have a few thousand miles on them
fuel pump
weber adapter plate to the one piece...if I can find one

replace some vac and fuel lines
adjust valves...got my hands full now!

those all sound like a good plan of attack.. keep us posted!

soooooooo.... I went to a mechanic that is known around here as a land cruiser specialist, but is good with all toyota 4wd models. We spent about an hour or more looking at different things and running quick checks. The vacuum checks out fine, my fuel pressure is good, but I do need to get a new fuel pump, and then we take it out for a test drive. He's amazed at how much power it still has, and thinks that the tick I am hearing is an exhaust leak, possibly on the manifold next to the #4 cylinder.
We pull back in and we start looking at the temp of some of the fuel lines, and we agree that I could route them to a better location, but then he notices that the spark plugs don't look completely seated.
The sad truth comes out.
When I did the spark plug change, I would feel resistance too soon while threading them, so I would back them out and try again and again until I got them to thread in smoothly. However, the threads in the hole were probably on their last legs.
When I had the compression test done, that shop probably cross threaded the compression gauge and then again when reinstalling the spark plugs. The only one that now seats correctly is #1. The rest were barely threaded in.
It's upsetting, but I think I cross threaded cyl #4 at one point and that lead to my initial problems.

There is a tool that will allow them to rethread it, but its expensive and it may not reach cyl #4. If it doesn't, then the head needs to come off and it will be retapped from the inside out and alleviate any shavings falling in.

If we have to take off the head, I am going to have some other items done at the same time, but it also made me start thinking about doing a 20r head swap so I am researching that too.

Anybody with an experience like this with some advice, I am all ears.

not to expensive.

http://www.google.com/products?hl=en...ed=0CCMQrQQwAg

I had to repair the threads for one of my plugs when I had the head off. I should have also installed heli-coils on all of the header studs while I had it off. I still have to install 2 more, one of them being the very back stud. Not to easy with the head installed.

I think the tool they need to buy will allow you to retap/chase the spark plug hole without having to take off the head. If they have to take off the head, then they can tap/rethread from the inside out and they indicated that doing that would not be a problem.

Now that I have been reading about the advantages of the 20R swap, I am kind of liking the idea if my engine block is the right style.

It was good to have a new set of eyes and a new perspective on my rig. In the hour or so that I was there, he figured out why I have so much body roll, showed me a better way to mount my shocks, and of course, found the problem that brought me there in the first place.

those tools i linked you are ment to be done with head installed. i dont see any reason why you would have to remove the head to retap them. i done it before on other size toyota engines before. once you tap it. all you need to do its get a long air nozzle
and spray out what you can. the metal is so fine that it will just burn up

http://www.supermaster.com.tw/produc...20gun-2(1).jpg

maybe i need to go see a 22r before i say you can lol