mastacox

So I've been having a very annoying problem the past couple of weeks that I want to get tracked down with my 4Runner. It's a 1998 Toyota 4Runner SR5 V-6 Supercharged w/ URD fuel kit for those that don't know. Have been running premium gas with cheapo-octane booster every tank for about 2 months, and haven't gotten any kind of check engine lights since I started using the octane booster (which is quite rare for a supercharged/URD'd 3.4l). I figure my tune is pretty well dialed in for the summer temps I've been seeing.

About a month ago, my engine started to display an intermittent power surging, where when I went into boost the engine would have good power, and then stumble/lose power for a fraction of a second, and then regain it. The "stumbles" were approximately equally spaced, and similar in length. From what I could tell, it would only happen in boost, starting at about 1psi on the gauge. This problem got progressively worse, until about 2 weeks ago going into boost the engine would just bog and make less power than in vacuum.

Strange thing is, this cannot be attributed to a fuel delivery problem because the AFR stays completely normal at or around 14.7 in very low boost, and 11.5-12.0 in the mid to higher boost range when the oxygen sensor calibrator kicks in (but before open-loop, for those of you that know what I'm talking about). Changing from 14.7:1 AFR to 12.0:1 AFR by pushing more boost did not make any difference in power or "hesitating." I have a permanently-installed AFR gauge on my a-pillar, so I have been monitoring AFR ratios in my engine ever since I installed the URD kit almost a year ago now. When the engine would "hesitate/bog" there was NO change in AFR reading. So, I'm thinking it's ignition or timing related, maybe my spark plugs are fouled/over-gapped/something.

So I took the spark plugs out, and they were all uniformly dry, and all had a light red coating on them. It was kind of like the dry white/gray coating you see on a normally used spark plug, except these had a slight red hue to them. I'm thinking this may be due to the cheap octane booster I have been using for the last 1.5-2 months, which comes in a bright red plastic bottle. They also had some carbon build-up which I attribute to my tuning the engine early on, when I would end up running too rich for extended periods of time. The red coloration isn't from leaking coolant/anti-freeze (IMO) because I'm using Prestone Dex-Cool which is bright orange in color, and all of the spark plugs look exactly the same.

Anyway I cleaned all of the plugs with a brass wire brush, and re-gapped then to .034". After cleaning the plugs, I put them back in, and have run a can of Seafoam in the tank for the last 2 tanks; this seems to have significantly helped the problem, but not eliminated it. On cold start-ups the engine will surge/bog/hesitate under boost, and once warmed up the problem is "better" but not gone, I can feel some slight jumping/hesitating under boost and WOT doesn't seem to have the power it used to until I get very high in the rpm's.

I'm thinking that my spark plugs are "fouled" and need to be replaced, and I need to do an aggressive seafoam treatment to help get rid of any carbon build-up in my cylinders from the rich tuning process. It sucks though, because I just changed my oil about 2 months ago (Amsoil W2000 0-W30). At about $70 a pop, I don't want to change my oil again if I don't have to (the oil should be good for 1 year/15,000 miles) I would also like to avoid fouling my oxygen sensor, since it has been working fine (I have confirmed that with my AFR gauge as well).

Anyway, this post has gotten way too long, but I'd like to hear a few more opinions to make sure I "seem" to be on the right track. Lemme know.

EDIT: Spark plugs are Denso Iridium IK-22's, which is why I tried "cleaning" them first. Have to order them, they're not cheap, and they're less than a year old.

terryjmatthew

Are you using the TRD one-way check valve? I had a similar problem prior to installing it.

mastacox

What? I've never heard of this valve... Where does it go and what does it do?

terryjmatthew

From Gadget Online:

The most common installation errors are miss routing vacuum lines, specifically the power steering idle up line and the 4x4 vacuum supply line so pay specific attention to those. The next most common error is not properly installing the throttle body gasket. Putting it in backwards will cause a check engine light in a short period of time showing a lean code. Make sure you use the gasket that comes in the kit and make sure it is in the right way. Lastly, it seems that many dealers forget to install the check valve in the air assist line. This prevents boost pressure from back flowing through the air passages in the fuel injector tip and back out toward the throttle body. This can take needed fuel with it preventing it from being injected into the engine under boost. Make real sure that the check valve is installed in the air assist line and in the proper direction.

On my 01 the air assist line is the only vacuum line running to the throttle body.

http://www.sporttruck.com/howto/58878/photo_08.html

terryjmatthew

Any news?

playswithfire

Mastacox:
Check the connections where the plug wires attach to the coilpaks for corrosion (this was my problem a while back when I was having the same symptoms). Also, try testing your coilpaks and plug wires with an ohm meter to see if they are within specs.
Good luck.