SunFox

My first post, so bear with me. I have a 1990 4runner 3.0 automatic I bought a year ago. My wife's kid had the truck for about a year and when it came back home it was running sluggish and had terrible fuel consumption. I checked and found the #5 cylinder had no compression; put a bunch of solvents and additives in and I now have compression, but weak. The engine misses up until about 2500 rpm then smooths out, but even over that engine speed the vehicle cannot climb hills or tow even a light trailer, and has to be going downhill for the overdrive to kick in. Gas mileage is an unfortunate 11 mpg - had a full-size Dodge V8 magnum that got better than that. I've had it suggested that I may want a valve job done, but I also ran into a shop which could get me a rebuilt 3.0 at a very reasonable price (still, it's about 3x the cost of the valve job). The vehicle has only 120K on the clock, so I'm thinking the valve job may do the trick (worked for a friend of mine with a '94 Toyota pickup w/3.0). It shouldn't be ready to die at 120K - it's a Toyota! Any opinions? Is there anything else that could be wrong besides the valves? And is anything I do to this rig going to help the lack of power, which the 3.0 is famous for? Thanks.

rdharper

There are some real experts on this forum. But until they chime in, I'll take a shot.

The 3L V6 is famous for HG problems. Long story to do with asbestos taken out of gaskets etc. Anyway, although its probably been done in that rig early on, it is still the best bet.

You didn't mention if you were losing coolant, or overheating, so I assume neither.

The appropriate first test is a compression test, or better, a leakdown test.
Chase down how much difference their is in that #5 cyliner. The leakdown can give you more specific information as to the source of a compression problem.

oilcooler

since this board made me aware of a recall, i will tell you that you should call toyota and give them the VIN. there may be a recall on that engine or at least on a steering component (i forgot which component).

anyhows, toyota replaced the steering component, short block and heads my family's 90 4runner under some of these recalls. ironically, the engine had 180K miles and was running great. but now, i basically have a new engine!

the number is located on the first sticky (i think it is the first one) or call your local dealer.

Radyota

Yup, recall for the steering relay rod Campaign #50N replaces that part on 4x4's. There's a long thread on it stickied on the '86-'95 trucks and 4Runners section. Don't be afraid to use the yellow blinking "search" button at the top of the page.

Now for your engine: yes, that sounds like a burnt exhaust valve. These 3.0's are known for blowing headgaskets and burning exhaust valves, particularly cylinders 5 and 6. The cause is the poorly-designed exhaust crossover pipe and manifolds. It can also be attributed to not keeping the valve clearances adjusted, which should be done every 60,000 miles. There are 3 things you can replace to make this engine better and more durable.

1) Head gasket - Don't use Fel-Pro. I've had good luck with factory Toyota updated headgaskets, but others like Victor NitroSeals from CarQuest or The Rock gasket that Engnbldr includes in his kits are also exceptional.

2) Head bolts - The factory headbolts are a one use only, torque-to-yield type fastener that shouldn't be reused. Studs are stronger but more expensive, and the factory bolts are also expensive. DOA studs are of poor quality and are known to break, so I'd avoid those. Once again, Engnbldr has come thru with his newly-developed, REUSABLE head bolts that are stronger and cheaper than the factory bolts. He also recommends torquing the head bolts down in many repeated steps before applying the final torque to create consistant clamping pressure across the whole head.

3) Exhaust - Get rid of the exhaust crossover pipe that connects the 2 exhaust manifolds. It dumps all of the heat from the passenger side of the engine into the driver's side manifold right at cylinder #6, burning the valve. The factory exhaust is also restrictive at this point, limiting power. The easy fix is to replace it all with a pair of headers from Downey Off-Road. Some like to have a custom crossover pipe for the headers fabbed up at their local exhaust place because the Downey one doesn't fit very well. You might be able to get by with the factory exhaust if you have the exhaust valve clearances set to the maximum clearance. The engine will tick louder, but it will save the valves if you keep the factory exhaust and check/adjust the valve clearances every 50-60,000 miles.

Hope that gives you a nice overview of what to look at. My truck started doing the same thing, and got worse and worse. I went from 17-18 mpg down to 14mpg and then to 10-11mpg and a top speed of 45mph. 5th gear was useless. Tore the engine down and all of the exhaust valves were shot! Only 1 could be reground and reused. Oh, and as long as the engine is apart, it wouldn't be a bad idea to replace the water pump, timing belt and all of it's idler/tensioner pulleys and also the knock sensor wire. Hope that helps, and good luck!

SunFox

Guys, thanks for your input. I had the recall on the steering taken care of, and when I called about the head recall, the dealership said the original owner had it done already. So no free head gaskets et al (damn, was hoping...). I am not losing coolant or having any other funky stuff going on, just the signs of one or more bad valves, like #5, or maybe all of them. I'll be "rich" this fall, so that'll be when I make the decision, but I'm thinking maybe the valve job and keep the engine.

Radyota, thanks much for all the additional suggestions. I'll do what I can.