I have a 90 4runner with a 3vze. It has been running rough for a while and I am tired of it. When I unplug cylinder #3, nothing changes. it is getting a spark but not firing. I also pulled plug #3 (new) and it is already black.looks burnt. Is it a burnt valve?

Any advice would be appreciated.Thanks.

 

Do a search for Compression Check.. That will put you in the right direction.

 

I would start with a compression check as well but it could also be a plugged injector. I had that happen to one cylinder on my 22RE.

 

I think i will send the fuel injectors in to WitchHunter to be cleaned and see what that does.

Edit: I went ahead and bought 6 new injectors and put them in and still nothing from cylinder #3. It also has a new distributor cap and rotor. Could it just be that plug wire? Please help!!

 

I have a 93 fourrunner V6 and mine has recently started running rough when in gear. I replaced the intake tube because it ripped and I heard that could make it run rough. my next step is to get a complete tune-up. I have put 70,000 miles on it and have only replaced the plugs before.

 

injector or possibly a blown head gasket. could be blown between two cylinders therfor losing compresion. take of your air filter hose and see if it blows back out when it misses

 

When my headgasket went, it was pouring out white smoke out of my tailpipe, so hopefully that is not your issue...... My is not running right either and I am putting new cap and rotor on and new plugs tonight. The toyota dealer told me to hold off on the wires, since the cap and rotor spark off of eachother, it may not be them, which is good because they are 104.00 for the dealer ones, dont want to mess with the after market.

 

Replace the ignition wire to #3. Its likely that part or a mechanical problem with #3. Those engines habitually burn and pit the exhaust valves. Happens as the valve clearances are reduced over time. Toyota recommends the valves clearances be checked and adjusted on a regular schedule to prevent this problem. Unfortunately, adjusting the valves is a time consuming, read expensive, and royal pain in the a$$. May also be the head gasket. Have a radiator shop test the coolant for signs of CO.

When troubleshooting, start with the easy/cheap option and work your way up if you are doing the "replace parts until fixed" route.

My $0.02

 

Update: cylinders #3 and 4 have no compression.