Diagnosing The 3VZE
I have a poor running 3vze. It starts like a champ, but it is very weak under load. Under load it is barely even responsive to the throttle until fully warmed up. With no load though it sounds alright. The main diagnostic points are:
1. Low vacuum: 12 " at idle or any steady rpm.
2. uneven compression: #1=170 psi, #2= 140 psi, #3= 170 psi, #4= 160 psi, #5= 175 psi, #6= 160 psi
3. diagnostic code #25 (lean fuel condition)
I have done the following:
1. new cap & rotor
2. checked timing: 12 deg. btdc
3. tested spark plug/coil wires: range 3k ohms - 16k ohms
4. compression test. (see list above)
5. spark plugs: look newer, light tan
6. checked air flow meter (AFM): ohms ok at specified points, air temp sensor ok
7. checked and adjusted throttle body
8. checked and adjusted throttle position sensor (TPS)
9. checked for vacuum leaks: looked for disconnected hoses, I blocked suspect vac lines to test for leaks down stream, eg.,PCV, Brake Booster, etc.
10. tested EGR: EGR not leaking vacuum.
I was getting a reading of 15" of vac at idle until I worked on the throttle body. I found that the throttle valve was cracked open a small amount because of maladjustment at the stop screw. I backed off the screw until the throttle valve was fully closed. Then I adjusted the TPS to the specified settings. After that my manifold vac was running around 12"! I also checked for vacuum leaks by spraying starting fluid (ether) around major vacuum and intake hoses and under the intake plenum. I am able to bring the vac up a few inches by advancing the timing to the maximum allowed by the adjusting slot on the distributor base, but that gets it to something like 30 deg, btdc!
This engine has 180k miles and had a head gasket job just before I bought it. The job was done by students at the local high school vo-tech shop. The only thing I found obviously wrong with the work on the engine so far is the throttle valve adjustment issue. The 140 psi cylinder reading is troubling, but I don't if it explains the low vac reading. A bad intake valve could screw up the manifold vac, but I think I'd see the needle on vac gauge jumping around a bit if that was the case.
Another reason for low vacuum can be valve timing, so I'm thinking maybe the lads at the high school may have gotten one of the cams a tooth off on the timing belt. Maybe that even explains the fact that all of the driver's side cylinders (except #2) are reading uniformly lower compression than the passenger side cylinders. Anyway, I'm eager to read what other troubleshooting, diagnostic minded yota brains think.
Here are some jobs I'm contemplating attacking next:
1. get the timing belt cover off to take a look at the cam timing.
2. do a cylinder leak-down test generally, and to check out #2, the cylinder with 140 psi compression.
3. pull off the intake plenum to redo all the intake gaskets
4. retorque the head bolts
5. check the valve clearances
6. test the fuel pressure
7. get the injectors rebuilt.
'89 4runner SR5, 3.0, auto (fun)
'93 xtra cab, dlx,3.0, 5spd (work truck)