wrenchtech

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.

-- Matt

tc

Sounds like you need to swing it by the vo-tech so they can practice some diagnostic ... best way for them to learn to do it right is to see what a PITA it is to diagnose it after! LOL

yayfortrees

I would agree, except that I don't know if I would want a bunch of high schoolers touching my vehicle, even if they worked on it before. I wouldn't want them to screw anything else up.

The throttle body adjustments that you have done so far, have all of them been to FSM spec? Is the throttle stop screw also the idle adjustment on the V6? It almost seems like that should be slightly open at idle, but I'm not familiar with that motor. Assuming all of that is correct, it sounds like you're on the right track. I would maybe try the leakdown test before pulling the valve covers, but it would just depend on which was easiest to do.

limon32

I'd replace the O2 sensor, but that low cylinder is not good. Did you do the oil test to see if its rings or valves?

Team420

^ what he said.... also, when you adjusted the throttle stop screw, and tps. did you apply vacuum? In order to set the tps correctly, there needs to be sufficient vacuum....... It seems to me that you must have a vacuum leak..... how are the valve covers? How about the tb gasket, did you replace it, or reuse it? Next I would start to look at the million miles of little vacuum hoses, and then the intake itself, and next on to the plenum/manifold. You cant always find vacuum leaks with the ether test.....so good luck.

wrenchtech

FSM spec yes. The idle is handled by the Auxiliary Air Valve. The throttle plate should be shut when it is on the stop screw per the FSM.

As far as the suggestion that I might have a vacuum leak at the valve covers, I think I eliminated that possibility by disconnecting and blocking the PCV hoses and PCV manifold port.

I think I have my work cut out for me. I just have to keep going down the line and eliminating problems. I'm headed over to Harbor Freight today to buy a leak-down tester They are on sale right now for $29.95!!

I have an extra O2 sensor from my dead '89 4cyl 4runner. I found out that the '89 V6 and 4cyl 4runners share a lot of the same parts, like the TPS and o2 sensor. -- Matt

sb5walker

It's probably a tight exhaust valve, but it's a good idea to run the leakdown test first to see for sure where you're losing compression. If it's the valve, of course check clearances. Hopefully it won't be burnt, but that's a possibility. Checking the cam timing also a good idea. If leakdown points to the valve but none of the valves are out of spec tight and cam timing's okay, then the valve is probably burnt and the head will need to come off to address it. Even if you do find #2 exhaust valve tight, I would re-check compression after adjusting it but before the valve covers go back on.

If the leakdown points to head gasket, then retorquing the bolts is worth a try, but it's tough to get it right with tty bolts. You just have to make your best guess.

If you have the budget, send the injectors to witchhunter while you have the plenum off - it would be good to have them flow tested. But if that's not in the budget, after taking care of the compression issue, pour a bottle of injector cleaner containing polyether amine into the tank. Only two products still have it: Red Line SI-1 Complete Fuel System Cleaner (most PEA) or CRC's "Guaranteed to Pass Emissions Test Formula" (a little less but still decent amount PEA). Or if you have access to the concentrated stuff that goes directly into the rails, even better.

Then see where your mixture stands. If still lean, check the PAIR system; maybe the kids got a vacuum line misrouted. In fact, checking all the vacuum lines would be a good idea, a pita tho. Also check O2 sensor switching, see the fsm. A dirty/corroded O2 sensor connector also could give a lean code, since a lean reading is low voltage. Nothing beats this stuff for cleaning up an electrical connection. And check for exhaust leaks.

Good luck.

thook

A low cylinder would cause low vacuum readings.

If you're able to get the ignition dialed in correctly, then you're not having a problem with the mechanical timing (belt/cam/crank positions)

I'd check those valves.

yotaman85

#2 cylinder valve seals..

wrenchtech

The driver's side cylinder bank is the one with all of the lower readings. The passenger side is excellent. Maybe the driver's side was where the bad head gasket was. Perhaps damage to the valves occured from overheating related to the head gasket issue. I don't know though, I wasn't there I would think that the vacuum gauge would would have an pulsating needle if an intake valve was the issue. If it was an exhaust valve it would have less effect on the vacuum. A leakdown test should provide answers about the valves. I have no overheating or coolant/combustion issues at present. Thanks for the thoughtful input. Makes me feel like I've got friends in high places. -- Matt

thook

Well, you may be right about that. Hmmm. The one cam being off is probably the issue. Golly....before you go through all the trouble of a leakdown test, why don't you check the cam position first?

betelnut

Heh! I'd rather pull my spark plugs than drain half my coolant & redo the upper radiator hose inlet FIPG any day.

I agree though, I'm betting on the cam. Kids.

wrenchtech

I am now thinking you were right when you said that if the ignition timing is right, the timing cam must be right. I think the timing is right so I'm putting that idea on the back burner. I also think that the #2 cylinder has a valve that doesn't seal properly, but I think that the main problem is still something else.

I now suspect the fuel system, maybe the injectors and/or the O2 sensor. Remember, I'm still getting an ECU diagnostic code #25 (lean fuel condition). The engine has trouble idling at more than 650 rpm, even with the auxiliary air valve (AAV) idle screw wide open. Two things I've tried will bring my vacuum and rpm up into a normal range.

1. Advancing the timing
2. A small shot of ether in the air cleaner

If a very small spray of ether will get things right it may be an indication that the ether is making up for the lean condition. I've got spare set of injectors I could swap in and an extra O2 sensor that I know works. I'd want to check the fuel pressure at the injector rail as well. In the mean time I'm gonna try another test, putting some propane into a vacuum line at idle. -- Matt

betelnut

That's not necessarily true. Even though the cams are out of whack, you can still time the distributor to the mark on the crank. It may run poorly, or not at all, or even make fire out the tailpipe, but your timing light will show the (appearance of) correct ignition timing.

wrenchtech

After I pick the low hanging fruit (eliminate the easier stuff) I'll probably get to pulling off the timing cover to look at the cam timing. It looks like pulling out the radiator and the fan is a prerequisite for the leak-down test. If I'm gonna turn over the engine by hand to find TDC on each cylinder I'll need access to the crankshaft pulley bolt. If I do all that I'll be more than half way to a timing belt job. -- Matt

wrenchtech

I got the timing cover off today. I think both the cams are off at least one tooth (crank pulley is at 0 TDC)! This is only the second time I've looked at a 3vze with the timing belt exposed (the first was yesterday) so I'm putting up some pictures of what I found today.

Also, at first I thought that the passenger side cam gear was on backwards/inside-out, but that's the way it looks in the FSM diagram. The '93 I looked at yesterday had both gears with the guide lip facing out. I believe that that was an amateur job as well, so maybe it's wrong (a quick look at the '93 FSM here confirms that the '93 I looked at yesterday is buggered).

Pictures below: Driver's side first and below that passenger side -->

sb5walker

It does look like both cams may be off a tooth. At least it's clear the drivers side is off; the passenger side shows why it's hard to time this engine - the timing mark on the backplate doesn't really line up with any tooth. It may be easier with a new belt, especially if it is from Toyota and has the timing marks.

It's really important to tension the new belt by rotating the motor 2 full revolutions with the lower tensioner spring in place and the pivot bolt not tightened, and to make sure the cam gear marks still line up with the index marks on the rear timing cover. Looks like the kids may have flubbed that step.

You're right that the cam gears are oriented correctly.

wrenchtech

I don't have time to put up pictures right now, but I can say that I was able to get the cam timing marks to line up properly. It didn't change the ignition timing enough to require pulling out the distributor and realigning it. I did gain about 15 degrees of ignition timing advance though. That was easy to dial back within the normal range of the distributor as it was. My manifold vac at idle is up from 12" to about 16". Didn't get to drive it yet. I'll do that first thing in the morning.

I suspect that there are other issues, like tired valves or rings (there's still that #2 cylinder with 140 psi compression), which I'll work on in due course. After all I've got a new leak-down tester just waiting to be put to work. -- Matt

thook

Yeah, but if I remember correctly the timing mark shown by the light will jump around more so than is normal.

The cam marks are definitely off in the pics. When they are lined up correctly, the rotor should also be at around 11 o'clock and/or pointing at the #1 spark terminal. If it is when you have the cams right, you don't need to mess with it.

So, if you have the timing right and motor's still ragged, yeah....other issues. Haha....I hate that.

yayfortrees

I would drive it first, before checking compression again, and checking leakdown. With cam timing not spot on, that will affect compression. Since that problem is fixed, I bet your compression will be fixed as well.

Good luck, I can't wait to hear the results!