Hesitation with no top-end power.

C

clunker

New member
I have a 92 4Runner with 3VZE and manual transmission that has had a hesitation issue since I bought it. I have replaced almost every part imaginable to no avail. The engine seems to run better for a few days, then the hesitation returns. All parts used are the highest quality available (Denso, NGK, Aisin, Mitsuboshi, etc.). Here is a list of symptoms.

• Starts every time and idles smooth
• MPGs and top end power keep dropping every tank no matter what I do
• RPMs will not go beyond 4500 in any gear (like it is starving for fuel)
• Hesitation is worst when engine is cold but is still a problem when warm
• No strange noises other than the engine is loud (exhaust sounds normal)
• Exhaust backpressure measured zero at idle
• All intake and fuel system components appear clean
• Only check engine code it ever threw was for oxygen sensor until it was replaced
• No leaks or issues with coolant/oil

Here is a list of replacements:

• EFI fuse pulled and reset after each engine part replacement/adjustment
• TPS replaced and adjusted
• Fuel pump with filter
• Fuel filter
• Plugs, wires, cap, rotor
• K&N air filter from previous owner with way too much oil (cleaned and properly oiled by me)
• Oxygen sensor
• EGR valve
• Timing belt, water pump, idler bearings, thermostat
• Throttle body intake boot
• Thorough fuel system treatment

What else is left?
Knock sensor, crankshaft sensor, cam sensor, coolant temp sensor, VAFM, Catalytic convertor (clogged), fuel injectors, vacuum leak, ECU. Everything I try seems to reduce the hesitation slightly and increases off idle torque, but I have no top end power. Any suggestions would be greatly appreciated. Sorry for the long post.
 
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Was gonna say the same thing! Compression test first, see where the numbers are at. Could also be valves, compression test will help determine if the valves are closing completely or not.

Can you rev in neutral over 4500rpm?

Is there a lot of valvetrain noise at idle and around 1200rpm?
 
Hmmm! Hadn't thought about compression. Based on my experience with everything that was neglected by previous owners, it would not surprise me if the valves have never been adjusted. At 170K miles, it would be long overdue.

Fairly quiet at idle (at least as quiet as you can expect with the 3VZE). There is some slight valvetrain noise, but I heard that was normal for this engine. Haven't tried revving in neutral. Call it a phobia, but it makes me nervous to approach redline when not in gear. I'll give that a shot. Compression is easy enough to test, so I'll look into that this weekend.

I advanced timing to 12 BTDC, and that helped with throttle response with no sign of pinging, so I don't think timing is an issue. Thanks for the suggestions everyone. I'll report back after some diagnostics.
 
Unmetered air? How is the air intake plumbing? is there a large crack r leak after the MAF sensor? The intake plubling is so wikdly elaborate that it happens all the time.
 
There are fine screens on the inlet of the injectors. I had those clog up before. It would idle fine but couldn't get out of its own way.
 
Great info. Thanks everyone.

I thoroughly inspected the intake from the duct before the air filter, all the way through the throttle body and didn't find anything other than the throttle body boot was cracked, and that has been replaced. I am a little concerned that the previous owner put far too much oil on the K&N filter. The vane seems to move freely, but I have read that any oil in the VAFM can foul the mechanism.

Supposing that my compression throws a red flag, I think I read that valve adjustment on the 3VZE requires a special tool. Can anyone verify this and tell me what tool I should order. I guarantee it will not be available at any of the local stores, and I need to get this sorted out over the weekend. Long road trip planned for Thanksgiving.

Thanks all
 
clunker said:
Great info. Thanks everyone.

I thoroughly inspected the intake from the duct before the air filter, all the way through the throttle body and didn't find anything other than the throttle body boot was cracked, and that has been replaced. I am a little concerned that the previous owner put far too much oil on the K&N filter. The vane seems to move freely, but I have read that any oil in the VAFM can foul the mechanism.

Supposing that my compression throws a red flag, I think I read that valve adjustment on the 3VZE requires a special tool. Can anyone verify this and tell me what tool I should order. I guarantee it will not be available at any of the local stores, and I need to get this sorted out over the weekend. Long road trip planned for Thanksgiving.

Thanks all
Click to expand...

I had the heads off when I adjusted the valves and even that was a pain. Checking the clearance is only as hard as getting the valve covers off.

Maybe someone else can answer this, but is there any reason not to take the cams out to gain access to the shims? That would be easier than trying to use the "tool". The hardest part for me was separating the shim from the bucket they sit in. Trying to hold the valve open while prying out the shim sounds like a PITA to me. Just as a fair warning, I did have a bunch of the threads strip out on me on the end caps. I had to drill them out and install heli-coils. that might be reason enough not to do it.

If the compression is way off, it might be time to pull the heads anyways and take them to the shop.
 
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The only reason I wouldn't pull cams is if you only need to adjust one valve. I had one exceptionally loud valve after an adjust and timing kit so I tore into it again but just for the one valve. It is easily a two person job with the right pick and some pry bars.

Also if you find the compression specs and if they check out, pull your plugs to see what they look like that could tell you something.
 
clunker said:
Great info. Thanks everyone.

I thoroughly inspected the intake from the duct before the air filter, all the way through the throttle body and didn't find anything other than the throttle body boot was cracked, and that has been replaced. I am a little concerned that the previous owner put far too much oil on the K&N filter. The vane seems to move freely, but I have read that any oil in the VAFM can foul the mechanism.

Supposing that my compression throws a red flag, I think I read that valve adjustment on the 3VZE requires a special tool. Can anyone verify this and tell me what tool I should order. I guarantee it will not be available at any of the local stores, and I need to get this sorted out over the weekend. Long road trip planned for Thanksgiving.

Thanks all
Click to expand...

Yes, you need this: http://www.amazon.com/Zdmak-Valve-T...37168&sr=8-4&keywords=toyota+valve+adjustment. Might find it cheaper somewhere else. How it works is you take the plier-type tool and clamp the cam shaft beside the lobe (not on the lobe, you can damage it) and then slide it down until it completely compressed the shim bucket beneath the lobe. Then you have to precariously use the little wedge tool and jam it between the cam shaft and the bucket but done in a way that does not restrict the shim coming out. Make sure the lip in the bucket is facing away from the engine. Then use a magnetic tool and it pops right out. Takes 30 min of practice but once you figure it out it goes quicker.

Also, with you VAFM be sure to clean the air temp sensor that's in the white capsule that hangs down from the top. If that's all messed up it won't be able to read the air temps right and could mess with your MPG's.
 
Thanks gamefreak. That's the tool I was looking for. I haven't tested the compression yet, but I pulled the catalytic converter. There is no visible carbon buildup, and I can see daylight clear through it. I assume that means there is no blockage, but someone please correct me if there is more I should be looking for in the cat. I'll report back when I have compression numbers.
 
Here is the verdict. Best cylinder is 147 PSI and worst is #6 at 142. Much lower than I was hoping for, but not surprising considering that the previous owner never changed the oil and it has 170k miles on it.

Is that seriously bad enough to rob all top end power? Valve adjustments are one thing, but it's questionable whether it is worth doing any head work at all. The investment would never pencil. Am I risking more damage by driving it with such low compression?
 
Since its that low, try doing a leakdown test next. See if its rings or valves.

You could burn the valves if that's the problem with low compression, so a leakdown would be essential at this point. If its the rings and not the valves, then you could continue running it for a while, those numbers are bad but not super-horrible. You'll notice your oil turns black faster, and pushing that engine you'll find more pressure into the crankcase. You can also burn up the pistons too, as you'll have more detonation.

If you can afford it, get the engine pulled and rebuild it sooner rather than later. Don't end up with what I have right now:

Cracked ring lands from detonation:
piston%2002.jpg


Lead to completely broken ring lands!
piston%2003.jpg
 
Ouch flyin! That looks like a nightmare. The valve tool kit arrived today, and I will be getting started on the project Wednesday (cancelling the Thanksgiving trip). Based on some research, I think valves are the issue and not rings. The sounds described in some forums are similar to what I'm hearing.

Unfortunately, I did not realize that the 3VZE valves are adjusted by installing new shims. Is there a procedure for determining what size shims are needed? Are the existing shims labeled? Do you order a kit, or do I need to measure each valve and just order those specific shims?

Thanks
 
I've never had the pleasure of shimming a 3vze valvetrain, but I've read about how much of a pain in the ass they are to do! You will absolutely need the manual for a 3vze engine, search here for the links to it.

The shims should be available at the dealership and if they're big enough, they should have the various sizes in stock.

This thread might be of help to you on checking the valve clearances and calculating which ones you need.

3vze valve shims? - YotaTech Forums

If you can, take photos of your progress, it would help the next person here that's tackling this job.
 
So what did you find when you got in there? My rig is having the same symptoms that you were describing AFTER the shop did a valve job and new head gaskets, so I am wandering if they got the clearances right, or if there may be another explanation.
 
Have you attempted to test the things you have not looked into yet in your original post? Like a possible Cat clog?

I have the 3VZE in an 89, and it has 348,000 original miles on it - and the engine has never been rebuilt. It has that classic seeming surge of power at 3000rpms, but its had that for years. It idles rough when doing a warm start - but again it has for years.

It can push past 4500rpm without an issue (As far as 1st, 2nd and 3rd go, never tried in 4th or 5th).

My compression HAS to be lower than yours - it has to be something else, no? Of course Im assuming.
 
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