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Last month when I drove home, my Highlander lost all coolant on highway. I immediately exit from highway and engine stop; I manager stop on a local road. I wait until engine cold and fill water. Engine cannot start.

I called a towing and repair shop and tow car to their shop for repair. I called the repair shop next day, the manager told me they will check problem and call me back. After few days, the manager called. He told me engine need replaced and cost $3000 for parts and labor. My 2003 Highlander only has 70K and engine should be in good condition. I ask the manager what engine compression is. He said all are zero. My highlander is V6, it is not possible cylinders on both banks have no compression. Also, after I find coolant leak and stop car in new minutes.

I ask repair shop tow to my garage and start diagnosis myself. I find that many cylinders have water in it, and I think it is header gasket issue. I take off both cylinder header and found cylinder header need re-surface and many valves need re-seat.

I ordered re-build cylinder header from a Texas company. After putting new cylinder header back, engine still cannot start. Out of six ignition coils, three don’t work. After replacing all ignition coils, engine run as before. But check engine light is on, and scanner said I need replace Oxygen sensor.

After replace Oxygen sensor check engine light still on, report Knock sensor has problem. I ordered Knock sensors and Camshaft position sensors and prepare to replace next weekend.

On a Friday when drove home, highlander stop on highway again. This time is due to timing belt broken. I should replace timing belt when I replace cylinder heads.

Then, I replaced timing belt, Knock sensors and Camshaft position sensors. Engine running OK, but check engine light still on. Also, engine is rough on idle. Scanner said multiple cylinders misfire. After I clear code, scan again, it said cylinder 1,3,5 misfire.

I check web, many people suggested that I is caused by vacuum leaks. I try many ways to fix vacuum leaks. Check engine is always on, scanner said multiple cylinder misfire or cylinder 1,3,5 misfire.

I really cannot find any vacuum leaks by inspect intake manifold and hoses. Use start fluid to find leaks is a little dangerous.

In this article (https://www.autocodes.com/p0300_2001_toyota_highlander.html), multiple cylinders misfire may cause by:
Faulty spark plug (s), all spark plugs are new.
Faulty ignition coil (s), not possible, all coils are new, engine running fine before timing belt broken.
Fuel injectors problems, rule out because engine running fine before timing belt broken.
Intake air leak, very likely.
Insufficient cylinders compression, not possible, all cylinder’s compression are normal after replace cylinder headers, (160-190psi on cold engine).
Mass air flow sensor: Sensor is quite clean. I use alcohol washed; it didn't help.

Current condition is very like what this article:

Engine running fine on high RPM, rough on idle. I ordered intake manifold gasket set and will replace them after I back from vocation. I will try start fluid if engine still has problem.

What else should try? What is your suggestion?

Thanks in advance!
 

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Like MGeorge said, start with the mechanical or you may chase this without success.
Do the compression and leak-down tests.
Be sure to disable the ignition and fuel. Compression tests without disabling can damage the coils and flood the catalytic converters.
Are you certain the cams are timed correctly? Being a tooth off on Bank 1 could cause misfire in those cylinders
If you are not using Toyota or Denso cools and sensors, the new ones may have failed.
Does your scanner read real-time data? If so, what are your fuel trims at idle and while at highway speeds?
Use a stethoscope to listen around the intake manifold and vacuum hoses.
You can get a smoke tester at Amazon to check for vacuum leaks. Look on YouTube for the procedure.
Misfire with good fuel trims would point to ignition, mechanical, or timing.
What was the original cause of the coolant loss? The 1MZ does not usually blow head gaskets without overheating.
 

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Discussion Starter #5
Like MGeorge said, start with the mechanical or you may chase this without success.
Do the compression and leak-down tests.
Be sure to disable the ignition and fuel. Compression tests without disabling can damage the coils and flood the catalytic converters.
Are you certain the cams are timed correctly? Being a tooth off on Bank 1 could cause misfire in those cylinders
If you are not using Toyota or Denso cools and sensors, the new ones may have failed.
Does your scanner read real-time data? If so, what are your fuel trims at idle and while at highway speeds?
Use a stethoscope to listen around the intake manifold and vacuum hoses.
You can get a smoke tester at Amazon to check for vacuum leaks. Look on YouTube for the procedure.
Misfire with good fuel trims would point to ignition, mechanical, or timing.
What was the original cause of the coolant loss? The 1MZ does not usually blow head gaskets without overheating.
Thank you.
To disable fuel, I un-plug fuel pump fuse.
To disable ignition, I remove all coils, is that correct? Should I remove fuse as well?
 

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If you just unplug the fuel pump there will still be pressure in the fuel rail to inject fuel. The Haynes manual instructions are to remove the fuel cap and unplug the fuel pump and run the engine until it stalls. I don’t know the details of the 2003 wiring to know if you can unplug a fuel pump fuse and still run the engine. On the 2005 there are two EFI fuses. For the ignition system, I unplug and remove the coils. If you don’t have the Haynes manual yet, I think it is a good investment.
 

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Well, if you had catastrophic coolant loss INTO the engine, you hydrolocked it. Or overheated. or both. As engines are now aluminum, you might as well cracked engine block or done damage to connecting rods/bearings. Who knows. Hydrolocked engines are pretty much toast.
that's, of course, if you had coolant in cylinders because of head gasket failure, not just because you removed engine heads and coolant leaked into them.Your call, you did the job.
Also, out of curiosity. Shop offered you rebuilt engine (no new engines for that money) for $3000. How much did it cost YOU to do all the work? New heads, sensors, coils, etc?
 

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Discussion Starter #8
I am back from vocation and start working on my Highlander.
I have two cars; highlander is just for move large item and go out with my wife on weekend.
Highlander has only 70K and I just don’t want junk this engine.

I made smoke tester; no clear vacuum leaks found.
I re-check timing is correct for bank 1. No error found.
I open cylinder header cover, and make sure timing is correct on marks on camshaft gears (there are one dot and two dots marks on gears).

I than did compress test.
For Bank 2 (front), all cylinders are ~160 psi.
For Bank 1 (close to driver), all cylinders are ~60 psi.
I did compression test with my compressor:
  • Remove camshaft and make sure all valves are seated.
  • All six cylinders reaches 120 psi, when I stop compressor, pressure drop slowly in the same way.
I use a Wi-Fi endoscope to inspect inside cylinders, no clear damages found. All valve looks OK.
I removed shim one by one, all valve is installed correctly, no sign locker pops up.

After all this, my compulsion is:
It is timing caused low compression on bank one.
The only possibility is bank 1 VVT timing is wrong. I just cannot find any error on timing mark alignment.

I tested VVT solenoid, both are working. I ordered two new solenoids, but I don’t think it will help.
The other possibility is bank one intake camshaft gear damaged. I googled for hours, cannot find any article on how to diagnosis that.

I order a scanner with read real-time data, will do test when I put everything back.

Any suggestions are greatly appreciated.
 

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You did a good job of troubleshooting. If all Bank 1 cylinders are 60 during a compression test but 120 during a leak-down yes with a compressor then it sounds like camshaft timing is off by a couple of teeth
You need to check timing in two places on bank1. 1) Camshaft to crankshaft timing at the timing belt. 2) intake and exhaust camshaft gear timing at the back of the head.
It is not clear to me that you checked both. If not then check the timing belt again.
One other way- Move each piston to top dead center (TDC) on the compression stroke and check the angle of the cam lobes for the cylinder. The angles for the intake and exhaust lobes should be the same for all cylinders. I think you will find that Bank 1 doesn’t match Bank 2.
I suppose it is possible that the cam phaser is stuck but I think it would be in the phaser mechanism and not in the solenoid to show up in a compression test.
 

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Discussion Starter #10
You did a good job of troubleshooting. If all Bank 1 cylinders are 60 during a compression test but 120 during a leak-down yes with a compressor then it sounds like camshaft timing is off by a couple of teeth
You need to check timing in two places on bank1. 1) Camshaft to crankshaft timing at the timing belt. 2) intake and exhaust camshaft gear timing at the back of the head.
It is not clear to me that you checked both. If not then check the timing belt again.
One other way- Move each piston to top dead center (TDC) on the compression stroke and check the angle of the cam lobes for the cylinder. The angles for the intake and exhaust lobes should be the same for all cylinders. I think you will find that Bank 1 doesn’t match Bank 2.
I suppose it is possible that the cam phaser is stuck but I think it would be in the phaser mechanism and not in the solenoid to show up in a compression test.
A new intake gear cost only $100 on Ebay, may be I should order one.
I am not sure how easy to replace it.

Thanks!
 

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Well, I think I would do more diagnostics.

The Haynes manual has a lot of good information on the cams and phasers. If you don’t have it, consider getting it.
 

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Discussion Starter #12
I do have Haynes manual.
Following Haynes manual:
  • First, I make sure sprocket/actuator cannot rotate.
  • I use compressor, released locker and actuator rotate freely by hand.
  • When I rotate all the way to right, actuator lock again.
  • Compare new lock position to previous position, at least more than one tooth different.
I use gasoline cleaned vvt gear and fill some clean oil.

Tomorrow I will test compression again. If compression is good, I will make engine run again. I think I don’t need replace sprocket/actuator.

I find an article on web, it said that if VVT gear in on activated phase and engine quickly stop, sprocket/actuator may get stuck. That is what happened when timing belt broken.
 

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Nice work. Just be careful with using gasoline as a solvent. I use Chemtool or other carburetor cleaners
 
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