Been struggling with this problem for a bit, wondering if anyone has some input before doing some exploration in the motor...
I've got the case of the intermittent VTEC... on one head only.
Got my motor together and in the car, have a Vipec ECU and dual widebands.
Tuner noticed that the Vipec sends the signal to both spool at the same time, but the signal from the pressure switch on the front bank spool valve (that verify the spool valves have opened as oil pressure has increased inside) comes on after a couple seconds if at all. (the rear bank sensor shows oil pressure coming up immediately as it should).
The A/F trace from the widebands shows the front bank going rich as the front bank gets the signal to go into VTEC and the Vipec map tries to add fuel for the correct A/F ratio (the Vipec map was made on a car that VTEC operated correctly on). This confirms that it isn't a faulty pressure switch on the spool valve, as it is clear that the front bank isn't actually going into VTEC immediately if at all.
So.. okay, got a sticky spool valve... or a bad connection to the spool valve solenoid...right?
Check connection, apply dielectric grease, same result. Jumper the spool valve solenoid to 12v, same result. Pull off spool valve, disassemble, clean, inspect, bench test, reinstall, same result.
Then I realize the front / rear spool valves are the same, so swap them front to back. The problem stays on the front bank, so it's not the spool valve or the connection to it.
So... put a mechanical oil pressure gauge in various places to see just what is going on.
For the following tests, the Vipec is setup to engage VTEC at 4000rpm no load, videos show oil pressure gauge and tach. You can see what happens when the VTEC engages on the oil pressure gauge.
In the first video, I test the oil pressure at a tee installed by the factory engine oil pressure sender on the front bank. Pressure rises to 54psi as engine revs, until VTEC engages (spool valves open) at 4k causing pressure to drop (which is normal):
http://youtu.be/qI3OSIhrPu0
In the second video, I removed the pressure switch from the front spool valve and installed the mechanical gauge. This gauge should read zero until VTEC engages, then should quickly rise. It reads zero, then slowly rises to 11psi. This explains why VTEC is engaging slowly, (if at all) as that isn't enough pressure to quickly / reliably lock the rockers together:
http://youtu.be/M5Qo8vqgvPI
The third video is the same test done on the rear spool valve. The oil pressure quickly rises to 72 psi, which interestingly is more pressure than is shown at the oil pressure sender, which may be a clue as I don't know why the rear spool valve is seeing 18 psi more than the oil pressure sender:
http://youtu.be/yzZESTweESA
So, at this point, I've deduced the front spool valve is opening, is being fed by 54psi oil, but is only building 11psi in the system.
This is where the limited information in the service manual and my limited knowledge of where the oil actually goes after the spool valve makes things... murky.
I am under the impression that the oil flows past the spool valve into the rocker shafts, where it is restricted at the far end by the rocker shaft orifices at the far end (see schematic in the 1991 service manual page 5-11 and / or illustration of the actual pin on 6-33).
This causes pressure build up that flows through holes in the rocker shaft into the rocker arms, and pushes the hydraulic piston to the side that locks the rockers together (page 5-6)
What is less clear is where the oil goes after the restrictors, and here's where some speculation comes in, as it's not shown on the schematic of page 5-11. I believe it flows back to the other end of the head (although it doesn't make a whole lot of sense) and flows out the "relief hole" close to the spool valve (see page 6-52). This is the hole that you plug with the VTEC plug to bench test the valve train by putting air into the VTEC inspection hole. That would make sense, as the air you put in then doesn't escape past the restrictors and out the relief hole because it is plugged.
I can only guess where the "VTEC inspection hole" that you introduce air into for this test (which looks like a bolt on the side of the cylinder head) taps into the VTEC oil system. It would make sense that it taps in after the spool valve and before the restrictors, but given it's location is almost seems like it's after the restrictors and before the relief hole.
Anyhoooo....
I figured that maybe one of the hydraulic pistons between the rockers fell out when they were out of the head or something, so I devised a test.
In the last test, I removed the valve cover and filled a bottle with oil pressurized to 60psi and connected it to a tap where the factory oil pressure sender is on the front bank (just before the front spool valve), then took a video while I opened a valve on the bottle. I was expecting to see oil leaking out from in between one set of rockers, but it all seemed to come out the VTEC relief hole (ignore my "aha! it's so simmmmple to fix comment on the vid; this was before I knew what the relief hole was for):
http://youtu.be/L5M-QGyTKtk
So, now my guess is that one of the restrictor pins is... what.... missing? I doubt it. Has too big of hole? How the heck would that happen? Missing an O-ring? hard to not notice when putting it back together, but also didn't see oil coming out here, just from the relief hole.
These heads have been apart several times, and have had machine work done, bigger valves installed, been hot tanked etc. I don't know if there's a galley plug missing somewhere, or what. My fear is that I pull the cams, inspect the restrictors, find that they're there, that there are ... well normal looking holes in them and that the o-rings are in place... and all the rocker hydraulic pistons are in place... and then what??
Hoping to find someone with intimate knowledge of the VTEC system parts to give some insight ...
As a side note, this issue has probably been with the motor for the last couple rebuilds, and could have easily contributed to a failure. It explains some of the mysterious goings on in the past that could only be seen with 2 widebands and an attentive tuner....
Any input / insight would be appreciated before ....ugh... I really don't want to pull the cams and rocker shafts in the car...
- C
I've got the case of the intermittent VTEC... on one head only.
Got my motor together and in the car, have a Vipec ECU and dual widebands.
Tuner noticed that the Vipec sends the signal to both spool at the same time, but the signal from the pressure switch on the front bank spool valve (that verify the spool valves have opened as oil pressure has increased inside) comes on after a couple seconds if at all. (the rear bank sensor shows oil pressure coming up immediately as it should).
The A/F trace from the widebands shows the front bank going rich as the front bank gets the signal to go into VTEC and the Vipec map tries to add fuel for the correct A/F ratio (the Vipec map was made on a car that VTEC operated correctly on). This confirms that it isn't a faulty pressure switch on the spool valve, as it is clear that the front bank isn't actually going into VTEC immediately if at all.
So.. okay, got a sticky spool valve... or a bad connection to the spool valve solenoid...right?
Check connection, apply dielectric grease, same result. Jumper the spool valve solenoid to 12v, same result. Pull off spool valve, disassemble, clean, inspect, bench test, reinstall, same result.
Then I realize the front / rear spool valves are the same, so swap them front to back. The problem stays on the front bank, so it's not the spool valve or the connection to it.
So... put a mechanical oil pressure gauge in various places to see just what is going on.
For the following tests, the Vipec is setup to engage VTEC at 4000rpm no load, videos show oil pressure gauge and tach. You can see what happens when the VTEC engages on the oil pressure gauge.
In the first video, I test the oil pressure at a tee installed by the factory engine oil pressure sender on the front bank. Pressure rises to 54psi as engine revs, until VTEC engages (spool valves open) at 4k causing pressure to drop (which is normal):
http://youtu.be/qI3OSIhrPu0
In the second video, I removed the pressure switch from the front spool valve and installed the mechanical gauge. This gauge should read zero until VTEC engages, then should quickly rise. It reads zero, then slowly rises to 11psi. This explains why VTEC is engaging slowly, (if at all) as that isn't enough pressure to quickly / reliably lock the rockers together:
http://youtu.be/M5Qo8vqgvPI
The third video is the same test done on the rear spool valve. The oil pressure quickly rises to 72 psi, which interestingly is more pressure than is shown at the oil pressure sender, which may be a clue as I don't know why the rear spool valve is seeing 18 psi more than the oil pressure sender:
http://youtu.be/yzZESTweESA
So, at this point, I've deduced the front spool valve is opening, is being fed by 54psi oil, but is only building 11psi in the system.
This is where the limited information in the service manual and my limited knowledge of where the oil actually goes after the spool valve makes things... murky.
I am under the impression that the oil flows past the spool valve into the rocker shafts, where it is restricted at the far end by the rocker shaft orifices at the far end (see schematic in the 1991 service manual page 5-11 and / or illustration of the actual pin on 6-33).
This causes pressure build up that flows through holes in the rocker shaft into the rocker arms, and pushes the hydraulic piston to the side that locks the rockers together (page 5-6)
What is less clear is where the oil goes after the restrictors, and here's where some speculation comes in, as it's not shown on the schematic of page 5-11. I believe it flows back to the other end of the head (although it doesn't make a whole lot of sense) and flows out the "relief hole" close to the spool valve (see page 6-52). This is the hole that you plug with the VTEC plug to bench test the valve train by putting air into the VTEC inspection hole. That would make sense, as the air you put in then doesn't escape past the restrictors and out the relief hole because it is plugged.
I can only guess where the "VTEC inspection hole" that you introduce air into for this test (which looks like a bolt on the side of the cylinder head) taps into the VTEC oil system. It would make sense that it taps in after the spool valve and before the restrictors, but given it's location is almost seems like it's after the restrictors and before the relief hole.
Anyhoooo....
I figured that maybe one of the hydraulic pistons between the rockers fell out when they were out of the head or something, so I devised a test.
In the last test, I removed the valve cover and filled a bottle with oil pressurized to 60psi and connected it to a tap where the factory oil pressure sender is on the front bank (just before the front spool valve), then took a video while I opened a valve on the bottle. I was expecting to see oil leaking out from in between one set of rockers, but it all seemed to come out the VTEC relief hole (ignore my "aha! it's so simmmmple to fix comment on the vid; this was before I knew what the relief hole was for):
http://youtu.be/L5M-QGyTKtk
So, now my guess is that one of the restrictor pins is... what.... missing? I doubt it. Has too big of hole? How the heck would that happen? Missing an O-ring? hard to not notice when putting it back together, but also didn't see oil coming out here, just from the relief hole.
These heads have been apart several times, and have had machine work done, bigger valves installed, been hot tanked etc. I don't know if there's a galley plug missing somewhere, or what. My fear is that I pull the cams, inspect the restrictors, find that they're there, that there are ... well normal looking holes in them and that the o-rings are in place... and all the rocker hydraulic pistons are in place... and then what??
Hoping to find someone with intimate knowledge of the VTEC system parts to give some insight ...
As a side note, this issue has probably been with the motor for the last couple rebuilds, and could have easily contributed to a failure. It explains some of the mysterious goings on in the past that could only be seen with 2 widebands and an attentive tuner....
Any input / insight would be appreciated before ....ugh... I really don't want to pull the cams and rocker shafts in the car...
- C
. You can also remove one cam pipe(intake) them you can use some washers to hold the cam holders in place with the original bolts, same with the exhaust cam pipe.
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