Tach drops to zero during drive
04-21-2024, 01:56 PM
#16
Registered User
Thread Starter
Join Date: Nov 2011
Location: Sweden
Posts: 17
Re: Tach drops to zero during drive
Answers:
"Your original problem was the engine shutting off and the tach dropping to “0”. I don’t see how this can possibly be related to the Opti not holding vacuum or pressure. And I don’t feel the pressure test is even meaningful. The seals are not designed to contain pressure". I'm not sure how the vacuum problem can be related to the tach dropping to 0 that´s what I'm trying to find out. However there is problem with the opti and vacuum leaks that creat strange opti-problems like the opti sucking in moist etc and gives all kind of wierd issues. My first test was to check if the old and new opti holds vacuum - they didn't. The old one due to old sealings etc and the new didn't iver hold the vacuum.
My second test (putting a small amount of air pressure into the opti) was to find the vacuum leaks. During this test I found out the leaks was under the round metal part attached to the cam shaft, as show on previuse pictures.
Third test was to trying to seal the leaks under under the round metal part attached to the cam shaft. This isn't solved yet. Of course I can install the new opti as is but sooner or later I will have same problem as with old opti - the opti full of moist and not working. I see this as a first step in the process to: A. have a opti not leaking vacuum and B. Investegate if this is the problem that during time (with moist inside) give strange signals to the PCM.
"It is also very hard for me to understand how it is even possible for a reasonably new Opti, with an intact seal between the tightly clamped Opti cap and body, and a plugged air inlet nipple will not create/support any vacuum at all. But, I have never done such a test." I agress. I guess poor quality is the answer. I have read about a Doc. Opti on internet that before used to rebuilt opti. It had been interesting to get in contact with him and ask him. During my test I noticed leaks was under the round metal part attached to the cam shaft.
You indicate you have seen reports of this problem elsewhere. Do you mean the engine/tach shutting off, only the engine restarting? I don't recall this being a common problem. Or do you mean the problem with the vacuum? I was refereing to the problem with opti leaking/soaking from poor seeling. I have found two other persons on different forums that had same problem (tach dropping to 0) but none solutions was written.
You indicate you believe this forum is possibly superior to Facebook. But there is no one left here any more. Apparently they have all migrated to Facebook, or so they tell me. I'm basically the only person left on this site. There are maybe a 1/2-dozen others who drop in from time-to-time to help. But after many weeks, no one else has jumped into this thread. I have been here for 25+ years, and end up answering 95% of the LT1 questions. But this one has me puzzled. Facebook can be great for a lot of things, but the problems/answers are not saved for many years or even weeks. Therefore i thinkt forums like this is great. All treads are stored and easy to find and you can find the treads easy using Google - even if many years passing by. I regret there so few still using forums but you and others keep them running makes a wounderful work! So much knowledge stored in one place!
If I still owned my 1994 Formula (which was converted to a vented Opti 24 years ago) I would get out my Mighty Vac and see if I could pull a vacuum. But I cannot. I suspect it should be able to build a few inches Hg, while the vacuum pump is being operated, and that whatever vacuum is developed would drop slowly. But that's just a guess. I have owned my 1997 Z28 since 2011 but never come across tach dropping to 0 before ( I have onwned a lot of different Camaros since I got my driving licence back in 1979). Founded Camaro Club of Sweden 1982 and still being a huge Camaro-entusiast.
”Shot in the dark” - try to contact tech support at Petris Enterprises. Ask them about the problem with the engine shutting off. Ask them if the Opti is supposed to hold any appreciable amount of vacuum with suction on the air outlet, and the air inlet plugged. Hint that the answers would help you decide to buy a new Opti, possibly from them. That's a good idea. I will do so!
Sorry that I can’t help you solve the problem(s). No problem. This is a tricky issue. I will update i the forum how it will work out. Can perhaps be to help for others. Keep up the good work with keeping this forum alive!
"Your original problem was the engine shutting off and the tach dropping to “0”. I don’t see how this can possibly be related to the Opti not holding vacuum or pressure. And I don’t feel the pressure test is even meaningful. The seals are not designed to contain pressure". I'm not sure how the vacuum problem can be related to the tach dropping to 0 that´s what I'm trying to find out. However there is problem with the opti and vacuum leaks that creat strange opti-problems like the opti sucking in moist etc and gives all kind of wierd issues. My first test was to check if the old and new opti holds vacuum - they didn't. The old one due to old sealings etc and the new didn't iver hold the vacuum.
My second test (putting a small amount of air pressure into the opti) was to find the vacuum leaks. During this test I found out the leaks was under the round metal part attached to the cam shaft, as show on previuse pictures.
Third test was to trying to seal the leaks under under the round metal part attached to the cam shaft. This isn't solved yet. Of course I can install the new opti as is but sooner or later I will have same problem as with old opti - the opti full of moist and not working. I see this as a first step in the process to: A. have a opti not leaking vacuum and B. Investegate if this is the problem that during time (with moist inside) give strange signals to the PCM.
"It is also very hard for me to understand how it is even possible for a reasonably new Opti, with an intact seal between the tightly clamped Opti cap and body, and a plugged air inlet nipple will not create/support any vacuum at all. But, I have never done such a test." I agress. I guess poor quality is the answer. I have read about a Doc. Opti on internet that before used to rebuilt opti. It had been interesting to get in contact with him and ask him. During my test I noticed leaks was under the round metal part attached to the cam shaft.
You indicate you have seen reports of this problem elsewhere. Do you mean the engine/tach shutting off, only the engine restarting? I don't recall this being a common problem. Or do you mean the problem with the vacuum? I was refereing to the problem with opti leaking/soaking from poor seeling. I have found two other persons on different forums that had same problem (tach dropping to 0) but none solutions was written.
You indicate you believe this forum is possibly superior to Facebook. But there is no one left here any more. Apparently they have all migrated to Facebook, or so they tell me. I'm basically the only person left on this site. There are maybe a 1/2-dozen others who drop in from time-to-time to help. But after many weeks, no one else has jumped into this thread. I have been here for 25+ years, and end up answering 95% of the LT1 questions. But this one has me puzzled. Facebook can be great for a lot of things, but the problems/answers are not saved for many years or even weeks. Therefore i thinkt forums like this is great. All treads are stored and easy to find and you can find the treads easy using Google - even if many years passing by. I regret there so few still using forums but you and others keep them running makes a wounderful work! So much knowledge stored in one place!
If I still owned my 1994 Formula (which was converted to a vented Opti 24 years ago) I would get out my Mighty Vac and see if I could pull a vacuum. But I cannot. I suspect it should be able to build a few inches Hg, while the vacuum pump is being operated, and that whatever vacuum is developed would drop slowly. But that's just a guess. I have owned my 1997 Z28 since 2011 but never come across tach dropping to 0 before ( I have onwned a lot of different Camaros since I got my driving licence back in 1979). Founded Camaro Club of Sweden 1982 and still being a huge Camaro-entusiast.
”Shot in the dark” - try to contact tech support at Petris Enterprises. Ask them about the problem with the engine shutting off. Ask them if the Opti is supposed to hold any appreciable amount of vacuum with suction on the air outlet, and the air inlet plugged. Hint that the answers would help you decide to buy a new Opti, possibly from them. That's a good idea. I will do so!
Sorry that I can’t help you solve the problem(s). No problem. This is a tricky issue. I will update i the forum how it will work out. Can perhaps be to help for others. Keep up the good work with keeping this forum alive!
Last edited by aaberg; 04-21-2024 at 02:00 PM.
04-21-2024, 07:23 PM
#17
Administrator
Join Date: Nov 1998
Location: Hell was full so they sent me to NJ
Posts: 70,673
Re: Tach drops to zero during drive
Just some final observations…….
I'm not sure where “sucking in moist” comes from. The majority of the air inflow with the Opti installed correctly in the system, will be filtered air from the inlet elbow. The air, at the temperature the Opti operates at, will be above the dew point. Do you feel the seal between the cap and the body is a source of leakage, preventing vacuum? Moisture (in the form of humidity) will not condense out and coat the Opti components.
If there is no vacuum in the Opti (there has to be a small difference in negative pressure between the suction (engine) side and the air duct elbow side - other wise there would be no flow) what is going to pull oil vapor or oil through the drive shaft seal? Where else is all this moisture coming from?
Whatever air is leaking into the Opti should be pulled out by the intake manifold vacuum, removing the ozone generated by the high voltage discharge. That is GM's stated purpose in adding the vacuum powered vent system in 1995.
The Cardone has not proven to be a reliable Opti. Maybe you got a defective unit if the cap seals and the drive seals are leaking so badly there is no vacuum.
We will just have to disagree on the validity and relevance of the pressure test.
I'm not sure where “sucking in moist” comes from. The majority of the air inflow with the Opti installed correctly in the system, will be filtered air from the inlet elbow. The air, at the temperature the Opti operates at, will be above the dew point. Do you feel the seal between the cap and the body is a source of leakage, preventing vacuum? Moisture (in the form of humidity) will not condense out and coat the Opti components.
If there is no vacuum in the Opti (there has to be a small difference in negative pressure between the suction (engine) side and the air duct elbow side - other wise there would be no flow) what is going to pull oil vapor or oil through the drive shaft seal? Where else is all this moisture coming from?
Whatever air is leaking into the Opti should be pulled out by the intake manifold vacuum, removing the ozone generated by the high voltage discharge. That is GM's stated purpose in adding the vacuum powered vent system in 1995.
The Cardone has not proven to be a reliable Opti. Maybe you got a defective unit if the cap seals and the drive seals are leaking so badly there is no vacuum.
We will just have to disagree on the validity and relevance of the pressure test.
04-25-2024, 12:18 AM
#18
Registered User
Join Date: Mar 1999
Location: Kernersville, NC
Posts: 2,059
Re: Tach drops to zero during drive
I don't think I'd get hung up on it not holding a vacuum. I put in new GM unit as preventive maintenance back in '08 when I put in my CC503. I've still got the OEM original opti as a backup. 97K, ran just fine when pulled it. I just did a vacuum check on it with the OEM opti harness(I replaced it in '08 as well). The OEM opti will not hold a vacuum. All the hoses hold vacuum fine. The ~30 year old check valve is working fine as well.
I also checked the one on my Z28 and it will not hold a vacuum either. Quick video on that check....
I also checked the one on my Z28 and it will not hold a vacuum either. Quick video on that check....
Thread
Thread Starter
Forum
Replies
Last Post
aaberg
LT1 Based Engine Tech
1
06-07-2023 04:29 PM