CIS blown airbox symptom, Was Big Bang thread last week Options

[Kansas 914]

This is a follow up to the BIG BANG thread where the pop off valve was blown to pieces.

I installed a new pop off valve in the existing airbox hoping it would be a quick fix. The car "starts" but doesn't "run". If this was a carbed car I would say it is running on the prime. Maybe the cold start valve is giving it gas to fire then stops? Is this fuel delivery issue (maybe it lead to a lean backfire) or blown airbox?

I am hesitant to pull all the CIS stuff off to get to the airbox as I know I will be in over my head. I have read a few 911 threads on removing the airbox and it is something I have never done. How do you get to the runners under the box (4 -5 6)?


https://www.youtube.com/watch?v=vaA44-K30QA


Engine is a 2.7L from a 1976 911S

Thanks in advance!

[Root_Werks]

Something else cracked or popped off. When CIS does that, it's usually because of a pretty large vacuum leak. Careful trying to start it while the leak is there, could go bang again.

[Kansas 914]

Something else cracked or popped off. When CIS does that, it's usually because of a pretty large vacuum leak. Careful trying to start it while the leak is there, could go bang again.

Thanks!

I had hoped for a quick fix.

[914Toy]

Make sure the big rubber boot is secure on both ends.

[Kansas 914]

Make sure the big rubber boot is secure on both ends.

Thanks.

I removed and reinstalled it on my first inspection - I will double check.

I assume you are referring to #12 in this picture?

[Kansas 914]

My thoughts right now are to remove the entire CIS and inspect everything.

I really like this car - it is so civilized to drive. It is mostly 911 (engine - suspension) with a heater and defroster which is important at 6600 above sea level.

I plan to yank it out in a lump like this. I am sure I will learn from this process.



Here is Rosebud (Raspberry) with newly backdated bumpers.

[914Toy]

Make sure the big rubber boot is secure on both ends.

Thanks.

I removed and reinstalled it on my first inspection - I will double check.

I assume you are referring to #12 in this picture?

Yes, #12.

[Superhawk996]

I'll chime in but let me be clear that I don't currently have a six with CIS in the car so I'm not speaking about a /6 with CIS from experience.

I'd revert to my usual postion that trying to work on the engine in the car is largely a lost cause for anthying other than basic maintenance.

Mid engine cars by their very nature, lend themselves to quick engine drops. As with the T4 engine, most work on the engine was intended to be performed by dropping the engine 1st.

At that point, everyting is much more accessible. For me it's just a sanity thing. I'd much rather have easy access than work laying off the trunk, scratching the paint, and contorting my neck head, and arms to try to work on it from the top side though the engine cover. The whole thing is is Hell Hole.

Once you've done it a few times, the engine can be dropped and/or reinstalled in about 75 minutes. I've heard of guys doing it in less time. I'm OCD about double checking things before I drop it and have it hang up on a forgotten item like the ground strap (been there done that (IMG:style_emoticons/default/headbang.gif)) Obviously the 1st time or two takes longer.

Side note: Car looks GREAT!

[Kansas 914]

I'll chime in but let me be clear that I don't currently have a six with CIS in the car so I'm not speaking about a /6 with CIS from experience.

I'd revert to my usual postion that trying to work on the engine in the car is largely a lost cause for anthying other than basic maintenance.

Mid engine cars by their very nature, lend themselves to quick engine drops. As with the T4 engine, most work on the engine was intended to be performed by dropping the engine 1st.

At that point, everyting is much more accessible. For me it's just a sanity thing. I'd much rather have easy access than work laying off the trunk, scratching the paint, and contorting my neck head, and arms to try to work on it from the top side though the engine cover. The whole thing is is Hell Hole.

Once you've done it a few times, the engine can be dropped and/or reinstalled in about 75 minutes. I've heard of guys doing it in less time. I'm OCD about double checking things before I drop it and have it hang up on a forgotten item like the ground strap (been there done that (IMG:style_emoticons/default/headbang.gif)) Obviously the 1st time or two takes longer.

Side note: Car looks GREAT!

I don't hesitate to drop the drivetrain on my /4 and can do it in just over an hour, but the /6 intimidates me for some reason. I know the process is about the same. As a one man shop it makes thing tougher.

[Superhawk996]

I'll chime in but let me be clear that I don't currently have a six with CIS in the car so I'm not speaking about a /6 with CIS from experience.

I'd revert to my usual postion that trying to work on the engine in the car is largely a lost cause for anthying other than basic maintenance.

Mid engine cars by their very nature, lend themselves to quick engine drops. As with the T4 engine, most work on the engine was intended to be performed by dropping the engine 1st.

At that point, everyting is much more accessible. For me it's just a sanity thing. I'd much rather have easy access than work laying off the trunk, scratching the paint, and contorting my neck head, and arms to try to work on it from the top side though the engine cover. The whole thing is is Hell Hole.

Once you've done it a few times, the engine can be dropped and/or reinstalled in about 75 minutes. I've heard of guys doing it in less time. I'm OCD about double checking things before I drop it and have it hang up on a forgotten item like the ground strap (been there done that (IMG:style_emoticons/default/headbang.gif)) Obviously the 1st time or two takes longer.

Side note: Car looks GREAT!

I don't hesitate to drop the drivetrain on my /4 and can do it in just over an hour, but the /6 intimidates me for some reason. I know the process is about the same. As a one man shop it makes thing tougher.

Can totally appreciate that. In either case - you're letting the jack do the work so T4 vs. H6 is minimal difference w.r.t. physical work.

I really love my Tangerine lift plate for T4 Suspecting someone probably makes something similar for 911 H6. I'll either need to find one or make one when I finally do the H6 swap.

You could always rig up some extra straps from above to limit risk of engine cocking and/or falling. Better yet, get a buddy for a 2nd set of eyes and hands for the 1st drop.

[Kansas 914]

Can totally appreciate that. In either case - you're letting the jack do the work so T4 vs. H6 is minimal difference w.r.t. physical work.

I really love my Tangerine lift plate for T4 Suspecting someone probably makes something similar for 911 H6. I'll either need to find one or make one when I finally do the H6 swap.

You could always rig up some extra straps from above to limit risk of engine cocking and/or falling. Better yet, get a buddy for a 2nd set of eyes and hands for the 1st drop.

I may resort to a drop - or partial drop. Really just now diffing into this. Hopefully I will kow more by the end of the afternoon.

[sixnotfour]

make sure off fuel delivery 1st..with air cleaner off lift the sensor plate you will hear , feel fuel flow.

[Kansas 914]

make sure off fuel delivery 1st..with air cleaner off lift the sensor plate you will hear , feel fuel flow.

Thanks Jeff,

I have started removing CIS components. Glad I did. The back nut on #5 and #6 runners were finger tight.

I can't trust anything done before I bought it.

It will be a good learning exercise for me.

[Kansas 914]

[quote name='Kansas 914' date='Jul 19 2020, 12:51 PM' post='2835190']
[quote name='sixnotfour' post='2835176' date='Jul 19 2020, 12:00 PM']
make sure off fuel delivery 1st..with air cleaner off lift the sensor plate you will hear , feel fuel flow.
[/quote]


I think this airbox has been repaired before...

[ClayPerrine]

Mike,
I would suggest that you get a replacement airbox. False air (that's what it is called when the air bypasses the metering plate) will make the car run lean and can burn it up inside. Also, it is possible to warp the metering plate and/or bend the arm for the metering plate. Simplest solution would be to buy a used CIS system to get the parts. Or you could do an EFI conversion on it. There is a kit available that will convert it. The kit comes complete with the Megasquirt, the injector adapters, injectors, wiring and plumbing.

BitzRacing CIS to EFI kit

(IMG:http://www.914world.com/bbs2/uploads_offsite/www.bitzracing.com-1143-1595189549.1.jpg)

[porschetub]

make sure off fuel delivery 1st..with air cleaner off lift the sensor plate you will hear , feel fuel flow.

Thanks Jeff,

I have started removing CIS components. Glad I did. The back nut on #5 and #6 runners were finger tight.

I can't trust anything done before I bought it.

It will be a good learning exercise for me.

Yes that will do it as I mentioned,I researched these motors as I was offered one @ a good price,the issue with loose plenum runners appear to be fairly common,the cure was to use thinner gaskets and locknuts if I remember correctly.
Looks like the airbox has been glued up with construction adhesive (IMG:style_emoticons/default/chair.gif) ,I don't know if finding a replacement will be too easy or cheap,you could take the part to a plastic repair guy and get it assessed for repair.
Good luck.

[Kansas 914]

Mike,
I would suggest that you get a replacement airbox. False air (that's what it is called when the air bypasses the metering plate) will make the car run lean and can burn it up inside. Also, it is possible to warp the metering plate and/or bend the arm for the metering plate. Simplest solution would be to buy a used CIS system to get the parts. Or you could do an EFI conversion on it. There is a kit available that will convert it. The kit comes complete with the Megasquirt, the injector adapters, injectors, wiring and plumbing.

BitzRacing CIS to EFI kit

Hi Clay,

It is very tempting for sure. I looked at it and a friend here in town did that to his 2.7L CIS 911. I haven't ruled it out...

I have a line on a good used air box and also new one ($300).

Say Hi to Betty - cheers!

[Kansas 914]

Yes that will do it as I mentioned,I researched these motors as I was offered one @ a good price,the issue with loose plenum runners appear to be fairly common,the cure was to use thinner gaskets and locknuts if I remember correctly.
Looks like the airbox has been glued up with construction adhesive (IMG:style_emoticons/default/chair.gif) ,I don't know if finding a replacement will be too easy or cheap,you could take the part to a plastic repair guy and get it assessed for repair.
Good luck.

Thanks - I have a line on a good used air box ($200) and a brand new one ($300).

The more I dig into this motor things are loose - vacuum lines are suspect all could have been part of the problem. I have had this car for 3 years and it has been a champ until the CIS backfire. I went to lift the 4-5-6 side of the air box up and the boots fell off the air box.... (IMG:style_emoticons/default/mad.gif)

[Jim2]

Hi I'm from pelican. I had asked you about the status of your airbox because in the event it's boogered I likely have a good deal for you, if you are interested. The repair to your airbox doesn't look great but maybe it's just fine. If not speak up.

Jim

Yes that will do it as I mentioned,I researched these motors as I was offered one @ a good price,the issue with loose plenum runners appear to be fairly common,the cure was to use thinner gaskets and locknuts if I remember correctly.
Looks like the airbox has been glued up with construction adhesive (IMG:style_emoticons/default/chair.gif) ,I don't know if finding a replacement will be too easy or cheap,you could take the part to a plastic repair guy and get it assessed for repair.
Good luck.

Thanks - I have a line on a good used air box ($200) and a brand new one ($300).

The more I dig into this motor things are loose - vacuum lines are suspect all could have been part of the problem. I have had this car for 3 years and it has been a champ until the CIS backfire. I went to lift the 4-5-6 side of the air box up and the boots fell off the air box.... (IMG:style_emoticons/default/mad.gif)

[Kansas 914]

Hi I'm from pelican. I had asked you about the status of your airbox because in the event it's boogered I likely have a good deal for you, if you are interested. The repair to your airbox doesn't look great but maybe it's just fine. If not speak up.

Jim

Hi Jim,

Yes I remember you from the Bird Board.

I am on the fence as to what direction to go. I don't trust the air box that was in the car nor do I trust anything related to the fuel management system. I will probably replace the air box - injector inserts - O-rings - runner boots and all vacuum lines.