Blown airbox - replace, prevent and while I'm in there

[bsimonson]

Originally Posted by manbridge 74

@bsimonson: I'd apply 12 volts to your CSV and backflush it, then connecting it to fuel pressure and checking spray pattern before re-installing it.

I've planned to do the latter part but I'm not sure on how to backflush it...

Originally Posted by boyt911sc

bsimonson,

You have done the easy part (removal in situ). If you could do the installation under 12 hours (no cheating), you are A+ DIY'er in my book. You are a good example to others for initiative and effort. I've removed my CIS before this way and I'll never do it again because it's a back breaking task.

Tony

Yes, my back is a bit sore...we'll see how long it takes to get it back in but I sure hope that it will be less than 12h

Originally Posted by Peter Zimmermann

bsimonson; Be sure to cap off those fuel lines! A tiny piece of crud in the gasoline/fuel distributor/injector can make your life miserable on start-up!

BTW; the unused hose nipple is that way because the vacuum hose nearby used to be connected to that valve. If you re-connect the hose the car will probably have fast idle issues. To make it tidy, most of the time the hose will have a BB, or similar, shoved into it, and then it gets connected to it's nipple.

Ok, and the idle is not affected by the nipple not being connected at all?

/b

[bsimonson]

Today I've made a quick clean of the parts that might need replacement.

The sensor plate seemed find but needed a small adjustment to the rest height.

One of the screws that hold the mixture control unit was a pain to get out and there was a bit or rust between the distributor and the housing, but other than that it seemed fine, the plunger was clean and moved freely.



The smaller, non-braided breather hose was definitely past it and the bigger one probably needs to be replaced as well. The other vacuum and AA lines are fine.

The throttle housing was dirty (and still needs some more cleaning) but I could not see anything that was wrong. Is it possible to verify that the TPS is ok?



I also looked over the wires still in the car and the wires to the connector that goes on the back of the sensor plate housing looked slightly burned and not in a good shape. Is it possible to open the connector and replace the wires or do I need a new connector?

So, seems that Peter was pretty much right on the money with his list:

6x intake manifold gaskets
6x intake runner/airbox sleeves
6x injector o-rings
6x injector sleeves
6x injector sleeve o-rings
1x thermostat o-ring
1x oil pressure switch (for the idiot light)
2x throttle lever (bell crank) bushings for the throttle linkage console on top of the engine
2x rubber bushings that secure the airbox brackets to the airbox (at cyl #6 & at the throttle lever console)
1x cold start injector o-ring
1x cold start injector spacer o-ring
1x throttle body o-ring
1x sensor plate housing gasket

The only thing I will add are:

1x mixture unit o-ring
1x large breather hose
1x small(er) breather hose

Is it possible/worthwhile to replace the crankcase breathing gasket?

/b

[bsimonson]

I've been on vacation the past week but my order from PP has cleared Swedish customs and should be here in a few days

What I did not order was the crankcase breather hose and I'm now having second thoughts about not replacing it...so today I found a generic hose that might be suitable. My only concern is that it is only rated up to 100 deg C / 212 deg F, is that enough?

I also have a question about the connector type that goes on the AAR, CSV etc, can they be opened to have the wires replaced?

/b

[Peter Zimmermann]

Originally Posted by bsimonson

I've been on vacation the past week but my order from PP has cleared Swedish customs and should be here in a few days

What I did not order was the crankcase breather hose and I'm now having second thoughts about not replacing it...so today I found a generic hose that might be suitable. My only concern is that it is only rated up to 100 deg C / 212 deg F, is that enough?

I also have a question about the connector type that goes on the AAR, CSV etc, can they be opened to have the wires replaced?

/b

For your electrical plug question; write to: Replacement Porsche 914 Wiring Harnesses

Yes, he's a 914 guy, but I'm sure that he can answer your question. Regarding the plugs, if you look into their open end, you will see a tiny lock tab which must be bent toward the metal connector. After that you can push the connector/wire out of the plastic plug.

Breather hose. Never used an after market breather hose; wouldn't risk it. Remember, it not only has to seal air, it must seal oil residue.

[bsimonson]

Well, I'm halfway there I think. Almost all the CIS-parts are cleaned and checked over and the engine/engine bay is cleaner than in a long time. I'm also done with the while-you're-in-there stuff + some more. There is a picture on my blog - engine cleaned up and seals replaced

I've decided to make an attempt to glue the air box back together, we'll see how that works out...

I hope to have it finished by Saturday so I can go to the Porsche meet on Sunday!

[bsimonson]

Originally Posted by Peter Zimmermann

For your electrical plug question; write to: Replacement Porsche 914 Wiring Harnesses

Yes, he's a 914 guy, but I'm sure that he can answer your question. Regarding the plugs, if you look into their open end, you will see a tiny lock tab which must be bent toward the metal connector. After that you can push the connector/wire out of the plastic plug.

Breather hose. Never used an after market breather hose; wouldn't risk it. Remember, it not only has to seal air, it must seal oil residue.

I failed to get the connectors out even though I tried using just about anything I could find to get the lock tab down. Luckily there were enough good wire left on the connector side to attach crimp connectors so that is sorted.

The hose is oil/fuel rated so that is reassuring, but obviously an original part would be best.

Thanks for taking the time to help out!

/Bjφrn

[tirwin]

Originally Posted by Peter Zimmermann

Pop-Off Valve - PART 2:

I just want to say thanks to Peter Z for posting this. I've owned my '83 for about a year and when I got it I had to sort out a whole bunch of issues with the CIS. (I'm still not entirely confident it's all sorted but I'm continuing to work on it.)

I have been bumbling and fumbling my way along trying to understand the CIS system so the suggestions people were giving me would make sense as far as what they were intended to accomplish. I think I frustrated a few of the CIS experts on here in the process of my dumbness. (sorry fellas) The lightbulb was just not clicking for me.

Then I read these two posts. CLICK. I have read a lot but I always felt like some piece of the explanation was missing. Now I think I get it. Thanks again, Peter! HUGE help for me.

[bsimonson]

Last Saturday I began putting the CIS back in and it went well, it took about 3 hours.

Unfortunately I sheared one of the banjo bolts in the process so that has held me up until today with the preparations before the first start.

I've now checked the following:

That there are no fuel-leaks.

Cold system pressure: 4,9 - OK
Cold control pressure: 2,5 (@ 20 degree C) - OK
Cold residual pressure: 1,5 after 10 minutes - OK

Spray patterns: All injectors spray and does not leak, but their patterns look a bit off although quite similar, I'm thinking I should replace all of them although they probably work for now (?).

Ignition timing: Here I got a bit confused. The red marking just past the fan housing marking is the one marked with Z1, but why would there be a marking at 5 deg ATDC? Or is the other mark the TDC? I guess I can always pull the plug on cylinder one and see where TDC really is...



(Sry about the pic, it's shot off a pocket mirror)


I also need to check that the CSV injects as meant, but for that I need a helper so I will have to do it tomorrow.

Any other ideas for stuff to check before turning the key for real?

/b

[bsimonson]

So, today I verified that the CSV is spraying and made the final adjustment to the ignition before taking a deep breath and turning the key

The car fired right up and settled on a high idle. I had a quick look in the back but could not see anything worrying so I took it for a drive around the block. It was way more responsive than it has ever been and what was normal throttle input before was now way too much.

Unfortunately I have commitments the rest of the day so I can't take it for a longer drive but it feels great to have running again.

Many thanks to Peter Z for your advice and to the rest of you guys too!

[HarryD]

Originally Posted by Peter Zimmermann

Yes, all replacement airboxes, except the unit (last time that I checked) made specifically for the '73.5 T, are fitted with the internal diffuser. And, please, don't forget to either set, or have it done professionally, the cold control pressure. I can't stress the importance of doing that, as well as being sure that the sensor plate height is correct and the plate is not bent.

When cold control pressure is ideal, the car will cold idle "surge" gently for a few seconds (sometimes as many as 30 seconds) after being cold started. This is because the cold mixture is set on the rich side of the range that can be found in the factory repair manual.

Pete,

As the happy owner of a 1973.5 CIS car, I do have a pop off in my car. Sadly, it has been called to duty several times during my period of ownership since 2002.

About 2 years ago, I had a back fire that caused the valve to be shot out of it's hole. I pushed it back in and verifed no air leaks and continued to motor on (I was on the road at the time). when I returned home, I decided to glue it back in but instead of using epoxy or urethane glue. I used a thin bead of of silicone sealant. Why? By my reasoning, it does not hold as well as some of the other glues but is adequate. In the event of the next backfire (which I typically notice when the car is very hot and then restarted), if the valve does not open, the glue may fail and allow the pop out valve to unseat. Since the silicone is soft, I figured it would allow me to reseat the valve and get a decent seal. I tested the box for leaks, found none and continued on my way.

Since then, I have had maybe 3 backfire events, two of which unseated the valve. I merely pushed the valve back in, verified no leaks and drove off.

While not ideal, I am not sure I truly have a better option given the year of my car.

I have had my mixture and other settings checked by a local garage who seems knowleagable in CIS and all is in order.

Sir, your thoughts?

[stlrj]

Originally Posted by HarryD

Pete,

As the happy owner of a 1973.5 CIS car, I do have a pop off in my car. Sadly, it has been called to duty several times during my period of ownership since 2002...

While not ideal, I am not sure I truly have a better option given the year of my car....

I have had my mixture and other settings checked by a local garage who seems knowleagable in CIS and all is in order.

Sir, your thoughts?

One option you might try would be to update your injection to the later '76 style with the updated diffuser inside the air box and your steel intake runners connected, along with some additional electrical connections for the aux air reg.

Done it on a '74, so it should work on a '73.5 and make air box explosions a thing of the past.


Cheers,

Joe

[donlan]

Hello, An interesting read[for me]. I printed out Peter Zimmermann's article about the pop-off valve,[Damm I had just installed one].had ALL the CIS components replaced/re-conditioned.Never had a backfire BEFORE but that's about all I get now. long story will have to start a "thread" of my own when I learn how to.Michael.

[Farrell]

how big of a backfire must you get to crack the airbox? my airbox is supposedly cracked from some very very MINOR backfires, as if you were poping small bubble wrap. is that all it takes?

Ive pretty much disconnected everything and am ready to remove my motor to replace this airbox but these seem like so much of a hassle to replace everything. i have a set of 46mm PMOs on the shelf that I'm thinking of installing over the new airbox, because i don't want to blow the new airbox and be in the same position. i just want to be able to drive this thing while we have nice weather.

[RDM]

Resurrecting an old, very helpful thread to add a little information. I'm in the middle of airbox replacement now. I have glued the halves of my backup box with 3M 8005, I have leak tested with water and stoppers (using lung pressure- I don't have compressed air handy), and am currently in the remove/replace stage. As help to those who come after, here is Peter Z's parts list, with numbers.

930 110 197 12 6x intake manifold gaskets
930 110 885 00 6x intake runner/airbox sleeves
999 701 423 40 6x injector o-rings
911 110 886 03 6x injector sleeves
999 701 446 40 6x injector sleeve o-rings
999 707 314 40 1x thermostat o-ring
900 123 101 30 1x oil pressure switch sealing ring (for the idiot light)
914 423 211 00 2x throttle lever (bell crank) bushings for the throttle linkage console on top of the engine
911 110 154 00 2x rubber bushings that secure the airbox brackets to the airbox (at cyl #6 & at the throttle lever console)
999 701 210 4A 1x cold start injector o-ring
999 701 395 50 1x cold start injector spacer o-ring
999 701 124 00 1x throttle body o-ring
911 110 394 02 1x sensor plate housing gasket

I found I had to order 4 o-rings from my local dealer to ensure I had all I need. I also have the crankcase breather cover on hand, just in case.
930 107 791 02 Crankcase breather cover

If I needed incentive for ITB/EFI, it's all these little hoses and gaskets and triple-jointed access required. But, one more try with the CIS....

[RDM]

OK, I'm 95% confident I know where the two identical connectors go, but that extra 5% would be really welcome. I saw this question on another thread, and the consequences for being wrong were fairly disastrous.

I say identical connectors, but that's only on the male end. On the female end, one connector is green and one is blue:


The green one has a brown and brown/red wire.

I think this is reflected in the 1978 factory wiring diagram trace 105, which shows brown and brown/black (as does the Bentley on 970-9), which would make this the air meter switch-component G19(associated with the fuel pump relay)

The blue one has three (!) wires, yellow, yellow/blue, and red, though it's only a two-wire connector.

This is somewhat consistent with the wiring diagrams, which show yellow, yellow/red, and red on trace 111 component N17 (Bentley 970-11), cold start valve, associated with the starter and thermo switch.

The colors aren't exactly the same, but neither are the wiring diagrams for my year (1980). So can someone confirm where the blue and green connectors connect too?

Many thanks.

[mike sampsel]

Hi Dru,

I think you’ll find answers here.

need help piecing together my CIS - 1981

I think the blue is cold start and is closer to cylinders 4,5,6 than the green one. Which best I recall. Seems if you get them reversed it will be obvious at run time per some other posts herein.

[RDM]

Originally Posted by mike sampsel

Hi Dru,

I think you’ll find answers here.

need help piecing together my CIS - 1981

I think the blue is cold start and is closer to cylinders 4,5,6 than the green one. Which best I recall. Seems if you get them reversed it will be obvious at run time per some other posts herein.

Very helpful link, thanks. A little more light in the engine bay and I can just make out that the air metering sensor has a slightly green plug and the cold start valve is slightly bluer. Everything points in the same direction; tomorrow is the day.

[Flojo]

either you're driving again and thus cannot post.
or it all blew up and you cannot post.

any news?

[47silver]

i used cigarette rolling paper to fit the sensor plate back into the assembly, I was able to place them completely around the inside of the plate and that gave a perfect fit.. that was 7 or so years ago and my 75 runs great.