AT Decel in a Manual FI Bug?

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JRR
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AT Decel in a Manual FI Bug?

Post by JRR » Tue May 21, 2019 10:50 am

Hello,

On an earlier episode, I thought my decel valve was removed and replaced with some sort of manifold block off. But with further study, I think that I have a AT decel valve:

I am backfiring (....popping) quietly on slow down in gear. I'm suspecting that this misapplication is the culprit. Can this be made to work with a manual, or should I pick up the specified valve?
2019-05-21 (1).jpeg
2019-05-21 (1).jpeg (63.09 KiB) Viewed 7669 times
Also, on a completely different note purely for the love of knowledge, how does the EGR valve logic work from the ECU? What conditions activate/deactivate? I installed a new exhaust and egr filter and removed the PO's block-off plate.

Thanks as always.

Jeff

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asiab3
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Re: AT Decel in a Manual FI Bug?

Post by asiab3 » Tue May 21, 2019 10:45 pm

Hi Jeff,

That sorta looks like the standard decel valve to me.* It should have another hose (4mm) tee'd into the intake plenum vacuum hose, shared with the fuel pressure regulator. A vacuum leak could certainly cause a leaner mixture and result in little backfires. Check any VW decel valve by disconnecting its outlet hose and plugging the hose. Have a helper start the car while your put your thumb over the decel valve nipple. Rev the engine a bit and let the throttle snap shut; you will feel suction at the nipple if the valve is working properly.

*But it also looks like the fuel pressure regulator, with those clamped hoses coming out of it. Check the front right side of the engine compartment for the FPR, and see if it's plumbed in correctly. It would not be the first time we've seen fuel injection components hooked up improperly…

Just like an early fuel-injected bus, you have a vacuum-electrical EGR valve- that means the vacuum signal is used to close a ball valve when allowed electronically. Your throttle body has a switch used to detect idle and full throttle conditions. At idle the air:fuel mixture can be picky, so we don't want gas recirculation, and under full throttle we want maximum power, so EGR is again cut out. (Later buses did this with a two-sided mechanical valve.) It's possible the ECU doesn't even process the signal from the throttle switch; the valve is just a solenoid-type-device that closes off when 12v is applied to it. On the other hand, the ECU could also take engine temperature or speed into account too, but I don't know for certain.

Test the vacuum-electric EGR valve and throttle switch with a test light or voltmeter in the sockets of the EGR plug, (disconnected.) Ignition on, there should be 12v across the wires with the throttle at idle and full throttle only. Reconnecting the EGR plug, you should also hear a click when actuating the throttle from idle and when reaching full throttle. With the engine on at idle, speed should drop when disconnecting the EGR plug.

See you on the road,
Robbie
1969 bus, "Buddy."
145k miles with me.
322k miles on Earth.

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JRR
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Re: AT Decel in a Manual FI Bug?

Post by JRR » Wed May 22, 2019 4:54 am

Awesome. Thanks very much.

On the decel valve, the is not a vacuum "booster" or nipple for another vacuum line. But, I think my question was moot anyway. I went exhaust leak hunting again and while crawling under the car, found a small crack in the DS heater box/exhaust manifold flange that I missed earlier. I bet that's the backfiring issue. But I'll test the decel valve for kicks.

Very interesting information about the EGR, appreciate it very much.

As always,

Jeff

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Re: AT Decel in a Manual FI Bug?

Post by JRR » Thu May 23, 2019 5:22 am

Hello,

More EGR questions, if I may. I got the 12v across the EGR plug and heard the click when re-attaching the socket. However I did not get the drop in RPM while idling when plug disconnected. After some reading, I think that the EGR nozzle is clogged, cut cannot find an online resource about what I should look for before I disassemble the unit. Is there a link or documentation I am missing?

Thanks again.

Jeff

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Re: AT Decel in a Manual FI Bug?

Post by asiab3 » Fri May 24, 2019 2:30 am

There isn't much documentation out there that I've found, but a 10mm wrench or two and a cold engine can have you seeing almost-cut-away views followed by reassembly of all the parts in an hour or two. (The last paragraph in Bug Bentley Land, Engine Chapter regards the EGR assembly, so that can help with order of operations.)

If you have the EGR valve removed, a short 4mm vacuum hose will allow your best milkshake-sucking technique to move the check ball and visibly open the valve. If the car sat for a while or has a dirty filter, I suspect that valve could be quite hard to actuate. If bugs and buses use the exact same part, you are welcome to my spare for the cost of shipping.

If your PO did not understand the benign nature of EGR, they may have blocked off the plumbing at either end of the muffler, filter, riser pipe, or valve. I haven't witnessed a clogged EGR filter personally, but VW thought it was important enough to add a 30,000 mile maintenance light to the dash on late bugs, so it's either a possibility too, or a marketing gimmick.

That being said, a clogged EGR system will not make the car undrivable. In fact it will run quite well if nothing is leaking air, though combustion temperature and NOx emissions will be increased.

Good luck,
Robbie
1969 bus, "Buddy."
145k miles with me.
322k miles on Earth.

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Re: AT Decel in a Manual FI Bug?

Post by JRR » Fri May 24, 2019 4:04 am

Thanks Robbie,

When I replaced the exhaust, I found the PO's copper block off in the joint between the connector pipe and the filter. My interest in it is almost purely academic, and it sits right there.

Will update as I go,

Jeff

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Re: AT Decel in a Manual FI Bug?

Post by Amskeptic » Fri May 24, 2019 7:12 am

JRR wrote:
Fri May 24, 2019 4:04 am
Thanks Robbie,

When I replaced the exhaust, I found the PO's copper block off in the joint between the connector pipe and the filter. My interest in it is almost purely academic, and it sits right there.

Will update as I go,

Jeff
Only a clear egr system will give you the engine stall test.

Robbie, a rich mixture can clog an egr system in no time, and 1970's fuel formulations had a lot of ash.
VW HAD to offer EGR service to comply with US law. I think we all know how much they respect US laws.
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

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Re: AT Decel in a Manual FI Bug?

Post by asiab3 » Fri May 24, 2019 11:52 am

You mean gasoline wasn't always perfect and pure in the good 'ol days like the guys at the car shows tell me about?? I mean, they said I didn't need any of that fuel injection stuff anyway…

Just yesterday I just learned about the 1968 nine-pin flasher relay, as VW's wonky attempt to satisfy new turn signal laws requiring dash flashing to noticeably change when a bulb burns out. Seems like they cared a lot more back then. :)

Robbie
1969 bus, "Buddy."
145k miles with me.
322k miles on Earth.

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Re: AT Decel in a Manual FI Bug?

Post by Amskeptic » Fri May 24, 2019 8:00 pm

asiab3 wrote:
Fri May 24, 2019 11:52 am
Just yesterday I just learned about the 1968 nine-pin flasher relay, as VW's wonky attempt to satisfy new turn signal laws requiring dash flashing to noticeably change when a bulb burns out.
Got cite?
Colin
( I remember that a missing bulb changes the frequency of the bimetal due to less heat at the "make" and cools rapidly back to "break" ...)
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

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Re: AT Decel in a Manual FI Bug?

Post by asiab3 » Mon May 27, 2019 10:54 pm

Amskeptic wrote:
Fri May 24, 2019 8:00 pm
Got cite?
Colin
( I remember that a missing bulb changes the frequency of the bimetal due to less heat at the "make" and cools rapidly back to "break" ...)
Telford's troubleshooting article briefly mentions it…
http://flowcon.us/td/9pinRelay/
(available during west coast daylight hours only, usually)

But this is the article I read the other night when a friend's '68 bus inner dash light stopped working. (My diagnosis: unpure grounds; the bulbs lit up enough to make us think that they were working, but they weren't carrying enough current to trip the load-based section of the relay talked about here:)
http://www.type2.com/library/electris/vw-9prong.html

(Cleaning the bulb sockets and adding the silly '68 and earlier missing taillamp housing ground wires a la '69-'71 buses cured the issue.)

For a legal cite:
*49 CFR § 571.108 - Standard No. 108; Lamps, reflective devices, and associated equipment. S9.3.6 "Turn signal lamp failure. Failure of one or more turn signal lamps such that the minimum photometric performance… …is not being met must be indicated by the turn signal pilot indicator by a… …significant change in the flashing rate…"
https://www.law.cornell.edu/cfr/text/49/571.108

I parsed the end because it talked a lot about trailer light wiring exemptions, which the bus in question was wired and equipped for…
Robbie
1969 bus, "Buddy."
145k miles with me.
322k miles on Earth.

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Re: AT Decel in a Manual FI Bug?

Post by Amskeptic » Tue May 28, 2019 6:44 am

asiab3 wrote:
Mon May 27, 2019 10:54 pm
Amskeptic wrote:
Fri May 24, 2019 8:00 pm
Got cite?
Colin
( I remember that a missing bulb changes the frequency of the bimetal due to less heat at the "make" and cools rapidly back to "break" ...)
Telford's troubleshooting article briefly mentions it…
http://flowcon.us/td/9pinRelay/
(available during west coast daylight hours only, usually)

But this is the article I read the other night when a friend's '68 bus inner dash light stopped working. (My diagnosis: unpure grounds; the bulbs lit up enough to make us think that they were working, but they weren't carrying enough current to trip the load-based section of the relay talked about here:)
http://www.type2.com/library/electris/vw-9prong.html

(Cleaning the bulb sockets and adding the silly '68 and earlier missing taillamp housing ground wires a la '69-'71 buses cured the issue.)

For a legal cite:
*49 CFR § 571.108 - Standard No. 108; Lamps, reflective devices, and associated equipment. S9.3.6 "Turn signal lamp failure. Failure of one or more turn signal lamps such that the minimum photometric performance… …is not being met must be indicated by the turn signal pilot indicator by a… …significant change in the flashing rate…"
https://www.law.cornell.edu/cfr/text/49/571.108

I parsed the end because it talked a lot about trailer light wiring exemptions, which the bus in question was wired and equipped for…
Robbie
Thank-you Robbie. I will plow into this after I get to new York City later today over the Tappan Zee Bridge in the rain, same as when I left on September 3rd , 2018, watch out New York, don't make me blow a fuse ...
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

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JRR
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Re: AT Decel in a Manual FI Bug?

Post by JRR » Sat Jun 08, 2019 6:12 pm

Hello,

Took apart the EGR valve as threatened. Pics below of the exploratory surgery:
IMG_3188.jpg
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The EGR side was clogged with white chalky substance which I assume was fully oxidized carbon deposit. The EGR was copper gasket-ed off from the exhaust delivery pipe. Cleared the blockage and removed the copper. Everything came apart and went back together pretty easily.

The EGR diaphragm seems good and will hold the plunger with mouth vacuum. The throttle switch seems to activate the solenoid appropriately. Tested with ignition on and engine not running.

But I'm not getting the idle slowdown when I remove the electrical connector. Is this a foolproof test? Could there be more blockage down the plenum? I did not see anything before the curve.

Also, does anybody have a couple of the EGR gaskets I can peel off them? I'll send a SASE and however many clams within reason they want.

Thanks

Jeff
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asiab3
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Re: AT Decel in a Manual FI Bug?

Post by asiab3 » Sun Jun 09, 2019 8:31 am

Nice find! I’m away from Bentley right now and can’t recall if there are any other tests mentioned... Does your EGR plumbing get hot while driving? Most functioning pipes will get hot to the touch after a few minutes on the road.

Exhaust gasket paper can be purchased online or at an old fashioned muffler shop, you know the kind with the older staff, thousands of gaskets hanging from the wall, and general clutter from 1973 laying around... Harbor Freight sells a decent leather hole punch kit that should have both sizes to punch holes in the gaskets. By the time you’ve purchased three or four gaskets and shipping, you’ll break even and have supplies to make more in the future. :)
Good luck,
Robbie
1969 bus, "Buddy."
145k miles with me.
322k miles on Earth.

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Re: AT Decel in a Manual FI Bug?

Post by JRR » Sun Jun 09, 2019 5:15 pm

Hello,

EGR Working. Removed Throttle Body to clear the 90deg tube from EGR to TB. Also the TB port was blocked. The TB port is smaller than I expected +/- 4mm. I understand the yearly maintenance requirement. Also, not easy to remove bug TB. Keep magnet handy to fish out the 13mm nut and washers from between the fan shroud and intake plenum. Will need magnet to set the washer and nut on the rear TB stud.

Removing the EGR electrical connector at idle does drop the idle noticeably.

Thanks for your help!

Jeff

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Re: AT Decel in a Manual FI Bug?

Post by asiab3 » Mon Jun 10, 2019 12:32 am

Glad you got it all sorted out! Are you subject to emissions testing, or just want a docile and smooth New VW Experience?
Robbie
1969 bus, "Buddy."
145k miles with me.
322k miles on Earth.

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