Bucking

Fastback, Squareback, Notchback, T-3 Karmann Ghia.

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whc03grady
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Post by whc03grady » Tue Feb 23, 2010 9:39 pm

Latest post of the previous page:

tristessa wrote:Please tell me you got that "new" muffler installed since that picture was taken.
No, but I've taken the overriders off and cleaned it off some. It's getting there....
Ludwig--1974 Westfalia, 2.0L (GD035193), Solex 34PDSIT-2/3 carburetors.
Gertie--1971 Squareback, 1600cc with Bosch D-Jetronic fuel injection from a '72 (E brain).
Read about their adventures:
http://www.ludwigandgertie.blogspot.com

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Amskeptic
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Post by Amskeptic » Wed Feb 24, 2010 12:57 am

whc03grady wrote:
tristessa wrote:Please tell me you got that "new" muffler installed since that picture was taken.
No, but I've taken the overriders off and cleaned it off some. It's getting there....
P.S. Air leaks cause rich in D-Jet, lean in L-Jet.

A vacuum leak drops vacuum. The MPS reads vacuum. Any drop in vacuum is an assumed call for more fuel. This is a great fail-safe.

L-Jet reads air flow, not vacuum. Any leak reduces airflow and the ECU leans the mixture. Bad.
How's it tracking down the road? Like a cute little crab scampering back to the water or like a CAR?
Colin
BobD - 1978 Bus . . . . . . . . . . .111,130 miles
Chloe - 1970 bus . . . . . . . . . . . 206,787 miles
Naranja - 1977 Westfalia . . . . . 93,996 miles
Pluck - 1973 Squareback . . . . . 55,510 miles
Alexus - 1991 Lexus LS400 . . . 72,113 miles

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Bleyseng
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Post by Bleyseng » Wed Feb 24, 2010 8:52 am

true but "bucking" in djet is usually a lean condition as the AFR is just too lean say above 15 to one.
Geoff
77 Sage Green Westy- CS 2.0L-160,000 miles
70 Ghia vert, black, stock 1600SP,- 139,000 miles,
76 914 2.1L-Nepal Orange- 160,000+ miles
http://bleysengaway.blogspot.com/

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whc03grady
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Post by whc03grady » Wed Feb 24, 2010 3:15 pm

I was working with the assumption that the bucking and the richness were not closely related. Since the "new" MPS seems to have eliminated the bucking, I made the additional assumption that the bucking wasn't caused by vacuum leaks. (As you might guess, I clearly do a lot of a priori mechanicking, since I'm such a scaredy-cat.)
Ludwig--1974 Westfalia, 2.0L (GD035193), Solex 34PDSIT-2/3 carburetors.
Gertie--1971 Squareback, 1600cc with Bosch D-Jetronic fuel injection from a '72 (E brain).
Read about their adventures:
http://www.ludwigandgertie.blogspot.com

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hambone
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Post by hambone » Wed Feb 24, 2010 3:29 pm

Ya gotta go on a hunch first. Heck it's usually correct.
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Bleyseng
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Post by Bleyseng » Wed Feb 24, 2010 5:07 pm

you could have "two" problems...a cold start richness which shows up on the bumper and a leaning out issue.
Ok, as Colin stated- vacuum leaks cause richness in Djet as the MPS is calibrated to the engine vacuum. Over 15hg of vacuum is idle circuit, the part-load is from 6 to 4 hg (which is where you drive at. Off idle 2000 to 2500 rpms), WOT is Ohg of vacuum.
So if you have cold start richness, it could be the CHT is going/resistance is off.
OR vacuum leaks when the engine is cold so the engine vacuum is reading low say at idle in the 12 to 13 range. Again this richens the mix but as the engine heats up all the metal expands sealing the vacuum leak healing the AFR..
Yep, been there done that! So if you have a vacuum gauge that you can plug into the engines vacuum ports, run a test cold start up and see the results..
Does the needle swing or read a low vacuum at idle?
The other issue you solved by installing a different MPS but is that the correct MPS for your Djet FI setup. Each year they damn near changed it alittle to correct or improve on it so if your off it can affect the AFR because the MPS is calibrated for a different setup of parts. Its not a mix and match system as its all hard wired in the ECU and the MPS is calibrated (injection pulse width via the inductance reading) to the vacuum signature.

I do have a Janbo Djet tester I drag out to test guys setup when they are ready to rip their hair out in frustration.
Geoff
77 Sage Green Westy- CS 2.0L-160,000 miles
70 Ghia vert, black, stock 1600SP,- 139,000 miles,
76 914 2.1L-Nepal Orange- 160,000+ miles
http://bleysengaway.blogspot.com/

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whc03grady
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Post by whc03grady » Thu Mar 04, 2010 2:45 pm

Bleyseng wrote: The other issue you solved by installing a different MPS but is that the correct MPS for your Djet FI setup?
I believe that it is. The car is a '71, but the engine (or the injection system anyway) is a California '72: it has an E brain--and hence, a 311 906 051E MPS--and the funny little extra gizmo hanging out by the MPS, whose name escapes me at the moment.
I think I am now in the market for a vacuum tester. And the Craftsman catalog came just this week! Kismet.
Ludwig--1974 Westfalia, 2.0L (GD035193), Solex 34PDSIT-2/3 carburetors.
Gertie--1971 Squareback, 1600cc with Bosch D-Jetronic fuel injection from a '72 (E brain).
Read about their adventures:
http://www.ludwigandgertie.blogspot.com

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whc03grady
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Re: Bucking

Post by whc03grady » Wed Sep 19, 2012 7:15 pm

Okay, the bucking/loping/whatever you want to call it returned out of nowhere, with a vengeance. It was running really well after Colin's visit (I don't remember exactly what we did, besides take apart and clean the throttle valve switch) for 600 miles and then, alla sudden this afternoon it's back at it. At steady throttle and under load it runs, dies off, picks back up, dies off, etc. etc. At idle it is much less apparent, sometimes not misbehaving at all. In neutral, it seems to take the revs in stride and doesn't act funny.

I looked at the fuses because Melissa said she thought she heard one blow and sure enough, the fuel pump fuse was blown. But it still ran. Hmmmm. I took the fuel pump fuse out while the car was running--no change. Double hmmmmm.

So that's where I am. I'm clueless. Why the fine running (well, pretty fine: there was occasional stumbling at transition) for all those miles and then this?
Ludwig--1974 Westfalia, 2.0L (GD035193), Solex 34PDSIT-2/3 carburetors.
Gertie--1971 Squareback, 1600cc with Bosch D-Jetronic fuel injection from a '72 (E brain).
Read about their adventures:
http://www.ludwigandgertie.blogspot.com

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Amskeptic
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Re: Bucking

Post by Amskeptic » Mon Sep 24, 2012 7:14 am

whc03grady wrote:Okay, the bucking/loping/whatever you want to call it returned out of nowhere, with a vengeance.
I looked at the fuses because Melissa said she thought she heard one blow and sure enough, the fuel pump fuse was blown. But it still ran. Hmmmm.
Did Melissa hear the fuse blow *in relation to* the return of the bucking?
ColinCheckGroundAtManifoldSensorToo
BobD - 1978 Bus . . . . . . . . . . .111,130 miles
Chloe - 1970 bus . . . . . . . . . . . 206,787 miles
Naranja - 1977 Westfalia . . . . . 93,996 miles
Pluck - 1973 Squareback . . . . . 55,510 miles
Alexus - 1991 Lexus LS400 . . . 72,113 miles

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whc03grady
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Re: Bucking

Post by whc03grady » Tue Sep 25, 2012 5:31 am

Amskeptic wrote:
whc03grady wrote:Okay, the bucking/loping/whatever you want to call it returned out of nowhere, with a vengeance.
I looked at the fuses because Melissa said she thought she heard one blow and sure enough, the fuel pump fuse was blown. But it still ran. Hmmmm.
Did Melissa hear the fuse blow *in relation to* the return of the bucking?
ColinCheckGroundAtManifoldSensorToo
There was no seeming correspondence betwixt the two; the fuse blew one day, it drove fine home from the grocery store, and the next day it started acting up.
Ludwig--1974 Westfalia, 2.0L (GD035193), Solex 34PDSIT-2/3 carburetors.
Gertie--1971 Squareback, 1600cc with Bosch D-Jetronic fuel injection from a '72 (E brain).
Read about their adventures:
http://www.ludwigandgertie.blogspot.com

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Amskeptic
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Re: Bucking

Post by Amskeptic » Wed Sep 26, 2012 8:04 am

whc03grady wrote:
Amskeptic wrote:
whc03grady wrote:Okay, the bucking/loping/whatever you want to call it returned out of nowhere, with a vengeance.
I looked at the fuses because Melissa said she thought she heard one blow and sure enough, the fuel pump fuse was blown. But it still ran. Hmmmm.
Did Melissa hear the fuse blow *in relation to* the return of the bucking?
ColinCheckGroundAtManifoldSensorToo
There was no seeming correspondence betwixt the two; the fuse blew one day, it drove fine home from the grocery store, and the next day it started acting up.
OK, it still ran because your fuel pump has a private owner-installed circuit.
Do your due diligence in looking at grounds connections I shall pray . . .
Colin
BobD - 1978 Bus . . . . . . . . . . .111,130 miles
Chloe - 1970 bus . . . . . . . . . . . 206,787 miles
Naranja - 1977 Westfalia . . . . . 93,996 miles
Pluck - 1973 Squareback . . . . . 55,510 miles
Alexus - 1991 Lexus LS400 . . . 72,113 miles

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