Profile Picture

Need pt pump guru for AFC issue

Posted By Workshoprat92 2 Months Ago
You don't have permission to rate!
Author
Message
glenn akers
Posted 2 Months Ago
View Quick Profile
6th Direct

6th Direct (1.9K reputation)6th Direct (1.9K reputation)6th Direct (1.9K reputation)6th Direct (1.9K reputation)6th Direct (1.9K reputation)6th Direct (1.9K reputation)6th Direct (1.9K reputation)6th Direct (1.9K reputation)6th Direct (1.9K reputation)

Group: Forum Members
Last Active: 6 hours ago
Posts: 1.4K, Visits: 8.7K
The first AFC pump did vent to the outside but the older plunger had a glide ring or seal and it would leak causing a fuel leak.So I remember the fix some what and it was plumbing it to the tank.Some of the first one vented thru a vent on top and some thru the front cover top rear bolt.I remember doing many of the updated but many years ago.Oil on the back side of the late diaphragm is common.

Glenn Akers
Geoff Weeks
Posted 2 Months Ago
View Quick Profile
13th direct

13th direct (3.3K reputation)13th direct (3.3K reputation)13th direct (3.3K reputation)13th direct (3.3K reputation)13th direct (3.3K reputation)13th direct (3.3K reputation)13th direct (3.3K reputation)13th direct (3.3K reputation)13th direct (3.3K reputation)

Group: Forum Members
Last Active: 6 hours ago
Posts: 2.7K, Visits: 17.6K
Ok, may be I am wrong, I thought I traced out that passage and found it vented at that point. I am not about to pull the pump and look, that was the way I remembered it.
 What did I get wrong on the operation of the system? I am open to learning!
jimfols
Posted 2 Months Ago
View Quick Profile
First Gear

First Gear (22 reputation)First Gear (22 reputation)First Gear (22 reputation)First Gear (22 reputation)First Gear (22 reputation)First Gear (22 reputation)First Gear (22 reputation)First Gear (22 reputation)First Gear (22 reputation)

Group: Forum Members
Last Active: 3 hours ago
Posts: 22, Visits: 885
Geoff Weeks (3/28/2019)

If you look close, above the middle bolt holding the front case on the body, you'll see a little hole, this is where the cavity vents. unless the seals on the shaft are bad, it should be dry. it is where the passage behind the afc diaphragm vents to.
 The plug you are pointing to should be 1/16" NPT, an odd size exactly so you don't go putting  line there. On earlier pumps with the line, that port is 1/8" NPT.  Earlier pumps with the looser fit AFC barrel did pass some fuel, and was vented back to the return line along with the pump cooling line. The class fit (or shape AFC) is so tight a tolerance on the plunger fit that no fuel should pass back there.  

Back when I helped you with your 0840 pump I said the AFC cavity vents through a hole in the front cover. That hole goes to the air compressor and on to the crankcase. Not to the weep hole.


Jim
jimfols
Posted 2 Months Ago
View Quick Profile
First Gear

First Gear (22 reputation)First Gear (22 reputation)First Gear (22 reputation)First Gear (22 reputation)First Gear (22 reputation)First Gear (22 reputation)First Gear (22 reputation)First Gear (22 reputation)First Gear (22 reputation)

Group: Forum Members
Last Active: 3 hours ago
Posts: 22, Visits: 885
Geoff Weeks (3/28/2019)
Just to be clear, the AFC vents not to the crankcase but to the point on the pump where the two shaft seals and bearing is on the input shaft of the pump. There is a seal to keep engine oil out on one side and to keep fuel out on the other. In between there is a little space and a slot cut in the pump housing so anything that gets past the seals will drain down the side of the block. the AFC is vented to this same space.
 I had the same question a while back and someone put me straight on it. Once I had the pump out and apart, it was clear.
 One question, was the oily black stuff on the pump side of the bellows or the aftercooler side? The plunger is a select fit (read close tolerance) so there shouldn't be fuel on the back side  Edit, re read and see it is on the pump side. How did the plunger fit in the bore? was it like a dick in a barrel or was it fairly tight? 

Please do not take it personally, there are some things in this post that do not reflect the true operating principal of the system.


Jim
Geoff Weeks
Posted 2 Months Ago
View Quick Profile
13th direct

13th direct (3.3K reputation)13th direct (3.3K reputation)13th direct (3.3K reputation)13th direct (3.3K reputation)13th direct (3.3K reputation)13th direct (3.3K reputation)13th direct (3.3K reputation)13th direct (3.3K reputation)13th direct (3.3K reputation)

Group: Forum Members
Last Active: 6 hours ago
Posts: 2.7K, Visits: 17.6K
Jim since you seam to be one of the go-to guys on the Big Cam's I have a question about the time roll out of the Big Cam 4's. It seams like all the different engines in that family (Big Cam 4, New Big Cam 4 , and NT88) all came out within a year or so of each other. I have a CPL 676 with an 1987 date and a NT88 with a Nov 88 build date. The 676 would be the early Big Cam 4 and the NT88 the last version all in the same year.  The NT88 is quite a bit different, but the New Big Cam 4 and the original Big Cam 4 aren't that different. The Updated fuel pump being one of the differences, along with STC on the higher HP and the intergraded full flow/ bypass oil filter.   It almost seams like they were changing things as the engines moved down the assembly line!  
Geoff Weeks
Posted 2 Months Ago
View Quick Profile
13th direct

13th direct (3.3K reputation)13th direct (3.3K reputation)13th direct (3.3K reputation)13th direct (3.3K reputation)13th direct (3.3K reputation)13th direct (3.3K reputation)13th direct (3.3K reputation)13th direct (3.3K reputation)13th direct (3.3K reputation)

Group: Forum Members
Last Active: 6 hours ago
Posts: 2.7K, Visits: 17.6K

If you look close, above the middle bolt holding the front case on the body, you'll see a little hole, this is where the cavity vents. unless the seals on the shaft are bad, it should be dry. it is where the passage behind the afc diaphragm vents to.
 The plug you are pointing to should be 1/16" NPT, an odd size exactly so you don't go putting  line there. On earlier pumps with the line, that port is 1/8" NPT.  Earlier pumps with the looser fit AFC barrel did pass some fuel, and was vented back to the return line along with the pump cooling line. The class fit (or shape AFC) is so tight a tolerance on the plunger fit that no fuel should pass back there.  
Geoff Weeks
Posted 2 Months Ago
View Quick Profile
13th direct

13th direct (3.3K reputation)13th direct (3.3K reputation)13th direct (3.3K reputation)13th direct (3.3K reputation)13th direct (3.3K reputation)13th direct (3.3K reputation)13th direct (3.3K reputation)13th direct (3.3K reputation)13th direct (3.3K reputation)

Group: Forum Members
Last Active: 6 hours ago
Posts: 2.7K, Visits: 17.6K
Just to be clear, the AFC vents not to the crankcase but to the point on the pump where the two shaft seals and bearing is on the input shaft of the pump. There is a seal to keep engine oil out on one side and to keep fuel out on the other. In between there is a little space and a slot cut in the pump housing so anything that gets past the seals will drain down the side of the block. the AFC is vented to this same space.
 I had the same question a while back and someone put me straight on it. Once I had the pump out and apart, it was clear.
 One question, was the oily black stuff on the pump side of the bellows or the aftercooler side? The plunger is a select fit (read close tolerance) so there shouldn't be fuel on the back side  Edit, re read and see it is on the pump side. How did the plunger fit in the bore? was it like a dick in a barrel or was it fairly tight? 
jimfols
Posted 2 Months Ago
View Quick Profile
First Gear

First Gear (22 reputation)First Gear (22 reputation)First Gear (22 reputation)First Gear (22 reputation)First Gear (22 reputation)First Gear (22 reputation)First Gear (22 reputation)First Gear (22 reputation)First Gear (22 reputation)

Group: Forum Members
Last Active: 3 hours ago
Posts: 22, Visits: 885
The fuel code is 4405. It is for CPL-0796 an NTC 315 New BCIV.
The New BCIV is not the same as an 88 BCIV.
It uses a Class Fit AFC barrel and plunger.
The AFC cavity must be vented to the atmosphere on all AFC pumps.
On the class fit assemblies the cavity is vented through the fuel pump front cover into the crankcase.
Please do not take it personally, there are some things in the original post that do not reflect the true operating principal of the system.
Did you change the fuel filter?


Jim
Jeff Lakaszcyck
Posted 2 Months Ago
View Quick Profile
13th Over

13th Over (11.1K reputation)13th Over (11.1K reputation)13th Over (11.1K reputation)13th Over (11.1K reputation)13th Over (11.1K reputation)13th Over (11.1K reputation)13th Over (11.1K reputation)13th Over (11.1K reputation)13th Over (11.1K reputation)

Group: Administrators
Last Active: 5 hours ago
Posts: 7.9K, Visits: 140.4K
This should be better.

http://forums.justoldtrucks.com/uploads/images/2bd36f55-4ffb-4712-97c2-819b.jpg

Jeff
Workshoprat92
Posted 2 Months Ago
View Quick Profile
First Gear

First Gear (3 reputation)First Gear (3 reputation)First Gear (3 reputation)First Gear (3 reputation)First Gear (3 reputation)First Gear (3 reputation)First Gear (3 reputation)First Gear (3 reputation)First Gear (3 reputation)

Group: Forum Members
Last Active: 2 Months Ago
Posts: 2, Visits: 14

Not sure why it posts the picture upside down lol


Similar Topics