For the last few weeks, finally driving my 88 XJS a lot, I’ve noticed my new bosch fuel pump was always noisy. (I renewed entire fuel system and tank) I also noticed I always had high positive pressure in gas tank, I’d open gas cap after a drive and gas vapor would burst out.
So I was starting to assume my Rochester valve was stuck.
Suddenly a few days ago, the fuel pump noise went away, as did the vapor pressure at gas cap. So far so good.
I assume the Rochester valve somehow unstuck, if it was that in the first place? Car was sitting for years before I got it.
I still am going to investigate the valve, but I’m wondering if this all makes sense.
My 91 started that back pressure when lifting the gas lid to fill up. Long story short I drilled a 1/16 hole in a none conspicuous spot, not the cap. In other words vented to the outside.
If the Rochester valve was stuck you would have excessive vacuum Greg, not pressure, and that would maybe explain your fuel pump noise.
Check it out because without venting the pump can create enough vacuum to implode your tank.
Every time I think I is apparent that I don’t or it escapes me.
In an open system as Larry226 did, Atmospheric pressure replaces the vacuum created as the fuel is used. “old saying on physics, nature abhors a vacuum”.
But, when the fuel is not being displaced,
the fuel vaporizes, and that vapor escapes to the atmosphere. The emission folks don’t like that.
Hence the closed vent system. Via a charcoal cannister, purge valve, one way valve r and closed plumbing, tis process eliminates vapor escape to the atmosphere.
But how is atmospheric air introduced to allow the avoidance of the vacuum?
An emsion test includes determing if the system is indeed closed and hold vacuum!!!
My Jeep flunked it’s last test ! Cracked plastic filler cap. New generic one, also plastic for 12 bucks and it passed. Apparently common, the test station had a supply!!!
No smog checks here in Washington state starting in 2020! And my 88 was over 25 years old anyways, so didn’t need one.
Yesterday, the fuel pump noise came back, but instead of all the time, intermittently.
I decided to keep vapor recovery a closed system, and replaced the Rochester valve today. I bench tested the old one, and it sort of worked, but not as well as the new AC Delco one. BTW, an archive post was right, the new part has the vacuum hookup on the other side. The main blow by goes one way, but needs 2psi to open the valve the other way, which seems important. So physically the new valve looks to be rotated 180, even though exact same plumbing.
Test drove today, and the fuel pump is even more quiet!
I hope this solves the issue. Together with my boing noise gone, my XJS is becoming the quiet cruiser it’s supposed to be!
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
6
When there is no vacuum, it’s supposed to require 2 PSI to open both ways. When there is vacuum, it’s supposed to be freely open both ways.
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
7
BTW, there is some indication that the failure mode of these Rochester valves is getting crud in them, either carbon particles from the carbon canister or just rust scale or whatnot from the plumbing. That’s why I have long recommended inline fuel filters on either side of the valve. Can’t hurt.
Would you share a photo of exactly where your replacement valve has been installed? Everything you say makes sense I’d just like to see how it looks as compared to what I did/might do further!
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
10
Please post part number and a photo of the valve, if possible. Thanks!
BTW, I found this plastic valve in front/left engine bay that had vacuum to it, and it served in between the hose from charcoal canister to pcv intake. Where the vapors I guess get burned up in the engine.
I didn’t see a need for this, and didn’t see it on my car’s vacuum chart. I guess it stays closed when the engine is not running so gas vapor from the canister doesn’t go into engine when it’s not running? So removed it for now. One less vacuum line to worry about.
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
15
So, your policy is if you don’t understand something, you toss it? That’s probably not a good policy when working on Jags.
I believe that’s part of the purge control system that was updated via a recall, which is why it’s not on your charts. It was designed to prevent the engine running rich after startup because it was sucking too many hydrocarbons from the carbon canister.
My policy is toss something I don’t see a need for, post it in the Jag forum, wait for experts to weigh in, and then put it back if needed. Ok it’s back in.
Greg,
One of the reasons why I enjoy reading Jag-Lovers posts is the wide ranging opinions on pretty much every subject and the different approaches that members haveto working on these amazing machines.
It is my opinion that Jaguar never put any parts on their cars unless they were absolutely necessary. They were after all “trying to make a buck”.
I do not have the automotive engineering background that their design engineers had and so I try my best to keep all five of my Jaguars as original and authentic as possible. I have a comprehensive technical library of owners manuals, Repair Operations Manuals, Parts Catalogues, Electrical Guides, and in some cases the dealership technician training manuals for my Jaguars. I have also had a lot of support from Jag-Lovers over the past 20 years to keep most of them running most of the time.
I would never casually remove any component from my Jaguars simply because I didn’t know what it was or what it did. Given that, I have made some modest modifications and “upgrades” to my Jaguars for reliability or usability reasons to improve the driving experience for me or the others who drive these cars.
So I am not opposed to modifying these cars when I feel it is needed and I have done some thorough research and testing. But I like to think that every part is needed unless proven otherwise.
Yeah, the factory engineers are generally pretty smart guys/gals. Even when the bean counters and design folks mess with them.
Simple is best?? Or is it? cost less. Example the “interesting” transmission mount.
Is this stuff on the driver side??? LHD car?
My LHD has I under the fender on the passenger side. It is as it was. Merely plumbed in to the LT1 intake. Seems to work just fine.
Mine does lope rich a bit on start up!!! is the charcoal cannister feeding it too? Aha !!
Not objectionable to me. It clears quickly. And only occurs off a cold start.
