Urgent help needed please where does this vacuum hose go?

(JLo) #1

1989 Jaguar xjs 5.3 coupe
Hello I have a vacuum hose in which I do not know where it is supposed to go it has a red or orange stripe on it and also a small canister says DC6T-AA
Thank you in advance
My problems are power brakes are not working. Perhaps other issues.

(Paul M. Novak) #2


You don’t mention specifically where that vacuum hose is located or the year, engine of your car. So I can’t be positive about this. But if this vacuum hose is located in the trunk (boot) as it appears from the pictures, it might be the vacuum hose coming from the engine bay and going to the EFI ECU located over the right side wheel well. The small canister looks like the “Reservoir”, Jaguar Part Number CAC4968. This hose is how the EFI ECU get intake manifold vacuum for fueling calculations, at least in my wife’s 1990 XJ-S convertible (5.3L w/ Marelli ignition).

I don’t believe that this hose would have anything to do with power brakes issues, but they both use vacuum so it is possible that it might.  


Paul M. Novak

1990 Series III V12 Vanden Plas

1990 XJ-S Classic Collection convertible

1987 XJ6 Vanden Plas

1984 XJ6 Vanden Plas

1969 E-Type FHC

1957 MK VIII Saloon

Ramona, CA USA

(JLo) #3

Thanks so much for the response Paul. It’s an 89’ xjs coupe V12.
Yes it’s in the boot area.
Thanks for your responses. I will investigate tomorrow.

(JLo) #4

Found this on eBay looks to be the ecu, with the hose. What does this vacuum hose control on the ecu exactly?

(DavetheLimey) #5

Hi James, the vacuum hose connected to the ECU “tells” the ECU the load on the engine- accel, cruise, etc. The ECU then determines the appropriate fueling for that condition. If the hose is disconnected, then the ECU responds by giving your engine the same amount of fuel as if you were at WOT. Very important hose! IIRC, the hose is connected to the engine close to where your power brake vacuum hose is hooked up- the aft end of “A” bank intake manifold, so a disconnected hose would very likely affect your power brakes, and the engine would run very rich, if at all! Hope that helps! Edit- Thinking more clearly, the crossover pipe BETWEEN the intakes is where your ECU hose is attached. Still, pretty close to the power brake vacuum take-off. Not sure whether one would affect the other or not. Easy enough to find out, though.

(Harry Price) #6

Can’t believe it. Car Quest had black sunvisor brackets for my 1984. They also list a tan one for a 1988.Car Quest Part# for the black ones is O606641990OES.$15.67/pair with sales tax. No shipping! And you can order singles.

Package has the Jaguar Leaper Logo and ‘Made to Jaguar Specification in UK’ on the label. Harry Price1984 XJ-SC 6cyl/five speed1957 TR3

(paul davies) #7

Hi Jlo I have resurrected this as ime curious about the sump tank. It appears to be under the floor as it shows a shocker in the shot
In the picture of your fuel sump tank where is it mounted. Pls

(WayneC) #8

Seems to me that ANY vacuum leak on a hose coming from the engine (as opposed to a leaking hose from a separate electrical or mechanical vaccum pump) has to affect all other vacuum sources on the engine.

(Greg) #9

Wow, is that what it’s for? While I was redoing the trunk area for my new tank, I saw this vacuum hose connected to the ECU. Thought it was for keeping it cool (like the one going to distributor)! LOL

I replaced mine with good silicone line. I will now check the entire line going back to the engine, as it does sound pretty important.

And why not have a vacuum sensor in the engine bay, with a wire going back to the ECU, instead of a vacuum line?!?!? Jaguar.

(Greg) #10

Regarding vacuum, what would be a good vacuum at idle for the HE V12, warmed up? 15-20 inHg?

(JLo) #11

Mine shows 20 plus at idle after I re-did vacuum lines. But please someone else let me know their thoughts? I T’d in a cheap vacuum guage.

(Greg) #12

I assume that is good? All my non-Jags are supposed to be around 17 at idle, and then 20 at cruising (with no throttle)

(DavetheLimey) #13

From Smiths Industries pamphlet, circa 1968-
At tickover, (Idle to you Yanks!) an engine in good condition should have a reading of 17-21(in HG)
and hand should be steady.
(this is followed by 15 more descriptions of identifiable faults, using the gauge!)