Exhaust Back Pressure Valve

[Daniel]

Just fitted a de-cat pipe to my S4, noticed that the EBPV was removed when it had an after market exhaust fitted.

What will the consequences of this be?

I'm assuming like the old EXUP valve on Yamaha bikes of old, this valve closed at mid revs to provide more mid range to the engine.......

Am I now missing this vital torque?

[fflyingdog]

Just fitted a de-cat pipe to my S4, noticed that the EBPV was removed when it had an after market exhaust fitted.

What will the consequences of this be?

I'm assuming like the old EXUP valve on Yamaha bikes of old, this valve closed at mid revs to provide more mid range to the engine.......

Am I now missing this vital torque?

<{POST_SNAPBACK}>

The only reason it has an EBPV was for it to heat the cat up quicker once the cats up to temp it opens ,it doesnt work the same way as an EXUP valve. Get rid of the EBPV its a rattley piece of crap only purpose it serves is a door stop.

Cheers

Nick S4s

Edited December 10, 2005 by fflyingdog

[Jonathan]

...and get the EBPV spacer from PUK Esprit, cost a few quid but is made from alloy - wont rust (essential if you have a stainless system) and weighs a whole metric ton less than the other kit (it's true, I've measured it).

[Daniel]

Yeah it's got the spacer......now one other question

Had major problems removing the O2 sensor.....and yes it broke so I need a new one.....

Had to drive the car to storage this morning approx 20 miles with no O2 sensor.....could this have done any damage?

The engine light was on

[Paul C]

Have dug out an old post of mine, no-one said this

was a load of rubbish at the time, so i think i have

it right here...

The EBPV is a 'butterfly' valve that is located in the exhaust system

between the Cat and the rear silencer, it is a normally closed gate on the exhaust

with a vaccum actuator that holds it open. On start up the EPBV is kept closed by

the car, obviously this chokes the exhaust system by blocking it. The purpose of

this action is to build up heat in the Cat as part of the warm up cycle/emmissions

control.

While this is happening (with the exhaust essentially blocked) the engine requires

the revs raising to prevent stalling, enter Mr Throttle Jack. The TJ is a rod

assembly attached to the throttle linkage, the end of the rod goes into another

vaccum actuator. When the EBPV is closed, the TJ is actuator is operated

and 'jacks' the revs up to around 2000rpm. This happens for a minute or

so and then idling returns to normal as the TJ is released and the EBPV is held

open by a vaccum feed.

'But who needs cat warm up and emmision stuff?'We don't 'need' it at all...

The main reasons a lot of Esprit no longer have this system is the EBPV is a

weakness. Because it is naturally shut, when it fails (IE actuator breaks,vaccum

line comes off) it will block the exhaust system. Some owners just use

some 'coathanger' style material to wire it open, some (as with me) have

purchased a spacer to put in the Exhaust system in place of the entire EBPV

assembly.

A third option is to lose the cat and EBPV entirely. A cat replacement pipe will not

only replace the cat with a straight through pipe, but will also be a longer section

of pipe so it will replace the EBPV (or the spacer) too. Obviously you need to block

the end of the vaccum hose when you remove the EBPV, otherwise your vaccum

pump will burn up trying to vaccum the entire world!

Something that gets fogotten in the removal of the EBPV is the throttle Jack. Mine

still had it, and it still raises revs to 2000 at startup thinking the EBPV is still there

doing it's job. This action was 100% pointless, so i have pulled the vaccum line for

the TJ and plugged it too.

It is important to deal with this at the vaccum line point rather than just pulling the

plug on the solenoid that controls the vaccum feed, this action would result in the

ECU giving an engine check light and the dreaded 'code 26' would appear should

you run a scan.

[mchlrodrigues]

While this is happening (with the exhaust essentially blocked) the engine requires

the revs raising to prevent stalling, enter Mr Throttle Jack.

<{POST_SNAPBACK}>

While the throttle jacking capsule may compensate for the exhaust restriction created by the EBPV, it's use was not limited to EBPV equipped vehicles. Earlier carbureted cars used an electric solenoid to "jack" the idle during warmup, and the HCI cars came with throttle jacking capsules although they used a "starter cat" as opposed to an EBPV to reduce cold start emissions.

In spite of having changed the entire engine management system on my '87, I've reinstalled the throttle jacking capsule, after having tested the car without. When properly adjusted it's useful in maintaining stable idle speed during warm up and aids in warming up the motor more quickly, independent of whether the cat had been retained or not.

The throttle jacking capsule, other than taking up a little space, has no detrimental effect. Without it, the motor will still idle when cold, but at a lower speed and not as smoothly. I'd recommend removing the EBPV and readjusting the throttle jacking capsule to produce a 1300-1500rpm idle with a warm engine. Many newer cars use electronic throttle bodies with stepper motors to achieve the same thing.

The actuator rods have been known to come loose, but I reinstalled mine with Super Glue (cyanoacrylate) and it's remained in place for years. You can glue the vacuum line on with a little Barge Cement or 3M Weatherstrip Adhesive applied the the exterior of the dash pot vacuum spigot and it won't come off unless you want it to.

This is once instance where I agree with the factory. While it would be possible to make a better jacking capsule (similar to aftermarket wastegate actuators), it's hardly worth the expense or effort, and the capsule is there for a reason.

M---

[Backmarker]

Paul,

I need to replace my exhaust next spring and intend to dump the Cat/EBPV at the same time. Tell me how/where to plug the vaccum line at the throttle jack. PNM will be doing this work for me so perhaps I'm worrying unnecessarily.

Cheers,

Graham.

[Paul C]

Paul,

I need to replace my exhaust next spring and intend to dump the Cat/EBPV at the same time. Tell me how/where to plug the vaccum line at the throttle jack. PNM will be doing this work for me so perhaps I'm worrying unnecessarily.

Cheers,

Graham.

<{POST_SNAPBACK}>

No.

Well, i can, but on the SE. It is very easy job to do. I hesitate to give you

advice on the S4 because some of them may have different vaccum layouts.

I posted a picture some time ago of my layout and turns out the S4 being

worked on differred and the owner had problems...

The thread is here

http://www.glcforum.com/ukesprit/forums/in...311&hl=solenoid

[Paul C]

While the throttle jacking capsule may compensate for the exhaust restriction created by the EBPV, it's use was not limited to EBPV equipped vehicles.  Earlier carbureted cars used an electric solenoid to "jack" the idle during warmup, and the HCI cars came with throttle jacking capsules although they used a "starter cat" as opposed to an EBPV to reduce cold start emissions.

Cheers for that

Note all then that the TJ performs useful functions on non delco cars.

As far as i know, idle is controlled by the ECU on the later cars, i say

this because the one concern i had was that the car used the TJ to raise

revs for the aircon load, but is does not (on the SE anyway).

Without the EBPV to choke it, i felt the extra 1000 revs that the TJ raised to

on starting was a bit too harsh. Maybe the non EBPV cars have a TJ that raises

it less so? Mine idles nicely without it and i'm free to pile the revs on for the first

two minutes should i need to ever.

As ever, the invitation to declare my tech posts rubbish

is always open, and i'll always thank you for doing so,

Plenty of people here know plenty more than me!

[Guest teigan]

i removed mine as well. it just looked like such a low quality part, and didn't look as if it was gonna last. will consider putting in something more robust in future, but for now, the choke is enough of a help at warmup.

[CarlC]

I posted a picture some time ago of my layout and turns out the S4 being

worked on differred and the owner had problems...

The thread is here

http://www.glcforum.com/ukesprit/forums/in...311&hl=solenoid

<{POST_SNAPBACK}>

I was the owner with the problem. PNM will easily sort this out for you. The only real problem was IIRC that the S4 uses the vacuum pump to not only control the EBPV and TJ but it also has a vacuum line running to the front of the car to open and close the heater vents and I think air flow to face, floor or demist window vents.

I took pauls advice and just circled a pipe back on its self with a T joint. Really easy. But obviously unknown at the time the heater vents dont work. So all that was actually necessary is to locate your vacuum pump and just plumb the heater matrix pressure pipe stright into the vacuum pump.

I have actually now wired open the EBPV and removed the TJ Capsule and all the black pressure pipe associated with these devices. Just to clean up the engine bay a bit, but you must leave the solenoids connected to the ECU or you'll get a check engine light on.

[mchlrodrigues]

Cheers for that 

Note all then that the TJ performs useful functions on non delco cars.

As far as i know, idle is controlled by the ECU on the later cars, i say

this because the one concern i had was that the car used the TJ to raise

revs for the aircon load, but is does not (on the SE anyway).

Without the EBPV to choke it, i felt the extra 1000 revs that the TJ raised to

on starting was a bit too harsh. Maybe the non EBPV cars have a TJ that raises

it less so? Mine idles nicely without it and i'm free to pile the revs on for the first

two minutes should i need to ever.

As ever, the invitation to declare my tech posts rubbish

is always open, and i'll always thank you for doing so,

Plenty of people here know plenty more than me!

<{POST_SNAPBACK}>

The delco cars do use the IAC to stabilize idle speed and compensate for A/C once the car is warm.

The TJ is not a fixed 1000 rpm, it's adjustable. The rod coming out of the capsule is secured by a set screw in the barrel fitting on the throttle lever. Warm up the motor. Loosen the set screw, actuate the solenoid and adjust the idle with the TJ lever then tighten the set screw. TJ idle up can be adjusted to whatever one determines is desirable. The throttle will be released once coolant temp reaches 70C.

How to actuate the solenoid? On the Bosch cars simply install a jumper between the two wires going to the high temperature switch. On later cars I imagine that one could use a pair of jumper wires to trigger the solenoid or use a hose union to join the vacuum feed to the solenoid with the vacuum line out going to the TJ capsule.

M---

[mchlrodrigues]

Cheers for that 

Maybe the non EBPV cars have a TJ that raises

it less so? Mine idles nicely without it and i'm free to pile the revs on for the first

two minutes should i need to ever.

<{POST_SNAPBACK}>

Paul,

The difference is the IAC which the Bosch cars didn't have, nor does my car with a stand alone ECU.

It appears that if I had a way to control the IAC, that the TJ capsule could be done away with. But without IAC, I've found it to be useful. With the capsule residing below the chargecooler, it's hardly in the way.

But thanks for setting me straight. That's good information.