S4 no Power

[OASIS1]

  I recently took my S4 out of winter storage. It started fine, still starts fine. However on the road I struggle to do the speed limit and not in the way you would think. IT has no power and the turbo gauge does not move. Help? Thanks Jmes

[Barrykearley]

Check the turbo wastegate actuator moves 👍

[ramjet]

My thought as well.

[cammmy]

If it drove fine when you parked up, I would look at the boost solenoid. If the wastegate or actuator were faulty, I would expect it to be stuck shut and overboost. The boost solenoid creates a controlled leak in the signal to the actuator, opening it later and allowing a higher boost level than the actuator is set for.

As long as you are confident it's not a fuel supply issue, I would suggest you could go WOT to the redline and see if it builds any boost at all I believe these have something like .6 bar wastegate spring? So if the actuator is faulty, it would be slower but still generate boost.

If the wastegate was stuck open, it should still build some boost eventually, but it would be extremely sluggish until maybe 5000rpm. It would be good to get a picture of the actuator and the wastegate arm, so we can see if it's closed.

I'm currently dealing with the opposite problem; my new turbo is overboosting. Even with the actuator disconnected from the wastegate (which is free to fully open at all times), it's still been overboosting by about 6,000rpm but it's absolutely gutless up until about 4.5k

Edited June 7, 2019 by cammmy

[Chillidoggy]

Might be worth checking to see if the wastegate solenoid pipe is intact/not split while you're getting tucked into it. EMH2 refers.

[Giniw]

Even without boost I suspect it would go faster than the speed limit. And I suspect the wastegate would stick closed and overboost after a long storage more than be kept opened?

If I were you I would quickly check any restriction in the exhaust (typically broken catalyst, or stuck exhaust back pressure valve).
I once had no power and very low boost as well and it was my catalyst internal which had broken loose and were restricting the exhaust badly.

[Giniw]

 

[Barrykearley]

My wastegate actuator rod snapped - made the car utterly flat and gutless.

[Giniw]

Wow!

Maybe when there is no rod the waste gate can open freely? I am not sure whether it has a dedicated spring inside to keep it closed?

[cammmy]

That rod is the only thing that holds it closed. When it's snapped it will just flap open and make the car really sluggish

[Giniw]

Thanks.

By the way, my wastegate capsule leaks a little, so I will change it. Should I go for the OEM one (A910E6915F https://www.sjsportscars.com/parts-and-accessories/A910E6915F.htm) or is the alloy one (sjsportscar/Forge? https://www.ebay.fr/itm/350180257315 or https://www.sjsportscars.com/parts-and-accessories/SJ910E0032.htm) any better? I usually always prefer the OEM stuff but maybe the allow one wouldn't rust? (sorry for the little off topic ^^')

[Giniw]

(-allow +alloy, sorry I can't edit any more)

[Sparky]

The Forge capsule is fine and, in my opinion, a permissible upgrade.  I have one.

[Giniw]

Does it have the same characteristics? (spring tension?) I suspect it is meant to be adjusted with the rod while monitoring the pressure (as per the workshop manual specification) when it starts to move but I prefer to ask to be sure!

[cammmy]

In my opinion, the spring pressure isn't that critical. It doesn't matter if it's slightly above or below factory as it only really counts if the boost controller isn't working. It just sets the absolute minimum boost level you will get. So as long as it's sensible, you will be fine.

[sailorbob]

Wastegate actuator spring pressure does matter, it dictates the amount the wastegate valve opens for a given inlet air pressure.

[cammmy]

It does but with the aim of holding a certain level of boost i.e. 0.6 bar. Once you put a wastegate solenoid in there, you are using that to bleed air and push the boost up, effectively overriding the spring. It should bleed all of the signal and hold the gate fully shut until it reaches the desired boost, then feed the right amount of signal back in to the actuator to hold the desired boost level. Unless the standard ECU is just reading straight from a table, it should be able to compensate if the spring rate is slightly different.

I'm not saying stick something vastly different in. Just that, in my opinion, it should be able to compensate for a slight difference.

[sailorbob]

The wastegate solenoid does not operate like that on the 4 cylinder Esprits.

[cammmy]

Ah, fair enough then. I'm running a standalone ECU now.

[tjs98jetta]

I've had the Forge unit for 6 years or more with no problems. It has an aluminium body, so no rust problems, still looks shiny and beautiful. 🙂  You order with selected spring tension that includes the maximum Esprit mechanical setting (SE in my case) of 0.65 bar.  As I recall, set up installed in car with external pressure gauge so that opening is at 0.65 bar or slightly above by adjusting the length of the actuator rod.  Then the bleed relay will be controlled by the ECU and allow boost pressures up to just over 1 bar by bleeding off pressure sensed by the wastegate actuator as long as everything else is within specs and the engine up to normal temperature.

 

[Giniw]

Thanks!

Apparently the Forge Motorsports closest spring to OE spec is thee green one, calibrated for a target pressure of 0.7 bar though? It's not that far but on the other hand the workshop manual tells to tune the rod to let it move at a very precise pressure, so I think I would be better to order the OE one, wouldn't I?

[Escape]

I'm pretty sure 0.7bar should be OK. You can still set is as described in the manual. Even if you get a slightly higher default boost, it's still well within spec.

On the other hand, if OEM is available, why not fit that?

[Barrykearley]

Turbo technics were very specific in their advice against using the aftermarket ones. Oem is cheaper and I didn’t end up fitting the shiney one that came with the S4s

[tjs98jetta]

In the freescan manual,  a setting of 0.65-0.75 bar is suggested, BTW.  I agree with Barry, 0.70  bar is fine.  I don't believe the accuracy of the sensor in the engine is good enough to warrant the precision quoted in the manual, especially given the age of the cars now.  If you set it too low, the engine's sensor thinks the boost is never reaching the limit and you never get higher boost, so loose a lot of performance.  

I don't recall the colour of the actuator spring in my Forge unit, but it was definitely possible to set it to open at below and above the 0.65 setting by adjusting the rod length.  Any of the available possibilities will work fine, I am sure.  

 

[Giniw]

6 hours ago, Escape said:

On the other hand, if OEM is available, why not fit that?

The Forge one is shiny!!
Seriously, I was considering the fact the forge one wouldn't rust, but that's all, they are about the same price anyway (the Forge one is often more expensive but I found a French website which is selling it at only 129,70€ including tax and shipping, so it's actually a bit cheaper than OEM)

https://www.gt2i.com/fr/wastegate/78367-wastegate-forge-lotus-esprit-4-cylindres-3661768598801.html