I finally got my S4 Convertible on a dyno this week (with a new K&N Air intake, new plugs & leads), and it seems I have a problem

First run on the dyno produced about a 100kw at the rear wheels, with 5.5 pounds boost.
Everything was running REAL rich, so they remapped the Haltech to bring things back to normal, (and found another 20kw) and then the fun started!

At around 6K there was a fairly dramatic lean-off which led to a reasonable conclusion that the stock (not even Turbo) fuel pump was not up to the Job.

Replacing the fuel pump with a 230kw VL pump made very little difference, and we then ran out of time.

So at the moment I'm getting about 120RWkw, at 5.5lbs boost, but am wary of running over 6K for too long

The guys are now thinking that we've got a bad injector (or two) which aren't doing the business at high RPM.. they're going to pull the injectors and check/replace them next week..

I really want to get the boost up a bit (probably 10lb), but there's obviously not much point if it's just gonna run lean and blow something...

Anybody have any other ideas I can throw around as to what the problem might be?

Thanks in Advance!
Dave

 

Have you tried richening the map in the area where it's running lean?

What size injectors do you have on the car?

Check for fuel pressure drop.

 

Thanks for the reply!

Yes, but we still can't get enough fuel in there

They are standard Injectors from a Series 5 (I believe).

Fuel pressure is good.. we even checked for a kinked delivery line or similar, but it is all good...

Cheers,
Dave

 

You may need to go to larger injectors or raise your fuel pressure ,if you have an adjustable regulator , I had a second gen. with all the bolt on mods and a street port and also started to run lean at 5.5psi and 6500rmp.

 

Stock turbo?
If it's a larger turbo, you're hitting the max on the stock fuel injectors.&nbsp The stock fuel injectors (4x550) can only support up to 250bhp (flywheel) - sorry, I don't know the converion for your power units.



-Ted

 

one HP is 746 watts, therefore 1hp = .746kw

120kw divided by .746 is 160hp... at the wheels... on an Australian dyno...

 

It is a stock Series 5 Turbo...

Cheers,
Dave

 

That's certainly how it's sounding, isn't it?

I'm not sure about the adjustable regulator - I'll check into that - thanks!

Cheers,
Dave

 

What difference does it make being an Australian Dyno, peejay?

Cheers,
Dave

 

What kinda Haltech?&nbsp E6 series?



-Ted

 

Hi ted,

It is an F9....

Cheers,
Dave

 

That explains it...
You've got voltage drop at your fuel pump.&nbsp Check the voltage as close to your fuel pump power wire.&nbsp I bet it's dropping pretty badly; typical problem with these cars, and this leads to dead engines...



-Ted

 

Thanks Ted....

I'll check that...

I've never seen this mentioned anywhere before - what's the usual cure - wires straight to the Battery?

Cheers,
Dave

 

I keep hearing that a certain brand of chassis dyno in Australia reads quite a bit lower than the commonly-used chassis dynos in the US, and you have to multiply by 17(?) percent to "equate" it to a Dynojet reading. (Not that inertial dynos are a good idea, but they ARE what is common, so...)

 

Jeez - as if the world isnt confused enough already

The Dyno was a Dyno-Max if I remember correctly...

Cheers,
Dave

 

Hey Ted,

Will the voltage drop be apparent at all Revs, or is it somehow controlled by the ECU and likely to be low only at 6K+ ??

(Thanks for your help, BTW)...

Cheers,
Dave

 

For some reason this post would FREEZE my computer over the last few days. The HD finally crashed yesterday.

Well, you're worried about WOT runs, right?&nbsp The FC does have a two-stage fuel pump voltage system where it runs through a resistor most of the time, but the resistor gets bypassed at "0" or + pressure.&nbsp The problem is with corrosion and aging electrical wire that causes the voltage drop from the front to the rear of the vehicle.



-Ted

 

2nd go at this post! Darned server busied out on me!!

We've already replaced the pump with a new high-pressure unit that is supposedly good for at least 230kw, so that shouldn't be it...

Well, she goes back on the Dyno tomorrow for some more fiddling, so I'll keep my fingers crossed and let you know how it goes..

Thanks for your help Ted (in particular), and everyone else who offered advice!

Cheers,
Dave

 

Probe the power wire at the pump while its running on the dyno (if possible) and see if you're getting 13-14v.

 

Well, I just picked my car up - and WHAT a difference!!

The guys at RPM Performance tracked the problem down to rubbish in the fuel tank which was being picked up at WOT, and causing enough of a blockage to the pump intake to restrict the flow

Unfortunately she is now making enough power that the clutch won't hold, so they were unable to do full-power testing.

So I guess now I have another project! Light-weight flywheel while the box is out, do you think?

Thanks all of you for your suggestions, and to Tim at RPM for doing a GREAT job at a very reasonable price!

Cheers,
Dave

 

Forgot to mention - they did replace two injectors that we border-line too!

Cheers,
Dave

 

Get a Walbro fuel pump. Relatively cheap, and will save you in the long run. Good luck