Zirconocene

I need to eat some public crow, in the hope that future RLers can learn from my mistake.

My S4 was running pretty terribly: uneven idle, minor cutouts during cruising and, worst of all, a couple of times where the car just straight up died on me. When the engine would just die, it would fire up again most of the time, but one time in particular it was a real bear to get restarted to get it home.

I went through a few of the usual suspects: new CPS (the one I took out was original it seems), new 53B relays on the CEB, new narrowband O2 sensor, and I put new connector housings on the temperature sensors at the front of the engine. None of it helped and I was going down the path of thinking that I had an LH problem, which is a whole order of magnitude different problem.

Before I got into that, though, I decided to go back and check fuel pressure and, sure enough, when I installed the FPR I screwed up the pressure setting. The car was running on about 40 psi fuel pressure. Note to the group: the cars do not run great at this setting!

I've only driven it around the block and watched it idle for a little bit but next up is to see if the WBO2 I installed is working (wired correctly, is what I mean, for the SharkTuner), and to see what the diagnostics from the ST tell me. Should be healthier!

Cheers

FredR

Presumably you have an adjustable FPR fitted- this was a common 928 "bodge" 20 years ago in the days before Shark tuner was available. The S4 seemed to benefit from a bit more fuel mid range but with stock overfuelling at top end, that of course would be exagerrated some.

Needless to say with the engine running, vacuum connected and all working correctly, the fuel pressure should be 3.3 barg [50 psig]. If the fuel pump is running but the engine is static that value should be around 58 psig. So, in the correct state 40 psig would result in the fuel rate being about 12% less than it should be relative to stock programing.

No idea why you have an adjustable FPR fitted- just that something that is "infinitely variable" has one correct setting and an "infinite number minus one" wrong ones!

Zirconocene

Hi Fred-

Indeed, the FPR in question is the Radium unit, adjusted poorly.

It is now set for 3.8 bar/55 psi with the engine off (activated and tested via the jumpered fuel pump relay).

Cheers

FredR

Ah yes- you used the Radium FPR along with the dampers you fitted. Did you use the separate units or the combination unit as a matter of interest?

Look forward to hearing how you get on and given you have ST2 it will be good to see some AFR data logs that will help indicate how well the Radium units deal with the pressure pulsation problem the stock items exhibit. I suspect you will see an improvement.

ST2 should integrate seamlessly with a WBO2 sensor. I use the original Innovate system- as I recall there is one parameter that may need to be adjusted in the Innovate system software but otherwise it is plug and play with ST2. The WBO2 should be kept completely separate from the NBO2 sensor. Thus if you have a NBO2 you need a separate bung to mount the WBO2 sensor. Fortunately I did not have that problem as the 928's delivered over here had to run on leaded fuel up to 1993 when the local refinery was upgraded to produce unleaded gasoline.

Kevin in Atlanta

Could you expand on the pressure pulsation problem?

Zirconocene

Hi Fred-

I used separate Radium units for the FPR and dampers. They do offer a slick combined unit but I was a little under the gun in my frenzy to attend Frenzy. So far, so good, but I only just today collected some data from the SharkTuner, with the proper fuel pressure and the WBO2. It was only a short drive, however, so it was really more of an exercise to see if the demons in my engine had been exorcised.

The car will likely receive Kevin's NLA Industries units in the future, as the placement in the car works, but it's not as elegant as the original setup. I'm not an originalist but I do like a tidy engine bay, even if I never actually can produce what I envision. It's the journey, right?

Finally, perhaps you can answer a tangential question. I installed an Innovate LC2 and, from what I understand, it is supposed to be connected to the SharkTuner via a 3.5mm plug. How does the ST know which AFR to report? I clicked around a little bit but could only find a single reported output.

Cheers

FredR

Kevin,

Despite being fitted with two dampers, the stock S4/GTS fuel system has two specific frequencies [engine speed] wherein there is a distinct "leaning out" of the AFR when using the stock chipset. This can manifest itself as a slight but barely noticeable hesitancy. ST2 permits the owner to tune this out to some extent but then the rest of the cell width ends up over fuelled. It is not a major problem and invariably most would not even know of its existence. I cannot remember the exact frequency this phenomena happens at, something around 3k and 4k rpms as I recall. It can typically be seen graphically when using Jim's sharkplotter software and one sees a distinct vertical line that is blueish in colour.

I do not have access to my historical data at the moment but if I can find a plot showing this will post such a bit later.

Speedtoys

On new or 30yr old dampers?

FredR

This is a natural resonance phenomena- and highlights very clearly the reason why dampers are needed. It is more prominent at lighter loads and tends to reduce as load increases and happens over several very narrow rpm bands [as I recall].

Old or knackered dampers will do nothing for any system other than exacerbate the phenomena. When I acquired ST2 [one of the early users as I recall] my dampers were a couple of years old and are still in the system today but I have not done any ST2 runs for years. Might be an interesting project to log some data and see if there are any obvious signs of this phenomena growing as it were given I rate them for 20 years use and mine ae now in that age range.

I suspect that more modern dampers from a company that knows their onions may well produce better results than the stock system that is OK but less than what it might be or so I suspect. Similarly it would be interesting to see some data plots from a system kitted out with the latest after market offerings. The definitive plot that I saw was one made by Jim [Corenham] on his S4- when I first saw this it really caught my attention and sure enough I saw similar characteristics when I made my first ST2 plots and on many plots since as and when posted.

FredR

[QUOTE=Zirconocene;17844164

Finally, perhaps you can answer a tangential question. I installed an Innovate LC2 and, from what I understand, it is supposed to be connected to the SharkTuner via a 3.5mm plug. How does the ST know which AFR to report? I clicked around a little bit but could only find a single reported output.

Cheers[/QUOTE]

The system is powered up via a 3 pin barrel connector that sits next to the computers. For ST2 John used a connector block strip to connect everything up- it is functional but not very elegant. This supplies power to both the ST2 and the WBO2 control unit. The output from the Innovate LC1 kit that I have connects via what I refer to as a mini jack plug and I suspect that is what you refer to as the 3.5mm plug. The Innovate box drives the WBO2 sensor.