chapstic951

I just installed a fuel pressure gauge at the end of the fuel rail to get a better understanding of why I am running lean per my narrow band A/F gauge. Using Clarks guidance here are my numbers.

Jumpered: 37.5 psi
Idle: 31.5 psi
20-min leak down: 35 psi (40-minutes I am at 25 psi)

The first two numbers seem spot on which may explain running lean but the leak down is wicked slow going down to the 14.5 psi as it should be. I was hoping it was a fuel pump, filter (pre and post) causing the lean reading, but the fuel pressure is where it should be.

I am trying to track down a known good DME locally to see if that is the problem, but for now I am stumped.

Postnotes: injectors were recently rebuilt and matched, the o2 sensor is new, the DME relay is new, the A/F gauge reads a normal when car is first started, but goes way lean then off the gauge (literally) after a couple of minutes. Car is very sluggish upon acceleration.

TRP951

maybe your FPR is bad have you checked that?

chapstic951

I have not. From everything I have read, a faulty FPR causes the engine to run rich, not lean. I suppose it would not hurt to replace.

Update (well not really. nothing changed. just an observation). I just went for a spin, no faster than 3rd. I was running lean, stopped and looked at the fuel pressure gauge and it was reading 30 psi while the AF gauge said way lean (only one red dask illuminated.) WTF!!!!

Damit this is frustrating.

Chris White

Must be a narrow band O2 sensor and the old arc LED meter…

Chances are that you are not running lean – the narrow band O2 sensors will get non linear as they gets too hot. Then it won’t produce any meaningful readings.

What are your other mods?

Chris White

chapstic951

Chris, you got the gauge pegged. It is an Autometer narrow A/F gauge (carbon for what it is worth, zero!). Regarding mods / specifics.

Rebuilt and matched OEM injectors
Ported/polished/o-ringed Pauerhaus head
WFHG
Billet Diverter valve
Tial 38 WG
Weltmeister chips (both DME and KLR)
New bosch fuel filter
Replaced all vaccum lines (LR)
Stock turbo and exhaust

Nothing fancy.

Rock

Dude I dont think youre running lean, those narrow bands are always just wrong

chapstic951

Short of getting a WB gauge, what can I do to ensure I am not running lean? Would an emissions test at the local Goodyear be worth it?

special tool

One of the most important things on any 951 is the vac/boost signal to the fuel pressure regulator.
Since you have just changed yours, double check that you have a good signal to the regulator, and THAT IS NOT OPEN OR DISCONNECTED ANYWHERE DOWNSTREAM.
You can easily blow a 951 headgasket under boost if this little plastic K-mart tube pops off.

Chris White

I see a wideband in your future....

If you are runngin boost any higher than stock you will be overheatign teh narrowband adn it won't help you.

Chris

chapstic951

Stock boost for now, 11.5 psi. I will call around tomorrow to some local Porsche shops and see if they can look at it on a machine.

hosrom_951

Weltmeister chips are designed for stock cars, looking for more oomph. I see the p&p pauerhause head with welt. chips, that's where you will run lean, since more air is introduced down the combustion chamber (or faster travelling air). You would need a piggyback or fuel controller to dial in more fuel, along with an adjustable FPR, or a 3bar FPR at least.

Get to he dyno, see what the AFR is really like.

Also, i heard welt. chips require the 3 bar FPR to run properly, on stock engines.

My $0.02

hally

better to spend the money on a wideband, you will use it time and time again to diagnose probs, and maybe down the track tune your car.

chapstic951

So I am looking at an adjustable fuel regulator, piggy back and wideband? Would a piggy back system take the place of a remotely adjustable fuel regulator (not the regulator itself, just the remote part)?

jy951

I use MAFterburner (piggy back system from LR) in conjunction with the LR (Lindsey Racing) fuel rail, AFPR, and an AEM wideband 02 sensor. You don't need the fuel rail but I swear by the other three - because my 951 is modded (bigger turbo, IC, etc.). Like Chris White and Hally said 'BUY THE WIDEBAND 02 SENSOR!', it's the best investment for a modded 951 (or any forced induction car). Make sure to buy a wideband 02 that has data logging capability - so you can see where u r running lean - MAFterburner also has data looging. You can use the AFPR too increase or decrease fuel pressure (to richen or lean out your tune - the piggyback gives u more granularity to richen or lean out your tune above and beyond the AFPR) The combination of the three works great for me when tuning.

toddk911

Keep turning up your fuel pressure until the car stumbles from being too rich, then dial it back slightly.