Finally my parcel arrived from the US with a few goodies (K&N's,fuel pressure gauge,poly trans mount)

A quick rundown of my vehicle.

I have been getting 2 plugs fouling up (5,7 cylinder and the rest are pretty good) I have always smelled a strong GAS smell when idling etc.

I have taken heaps of data logs and have tuned the BLM's as close as possible to 128 I am pretty close to this value with about +-5 deviation from 128.

I was surprised that the Scanner was showing me that I was running mostly LEAN with BLM values above 140 when I first started tuning. Since I have tuned the car the strong gas smell is still evident.

Today I hooked up my fuel pressure gauge to check the fuel pressure. With the car idling it showed a pressure of 37PSI. I still have the stock regulator on the car.

Now here comes my main question. Having a presssure of 37PSI means that I would be getting more fuel then required? (spraying to much) So why would I have gotten 140+ BLMS across the board when I data logged to begin with?

I thought the more pressure the less fuel is injected?

I know the stock pressure should be around 43 what could be causing my fuel pressure to be at 37?

Could this be causing my plug fouling problems on my 2 cylinders?

Would running a lower pressure like 37 be hampeing my performance greatly? Looks like I might need to get a AFPR and adjust the pressure and then redo my BLM's.

What are your thoughts?

What is it best to adjust fuel pressure to 43 or a little higher like 46?

I have just been reading up on FP. Peaople say to check the FP with the Vacuum line disconnected now why don't they write that on the Hypertech instruction sheet that comes with the fuel pressure gauge. I unplugged the vacuum line that runs into the plenum above the fuel pressure test port with the vacuum line unplugged the Fuel Pressure was 47PSI. When I plugged the vaccum line in it read 37PSI. Is this within normal specifications?

Mike

 

Your fuel pressure reg is vacuum referenced.. What this means is that at WOT, vac is near zero and it will bump the fuel pressure up to allow MORE fuel to pass the injectors.

 

I always thought of it that the more Fuel Pressure less fuel used.

I always compared it to a hose. If you just run a hose without an end on it there will be more water coming out through it then having a nozzle on it with a jet stream causing it to have bigger pressure.

Just like high powered high pressure hoses.

Is this my correct way of thinking? Or will having more pressure in the fuel lines mean more fuel?

 

You're not correct. Flow1/Flow2 = SQRT(Pressure 1/Pressure 2). That means if you double the available pressure drop across a fuel injector, you increase the flow by 141% (ie, SQRT2 x 100%).

In the hose example you're thinking of, you need to think of the open end allowing a greater pressure drop from the beginning of the hose to the end, (ie, you lose all the pressure in the hose along its length), while if you have a nozzle fitted to the end of the hose, the pressure loss might happen mostly in the nozzle (energy used to increase velocity/ kinetic energy), meaning less pressure drop along the length of the hose and so less flow.

John

 

Mike, if you increase the FP to 46 psi, you'll increase the flow and that will worsen your rich problem, unless you increase your injector constant (if it's an injector flow rate constant, otherwise if it's the L/G per sec, you'll need to decrease it) by SQRT (46/43) = 3.4%.

John

 

John thanks for the reply might have to re-read it a few times to understand the difference in FP.

I actually checked the FP with the vacuum line connected DOH. But when I disconnected it the pressure read 47PSI so it is high enough. Maybe be better off dropping it a little but dont have AFPR.

But my BLM's are very close to 128 so I really dont know why I get that rich gas smell?

 

It sounds like you may have a couple injectors not closing properly, letting some extra fuel into the cylinders in question. Where is the fuel pressure after the pump shuts off for a couple minutes? It should hold for a few minutes pretty close to the pressure. Just turn the key on for the 2 second fuel pump prime, then after you hear the relay kick off, or the pump shut off, watch the pressure.

Also, if those 2 cylinders are low on compression, you wouldn't be burning all the fuel that is injected into those cylinders.

If it's just 2 cylinders, and causing the plugs to foul on only those 2, I doubt it's anything that would affect all the cylinders, such as fuel pressure, or anything in the tune.

 

The fuel pressure holds pretty well for at least 10 mins after I turn the car off. After about 20mins+ the fuel pressure lowers to about 25PSI.

The cylinders are all good on compression as I did a compression test when I had this problem and all the cylinders checked out at 200PSI +- 10PSI either way.

Can't see to find out why it is fouling the plugs though. I did disconnect the CSI and I will be checking the plugs again to see if that helped.