Originally Posted by GREGGPENN

I think this is worth verifying. My stock FPR shows 34PSI (but with a larger injector). OTOH, I believe many have reported pressures in the low-mid 30's -- while the motor is running. This means a jump to 40PSI could send in significantly more fuel!

Pressure while the engine is running will be lower than in the "on" position.

One thing I forgot to mention is than an AFPR can not operate as low as stock pressure. There was a thread on this a few years back. It has to do with the "slug" inside the regulator. By design, that slug raises pressure above stock. So, you're starting higher than normal.

This could be alot of the difference.

Originally Posted by FICINJECTORS

To keep you updated on what we are doing, We have been monitoring our customers for several years, some have no problems, some do. Lets face it. The stock injector is the only one that will work 100% in the cars. We also know they are failing. The alternative is to find an injector that is affordable and easy to install. 5 yrs ago we did. Now we are stepping into another phase of technology. We are now able to fully characterize injectors. Knowing exactly how the injector flows based on PW instead of static, wide open flow. What we have done for the past year is develop a new concept on how we flow injectors. We now have software to determine the flow for PW’s from .5 to 10ms based on any voltage input and pressure. We use a PD flow meter (positive displacement) instead of measuring tubes. The acquisition software can accurately measure these small flow numbers out to 3 sig figs! How we do this is complicated but, easy enough to understand. We flow the injector at lets say 12.8 volts. Set the computer to drive the injector for 200 pulses at 1.5ms. Divide the numbers and come up with the flow per pulse. This number is acquired by another computer. We continue to do this at different PW’s and after lets say 5 tests a X Y graph is drawn on the screen. We can now see where X and Y intersect to determine the theoretical dead time or offset. We then do this at other voltages for an accurate diagnoses of flow. So you say big deal!!! Now we can characterize injectors based on real flow as it performs in the engine. Furthermore, we decided to go one step further. We now have this data from a stock 1991 speed density OEM multec. Now that we know EXACTLY what it is. We can now copy it. We have and always been modifying the Bosch 3 injector to flow whatever we want. We make 30’s 36’s 42’s and 50 lb injector out of them. Of course these always require a tune. So, we have completed a few sets of modified injectors that mimic the 91 multec in per pulse flow. Now we need someone to test them in a real car. So volunteers please PM me. What this means is that we are trying to tune the injector to the computer that is already programmed instead of tuning the car to the injector. Remember, ALL aftermarket injectors will perform differently than stock. Tuning the computer to the new injector is satisfactory, however it is in the dark. Guessing on offsets and modifying VE tables is time consuming and quite frankly a pain in the ***. The masses just want a drop in and go. The guys that mod their cars need a tune regardless.
We have invested a ton of time and money into this project, if I can put it to use for the C4 crowd it would be great. All these tests have been done on a prototype flow bench. We are now in the final stages of completing the hardware etc. A pic is attached of the cabinet I have fabricated to house the internal pumps, pressure regulators, computers, flow meters, power supplys etc. As you can see it will be something that no one has. Software and operation has been verified so we are close. Once done we will characterize each year of the C4 and match up the replacements accordingly. We will also replace any existing set that is not working to the customer’s satisfaction.
I would like to ask Mick who happens to be a good tuner to call me and offer any of his expertise to this program.
Others that would like to participate in the testing I welcome you also.
Please don’t turn this thread into some ******** fight between the members. Our only goal is to find the right solution and continue our support of my favorite forum.
Thanks

Originally Posted by ddahlgren

Your new way is only new to you. OEMs have done this for over 2 decades and it is the reason for pulse with corrections vs. pulse width a table in any ECU sice the early 90's at least along with the battery comp tables. I harped on this a while back as a big need and the fact that staic flow is useless as they never run or should never run static so a meaningless number. It is nice to see you are stepping up your program to current standards for quality race injectors.
Dave

Originally Posted by leesvet

There are some other clues here...
Think this thru...
If the key ON FP is 40, and the eng idling drops it to low 30s....thats an indication that the injectors are using that fuel and delivering. As the eng runs it takes part of that pressure thats seen on the gauge. It gets replaced IF the fuel pump is in good shape and able to keep up. This is the reason that we like better pumps so there is no lag behind what fuel is used and what the pump can resupply.

If the idle FP does NOT lower by more than 3 psi from key ON....then thats more normal and it says that the FP is keeping up, and the problem is more likely a pulse width/duration issue and not the actual inj size.

Originally Posted by GREGGPENN

I think this is worth verifying. My stock FPR shows 34PSI (but with a larger injector). OTOH, I believe many have reported pressures in the low-mid 30's -- while the motor is running. This means a jump to 40PSI could send in significantly more fuel!

Pressure while the engine is running will be lower than in the "on" position.

One thing I forgot to mention is than an AFPR can not operate as low as stock pressure. There was a thread on this a few years back. It has to do with the "slug" inside the regulator. By design, that slug raises pressure above stock. So, you're starting higher than normal.

This could be alot of the difference.

Originally Posted by oldalaskaman

if I had a 91 , I'd be all over this

Originally Posted by vette 15x

MAX fuel pressure controlled by fuel pump.The regulator ,controls pressure at fuel rail.Spring pressure in regulator set static pressure.Dynamic or running pressure is controlled by a combination of manifold pressure and or on spring pressure.HIGH VAC. lowers fuel pressrue for economy and emissions.WIDE open throttle, spring pressure unefected by vac. set fuel pressure higher for performance.With vac. line off, pressure shouldn't drop at all.If any thing it might go up due to charging system volt.If pump is strong enough,pressure should not drop off ,even at high rpms.And I would not like normal running pressure below 38 to 40 psi,vac hose connected.I usually buy pumps for vortec engines and install adjustable regulators to set pressure where I like.

Originally Posted by GREGGPENN

You missed the point...which was to let the OP know his original FP likely went up with the installation of an AFPR. And, if higher, it would account for at least part of his difference.

Originally Posted by Fredbird

The Fuel Pressure Guage I bought from HF didn't fit my fuel rail so I've spoken with a friend of mine and he's got one that will fit so I can check it at that time and let you know the pressure.

As to the Fuel Pressure Regulator I replaced, it was listed as " OE Style; Fuel pressure regulator diaphragm kit" Manufactured by BWD. -So it should be the same pressure as the original when it was new.

Once I get the Fuel Pressure measured at the rail, I will report it here... Just haven't had time to do it yet.

Originally Posted by GREGGPENN

If you know the FP before everything was swapped, that's a good test. If not, I would bet against the new AFPR being the same as stock. "OE style" only refers to appearance IMO.

If you don't know the before/after FP, consider running a poll to see how many people ended up with higher FP after installing an adjustable unit. I tried to explain the reason earlier in this thread. If I had pics, I'd show the reason. But, my camera wasn't working at the time of that discovery.

There was a thread about two years ago the clued me into the issue. If you saw an OEM unit disassembled then saw an AFPR, you'd understand my point.

Edit: This is probably the thread I am thinking of....
http://forums.corvetteforum.com/c4-t...46psi-why.html

Originally Posted by Fredbird

Took the car to my friend's shop yesterday and he put the Fuel Pressure Guage on it.
Ignition in "ON" Position without having the engine on - 38-39lbs (According to what I had been reading before, that should be correct.)

At Idle - dropped to 30lbs
As he revved the engine it was fluctuating between 30-40 lbs

He checked his shop computer and looked up what the car should be at. He said it should be between 40 - 47lbs

So, according to him, my fuel pressure is low.

So, within the fuel path I've already replaced the "In-Line" fuel filter this past summer, the Fuel pressure regulator diaphram (as you know) and the injectors. The only thing left in the system would be the fuel pump itself. However, at ignition on, the pressure is correct.

Also, maybe it's my ignorance speaking, but how could "LOW" fuel pressure cause poor gas mileage.

Would the injectors be allowing too much fuel to flow and that's what's dropping the pressure in the line when the engine is started? (I don't have enough understanding in this area, that's why I'm asking)