SATAN

iTrader: (2)

I have noticed on many tunes, that the flow rate changes in the "injector flow rate vs Kpa" table in HP tuners. However, my stock tune for my 5.3 Silverado PCM says 21.8 lbs all across the whole table. This makes sense to me if I have a vacuum referenced fuel pressure regulator. The vacuum adjusts the diaphragm in the FPR and this in turn appropriately changes the the fuel pressure in reference to manifold vacuum.

The only reason I can think of to enter different flow ratings for manifold vacuum is... You have a fixed fuel pressure all the time. Then when your manifold vacuum increases, so does the flow of fuel. As the vacuum decreases, again, so would the flow of fuel. The computer would need to know the different values at different manifold pressures then.

I however, am not running a fixed fuel pressure. As vacuum increases, my fuel pressure drops. As boost comes on, my fuel pressure compensates on a 1:1 ratio. Therefore, my injectors should always flow the same amount regardless of manifold pressure. That being said, shouldn't my flow rating be the same across the entire table, just like the OEM Silverado tune?

Sorry for sounding redundant, I just want to make sure my rambling is understood.

01ssreda4

iTrader: (96)

I thought 5.3s did have some kinda vacuum thing on the fuel rail. I dunno what it is though

lsxnation

iTrader: (2)

do you mean this table?

Sarg

iTrader: (6)

Makes sense. If the stock system has a vacuum referenced regulator it would be the same all the way across, if not the table would need to be adjusted. Possible it is there for cars that do not have a vacuum referenced fpr?

SATAN

iTrader: (2)

Yes, that is the table I am talking about. Mine is in KPA from 0-80 right now though. Either way, yes that is it.

Why does the flow rate change though? I thought that was the main purpose of having a vacuum referenced fuel pressure regulator, so the flow rate was always constant regardless of manifold pressure.

I PM'd one member on here after looking at his tune. His flow ratings also changed across that table as well. When he replied, he told me that he did it like I was talking about and did one consistent number all across the table. Once he did this, his car smoothed out.

His quote is...
"I ended up putting them all back to 160 across the table like you said. Car is running pretty well now."

I guess over all, I am just wondering where people are getting these varying numbers from?

SATAN

iTrader: (2)

I don't know about the 5.3's. I have an LQ4 which does seem to have a vacuum referenced FPR though. But when I pulled up the program on the stock 5.3 tune (my computer is for a 5.3), it showed it being consistent across the entire table.

01ssreda4

iTrader: (96)

I have seen a truck rail like this as well. Origin is unknown.

2xLS1

iTrader: (25)

Depends on the year of the truck. Most through 03 have a vacc referenced regulator on the rail with a return line to the tank. Those will have the same value in the IFR table. 04+ are returnless with the regulator in the tank. Different values in the IFR table. You set up your IFR table based on the type of fuel system you are using. Also don't confuse a pulse damper on the fuel rail for a regulator.

SATAN

iTrader: (2)

Gotcha, that is probably what I have on my 6.0 truck manifold (99 LQ4). Thank you for clearing this up. I was unaware that some came with FPR's and some came with pulse dampers.

2xLS1

iTrader: (25)

Pulse dampers don't have vacuum lines, FPRs on the fuel rail do. A 99 should have a FPR on the rail with a return line to the tank.

SATAN

iTrader: (2)

I had to go look after reading about the dampers. Mine is an FPR, as it does have both the vacuum line and the return line. I always noticed it, but also always just assumed it was the factory FPR, therefore not paying much attention to it.

Either way, it answers the question as to why I see some tunes where the flow values change across the table.

Thanks again.

Sarg

iTrader: (6)

Exactly. If there is no vacuum reference there are only two ways of dealing with it. One would be a table such as the one posted above (correct way), and the other would be to account for it in the fueling tables. Adding the above table would account for a greater amount of situations than just trying to hack around it in the fuel tables or maf tables. We have had to just try to account for it in the MAF tables in vehicles without that table running non-regulated fuel pressure regulators. Pain in the bum.