Been poking around, asked a few people, but... no answers that fit...

Pump prime time. At key-on, you get a 2 sec. fuel pump prime. If you hit start right away (within a second or so) you've still got all that pressure behind the injectors.
Instant start up (well, for me anyhow!).

In the $42 (1227747) code though, nobody seems to have made this 'on duration' adjustable. I'd much rather have a 10-20 seconds prime to give me ample time to hit start, or even just enough time to watch my fuel pressure gauge and see where I'm at.

Also - and it could be inaccurate info - one of my GM manuals in the wiring charts (see footnote #4 below for a scan of it), says that the 4.3 & 5.0 got the 2sec prime, but 5.7 & 7.4's got a 20 second prime.



So... is this findable in the code, and to make it adjustable?

I'm assuming your using TunerPro.

I've not worked with $42 code before, but there will be a place to change this in the calibration. You will need to get a copy of the $42 hack and see what the chip address is for this and then add this as a constant to your xdf. The process isn't very hard once you get the hang of it. Just take your time and read the help files in TunerPro for more info. Also , look at how the other constants are set up in your xdf for clues on how to get started.

Pump prime time at key-on is a function of the ECM hardware. Pull the PROM out and you still get the same prime time.

The 20-second primes on some trucks is from an add-on module. It is known as the hot fuel restart module (or something close to that). Wired in parallel to the fuel pump relay and oil pressure switch, it is a simple timer and high side transister to provide power to the fuel pump.

RBob.

On 93+ PCMs the prime time is controllable in the PCM code and there is a constant for it.

Hot Fuel Modules were common in Fullsize Vans and 3/4+ ton trucks through 1992. In 1993 with the PCM controlled fuel pump prime, it was deleted. FWIW, I would take the Hot Fuel Module off of ANY vehicle so equipped. Word of experience here as I have had TWO of them short out! The 2nd time it almost caused a FIRE!

The issue with the hot fuel modules is that the transistor wont handle more pump. There isn't any heat sink for it. So put in a pump that draws a little more current and the transistor heats up and sets the plastic case on fire.

RBob.

I can tell you first hand it won't handle a TPI pump at higher pressure, the transistor burns up.

Well, as I read all the above, that quickly took me from a 'cool, gotta get one!' to a 'hot, gotta avoid those'.

Ok, so it looks like I need to make my own timer it looks like. At least now I can stop scrolling through the 193 page hack I found of the $42 code!


Thanks as usual guys.

I would at least get one of the GM hot fuel timers. Can always add a heat sink to the transistor. Along with possibly replacing it with a different one. IIRC, it is a TO-220 case style. It just sits out in the open, a strip of aluminum could be used.

In the full size vans the module is located with the ECM. Black plastic box with a flip top. Has an edge-card connector type of plug in.

RBob.

Sorry for the misinformation.