Can you make TBI squirt fuel like carb

[joegreen]

Hello. I read somewhere on some other forum (i do not remember where ) that someone made their tbi squirt fuel like a carb accelerator pump before starting. This sounds very cool and i would like to know if it is possible to make a tbi injector do a quick pulse by putting your foot to the floor and back before starting. I have chip burning equipment if this is possible. My truck starts pretty fast but in the morning it turns over like 5 times. When i had my quadrajet on it it used to practically start before you finished turning the key. I miss that:sad:

[buddrow]

You can try just increasing the cranking fuel to see if that helps. I havent seen anything about the squirt idea on a TBI. Sounds like the old TPI cold start injector. Not sure if you could hack that into the ecm/pcm code but could be done externally with minimal hardware.

Buddrow

[steveo]

i know exactly what you mean, with a carb you give 'er pump shot, and by the time you turn the key, that shot of fuel has vaporized and is hanging around in your manifold, so it starts more quickly.

would be nice to do it in code but it'd be a pain, since it doesn't have any reference pulses yet. there's usually a control loop for 'not running yet' in ecm code, if you could insert a 'if tps > 90%, pulse injectors a bunch' kinda routine, and just make sure you dont flood it.

personally i just dont care, long cranking times on tbi engines is kinda normal.

[joegreen]

Its more of a neat thing i miss having. It would be cool to have but would it mess with clear flood mode?

[steveo]

clear flood should never be needed on a healthy engine anyway

whether it messed with it or not depends on how you program it

[joegreen]

so is it possible to set a parameter that when certain tps value the injectors squirt?

[RobertISaar]

which ECM are we talking about? a P4/P6 can have code added to it pretty easily, a C3 cannot.

would just need to watch TPS before cranking, if it exceeds xx%, trigger an async burst of xx mSec.

[1project2many]

What made carb engines start so fast when warm was fuel vapors in the intake, often from a small leak in the carb. An excess of fuel would enter the cylinder immediately on cranking but without any oil getting a chance to splash on the cylinder bores it can negatively affect ring life. Also, if the bearing clearances are high there's a chance the oil cushion around the crank has drained away as well.. You can make TBI start fairly quickly without any priming shot of fuel by reducing the number of pulses before fuel and spark begin. If your engine's in great shape there's no worry but with a high mileage engine and the thinner oils used today it's not a bad idea to delay the start to get some oil moving first.


clear flood should never be needed on a healthy engine anyway
Plenty of situations I can think of that could cause plugs to get wet from fuel. Most common in our fleet is condensation in van engine compartment. I can often play with clear flood to get a few plugs to fire and warm up so vehicle will start. In MT it was extremely cold temperatures. With clear flood and some ether it was sometimes possible to get plugs to fire just enough to light off the gasoline.

OTOH many Chrysler products have no clear flood mode and require some type extra work to get wet plugs dried out. Dodge / Chrysler PFI V8's were known for random / multiple misfire codes on wet days and drivers would shut vehicle off while running rough only to find they wouldn't restart. Much harder to dry those plugs out.

[joegreen]

Im sorry its a 1227747. How would you reduce pulses before fuel and spark start?

[1BadAction]

My TBI lights off on the first hit... It starts just as fast, if not faster than the LS3 in my 2013 Camaro.

[blue68deville]

The Caddy and my 93 both fire off pretty fast.
I had a retrofit tbi on a 454 that always took a few revolutions to fire. Never figured out why. It was using the same starter bin as I used for the caddy, so????

[joegreen]

From my research the 1227747 is a c3 ecu. So you are saying it would be hard to make it squirt fuel but not impossible? What does c3, p4 p6 mean? Thanks for everyones fast replys.

[RobertISaar]

C3 = motorola 680x processor
P4 = motorola 6811(based) processor
P6 = motorola 6811F1 processor

the C3 units have the issue of more or less only the calibration stored on the removable PROM, so while you're able to change calibration data, adding code(instructions) is tricky. sometimes, GM's code overlapped onto that PROM so you have a window or two to interrupt the existing code to do some of your custom code, but the windows of opportunity won't always work for what you need them to do, like code that only gets executed while the engine is running can't be used to trigger fuel pulses while the engine isn't spinning.

the P4 and P6 stored both calibration and code on a single PROM that with very few exceptions, is removable from the PCM and can be read/written with pretty much any PROM burner. some P6 are flash units and do everything over ALDL. some P6 are actually P66 and have dual processors(and dual PROMs).


there are exceptions to those 3 categories of OBD1 ECMs, but not too many.