Hot Rod Roy

My '84 suffers from the same problem, scratch that, inconvenience, that we all learn to live with:

The engine starts right away when I've previously driven it that day, but if I haven't driven it for a few days, it takes a few seconds longer, because it needs to build fuel pressure before it will start. No big deal, but can it be better? Hmmm (Thinking cap!)

What if there was some way to prime the fuel system before I turn the key? Hmmm

Okay, what works when I first enter the car? Hmmm

On my newer DD with push-button start, I need to step on the brakes before I press the start button. Hmmm

The Brake Lights! The brake pedal is kind of an automatic reaction! Hmmm

I've been puzzled about the ALDL pin G. What's its purpose? I'm sure they used it at the factory to prime the fuel system for the car's first start, since applying 12 v. to that pin will run the fuel pump, but is that the only purpose? How is that useful to me now? Hmmm

I can do that! If I put a jumper between the brake light circuit and the ALDL pin G, I get an immediate fuel pump activation!

Okay, any down sides? The FP relay disconnects the pin G as soon as the engine starts, so there's no feed back to turn the brake lights on at the wrong time! That's good. Fuse overload? Checked that. No problem! Guy's, is there anything I've forgotten? (I promise to take my foot off the brakes if I get upside-down!)

Does it work? My FP is so quiet, I can't hear it run, so I stuck a hose into my gas tank filler, then put the other end to my ear. Sure enough, The pump runs when I touch the brake pedal!

And yes, I now have quick starts, even if I haven't driven the car for a week!

Brake light switch, light blue or white wire, to ALDL pin G, red wire! Easy!

jmgtp

Gotta ask - is this really worth it? Seems like it might be a wiring headache down the road. Does you car not prime the pump when you key to run before cranking? You could just pause momentarily in run before cranking and achieve the same thing.

I'm not familiar with the 84s so maybe in fact the 84s don't behave this way. But my 94, and for that matter all of the dozen or so fuel injected vehicles I've owned, all prime the pump and pressurize the system as soon as the key passes through the run position.

If the 84 is the same (primes in run) then I'd look into a fuel pump or check valve issue rather than modify the wiring to prime with the brake lights.

Hot Rod Roy

jmgtp, I gotta ask. Your LTCC-LS1 ignition mod in your '94 might be a wiring headache down the road! How did you benefit from this mod? I won't ask the cost.

I got a genuine benefit from my free mod. There was nothing wrong with my '84. Lots of C4 owners have this same issue! But who wants to wait for a second or two after you turn the key? I've got better things to do!

If I don't step on the brake pedal, it starts just fine, but it may take an extra few seconds if I haven't driven it for a week, so I can easily see the difference! My fuel pump is good.

jmgtp

Didn't mean to upset - just asking a question since tying the fuel pump the to the brake lights is odd.

The LTCC is a different animal altogether, it's also plug and play - the high voltage side of my Opti was failing. I know aftermarket Optis can be crap and the LTCC allowed me to continue using the Mitsu sensor for resolution signal. It was a win/win for me - I hope your fuel pump mod turns out the same for you

billschroeder5842

Genius. Well done. This type of ingenuity is what this forum is about.

C409

..... In the event of an accident that compromises the fuel system and leaves the driver unconscious , the weight of a foot or anything on the brake pedal would then activate the fuel pump ? ... I realize that the chances of this happening might be rather remote , but now the chances have improved by the number of people (other than you) who perform this modification ... why not just install a push button momentary contact switch somewhere on the dash or console (hide it if you must) ? .....

84 4+3

I'm curious. How much longer is it when it sits? I only ask because I've never really noticed it on mine but then again I almost always wait until the dash settles down before I go cranking anyway. I do that in all the vehicles actually... either way it's pretty cool. Nice thinking.

slow-vette

My 86 cycles the fuel pump as soon as the key turns and before the starter engages. I have watched my pressure gauge while someone turned the key and fuel pressure comes up almost instantly. Perhaps if you are having a hard start after sitting you could have a fuel pressure regulation issue or a pre-run relay issue. I would look into those before I bypassed a safety system and wired my fuel pump into the brake lights. My car starts on the first hit of the key in the morning when cold and usually within a couple of revolutions when hot. It starts just as fast or faster then my wife's new car.

Bfenty

I have an '85 and also don't see much, if any hesitation to starting even when cold. No more than I get from any other car I own, anyway. While I applaud your ingenuity on solving this issue, I'm wondering if there's something else that you could do to make it come on more quickly?

Pwnage1337

I'll take my half second of cranking to build oil pressure

ex-x-fire

Most GM tbi systems (like cfi & the truck tbi) don't hold fuel pressure after shut off, they should hold fuel in the main feed line. You could do a pressure check and pinch off the return at a rubber section. It should hold fuel pressure at that point. If it doesn't then the check valve could be bad.