TBI hard starting after sitting

[Mastiff]

I haven't dug in yet, but maybe you guys have some ideas where to focus when I do. Retrofit GM TBI setup. Recently, when the truck sits for a few weeks (which is common) it takes 10-20 seconds of cranking to fire up. It fires fine after that, say 4 hours later. I turn the key and hear the pump before I start cranking. The one thing that maybe could be contributing is that my batteries are both old and weak, so it's not cranking as fast as it could, but it's not super slow either. I've never heard of the spark system itself being compromised by low voltage, but maybe? I'm putting off dumping hundreds of dollars into a new set of batteries... I've always gone with AGM's, which are now about $250 a pop.

 

[flatland]

Try a battery maintainer, ( or even a jump box), it makes a big difference on mine. Also, I wait for the pump to stop and turn it over a few seconds then switch off and repeat, letting the pump prime again. Seems to help.

 

[Mastiff]

Try a battery maintainer, ( or even a jump box), it makes a big difference on mine. Also, I wait for the pump to stop and turn it over a few seconds then switch off and repeat, letting the pump prime again. Seems to help.

Yeah, I've been keeping these old batteries alive with a battery tender for a while. I still have to run electrical to my new shop though, so the batteries have been on their own recently.

 

[ktmoutfront]

Multiple on/off of the ignition before you crank. The pump only runs a couple of seconds each time. Doing it multiple times charges the fuel system.

 

[dyeager535]

I'd agree that it's probably bleeding back over time, although should that REALLY happen without an internal leak from the FPR, or injector?

Only way fuel is draining out of the fuel line is if it goes back into the tank (lowest point of the fuel system), and the injectors and regulator should both not allow air into the pressurized side I'm thinking.

 

[Blue85]

Mine did this until I replaced the fuel pump. I would turn the key a few times before cranking, as it took several seconds to get in the neighborhood of 50psi. The fuel pump prime was about 2 seconds, so I increased it to 5 seconds IIRC. For a TBI system, it make take fewer key cycles. The only way to know is with a pressure gauge.

The other normal culprit for extended crank is a bad fuel pump relay or wiring, so you have to build oil pressure before the pump kicks in.

 

[Mastiff]

I'll have to refresh my memory on the oil pressure thing. It's a safety thing to cut the fuel pump if there's no oil pressure I think? But the fuel pump runs for the short prime...

 

[dyeager535]

I'll have to refresh my memory on the oil pressure thing. It's a safety thing to cut the fuel pump if there's no oil pressure I think? But the fuel pump runs for the short prime...

No, the oil pressure switch is redundant in case the fuel pump relay (Edit thanks Wes lol) fails. If the pump primes with key on/engine off (I believe it's on a timer, so need to wait 15 seconds or so to cycle it again), the relay is good.

 

[Wes Harden]

I'll have to refresh my memory on the oil pressure thing. It's a safety thing to cut the fuel pump if there's no oil pressure I think? But the fuel pump runs for the short prime...

No, the oil pressure switch is redundant in case the fuel pump fails. If the pump primes with key on/engine off (I believe it's on a timer, so need to wait 15 seconds or so to cycle it again), the relay is good.

What Dyeager said, except he meant to say fuel pump RELAY fails. Then the oil pressure switch will close and allow the fuel pump to run. The 2 parts are wired in parallel.

I am in the cycle the key a few times to pump fuel up to the injectors, group.

Starting an injected engine on weak batteries could be the hard start. You need power to run fuel pump, injectors and enough left over to supply spark, all while a starter is drawing 150-300 amps.

 

[Mastiff]

Yeah, I'm going to refresh the batteries first and see where that gets me. Thanks for the ideas.

 

[imiceman44]

Yeah, I'm going to refresh the batteries first and see where that gets me. Thanks for the ideas.

Definitely make sure the batteries are either new or topped off and hooked up to the charger, that is most likely your issue.
I had that a few times.
Now I don't skimp on batteries, when in doubt put new ones