I have a 1988 Chevy C1500 (350 engine) that will not start after sitting overnight. It cranks over fine but does not seem to be getting fuel even if I pump the accelerator. If I pour gasoline into the intake it will start right up and continue to run great. I can shut it off and it starts right back up. It will continue to start as long a it has not been sitting for a while. However, the next morning it will not start again. I am not familiar with throttle body operation, so I don't know it it has an accelerator pump as with older conventional carburetors. I have also seen reference to injection problem, but I don't know where to start looking. Any help would be much appreciated.
There's no accelerator pump on those. I don't think there's a separate cold start injector either like many multi-port systems use. The computer is supposed to make the throttle body injectors spray extra fuel to assist cold starts dependent on engine temperature. Check the following where on a throttle body system a cold start problem was caused by a bad temperature sensor:
https://ck5.com/forums/threads/tbi-cold-start-latest-drama-edit-solved.56793/
Thanks for the lead. After much searching I found info that may point to the fuel pump relay. I understand that, when the ignition is first turned on, the relay pulls in and energizes the fuel pump for 2 seconds - then shuts off. It appears that this sprays fuel through the injectors to prime the throttle body. Then the fuel pump turns back on when the engine is started. If this is the case, a defective relay could prevent this priming phase and keep the engine from starting. Pouring fuel into the intake would then serve as the primer. My Haynes manual makes no mention whatsoever of this, but it makes sense. I intend to follow up on this in the next day or two.
Interesting way to enrich the mixture for startup, could very well be that relay!
You seem to be on the right track suspecting that fuel pump relay.
Just to clarify, when the fuel pump relay is energized with key in RUN it primes the fuel system. It doesn't pulse your fuel injectors.
On most fuel pump circuits the premise wouldn't make any sense.
A relay that doesn't work in the morning? Sounds more like a brother-in-law than a relay.
But I suspect that fuel pump relay never works. Sounding more like a brother-in-law all the time.
You have a unique fuel pump circuit on that old Chevy TBI.
You have 2 oil sender/switches.
One of them is wired in the fuel pump circuit and when sufficient oil pressure closes that oil pressure switch it bypasses the fuel pump relay. In fact, with the engine running (as long as there's oil pressure) you could unplug your fuel pump relay and the fuel pump would still get power.
(That one is the oil pressure switch in the back of the engine by the firewall).
The circuit looks like this.
See how when that oil pressure switch closes it completely bypasses the fuel pump relay and provides power to the fuel pump?
So maybe for whatever reason, the starter isn't cranking as fast after the battery has sat for awhile, or all the oil drained down to the pan, ...whatever, the oil pressure isn't building up enough to close that oil pressure switch during a "cold start" but it is with a freshly charged-up battery and warm oil.
I think you're on solid ground here.
So maybe the first thing to do is listen for the fuel pump to run for a few seconds when you turn the key to Run. That would help to confirm your (and my) suspicions of a faulty fuel pump relay.
Sorry for the delay (due to major illness). I really appreciate your reply and the diagram. Great info to follow up on. I did replace the fuel pump relay but did not seem to help. Some of my problem appears to have been the battery. I could jump start from my Wrangler and it started right up. This would not work with my jump box. Apparently, the battery was so weak it would still not turn over fast enough with the box. New battery seemed to help tremendously. The battery was not very old, so I did not suspect that at the time. Goes to show that new does not mean flawless. The dealer replaced it free. Truck is still a little hesitant to start on cold mornings, but usually will start after a couple of tries and some sputtering. At least I don't have to pour fuel in. Thank you so much for taking the the time to help.
I am probably wrong on this but doesn't the old TBI setups have a separate, cold start injector?
