73-87chevytrucks.com
73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: Blazin on February 06, 2015, 02:09:25 pm
-
Once in a while on very cold mornings 0 or below. I have to give my TBI 350 a shot of gas down the throat. Other times it will fire right up when its that cold. Any ideas?
-
when its that cold do you hear the fuel pump prime when you first turn the key on?
-
Yes fuel pumps runs.
Prior to me owning someone hot wired the pump to come on, & stay on when they key is on. While I don't think this is correct, I also don't think it should affect cold weather starting.
-
Does it struggle to crank or just turns over a lot? What kind of truck? Nevermind it is in the topic.
-
Turns over fine, just won't fire. Give it a little shot of gas in the TBI it fires right up. Runs rough for a second but comes right into it.
-
You should fix the fuel pump circuit and check your fuel pressure.
You need to scan it. List ECT reading, Fuel Integrator, TPS Voltage, MAP voltage.
-
Starting Mode:
When the ignition is first turned ON, the Electronic Control Module (ECM) turns ON the fuel pump relay for two seconds, allowing the fuel pump to build up system pressure. On Heavy Duty models, a fuel module will override the ECM two second timer and the fuel pump will run for twenty seconds and then shut OFF if the vehicle is not started. This circuit corrects a hot restart (vapor lock) during high ambient temperature conditions. If the engine is immediately started, the fuel pump will continue to operate. If the key is left in the ON position, but the engine is not started, the ECM will turn the pump OFF. The fuel pump will remain OFF until the ECM detects the crank signal, or in the case of a faulty fuel pump relay, the oil pressure switch detects approximately 4 psi of oil pressure which will then bypass the fuel pump relay.
Fuel delivery from the injectors (which deliver fuel in all operating modes) is controlled by changing the amount of time the injectors are turned on or "pulsed" by the ECM. The ECM checks the Coolant Temperature Sensor (CTS), Throttle Position Sensor (TPS), and the crank signal, and determines the proper air/fuel ratio for starting. This ranges from 1.5:1 at -36°C (-33°F) to 14.7:1 at 94°C (201°F).
Clear Flood Mode:
If the engine floods, it may be cleared by pushing the accelerator pedal down all the way. The ECM then pulses the injector at a 20:1 air fuel ratio. The ECM holds this injector rate as long as the throttle stays wide open, and the engine speed is below approximately 600 rpm. If the throttle position becomes less than approximately 80%, the ECM returns to the starting mode.
Run Mode:
The run mode has two conditions, called OPEN LOOP and CLOSED LOOP.
Open Loop:
When the engine is first started, and engine speed is above 400 rpm, the system goes into OPEN LOOP operation. In OPEN LOOP, the ECM ignores the signal from the Oxygen sensor, and calculates the air/fuel ratio based on inputs from the coolant temperature and Manifold Absolute Pressure (MAP) sensors.
(working on a source)
-
http://forum.73-87chevytrucks.com/smforum/index.php?topic=29825.msg249755#msg249755
-
Have scanned it for codes, comes up with nothing even though the check engine light comes on at least once a day. Right now its my only plow truck running as I never got the motor in yellow snow. So tearing into the wire problem might not be doable for a few weeks!
Pretty sure its not a flood condition as dumping a little fuels into the TBI solves the no start problem.
-
yeah dont think flooding is the problem lol but wanted to post the whole thing. but what happens when you unplug the cts? have you checked the ohm readings from the cts?
-
Haven't checked anything as its been to darn cold out, & it doesn't do it if I leave it in the shop overnight! lol.
-
how you making out with all that wonderful white stuff ???
also
try this (http://www.73-87chevytrucks.com/techinfo/7387CKMans//Fuel_Emissions/X8736_1987_GMC_Light_Duty_Truck_Fuel_and_Emissions_Including_Driveability.pdf#page=46)