73-87chevytrucks.com
73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: MuddiGGEr25 on May 17, 2017, 01:58:52 pm
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just noticed that the CKP sensor on the 454 i just dropped in is hanging off the side, it might be possible to plastic weld the it back on as it is a clean break, but just wondering how critical is the sensor to the TBI computer? my 87 TBI did not have one, so it kinda threw me off.
I found one online at rock auto for $45 so i can order one if its really picky.
Engine/trans 454/4L80E from a 1995 K2500 with the 32PSI TBI system.
Put into a 1988 V20 Suburban
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Post a pic
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I can after work, I'll be home a little after midnight my time
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pictures as promised, and the wire colors appear to be orange yellow and tan, but i cant tell for sure due to weather fading. but one definitly seems to be orange, my 1200 lumen flashlight is a bit overpowering for my phone camera.
It doesnt match up with any of the crankshaft position sensors on any website because they only have 2 wires and a entirely different connector
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a little more google and some energy drink i managed to figure it out... its the oil pressure sensor, i think its the one for the fuel pump relay to cut it off like in an accident. Not entirely sure if i am even wiring my pump through the factory relay or not yet, since im putting an inline pump in thats about 10% more powerful than stock (excess will just go back to the tank, no biggie) i just wanted more fuel available for when i swap the cam in the fall/winter
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Yeah no ckp, oil pressure and you need to replace it.
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God...I was gonna say that yesterday Vile! I got to thinking...maybe I don't know everything about the TBI system. I was thinking...there is no crank sensor on a TBI, and I was thinking...it must be the oil pressure sensor that is on the front, lower left of the engine, but then he had the weird, higher pressure TBI and he said he found a CKP on RockAuto for his engine.
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well actually according to every parts store, both my 95 454 and my wifes 95 350 have a crank position sensor, dont believe me, pick any parts store with an online search and enter either one 1995 K2500 7.4L auto or 1995 K1500 5.7L auto, not sure where its located but it shows both of them as having one, and i tried 1994, and it shows one that year too, its weird but its all i know lol
But my question is (and ill search those diagrams to find out later) is do i NEED that sensor? im more than likely running my own relay independent of the PCM, so my inline fuel pump wont be needing that signal, or does that one also prove signal for the gauges too?
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Don't have my 1991 diagrams with me right now, I will have to check those, but I believe it feeds into the PCM and on my 7.4 L I don't remember a separate sender for the gauge!
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keep the oil pressure/fuel pump relay, if your ever in an accident and the engine shuts off you don't want the fuel pump to keep going, it could make a bad situation much worse very quickly.
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Yeah ill try super glueing it on there, and see if thats good enough to pick up the reading, worst case ill just buy another one down the road
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keep the oil pressure/fuel pump relay, if your ever in an accident and the engine shuts off you don't want the fuel pump to keep going, it could make a bad situation much worse very quickly.
not true. most think its a fail safe for an accident but in reality the ecm trips the fuel pump relay for priming and running the fuel pump. if the fuel pump relay fails prolong cranking will build up the oil pressure and trip the OPS and the switch will then power the fuel pump
(http://forum.73-87chevytrucks.com/smforum/index.php?action=dlattach;topic=29825.0;attach=27609;image)
i know on my 91 it powers the fuel pump and also the gauge. i also know theres a few to choose from, i dont know why theres more than one choice
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im 100% sure my 91 doesnt have a crank position sensor. they have all those things in the distributor, the distributor tells the injectors when to fire. maybe a knock sensor?
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keep the oil pressure/fuel pump relay, if your ever in an accident and the engine shuts off you don't want the fuel pump to keep going, it could make a bad situation much worse very quickly.
not true. most think its a fail safe for an accident but in reality the ecm trips the fuel pump relay for priming and running the fuel pump. if the fuel pump relay fails prolong cranking will build up the oil pressure and trip the OPS and the switch will then power the fuel pump
(http://forum.73-87chevytrucks.com/smforum/index.php?action=dlattach;topic=29825.0;attach=27609;image)
i know on my 91 it powers the fuel pump and also the gauge. i also know theres a few to choose from, i dont know why theres more than one choice
How is it not a safety feature? the priming when the key comes on is to ensure fuel pressure when you start cranking, while cranking the crank signal keeps the pump on and when the engine builds oil pressure the fuel pump stays on as long as the engine is making oil pressure. the system is designed to cease fuel pump operation if the engine stops running or suffers a catastrophic loss of oil pressure, such as in an accident
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keep the oil pressure/fuel pump relay, if your ever in an accident and the engine shuts off you don't want the fuel pump to keep going, it could make a bad situation much worse very quickly.
not true. most think its a fail safe for an accident but in reality the ecm trips the fuel pump relay for priming and running the fuel pump. if the fuel pump relay fails prolong cranking will build up the oil pressure and trip the OPS and the switch will then power the fuel pump
(http://forum.73-87chevytrucks.com/smforum/index.php?action=dlattach;topic=29825.0;attach=27609;image)
i know on my 91 it powers the fuel pump and also the gauge. i also know theres a few to choose from, i dont know why theres more than one choice
How is it not a safety feature? the priming when the key comes on is to ensure fuel pressure when you start cranking, while cranking the crank signal keeps the pump on and when the engine builds oil pressure the fuel pump stays on as long as the engine is making oil pressure. the system is designed to cease fuel pump operation if the engine stops running or suffers a catastrophic loss of oil pressure, such as in an accident
That is not the case, look at the schematic. The oil pressure switch serves as a backup should the fuel pump relay fail. If you unplug the o/p connector the vehicle will continue to run.
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the oil pressure switch and the relay are wired in parallel as far as supplying 12v to the fuel pump however the oil pressure switch also sends oil pressure signal to the ECM, the ECM supplies power to the fuel pump relay under the following conditions: for five seconds upon key on, while seeing a crank signal, and while the ecm sees the engine running. Now i'm sure the ECM will shut down an engine under a variety of conditions but since the ECM sees a signal from the oil pressure switch it would make sense that the ECM would shut off the fuel pump relay upon the loss of oil pressure signal and assuming that the engine really has lost oil pressure the oil pressure switch would also shut off leaving the fuel pumps unpowered, hence safety feature.
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Not sure how shutting off the engine while driving would be a safety feature....
BASIC SYSTEM OPERATION:
The fuel supply system begins with gasoline in the fuel tank. An electric fuel pump, located in the fuel tank with the fuel level gauge sending unit, pumps fuel to the fuel rail through an in-line filter. The pump is designed to supply fuel at a pressure above the pressure needed by the injectors. A pressure regulator located in the throttle body assembly keeps the fuel available to the injectors at a constant pressure. The unused fuel is returned to the fuel tank by a separate line.
MODES OF OPERATION:
The ECM uses voltage inputs from several sensors to determine how much fuel to give the engine. The fuel is delivered under several conditions, called "Modes." All modes are controlled by the ECM, and are described below.
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, throttle position sensor, 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.
The system will stay in Open Loop until the following conditions are met:
The Oxygen sensor has a varying voltage output, showing that it is hot enough to operate properly. (This depends on temperature)
The Coolant temperature is above a specified temperature.
A specified amount of time has elapsed after starting the engine.
CLOSED LOOP:
The specified operating conditions vary with different engines, and are stored in the programmable read only memory (PROM). When these conditions are met, the system goes into Closed Loop operation. In Closed Loop, the ECM calculates the air/fuel ratio (injector on-time) based on the signal from the Oxygen sensor. This allows the air/fuel ratio to stay very close to 14.7:1.
ACCELERATION MODE:
The ECM responds to rapid changes in throttle position and manifold pressure or air flow, and provides extra fuel.
DECELERATI0N MODE:
The ECM responds to changes in throttle position and manifold pressure and reduces the amount of fuel. When deceleration is very fast, the ECM can cut off fuel completely for short periods.
BATTERY CORRECTION MODE:
When battery voltage is low, the ECM can compensate for the weak spark by:
Increasing the amount of fuel delivered.
Increasing the idle speed.
Increasing the ignition dwell time.
FUEL CUT-OFF MODE:
No fuel is delivered by the injector when the ignition is OFF. This prevents dieseling. Also, fuel is not delivered if no reference pulses are seen from the distributor, which means the engine is not running. This prevents flooding. Fuel cut-off also occurs at high engine rpm, to protect internal engine components from damage.
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like vile said if you unplug the ops the truck will start and continue to run as long as the fuel pump relay is working. you can tell when a relay has given up if you ever ear a TBI motor crank for 5 or so seconds then firing up. that means the relay has quit and it need oil pressure to power the pump.
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if you engine has no oil pressure and you keep driving you will seize the engine ending in an unpowered coasting scenario, if the ECM detects low/no oil pressure and shuts off the engine your still coasting unpowered but now you don't necessarily have a blown motor to go along with it. As far as the oil pressure switch goes it was wired in parallel with the relay so that in the unexpected event of fuel pump relay failure while driving so long as you still have engine oil pressure you won't shut down in the middle of the road. Now insofar as what the ECM will do if it loses the signal from the oil pressure switch will take some more research however everything I've found so far has indicated that the ECM should shut down the fuel pump relay in a no oil pressure situation to prevent engine destruction. My original point however about not wanting the fuel pump to continue running after an accident still stands, although the fuel pump will keep running if the engine does
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if the ecm kills the engine without giving you sometime to react (to pull over) you will lose power steering and brakes. for most we can handle this, but for some this would be a liability issue with gm cause they might not know how to tell the engine isnt working and they no longer have power brakes or if youre in the mountains and are now trying to stop a trailer while going downhill. as far as low oil pressure, if you wreck your motor cause you ignored a "check engine" light or the oil gauge being below 3 psi then thats solely on the operator of the vehicle.
as far as the event of the relay failing while driving is kind of hard for me to understand. most times when they fail its due to arching and burning up the contacts. this is done when power is applied and when its turned off.
you have an 88 so it would take less time to reply to a comment than start the truck up and unplug the OPS or even start it with the OPS unplugged
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power assist brakes weather vacuum or hydroboost have an internal boost/vacuum reservoir that gives you 1-3 good assisted pedal pushes, this feature was implemented so that in the event of unexpected engine shut down you still have brake assist to bring the vehicle to a safe stop. Power steering is only needed in parking lots or downtown traffic, it's nice to have but it's a luxury not a necessity, cars are very easy to steer so long as they're rolling, even the flat bed tow truck (10,000 lbs deck capacity) at work can be steered strong arm style as long as it's rolling. As for unplugging the oil pressure switch i will be trying that after i get a new fuel pump relay (hopefully just need a relay) and stop feeling like death, I've been home sick the last two days
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FWIW. I haven't gotten the OP sensor repaired or replaced yet.. mainly working on a billion other things. But yesterday I got the engine wired and started. It idled and moved around in the driveway under its own power with no oil pressure switch.