RE: fuel pump relay
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RE: fuel pump relay - 10/12/2007 8:14:12 AM
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cwb
Posts: 1508
Joined: 5/13/2007
From: eastern NC
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quote:
ORIGINAL: rshiver
Lots of good info there cwb, thanks for posting the link.
If the ECM doesn't get a signal from the temp sensor to let it know it's above 100 degrees, I wonder if the cold start injector is activated even though the engine is hot. Wouldn't that cause a rich, and/or hard start condition?
Could be, but it says '8 seconds max'...
Depends on the timing mechanism. If it's electronic, as in controlled by the computer, the only way that's gonna' fail is if the computer fails. If it's mechanical, as in quartz timing, THAT couldn't fail such that it kept runnin' either...
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RE: fuel pump relay - 10/12/2007 9:08:59 AM
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rshiver
Posts: 381
Joined: 8/4/2007
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What I'm trying to figure out is, where does the ECM get it's info regarding the temperature of the engine at startup. I would assume it has to have some input from somewhere as to whether the engine is above or below 100 degrees.
I'm wondering if this scenario is even possiable....
If, trying to start an engine that's already at an operating temp of 180 degrees or more, and the ECM "thinks" the engine is cold, would the ECM provide a rich fuel mixture from the injectors, and, on mine anyway, activate the cold start injector for 8 seconds, in effect, causing a border line flooded condition when trying to crank an already hot engine.
_____________________________
"Giving up" is never an option.
..............(o o)
~~~o00o~(_)~o00o~~~
2000 Limited Edition Ford F-350 Lariat 4x4 Dually, 7.3 Liter Powerstroke Diesel
1985 L98 Corvette
1978 Chevy Camaro LT
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RE: fuel pump relay - 10/12/2007 10:01:14 AM
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rshiver
Posts: 381
Joined: 8/4/2007
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OK, I've found that there's a cold start switch, that disables the cold start injector if the engine temp is over 100 degrees on '85-'88 L98's. Also, the cold start injector can leak too, so that's something for me to check into.
This wouldn't apply to dfwgsx's problem though, he has a '95.
Found this info on the cold start injector, but according to it the injector stays on until the engine warms up.
quote:
Since cold starting requires considerably more fuel than a warm engine, it must have some means of enrichening the fuel to air ratio until the temperature of the engine rises to where the fuel will vaporize more readily. The choke systems restricted the air intake so that there was less air moving thru the carburetor while at the same time opening the throttle plate below the choke plate and drawing more fuel. This causes a rich fuel mixture that will enable the engine to run.
The cold start injector (or valve) is mounted in the intake manifold at a centrally located area where it can open and allow extra fuel to enter the engine. This is in addition to the normal fuel injection system. The extra cold start injector is electronically controlled by the computer (ECM) and when the temperature sending units signal the computer that the engine is cold, the computer will send a signal to the cold start injector to inject fuel at the same time as the normal injection system. This makes the air fuel mixture richer to compensate for the cold engine requirements.
The cold start injector delivers fuel to all the cylinders and is controlled by a thermo switch and time control. Thermo switches are located in an area in the engine where engine temperatures can be sensed such as the coolant or head temperature. The temperature sensor has the ability to open the switch when the engine is warm enough to run on the regular injection system or close when the engine is cold and needs more fuel. It activates the cold start injector until the temperature deactivates the thermo switch. (The temperature rating on the switches can be checked in shop manuals).
Whether the sensor is controlling the cold start injector long enough can be felt by cold engine hesitations after the vehicle has run for a few minutes and prior to normal engine temperature. If the temperature sensor rating is too high or staying on too long, there can be some flooding or black tailpipe smoke generated for awhile at about normal engine temperature and also lower gas mileage. It is critical that the correct temperature sensors are used so as not to overload the catalytic converters and foul the oxygen sensors or cause the cold start injectors to work improperly.
HOW TO TEST A COLD START INJECTOR -- when the cold start injector is in a hard to reach area, a pressure drop test with the injector in place can be made. A pressure gauge can be installed at the fuel filter location or at the fuel rail connector. The fuel system can be pressurized by momentarily by-passing the fuel pump relay and then connecting an injector activator to the cold start injector to energize it. This will cause a pressure drop on the gauge if the injector is working. It can also be tested to see if up and then activating the cold start injector. The engine should falter or miss when this is done and possibly black smoke appear from the tailpipe due to the excessively rich mixture.
When the cold start injector is easy to get to and can be removed easily, it may be removed and activated in a container to check the fuel spray pattern. This will enable the injector to be cleaned with a commercial spray cleaner if desired when the spray pattern is not conical or when the injector drips while pressurized.
Loss of electrical power could also be a reason for the cold start injector not working. This can be checked by disabling the engine so it won't start and then connect a test light into the cold start injector connector. The test light should stay on for a short duration when the ignition is turned on. A stop watch can be used to measure the duration of the light staying on. Shop manuals will tell how long each duration of activated injector time is required. The above test should be performed on an engine that is cooled off and prior to start up in order for the injector to work in the time established for proper performance.
Source....
http://www.corvetteactioncenter.com/forums/showthread.php?t=9073
< Message edited by rshiver -- 10/12/2007 10:48:55 AM >
_____________________________
"Giving up" is never an option.
..............(o o)
~~~o00o~(_)~o00o~~~
2000 Limited Edition Ford F-350 Lariat 4x4 Dually, 7.3 Liter Powerstroke Diesel
1985 L98 Corvette
1978 Chevy Camaro LT
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RE: fuel pump relay - 10/12/2007 12:01:26 PM
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cwb
Posts: 1508
Joined: 5/13/2007
From: eastern NC
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I understand what yer askin' about if the computer thinks the engine don't ever warm up. And it would then keep the cold start injector pumpin' fuel. But if the thermo switch fails, it's still timer controlled.
So how much flooding could be caused by 8 seconds of unecessary cold start injector fuel?
quote:
ORIGINAL: rshiver
OK, I've found that there's a cold start switch, that disables the cold start injector if the engine temp is over 100 degrees on '85-'88 L98's. Also, the cold start injector can leak too, so that's something for me to check into.
This wouldn't apply to dfwgsx's problem though, he has a '95.
Found this info on the cold start injector, but according to it the injector stays on until the engine warms up.
quote:
Since cold starting requires considerably more fuel than a warm engine, it must have some means of enrichening the fuel to air ratio until the temperature of the engine rises to where the fuel will vaporize more readily. The choke systems restricted the air intake so that there was less air moving thru the carburetor while at the same time opening the throttle plate below the choke plate and drawing more fuel. This causes a rich fuel mixture that will enable the engine to run.
The cold start injector (or valve) is mounted in the intake manifold at a centrally located area where it can open and allow extra fuel to enter the engine. This is in addition to the normal fuel injection system. The extra cold start injector is electronically controlled by the computer (ECM) and when the temperature sending units signal the computer that the engine is cold, the computer will send a signal to the cold start injector to inject fuel at the same time as the normal injection system. This makes the air fuel mixture richer to compensate for the cold engine requirements.
The cold start injector delivers fuel to all the cylinders and is controlled by a thermo switch and time control. Thermo switches are located in an area in the engine where engine temperatures can be sensed such as the coolant or head temperature. The temperature sensor has the ability to open the switch when the engine is warm enough to run on the regular injection system or close when the engine is cold and needs more fuel. It activates the cold start injector until the temperature deactivates the thermo switch. (The temperature rating on the switches can be checked in shop manuals).
Whether the sensor is controlling the cold start injector long enough can be felt by cold engine hesitations after the vehicle has run for a few minutes and prior to normal engine temperature. If the temperature sensor rating is too high or staying on too long, there can be some flooding or black tailpipe smoke generated for awhile at about normal engine temperature and also lower gas mileage. It is critical that the correct temperature sensors are used so as not to overload the catalytic converters and foul the oxygen sensors or cause the cold start injectors to work improperly.
HOW TO TEST A COLD START INJECTOR -- when the cold start injector is in a hard to reach area, a pressure drop test with the injector in place can be made. A pressure gauge can be installed at the fuel filter location or at the fuel rail connector. The fuel system can be pressurized by momentarily by-passing the fuel pump relay and then connecting an injector activator to the cold start injector to energize it. This will cause a pressure drop on the gauge if the injector is working. It can also be tested to see if up and then activating the cold start injector. The engine should falter or miss when this is done and possibly black smoke appear from the tailpipe due to the excessively rich mixture.
When the cold start injector is easy to get to and can be removed easily, it may be removed and activated in a container to check the fuel spray pattern. This will enable the injector to be cleaned with a commercial spray cleaner if desired when the spray pattern is not conical or when the injector drips while pressurized.
Loss of electrical power could also be a reason for the cold start injector not working. This can be checked by disabling the engine so it won't start and then connect a test light into the cold start injector connector. The test light should stay on for a short duration when the ignition is turned on. A stop watch can be used to measure the duration of the light staying on. Shop manuals will tell how long each duration of activated injector time is required. The above test should be performed on an engine that is cooled off and prior to start up in order for the injector to work in the time established for proper performance.
Source....
http://www.corvetteactioncenter.com/forums/showthread.php?t=9073
_____________________________
Don''t know nuthin''; ain''t never got paid for wrenchin''...
[image]
http://www.stripers247.com/phpBB2/images/smilies/th_icon_stooges.gif[/image]
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RE: fuel pump relay - 10/12/2007 12:23:20 PM
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rshiver
Posts: 381
Joined: 8/4/2007
Status: offline
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quote:
So how much flooding could be caused by 8 seconds of unnecessary cold start injector fuel?
That's a good question cwb, maybe just enough to cause a rich start condition when the engine is warm, and cause the engine to have to turn over several times before it catches?
One things for sure, something is causing a rich, hard start condition when the engine is hot, after it sets for a little while.
< Message edited by rshiver -- 10/12/2007 4:11:34 PM >
_____________________________
"Giving up" is never an option.
..............(o o)
~~~o00o~(_)~o00o~~~
2000 Limited Edition Ford F-350 Lariat 4x4 Dually, 7.3 Liter Powerstroke Diesel
1985 L98 Corvette
1978 Chevy Camaro LT
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