Hard start on 85 Vette
Thread Starter
Heel & Toe
Joined: Jan 2003
Posts: 15
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From: Murfreesboro Tn
Hard start on 85 Vette
My fuel pump does not come on when I turn the ignition on. The motor has to crank a certain amount of time before the it starts. When I turn the key on I get no fuel pressure, but when I put a hot wire from the battery to the diagnostic center under the dash, the fuel pump comes on and the car starts instantly. I only use the hot wire to start the car, then I disconnect it. The car will run fine. The fuel pump fuse has no voltage when the ignition is on but has power when the car is running. When the car is running the fuel pressure is a constant 39 pounds. I have replaced the fuel pump, fuel pump relay, mass air flow sensor, and the computer. It seems to be a ground issue but I am not sure. If someone can steer me into a starting point I would appreciate it. Thanks in advance, I read this forum often and have learned alot from various people who post.
Le Mans Master
Joined: Jun 2003
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From: Ignore this post
St. Jude Donor '03
Re: Hard start on 85 Vette (sgtbrum)
Acording to my 85 manual the power to the fuel pump is switched on by the ECM computer during startup, until the oil preasure switch reaches pressure and sends power to the pump
Pro
Joined: Jul 2002
Posts: 729
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From: Yukon OK
Re: Hard start on 85 Vette (sgtbrum)
On my 85 the fuel pump is engergized by the ECM for about 2 sec every time the ignition key applies power to the system. You might have an ECM problem or bad connection to the ECM. Try unplugging the two connectors and re-seat them.
[Modified by LaVidaLoca, 10:18 PM 7/13/2003]
[Modified by LaVidaLoca, 10:18 PM 7/13/2003]
Thread Starter
Heel & Toe
Joined: Jan 2003
Posts: 15
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From: Murfreesboro Tn
Re: Hard start on 85 Vette (sgtbrum)
Thanks for the help. I will try to reseat the connectors and see if that does it. I have changed the ECM out with a new one but used the old CALPAK. Could this be my problem? I'll check into it a little further tommorrow night and let everyone know what I find. Thanks again for everyone's help
Pro
Joined: Jul 2002
Posts: 729
Likes: 4
From: Yukon OK
Re: Hard start on 85 Vette (sgtbrum)
When back and looked over the wiring diagrams. The fuel pump relay could be a problem. After the engine is running it is no longer needed because power comes from the oil pressure switch. (no oil pressure = cut the fuel). So the relay is just used to get the engine going.
Hope this helps. :cheers:
Hope this helps. :cheers:
- 1986 Original Owner -
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Re: Hard start on 85 Vette (LaVidaLoca)
When back and looked over the wiring diagrams. The fuel pump relay could be a problem. After the engine is running it is no longer needed because power comes from the oil pressure switch. (no oil pressure = cut the fuel). So the relay is just used to get the engine going.
sgtbrum,
Are you sure when you replaced the Fuel Pump Relay, you got the right one?
[Modified by Ray Quayle, 6:46 PM 7/14/2003]
Thread Starter
Heel & Toe
Joined: Jan 2003
Posts: 15
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From: Murfreesboro Tn
Re: Hard start on 85 Vette (Ray Quayle)
I am sure I got the right one but will double check to make sure. I kept the old one so I may put that one back in and see what it does. I replaced so many things on the car I could have over looked something. Thanks for you help.
- 1986 Original Owner -
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Re: Hard start on 85 Vette (sgtbrum)
This is the one you changed,
just inboard for the brake booster, right? Should be two red wires, an orange, a black/white, and a green/white. I hope this is right for '85.
If so, pull the relay and use a meter to check for 12v between pin C where the green/white goes to pin B where the black/white goes. Watch the meter when you switch the ignition from OFF to ON. You're looking for 12v for about 2 seconds or any time the engine is turning (running or cranking). If no good, Ohm out pin B to battery ground. You're looking for very low resistance.
Let us know.
just inboard for the brake booster, right? Should be two red wires, an orange, a black/white, and a green/white. I hope this is right for '85.
If so, pull the relay and use a meter to check for 12v between pin C where the green/white goes to pin B where the black/white goes. Watch the meter when you switch the ignition from OFF to ON. You're looking for 12v for about 2 seconds or any time the engine is turning (running or cranking). If no good, Ohm out pin B to battery ground. You're looking for very low resistance.
Let us know.
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Thread Starter
Heel & Toe
Joined: Jan 2003
Posts: 15
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From: Murfreesboro Tn
Re: Hard start on 85 Vette (Ray Quayle)
Thanks Ray for the pic, I will check it out as soon as I get home from work. The overdrive is not working also, I may have a relay out on it also. Thanks.
Drifting
Joined: Mar 2003
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From: Charlestown IN
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Re: Hard start on 85 Vette (sgtbrum)
Wait a minute folks, don't these things have a "cold start valve"? Found this in my manual: When the key is first turned "on", the ECM will turn on the fuel pump relay, for two seconds, and the fuel system should build up pressure. The ECM then checks the coolant temperature sensor, throttle position sensor, and determines the proper air/fuel ratio for starting.
The ECM contols the amount of fuel delivered in the STARTING mode by changing how long the injectors are turned on and off. This is done by "pulsing" the injectors for short times.
The cold start valve, not controlled by the ECM, is used to provide additional fuel during the starting mode to improve cold start-ups. This circuit is important when engine coolant temperature is very low because the other eight injectors would not be pulsed "ON" long enough to provide the needed amount of fuel to start.
The circuit is activated only in the crank mode. The power is supplied directly from the starter solenoid and is protected by the crank fuse. The system is controlled by a Thermal Time switch which provides a ground path for the valve during cranking whenever engine coolant is below 35 degrees C (95 degrees F). Does this help?
The ECM contols the amount of fuel delivered in the STARTING mode by changing how long the injectors are turned on and off. This is done by "pulsing" the injectors for short times.
The cold start valve, not controlled by the ECM, is used to provide additional fuel during the starting mode to improve cold start-ups. This circuit is important when engine coolant temperature is very low because the other eight injectors would not be pulsed "ON" long enough to provide the needed amount of fuel to start.
The circuit is activated only in the crank mode. The power is supplied directly from the starter solenoid and is protected by the crank fuse. The system is controlled by a Thermal Time switch which provides a ground path for the valve during cranking whenever engine coolant is below 35 degrees C (95 degrees F). Does this help?
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Re: Hard start on 85 Vette (ductape)
Getting too much fuel is always a possibility on hard warm starts. We keyed on the fuel pump prime as the questioner said this is something he doesn't get. No fuel pump noise and no fuel rail pressure. He only gets fuel line pressure when the engine cranks enough to reach 4psi of oil pressure. If it were the CSI in his case, it would be magically supplying too much fuel on warm start, because he has no fuel rail pressure. Start with what you know. Once this is corrected, if there is still a hard warm start problem, then we can move on.
Good thought though and I'm sure the Thermo-Time Switch has caused many problems like this before.
Good thought though and I'm sure the Thermo-Time Switch has caused many problems like this before.
