85 Hard Start When Warm

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Mar 18, 2002 | 12:56 PM

OnDVirg

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From: San Francisco, CA, USA

85 Hard Start When Warm

I have a stock 85 that doesn't start well when warm. When I hook the fuel pressure gauge up and turn on the key, there isn't any pressure till I actually start cranking the motor. Then it takes awhile for pressure to build and at about 20-25 lbs the motor kicks over. It gets worse and worse depending on how warm the engine is.

Is this a problem related to the fuel pump? The car seems to run fine after this initial starting problem.

Mar 18, 2002 | 01:04 PM

JonM

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Re: 85 Hard Start When Warm (OnDVirg)

When was the last time you changed the fuel filter?

Mar 18, 2002 | 02:35 PM

OnDVirg

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Re: 85 Hard Start When Warm (JonM)

I changed the fuel filter about 3 months ago. I was really hoping that was the problem, but it didn't changed the situation at all.

Mar 18, 2002 | 02:40 PM

Bluevette85

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Re: 85 Hard Start When Warm (OnDVirg)

When you turn the key to the 'on' position without starting it, you should hear the fuel pump working and you should have pressure at the rail. If this doesn't happen, check the fuel pump relay I think it's located on the firewall by the brake booster but I'm not 100% sure. Try removing and cleaning the fuel pump electrical contacts at the tank. Remove the rubber gasket around the fuel filler neck and you will see it.

Mar 18, 2002 | 03:01 PM

CFI-EFI

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Re: 85 Hard Start When Warm (OnDVirg)

If a clogged filter isn't the cause of a slow pressure rise, as JonM suggests, I have two concerns. First, isn't that pressure pretty low for an '85? I would check the pressure with the new filter. Second you might want to look at the ECM. When you turn on the ignition, the ECM should energize the fuel pump relay for about 2 seconds, "priming" the fuel system. Without the "prime" sequence, you have to crank the engine long enough to build 4-6 lbs of oil pressure to close the primary circuit in the fuel pump relay to activate the pump. Hence, the cause of prolonged cranking to start the engine. The hotter the engine (and oil) the longer it takes to build sufficent oil pressure to close the relay. If, without a restricted fuel filter, you don't get pressure when you turn on the key, you have an ECM problem. If the pressure is low when you have pressure, it is either a faulty regulator, or a weak pump. Good luck.

Mar 18, 2002 | 06:06 PM

OnDVirg

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Re: 85 Hard Start When Warm (CFI-EFI)

Actually, that's about where the pressure is when the engine will start. Once started it goes up to I think between 30-35lbs.

Mar 18, 2002 | 07:08 PM

CFI-EFI

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Re: 85 Hard Start When Warm (OnDVirg)

That is about all the oil pressure you can get at cranking speed. With hotter thinner oil, it isn't as easy to get. That is why it is harder to start when it's hot. I zapped the "prime" circuit in my ECM, so I know exactly what you're going through. Wait until the weather warms up!