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Topic: 85 hard start when engine hot

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85 hard start when engine hot (1/2)
 8/26/18 2:09pm
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Cambridge, MD - USA

1985 Red Coupe

Joined: 8/26/2018
Posts: 1

turns over long cranck time
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Re: 85 hard start when engine hot (2/2)
 9/3/18 12:57am
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Fresno, CA - USA

1990 C4 coupe, Bright Red, L98, auto (stock)

Joined: 6/12/2017
Posts: 4

On a lot of fuel injected engines like in the C4s this is usually caused by a bad fuel injector. An injector is leaking and not sealing off correctly when is it not energized. Usually the engine will run OK once it is started, but it is hard to start only when hot. They start just fine when they are cold. When the engine is shut off and hot the fuel pressure will leak through one injector and deposit this excess fuel in the intake manifold. This will cause a long crank time to clear the fuel and allow the engine to start. However if the engine is cold this excess fuel has dissipated or evaporated and the engine does not have to crank to clear the fuel, therefore allowing for immediate and normal startup. To test for this bad injector condition, put a fuel pressure gauge on the fuel injector pressure rail and read the pressure while the engine is idling. (There should be a pressure test port on the rear end of the right fuel rail near the back of the engine). Then shut off the engine and watch the gauge. If it drops at all, there is a leaking injector. In a healthy engine the gauge should maintain it's same pressure reading for hours. If the reading slowly drops off, then this indicates a leaky injector. Also if it drops off, the real work of pulling and replacing injectors now starts, and this is not easy. Each individual injector then needs to be pulled and pressure tested to find the leaker (note: there may be more that one leaking). A good repair shop usually has special testers for this purpose, however you can make you own with some fittings, a gauge, and a compressed air source. If any leakage is found on an injector it must be replaced. In general the injectors on a 85 L98 engine are not hard to reach "once the upper manifold runners and plenum is removed". Good luck !

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