1990 fuel pump problems
Thread Starter
2nd Gear
Joined: Feb 2014
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1990 fuel pump problems
I have a 1990 non ZR1 with no gas in fuel rails pump does not turn on power to the fuse when key turned on but stays on all the time when key is on is this correct I was under the under standing that it would only have power for 2 sec till engine oil pressure switch takes over?
Race Director
Joined: Apr 2002
Posts: 10,036
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From: Anaheim CA
The fuel pump is controlled by the ECM through the fuel pump relay. The ECM turns on the fuel pump for 2 seconds when the key is turned on to pressurize the fuel rails in preparation for starting. It shuts off after 2 seconds to prevent the fuel pump from running continuously if you turn on the ignition without starting the engine.
When the ECM sees DRPs (Distributor Reference Pulses) from the ignition module in the distributor it turns on the fuel pump. DRPs are produced whenever the engine is rotating, whether cranking or running.
The oil pressure switch is a backup in case the fuel pump relay fails. If everything else is OK it is not needed. Contrary to popular folklore, the oil pressure switch does NOT protect the engine in case the oil pressure drops to zero.
When the ECM sees DRPs (Distributor Reference Pulses) from the ignition module in the distributor it turns on the fuel pump. DRPs are produced whenever the engine is rotating, whether cranking or running.
The oil pressure switch is a backup in case the fuel pump relay fails. If everything else is OK it is not needed. Contrary to popular folklore, the oil pressure switch does NOT protect the engine in case the oil pressure drops to zero.
Thread Starter
2nd Gear
Joined: Feb 2014
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Ok so why do you think I have power to the fuel pump fuse all the time when the key is turned on but not turning over engine? I also seem to hear a relay click or the right side where the fpr is located after 2 sec when key is turned on but I still have power to the fpf and still no fp running should I check fp connection for power next and replace fp if power there ?
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
The fuel pump relay is located on the firewall between the brake booster and the distributor. The oil pressure switch is located on the rear of the block behind and below the distributor. Here's a diagram of the fuel pump circuit:
Burning Brakes
Joined: May 2011
Posts: 838
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From: Louisville Ky
Ok so why do you think I have power to the fuel pump fuse all the time when the key is turned on but not turning over engine? I also seem to hear a relay click or the right side where the fpr is located after 2 sec when key is turned on but I still have power to the fpf and still no fp running should I check fp connection for power next and replace fp if power there ?
do you have power with key off? if so, the pump may have failed from being on all the time. the relay may be defective, or the oil pressure switch may have failed closed, keeping the current on. your OPS may have a third wire, tan, that goes to oil gage.
with power to fuse, the pump will/should have power. I would check that with a meter or test light. if you have 12v, part of the problem is the pump or wiring. the real problem is that the relay is apparently on all the time. as Cliff said, it is only on for 2 secs, unless engine is cranking/running.
Last edited by joe paco; Feb 19, 2014 at 04:13 PM. Reason: wording
8th Gear
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1990 fuel pump relay
Racer
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From: Guilford NY
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