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How do I isolate a prob in the fuel line? 900 1993

posted by  someone claiming to be Squire on  Tue Sep 14 10:59 CST 2004 [RELATED]

93 940 turbo

I have somewhat narrowed a problem down to either the fuel pump relay or the in-tank pump. I recently replaced the main pump and filter because it cut out a couple of times when tank got under 1/8. On a long drive it also stalled all together with over half a tank. I was able to start it 15 min later. Also, the cold start takes 3 or 4 cranks until the engine gets fuel. It was also whining louder than I thought it should. I replaced it, but still same problems and whining. I can here it pump just prior to starting, so I think the problem is in the other pump.

I have checked the faq page, but am still puzzled. There is mention of a fuel pump relay and a fuel injection relay (radio supression relay).Does the fuel pump relay control both pumps? If so, if its bad, wouldn't both pumps fail? What is the fuel injector relay's function?

I'm just looking for the best way to diagnose this. Some say listen for the pump running. Another said to pop the top of one of the relays and manually switch it on, but I'm confused as to which relay he's talking about.








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    How do I isolate a prob in the fuel line? 900 1993

    uid 6573's pic
    posted by  javalion on  Tue Sep 14 15:36 CST 2004
    Author: [PROFILE] [EVERY POST] [THREADS] [BEST POSTS] RSS Feed     [IGNORE ALL POSTS]
    last visit: Wed Jul 23 09:57 CST 2014
    [RELATED]

    The fuel injector relay or radio suppression relay is located just behind the battery on a na and I forgot where in the turbo. Same area though, forgot which side. (The turbo is at college.) It is black hangs on the fender side directly under a wire bundle. The only relay there. It will have among others and fatter red wire that comes directly from the battery

    The FP relay, behind the fuses, controls both fuel pumps via the same contacts. Because “BTDT”, if it was me, would have changed the FP relay first, than the crank sensor, and the FI relay third. Well if it happens to me again, all three at the same time for $67 plus shipping from FCPG, and not even think about anything else until it they were installed. Your symptions did not completely rule out any one of the three. I did attempt to re-solder a fuel pump relay once. The soldering job failed. Once the wire or pin starts to burn it forms a coating that solder can’t adhere to unless it is cleaned (mechanically) and fluxed.

    I did check the fuel pressure because of a similar situation in my Rex/Regina, but it has only one pump. The procedure in the FAQ also explains how to isolate the fuel pressure regulator while checking the fuel presure.

    I have read several times that a cold start problem is due to a failed check valve in the fuel line. I am not sure where it is at. One post said at the in-tank pump and another post said it is ahead of the fuel filter.

    Good luck
    --
    Tom F. Three 940s. The '93 T-Rex (Regina) is now running very well. Mods, RainX & cup holders. Lien holder on two more (the kid's). Rust In Pieces, '78 245








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      How do I isolate a prob in the fuel line? 900 1993

      posted by  norfleet on  Tue Sep 14 18:44 CST 2004
      Author: [PROFILE] [EVERY POST] [THREADS] [BEST POSTS] RSS Feed     [IGNORE ALL POSTS]
      last visit: Thu Dec 26 15:33 CST 2013
      [RELATED]

      the fuel pump/injector relays really do not control the pumps in the classical sense. The relays are mainly safety devices to shut off the fuel pumps in case of an accident. when you turn on the ignition switch, the pumps run for about 3 seconds to pressurize the system. they then shut off. When you crank the engine, the rpm sensor tells the relays that the engine is running and the relays turn on the fuel pumps. when the engine stops, the pumps stop.








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        How do I isolate a prob in the fuel line? 900 1993

        uid 6573's pic
        posted by  javalion on  Wed Sep 15 11:46 CST 2004
        Author: [PROFILE] [EVERY POST] [THREADS] [BEST POSTS] RSS Feed     [IGNORE ALL POSTS]
        last visit: Wed Jul 23 09:57 CST 2014
        [RELATED]

        So, if your telling me there isn't a wire branching directly off the battery going to fuse 11 then going directly to a single contact that feeds the both fuel pumps, in the classical sense, is not correct, and the failed solder joint won't cause the symptoms Squire is having you better response to him and not me. Weren't you looking for the fuel pump relay a few posts down?
        --
        Tom F. Three 940s. The '93 T-Rex (Regina) is now running very well. Mods, RainX & cup holders. Lien holder on two more (the kid's). Rust In Pieces, '78 245







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