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Fuel Injection Relay incompatibility? Or is this something else? 700 1990

posted by  twtech on  Sat Aug 8 03:43 CST 2009
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last visit: Sun Sep 30 18:08 CST 2012
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1990 740GL with Regina system. 175,000 miles. History of problem, Intermittent Hot start issue, lived with it for a couple years because it was so infrequent. Now no start at all, purchased a Fuel Injection Relay, which I thought would fix the issue. It did not.
So for further testing, I swapped Radio Suppression Relay with the Aux Fan relay, made no difference. Jumpered Large wires on Radio Suppression leads. No difference. During these tests, Fuel pump does not run momentarily, so I thought fuel pump. Here's what I did next, and also where it gets illogical (at least in my mind).
I took the cover off the old FIR, turned the key to position 2. No relay activity. I put the New Relay in, turned key on, immediately the electromagnet on the relay closed the front contact, however no fuel pump noise. However, if I manually close the second switch in the relay, the fuel pump runs, the car will start and run as long as I keep the switch closed.

So, I am wondering why no fuel pump noise briefly, even though first contact is closing. So, switched back to the original FIR, front contact or rear contact not closing on the relay. So, I manually closed the front contact, fuel pump runs briefly, car starts... As long as I keep the front contact closed.

So, after this long winded statement, Did I get an incompatible relay? The relay I purchased from Autozone, and it's black where as the original is white? I really love my volvo, but I've had this problem and want to keep it if I can get it fixed. Please, anyone? Both relays look completely identical other than the cover is black on the new relay, the old is white, and they behave differently.

One other question, will it hurt to manually keep the front contact on the old relay closed, so I can drive the car in the interim while I try to fix it and/or get a new, compatible FIR? It seems like that's the problem as it behaves and run normally as long as I keep the first (front contact) closed on the old FIR.

Thanks, I will be contributing due to the great help I've received so far from this great resource!







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    Fuel Injection Relay incompatibility? Or is this something else? 700 1990

    uid 27's pic
    posted by  Art Benstein on  Sat Aug 8 03:58 CST 2009
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    last visit: Fri Oct 17 20:10 CST 2014
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    Hi there,

    I followed your other thread Fuel Pump's not running even with tests where lucid was helping you narrow this down, and knowing Bruce may not be responding immediately, figured I'd take up the train of thought.

    It is true the Regina ECU does not have the same syndrome for which the early LH2.4 Bosch ECUs are notorious - not grounding the fuel pump relay coil. But your last tests pointed toward that - with the latest relay replacement. In theory, the Regina ECU could be damaged, by a slip of the probe, and it might be damaged in the same way the "pink label" Bosch ECUs do entirely on their own, but your latest test tells me this is not the case for you.

    Your latest experience has me agreeing with your incompatibility theory. Or at the very least - you have an out-of-box failure with that Autozone relay. Now you have two FI relays with two different failure modes!

    When you hold in the system relay clapper - that's the one that comes on and stays on with the ignition in your first relay - that gets power to the whole fuel injection system. The second clapper, that does not pull in on one relay, but does on the other one with the first clapper held, runs the fuel pump.

    Bottom line - I think you'll have success by getting a third, correct FI relay. Before you go to that extent, just verify the under-hood Radio Suppression relay you currently have in place is OK, then button that up and put it behind you - just for the sake of narrowing your focus.


    --
    Art Benstein near Baltimore

    Did Noah keep his bees in archives?








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      Fuel Injection Relay incompatibility? Or is this something else? 700 1990

      posted by  twtech on  Sat Aug 8 04:16 CST 2009
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      last visit: Sun Sep 30 18:08 CST 2012
      [RELATED]

      Thanks Art, Bruce has been a great help too, I'm glad you responded.

      I did check the Radio Suppression relay by swapping back and forth with Aux cooling Fan Relay, (they're identical other than one was made in Belgium, the other in Germany), and I also grounded the two large wires to bypass at Bruces Suggestions thinking maybe.. I've got two bad Radio Suppression relays!. It didn't make any difference in the behavior between the two FIR's.

      I'll be returning the relay back to Autozone and getting new one. It's going to take them a while to get the part. In the meantime, I need a car for occaisonal use (less than 25 miles twice a week or so). Can I put a rubber band around that front contact on the old relay to keep it closed in the meantime, till the part arrives so I can drive it? Your thoughts?







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        Fuel Injection Relay incompatibility? Or is this something else? 700 1990

        uid 27's pic
        posted by  Art Benstein on  Sat Aug 8 04:31 CST 2009
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        last visit: Fri Oct 17 20:10 CST 2014
        [RELATED]

        I only mentioned the Radio Suppression relay so you could get the jumper out and button it all back up and take it out of the suspect list. I think you already confirmed it (or even both - between fan and RS relays) is working.

        Using a short piece of vacuum hose, as Bruce does, looks to be a pretty stable way to hold the clapper in for testing. We're clear about it being the system side and not the fuel pump side you want to lock down, as the fuel pump side is a safety issue. The fuel pump side is the one that pulls in just momentarily at key on, then pulls in again while cranking, to run the pump. If you cheat the system relay, be sure to pull the unit when you park it, or your battery might be drained.

        Do any of your relays look like these? I'm a 240 guy.


        --
        Art Benstein near Baltimore

        I fired my masseuse today. She just rubbed me the wrong way.








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          Fuel Injection Relay incompatibility? Or is this something else? 700 1990

          uid 55's pic
          posted by  john sargent on  Sat Aug 8 17:56 CST 2009
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          last visit: Wed Oct 22 09:07 CST 2014
          [RELATED]

          I've found the Hungarian made relays to be the best quality, but they can also have bad solder joints.
          --
          john







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