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Thread: Hot start issues - do these details sound like my accumulator is bad?

  1. #1
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    Hot start issues - do these details sound like my accumulator is bad?

    I've been having hot start issues this summer, and I think it's the accumulator, but would like to know if there is a better fault isolation process. I don't have the funds to replace parts unnecessarily.

    When I go to start the car, it turns over and fires up instantly, and dies just as fast (making me think that was the fuel the CSV injected into the intake manifold, and the lines to the injectors are still empty from vapor lock created the previous time it had been operated). Further attempts to start take significant cranking, and when it does fire up it runs rough for a few (4-5) seconds, then perfectly fine after that.

    I let it get up to temperature yesterday in the garage (shaded, but almost 100* (Las Vegas) outside) and turned it off.
    If I restart immediately it fires right up no problem.
    If I let it sit 2 minutes it fires right up no problem.
    If I let it sit 5 minutes it fires up on the second turn (key to start, ruh-ruh-rrmmmmmmmm) no problem
    If I let it sit 10 minutes it fires up on the third turn (key to start, ruh-ruh-ruh-rmmmmmmmm). Not a super long start, but noticeably abnormal.
    If I let it sit 25 minutes it take significant cranking until it starts. To the point that I let off the key to avoid burning out the starter. It does eventually start, run rough for a few seconds, then runs perfectly.

    I tapped the air plate to measure resistance before each start attempt. It was very firm for the starts up to 5 minutes, and slightly less firm prior to the 10 and 25 minute starts.

    It has the factory relays, and I 100% plan on replacing them with Bitsyncmasters as an upgrade, but fixing it mechanically is the first priority. As soon as funds are available the relays will get swapped as an upgrade/preventative maintenance.

    Is my accumulator bad?
    Any way to isolate that part as the fault?
    Any other tests to run?

    I did read this on DMC's support page:
    The most conclusive test of the accumulator is to disconnect the hose from the end of the accumulator that faces the rear of the car. Plug the hose. Connect a second section of 1/4" hose to the nipple on the accumulator and direct it into a suitable container. Start the engine. After an initial spurt of fuel, no fuel should flow from the accumulator. If it does, the internal diaphragm has failed.
    But when is it saying to do that? When it is cold and will not start (because the lines are empty from the last shutdown)? Hot and won't start? Hot and will start, immediately after shutting down?

    Assuming it is the accumulator, I've read a lot about replacing it. Everyone says it's a giant pain, but it looks pretty straighforward to me... just disconnect the hard line while restraining the union, remove the bracket, and disconnect the two hoses. Is it made difficult solely by the tight access/doing it blind?
    Last edited by jackb; 09-10-2018 at 09:58 PM.
    5 speed, grooved hood, grey interior (Nov '81)
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  2. #2
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    Before you go too far down that road, try the same test but with the CSV unplugged.

  3. #3
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    That accumulator test doesn't matter whether your engine is hot or cold. The point of the test is to see if any fuel is coming out of that hose. It will only come out of that hose if the diaphragm has failed. It will tell you the same thing regardless of whether you do it with a cold engine or a hot one. The reason a failed accumulator gets identified with a hot engine is because of what happens when you lose the ability to hold pressure from a failed diaphragm. The car will run fine when it is on, but when you turn it off, the leaking pressure (back to the tank through that hose mentioned) takes the pressure away from the lines on top of the engine. Once that pressure is gone on top of a hot engine, it leads to the fuel getting vaporized and you get a "vapor lock" where the normal fuel supply can't overcome it to get the engine started. Once the engine cools down enough to enable the cold start valve (CSV) to squirt in some additional fuel directly, it will chug chug and eventually start. That's why that CSV plug swap idea will sometimes work on a failed accumulator hot start problem car.

    All that being said, yours doesn't really sound like a hot start problem if you can get it to start eventually. It might be, but I'm more inclined to say it might be getting flooded by a leaky injector or two. Or something else. Could be the CSV is leaking. Or maybe it is just a failed accumulator.

    I would try and do that accumulator test with the extra hose and bucket and see what you get. Accumulator replacement is only a pain because of the poor access. Actually, not poor access. Terrible access. Like trying to work on something the size of a pop can through an opening the size of a DVD case. Oh, and from directly underneath, which, if you don't have a lift, means you're under the car while it's on ramps, trying to get the leverage you need to loosen 37 year old rusty fittings using your Tyrannosaurus like arms that you can't fully extend and if you're lucky and don't damage a hard line from your awkward twisting, you get a face full of fuel for your taste of victory.

    You mentioned not having a ton of extra budget for willy-nilly replacing parts. If you are going to get under there and do that hose/bucket test, I would plan on just replacing the accumulator while you're at it (i.e. getting a new accumulator in advance). If the one on your car is the original, it's more than likely the culprit anyway.


    Sept. 81, auto, black interior

  4. #4
    Senior Member Bitsyncmaster's Avatar
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    Quote Originally Posted by dmcnc View Post
    Before you go too far down that road, try the same test but with the CSV unplugged.
    +1
    I've found my car starts faster in the summer when the CSV is not firing (if car has not sat for many days). I do need the CSV if the car sits for a week or longer to get it started.

    But the first thing to check is the mixture via looking at the dwell reading on a warmed up engine. Mixture adjustment is everything to getting the engine to start instantly when cold or hot.
    Dave M vin 03572
    http://dm-eng.weebly.com/

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    You should get a test fuel pressure gauge suitable for a K-jet system - available for less than $100. You can then test 'rest' pressure by momentarily energizing the fuel pump until you see the nominal 5-bar pressure, and then watching the pressure as it declines over a period of time. If the system holds rest pressure, then the hot start issue is NOT due to the accumulator.
    Robert
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  6. #6
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    Quote Originally Posted by DMC1890 View Post
    You should get a test fuel pressure gauge suitable for a K-jet system - available for less than $100. You can then test 'rest' pressure by momentarily energizing the fuel pump until you see the nominal 5-bar pressure, and then watching the pressure as it declines over a period of time. If the system holds rest pressure, then the hot start issue is NOT due to the accumulator.
    What type of guage do you recommend .Only type I own and familiar with is the one where the nipple is on the fuel rail

  7. #7
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    Quote Originally Posted by Dontilgon View Post
    What type of guage do you recommend .Only type I own and familiar with is the one where the nipple is on the fuel rail
    John Hervey (Delorean Auto Parts) sells a 'CIS Fuel Pressure Test Kit' for $99. You can find these on eBay or Amazon as well. You temporarily install it in place of the hose from the warm-up (or control pressure) regulator to the fuel distributor. It has a valve, when closed (engine off), lets you see the full primary fuel pressure, which is good to know. When open, you can see the 'control pressure'. A very useful tool that any DeLorean owner should have.
    Robert
    1981 DeLorean #1890
    1976 Datsun 280Z
    1968 Pontiac Le Mans convertible

  8. #8
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    ^+1^

    Quote Originally Posted by jackb View Post
    If I let it sit 25 minutes it take significant cranking until it starts. To the point that I let off the key to avoid burning out the starter. It does eventually start, run rough for a few seconds, then runs perfectly.
    To help narrow it down meanwhile since the plate is fairly firm, you might try:
    When it gets to this point, first double check the pressure plate. If it is firm, press it to the bottom and release it, VERY quickly, then try it. This will make all of the injectors open. If it's a classic Hot Start problem ("vapor locked"), this will purge the system, some. If it was flooding (leaky injector, CSV..., etc.), it will be probably be worse. If it was starving for fuel (WUR/CPR/ETC, vapor locked) is should start better.

    I like the idea of unpluging the CSV too....

  9. #9
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    Ok, solid avice from everybody, thank you. Here is an update:

    Last night I got the car started (difficult, same vapor lock symptoms as usual) let it run for a few seconds, and shut it off. I did not let it get warmed up, so the fuel in the lines were not exposed to the heat to vapor lock.

    This afternoon it started right up. Then I let it get nice and warm, up to temperature/fans cycling, and shut it off.
    Came back a few hours later and no start.
    I unplugged the CSV and no start.
    I pushed down and let go of the air plate once, no start.
    I pushed the air plate down twice more rapidly in succession and the motor started.

    So, it is not a leaky injector, and the CSV made no difference.

    I canít get a $100 tester for the fuel pressure. Iíd love to get one, and I will someday, but itís just not happening right now.

    I will try disconnecting the hose at the accumulator tomorrow to check that.

  10. #10
    absotively posilutely bytes311's Avatar
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    See if the plug swap gets you started (disconnect the WUR connector and connect it to the CSV connector) and crank the motor. If that gets you started you have a fuel pressure problem. Make sure you quickly put the plugs back or you'll flood the motor.

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