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fuel pump priming ???

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Old 12-28-2014, 10:38 AM
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2dogsjohn
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Default fuel pump priming ???

hi this has probably been dealt with before somewhere but should i be able to hear the pump prime at ignition on the key ie before cranking ? i feel sure it should but there is nothing, pump runs fine otherwise so not sure if fuel pump relay is defective or does another relay control the priming? cars a 82 928S euro
car starts and runs ok but always takes a fair bit of cranking to start, cold start injector works fine . can anyone help
Old 12-28-2014, 01:36 PM
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Mrmerlin
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you car should have the pump come on when the key is turned on to run so maybe the relay or the fuse for the pump is bad,

For the fuel system ,, a few things need to be in excellent condition.
The fuel distributor,
the warm up regulator,
the fuel accumulator,
and the pump check valve.

Of these its easiest to replace the check valve and fuel accumulator first.
Old 12-28-2014, 05:19 PM
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2dogsjohn
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if the fuse was bad surely it wouldnt run at all , relay is a possible but i dont know how to test the priming connection. difficult say if the rest of the fuel system is good or bad all i know is car runs pretty good once running, just takes a while to start when cold, even then once started even if stopped imediately it will fire up in a 1/4 turn. as far as the fuel accumulator, i have never managed to find one ; looked in all the usual places
one final thing ,i found that the diverter valve diaphram is blown so big vac leak there,will that affect starting?
Old 12-28-2014, 06:48 PM
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Dave928S
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Originally Posted by 2dogsjohn
if the fuse was bad surely it wouldnt run at all , relay is a possible but i dont know how to test the priming connection. difficult say if the rest of the fuel system is good or bad all i know is car runs pretty good once running, just takes a while to start when cold, even then once started even if stopped imediately it will fire up in a 1/4 turn. as far as the fuel accumulator, i have never managed to find one ; looked in all the usual places
one final thing ,i found that the diverter valve diaphram is blown so big vac leak there,will that affect starting?
The fuse and holder, after all this time might be giving a resistive connection, so very through cleaning of the contacts and putting in a new fuse is a good idea, no matter what. It is also worth putting in a new relay to rule that out as the culprit, and making sure all connections, including earths, are clean and tight. Even if not the cause of the problem, you need to be certain of reliable power supply to the pump.

Any vac leak will affect cold staring more than hot as it will tend to lean the mix to a degree. Fix any vac leaks. You can just plug the vac line to the diverter valve to check if that is the cause, as it will only disable air injection to the exhaust.

Sorting electrical and vac leaks will be a good start. If it persists then I'd be looking at the check valve and accumulator, and doing pressure tests.
Old 12-29-2014, 02:14 AM
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Alan
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On an '82 the relay is the only thing that controls the ~ 2 sec priming pulse that occurs after the ignition first goes active. If you don't get that - just get a new fuel pump relay - don't look at anything else - nothing else is involved with this function. If everything else works quickly from a restart - you likely have no other issues.

This seems not to be an uncommon problem - the fuel relays seem to lose this priming function but otherwise function OK (with delayed start) by pumping only after the engine is rotating. Likely many cars do this and the owners don't even realize there is an issue.

Alan
Old 12-29-2014, 04:31 AM
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2dogsjohn
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ok thanks for the replies ; i will try and track down a new relay; does anyone know if my car even has an accumulator.
another point to mention is that i noticed that the plugs always look a bit on the lean side for my liking.would the vac leak cause this or is there another area i should be looking in ?
Old 12-29-2014, 10:02 AM
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the accumulator is in the forward area of the RR wheel well,
to find it remove the wheel then the front cover
Old 12-29-2014, 03:51 PM
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James Bailey
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you need to fix the air leaks then read up on C I S injection learn about system pressure and control pressures. Buy the two gauge pressure kit so you can actually see what is happening with both.
Old 12-29-2014, 09:11 PM
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Alan raises an important and, as he points out, probably often overlooked issue. The fuel pump relay on this '82 car is not the usual 53B as is the case on later cars, and has a transistor added to energise the coil for the priming time on switch on. Failure of that component reverts them to standard relay function with no initial prime pulse ... seen that exact scenario twice on '82's

Here's a link to the correct relay on 928Intl site .... http://shop.site-link.com/928intl/pr...928-615-113-01



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