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502 mpi coil fuel pressure issue

Old 05-19-2018, 01:17 PM
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Default 502 mpi coil fuel pressure issue

Hi
I messure my fuel pressure one week ago and the pressure whas 55 psi at idle. I disconnect the vacum hose from the regulator and nothing happend. The pressure did not change if I rev up the engine. Still 55 psi. I then ordered a new original regulator from a local store and mount it today. I messured the pressure at idle to 35 psi. I disconect the vacum hose and the pressure jumped up to 43 psi. The pressure did not change if I rev up the engine to about 3000 rpm with the vacum hose connected. Stable at 35 psi. Does anyone have a solution to my problem. I thought the pressure should be 43 psi with the vacum hose connected.

From What I have read before, this engine should have 43 psi at idle. Is that correct?

Hope you guys can help me 😀

Dan/Norway

Last edited by danse78; 05-19-2018 at 01:22 PM.
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Old 05-19-2018, 02:57 PM
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Reving the motor is not the same as getting up on plane. The vacuum will not change much just reving. To prove it, put a Tee fitting on the line with the vacuum gauge, then rev and also take it for a run
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Old 05-21-2018, 10:01 AM
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I have always went by 38 psi. Merc manual #23 says 34-38 psi
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Old 05-21-2018, 09:58 PM
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Originally Posted by danse78 View Post
Hi
I messure my fuel pressure one week ago and the pressure whas 55 psi at idle. I disconnect the vacum hose from the regulator and nothing happend.
You don't have the regulator hooked to vaccum. Very common for the 502MPI hoses to fall off their connections even when close to knew. Also not uncommon to get a piece of crap stuck in vacuum nipple. If all is good, look for cuts in the hose.

The fuel psi will most definitely reduce when you hook to vacuum which there is a lot of at idle.
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