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While at idle fuel pressure reads 42 psi

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After engine off for 60 seconds pressure drops to 21 psi and stops there.




How long should it hold pressure?

Engine runs and starts right up.

Anthony,

My understanding of all modern injection systems is they are designed to maintain pressure all the time. Not sure if 21psi is correct but others may know here. I like your FP gauge can I ask where you bought it? Jeff

I think the M30B35 wants 3 bar (43.5 psi), so you are pretty close. Standard E12 M30's wanted 2.5 bar (36 psi). I imagine that some of that is maintained by the fuel pump, as the pump is not really a sealing valve.

What is your concern?

The fuel gauge is an Auto meter that I purchased online but can't remember the site.

About a month ago I replaced my fuel pump because it was starting to work intermittently . However, I did not replace it with a new pump, but one that I had around. I must have gotten it a pick n pull thinking it may come in handy, and it did. This replacement is loosing pressure in minute what took the original a couple of hours.

I was thinking of getting a new pump but wanted to be clear if I was replacing a pump be cause it was a proplem or just didn't trust it. Other than the gauge I would have no other reason to be suspect.

I have been experiencing poor engine performance so much my mpg dipped below 20mpg for the first time. So I add techron and noticed an improvement.

But the surprise is it is now holding fuel pressure for an hour and a half. That is a bigg increase from compared to not holding pressure for one minute.

So I believe injectors can be a cause of lack in fuel pressure holding.

anthony wrote:I have been experiencing poor engine performance so much my mpg dipped below 20mpg for the first time. So I add techron and noticed an improvement.

But the surprise is it is now holding fuel pressure for an hour and a half. That is a bigg increase from compared to not holding pressure for one minute.

So I believe injectors can be a cause of lack in fuel pressure holding.

A shot in the dark here but is it possible that you have a leaking cold start injector? This could explain the pressure drop and the drop in fuel economy.

OcCoupe wrote:

anthony wrote:I have been experiencing poor engine performance so much my mpg dipped below 20mpg for the first time. So I add techron and noticed an improvement.

But the surprise is it is now holding fuel pressure for an hour and a half. That is a bigg increase from compared to not holding pressure for one minute.

So I believe injectors can be a cause of lack in fuel pressure holding.

A shot in the dark here but is it possible that you have a leaking cold start injector? This could explain the pressure drop and the drop in fuel economy.

I don't think motronic 1.3 uses the cold start valve.

anthony wrote:I have been experiencing poor engine performance so much my mpg dipped below 20mpg for the first time. So I add techron and noticed an improvement.

But the surprise is it is now holding fuel pressure for an hour and a half. That is a bigg increase from compared to not holding pressure for one minute.

So I believe injectors can be a cause of lack in fuel pressure holding.

Injectors could be the cause. On my E28, the ones in it when I got it had terrible leak down, more than about 15 minutes of sitting and it would be hard to start due to being flooded. Overnight was actually a little better, kind of like an extra duty cold start valve. I went thru about 3 sets before getting ones that didn't leak. I think my driving pattern at the time contributed to it, but hey, it was how and where I needed to go.

Blaise wrote:I don't think motronic 1.3 uses the cold start valve.

Sorry, I didn't read your sig, I assumed you were running stock.

Mike W. wrote: I went thru about 3 sets before getting ones that didn't leak. :

Were any of the bummers sourced from AutoHausArizona ?
I have some still packaged......

alotawatts wrote:

Mike W. wrote: I went thru about 3 sets before getting ones that didn't leak. :

Were any of the bummers sourced from AutoHausArizona ?
I have some still packaged......

Nope, all were used. And all were better when I installed them, but started leaking before long. Until the last set which were -714 instead of -203. I don't know if the later ones were better or if I just got a good set.