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Discussion Starter #1
Found some good info on the Internet and youtube on doing fuel pressure leak down tests (forums.nicoclub.com for Infiniti very good), but when I searched the CarDisc and the alfabb, couldn't fine the specific values, so wondering if anyone knows offhand what to look for on the Alfa 164 leak down test?
 

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The procedure is on page 04-22 of the shop manual (pg 216 of pdf file) Pressure should be 42-47 psi at at idle with open regulator and should drop about 7 psi when regulator hose is reconnected.
 

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Discussion Starter #3
Thanks kcabpilot.

I'm familiar with that part, but I was looking to see if there was a value for after it was turned off how long it should hold pressure, i.e. not leak down, checking for leaking fuel injectors or a bad fuel pump check valve.

Some car manuals apparently give a value for this.

I note that it says at the end of page 04-22, "and no leaks are detected, check filter and/or pump operation."
 

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Discussion Starter #4
Results of my fuel pressure testing (3 three runs, same results each time);

42 psi Fuel pressure regulator hose OFF at idle rpm
34 psi Fuel pressure regulator hose ON at idle rpm
32 psi Fuel pressure regulator hose ON at a steady 2,000 rpm
32 psi Fuel pressure regulator hose ON at a steady 3,000 rpm

On snap acceleration: went from 34 psi to 40 psi, and as I released the gas pedal dropped to 30 psi then rose back to 34 psi at steady idle

With fuel system pressure at 35 psi after shutdown, still had 35 psi 15 minutes after shutdown

System tightness check tested good when fuel return hose was choked with a pressure rise
 

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When I did mine I noticed it dropped a little bit after about half an hour, maybe that is due to the drop in temperature as everything cools down. I think if you had a leak it would just continue to fall or it would at least initially fall significantly and maybe taper off as it got lower.

I'd say your results indicate no problems.
 

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But Mad North-Northwest
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Sounds like perfectly normal behavior provided the 164 has a 42 psi spec for the regulator. Basically the regulator maintains a set PSI value between the fuel rail and the plenum. So if you've got 10 PSI of vacuum in the plenum the fuel pressure at that point should be 32 psi. With the hose to the plenum disconnected the fuel pressure should be steady at whatever the FPR spec is.
 

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Discussion Starter #7
Thanks Gubi, I was hoping someone, anyone would tell me I'm normal.

Alfa 164 specs call for "42 to 47 psi" with FPR hose OFF, and a drop of 7.3 psi when you connect the FPR to the plenum.

When I connect the FPR vacuum hose I get about an 8 psi drop, but that's on an Autozone loaner test kit.

BTW, I bought this Alfa from a guy who lived there in SF and had it shipped back to Dallas. He had it maintained at the Alfa Center near where he lived on Van Ness, and at the Alfa dealer he bought it from before that.
 

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But Mad North-Northwest
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Thanks Gubi, I was hoping someone, anyone would tell me I'm normal.
You own an Alfa. No hope there.

I'm surprised the Bosch spec range is that wide with the hose disconnected, but sounds like you don't have any issues.
 

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Discussion Starter #9
Thanks also kcab, and fly safe.

I didn't want to wait any longer than 15 minutes, it's not like a cylinder leak down test.

Most of the other auto websites talking about testing fuel pressure/the fuel pump/fuel pump check valve leaking made it seem like it would happen pretty quickly, maybe not fast, but you would certainly see somehting in 15-30 minutes.

The "Infiniti/nico" and "clarks-garage" wesbsites for the Infiniti and the 944 and some youtube vids I watched are what I'm referencing.
 

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Are you getting any puffs/whisps of smoke out the exhaust when you first start it cold after it has set for at least overnite? Reason I'm going down this path is...typical internet reply - I had a car that acted similar. All the testing was good. Came down to a leaky injector dribbling down over time causing all sortsa grief....we found it by a spark plug check. Weird I know but some times, weird and normal are synonymous. ciao, jc
 

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Discussion Starter #11
No puffs/whisps of smoke when it first starts cold, but I do sometimes think I smell fuel on first startup.

One sign of leaking injectors is supposed to be the fuel pressure going down after you turn the fuel pump off, but my fuel system held pressure for 15 minutes after shutdown before I quit.

That said, I'll check the plugs when I retorque the heads in about 200 more miles (although with no oil or coolant leaks now, I'm debating doing this).

Five of my injectors are original, 24 years old, and one is rebuild, so I may have thme cleaned and flow checked also.

I'll update.
 

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Try using Techron for several tank fillings. Stuff works to clean that stuff, but takes a few fillings.
 

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I would think that is a given.

I know that when I started getting chocolate mousse on the inside of the filler cap of the 91S at 100k miles, I retorqued the heads and found that the rear had relaxed to about 55 ft-lb instead of the shop manual stated value, the front relaxed at about 65.

Been ~70k miles since, and no problems yet.

I think that it is essential to retorque the heads at every 50k-70k miles, at least with the 12V engine.
 
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