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Discussion Starter #1
Slowly getting my Milano back into drivable shape.

I've put about 100 miles on it since this start of the summer. Recently, on a drive, I lost power off idle. History in thread fuel pressure issue?

Things were going well. I parked for about 10 days to pull the driveshaft, replace Giubos, and do some exhaust work (install 3.0 headers, new exhaust sections from Centerline). While it was up, I replaced the fuel filter (first since tank flush, planned work). There was a good amount of crud in the inlet, which was not entirely unanticipated. I had planned on a sacrificial set of filters for the first tank of gas.

I just finished up buttoning everything back up. The car fires up as always when cold (half crank). Little harder when hot (as always). However, it's really struggling to get off idle again, even without load. These symptoms were fuel pressure related the last time they surfaced, so it seems reasonable to assume that might be the case again.

Maybe the pump had enough crud pass through it to diminish performance enough to cause these issues? I inspected the lines prior to the pump today and the fuel coming out is clean.


It's hard to see in the video, but timing is factory at +7 ("F" mark on pulley).

Any ideas? Think there is anything there with the pump theory?

Thanks in advance. I'm only this far because of all of you!
 

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Discussion Starter #2
This morning, I went out to take another look. It's doing the old "start and immediately stop" now. Fuel pressure gauge shows 0 and doesn't rise when cranking, so there is definitely something going on with the fuel delivery system.

Checked the battery - 12.6 volts.

Put the multimeter on the pump and checked voltage when cranking. Got a zero reading, which I though just couldn't be right.

Then I pulled the pump completely and attached the multimeter directly to the power leads supplying the pump. It's measuring less than 1 volt currently!!! (video below)


Alright. So I at least have a fuel pump voltage problem. Is this something that could fail in the double relay?
 

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Does your fuel pump physically work? If yes, then have a look at the info in this post.
 

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Discussion Starter #4
It did yesterday. I also have a new one I had planned to put on sometime later, so I can definitely have a known good.

I did have a blown +30 service fuse that I just found (fuse 20). Fuel pump fuse was good.

Sounds like that could cause these issues.

Thanks for the input. I’ll have a read through that thread!
 

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On the right hand side in the dashboard there is a plug that connects the relays on the firewall to the fuel pump wiring.
This is a pink/white wire.

Those plugs tend to burn out, since quite a lot of amps are asked by the pump and it has to travel though a 2mm2 wire with 30 years of resistance in the connectors.

A very quick diagnosis is to run a wire outboard directly from the battery to the fuel pump and see if that allows the car to idle properly.
 

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I was losing about 3v to pump as connectors onto pump badly corroded. If they look bad, cut them off, strip wire till its good and stick new ones on.
 

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Discussion Starter #7
After replacing the engine service fuse, I have voltage at the pump again. 11.7-11.9 on crank, which seems ok. Pump connectors were new last year and are still shiny.

I'm going to put on the new pump tomorrow and see what pressure is at.

Thanks for the help so far!
 

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Discussion Starter #8
Alright, lots of updates.

Firstly, I've installed new Bosch pump, terminal connectors, and pump boots.

Secondly, that didn't seem to change anything.

Conditions as of today:

Car starts immediately when cold, and starts fine after a few cranks when hot.
Car preforms as intended when "cold" (about up to 150 on the gauge).
After 150, idle drops significantly and the lean condition described in the original post occurs.

Things tried today:

TEST: Unplugging the O2 sensor while running poorly.
RESULT: No change at idle. I am able to VERY SLOWLY crack the throttle and the revs will climb up to a certain point, then power loss. I can't tell how much a difference this is making, but it seems to be a change.

TEST: Removing gas cap when running poorly.
RESULT: No change at idle or on throttle.

TEST: Removing fuel regulator vacuum line while running poorly.
RESULT: Still runs poorly, but in a different way. Probably an over-rich condition.

I did notice something while I was out there today, though. After initially fixing the fuel system, I was getting ~26 PSI at idle and around ~38 on throttle. That seem to be down across the board. Maybe 20 at idle now and 35-36 on throttle. The symptoms still seem fuel pressure related to me. The question is WHY is there reduced fuel pressure?

  • new pump (factory)
  • new fuel filter (cheap)
  • fresh high-flow fuel filter before pump (aftermarket, installed several years ago)
I have been given advice that the system might not like that pre-pump filter, which sounds plausible. However, I've put over 100 miles on the car with that in place and it running without issue, so it's hard for me to believe it CAN'T run properly with that in place.

Ugh. Frustrating. I suppose the next step is to put a pressure gauge at various points in the system and see if I can find where the drop is coming from.
 

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Check your coolant temp sensor. It is very important for telling the computer how much fuel engine should get and at what temperature. If it's old just replace they are cheap.
 

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Discussion Starter #10
Check your coolant temp sensor. It is very important for telling the computer how much fuel engine should get and at what temperature. If it's old just replace they are cheap.
Thanks for the suggestion. I have an extra. Both measured good with a multimeter (tested under various temp conditions). Easy enough to swap the other one in and see if there is any difference. I'll do that tomorrow and report back.
 

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My fuel return lime was blockes, resulted in OK idle but bad driving. Also looked over rich as the fuel pressure was too high
 

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Discussion Starter #12
After thinking about this for hours last night and reading through other threads, another possibility has unfolded.

I've had issues similar to this in the past. Years ago, the ultimately issue was poor fuel flow caused by a blocked fuel strainer in the tank. I think that's a possibility again (unfortunately). Open to opinions here, but I believe that could explainably be the cause of less fuel pressure across the spectrum of conditions.

I have an extra tank, which I plan on dropping off to get professionally cleaned today. Now I just need to track down a new strainer...
 

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27mm and 32mm sockets to get the strainer out. If your spare tank has it, remove it before sending for cleaning. Does your car only have problems with 1/3 tank or less? I would guess if the tank is fuller even a so so strainer would pass enough fuel.
 

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Discussion Starter #16
27mm and 32mm sockets to get the strainer out. If your spare tank has it, remove it before sending for cleaning. Does your car only have problems with 1/3 tank or less? I would guess if the tank is fuller even a so so strainer would pass enough fuel.
Thanks. Unfortunately for me, I did this tank job only 4 months ago (and a year before that). I'm getting pretty good at a few hour swap. It's such a pain to drain the tank though.

My car has problems all the time (when hot) right now. The only think I can confirm FOR SURE is that fuel pressure is about 6 PSI too low across the board. New pump and filter yesterday, so I know those are good.

I have about 120 miles since the tank swap a few months ago. Just filled it up with the second tank of fuel right before I parked for a few weeks to do some prop shaft and exhaust work. The Milano was driving well when I put it up on the stands to do that work. Now things aren't going well. Really confusing.
 

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To drain the tank could you just run a length of hose off the fuel pressure regulator and into a gas can then just use the fuel pump to drain the tank? Just turn it off as it starts to draw air, should only leave about 3 litres in the tank.
 

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You were working under the car, and changing fuel tank?
Might you have accidentally kinked/dented/squashed a fuel line, or refitted something incorrectly?
Coincidental timing points to potential operator error....ask me how I know.
It’s often said here on the BB (for good reason) - what was the last thing you touched?
 

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Discussion Starter #19
To drain the tank could you just run a length of hose off the fuel pressure regulator and into a gas can then just use the fuel pump to drain the tank? Just turn it off as it starts to draw air, should only leave about 3 litres in the tank.
That's the plan... again :)

You were working under the car, and changing fuel tank?
Might you have accidentally kinked/dented/squashed a fuel line, or refitted something incorrectly?
Coincidental timing points to potential operator error....ask me how I know.
It’s often said here on the BB (for good reason) - what was the last thing you touched?
Oh yeah. It's almost certainly something I did. Just WHAT is the question. The fuel work was done in early summer and I actually got to enjoy most of the summer with the car. The most recent round was driveshaft repairs and exhaust work. The most likely thing I did wrong was improperly or poor refinishing the tank I put in.

It fixed similar issues, at least for a few months. However, when I pulled the fuel screen I'd put inline before the pump last month, there was a concerning amount of crud in there, so I probably didn't do quite the job I had hoped. I've dropped off my spare tank at a professional refinisher this morning in hopes of at least eliminating this part of the system once and for all.
 

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What is your pump voltage when the car is hot?

Resistance changes with heat
 
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