Engine rough running - at wits end

[the_tool_man]

Throw an inline gauge coming off the filter, put a GoPro pointing at it or an old Iphone on video and go for a ride again. Go back and watch the video. 

One of the "loose ends" was removing the fuel pressure gauge I'd had in there for a year, . I thought I might put it back and run it through the passenger side hood vent. I have to remove and repair that piece anyway at some point. And I don't have a go-pro or spare phone.

Regardless, the fuel gauge isn't working right. The sender will have to come out for cleaning/replacement. And I noticed in the last week the fuel pressure drops to zero pretty quickly after shutdown. So I should probably replace the check valve. I might as well do the tank while I'm doing all the other stuff. Then I'll have confidence in the fuel system.

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[JSM]

1 hour ago, the_tool_man said:

 

One of the "loose ends" was removing the fuel pressure gauge I'd had in there for a year, . I thought I might put it back and run it through the passenger side hood vent. I have to remove and repair that piece anyway at some point. And I don't have a go-pro or spare phone.

Regardless, the fuel gauge isn't working right. The sender will have to come out for cleaning/replacement. And I noticed in the last week the fuel pressure drops to zero pretty quickly after shutdown. So I should probably replace the check valve. I might as well do the tank while I'm doing all the other stuff. Then I'll have confidence in the fuel system.

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Forgive me but where is the check valve? If there is one I've never known this. Are you referencing the fuel damper right after the fuel pump?

[Dave WM]

OE pumps had a check valve built in at the outlet. I recently replaced my airtex unit, do not know if the skinny after market pumps came with one, I assume so  but cant say for sure.

when I was chasing fuel pressure leak down I noticed it was all over the place. Sometime it would hold for days, other times it would leak in minutes. The thing is there is not a lot of fuel to start with, can't compress a liquid anyway, so pressure would have to be maintained in the rubber fuel lines I presume. That being said it would not take a lot of leakage for the pressure to drop. My guess is between the check valve and all the injectors and lets not forget heat (latent engine heat increasing pressure in the lines, regulator bleeds it off, then everything cools down  and pressure it gone). So after chasing pressure holding for weeks I finally decided the best course of action is to simply go out and drive it. I thing regular driving putting lots of miles on the car is the best thing you can do to make it run right.

[the_tool_man]

I like that answer. Also, I STILL haven't checked the CSV. It may be leaking. I do have a spare now, which will make checking easier.

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[siteunseen]

1 hour ago, the_tool_man said:

I like that answer. Also, I STILL haven't checked the CSV. It may be leaking. I do have a spare now, which will make checking easier.

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If you pull the fuel line off the cold start valve and plug it with a bolt that should stop any fuel from leaking at that spot if it it is bad.  I've read there's a lot of people that don't even run the CSV, I assume they all live in warmer climates or keep there cars in a garage where it stays warm for start up.

[JSM]

I'd be Interested to know when the newer style slender FP came out and if they were ever factory.  I checked both the 82 and 83 FSM and they show the same style as the 77 FSM.  I bet Dave is right your pump check valve is going bad.  See yellow comments.  This is from the 82, but it had the pump pic and verbiage in one shot:

 

[siteunseen]

5 hours ago, JSM said:

Forgive me but where is the check valve? If there is one I've never known this. Are you referencing the fuel damper right after the fuel pump?

[JSM]

That is the relief valve according to the FSM.


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[the_tool_man]

If you pull the fuel line off the cold start valve and plug it with a bolt that should stop any fuel from leaking at that spot if it it is bad.  I've read there's a lot of people that don't even run the CSV, I assume they all live in warmer climates or keep there cars in a garage where it stays warm for start up.

I bought an N42 intake from a local forum member for future use. It has a CSV on it that I can use to plug my intake while I test mine for correct function and leaks. Anyone know approximately how much fuel is supposed to come out during a cold start?

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[JSM]

3 minutes ago, the_tool_man said:

 

 

I bought an N42 intake from a local forum member for future use. It has a CSV on it that I can use to plug my intake while I test mine for correct function and leaks. Anyone know approximately how much fuel is supposed to come out during a cold start?

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Pressure or volume?  The pressure is going to be the standard 36PSI from the fuel rail.  If you figure out the volume let me know!

[siteunseen]

You're right.  My dumb self took mine out of an old pump and measured it and completely forgot about doing that. 

Here's the check valve Captain Obvious used.

 

[Zed Head]

16 hours ago, the_tool_man said:

 It would hesitate at times under acceleration.

Then tonight I took it out for a longer drive. After a few miles it started to bog really badly around 3k rpm. It would occasionally backfire out the tailpipe too. It only does it while driving.

 I figure it's rust from the fuel tank getting sucked up while in motion. So I guess it's time to drop the fuel tank and have it cleaned and coated.

Not uncommon for the old EFI systems to run lean.  A "few miles" implies that it's the first time you let the engine get fully warmed up.  The mixture gets leaner as things get warmer.

You might be disappointed if you drop the tank and don't find much rust.  Easier ways to diagnose a problem.  Just saying.

The FPR is the most common cause of pressure leak-down.  It's just a flat steel tube end sitting on a flat piece of steel.  Any small particles or rust pits allow leak-down.  I can't recall anyone actually finding a leaking CSV.  It's a mystery part that takes a lot of blame, but rarely causes a real problem.  The simple test for fuel system leakage is to remove the small wire from the starter solenoid and turn the key to Start.  That will power the pump.  No need to block the hole in the manifold, just pop the CSV out enough to see the squirting end, and run the pump.

Edited March 13, 2017 by Zed Head