Air in fuel?

[OVERDRIVE]

1990 240: I did a fuel pressure test today. Pressure was correct but took a while to build. I used a fuel pressure tester kit off of the valve on the fuel rail, there were no leaks. The air never bled out of the pressure gauge, there's a video online of someone doing the same thing, and his gauge bled in seconds. While running it seemed to be pretty lazy about finding the correct pressure. The air that never bled out of the system concerned me, so I put a clear vinyl tube on the return, and jumped the pumps. The fuel coming out of the rail was very bubbly. Basically straight froth. I pulled my fuel sender and I can't find any issues. I was low on fuel (not in the red though, I've gone way below the red without running issues). Am I crazy? Even if the sock stuck up above the fuel line, the pump intake would still be 100% fuel, as that is the part that is submerged. I do not smell fuel while under or around the car.

 

[dl242gt]

See how the fuel pressure regulator responds to revving up the engine. Should see that second or so of enrichment from revving up. If the diaphragm inside is going bad it could affect the pressure readings that way. Maybe also letting air get in from the vacuum line?

 

[OVERDRIVE]

See how the fuel pressure regulator responds to revving up the engine. Should see that second or so of enrichment from revving up. If the diaphragm inside is going bad it could affect the pressure readings that way. Maybe also letting air get in from the vacuum line?

36psi or so at idle. A strong rev sees it zip to 40psi, then with the throttle closed it drops to maybe 32 and right back up to 36psi. Pressure was also tested with the car off, and I got 40psi. But like I said, after pressing the bleed button and venting the fuel pressure, it took 1.5 seconds before the pressure recovered. I will get some 1/2" clear hose in the morning and route the pressure out of the sending unit to the fuel filler neck and take a video.

 

[apachechef]

air or fueal vapor?

 

[Harry Tuttle]

Does it run alright? Was there some symptom that led you to check pressure?

 

[OVERDRIVE]

air or fueal vapor?

This is something that I've thought of, I'll find out today. Though that high of volume running through the rail shouldn't be vaporizing the fuel.

Does it run alright? Was there some symptom that led you to check pressure?

I installed some chips that others with a similar setup to mine run, and I have a dead spot under load.

 

[240 240]

 

[OVERDRIVE]

After studying the ancient text (cleanflametrap.com, thanks Art) I found the issue. The in tank pump was siezed. I gave it a good smack while supplying 12V directly to it and it woke back up. This may explain why sometimes my hot idle was smooth, and other times it wasn't. Other than that, I had zero symptoms that would point to any issue with the stock LH module.

Pivoting topics, what's the best in tank pump replacement available right now? The last time I replaced one was 2016.

 

[240 240]

IPD complete kit is my go to ,literally 1st thing I do when I get a 240.

use a 740 turbo pump if you have one laying around and don't want to spend $

 

[dl242gt]

I've bought Carter branded ones that have worked for me. I think that was bought from Rock Auto. FCP should have something worth their warranty. At least you hope so.

 

[OVERDRIVE]

This is one of those anticlimactic threads where I found the issue, fixed it, and saw no change in operation. An AutoZone kinda near me had a Delphi, so instead of leaving my car inoperable parked on the street, I threw in a new Delphi. Fuel leaving the sending unit is completely bubble-free. Fuel leaving the rail while running is just a little bubbly, nowhere near as bad as before, I suspect there was still some air in my fuel filter when testing. So far, after a quick drive, I can't pin point any change in how it runs.

The lesson from this is you might have a dead in tank pump and not even know it.