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Is 40 psi fuel pressure too low?

colbert190

New Member
Joined
Sep 12, 2019
Messages
7
Location
Watertown, NY
1998, TJ, 4.0, 5spd.

Have had some stumbling issues while driving recently, and have always had the long start issue, but always when hot. Always starts on first crank in the morning. bought a pressure tester and showed 40-42 psi while running hooked up to the serader valve. When rev'd psi would drop to 37 very very briefly and shoot back up to 41. After shut down, psi would leak at 10 psi per minute until it got to 0 (about 4-5 minutes after shutdown).

Is 40 psi way too low? Fuel pump starting to go? Leaking injector? thank you.
 

Steel City 06

TJ Addict
Joined
Mar 12, 2019
Messages
1,230
Location
Pittsburgh, PA
1998, TJ, 4.0, 5spd.

Have had some stumbling issues while driving recently, and have always had the long start issue, but always when hot. Always starts on first crank in the morning. bought a pressure tester and showed 40-42 psi while running hooked up to the serader valve. When rev'd psi would drop to 37 very very briefly and shoot back up to 41. After shut down, psi would leak at 10 psi per minute until it got to 0 (about 4-5 minutes after shutdown).

Is 40 psi way too low? Fuel pump starting to go? Leaking injector? thank you.
Fuel pressure should be 49 +/- 5 PSI if I recall correctly. The loss of pressure may be due to a leaky check valve in the fuel pump assembly. It may be worth checking out the fuel pump.

Also, search around on the forum for the “heat soak” issue. That may or may not be related to your symptoms.
 
OP
C

colbert190

New Member
Joined
Sep 12, 2019
Messages
7
Location
Watertown, NY
ran another series of tests today, when primed the fuel pump will pressurize the rail to 30 psi no matter how many times the key is shut on then off. When started today the Jeep held pressure at 42 while running and when rev'd would dip just below 40 psi and jump right back up to 42.

When turned off the psi dropped to 30 in 2 minutes and 30 seconds. Then 20 psi in 5 minutes and 30 seconds, then at 10 minutes was at 14 psi, then 10 psi at 16 minutes, 5 psi at 30 minutes, and will eventually bleed all the way down to 0.

Is it time to change the pump? My main worry changing the pump is that since the complete Bosch unit is nearly impossible to find now, that I will be changing pumps again in the next 12 months.

If it is time to change the pump, what is the best complete sending unit to get other than the OEM Bosch unit that can not be found anymore?

Thank you again!
 
OP
C

colbert190

New Member
Joined
Sep 12, 2019
Messages
7
Location
Watertown, NY
Fuel pressure should be 49 +/- 5 PSI if I recall correctly. The loss of pressure may be due to a leaky check valve in the fuel pump assembly. It may be worth checking out the fuel pump.

Also, search around on the forum for the “heat soak” issue. That may or may not be related to your symptoms.
thank you for the reply. should i be looking to replace the entire assembly or just the pump? if replacing the entire assembly what is my best option? im seeing some stuff about delphi 1353, but more on what brands not to buy then with what to actually go with. Should I just replace the pump with Bosch 69316? Thanks you
 

Steel City 06

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Joined
Mar 12, 2019
Messages
1,230
Location
Pittsburgh, PA
I’m not familiar with the process myself as the later fuel pump assemblies are still available. You might read through these threads and reply to them if you have questions:



There’s a few other threads about it as well.

If you have the 15 gallon gas tank in your Jeep, this would be a very good time to do the fuel neck filler mod to convert it to a 19 gallon tank. The modification is free and doesn’t take a lot of time if you have the tank open already. (Most Jeeps came with the 19 gallon tank, so this likely won’t apply to you.)
 
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colbert190

New Member
Joined
Sep 12, 2019
Messages
7
Location
Watertown, NY
thank you both for the reply. Is 40-42 psi showing an issue which i should be concerned with immediately though? or is there some life left in the pump that i can squeeze out before she dies completely?