1989 Dodge Ram W150 5.9 TBI 360 with Vapor Lock

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JeepManDan

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Bought a 1989 Dodge Ram W150 5.9 360 with factory TBI with an apparent Vapor Lock issue. It starts and idles fine, but when driving for 3-4 minutes on a country road the engine bogs and stutters if more than 1/4 throttle is applied. After that starts it can only limp along at near idle engine speed. Once it cools off that goes away. No check engine light. Prior owner tried to solve this with magnets on the fuel line to cool it, replaced all plugs, wires, coil, cap/rotor, fuel filter, and fresh fuel but no luck. With a mechanic today we tested fuel pressure reads just under 14. We replaced one injector and both seem to be injecting good fuel spray, using ethanol free fuel still not change.

Any ideas? I think maybe fuel pump replacement could help, I will try wrapping fuel lines with heat block, and maybe replace entire throttle body. Any ideas would be very welcome. Thanks
 

crash68

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Has the fuel pressure regulator been replaced? Also check the fuel line along with the return line for any garbage in them, along with fuel filter. Your most likely losing fuel pressure, not a vapor lock issue.
Vapor lock was prevalent on carbureted engines that had an engine mounted fuel pump.
 
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JeepManDan

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Thanks crash68 I replaced the fuel pressure regulator and it runs much better. It still has some lurching and in one situation on a steep grade at very low speed it struggled and behaved like vapor lock again. I can hear a hum from the in tank fuel pump so it likely needs to be replaced soon. The filter was changed but I agree inspection of the fuel line makes sense. It is getting fuel but maybe the return lines have some restriction. I think will also clean the throttle body out completely. Thanks for the help.
 
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JeepManDan

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removed this comment I located the O2 sensor it was hiding well
 
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1970Pelle

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A EFI engine/vehicle will not vapor lock. The fuel pump will push the fuel right through and back to the tank. Given it has a return line. If not the fuel is just waiting to be used (patiently we hope) You have something else going on.
 
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JeepManDan

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Thanks for all of the input everyone. I replaced the Fuel Pressure Regulator and it ran better but still struggled to get up to highway speed. I replaced the Throttle Position Sensor and it now it gets up to speed much better. I did a 30 mile test drive this weekend and it did great up to the very last few miles, it struggled to get up a steep grade following a stop sign. After pulling over then going again it made it home. I think the in-tank fuel pump may be close to failing so will aim to replace that next. It makes a loud hum sometimes and with these symptoms I think it is likely causing intermittent issues.
 

Dean2

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When it acts up, tap the gas tank with a rubber mallet a few good wacks, then hop back in and see if it is running right. My odds on bet is you need a new pump. It is acting like it, the fact it doesn't like steep hills, and that loud hum is not normal.
 
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JeepManDan

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Update: replaced fuel pump and it runs like a champ. thanks all
 

Dean2

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Glad it worked out and appreciate the update. Remote diagnosis is tough, nice to know if you got it right.
 

WTB 2 Gen RAM

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Been through this remove gas tank clean or replace as well as the fuel lines or spray carburetor cleaner through them and maybe the fuel pump all filters clean pressure regulator and tbi= happy truck
 

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