mechanic unable to test fuel pump

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DrBeavis
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Joined: Thu Jul 07, 2011 7:40 pm

mechanic unable to test fuel pump

Postby DrBeavis » Thu May 23, 2019 1:04 pm

2005 SE 4x4

quick background, my pathy died in the middle of the interstate and was idling very rough while on the side of the road. and every time i would press a gas pedal, it would die immediately. had it towed to a local mechanic. they witnessed rough idling, but it went away immediately once they sprayed starting fluid into the break vacuum tube. i have put ~100 miles afterwards and have yet to experience any issues. nevertheless, i took it to one of my trusted mechanics who promised to perform tests on the pump to determine whether it is faulty and is in need of replacement. unfortunately, he was unable to perform such test, and said that this particular pump (or perhaps the vehicle) appears to require a special tool that he does not have, and suggested inquiring with the dealership. so my question is how do i go about testing a fuel pump? is there such a "special" tool? can i perhaps rent it from an auto store (napa, auto zone, etc) the way i have in the past with other tools, or is the dealership the only option? i really need to get to the bottom of this, as i am paranoid about having the car die on me in the middle of a busy highway once again. thanks!!!


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smj999smj
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Postby smj999smj » Fri May 24, 2019 3:13 am

You check pressure at the front of the left bank fuel rail. You need an adapter that goes between the fuel hose and the rail, which have quick-disconnect fittings, that will attach to a fuel pressure gauge. The Kent-Moore tool # is: J-44321-6. The tool to release the line from the rail is Kent-Moore J-45488. Personally, I use a Lisle # 39210 disconnect tool:

https://www.tooldiscounter.com/ItemDisp ... gKUJvD_BwE

Fuel pressure should be 50 PSI.

DrBeavis
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Postby DrBeavis » Mon Jun 10, 2019 11:10 pm

good info!
so if my fuel pump passes the pressure test, does that mean that its fully functional, or is there still a chance that its faulty? if latter is the case, what other test(s) should i perform in order to rule out the pump as the cause for my aforementioned stall?

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smj999smj
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Postby smj999smj » Tue Jun 11, 2019 1:21 am

I remember an issue I had on a small Dodge car that would pass a fuel pressure test when started cold, but when driving it and monitoring the fuel pressure, the pressure would slowly drop lower and lower. A new fuel pump fixed that. I also remember when I worked in a Nissan dealership, another tech had an issue with a 240SX which would pass a fuel pressure test but, when driven, it would start to run rough due to a misfire at #4 cylinder. In his case, someone had done a repair to the fuel system that involved clear RTV silicone sealant (if I remember correctly, they used the clear RTV on the fuel sending unit "O" ring). #4 was at the end of the fuel rail so it was at the spot where the RTV would end up. The latter is probably not what is happening to you, but there's slight chance that the former might apply. Only way to know would be to drive with the fuel pressure gauge installed until you can duplicate the problem to see if the pressure drops. If it's something that doesn't occur frequently, it'll make it a lot harder to diagnose.

DrBeavis
Posts: 49
Joined: Thu Jul 07, 2011 7:40 pm

Postby DrBeavis » Tue Jun 11, 2019 10:17 pm

its interesting that you brought up the idea of driving with a fuel pressure gauge installed. i floated that idea to my mechanic who is really good and trustworthy. and unlike most places, he lets me buy parts on my own and then only charges me for service. but even he declined to install a gauge that i wanted to be mounted on the interior to allow me to continuously monitor the pressure while driving. he claimed that it is unsafe to drive with such a setup due to a chance of fuel getting out and igniting, or something along those lines. what is your take on that? it is crazy and/or unsafe to have a permanent fuel pressure sensor installed, while feeding the data to the gauge in the cabin? or is there an alternative approach that would accomplish the same? i would really value you opinion on this one!


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