Intermittent power loss to fuel pump

[lambo]

How do? Started a week ago, every morning enroute to work,every evening leaving work. Happens after engine warms to operating range. While driving, power to fuel pump cuts off, I pull over, look at pressure gauge while key is on, and wait to hear fuel pump turn on and verify by gauge I have pressure, then restart and drive on. It happens 3 to 4 times within 1 mile after Norma operating temp, then after that never occurs till the next cycle to work or home. When it happens , I end up with 10 psi at rail, then after waiting, I resume to 41 psi , then restart and commence to driving again. Pump is a year old along with filter. ANY THOUGHTS

[lambo]

Literally while parked on side of road with hood up, fuel psi is 10 and hear no pump running with key on. As I wait and look and listen for roughly 3 min, I miracusly heart pump start and see gauge hit 40 , then it starts perfectly and I drive away

[enterusernamehere]

I'd check the fuel pump relay. Could also be the ECU.

[lambo]

Ok. So it cut off twice on the way home Sunday. Instantly restarts after fuel pressure builds ,roughly30seconds. Is all it took.
So yesterday I was off so had a chance to mess with it. I started it up and let idle too operating temp, about 15-20 mins, then pressure dropped and cut off. Pressure came back in about 30 sec and restarted and let idle for about 45 mins with no issue
I took the multifunction relay cover off to expose the 3 relays, determining that the bottom relay on the circuit board is for fuel, all appeared fine, no arc marks.
Any way to bypass this relay for testing purposses, still trackn down where the loss of power starts

[lambo]

Just went out to start truck and no go. Pulled cover off multifunction box and saw that fuel relay was open. I manually closed to get appropriate pressure to start, then it stayed closed to continue to supply pump
So think I'm on the rite path, now it's just a toss up between Comp and relay

[JoshB]

What about voltage at the pump? Might have a bad or corroded electricAL connection to, would be nice if it is the relay though.
If it is the relay you can get them through summit racing part num- 0332 014 0112, only 11 bucks and change plus 4 bucks shipping. Oh and it is a bosch part #.

[lambo]

Wrong relay, I wish it was only 11'. Believe it's about a 100. It's the sealed multifunction relay box beside evap canister inner pass fender

[lambo]

While truck is at idle and normal operating temp, I have 2 multimeters hooked up. 1 to the brown/green wire of MFrelay which is power in and 2nd meter to white/purple which is power out to inertia switch.
After about 20 minutes staring at meters, the output meter from MFrelay shows no voltage, and I hear and feel relay switch open, and fuel pump stops pumping resulting in engine cutting off.
Question is , COULD the ECM be controlling the relay to open or is this a pretty clear case of MFrelay failure, thanks for the feedback

[ihscouts]

I think the coil might be dropping out due to coil overheat or loss of signal. You can check the connector at the ECU to see if there is corrosion/arcing. What's the connector at the MF look like? If I was a betting man I'd say the MFU is going since it's fairly common......but I hate tossing parts a problem and I think your doing it the right way. Can you check the ohm's of the coil and then compare it with the other two?

[lambo]

Thanks for the reply. Connectors look good. Will check ohms later stuck at work due to weather. Thanks again H

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[lambo]

Ordered and received new MFRelay, installed and let idle for approximate 45 mins with no issues. Real test in morning while driving to work.
H, couldn't really get a accurate ohms reading, either I was doing it wrong or getting funky readings from the circuit board the relays are soldered to, was testing across stationary end and working end while closed, all 3 just kept reading all over the place.
Thanks for the input, will post final results tomorrow

[ihscouts]

I think you've nailed it down.

[lambo]

Nailed. Confirmed. Thank you sir

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[fishEH]

The MFU on my 98 wen wonky, too. It would randomly cause all sorts of clicking upon start up. Swapped it with a spare and good to go.