New fuel pump bad?

[Justinwht]

Friend has 2000 4L SOHC Explorer, similar to mine (OHC). He had the pump replaced six months ago, but didn't put in new filter sock. The original symptom was once a week the engine would miss about half a second. I suggested replacing the pump. That fixed the problem.

The problem came back. This time he replaced it with a pump and included filter from Rock Auto. The new symptom is it take about two seconds of starter turning over before engine runs. Engine runs fine after that over all RPM ranges, so no fuel starving.

I suggested taking it back to shop and have them check the pump pressure.

 

[Mbrooks420]

Did he buy a cheap pump?

 

[J_C]

While I'd first suspect the pump, the vehicle is getting up there in age and there are other things you can check that are easier than dropping the tank again so I'd try those first.

First measure fuel pressure, after it hasn't been running for the typical (minimal) amount of time to cause the problem. Turn the key to the run position but not to start position for a few seconds. Turn the key off. Measure fuel rail pressure.

It should be holding pressure and very slowly drop over hours. Another thing to try, is turn the key to run position, wait a couple seconds, then start position. Being lazy if this second test works, I'd think about just doing that from now on. I mean even if the pump has a warranty, I might not want to bother dropping the tank just to put another of the same brand in.

On the other hand there could be a leaking fuel injector(s), might not hurt to put a jug of Techron cleaner in a 1/2 tank of gas.

No need to pay a shop to check pressure, but if take it back to shop means they'll look at it for free because they did the repair previously, sure... on the other hand many auto parts stores have loaner fuel pressure gauges to do this. It should be around 60PSI.

My memory of the SOHC returnless system is a bit vague, but isn't there a damper (rather than regulator) on the fuel rail, with a vac line to it, and if the damper were to rupture its diaphragm then this would also cause loss of fuel rail pressure through the vac line when the pump's off? I think this is right, just looked at some on Rock Auto. This is easy enough to check, whether there is fuel coming out the damper vac line port.

WOW! Those dampers must be in short supply, Rock Auto wants $272+ for two out of three brands, a ridiculous price but most other sellers are doing same thing.

2000 FORD EXPLORER 4.0L V6 SOHC Fuel Injection Pressure Damper | RockAuto

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