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I'm thinking that fuel is draining out of the lines due to a bad check valve. Can I assume that Monty's have an internal one built into the pump?


There is a check valve and also a relief valve - both inside the fuel pump.

Several of the '89 vintage 3.0L fuel pumps have recently been replaced by folks on this forum. It's not a terribly difficult job to replace one - a couple of hours at the most if you don't run into a lot of rust on the access port fasteners. I replaced mine last week with a Denso (OE manufacturer) pump - cost about $120 delivered.

You need Denso # 950-0150 which includes a new filter that's necessary to install if the warranty is desired:

Order Denso Pumps Here

Sometimes, the fuel pressure regulator is the culprit. It requires an hour or so of work to replace, but it takes as much time to check it as it does to replace it. I'd put in a new one along with a new pump if you think either is bad.

It's possible that the injectors are leaking, but that's hard to diagnose without an installed pressure gauge - not practical on our trucks.

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The manual also talks about testing/checking the "fuel pump drive control system" -- is this referring to the ECUs ability to turn on the pump when you turn the key?


Yes, that and whether the relay and pump will work - but since your pump does eventually supply fuel, the ECU and relay would seem to be ok.

Good luck,
Frank

'89 [color:"white"]G-Raider[color:"white"] [color:"black"]Supercharged 3.0L, MegaSquirt 2, lockup A/T, 2.5" exhaust, 172k, Cibie H4s/Oscar SCs, Hella Micro DE fogs, Cobra CB, Superwinch hubs, LSD rear/Aussie Locker front, Bilsteins, Lifeline AGM, Rust-Oleum