I could contrive an alternative source of power for the pump. Do I need to worry that there is some other problem with the ECM?
Gordon,
Assuming that only the lift pump circuit has failed, then it doesn't automatically mean anything else is wrong with the ECM.
..... and I should replace it?
That's strictly your call of course after you weigh the pros and cons. If you have the money and like things to work properly as designed, then replace it. If you need to save some money and don't mind a little "re-engineering" of the lift pump circuit, then don't replace it.
I assume that is a Chrysler part [... . or is it a Cummins part], and roughly what do they cost?
The ECM is manufactured by (or for) Cummins, but contains Chrysler specific features and software. The PCM is the other computer module on the firewall primarily involved with controlling the transmission and is Chrysler's. Just to make sure I'm not creating any confusion by mentioning the PCM, it's NOT involved with the lift pump circuit.
In 2007 a computer was replaced by the Cummins dealer. The engine's computer is the ECM and the truck's computer is Chrysler's? I am assuming they replaced the ECM. The computer cost at that time was $1,200.
I wouldn't assume anything, but whatever they replaced, it was almost certainly a refurbished unit.
The only down side to rigging up your own lift pump (and not having it directly controlled by the ECM) circuit is this:
The ECM reduces the duty cycle of the lift pump to 25% (25% ON and 75% OFF) when the engine is being cranked to limit fuel pressure being supplied to the VP44 injection pump. For some reason the VP44 sometimes has trouble starting the engine when too much fuel pressure is being supplied by the lift pump. If you hook up your lift pump to turn on anytime the the ignition key is in the START or RUN positions, then you'd have a 100% duty cycle from the lift pump at all times. In reality though this issue doesn't seem to be a problem with the typical lowish pressures supplied by a stock lift pump, so you probably don't need to worry about it. It's when you start running a high pressure aftermarket system you may encounter difficult starting. Others here on the TDR forum have had the exact same problem you're currently having (the ECM failing to power the lift pump) and they've rigged up an alternate circuit for their lift pump with no problems reported.
As to replacement cost...
Auto Computer Exchange down in Florida sells refurbished Cummins ECM's for $695. A refurbished PCM is $495. Either unit comes with a 1 year warranty IF you return your old computer to them. If you decide to buy from this company, be advised that some here on the forum have reported they don't always live up to their promised ship dates. But if you're not in a rush to get the computer, then you have little to worry about. I've purchased a spare ECM and PCM from them a couple of years ago and had no problems whatsoever. They sell through eBay also, which is a purchase method to consider if you want 3rd party backing on some aspects of the sale... and you can leave negative feedback if something goes wrong.
Best regards,
John L.
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