Repair-It

This seems fairly recent. Unfortunately I have a habit of running the tank down to when the low fuel indication comes on (I can't even get 300 miles per tank on my commute so that is part of it). Not every time but maybe 25-50% of the time. Of course I do think about the fuel pump when I do this and at 149k I have been wondering...how long will it last? Well I've noticed a distinct increase in fuel pump noise lately. Usually it is on a cold start. Seems to go away after driving.

So I'm putting this here as a placeholder for if/when it decides to quit. I mean it could go years. Or quit this winter. Or possibly sooner. Hard to say. What I will say is I don't think I would sign up for proactive replacement just due to the noise (unless it increases to ridiculous levels), but I think if I have indications of insufficient fuel pressure (which would first surface under load) then I would probably strongly consider it. If nothing else, this thread puts me on notice that if something happens, I can't pretend there was no evidence of a problem brewing...but the obvious approach is just to monitor for the noise to get worse or any symptoms of losing fuel pressure. I can handle that.

Pricing isn't terribly insane. I can get GM OEM from Rockauto with level sender for $222 or just the pump assembly for $179. This car like all Sigma vehicles uses a saddle tank that is essentially a two tank design with a transfer pump, and two separate level senders. I think I would need to pull the tank down so I will see if I can post the instructions just to see what is required.

https://www.rockauto.com/en/moreinfo.ph ... 42&jsn=415
https://www.rockauto.com/en/moreinfo.ph ... 42&jsn=412

I'd probably leave the transfer pump ("auxiliary pump") alone. The symptom there would be running out of gas at half tank or something like that. GM OEM aux w/ sender is $191 for reference. That pump runs only when commanded and the general idea is to balance out the fuel level as the tank is depleted. So it only runs occasionally.

Quick research reveals the following....https://www.justanswer.com/cadillac/3kd ... 5-sts.html

- Remove exhaust (not actually that difficult - I think there are 2 bolts at each cat and just some hangers and the whole cat-back drops down)
- Remove driveshaft (not that difficult - bolts at front and rear, plus remove center carrier bearing)
- Unplug/disconnect all the required things
- Remove lower shock bolts, in prep for the next step
- At the rear subframe, remove front bolts and lower front of subframe down about 2 inches. This gives access to tank strap bolts.
- Remove tank straps and I think lower the tank per usual routine

The rear subframe part is annoying but I will say on a lift this job would be a hell of a lot easier. Like way easier. You just walk around under the car and buzz bolts off with an impact, vs struggling on my back for hours. Quickjack would also lift the car higher more conveniently. Also this doesn't sound all that different from what was required on a 4th gen F-body. I don't know what that means (probably the idea that it would be a cheap, serviceable vehicle - annoying repair activities were not invented with my Cadillacs).

Then there is always the approach where people cut a rectangular access hole in the floor under the rear seat....

I didn't hear any noise even on a cold start leaving work yesterday. I will continue to monitor. I can't really think of the noise being caused by anything else. I don't believe it was the air leveling compressor. There are no other motors in the rear of the vehicle. There is the aux pump I guess but I also heard it after filling the tank and the way that is all plumbed, filling fills both so the pump would not need to run.

A new pump would mean a new integrated check valve. This car has more or less always cranked more than the SRX and I assume that is due to losing some fuel pressure prime. I have done experiments where I set to ignition on to run the pump and then crank and it almost always results in less cranking before firing. It is annoying but a non-issue...other people wouldn't even notice.

New data point.

I got back into the car after stopping at a store. I merely opened the door and sat in the car. Before I hit any buttons, I heard the noise! It went away after 5 or 10 seconds. So....there are cars that run the fuel pump upon initial entry to prime the fuel system. I did not think this car did that.

So is this some other weird thing happening? When I get the Tech 2 back from Adam, I will probably just issue a bi-directional command to run the fuel pump so I can end the mystery. If the noise comes and goes at that point, well, I'll have my answer. I still think it's the fuel pump. It hasn't gotten worse or anything. Just seems noisier than it should be. I can probably run the aux pump separately and further isolate the noise.

Same thing again. Opened the door this morning, sat down, and I heard the noise even before closing the door.

I plan on getting the Tech 2 back this evening for the suspension thing so I'll see if I can use it to manually enable the fuel pump as a diagnostic aid.

Well this is interesting.

https://www.cadillacforums.com/threads/ ... ad.301129/

#5 • Jun 23, 2013

I hear my fuel pump before I start my car and also sometimes up to a minute after startup. Mine works fine.

Those are all my exact symptoms, though not all the time, which means it is either not running the pump every time (which is weird unless it has a fuel pressure sensor and I do not think it does) or the pump makes noise only sometimes. Car works fine. Ha. Need the Tech 2 to go any further unless the FSM explains some of the logic. I don't remember seeing it though.

I commanded the fuel pump to run with my Tech 2. It did not sound the same as the noise, and also sounded pretty normal. I am beginning to think the intermittent noise is something else but i have no idea what it could be. For now I think I can relax a little about the fuel pump, which is good.

Can you command the transfer pump separately? Intermittent pump, intermittent sound perhaps?

I could even imagine a situation where the level senders get jostled by a driver entering the car and command a transfer.

I am not sure I can actually command the transfer pump, which seems odd to me.

And your theory is interesting though if you shut the car off with more fuel in the main tank than the threshold, and it jostles a little, surely they could wait until the engine runs to push fuel around...just seems like an odd strategy.

Yeah, that occurred to me as well.. why waste precious battery juice at with the engine off if there is enough fuel available to start without doing that?

Adam has a probe kit.. can things like this still be run by just applying 12 volts? or do you have to also give it can-bus commands to run?