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My car died on me a few times while driving this week. Sometimes I could restart immediately, other times it would crank and not start. I'd give it a minute, try again and it would start, get me a few more miles down the road then die again.
I bought a fuel pressure gauge and watched it die in the driveway. The car drives and idles fine most of the time, but at some point the pressure starts steadily drop until the car dies at around 15psi.
With the gauge still hooked up I verified that when it won't restart, it's because the pumps didn't properly prime, rail pressure stayed at zero.
I gave it a minute to sit, primed the pumps again, and the rail pressure came up, and the car started fine.
So obviously I suspect the pumps are dying a slow death.
But when I pulled the seats out here's what I've found.
If I'm not mistaken these are the updated pumps, with a build date of 2018.
According to my records the car has only gained maybe 10k - 15k miles since these pumps went in.
Could the filter/regulator cause a similar issue?
Because they look to be way older.
But isn't this the updated wiring?
It's hard to read but I think that part number is A2114400507
If someone can help me decode what parts I have installed, then maybe I can figure out what's busted.
If there is no way the filter/regulator can cause the issue I have then I'll replace these barely used pumps, I guess.
Maybe the regulator is failing and venting all the fuel pressure back to the tank?
I'll check right now and see if the pumps are still running when the fuel pressure drops.
Thanks for any help.
You replace everything. While your hands and arms are soaked in gasoline. Three bars on the fuel gauge at the maximum or you run the risk of fuel spilling out of the tank.
And the 211-470-00-00 part number is a set of dual fuel pumps. You must use the third-gen fuel filter/regulator with it plus adapter cables. See my answer in your other post.
-211-470-00-00 Fuel Delivery Module (dual pumps) $411
-211-470-64-94 Tank Inner Module (actually filter and regulator) $489
-211-471-05-79 Fuel Sender Seal x 2 $34
-211-440-05-07 Cable Harness adapter for filter/regulator $15
-211-540-07-00 adapter cable to dual fuel pumps $15
-203-997-04-81 foam cushion $1
I just verified that the pump shuts off right before the pressure drops.
Any chance it's electrical? Because the pumps don't sound bad. They just... Stop
Could the fuel pump relay get warm and fail intermittently?
I just verified that the pump shuts off right before the pressure drops.
Any chance it's electrical? Because the pumps don't sound bad. They just... Stop
Could the fuel pump relay get warm and fail intermittently?
All the symptoms point to a failed fuel pump relay. The relay is hidden behind the panels on the passenger side of the trunk where the fuel filler door is located. The relay is not in the rear Sam as it is on the non-amg models. I recommend you upgrade to a 70 amp relay plus a new socket and the larger connectors. I have multiple posts on this. Perform an advanced search for "E55 fuel pump relay and fuse maintenance".
The relay gets hot enough to literally melt the plastic housing which has a melt point of 300° f. So, you could say it gets a little bit warm. It also burns the insulation off of the wiring harness. 🙂🙂
I'm a little perplexed still. My relay and wiring look great!
Tomorrow I think I'll test again and see how hot the relay gets when it shuts off.
Can I short the replay plug to bypass the relay? That would at least narrow down the problem.
This is the relay in question right? My car was built in Jan of '04
Mine was also a Jan 04 build but my pumps may have been original (143k). Last time I inspected my relay and wiring it all looked fine, like yours. I'm not sure why some cars melt their relay and others don't.
I ordered the parts for the relay upgrade.
But just to be clear, I'm using a 70A 4-prong relay in a 80A 5-prong socket?
Yes. The socket will accept both 4 and 5-prong relays. Swap one wire at a time. The ground "trigger"wire is small guage. I doubled mine over before crimping and soldering.
Just came back to give an update.
I got the upgraded relay soldered in.
And the car has run great ever since. So I'm feeling more confident with every mile that this was the right fix.
I owe @bbirdwell a beer. Thank you sir, you are a gentleman and a scholar. Saved me a heap of money.
Can you imagine how frustrated I would be if I threw money at the pump/regulator and that NOT be the problem?
I wish I could say that has been flawless since this repair. But that isn't the case.
A few days later this broke.
09-03-2022, 01:03 PM
Fuel pressure drop
