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check engine fuel pressure E320

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monarchd's picture
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I having a problem with check engine (electronics) light on 1998 E320 wagon.
The car came from my grandfather w/50k miles and the check engine light ON. Dealer confirmed previous garage diagnosis, check engine was due to bad mass air flow sensor, and replaced MAS. No problem for a month or so. Wife driving and the check engine light came on. Dealer found code indicating emission control issue. They checked the pressure in the gas tank and Identified gas cap as the problem, BUT, their claim was that the gas tank filler neck was out of round so the gas cap was not sealing properly. Their solution= $1500 for a new gas tank. We chose to forgo that option. Left the dealer with the reset check engine light, filled the tank and drove w/out incident UNTIL the low fuel light came (does it always flash?) as the low fuel light came on, so did the check engine light. Any insight or suggestions? Could a problem with the low fuel sensor cause the check engine light to come on?

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Ferdman's picture
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Vehicles
1998 E320 Sedan
1995 E320 Sedan
1991 300CE

The Low Fuel light on our 1998 E320 lights steady ... no flashing. Don't know for sure, but it doesn't make sense that the Low Fuel light would cause the Check Engine light to come on. It never has on our E320 anyway.

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Fred Hoelzle

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Thanks for the reply Fred. I spoke w/a service guy. He stands by the claim that the fuel filler neck is distorted and won't seal properly with the gas cap. The only fix is a new gas tank.

I'm going to see if there's some way that I can add an aditional gasket to the gas cap to compensate for the filler neck distortion.

The flashing low fuel light is part of the Check Engine signalling. I've got a Miata with OBDII, disconnecting the battery for a minute or 2 will reset "loose gas cap" codes. I'm going to give this a try with the E320.
I can think of lots of things I'd rather sink $1500.00 into, and a gas tank isn't one of 'em.

Doooh, MB service guy just called back, said "car's not designed to clear codes when battery is disconnected"

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FYI up-date
Went ahead and removed positive battery lead for ~1 minute. When I started the car, the Check Engine was OUT. We'll see how long it stays out. Beats the $*&% out of $85 for the reset or the cost of new tank. I know there's a down side to repeatedly resetting the light/code myself, but for the short term, I'll risk it.

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The system is designed to cause the low fuel light to flash when there is a leak in the evap system.The car is trying to tell you there is a problem.The first obvious check is to see if the gas cap is tight.If it keeps sensing a leak it will eventually throw a code.Very common for a bent filler neck to cause this.People lean on the gas nozzle while filling and bend it.There are a couple of valve that could cause the same code as well

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Gmazzini's picture
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I had the same problem on my 1998 E320 sedan. I changed the gas cap and the problem went away. Give it a try.

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Thanks for the replies. Light's still out.

The first time the light came on I took it to the dealer.

Dealer tested the tank and evap. system for leaks (they sealed the tank using something other than a standard gas cap) : found no leaks in the system.

They checked my gas cap found it was not leaking.

They leak checked the system using a new gas cap and found system leaked with the new cap.

They examined the filler neck and found it is not round and is not making a tight enough seal with the cap. For some reason the weakened seal seems to be more of a problem when the tank is less than 1/4 full.

I'm going to play around with trying to make and "auxiliary" gasket to get a better seal. If I ever get to the point of being willing to buy a new tank, I may try to bend the filler neck back into a nice round shape before I shell out the $. Sounds easy when I write it, doesn't it? :)

Thanks again.

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