1997 E320 M104 flat at low RPMs, backfiring? - PeachParts Mercedes-Benz Forum

gmercoleza · #1 06-19-2007, 10:25 PM

OK, my original thread basically outlined what I perceived to be performance issues with my new-to-me 1997 E320 M104:

Minor Performance Issues M104

On the way home from work today, things took a different turn. Rather than the upper RPMs seeming "choked" now it is the lower RPMs, specifically anything below 2500 to 3000. When I step on the gas, it just doesn't go anywhere. Accelerates very S - L - O - W - L - Y. But then once it gets into the neighborhood of 2500 to 3000, it comes alive. If I shift manually and keep the revs up, everything is great, at least until I come to a light and have to start from a standstill - then the game begins again. If I floor the gas when it's "choking" then I hear what sounds like a backfire, except it's from under the hood, presumably coming through the intake?

I have been driving this car for 2 weeks now and these problems just became apparent to me within the last couple of days; I didn't notice them before, so maybe they were just getting progressively worse.

* No codes
* No CEL
* Did a visual inspection of vacuum hoses, connectors, air intake/filter, etc. and all seem OK.
* coils, spark plugs, and all connectors/wires were replaced last year
* air and fuel filters are recent

suginami · #2 06-19-2007, 10:45 PM

When I first got my W124 E320, I had very similar symptoms.

After my indie replaced both fuel pumps, a mass air meter, and a throttle actuator, he gave up and sent the car to the dealer.

It came back as a bad coil wire connector.

Yes, one bad coil wire connector can cause very bad herky jerky acceleration and backfiring.

There are three of them. I'd replace all three, along with the plugs before I did anything else.

gmercoleza · #3 06-19-2007, 11:00 PM

Quote:

Originally Posted by gmercoleza

* coils, spark plugs, and all connectors/wires were replaced last year

Do you think it's time already? Can they be tested?

gmercoleza · #4 06-19-2007, 11:03 PM

Also, if indeed the coil connector(s) is/are bad, wouldn't the CEL come on and throw a misfire code? Not disagreeing with you (man I hope it's that simple) - just thinking out loud here...

saumil · #5 06-19-2007, 11:29 PM

Mass air sensor ?

G-Benz · #6 06-20-2007, 02:06 AM

A cracked intake manifold caused those problems for me...no codes when it happened.

It cracked at the inlet on the underside of the manifold. It would not have been detected if it wasn't for the head gasket job in progress.

Another thing...has your wiring harness been inspected and/or replaced?

gmercoleza · #7 06-20-2007, 07:40 AM

Quote:

Originally Posted by G-Benz

A cracked intake manifold caused those problems for me...no codes when it happened.

It cracked at the inlet on the underside of the manifold. It would not have been detected if it wasn't for the head gasket job in progress.

Another thing...has your wiring harness been inspected and/or replaced?

Wow - I really hope that's not my problem.

As for my wiring harness, I believe it is OK since this is a 1997, but will check it again.

I guess I'll be driving the W124 or the W126 for the next few days...

G-Benz · #8 06-20-2007, 09:59 AM

A new intake ram ran my total bill up an additional $300...

gmercoleza · #9 06-20-2007, 10:25 AM

I just checked receipts, and the plug set (including connectors) was purchased from Fastlane on August 7 2006. Anybody know what Fastlane's warranty policy is on these things? Also, in order to determine if they are bad, can I just measure the resistance across the connectors like I can on the wires for the M103?

david s poole · #10 06-20-2007, 10:58 AM

if the connectors below the coils were bad they would cause misfire code to set.much more likely is the maf.

gmercoleza · #11 06-20-2007, 11:04 AM

Quote:

Originally Posted by david s poole

if the connectors below the coils were bad they would cause misfire code to set.much more likely is the maf.

David, you are thinking exactly like I am thinking. Actually I replaced the connectors and wires for my friend (from whom I purchased the car) when he began getting misfire codes just last August. Replacing these along with the plugs resolved that issue. Actually, at the time the codes were being triggered, the car was running fine and you couldn't even "feel" a misfire.

I have been thinking about the MAF, but wouldn't that throw a code as well? Is MAF cleaner actually useful?

gmercoleza · #12 06-20-2007, 11:06 AM

Are there DIY tests for the MAF? I know with some asian cars I have owned in the past (Hyundai, Honda, GEO Metro) you could pull the MAF and perform some tests with a multimeter to verify that it was either out of spec or marginal before spending money on a replacement.

david s poole · #13 06-20-2007, 11:33 AM

with my scanner i can look at the adaptions and at live data from maf in real time.you will need to do same to get any more info BUT i think maf is like a 95% bet.

gmercoleza · #14 06-20-2007, 02:20 PM

Thank you everyone. I think I am going to first inspect the plugs/wires/connectors and then look for leaks of unmetered air through the intake. Afterwards, I will attempt to clean my MAF. If all else fails, I will break down and pick up the $250 MAF.

Anybody know if those $75 brand new units on eBay are any good? The part number through Bosch doesn't appear to be exact, but the sellers say they are for my vehicle. They even look the same. I just hate to ruin a cat or something like that. Any experience with those?

gmercoleza · #15 06-20-2007, 03:55 PM

I stumbled upon this at benzworld: http://www.benzworld.org/forums/w163-m-class/1288255-car-vibrates-idle-hesitant-accelerate-diagnosed-2.html?highlight=clean+maf

Quote:

Originally Posted by benzworld.org

The best (MBZ) way to check a MAF is with key-on, engine-off voltage. Specs are .980v-1.030v, if above or below this, you MAF is bad. The MAF usually goes bad after you replace the air filter, especially if you have not replaced it in a while

Does anybody know if this test sounds valid? Where exactly are the voltage measurements to be taken? I'd really prefer to test my MAF before messing with and potentially destroying an otherwise healthy component.