Hesitation on M104 300TE - PeachParts Mercedes-Benz Forum

ytr1903 · #1 08-14-2008, 10:55 AM

Hi Everyone,

My daughter is driving a 1993 M104 300TE. A week or so ago the CEL came on, but the car continued running well, so I didn't jump on the solution. As of a couple of days ago the CEL went out by itself. Yesterday, the car started exhibiting some hesitation issues. Here is an excerpt from an email that my daughter sent to me today, "started today (wed) the wagon is not acting right. when i start going, it takes about 10 seconds to kickinto gear to go. also, when i sit at a red light, the car acts like it is going to die several times and i can hear a rattling under the driver's side. also, it smells like fireworks burning". She has been trained (by yours truly) to observe the problem and report back to me. She is really pretty good at looking at changes in the car's behavior.

The wiring harness was replaced several years ago. I did a search on this subject and the spark plug connectors, the spark plugs and the coils seem to be a recurring theme. Am I on the right track? I will run the codes on the CEL when I get my hands on the car on Monday. I guess the fireworks smell is due to backfiring. Any help is truly appreciated here.

Thanks,
Tom

Ferdman · #2 08-14-2008, 11:59 AM

Tom, my first thought would be the OVP relay since the CEL came on. When the OVP relay craps out the CEL will illuminate, plus the OVP buzzes.

Arthur Dalton · #3 08-14-2008, 12:50 PM

Quote:

Originally Posted by Ferdman

Tom, my first thought would be the OVP relay since the CEL came on. When the OVP relay craps out the CEL will illuminate, plus the OVP buzzes.

I agree with Ferd diagnosis, except the CE lamp activation is seldom lit with a bad OVP..the lamp that lights is more often the ABS lamp b/c the OVP is both ECU and ABS power feed................

jcyuhn · #4 08-14-2008, 01:47 PM

This model won't run if the OVP fails. The fuel and ignition is completely managed by the ECU. No power to the ECU, no start, no run.

Sounds like the ECU has gone into limp-home mode, where it uses a fixed fuel/ignition map rather than taking inputs from the MAF and/or O2 sensor. I expect the codes will be telling.

It's a California car, yes? The 49 state '93s do not have a CEL.

- JimY

Arthur Dalton · #5 08-14-2008, 02:16 PM

He states he has a CE on.....

ytr1903 · #6 08-14-2008, 02:33 PM

I don't know if it is a California car. We bought it from the original owner who lives in Chicago. It definitely has a check engine light, though, and it was definitely on for a few days but went out a day or so before the symptoms occurred. The VIN number is WDBEA92E5PF247343, if that helps.

Thanks for the replies,
Tom

Edit, I APOLOGIZE. Per my daughter, there is no CEL on the instrument cluster. The light that was on was the "exterior lamp failure". I swear that everyday that goes by I get a little more senile.

Tom

Arthur Dalton · #7 08-14-2008, 02:59 PM

federal car.................

Ferdman · #8 08-15-2008, 08:54 AM

Arthur, perhaps the 1993 M104 engines react differently than the 1995 ones. I know that when my parents' 1995 E320 was running poorly, OVP relay was buzzing and the CEL was illuminated I swapped the OVP relay from our 1995 E320 to prove that was the problem.

Arthur Dalton · #9 08-15-2008, 10:10 AM

Fred

The OVP is feed to ECU for both years , which is why it solved the problem.
[All HFM/SFI use OVP feed system where the car will not run w/o OVP sig, unlike the earlier OVP/CIS systems]
The CE lamp on both chassis is Emmissions Module -N/59 and it is the ABS module that is tied to the OVP ECU feed . Which is why our second question is always if the owner sees an ABS light.
Ce lamp is not a common complaint on a bad OVP, ABS lamp is ..that is all I was pointing out.
..and we all know that the OVP gets blamed for everything, but often justifiably so....
If you have a CE lamp, then you go press the button under the hood and get ther codes first.

ytr1903 · #10 08-18-2008, 02:11 PM

I now have the car in my possession. Here is the scoop. The car starts right up and settles to a rough idle. Cold or hot. The ABS light does not come on. I drove it 25 or so miles home from my daughter's house. When given any throttle, the car will "miss" or accelerate poorly. When maintaining a given speed the engine doesn't seem to be missing, but as soon as the throttle is depressed, it starts missing again. I accelerated hard a couple of times and the miss was always there. The car doesn't overheat and the oil pressure is normal and the car will cruise at 75 mph once it finally get there. There is what seems to be an odor of unburned gasoline when accelerating. (My wife followed me home and could smell it)

Thanks,
Tom

Arthur Dalton · #11 08-18-2008, 02:28 PM

Have you done any of the recommendation we have made yet.??????????????????????????????

Do you know if thew OVP is the new style ???

Have you checked the search for Plug connectors ???

ytr1903 · #12 08-19-2008, 08:25 AM

Yes, I have followed the recommendations.

The OVP has 89 7219 000 "Made in Hungary" stamped on one side with another stamp of 170400 stamped on an adjacent side. Consequently, it is not new style or old style but I would guess some sort of aftermarket product.

I ordered 3 spark plug connectors and one coil over the weekend.

Tom

jcyuhn · #13 08-19-2008, 10:16 AM

You really need to build the code reader and pull fault codes from the ECU. Replacing plug connectors is fine, they are a maintenance item. But why the coil?

Based on the description of symptoms you might have an ignition problem, but you might also have a fuel mixture problem. The ECU goes into a default mode if it doesn't like the input from one of the sensors - e.g. the MAF. In this case the ECU is essentially guessing the required fuel injector pulse width. The car runs, but it runs lousy. Best way to diagnose this fault - build the code reader.

- JimY

Arthur Dalton · #14 08-19-2008, 12:43 PM

>

I would start with the coil connectors, but I would also see what plugs are in there while I was there . These 104 HFMs run terrible on Plats....
A coil fault will bring on a code at pin 8 with a led tool.
The reason fuel enters into the diagnosis when plug connectors are bad is b/c the ECU Defaults the Injector pulse @ the offending cyl. to ZERO when the Ignition module detects an ignition misfire .. This is to protect the Cat from raw fuel without ignition. [ Emmissions Mandate]. So , on HMF/SFI systems , there is always no fuel injection signal during a detected ignition misfire.

http://www.peachparts.com/shopforum/showthread.php?t=107630

ytr1903 · #15 08-21-2008, 11:42 AM

Arthur and Jim,

Last night I went over to Radio Shack and got the components for the LED tester. I will assemble it tonight and if the gods are willing I will be able to do the test this evening. I have ordered the proper spark plugs and should have them and the spark plug connectors tomorrow. Thanks so much for your patience. I am keeping my fingers crossed.

Tom