Hi friends,

First off, I am so grateful for the helpful knowledge and advice you contribute to these forums, whether via thread replies, articles, manuals, photos, or diagrams. I understand how valuable your time is and I really appreciate you offering your expertise to fellow Benz owners in need.

So here's the situation:
I've got a '93 300e 2.8 that starts right up every time (even without waiting a few seconds for other components to engage). Then the RPMs drop quickly and the engine stalls. The engine will shake rather vigorously when the RPMs fall to 200 or 100 as it tries to stay alive.

If I try to give it gas, I can keep it going, but barely. The motor speed is not reflected by the position of the accelerator pedal or the attached lever under the hood. For example, if the pedal is depressed rapidly and/or all the way, the RPMs rise slowly or not at all, with sudden bursts every 5 seconds or so. Once the pedal is left alone, the engine stumbles and dies.

This breakdown into limp mode occurred when, out of the blue, the gas pedal stopped working and fell to floor by itself! When it came back up, I pumped it several times, with no effect. I surrendered, slowed to a crawl, and the the engine went to sleep. I was able to "hop" a few more miles to my destination, but now can't drive home (90 miles).

I have searched for many hours, but was not able to find anyone with the same exact problem. If you have any ideas, I could sure use a hand troubleshooting. Though I've done some small repairs, when it comes to the mechanics of the computerized FI engine and the synergy that is required to make my Benz perform properly, I've got so much to learn.

Thank you kindly,
Casey

Well maybe it's something so simple (hopefully it is) that everyone's ignoring the post. Else they're just as stumped as I am. After all, it could probably be 1 of a few dozen things, or a combination. But since it happened so suddenly, maybe it can be fixed quickly.

The accel pedal and linkage seem normal (though still strange what happened at the outset).
It could probably use a new harness, but I found no bare wires, they're all pretty well wrapped.

Has anyone had success in making a code retrieval device? If I can get some solid info on how to then I'll put one together and pull the codes.

I'll update later.

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'93 300E 2.8, 188K

Subscribed.

I have the exact same issue with the '89 M103.

I have cycled the fuel pumps with the ignition three times in the hope to pin down a situation where the pressure has bled down............to no avail. An additional 9 seconds with the pumps does nothing to alleviate the stall.

I can get by it by starting the engine with no pedal and then instantly punching it through the dead spot once it catches. It's difficult, however............the timing must be perfect or is stalls. I have a sense that it is stalling rich as it's more difficult to get it to start if it stalls.

Redline. If that does not work, try new injectors.

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Eugene

10 E63 AMG
93 300te 4matic
07 BMW X3
14 Ford F-150 Fx2

Next tank.

I'm not quite grasping why the injectors would be the issue if it instantly starts...........but then immediately stalls..........??

The injectors, being mechanical, would prevent a start if they were the culprit...........???

Seems to get fuel just fine for one second............then loses it.

We'll see what the redline does. Goes in tomorrow night.

How old is the OVP relay. Try a known good one before you go much further.

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Jim

Ovp will solve nothing unfortunately. Brian, you look at the injectors as either working or not. That's not how they are.

Imagine 3 are partially clogged shut, 2 are stuck partially open, and one is fine. On the first cold start, you have 2 cylinders that are flooded, 3 that have minimal spray pattern, and one that is firing properly. The car will fire, but cannot overcome the 2 dead cylinders because the other three may or may not have fired. By the second crank you have cleared the other 2 cylinders and the car now has enough to fire and stay started.

Sometimes it will start but you get the "chug chug chug" before it actually catches.

The reason injectors are so hard to diagnose is because they still "work". The symptoms only really show on a cold engine.

Because there are so many ways that an injector can fail is why there is never a consistent symptom from owner to owner. Some get clogged, some weep, etc.

I hope my explanation makes sense. I can tell you from experience. I changed nearly every part on my car that cold have had anything to do with cold start issues and the injectors where the ones that really made the difference.

Having a proper ignition system is a must as well.

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Eugene

10 E63 AMG
93 300te 4matic
07 BMW X3
14 Ford F-150 Fx2

Yes, makes perfect sense.

Might also explain the rough idle that it has...........no good reason for that as well.

I'll head in that direction if the Redline doesn't significantly improve it. I'll also do plugs and cap and rotor just to feel good about it.

Brian,
That does sound very similar, especially the part where you mention "punching through the dead spot." I haven't had any trouble starting mine though. It fires up with ease again and again, then the RPMs fall as if there was never any fuel to begin with. It struggles for a second or two around 200 RPMs, as I mentioned, with the roughest idle I've ever seen, before stalling.

Eugene,
That explanation does make sense, thanks. In my case, however, I don't think the injectors are really an issue. Otherwise, how would it be able to start so well every time? And why would the failure occur so suddenly?

Another guy recommended looking at the OVP. Probably worth checking for any moisture/corrosion at least.

Casey

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'93 300E 2.8, 188K

start with fuel pressure if you got a Schrader valve at fuel line it is easy to check.

@ Xanadu: what you think is "starting" is just on or two cylinders firing causing a spike in the rpms. Your car never really started. It took me 4 years to reach that conclusion.

The punching through the bad spot is your car simply your car running on one or 2 cylinders until it clears all of the extra fuel that flooded out the other ones. To be able to get 1-2 cylinders to push the rest of the engine requires extra throttle. Not enough and it dies, to much and you flood it.

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Eugene

10 E63 AMG
93 300te 4matic
07 BMW X3
14 Ford F-150 Fx2

Retrieved codes with homemade pulse reader.

From pin #8 (HFM FI): codes 13 and 45.
- 13 (O2 sensor): Mixture too lean or too rich.
- 45: Fuel safety shut-off of EA or CC active.

From pin #14 (CC/ISC): codes 5, 7 and 11.
- 5: Stop lamp switch. Not a big deal.
- 7: Message from CC/ISC module faulty or reception from ECM faulty.
- 11: Fuel safety shut-off signal to ECM.

Hmmm...might need help interpreting/pinpointing 45, 7 and 11.

I checked the OVP. Fuse was good and part # is 540 67 45 (new version).

Also looked at the harness tag. FD (manufacture date) is 24.02.98. I'll be damned, apparently it was replaced by 1st owner.

Will be back on the case in the morning.

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'93 300E 2.8, 188K

Last few days have been crazy and I didn't get a chance to post my update from Saturday. Made a little headway, but not enough to drive home unfortunately.

I looked over the engine compartment very carefully and everything looked fine, for whatever that's worth—no obvious leaks or bare wires. I wasn't able to do any tests as I didn't have any specific tools, but things like the EGR valve and the purge valve appeared normal, well connected. I removed the cross-over air intake pipe and MAF, cleaned some of the gunk out (what I could without carb cleaner) and wiped the air intake valve as well.

I put the pieces back together tightly. When I started it up, to my surprise, it continued idling. It did not stall...until about 4 minutes later. I started it again and it kept running until I had to shut it off and leave.

This is what is happening now:
- The engine hunts between 500 and 1000 RPMs.
- When stepping on the accelerator pedal, there is a quick "sip" of air coming from the throttle area and the RPMs decrease to ~200. The engine struggles, but it stays alive and goes back to hunting.

It sounds, literally, like there's an air or vacuum leak. Might the air intake valve be sticking? Maybe the grime has gotten in the way of it's proper movement.

Anyway, that's what I've got so far. I WILL get to the bottom of this.

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'93 300E 2.8, 188K

If you've looked at this post previously, you've probably forgotten about it by now. Nevertheless, I want to keep you up to date.

My car has been resting 90 miles from where I live and due to work and other items on the schedule, it's been difficult to get away for a few days in a row to continue working on the case.

But I'm with it again this weekend and today I spent some time scoping out the area around the throttle body and intake manifold a little more closely, and thus getting more familiar with what's there. Thanks to my buddy who had shared some close-ups, I was able to locate my 104's vacuum cap (haha you can laugh if you want), one side of which had disintegrated. It probably wasn't doing its job. Not sure how that factors into the strange idling and acceleration response problems I've been having, but seemss like it's another piece to the puzzle.

Here's what happened when I turned the key:
- Started up no problem and ran fine for 9 minutes, then...
- Idle became a little whacky as it hunted between ~600 and 1000 RPMs
- RPMs would drop below 500 off and on, and engine would struggle to stay running when that happened
- It would then "boost itself back up" where it would continue hunting
- If accel pedal was pressed while RPMs were on the rise, engine would respond and RPMs would level out around 700 for about 10 seconds after the pedal was released
- If pedal was pressed while RPMs were falling or while engine was struggling (< 500), there would be no immediate response, but RPMs would surge a few seconds later
- Whenever engine was trying to avoid conking out (RPMs < 500) a "rolling or putt putting" sound could be heard from the exhaust pipes
- The air sucking noise I mentioned before could still be heard if the pedal was floored quickly

Plan for tomorrow:
* Erase and pull remaining/new codes from DTC
* Clean throttle intake with spray solvent
* Clean MAF sensor with other spray formula
* Install new F8DC4 spark plugs

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'93 300E 2.8, 188K

Made a new vacuum cap out of some air tubing. It fit incredibly well, but this in no way helped the cause.

Erased DTC memory and checked codes again. I now have a new one, code 4 from pin #8.
Here's what the manual reads:
4 ... 009 ... Hot film MAF sensor (B2/5) air flow implausibly high
4 ... 010 ... Hot film MAF sensor (B2/5) open circuit

On the bright side, if it counts as one, I'm no longer getting codes 5 and 7 on pin #14.

I did clean the MAF sensor and the throttle intake with special sprays, but this did not accomplish any improvement either. Maybe those CRC solvents are useless.

I did not end up installing the new plugs because worn plugs don't seem to be the problem, so I'll wait on those.

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'93 300E 2.8, 188K