Fuel Pressurization Puzzle - PeachParts Mercedes-Benz Forum

EricSilver · #1 09-23-2003, 05:17 PM

Car: 1989 260E
187,000+ miles

Scenario 1: First Cold Start of the day, or Cold Start After Sitting all Day

Turn key, engine fires up immediately and idles smoothly.
If I immediately begin driving, depressing the accelerator does not produce instantaneous acceleration. It feels as if fuel is only trickling in.

-- HOWEVER --

If I warm up the car for about two minutes, maintaining about 1500-2000 rpm, that fuel starvation feeling does not occur and the car behaves normally.

- - - - - - - - - - - -

Scenario 2: Hot Start After sitting for about 30 minutes
Turn key, engine cranks for about 3 to 5 seconds before firing normally. Idle tends to be lumpy. Higher revs are smooth, but acceleration seems a bit sluggish – again, as if fuel injection is not at peak.

I get the impression that one cylinder is misfiring because the feel and behavior has been so consistent. I know that the fuel/air mixture is a contributing factor but not the whole of the problem. The other potential culprits are:

* Dirty Fuel Injector
* Dirty Fuel Filter
* Faulty O2 Sensor
* Faulty Fuel Accumulator
* Faulty Fuel Pump(s)
* Vacuum leak (I have been experiencing hard shifting lately)
* Faulty Fuel Pump Relay
* Over voltage Relay (It is actually fairly new but since the OVP is
blamed for practically everything else, why not include it here.)

I welcome your good comments.

mike690003 · #2 09-23-2003, 06:13 PM

I have the same problem.

My first start of the day is quick, the car runs great for about 10 minutes. After that it starts to miss and hesitate from a stoplight. The warm stars are hirrible and take 3-5 seconds to start the car, it seems fuel starved. I can not use my A/C because when I stop and try to pull off, my car will hesitate to the point of almost shutting off.

I am lost to why my car does this.

EricSilver · #3 09-24-2003, 06:39 PM

I noticed that the problem decreases significantly when the temperature drops below 70 degrees. The stumbling is there, but softer.

Also, the 2 minute warmup, as I said, helps a lot too.

Duke2.6 · #4 09-24-2003, 07:49 PM

Did you read this thread further down the page?

190e fails start on first try

Duke

RKreutzer · #5 09-24-2003, 07:51 PM

Hi Eric,

While I don't know your car, I would think that the cold start is not yet impacted by the O2 sensor, as that only starts impacting once warm.
So if it has trouble while cold, the cold start valve (if your car has one) is suspicious. Once warmed up, the O2 sensor feeds the EHA and adjusts fuel mix as required.

You haven't given info about the specifics for all the usual suspects you list. How old is the fuel filter, how old the injectors etc. Have they been replaced at the recommended intervals?

I also have trouble with "warm starts" on my car (87 420) when the car has stood anywhere from 1 hour to 5 hours and haven't found a solution for it. I suspect fuel vaporization/fuel distributor problems.

Hope this will get some better experts than me to chime in.

Reinhard Kreutzer

EricSilver · #6 09-27-2003, 12:28 AM

Hi Reinhard,

Cold starts are great. On acceleration immediately after starting, the reaction is sluggish. As I said, if I rev the engin for a minute at 1500-2000 RPM, that sluggishness does not happen.

Once warm, the erratic idle kicks in, which could be O2 sensor related. However, now that the temperature is about 70, the problem is less pronounced. As the weather gets colder, the idle and overall performance greatly improve.

Obviously, some of this related to the fuel/air mixture. I already know I am running lean. And the cooler, denser, more oxygen-rich outside air is helping to compensate for that by apparently burning a limited fuel flow more thoroughly.

The O2 sensor is 4 years old. The (brass) fuel injectors could be original. I have never replaced them. Fuel filter is at least 3 years old. Fuel accumulator and pumps are probably original (I never had to replace them).

I noticed that since I implemented the 2 minute warm-up after each start, subsequent startups have been more immediate, even when the engine is hot. Then again, that could be related to the cooler weather we are experiencing.

DUKE: Saw the thread; sounds remarkbly similar to my problem(s)

RKreutzer · #7 09-27-2003, 11:12 AM

Hi Eric,

Well, my theory is that at that age and milage, many parts start to not perform anymore as they should and the combination of little variations makes for the annoying and hard to find small problems. If the injector seals are leaking a bit (may be more on a cold engine) it might take the warming up period to make them seal better. May be the idle control valve needs cleaning. You can look at the online catalog from FastLane how many parts are involved in fuel injection and fuel delivery.
There is a test for the idle control valve. When pulling off the electric connector, the idle is supposed to go up to 2,000 rpms or so. There is also a lot in previous posts how to test the O2 sensor with a Multimeter, but I don't think in your case the O2 is at fault, as it seems to be working once warm. Cold start valve seems also ok.
Spraying carb cleaner at the injectors might reveal a leak there, but to detect it better, the exhaust emission needs to be read simultaniously.
Did you try injector cleaner? That would be my first action.

BTW, I prefer driving the car right away with low rpms rather than let it rev for 2 minutes at 2000 rpms.

Good luck

Reinhard Kreutzer

EricSilver · #8 10-12-2003, 12:16 PM

Hi Reinhard,

Injector seals were repalced about 2 months ago so I assume they are OK. I agree with you that it is a combinatin of multiple part not working optimally, with electical quirks being either the cause or the symptom -- impossible to tell.

For example, when driving at night with headlights *and* stereo on, the idle speed will occasionally drop really low, causing one or more dash indicator lights to briefly illuminate. In the past week, the Bulb-out light stayed on when this happened, until the car was restarted. (All exterior lights are working.)

The only other time that the engine revs very low is after a cold start; it will idle normally, but once I shift into gear, RPM's drop to about 480-500 for a few seconds before climbing again.

In the light & radio case, the electrical load seems to be the culprit. In the cold start case, the mechanical load of shifting into drive appears to be the case -- unless it is impacting the alternator speed, and output, and thus triggering an electrical disturbace?

WHat I have learned is the sluggish acceleration has nothing to do with the above. In reality, I was (very) low on transmission fluid.