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  #1  
Old 10-04-2003, 02:24 PM
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Join Date: May 1999
Posts: 34
What sensor needs replacing?

I have an 89 300CE w/ 192k miles. The problem I'm having is that when the car first starts it runs fine, but within a few minutes runs poorly (hesitates on acceleration/poor pick-up and draws near max vacuum) until it warms to proper operational temp. (just under 80 on the guage), at which point it runs fine again.

What should I replace to fix this problem? Is it something with a "cold-start" injector? a bad computer? or just a sensor?

The problem is not as much of a problem in summer (warmer temp.s outside = faster time to operational temp.), and I used to just "warm-up" the car last winter to avoid the symptoms, but I don't have that option anymore, I so would like to avoid this, now that the weather is turning colder.

Thanks to all, in advance, for your help.
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85 300E euro-spec., twin-turbo AMG aero kit
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  #2  
Old 10-04-2003, 06:55 PM
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Location: Gainesville FL
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Would you like a list of parts by order of risk of failure or list price?

If you wish to throw parts at it I'm not much help. If you wish to fix the car read the DIY post about evaluating engine controls. Learn how to electrically monitor your fuel mixture and learn what duty cycle codes mean. Hundreds of posts on the subject.
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Continental Imports
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  #3  
Old 10-05-2003, 10:06 AM
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Join Date: May 1999
Posts: 34
My apologies...

I had read on engines stalling (in the DIY and previous posts), but when mine is warm (or cold for that matter) it doesn't stall, nor does it have the check engine light on. This is what I gleaned were the symptoms in the DIY you mentioned. I will go out and buy a Sears meter and try to do some readings, but my symptoms seem a bit different than what I've read.

Do I just want to throw parts at it? Well, if it was a simple fix that was a common problem, sure. lol. But, yes, I'd also like to know/understand what is going on.

To add clarification to the symptoms...
Car runs fine at all throttle positions when first started and when up to operational temp. (just under 80C). The problem comes in after a minute or two of running and the car hesitates while accelerating, has no problem at idle (at any time). While accelerating the car pulls good up to about 2.5-3k rpm then "bogs" (loses power/accelerates poorly) and gauge shows max. vacuum. If I back off the throttle a bit (to maybe 2/3 of where I happen to be) the engine will pull strong again, temporarily, then bog again. This leaves me "pumping" the throttle to accelerate at a decent/moderate rate. Again, once up to operational temp., the engine idles, accelerates, etc. fine.

Thanks for the input, I will get the meter. Any other thoughts though? Anyone?

Thanks in advance.
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  #4  
Old 10-05-2003, 11:10 AM
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Join Date: Oct 2002
Location: Toronto, Canada
Posts: 700
similar problem here

I had a similar problem with my 85 190E, but, it seems to have fixed itself. I had this happen only after driving in the rain, so my guess is that something got wet, and caused this to happen, probably a short.

Normally when something like this happens, I unplug the O2, of course, this will only have an effect when the car is actually warm, since the O2 does not provide any readings until it warms up, so it is not a part of the equation. However, I once had this problem happen to me on the road and since the O2 plug is within hands reach, I would unplug it and see if there is any difference or not.

This time, when the cold weather kicked in, and after driving in the rain, my car started to hesitate about a minute after a cold start in the morning, it would hesitate, for about two minutes, and then everything went back to normal. It just happened this past week, and just as I was getting ready to take a look at the problem, coming back after school, the problem dissapeared and has not come back since. My guess that this is one of the electrical gremilins or something on its way out, I'll find out soon enough.

xp
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  #5  
Old 10-05-2003, 12:14 PM
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Location: Soperton, Ga. USA
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quoted by xp190
Quote:
electrical gremilins or something on its way out, I'll find out soon enough.
Unfortunately, you are probably right. The unfortunate part is that if there is moisture in there then you can count that something like a electrical connection or a connection to ground is corroding.
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  #6  
Old 10-05-2003, 01:19 PM
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My approach on your symptoms as with most diagnostics is to understand what is supposed to happen and monitor the condition looking for pieces that are deficient and fit my hypothesis of how that part doing what the test results show causes the events as they unfold.

In the simplest of terms I would wish to know if fuel mixture, spark quality, or various timing elements were the cause.

A fuel explanation could be as simple as this: A rich mixture facilitates cold starting but overwhelms the warm-up phase. As lambda takes over the fuel system mixture is compensated for and again runs OK.

Some set of events of this nature or of individual nature (cylinder to cylinder) will be involved if mixture is involved with your problem. Basic mixture, improper fuel pressure control, air flow plate base centering, fuel distributor base settings, injector flow problems all can mix to form variations of the problem.

I would remove the aircleaner and have someone start the senario you have described. As the car starts to run bad slightly push the air flap down or lightly pull up. By doing this one can make quick evaluation of whether fuel is the cause of the problem. Doing such causes the base mixture to be changed up and down. Single cylinders with flow problems can be corrected by adding more fuel to all. The rich ones do fine untill some point where it they start dropping because of a rich mixture.

Use your knowledge of what causes what to change the situation untill the general cause is detected. They use simialr technique to zero in with further testing. The above test can specify or eliminate fuel from the equation in a few minutes with no tools.

Just remember that since you have never done this your judgement will be poor. Everyone owning a K-jet car should learn this evaluation technique by observing the general reaction and more specifically the electronic reaction on a closed loop situation on a functioning car.
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