QuestionJosh: thank you for your complete response. 2 Air Mass Sensors were from Caliber Motors (factory dealer) & both new units caused even more hesitation during warm up period. I assume now that old Air Mass Sensor was hiding problem. Is there a fuel/air mixture that is set by computer? I also previously replaced notorious wiring harness problem (deteriorated causing possible shorts). Car is about 50K, but was showing this hesitation problem during warm engine since I purchased at about 34K.
As you indicated, I am experiencing problem on transmission side on jerking between gear shifts (722.5 tranny), and suspect this may be frustrating diagnosing the "hesitation" feeling. I am informed & am in process of changing B2 Piston & sleeve to correct this well known problem as well.
Would you know how many oxygen sensors there are & their locations. I don't know how to test sensors. Can you advise on how to check compression? I've tried spraying engine w/ starter fluid and noticed no rpm surge.
Thank you for your help.
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The text above is a follow-up to ...
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Josh: I own a 1993 Benz 300SE, in line 6 M104 engine. I've had a stuttering/acceleration problem for years. Have changed the fuel filter, knock sensor, and recently the air mass sensor which did not completely eliminate the problem. When I replaced the air mass sensor recently though, the cold start up got worse & hesitated a bit more. I've a Baum Tester & it shows no fault codes for the engine. Could this be a problem with the oxygen sensors, or the fuel/air mixture. The original Air Mass Sensor did not stutter when cold, but the 2 new ones I've had installed both had the cold start hesitation problem. Original problem of sluggishness on takeoff, even when warm, still has not been completely elimated. Thank you for your help.
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From what you are describing, this symptom can be caused by a multitude of different problems. First off, is the new mass air sensor MB OEM replacement part or an aftermarket. Reason I ask is that many aftermarket air mass sensors do not solve problems or tend to add new ones for some reason.
As far as other causes...I hate to give you a laundry list but here are some things to consider:
The O2 sensors can be a big factor and will not always trip a code when they are faulty. You would need to look up a service manual and get the proper voltage specs for the sensors and test them with a volt meter.
You should test your fuel pressure to make sure that the pump and pressure regulator are maintaining correct fuel pressure as this is another common cause for this type of problem.
Worst case scenario, you could have internal engine problems such as bent valves or lack of compression due to worn piston rings. There are a couple other of possible internal engine problems but you can rule them all out with a simple compression test. I can help you with that if you are unsure how to perform it...it is pretty simple.
One other problem I have seen alot of is vacuum leaks. Vacuum leaks in the drivetrain can cause all kinds of crazy symptoms. The easy way to diagnose it quickly is to start the engine and let it warm up. Once it is at normal operating temperature, spray some carb cleaner around the engine bay and see if the engine begins to rev up on it's own. If so, then you have a vacuum leak and you will be able to locate it fairly easily.
You can also check to see if the cat convertors are clogged up. That can be a potential cause as well.
The last problem I have seen even though it is rare, is a transmission problem. Sometimes,warn out transmissions can cause symptoms similar to what you are talking about. The trans will sometimes start in 3rd gear or so, making it seem that the car is very low on power and sluggish when in actuality, it is taking off in the wrong gear. If you want to rule that problem out, simply put your shifter into the 2nd gear position and take off from there and see if your acceleration rate changes.
I didn't mean to write you a book here, but there are a lot of things that can contribute to a problem like that. Depending on how comfortable you are with working on cars, this is usually a job for a certified MB tech...DON'T take it to an independent shop as they will usually misdiagnose MB and wind up costing you a bundle.
You should get a service manual for this vehicle, that will help with your diagnosis. Good luck and let me know if I can help with anything else.
AnswerTo check engine compression, you will need to purchase a compression gauge (usually under $40 at any parts store). Remove one sprak plug at a time and screw the compr. testor in it's place. Make sure to remove the fuse to the fuel injection system before you test. Then crank the motor for just a couple seconds then turn off. Your compression gauge should read between 120 & 150psi (+-10). Do this on each cylinder and that will tell you if all are good or identify your weaker cylinders.
As far as the O2 sensors, the sensors are screwed in directly to the exhaust pipes BEFORE the cat convertor. There is at least one and usually two of them. Some MB's even have 3 or 4. They are easy to spot though. You will most likely want to have a trained tech inspect the sensors though.
Since you sound like you are repairing the transmission right now, I would hold off on any further engine diagnosis until the trans is fixed and operating properly. I am sure you know since you are doing it, but make sure to clean out all the passage ways of the valve body as well.
Let me know how it is once the trans problem is corrected and we can go from there.
