190E lazy throttle reponse - PeachParts Mercedes-Benz Forum

pentoman · #1 07-16-2007, 05:51 AM

I have a 16v, on which over the last month I have reconditioned the top end.
See http://www.benzworld.org/forums/w201-190e-d-class/1321311-head-coming-off-tuning.html
for all the pics. The compression had been low. I had 4 new valves and reseated all valves.It's all back together now and better than ever. The torque low down is much improved, 3500rpm flat spot gone, and throttle response much better.

However, the throttle response is still rather lazy. It takes between 0.5s - 1 second from hitting WOT to the engine giving full acceleration. It just isn't that response to the pedal. This happens at high and low revs, but worse at low revs. Any idea what can cause this? The mixture is spot-on. I tried unplugging the EHA... it was not very different, perhaps a little bit worse. The other thing I've checked is that the air flow meter plate is sitting in the right position and is not sticking. I don't know what else causes poor throttle response? The performance is fine when it arrives!

saumil · #2 07-17-2007, 12:10 AM

Disconnect the battery for about 10 mins first to see if it is not just a computer reset that is needed.

Can you check intake vaccum ? Should be 16-22 inch Hg at idle. If the vaccum is low, could be a clog in the exhaust, most likely the catalytic converter.

Also you can measure the current at the EHA. If you just have the ignition switch in run position, there should be between 10-20 ma thru the EHA. At idle the current will be lower. Now if you blip the accelerator, you should get greater than 15 ma thru the EHA. Note that the current must be measured in a series circuit not in a parallel circuit like measuring voltage. This test should be performed when the car is cold.

Does your car have a EGR valve ? Check the valve and the vaccum that operates the valve. At idle, the vaccum that controls this valve should be less than 2 inch Hg, i.e. the valve must be closed. At about 2000 rpm, the vaccum should be between 4 and 6 inch Hg, enough to open the valve. Malfunction in this valve's operation will cause problems at idle as well as rough acceleration. Make sure the car is cold when testing this.

Check the air sensor's potentiometer. The car is off. The resistance between the center and one of the neighbouring pin should be about 1 to 2K when the plate is all the way to the top. Now if you gradually press the plate, the resistance should gradually increase, there should be no jumps greater than 2K. If it is smooth, check the voltage across the same two terminals. Now the car is on (and you have to also connect the sensor's cable back to the sensor, can use some alligator clips). At idle, the voltage is between 0.5 and 1V. Now as you gradually depress the gas pedal, the voltage should smoothly increase, there should be no erratic voltage change.

Check the coolant temp sensor also. This sensor sends engine temp info to the fuel computer (as well as the ignition computer). When the engine temp is cold (about 20 degc), the resistance should be between 2.5 and 3.5K. When the engine temp reaches 80 degC, the resistance should drop to about 250-350 ohms, a factor of 8 to 10. Check the sensor's cable, if the cables are broken, the car will go into a limp mode.

saumil · #3 07-17-2007, 12:11 AM

I am not familiar with your car but am assuming you have the same system as my 87, 260E.

pentoman · #4 07-17-2007, 10:33 AM

It's broadly the same system yes. I think on a 16v there is more to the ignition computer - it's got an intake air temperature sensor and stuff. But pretty similar.

Thanks for the help I'll look into vacuum problems The previous owner had all vacuum lines replaced but there could still be a problem.

How does the vacuum affect the running of the engine, what does it do?

Russell

saumil · #5 07-17-2007, 11:59 AM

In a simple view, vaccum is produced in the intake manifold if the engine is operating correctly. Thus vaccum at the intake manifold can be a good tool to diagnose engine problems including leaky valves, timing problems and exhaust problems. When the exhaust system is not working properly, then the vaccum level (I will only refer to the intake vaccum) at idle drops dramatically, for e.g. if there is a clog, the vaccum would be much lower than 16 inch Hg. And normally, the vaccum drops some amount as you acclerate, because the throttle opening lets the air into the intake. But if the exhaust is clogged (or if EGR is always open, it should be closed at idle), it would dive down to zero.

The vaccum created at the manifold is also used to control other vaccum driven elements in the car such as your a/c vent control flaps, automatic door locks, brake booster etc.

On a diesel engine, there is normally a seperate vaccum pump because a diesel engine does not produce enough vaccum for anything useful.

And vaccum is one of the easiest way to control mechanical elements that are widely distributed across the car.

In short, vaccum levels at the intake manifold are critical for diagnosis as well as function of the car. If you dont have a mytivac, it is worthwhile to have and it has a little manual with it which lists all the engine functions you can diagnose with it, pretty handy tool.

pentoman · #6 07-18-2007, 05:50 AM

OK thanks.

So is the amount of vacuum used as an indication of the load on the engine? Why is it there on these cars, when there's also in air flow meter which would measure the load on the engine? Are the two combined?

There is for example a vacuum pipe to the ignition control module (I believe your car doesn't have this). Is this so the ignition module knows the load on the engine and can adjust ignition timing accordingly?

There's also vacuum lines from the sensor block (top front of engine), the bottom of the intake, the throttle body. Why so many? What's it all for?

pentoman · #7 07-26-2007, 05:34 AM

Yep I've tested continuity to coolant temp sensor :/

Today we're testing the ignition timing. My Dad reckons it is off when he had a quick look with a timing light yesterday. However we're being hampered in testing this because the area with the TDC markings on is damaged - half the readings are missing

. The stud (for some sensor I can't remember which) is there but the TDC marking missing, it looks like it's shattered away!

How could the ignition timing be off, and what could cause that which I could investigate in the meantime?

bpaz_ph · #8 07-26-2007, 06:59 AM

Did you replace your fuel filter?

pentoman · #9 08-02-2007, 09:07 AM

Ignition timing was on spec.

No I haven't replaced fuel filter. My Dad reckoned the fuel filter would be unlikely to cause this sort of problem (makes sense... the problem would most likely be there the whole time, or be worse at higher revs/fuel flow). Maybe I should replace it but I'm averse to randomly throwing money at a car to attempt to fix it.....

crhenkel · #10 08-03-2007, 11:09 AM

bump

pentoman · #11 10-08-2007, 07:54 AM

OK well with everything checked and verified, I took a deep breath and went for tweaking the EHA adjustment. As I understand, this varies the chamber pressure (lower pressure is supposed to be 0.4bar lower?). I wasn't measuring the chamber pressures so it was a bit hit-and-miss.

It's currently set to be richer than initially. This has improved the engine response greatly. However it's still not perfect with a very slight delay and without a crisp throttle response.

Russell

pentoman · #12 04-11-2008, 08:51 AM

Well I was probably over-eager to judge there (and maybe again now!). Went richer again and problem got worse. Right I thought, I'm sick of this, let's go wild.

So the EHA is now adjusted it hugely CCW (about 3/8 turn) - from what I read this means leaner.
And what do you know, the low down torque is massively improved and I am certain of this. It doesn't have the same throttle lag/delay either but can occasionally mildly hesitate.

Further adjustment required. I can't work out why it's better this way? Perhaps my fuel pressure regulator is actually the problem.