Flat spot during acceleration

Hello

During acceleration, flat spot with very short time happen intermittently.
Mainly this happens when accelerating to move a car from stationary condition and no influenced by engine temperature.

Recently I adjusted the rheostat of ECU for hunting problem. Is the flat spot related to the rheostat adjustment ?

I also checked fuel pressure.
When IG key was on without engine run, the pressure was 2.1 Kgf/cm2.  Immediately after, the pressure dropped down to 1.4. 
I did this test repeatedly 5 times within total 5 minutes. The result of the 5th was 2.1 when IG key was on, immediately after, the pressure dropped down to 0.6.
When engine run, the pressure is basically 2.1 Kgf/cm2 which is OK. 

How do you think about the above fuel pressure test result ?     

If you could give me your advice for solution, it would highly appreciated.


Many thanks, 

JUN

Hello,
it is normal if the pressure drops again shortly after the ignition is switched on. When the ignition is on, fuel pressure is applied only briefly to make starting easier.

If the pumps are to continue running, a speed signal is required. This is a security feature
, so that e.g. In the event of an accident, the fuel pump runs when the engine has stopped but the ignition is still on.

Grüße, Guido

Hi JUN,
when you switch off ignition, pressure is allowed to decrease about 10% within some seconds.
Then the system has to hold the pressure for some minutes...

What can be wrong?
- leaky hoses, connectors...
- leaky injector<s> or cold start valve (leaking to the outside or to the engine inlet)
- bad non-return-valve (part of the fuel-pump)
- bad fuel-pressure-regulator.

Regards
Norbert

 

Hallo,

Thank you for your advice.
Ok, I understood that it is normal!

Anyway, I think it will take a long way that D-Jetronic will continuously work perfectly on idling (~~)

Many thanks,

JUN  

Hello Norbert,

Thank you for your advice !!
Ok, I will check one by one..

By the way do you have experience the following ?
Engine run is OK at idling with "N" on automatic. However, when you shift to "D" with applying foot brake, Engine revolution drops a lot with some hunting (up and down).
When shifting back to "N", Engine revolution is OK again.

ATF quantity is OK. Torque converter was replaced with new one last year. 
This symptom occurred time to time and is exiting before.

Every day, idling condition is different ^^.

Norbert or does anyone give me a tip for improvement. 

 
Best Regards,

JUN

Hi JUN,
I had a look at the technical information about the 412.
There is no air or other connection between brake and engine / inlet - no brake booster is installed.
The problem can't be related to the brake.

Regards
Norbert

 

Hi,

pressure drop from 2.1 to 0.6 shortly after Ignition OFF is too fast.

Rheostat on D-Jetronic ECU only affects as long as idle-run contact on throttle switch is closed. Please remove electrical connector on throttle switch and try again.

Hi

Thank you for your information !
I understood there is no relationship between brake and engine control.

I am still wondering why idling condition obviously worsen when shifting "D" only.

Appreciate your usual great advice !!


JUN

Hi Dr-DJet,

Thank you for your advice.

I will disconnect the electrical connector on the throttle switch and see differences.

I think the throttle switch has never been adjusted properly when replaced it with new one during engine overhaul work 2 years ago.
I will try to adjust the throttle switch as well. It looks very difficult for me thought... 

BTW about the fuel pressure, I also think dropping pressure is too much. 
I changed the fuel pressure regulator with new, Fuel pump (3 ports type) replaced with new last year.
While engine is running the fuel pressure keeps 2.1 (some time drop to 1.8 momently)
I better to doubt the regulator and pump ?

I attached pics of the engine room. If you could let me know something wrong with the hose routine etc. it would be highly appreciated.
I am wondering if the blow-by gas hoses are correct routine.

Notes: I have disconnected the electrical connector from the air temperature sensor. And the hose between the diaphragm on the throttle valve body and AAV was disconnected. This is temporally solution to get better idling.

Thank you in advance for your support.

JUN