Alfa Romeo Forums banner

1 - 19 of 19 Posts

·
Registered
Joined
·
17 Posts
Discussion Starter #1
Hello! I've got a problem with rev. limit on my Alfa 75 3.0. When the temperature rises up to 80+ the rev. limit starts to be about 4700 rpm, which is not a norm for this engine. OR maybe it is not actually a rev. limit but a certain restriction somehow connected with a "hot engine"... Maybe someone has already come across such a problem or even knows a remedy? Thank you!
 

·
Registered
Joined
·
11 Posts
change your main bearings of you crankshaft, the BDP sensor losses "contact" and the comp cuts the engine.
had the same problem with my TS, new bearings fixed it.
 

·
Premium Member
Joined
·
13,993 Posts
If your 75 has Bosch L-Jetronic then there are two rev limiters, one in the fuel ECU and one in the ignition ECU. The fuel cut-off is at about 5800 and the ignition cut-off is at about 6500. They are both usually very stable. The fuel cut-off can be adjusted by changing a resistor. The ignition cut-off is controlled by a crystal oscillator and is difficult to adjust. Your problem is most likely in the ignition system or fuel pressure.
 

·
Registered
Joined
·
17 Posts
Discussion Starter #5
R106 ecu l-jet

I tried to change the R106, but it came to nothing lead :hang:
Help!
monitor the pressure gauge >3Bar
AFR 0.75-0.9
what else should I look?
 

·
Registered
Joined
·
17 Posts
Discussion Starter #7 (Edited)
3.0 America ECU

Thanks! You write that there are other ways of shifting the rev limit. Tom Zat changed several resistors in the Pandora's box to not only shift the rev limit but to change the ignition advance curve and the fuel air ratio.
I have two ECU's (fuel/ignition).
 

·
Registered
Joined
·
17 Posts
Discussion Starter #8 (Edited)
I repeat my question.
I've got a problem with rev. limit on my Alfa 75 3.0. When the temperature rises up to 80+ the rev. limit starts to be about 4700 rpm
Limits even lower on the 1st gear at full throttle 1700-2500 by sharp pressing on the accelerator.
my resistance measurements
P106 = 68K
P103 = 52K
r704 = 4,8k
r306 = 272k
P407 = 1,7k
P621 = 187k
(readings without dismantling)directly in the circuit board.
I see that someone has dismantled some of the resistances (R704 did not touch), so please inform about the standard values.
R106 lowered to 52k. What tseho be?
Please correct if wrong!
 

·
Premium Member
Joined
·
13,993 Posts
Tom Zat changed several resistors in the Pandora's box to not only shift the rev limit but to change the ignition advance curve and the fuel air ratio.
The ignition advance and ignition rev limit are in the ignition computer and are controlled by a crystal oscillator. Tom Zat changed the crystals.

You can look at two different ECU's with the same part number and you will find that some of the resistors are different. Bosch tuned the ecu's by selecting resistor values.
 

·
Registered
Joined
·
17 Posts
Discussion Starter #10
I fully agree with you!
I just can not decide which of the control units are not working correctly. Ignition or fuel supply control unit .
 

·
Premium Member
Joined
·
13,993 Posts
If you jumper the input to the output of your ignition computer you will have max advance all the time and no ignition rev limit.
 

·
Premium Member
Joined
·
13,993 Posts
Sorry, do not quite understand "If you jumper"?
Make an electrical connection between the input and the output.
 

·
Registered
Joined
·
243 Posts
are you reading the tach in dashboard? are you sure it is reading correctly? in my experience it is more likely that the ECUs are working correctly - but the tach is giving a false reading. i.e. hitting rev limiter at a real 5800 rpm but the tach shows 4700 when it is happening.
check rpm w an external tach.
andy
 

·
Registered
Joined
·
17 Posts
Discussion Starter #17
Thank you! You mean that I need to connect input and output, but I don't quiet see how to do it. If it is possible, can you draw a scheme (diagram)?
 

·
Premium Member
Joined
·
13,993 Posts
I no longer have a Milano manual as I gave it to the guy who bought my Verde. Try to find a schematic diagram for the ignition computer and find the terminal that is connected to the distributor and the terminal that connects to the coil module. They are the ones that should be "jumpered" to eliminate the rev limiter.
 
1 - 19 of 19 Posts
Top