Discussion
I have a MBE adaptive question. The ECU is fitted to a friend's Tuscan S which is experiencing adaptive problems. Symptom is unstable NB sensor voltage. I have read some excellent posts regarding earths etc. which we are working through.
However as with all problems, opinions differ so I'd just like to run through how the adaptives work.
My understanding is the ECU senses the voltage emitted by the NB sensors and adjusts the fueling depending on the lambda reading.The only input into the process is the NB sensor voltage.
Does manifold pressure play a part in the process. One opinion is because the air box fits poorly, the sensing tube plugged into the back of air box isn't accurately sensing air box (MAP) pressure. Is there an input into the adaptive calculation that monitors the amount of air entering the engine? My understand is no.
Of the speed six motors I have worked on here in Australia (unfortunately no TVR specialists are here), it makes no difference if the air box pressure tube is connected or not.
Any ideas?
However as with all problems, opinions differ so I'd just like to run through how the adaptives work.
My understanding is the ECU senses the voltage emitted by the NB sensors and adjusts the fueling depending on the lambda reading.The only input into the process is the NB sensor voltage.
Does manifold pressure play a part in the process. One opinion is because the air box fits poorly, the sensing tube plugged into the back of air box isn't accurately sensing air box (MAP) pressure. Is there an input into the adaptive calculation that monitors the amount of air entering the engine? My understand is no.
Of the speed six motors I have worked on here in Australia (unfortunately no TVR specialists are here), it makes no difference if the air box pressure tube is connected or not.
Any ideas?
is the voltage on both lambdas fluctuating correctly?Can you explain more about the problem?
Are you maxing out the adaptives?
Basically for a given engine speed the ecu tries to adjust the fuel charge by changing the injection duty cycle. The lambda output will ping pong between 0 and 1 with roughly equal measure of each when the mixture is correct. Over rich the lambda will sit high all the time and vice versa for lean
Seems that very little else matters...at least from a first approximation
No air metering and while there is a map sensor on the back of the airbox facing the bulkhead I don't think it does much
Are you maxing out the adaptives?
Basically for a given engine speed the ecu tries to adjust the fuel charge by changing the injection duty cycle. The lambda output will ping pong between 0 and 1 with roughly equal measure of each when the mixture is correct. Over rich the lambda will sit high all the time and vice versa for lean
Seems that very little else matters...at least from a first approximation
No air metering and while there is a map sensor on the back of the airbox facing the bulkhead I don't think it does much
Hi back..and thanks
Problem is that the voltage sensor output is unstable. The NB voltage floats randomly to either 0.12v or 1.12v, rev the motor and they read properly, then float either way again at idle.
I have compared the actual voltage with a scope to that reported by the MBE..and they match. I have separated the earths, ensured no +ve alternator/battery voltage drops and there is 0v drop across -ve battery, frame and motor. Lambda sensors have been replaced and wires crimped (not soldered) to the plugs.
To me is does smell of an earthing issue. The sensors are a lot more stable with the heater circuit disconnected (4 wire sensors) but the problem just takes longer to occur, so now after 30 minutes of driving the adaptive tables are screwed as opposed to 5 minutes with the heater circuit connected. Isolating the heater and sensor earths makes no difference.
Problem is that the voltage sensor output is unstable. The NB voltage floats randomly to either 0.12v or 1.12v, rev the motor and they read properly, then float either way again at idle.
I have compared the actual voltage with a scope to that reported by the MBE..and they match. I have separated the earths, ensured no +ve alternator/battery voltage drops and there is 0v drop across -ve battery, frame and motor. Lambda sensors have been replaced and wires crimped (not soldered) to the plugs.
To me is does smell of an earthing issue. The sensors are a lot more stable with the heater circuit disconnected (4 wire sensors) but the problem just takes longer to occur, so now after 30 minutes of driving the adaptive tables are screwed as opposed to 5 minutes with the heater circuit connected. Isolating the heater and sensor earths makes no difference.
Pete, I was a non believer and didn't believe it at all when I was told, tried it only as I have a box of spare bits and yep it runs sweet now, instant change. Makes sense as mine was laid up for 2 years before I got it. Did a reset and never looked back.
Matt, NBs, yep had me thinking for a while. I have BBs in the decats for 2 UEGO AFRS and the MBE actually does a really good job, keeping it between 13.8 to 14.7
J
Matt, NBs, yep had me thinking for a while. I have BBs in the decats for 2 UEGO AFRS and the MBE actually does a really good job, keeping it between 13.8 to 14.7
J
Is the battery for the Dallas chip actually in the chip...or is it a separate, replaceable battery in the ECU?
Also, my understanding is the mbe fueling map is simply based on butterfly position (provided by throttle pots) and rpm...so why is there a vacuum tube (map sensor) from the airbox. Our cars seem to idle and run well with this disconnected?
Also, my understanding is the mbe fueling map is simply based on butterfly position (provided by throttle pots) and rpm...so why is there a vacuum tube (map sensor) from the airbox. Our cars seem to idle and run well with this disconnected?
Edited by cinquecento on Thursday 2nd April 02:40
Looks like they could be approaching the end of their lives in terms of data retention according to this.
http://www.datasheet5.com/download/DS1230AB-55/707...
http://www.datasheet5.com/download/DS1230AB-55/707...
Battery backed ffsI think you can easily check if the lithium inside the dallas is at the end of lifetime. Reset adaptives and make some miles to let the ecu create a new map. Within diagnostic software save this map. Then either disconnect battery or ecu itself. Wait a few minutes and reconnect. Now save the map again and compare both. Normally the data in nvram is backed up by the internal lithium, so if this lithium is still ok, the map should also. If the map shows all zero, maybe the lithium is empty.
The TVR engines are mapped by tps not map like most modern engines. The lambda feedback is used to set a dynamic adjustment Map against that stored. The sensors used are titania type which are resistive, so the voltage shown in the software is just a result of the way they've been implemented. Crucially titanias are very fast. The flipping in and out of the "voltage" shows they're working. If the adaptives are sitting there wavering gently somewhere within +/- 10% of zero, then everything is healthy. Mine now sit around -7% since I removed and re sealed my throttle bodies' connection to the cylinder head. As a job it's not difficult and costs nothing in parts and can make a huge difference if it has never been done.
The barometric sensor is used as a measure for air density which is required (together with air intake temperature) to calculate air mass into each cylinder within the ECU and from that the amount of fuel for a required AFR. It will most relevant when driving into the mountains or generally driving at different altitudes or air pressures than the base air pressure that is used for the (base) map for both ignition and fueling.
That is also the reason for it making no difference to the running of the engine whether it is connects to the airbox or whether the sensor hose is not connected to anything.
Would the engine be controlled through air density to sense load as opposed to throttle position angle the take off for the baro sensorshould have been downstream of the throttle plates.
That is also the reason for it making no difference to the running of the engine whether it is connects to the airbox or whether the sensor hose is not connected to anything.
Would the engine be controlled through air density to sense load as opposed to throttle position angle the take off for the baro sensorshould have been downstream of the throttle plates.
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