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92 V12 facelift with cats and O2 sensors. I'm looking for a rebuilder for my ECU. Preferably there in the states. Can any of them test the I/O before and after? I had it gone through a few years back, but I believe they only did a visual inspection. The engine idles a poorly with about 15 inches of vacuum. That low vacuum causes a bit of hesitation on acceleration from stop lights. I've gone through all the input sensors and wiring. The check engine light is illuminated but it shows no codes. The manual says this is a symptom of ECU failure. I suspecting is running in open loop. The enrichment pot has no effect.
Might be easier if you want to look in the USA only, to source a second hand one. In the entire world, the only place I know of that can properly fix the ECU for sure, is AJ6 Engineering in the UK.
Autotek parts in California rescued my GEMS6 ECU, as well as another forum member here. AJ6 Engineering should be Option 2, but Autotek will probably be your only other option.
AJ6 does not service the AJ16 ECU, so it was not an option for me.
Like warrjon I would say to check the linkages and adjust the TPS to I believe 0,32V when stationary.
An other thing to adjust is this switch:
when the car is stationary the switch will be pressed, if you adjust it so it will be released after the butterflys has opened than the car doen't have that "dip" when driving away from standstill.
Thanks. I'll give these things another try. I've been through them at least 3 times. Of course if you do it wrong once then chances are good you'll repeat the mistake. Opening the idle switch (disconnecting) increases the timing about 8 degrees or so. Increasing the vacuum signal to the ignition control using a hand pump also increases the timing. Increased timing also increases the idle vacuum. There are no vacuum leaks. I've plugged every opening and been around the manifold with propane multiple times. Increasing the vacuum signal to the ECU with a hand pump has no effect.
Since the ECU has a known problem of showing a CEL with no code readout. Im thinking it may be running on a default map. ???
You can measure it (from Kirby Palm Book), best with oscilloscope (for 16ECU), but give some time O2 sensors to warm up (if You have O2 sensors):
FEEDBACK MONITOR SOCKET: Near the ECU within the trunk is a 4-connector socket on the end of a harness with a dummy plug in it. Two connectors are a black ground wire and a KB wire with battery voltage on it. The other two connectors provide a voltage between 0 and +5V (relative to the black ground wire) that corresponds to the amount of correction the ECU is providing in its attempts to maintain the proper Lambda feedback. The GW wire (pin 4 on the ECU) is for the A bank and the GK wire (pin 10) is for the B bank
While there is a special Lucas tool that plugs into this socket, Roger Bywater points out that an ordinary voltmeter can be used: “On a 6CU the monitors are voltage outputs. On a 16CU the monitor outputs are square waves which can be converted to a voltage reading by placing a 47 μF capacitor across the voltmeter leads.”
Now, trying to make sense of what voltages you find. First off, you need to figure out whether the EFI system is operating in open-loop or closed-loop mode. If the engine is cold, it will be in open-loop mode. If the car has a jumper in a red 2-connector socket at the end of a wire near the ECU and the shifter is in P or N, it will be in open-loop mode at idle. You will need to pull the jumper to get the system into closed loop at idle with the shifter in P or N. If the car is a later model with no jumper near the ECU and is warmed up, it will be in closed-loop mode.
If the ECU is in open-loop mode, both connectors should be reading a rock-solid voltage; this voltage will be 2.5V on the 6CU as well as the 26CU and later ECU’s, but it’s lower on 16CU ECU’s. Walter Petermann explains: “The μP on the 16CU does not put out a 0-5V signal. I just checked it with the scope, and it's about 3.8v max.” Since the openloop voltage is at the halfway point on the range, it will be about 1.9V on a 16CU. Whatever the open-loop voltage is, it is the voltage that indicates the ECU is providing no correction at all to the fuelling; whatever the baseline fuelling map calls for is what the engine is getting.
If the ECU is in closed-loop mode and the system is operating correctly, the voltages should be fluctuating up and down cyclically.
Thank you all for the suggestions. Keep them coming.
The idle switch may be a possibility. It is now adjusted to trip at the first movement of the throttle plate.
The ECU vacuum pipe is in good shape. I tested it by pumping a vacuum at the engine end and measuring it at the controller.
The car has o2 sensors. I haven't tested them. Both were replaced a wile back and have very few hours on them. I forgot about the Kirby o2 sensor test. As I understand it the o2 sensors only trim the fuel at idle and play no roll at cruse speeds. Is this correct? Of course this is where my problem is. I'll see what I get.
Love to have an oscilloscope. I do have an old Windows laptop I could dedicate. Is there a post somewhere here that has scope recommendations?
I ordered a couple wire piercing probes for my Fluke. They will make checking the throttle pot voltage easier. I've checked it numerous times by back probing but I need a third hand.
The reason I am looking hard at the ECU is because it shows the CEL but gives no codes. One of the manuals I read says the ECU is faulty in that situation.
O2 sensors have no function when engine idle, ECU goes with internal map.
When is engine in "D" or "R" mode, then ECU read O2 sensors and trim the fuel according sensors output (+/-, +/-, etc)
The car has o2 sensors. I haven't tested them. Both were replaced a wile back and have very few hours on them. I forgot about the Kirby o2 sensor test. As I understand it the o2 sensors only trim the fuel at idle and play no roll at cruse speeds. Is this correct? Of course this is where my problem is. I'll see what I get.
Love to have an oscilloscope. I do have an old Windows laptop I could dedicate. Is there a post somewhere here that has scope recommendations?
I ordered a couple wire piercing probes for my Fluke. They will make checking the throttle pot voltage easier. I've checked it numerous times by back probing but I need a third hand.
The reason I am looking hard at the ECU is because it shows the CEL but gives no codes. One of the manuals I read says the ECU is faulty in that situation.
I have Fluke leads with sharp pins but I still use sewing pins to pierce wires for testing,
O2 sensors do not work when warming up and at high throttle loads, they do operate at idle and cruising
I have been repairing electronics for over 30 years and most problems end up being simple, ie mechanical or bad connections. Start there and rule everything out.
I would assume the ECU is good until I PROVE it is bad.
O2 sensors have no function when engine idle, ECU goes with internal map.
When is engine in "D" or "R" mode, then ECU read O2 sensors and trim the fuel according sensors output (+/-, +/-, etc)
I have never heard that before. I certainly have not read that anywhere in any of the manuals I've come across.
I always thought that once the car goes closed loop, it continues to pull data from relevant sensors. I haven't noted a situation where a Transmission Sensor would tell the ECU to stop taking oxygen sensor data.
I have never heard that before. I certainly have not read that anywhere in any of the manuals I've come across.
I always thought that once the car goes closed loop, it continues to pull data from relevant sensors. I haven't noted a situation where a Transmission Sensor would tell the ECU to stop taking oxygen sensor data.
Not sure about later V12s such as a '92 but earlier ones....80s vintage HEs....did indeed go into open loop with the transmission in "P" or "N". This was accomplished very simply by a ground input to the ECU from the neutral safety switch at the gearshift. This circuit can be defeated by removing a small jumper wire in the feedback testing harness.
I've been busy and unable to work on the XJS until recently. Those on here who suggested going back through the throttle pot adjustment were correct. Seems I was measuring on the incorrect pair of wires. Measuring using the correct pair. I made it within range just barely before running out of adjustment slot but it performs much better now. Of course I still have the issue with the ECU giving a false CEL. I'll need to decide if it is worth replacing it or disabling the light.
I am now very curious about the idle switch. What is the function. When activated (at idle) it retards the timing 8 to 10 degrees ATDC. Manifold vacuum at idle drops to about 15". If I disconnect it the timing increases to about TDC and vacuum goes to a nice 18". I don't understand why they wanted the idle timing so retarded.
08-31-2018, 04:01 PM
Recommendation for ECU rebuilder
