Okay…my CTS is working for warm up mode…when going to idle something is wrong…very rough and lumpy…as though it is not in touch with the ECU…how do I check my ECu?
Which terminal ? etc. etc.
Thanks, Sloth
Would be great if you mentioned what model year and engine you had…
Also, is the check engine light on, and if it is, do you know what codes have come up.
It seems something is wrong when the car is warmed up and goes into closed loop. Again, working with the zero amount of information you provided, it is likely to be the oxygen sensor, MAF, Coolant Temp Sensor (which you claim works on warm up mode…), or the TPS.
I’d look at the oxygen sensors. How old are they? Might they be ready for replacement?
If you want to check the pins on your ECU, and you happen to drive a later model car, it is by the passengers feet (assuming this is a LHD car in the US). Water does get down there on some model years, and has been known to corrode the pins over time. When you unplug the two connectors, check for green corrosion stains. Even if you see none, make sure to give it a spray down with some electrical contact cleaner spray before plugging it back in.
If you have an older XJS, the ECU may be elsewhere.
Please make sure to add the details on your car in a signature so you don’t have to do it again.
Hi Veekay
Thanks for the return…'89 xjs (12)…the CTS is new , it starts right away and warms for five minutes
then goes to a gasping mode (either demanding air or fuel). When I apply throttle it smooths out and runs fine.
Remove foot and lumpy idle again. Booth sides butterflys cleaned and set to .005 clearance.
If CTS is talking to ECU for warm-up it should be talking for idle mode. I’m confused. (Note: my ECU is in the trunk, away from any moisture etc.etc.)
June 12If you want to check the pins on your ECU, and you happen to drive a later model car, it is by the passengers feet (assuming this is a LHD car in the US). Water does get down there on some model years, and has been known to corrode the pins over time. When you unplug the two connectors, check for green corrosion stains. Even if you see none, make sure to give it a spray down with some electrical contact cleaner spray before plugging it back in.
If you have an older XJS, the ECU may be elsewhere.
Please make sure to add the details on your car in a signature so you don’t have to do it again.
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Hi Veekay
I will try to k
Have you searched for a vacuum leak?
I am no expert on the v12 engines, but it does appear that you could have a vacuum leak, or some sensor that isn’t functioning that is only read once the engine goes closed loop.
I had mentioned this earlier, but did you pull a spark plug to see if you’re running rich or not?
Easy rich/lean test: trip the full throttle enrichment switch mounted on the throttle capstan.
If it livens up it’s lean. If it chokes down it’s rich.
Plugs will tell way more.
And if your engine is idling perfect fuel mixture, wouldn’t tripping the full throttle switch at idle make it run rich??
Greg, yep. Tripping it will cause a lean engine to run better, a rich one to go way too rich.
I tried tripping mine at idle, no difference. Is that good?
Not good in my opinion. This is a substantial enrichment. There should be a noticeable change in the idle.
Test the switch, or simply short the connectors and see if you get a response. Alternately, determine the ECU pin ( 5 in my 16CU I think? ) and see if you get a ground there BUT, you can only do this test with the car off. Which results in a ground at the ECU on the same pin, but from the vacuuum full throttle switch. Disconnect that then test to see if the FTS gives the ECU a ground. I’ll confirm the pin when I get home.
Getting enrichment all the time is bad. Not getting enrichment on full throttle could be terrible.
thanks, I will test it out.
I always wondered, why IS there a full throttle switch? Doesn’t the ECU get readings from the TPS, so it knows if it’s full throttle already. ?
I always wondered, why IS there a full throttle switch? Doesn’t the ECU get readings from the TPS, so it knows if it’s full throttle already. ?
The full throttle switch when activated causes an extra amount of fueling to the engine. I believe 10 %. It is suppose to make sure your engine has extra fuel (above and beyond the TPS fueling) so the heads/pistons don’t overheat and your engine doesn’t blow up. SD Faircloth
Apparently the Jaguar design engineers felt so strongly about preventing melted pistons that they included a redundant Throttle Control Valve (JLM473) in addition to the Throttle Switch (C35509) to enrich mixture at full throttle. Electrically either of these two Full Load Switches will do the job. Being a “belts and suspenders” guy myself I appreciate this design and tested both of them on my two V12 equipped Jaguars when I worked on their engine bays to make sure that they worked properly at full throttle.
Paul
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Good idea. I’ve also got the vacuum assisted one. I’ll check both this weekend with my volt/ohm meter.
The throttle switch puts out ?? when closed.
Vacuum throttle control valve should close circuit at full throttle, between 2 - 5 inHg. (Recommended 4 inHG)
Greg, the two switches are wired in parallel, so triggering either one (or both) gives the same result.
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OK…to be more current on my erratic idle…I have just used the spray starter fluid test (with fire equipment at hand) there seems to be no vacuum leak and the idle problem is still present…
I now turn to the ECU for inspection…what terminal controls the idle message ??? and who is recommended to send my ECU unit for check-up.???
Thanks to All
Sloth
The ECU depends a lot on vacuum and CTS. When i disconnected those one at a time and saw no difference in idle, I suspected ECU and was right.
AJ6 engineering is where I sent mine. Three month turn around though.
Full throttle enrichment switch testing method that I used when sorting a problem in my 86 with a 16cu ECU.
Checking pin 5 with the car off should show a ground. If not vac switch is bad.
Disconnect the vacuum switch electrical connectors and pin 5 should NOT show a ground. This confirms the wiring from the switches to the ECU.
With the vac switch still disconnected, trip the micro-switch and pin 5 should show a ground. This confirms the micro-switch functions.
Reconnect the ecu and start the car. Now, at idle, reconnect the vac switch.
No change in idle confirms the vac switch opens.