Air Condition control unit - ECU
- Thread starter Arvid
- Start date
Yes,sounds logic.
As I've read on forums that the control unit will raise engine rpm when engaging AC ? I'm still battling the everlasting erratic idling on my engine and just realised that when turning the AC totally off the engine will idle just fine. Turning it back on the engine rpm will rise to 1600-1700rpm. This is only present in cold weather.
There must be a connection here but I'm not sure where to begin.
As I've read on forums that the control unit will raise engine rpm when engaging AC ? I'm still battling the everlasting erratic idling on my engine and just realised that when turning the AC totally off the engine will idle just fine. Turning it back on the engine rpm will rise to 1600-1700rpm. This is only present in cold weather.
There must be a connection here but I'm not sure where to begin.
Oneball
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On BMWs of a similar era the AC control unit just sends a signal to the engine ECU that the AC is either on or off and the engine ECU adjusts the idle speed.
Is your AC actually blowing cold and does the compressor clutch engage? If it’s not working and there’s no resistance from the compressor maybe that’s the reason for the big idle change.
Is your AC actually blowing cold and does the compressor clutch engage? If it’s not working and there’s no resistance from the compressor maybe that’s the reason for the big idle change.
It does blow cold and was serviced last year. I've had this problem for some years and thought many times to have solved it. But sadly not. It doesn't happen every time but more often than not. It was only by chance that I turned off the AC right after I started the car and realised that it had an impact on the problem. Since then I have found many similar problems online on several makes so it's not unuasual.
Thought I would air it here and se if anyone has experienced same problem.
Thought I would air it here and se if anyone has experienced same problem.
I agree and I had them all changed a few years ago on pure suspicion. Maybe I should check them again for peace of mind. Again,the problem is solely in cold weather - typically when it creeps down under 5 dgr.C. I suspect the cold start function is there even when it's a bit hotter outside - say 10-15 dgr.C. But then all is much better and it idles in a much more normal way.
Does the cold start function in different stages or is it an on/off thing ? Suspect it regulates fuel/air at a more aggresively when it's really cold and it's there the problem lies. It probably also regulates the aux air valves as they are proportional after voltage input.
Does the cold start function in different stages or is it an on/off thing ? Suspect it regulates fuel/air at a more aggresively when it's really cold and it's there the problem lies. It probably also regulates the aux air valves as they are proportional after voltage input.
Hi,
When you turn the A/C on the A/C unit sends a signal to both ECUs so they slightly enrich the mixture, possibly raise RPM when engine cold (not sure).
The cold temperature enrichment is defined by a map with the engine temperature defining how rich must be the mixture. Above some temperature like 50C and after some delay the management goes to the closed loop mode with the richness at 1.0. So a gas analyser won't help much because they are usually made for a tight range of richness around 1.0 while a cold start is REALLY rich (easily 1.2-1.3, my QP4 v8 was running 1.3 just after start-up)
As already said: check both pairs of temperature sensors (I had both air sensors dead on my QP4). Use ohm-meter and the sensors spec, don't just compare sensors. Or compare all 4 sensors (they are almost identical).
But there is another aspect: the A/C clutch is a HUGE electrical consumer (I think 20-30A) so if there are loose contacts in the system it may put down the battery which was emptied by the start-up (if the battery isn't fresh).
There are actually many factors that may make the engine hesitate with the A/C on. Clogged injectors may be an issue. Or a worn idle regulator (try to disconnect one of them, try both one by one).
Alexis
Hi Alexis,
Thank you for good advice.
I am tempted to buy new idle regulators and see if it makes any difference. But they are very expensive so I might remove the O-ring gaskets and install new ones instead. They seem fine and still soft but may not seal properly. The solenoids regulates very even and smooth as tested with regulated voltage.
Both the air temp sensors and water temp sensors were changed two-three years ago. I have a set of new ones and will compare the old to the new. I will also check the AC clutch and connections.
I am more and more certain that the problem is to much air applied upon cold start. As you say the AC unit will enrich the mixture and if engine gets slightly more air - maybe through worn seals in idle regulator - the result will be an abnormally high idle.
Earlier I tried disconnecting the idle regulators and the engine still runs fine - although at a low rpm,700-800. When connected again and engine warm the idle is stable at 1000 rpm. Same on your car Alexis ?
Thank you for good advice.
I am tempted to buy new idle regulators and see if it makes any difference. But they are very expensive so I might remove the O-ring gaskets and install new ones instead. They seem fine and still soft but may not seal properly. The solenoids regulates very even and smooth as tested with regulated voltage.
Both the air temp sensors and water temp sensors were changed two-three years ago. I have a set of new ones and will compare the old to the new. I will also check the AC clutch and connections.
I am more and more certain that the problem is to much air applied upon cold start. As you say the AC unit will enrich the mixture and if engine gets slightly more air - maybe through worn seals in idle regulator - the result will be an abnormally high idle.
Earlier I tried disconnecting the idle regulators and the engine still runs fine - although at a low rpm,700-800. When connected again and engine warm the idle is stable at 1000 rpm. Same on your car Alexis ?
Well I don't have the QP4 any more but I don't remember having that much RPM increase with A/C.
If you disconnect the regulators RPM should fall somewhere to 800rpm when engine hot. Cold it may stop.
1700rpm is definitely too much for an idle especially with the A/C on load.
Issues are difficult to find because you have 2 identical ECUs each controlling a kind of 4cyl engine. They don't talk to each other so they could act against each other and this can lead to weird consequences. That's why I suggested to disconnect one of regulators: one remaining should be enough.
But I'd like first to be sure about the "1700rpm" statement. RPM gauges are not precise.
What do you mean by "erratic idling" ? Do you have any problem engine hot or warm ?
Is the engine able to idle when hot on 4 cylinders (disconnecting 2 on each bank) ?
These regulators are not expensive (may be 50e), they are the same as on Delta HF and many Fiat/Lancia cars that had the 4cyl Lancia engine (1.6,1.8,2.0), in 90s.
If you disconnect the regulators RPM should fall somewhere to 800rpm when engine hot. Cold it may stop.
1700rpm is definitely too much for an idle especially with the A/C on load.
Issues are difficult to find because you have 2 identical ECUs each controlling a kind of 4cyl engine. They don't talk to each other so they could act against each other and this can lead to weird consequences. That's why I suggested to disconnect one of regulators: one remaining should be enough.
But I'd like first to be sure about the "1700rpm" statement. RPM gauges are not precise.
What do you mean by "erratic idling" ? Do you have any problem engine hot or warm ?
Is the engine able to idle when hot on 4 cylinders (disconnecting 2 on each bank) ?
These regulators are not expensive (may be 50e), they are the same as on Delta HF and many Fiat/Lancia cars that had the 4cyl Lancia engine (1.6,1.8,2.0), in 90s.
I will do the test with just one regulator connected and see what happens. The erratic idle comes when AC is engaged and the engine has run for a few minutes with temp maybe 50 C. It will then start to fluctuate from approx. 1200 to 1600 rpm - up and down for many minutes. Before this - when totally cold - it will run at a steady 1600-1700 rpm.
If I leave it to idle with AC on it will eventually stop fluctuating and settle at normal 1000 rpm when turning 60-70 C. From here all is normal. If I start it cold with AC off it will run steady at idle but still to high I think - approx. 1200 rpm. It might be normal as I have nothing to compare with but I think maybe 1000-1100 rpm would be more normal for enriched cold start. That is why I suspect that it gets extra air somewhere.
Good news that the idle regulators are found on other makes and are fairly priced. From Maserati they are not at about 200-250 GBP. I will search for them and see what I find.
If I leave it to idle with AC on it will eventually stop fluctuating and settle at normal 1000 rpm when turning 60-70 C. From here all is normal. If I start it cold with AC off it will run steady at idle but still to high I think - approx. 1200 rpm. It might be normal as I have nothing to compare with but I think maybe 1000-1100 rpm would be more normal for enriched cold start. That is why I suspect that it gets extra air somewhere.
Good news that the idle regulators are found on other makes and are fairly priced. From Maserati they are not at about 200-250 GBP. I will search for them and see what I find.
Thanks for the precise description.
Your problem is probably an incorrect setting of the throttle: it's too opened. Or there is a leak in the intake plenum. In fact your idle RPM is not regulated, it just by accident sets about where it should be. Actually the v8 should idle very low, 850 rpm I think, may be 800.
Do you have the Otto or EVO version ? I'm not sure intake plenums are the same of both. On Otto the plenum did not have gasket on the back side. But if EVO had about the same plenum as 3200 then there could be a gasket, it's known to leak on 3200.
There are also gaskets between the plenum and the heads, many times they are incorrectly installed.
Note that the engines sucks a huge amount of air, so it should be an important leak that you'd hear, a slightly leaking o-ring won't be enough.
The other option: on the throttle body there should be a screw to adjust its minimal opening. On a new car this screw is plumbed. But many (most of ?) mechanics (given their fantastic level of incompetence) play with this screw in hope to resolve problems they don't understand.
Find this screw and see if you can close the throttle more. You should check however that throttle does not stick when it's closed, the danger is that if it does and you release gas pedal in high rpm the throttle could be definitely closed by the depression.
Also it'd be better to slightly release the screws of the throttle position sensor before touching the screw, and then fix it again once throttle adjusted. But I'm not sure about this part, I had an automatic v8 and this part is different on this version. It's not dramatic unless you change a lot the closed position.
You can start with a test: remove the intake hoses from the throttles. Start the engine, it'll be very noisy, don't panic. let it warm up until the low idle is reached. Then progressively close both throttles with your hands. Beware it sticks. If the engine dies when you totally close the throttles then gaskets should be OK and it's probably the throttle openning. If it does not die or it's managing to run then you have a leak.
Your problem is probably an incorrect setting of the throttle: it's too opened. Or there is a leak in the intake plenum. In fact your idle RPM is not regulated, it just by accident sets about where it should be. Actually the v8 should idle very low, 850 rpm I think, may be 800.
Do you have the Otto or EVO version ? I'm not sure intake plenums are the same of both. On Otto the plenum did not have gasket on the back side. But if EVO had about the same plenum as 3200 then there could be a gasket, it's known to leak on 3200.
There are also gaskets between the plenum and the heads, many times they are incorrectly installed.
Note that the engines sucks a huge amount of air, so it should be an important leak that you'd hear, a slightly leaking o-ring won't be enough.
The other option: on the throttle body there should be a screw to adjust its minimal opening. On a new car this screw is plumbed. But many (most of ?) mechanics (given their fantastic level of incompetence) play with this screw in hope to resolve problems they don't understand.
Find this screw and see if you can close the throttle more. You should check however that throttle does not stick when it's closed, the danger is that if it does and you release gas pedal in high rpm the throttle could be definitely closed by the depression.
Also it'd be better to slightly release the screws of the throttle position sensor before touching the screw, and then fix it again once throttle adjusted. But I'm not sure about this part, I had an automatic v8 and this part is different on this version. It's not dramatic unless you change a lot the closed position.
You can start with a test: remove the intake hoses from the throttles. Start the engine, it'll be very noisy, don't panic. let it warm up until the low idle is reached. Then progressively close both throttles with your hands. Beware it sticks. If the engine dies when you totally close the throttles then gaskets should be OK and it's probably the throttle openning. If it does not die or it's managing to run then you have a leak.
Very informative. Thank You. I have not checked the throttle plate opening and it might be something there.
When I did last cambelt change I removed the cam covers and intake plenum for refurbishing and new wrinkle finish. I found a squeezed and broken O-ring on one of the intake runners. I was sure I had found the problem but it still acts the same with all new gaskets. And yes,my car is an Evoluzione.
The problem could well be as you describe - a false air leak. I think I have deleted the plenum leak option as I've tried this with starter fluid. No response. Throttle plate opening could be a problem and I will check the stop screw and see if it has been tampered with.
I must confess that I have also tried to swap the throttle potensiometer as I suspected it could be the problem. I have tried adjusting it according to Ford Cosworth forums as they use same potmeter. I have tried different settings but found it to idle best at ca. 0.5 volts. The old potmeter was probably in order and I regret even touching it as I can not find any info from Maserati on how to adjust it correctly. I got a tip from a known German Maserati workshop that these potmeters are self learning and that I should try following procedure : "put on ignition , without running engine , gaspedal to floor for 30 sec., then let it idle for 5 sec. and switch ignition off." It did not change anything and I'm not sure if it was the correct way either. Probably the problem lies elsewhere but in any case tips on how to properly check the potmeter is appreciated.
Best regards,
Arvid
When I did last cambelt change I removed the cam covers and intake plenum for refurbishing and new wrinkle finish. I found a squeezed and broken O-ring on one of the intake runners. I was sure I had found the problem but it still acts the same with all new gaskets. And yes,my car is an Evoluzione.
The problem could well be as you describe - a false air leak. I think I have deleted the plenum leak option as I've tried this with starter fluid. No response. Throttle plate opening could be a problem and I will check the stop screw and see if it has been tampered with.
I must confess that I have also tried to swap the throttle potensiometer as I suspected it could be the problem. I have tried adjusting it according to Ford Cosworth forums as they use same potmeter. I have tried different settings but found it to idle best at ca. 0.5 volts. The old potmeter was probably in order and I regret even touching it as I can not find any info from Maserati on how to adjust it correctly. I got a tip from a known German Maserati workshop that these potmeters are self learning and that I should try following procedure : "put on ignition , without running engine , gaspedal to floor for 30 sec., then let it idle for 5 sec. and switch ignition off." It did not change anything and I'm not sure if it was the correct way either. Probably the problem lies elsewhere but in any case tips on how to properly check the potmeter is appreciated.
Best regards,
Arvid
find the QP4 v6 engine workshop man on the web. Same management, a slightly different firmware but almost the same. The TB pot adjustment must be the same. I think it's self adjusting.
Your pb isn't with the pit because otherwise idle would be oscillating engine hot. All you describe indicates an incapacity of the ECU to lower idle RPM, means an excessive air entry.
Your pb isn't with the pit because otherwise idle would be oscillating engine hot. All you describe indicates an incapacity of the ECU to lower idle RPM, means an excessive air entry.
Hi all,
I finnaly got around to check the QP. Several other cars and the kids 3 mopeds has taken most available time this spring so the work is well overdue. I checked the main points mentioned by "Alpa" and sure I found some faults.
Firstly it seems it does not have any false air leaks. So far so good. Secondly the right side plenum had much stronger vacuum then the left one. This can't be correct. They should be equal I guess ? There is no way to adjust the valves separatly so I guess it has to be done on the balance screw in the middle between the air valves. So I adjusted them equal with a carburettor sync tool. I adjusted the strongest vacuum down to the same value as the weaker left. The last fault I found was when measuring the mV from the TPS potmeter. It clearly was broken or at least not steady as I only got 10mV instead of the approx.155mv. When squeezing on the potmeters halves together it measured ca.150mv. I had a spare pot and it now shows a steady 150-160mV as pr.WSM.
It now idles at approx.800rpm when hot and that's 200rpm lower than before. Final test would be a cold start and hopefully it will keep under 1000rpm. The real cold start with winter temps is not easy to replicate but I'm not sure it will be different than our 8-10 C early mornings.
Regards,
Arvid
I finnaly got around to check the QP. Several other cars and the kids 3 mopeds has taken most available time this spring so the work is well overdue. I checked the main points mentioned by "Alpa" and sure I found some faults.
Firstly it seems it does not have any false air leaks. So far so good. Secondly the right side plenum had much stronger vacuum then the left one. This can't be correct. They should be equal I guess ? There is no way to adjust the valves separatly so I guess it has to be done on the balance screw in the middle between the air valves. So I adjusted them equal with a carburettor sync tool. I adjusted the strongest vacuum down to the same value as the weaker left. The last fault I found was when measuring the mV from the TPS potmeter. It clearly was broken or at least not steady as I only got 10mV instead of the approx.155mv. When squeezing on the potmeters halves together it measured ca.150mv. I had a spare pot and it now shows a steady 150-160mV as pr.WSM.
It now idles at approx.800rpm when hot and that's 200rpm lower than before. Final test would be a cold start and hopefully it will keep under 1000rpm. The real cold start with winter temps is not easy to replicate but I'm not sure it will be different than our 8-10 C early mornings.
Regards,
Arvid
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Fingers crossed. It has been a problem for several years so it would be good to finally have resolved it.