Other than the typical symptons of a dirty MAF connection, what else does it affect?
The reason I ask is cause I think I may have a bad MAF and not just a dirty connection. Same with the CAS??
For example, I get a code on the ECU for the CAS and MAF despite cleaning the connectors and applying di-electric grease; however, the normal symptoms of a bad MAF & CAS are not present. It doesn't cut out or limit the revs, what it does is run really bad.
It idles now at 850-1000 in park. When in gear the idle drops to 600-700. But it is a harsh idle, not smooth and I was wondering if perhaps this could be a result of an actual bad MAF and/or CAS sensor.
just wondering.............
MAF and CAS question?
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elwesso
- Posts: 30810
- Joined: Sun Feb 23, 2003 4:52 pm
- Car: 94 Infiniti Q45t 5 spd
2007 BMW M Coupe
2007 Infiniti G35 S 6MT - Location: Indiana
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The circuit to the CAS or MAF have to be completely shot in order to go into limp home mode. However, if the comptuer doesnt get adequate signal from the CAS it will throw a code, but it will NOT go into full limp mode (rev limiting).,..
I think that you nailed it, with the dirty connections. When the CAS doesnt work it relies on the sub CAS (or something like that) that isnt nearly as accurate.
I think that you nailed it, with the dirty connections. When the CAS doesnt work it relies on the sub CAS (or something like that) that isnt nearly as accurate.
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Q45tech
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- Car: 1990 Q45 342,400 miles 22 years ownership with original engine
1995 G20t 5 speed 334,000 miles 16" 2002 wheels - 205/50/16 Sr20ve vvl
Understand the CAS is the master clock for ecu. The cylinder must fire in a narrow range say 15-40 degrees before TDC depending on load [air density in cylinder] and injectors must open as soon as the exhaust valve is closed.
The ECU compares its counting of the 360 pulses with the 2 ZEROS [wider slots in both 90 degree and 1 degree circuits which use seperate electronics for redundantcy] that denote the starting point.
We have seen a few CAS that after 10 years get dirty inside and may obscure a few of the 1 degree slots causing a lack of pulse but the ecu compares both pulse trains.
At 1800 rpm thats 30 rps or 360 x 30= 10,800 pulse per second and 120 of the broad 90 degree pulses to check against.
Now being off time 2-5 degrees won't have much effect except at WOT or cruise [gas mileage].
http://www.picotech.com/auto/w....html
New designs have both a crank and cam angle sensor as a triple check.
The point is if you see both waveforms and there are few or no drops outs, the idle will be fine as the problems tend to show a very high rpms.
Since the CAS is adjustable the EXACTNESS of setting it to 15 degrees in CRITICALLY IMPORTANT! Every degree your are OFF with the timing light translates to the ecu being OFF 1 degree.
Chain stretch retards the CAS [and the cams since the CAS is attached to the drivers exhausr cam].
A perfectionist would check timing every 2 years [30k], hardly ever done so the CAS creeps towards retard by about a degree every 50k.
The important thing is that the sprark fire in the correct position of the piston [the cam positions just play with air amounts and are only significant at high rpms above the 5500 rpm range].
Peak torque is achieved when 66-70% of the fuel is burned at a 15-17 degree AFTER TDC.........function of rod leverage angle vs peak pressure..........too soon burning and the pistion is driven straight down wearing out the crank bearings fast, too late and the pressure has dissapated.
You read the MAF voltage at idle [1.2 volts], cruise [1.8] and WOT 4.0-4.4] at 6500 rpm.
Really impossible to diagnose these items without a Consult [ precision recording data monitors] or just simple substitution with brand new parts...........on EBAY you can just be buying other people's problems........they may or may not know.
The ECU compares its counting of the 360 pulses with the 2 ZEROS [wider slots in both 90 degree and 1 degree circuits which use seperate electronics for redundantcy] that denote the starting point.
We have seen a few CAS that after 10 years get dirty inside and may obscure a few of the 1 degree slots causing a lack of pulse but the ecu compares both pulse trains.
At 1800 rpm thats 30 rps or 360 x 30= 10,800 pulse per second and 120 of the broad 90 degree pulses to check against.
Now being off time 2-5 degrees won't have much effect except at WOT or cruise [gas mileage].
http://www.picotech.com/auto/w....html
New designs have both a crank and cam angle sensor as a triple check.
The point is if you see both waveforms and there are few or no drops outs, the idle will be fine as the problems tend to show a very high rpms.
Since the CAS is adjustable the EXACTNESS of setting it to 15 degrees in CRITICALLY IMPORTANT! Every degree your are OFF with the timing light translates to the ecu being OFF 1 degree.
Chain stretch retards the CAS [and the cams since the CAS is attached to the drivers exhausr cam].
A perfectionist would check timing every 2 years [30k], hardly ever done so the CAS creeps towards retard by about a degree every 50k.
The important thing is that the sprark fire in the correct position of the piston [the cam positions just play with air amounts and are only significant at high rpms above the 5500 rpm range].
Peak torque is achieved when 66-70% of the fuel is burned at a 15-17 degree AFTER TDC.........function of rod leverage angle vs peak pressure..........too soon burning and the pistion is driven straight down wearing out the crank bearings fast, too late and the pressure has dissapated.
You read the MAF voltage at idle [1.2 volts], cruise [1.8] and WOT 4.0-4.4] at 6500 rpm.
Really impossible to diagnose these items without a Consult [ precision recording data monitors] or just simple substitution with brand new parts...........on EBAY you can just be buying other people's problems........they may or may not know.
Wow!! That is detailed.
Well Q45tech, I know you probably didn't want to hear this, but my car is coming to T3. I will just have to set up an appointment. I guess that is how it works.
I just don't know what is wrong with her. You guys are the best so, that is where she goes.
It is not in full limp mode now. Today it is not even throwing the codes. Yesterday, I got a engine temp code, knock sensor, ignition circuit, MAF, and CAS. Now all I get is ignition circuit. ECU is weird!!
I split the damn hose next to the IAC in the back of the plenum last night. The vacuum leak is phenomenal. So I am getting a new one today and then taking her in.
Well Q45tech, I know you probably didn't want to hear this, but my car is coming to T3. I will just have to set up an appointment. I guess that is how it works.
I just don't know what is wrong with her. You guys are the best so, that is where she goes.
It is not in full limp mode now. Today it is not even throwing the codes. Yesterday, I got a engine temp code, knock sensor, ignition circuit, MAF, and CAS. Now all I get is ignition circuit. ECU is weird!!
I split the damn hose next to the IAC in the back of the plenum last night. The vacuum leak is phenomenal. So I am getting a new one today and then taking her in.