LH Jetronic Mass Air Sensor
04-05-2002, 05:21 AM
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LH Jetronic Mass Air Sensor
1984 euro s 4.7l 16V auto LH Ver 2.2 M28/22 engine
twin dizzies, no oxygen sensors.
work done:
fuel pressures and flow rates checked and verified.
ecu replaced.
injectors refurbished and flowed.
all sensors and throttle switch checked back to ecu connector.
no air leaks found around inlet tract...butane squirted over it...no rise in tick over.
problems:
to get a stoich mixture, fuel pressure has to be raised to 3.7 bar. at this pressure the mixture adjuster on the side of the hot wire sensor will swing the mixture over quite a range (lean to rich)
at 2 bar (correct fuel pressure) the mixture screw has no effect; CO locked at 0.1%.
if you set fuel pressure at 3.7 to get correct idle mixture (air pump blocked off) the engine sounds much happier (as you'd expect) but it now will not drive with any performance. rich mixture on the move.....as a result of lifting the fuel pressure i guess.
fuel pressure at 2 bar, engine stubbles at idle, and will not rev at all....farts and is generally unhappy.
not sure where to go from here.
i am going to double check every piece of plumbing this w/e to again check for remote air leaks. but my gut feeling is the hot wire sensor (mass air sensor) is faulty. i don't know how to test one of these for correct operation. i will have a play with it on a bench psu and a dvm plus a fan to see if i can make sense of it. i guess it should shove out a variable dc voltage depending on the rate of air flow. i will research on www for data today.
my guess is that is shoves out low volts for low air flow, and higher for high flow rates. the ecu must read this with a a/d converter and adjust fuel injector timing accordingly.
for some reason the ecu is only opening the injectors for a very small time at idle, hence the lean mixture.
(throttle switch is working, checked at ecu)
does the throttle switch cause the ecu to default to a fixed injector pattern for idle? off idle does it then start to follow the injector timing mapping? then at WOT it goes into max injector opening timing?
so does the ecu only really control the timing of the injectors above idle and below WOT? i wish i knew, getting hard facts on these systems is nigh on impossible.
car is going back specalist on monday, ecu is going back to manufacturers for a check....they have had troubles with LH versions higher than my 2.2, but not, so far, with LH version 2.2. maybe i am trusting that the new ecu is ok.....maybe its faulty.....ho hum.
how much of an air leak does it take to cause a permenant lean mixture?
a bit down today.......so is my bank balance!
onward, and upward!
johnb <img src="confused.gif" border="0">
twin dizzies, no oxygen sensors.
work done:
fuel pressures and flow rates checked and verified.
ecu replaced.
injectors refurbished and flowed.
all sensors and throttle switch checked back to ecu connector.
no air leaks found around inlet tract...butane squirted over it...no rise in tick over.
problems:
to get a stoich mixture, fuel pressure has to be raised to 3.7 bar. at this pressure the mixture adjuster on the side of the hot wire sensor will swing the mixture over quite a range (lean to rich)
at 2 bar (correct fuel pressure) the mixture screw has no effect; CO locked at 0.1%.
if you set fuel pressure at 3.7 to get correct idle mixture (air pump blocked off) the engine sounds much happier (as you'd expect) but it now will not drive with any performance. rich mixture on the move.....as a result of lifting the fuel pressure i guess.
fuel pressure at 2 bar, engine stubbles at idle, and will not rev at all....farts and is generally unhappy.
not sure where to go from here.
i am going to double check every piece of plumbing this w/e to again check for remote air leaks. but my gut feeling is the hot wire sensor (mass air sensor) is faulty. i don't know how to test one of these for correct operation. i will have a play with it on a bench psu and a dvm plus a fan to see if i can make sense of it. i guess it should shove out a variable dc voltage depending on the rate of air flow. i will research on www for data today.
my guess is that is shoves out low volts for low air flow, and higher for high flow rates. the ecu must read this with a a/d converter and adjust fuel injector timing accordingly.
for some reason the ecu is only opening the injectors for a very small time at idle, hence the lean mixture.
(throttle switch is working, checked at ecu)
does the throttle switch cause the ecu to default to a fixed injector pattern for idle? off idle does it then start to follow the injector timing mapping? then at WOT it goes into max injector opening timing?
so does the ecu only really control the timing of the injectors above idle and below WOT? i wish i knew, getting hard facts on these systems is nigh on impossible.
car is going back specalist on monday, ecu is going back to manufacturers for a check....they have had troubles with LH versions higher than my 2.2, but not, so far, with LH version 2.2. maybe i am trusting that the new ecu is ok.....maybe its faulty.....ho hum.
how much of an air leak does it take to cause a permenant lean mixture?
a bit down today.......so is my bank balance!
onward, and upward!
johnb <img src="confused.gif" border="0">
04-05-2002, 09:51 AM
#2
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Rennlist Site Sponsor
The idle/WOT switch is a two-part switch unit mounted on the throttle body. It has two functions:
At idle, the idle switch is closed, from just off idle it is open. This tells the ECU that the throttle is closed, so that the ECU can change the mixture for best idle, retard the ignition timing by about 10 deg, and cut the fuel flow off at above 1200 rpm.
The Wide Open Throttle (WOT) switch is open until close to full throttle, at which point it closes. This tells the ECU that the throttle is open, so that it can richen the mixture for best power. If this switch fails, the ECU will compensate anyway at very high air flow rates, but not at low air flow rates.
To test the switches:
Pull the plug from the EZK ECU. Hold the plug horizontal, facing the bare contacts, so that the cable comes in on your right end (up thru '89, reverse for '90 & up). Terminal 1 is on the right bottom, 18 on the left bottom, 19 on right top, 35
on left top.
Idle Switch:
Hook an ohmmeter between terminals 8 and 18. With the throttle closed, there should be very low (less than 10 Ohms)resistance between these two terminals. When the throttle pedal is VERY slightly depressed, the resistance should change to infinite.
WOT Switch:
Hook an ohmmeter between terminals 18 and 26. With the throttle closed, the resistance should be infinite, and should stay infinite until the throttle is almost fully open, at which point it should go to a very low resistance (less than 10 Ohms).
Mass Air Flow Sensor (MAF):
To test the MAF:
Disconnect the plug at the sensor, and hold it horizontally so that the three notches are at the bottom, and the two notches are at the top. Terminal 1 is on the left, terminal 6 on the right.
Hook a voltmeter between terminals 2 and 4. Disconnect the LH plug, and jumper between terminals 17 and 21 (numbering on the LH plug is the same as the EZK plug). There should now be battery voltage at the MAF plug. Reconnect the LH plug.
Hook an ohmmeter between terminals 3 and 5 of the MAF sensor. There should be 3.6 to 4.1 Ohms resistance - this checks the hot wire circuit (the actual sensor). Reconnect the MAF plug.
Remove the LH relay and jumper between terminals 30 and 87 to furnish power to the MAF sensor. Remove the LH plug and hook a voltmeter between terminals 6 and 7 of the plug. There should be 1.6 volts dc. Blow on the MAF sensor wire. The voltage must increase - should vary from 1.6 vdc to 5 vdc.
If the MAF sensor fails, the injection time will be about 3.5 ms below 2000 rpm, and about 6.3 ms above 2000 rpm.
At idle, the idle switch is closed, from just off idle it is open. This tells the ECU that the throttle is closed, so that the ECU can change the mixture for best idle, retard the ignition timing by about 10 deg, and cut the fuel flow off at above 1200 rpm.
The Wide Open Throttle (WOT) switch is open until close to full throttle, at which point it closes. This tells the ECU that the throttle is open, so that it can richen the mixture for best power. If this switch fails, the ECU will compensate anyway at very high air flow rates, but not at low air flow rates.
To test the switches:
Pull the plug from the EZK ECU. Hold the plug horizontal, facing the bare contacts, so that the cable comes in on your right end (up thru '89, reverse for '90 & up). Terminal 1 is on the right bottom, 18 on the left bottom, 19 on right top, 35
on left top.
Idle Switch:
Hook an ohmmeter between terminals 8 and 18. With the throttle closed, there should be very low (less than 10 Ohms)resistance between these two terminals. When the throttle pedal is VERY slightly depressed, the resistance should change to infinite.
WOT Switch:
Hook an ohmmeter between terminals 18 and 26. With the throttle closed, the resistance should be infinite, and should stay infinite until the throttle is almost fully open, at which point it should go to a very low resistance (less than 10 Ohms).
Mass Air Flow Sensor (MAF):
To test the MAF:
Disconnect the plug at the sensor, and hold it horizontally so that the three notches are at the bottom, and the two notches are at the top. Terminal 1 is on the left, terminal 6 on the right.
Hook a voltmeter between terminals 2 and 4. Disconnect the LH plug, and jumper between terminals 17 and 21 (numbering on the LH plug is the same as the EZK plug). There should now be battery voltage at the MAF plug. Reconnect the LH plug.
Hook an ohmmeter between terminals 3 and 5 of the MAF sensor. There should be 3.6 to 4.1 Ohms resistance - this checks the hot wire circuit (the actual sensor). Reconnect the MAF plug.
Remove the LH relay and jumper between terminals 30 and 87 to furnish power to the MAF sensor. Remove the LH plug and hook a voltmeter between terminals 6 and 7 of the plug. There should be 1.6 volts dc. Blow on the MAF sensor wire. The voltage must increase - should vary from 1.6 vdc to 5 vdc.
If the MAF sensor fails, the injection time will be about 3.5 ms below 2000 rpm, and about 6.3 ms above 2000 rpm.
04-08-2002, 05:07 AM
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hi wally
you're a star!
had my maf on the bench over the w/e. powered it up with a bench power supply and tested its output.
both ends blocked off (no air flow) 1.8 V
full air flow ('er indoors's hair drier) 4.85V
full variation between full rates.
checked wire burn off...that works fine. power maf and then splash feed to burn off terminal. wire glows red hot for a split second.
managed to find various graphs for typical mass air meters..they tend to indicate close to zero volts for no air flow, surprised to see 1.8V at no flow. maybe sensor has drifted with age?
car still will not run with any load.
starts fine, mixture wrong at idle (correct fuel pressure)
will not drive.....absolutely no power.
NO AIR LEAKS.....
you're a star!
had my maf on the bench over the w/e. powered it up with a bench power supply and tested its output.
both ends blocked off (no air flow) 1.8 V
full air flow ('er indoors's hair drier) 4.85V
full variation between full rates.
checked wire burn off...that works fine. power maf and then splash feed to burn off terminal. wire glows red hot for a split second.
managed to find various graphs for typical mass air meters..they tend to indicate close to zero volts for no air flow, surprised to see 1.8V at no flow. maybe sensor has drifted with age?
car still will not run with any load.
starts fine, mixture wrong at idle (correct fuel pressure)
will not drive.....absolutely no power.
NO AIR LEAKS.....
11-08-2002, 10:59 AM
#5
Nordschleife Master
Yo JB -
When it comes to electrical testing, I'm about out of place as an American in China. What I do know is where you can get an Euro 84 Mass Air. I sold my old one to 20th Street Auto Parts in PHX. Good as far as I know and it came off my parts car. 18009994911 - Just in case
When it comes to electrical testing, I'm about out of place as an American in China. What I do know is where you can get an Euro 84 Mass Air. I sold my old one to 20th Street Auto Parts in PHX. Good as far as I know and it came off my parts car. 18009994911 - Just in case
11-08-2002, 09:06 PM
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After reading this thread this morning, I decided to wander out to the garage and test the switches on the throttle body of my '85 S2, in an attempt to figure out a long-running problem with a miss under high throttle.
During my testing of the WOT switch, I discovered results just slightly different from what Wally described: With the throttle plate less than wide open I had infinite resistance, but with full throttle, I had 1.5 ohms, not the zero ohms he described. I tried this several times and the had same result each time.
The ignition section of the book describes testing between terminals 12 and 17 of the EZK connector, and also says that the switchover should take place at 2/3 throttle- mine dropped to 1.5 ohms at nearly full travel of the throttle plate...
So...is this switch bad? Does it need to be adjusted? And how in the world do you loosen the screws that hold it on?
Normy!
'85 S2 5 Speed
During my testing of the WOT switch, I discovered results just slightly different from what Wally described: With the throttle plate less than wide open I had infinite resistance, but with full throttle, I had 1.5 ohms, not the zero ohms he described. I tried this several times and the had same result each time.
The ignition section of the book describes testing between terminals 12 and 17 of the EZK connector, and also says that the switchover should take place at 2/3 throttle- mine dropped to 1.5 ohms at nearly full travel of the throttle plate...
So...is this switch bad? Does it need to be adjusted? And how in the world do you loosen the screws that hold it on?
Normy!
'85 S2 5 Speed
11-08-2002, 09:16 PM
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Sounds like the mass flow sensor is working fine.
When my LH brain failed, I purchased a rebuilt unit. After much effort rechecking everything, I concluded that the rebuilt unit also did not work. I sent it back and after 1 month they told me that they re-rebuilt it because it was bad (no cost). Hope to try it this weekend to verify.
There is no better way to determine which component is bad then to send it to someone who can try it in their car. Otherwise you are at the mercy of test/repair-for-money shop. And if they screw-up, you continue to search.
Good luck.
When my LH brain failed, I purchased a rebuilt unit. After much effort rechecking everything, I concluded that the rebuilt unit also did not work. I sent it back and after 1 month they told me that they re-rebuilt it because it was bad (no cost). Hope to try it this weekend to verify.
There is no better way to determine which component is bad then to send it to someone who can try it in their car. Otherwise you are at the mercy of test/repair-for-money shop. And if they screw-up, you continue to search.
Good luck.
