Page 9 (Updated 28-Nov-2008)
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Testing Engine Sensors
- General Overview
- Crank Angle Sensor
- Injectors
- Mass Airflow Sensor MAF
- Knock Sensor KS
- Oxygen Sensor O2
Free Service Manual, Free Download.....see FAVORITE LINKS -page 26- FAVORITE LINKS
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General Overview
Testing Sensors while they're still functional...
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VG30E sensor schematics; 2 pics (hopefully got it right after one year 'studies')
'Some' sensor connector pins and functions listed ...
One good car electronics testing link: http://www.aeswave.com/TechNotes/index1.htm#Tech%20Note%20003
Note: Some issues may be reliably tested only with Nissan Consult tester, like KS Knock Sensor (or DIY bypass resistor, see above). Rent or Buy($180) that tool (autozone.com).
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Note2: As long as engine & ECU wiring connectors, voltage supply and groundings have NOT been serviced (see pages 10, 14 & 15), ...any testings and measurements on a Maxima HAVE NO VALUE!
Empirical tests on a healthy engine, standing:
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1. TPS Throttle position Sensor potentiometer connector off
- No problems with idle or revs
2. TPS Throttle position Sensor switch connector off
- No problems with idle or revs
3. MAF Mass Airflow Sensor connector off
- Revving stutter, max 2200rpm, idle roaming
4. TPS Throttle position Sensor potentiometer connector back on
- No problems with idle or revs but max 2200rpm
5. TPS Throttle position Sensor switch connector back on
- No problems with idle or revs but max 2200rpm
6. IACV air feeder hose disconnection; idling engine dies. With little gas pedal press, engine starts and revs ok; no idle.
7. EGRC temp sensor connector off: High idle, 1500rpm, both fans maximum, warm engine.
8. Engine temp sensor (blk, RH) one pin connector off: no effect on idle
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See TPS Throttle Position Sensor adjustment on end of page 6
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See EGRC and Engine Temp Sensor measurements on page 8
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Crank Angle Sensor
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Crank Angle sensor connector (sensor inside the distributor). Oscilloscope displaying the distorted Crank Angle pulses due to bad grounding.
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TESTING Camshaft pos sensor = Crank angle in VG30E:
Mark distributor and engine block with one clear line for repositioning. Remove the distributor assembly from the engine. Disconnect the ignition wires and coil wire from the distributor. The camshaft position sensor electrical harness should remain connected. Turn the ignition switch ON. Measure voltage between terminals 3, 4 and ground.
With the engine's distributor shaft rotating slowly, voltage should fluctuate between 0 and 5 volts.
The sensor produces 120 degree and one degree pulses (from those connector outputs).
This is how the pulse looks at idle after all the maintenance I have described on page 10:
Clean square wave without spikes or distortion.
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Injectors
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TESTING INJECTOR Signals:
The test above results also in injectors being activated: If ECU is healthy, all injectors will click while rotating the cam sensor, ign on. This sound indicates that a injector winding is ok, and magnetic pulse moves the injector piston. This is not however a quarantee that injector is 100% healthy.
Injector connector. Oscilloscope displaying the Injector pulses.
Mechanical and electrical function can be audio-tested - listen for click. Use long screwdriver as mechanical noise stethoscope: tip on engine, handle on your ear; listen, compare.
"Nissan: do not to use injector cleaner, does not clog. The filter screen on the injector might get clogged; clean in a alcohol - paint brush to wash. The injector resistance (11-14 ohms). Two o-rings and two grommets per injector. (Beck/arnley o-ring kit). Injectors are color coded on the injector (top).
Solenoid core needle acceleration speed is determined with the voltage level and pulse rise-time given to the coil. After up spike from ECU, voltage gradually drops to decelerate [not to hit the end too hard].
Pulse level is 12V: Direct less than 1µs spike up, deep downhill from there, steady 12V ...
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What the oscilloscope tells: voltage increase along length increase; must be the driver FET characteristics, supply voltage variations due to alternator speed change - what?else...
- Voltage top spike variation: 45-80volt spike (80V ? around 2500rpm)...
- Length variation at same speed range: 120µs - 250µs [if zero trigged at 20V level]
- Length variation at same speed range: 400µs - 400µs [if zero trigged at 0V level]
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FSM and injection EF&EC 18:
- ECU self learning, works at least after ECU reset = batt off for 30min.:
"Accordingly, a difference between the basic and theoretical mixture is quantitatively monitored in this system, it is 'then' computed in terms of "fuel injection duration" to automatically compensate for the difference between the two ratios."
- At startup, multiport simultaneous injection is used: all injector fire simultaneously every revolution. Unsuccessful long startup can thus flood and moist plugs, causing further startup problems, even damage CAT.
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MAF Mass Airflow Sensor
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MAF assy and MAF thermistor filament assy inside the intake core.
Most cars use similar arrangement; here is one writeup for cleaning the filaments to get better reading to ECU: http://www.fordscorpio.info/cleanmaf.htm
How MAF works: http://www.autoshop101.com/forms/h34.pdf
How to tune: http://idriders.com/supras/maft/manual.htm
How to repair: http://www.geocities.com/tech4tdi/
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The air heating resistor is controlled via ECU. Its current, thus its temperature varies during different conditions. It heats the airflow passing by. The heat sensing sensor just after this heater, detects the passing airflow temperature and this resulting signal is used in approximating airflow.
Closer view to sensor elements; assembly shield mesh
MAF assy used to have two 'mosquito nets' on both ends; quite propably for storage and handling. They actually also do affect airflow causing flow to be more laminar = steady. This becomes visible on idle, especially with a tuned MAF. But. All nets and wires also reduce flow, and I do already have a filter to weed out mosquitoes, and now use these in my boat windows...
NOTE: Loose particles (or oil) from Air Filter degrade the sensor element, use only high quality filters.
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Testing MAF Signal with Multimeter:
Put a DMM probes into MAF pin b (second from left) & gnd
- Ign on, engine stopped 1V
- Idling, temp up 1-1,7V
- 2500 rpm 1.5-2.1V
- Important: look for linear voltage rise up to 4000rpm.
Note: When measuring MAF output signal, do NOT use MAF gnd-pin as your multimeter ground reference. This may damage output transistor. Multimeter ground should be placed somewhere on chassis. 2k2 Maxima FSM EC-194 says to check for linear voltage rise until 4000rpm.
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MAF Connector:
VGE: A B C D E (F not connected; pin letters stamped at MAF -connector)
E +12V Fusible Link F2 Br
D ECU26 B
C Shield, Ground
B ECU 27 W
A ECU 37 G/OR (not used)
MAF pins for VE-engine (no distributor): B C D E (A&F not connected)
E +12V Fusible Link F2 Br
D ECU26 B
C Shield, Ground
B ECU 27 W
(MAF's are interchangeable)
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Here MAF signal is being measured with a DMM and a oscilloscope...
Check my MAF measured -video click here
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Note that following numbers are for reference only, because:
- Stock MAF's components always vary [my MAF is not stock anymore]
- Charge Voltage varies ... alt, batt, harness condition etc
- Digital multimeter error margins between multimeters is quite wide.
- Airflow: filter etc are different
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MAF Signal; Engine OFF, ACC, 0.3V
1.3V - idle steady
1.67V - 2000rpm steady
2.01V - 3000rpm steady
2.34V - 4000rpm steady
2.54V - 5000rpm steady
4.1V - one push to wide open throttle 6500rpm [stock engine airflow reaches only 2.9V]
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Mass Air Flow MAF sensor connector. Oscilloscope displaying the MAF pulses.
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MAF, input to ECU: MAF gives input signal to ECU, based on airflow. Likewise, TPS gives input on gas pedal action. These are used by ECU to decide how injection is executed. After warm up, O2 sensors will give feedback how well the process went. Typically it didnt go perfectly (MAF signals not right etc) ... and this will be corrected by ECU. An correction table for MAF will be 'built' into the cleared ECU memory.
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Sensor malfunction: If the MAF voltage is below the specified value, the ECM senses a mass airflow sensor malfunction. In this case, the throttle position sensor TPS substitutes for the mass airflow sensor. Although the MAF is malfunctioning, it is possible to start the engine and drive. However, engine speed will not rise more than 2200rpm [ECU safe -mode]. (Some writeups claim that connecting the +5V directly to ECU signal [!NOT +12V], one can bypass the safe mode and 'get home', maybe worth ? trying in emergency)
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New MAF: After swapping or cleaning MAF, resetting ECU is mandatory. Reset = batt cable off for 30minutes.
As new (or cleaned) MAF input differs always from previous settings - this difference is to be reprogrammed to ECU using specific driving pattern [FSM claim]. Gathering this correction info -table into ECU memory, needs to meet all the specific driving situations. You may do the teach-driving if u follow the FSM guide (download, see p.26). Anyways, ECU can and will derive all that correction info by itself. In normal drive it just takes longer to hit those 'patterns' required to fill ECU tables = each required setting condition has to be met. ECU will automatically take care of rebuilding this MAF data, only ECU reset is needed.
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Test-disconnect a suspect MAF.
Disconnecting faulty acting MAF causes more steady idle. Will drop in safe mode = 2k rpm ceiling. See this video http://s271.photobucket.com/albums/j...eglide/Maxima/
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Knock Sensor KS
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Knock Sensor - "Only for Emergencies":
FSM page EF&EC-21 says this: "The retard system by knock sensor KS is designed only for emergencies. The basic ignition timing is pre-programmed within the anti-knocking zone. Consequently the retard system does not operate under normal driving conditions. However, if engine knocking occurs, the knock sensor monitors the condition and the signal is transmitted to the ECM. After receiving it, the ECM retards the ignition timing to avoid the knocking condition."
This emergency technology allows a 'global setup' -engine: whatever poor grade fuel or abuse is given, the electronics find out the abuse and then retard ignition to shield the engine. With good tuneup etc the whole KS system is no really needed, automotive industry 'survived' 100 years without it...
This piezo element detects [if any] ping, sends minuscle signal to ECU --> ECU retards ignition timing. Ping might come from too low octane gas, excess soot causing pre ign in engine. Seldom needed, but maximizes engine life, dealership revenue with unaware drivers...
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Knock sensor connector at the engine compartment left rear:
The knock sensor on VG30E engines is located under the rear exhaust manifold. Resistance to gnd should be around 0.5 MOhm (500,000 Ohms), bad one maybe 5 Mohm (5,000,000ohms).
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What Haynes Comic manual says:
- on VG30E: Disconnect the connector (near rear valve cover, left). Check for continuity on terminals a & b.
- VE30DE: Check for continuity on terminals a & ground.
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KS Bypass:
Engine off, unplug the Knock sensor connector, measure resistance between pins from sensor side [not ECU -side] with DMM... I found out it was "dead". Then I installed into the ECU side connector a 0.5mOhm resistor. Result: reduction in gas consumption. This was 05/2005 ...(Feb-2008: its still working...)
Knock Sensor Wire, sensor hidden there somewhere...
Resistors like this (2x1Mohm =500Kohm resistors)
substitute/bypass the knock sensor.
The KS is unplugged, resistor added on
the ECU side -connector.
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My "dead" Knock Sensor still gives pulse on the scope like this at idle, higher rpm just random spikes, dunno if its ok or not (will tell as the time comes).
This mod really changed my fuel consumption some 15% on highway down to incredible 30mpg [60mph]; means that my KS was bad and that this resistor jippo works. Note: I use minimum 95 octane gasoline always; there is great potential to damage the engine with low grade fuel when KS is off.
My BROKEN Knock Sensor pulses
Go and Buy New Sensor? "Discard any Knock Sensor which has been dropped..." FSM, p. EF&EC330 ... how do you know if your new KS has been dropped?
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If KS bypass is done, ign timing should be checked, gas octane known, engine 'cleaned'. Driving in hot weather, sooty engine, with full load may damage the engine if these conditions are not met.
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Cleaning the engine: Repair shops use 'seafoam' -like cleaners to get all accumulated dirt from inside the engine; pistons, valve stems. 'Cleaning' engine and injectors can be achieved by driving time to time few miles with 1st gear, at 5000rpm. Note that worn engines 300kmiles(?) may have an formed an edge on top of cylinder. In case former user has never been racing the engine, the first time its done, hi rpm's will cause pistons fly against this edge - this will destroy all pistons into bits.
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Oxygen Sensor O2
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Hod does it work? General description, See http://www.wps.com/LPG/o2sensor.html
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Here's couple of very short video clips of my DIY, O2 -Sensor bar graphs - this tells always wassup in the exhaust flow and mixture adjustment:
Engine running, steady 2000rpm... videoclip click here
Moderate accel to 25mph, then coasting... videoclip click here
The flat O2 led bar indicator peeking behind paneling...
From those videos you'll also get visualisation how the O2 sensor is sending its signal.
Signal Profile:
The sensor is 'tuned' to certain oxygen content mixture... 'START': When exhaust gas mixture (oxygen content) goes up, O2 sensor signal jumps to one Volt. This signal causes ECU to decrease injection -and- mixture goes down. Looping: As O2 sensor detects this change, its signal drops to zero ... and now ECU increases injection --->GO TO 'START'
The O2 sensor output signal fluctuates between 0 and 1 Volts. The higher the rpm, the more the signal fluctuation speed.
In essence, mixture is all the time 'sailing' up/down/up/down -course. ECU keeps tuning nozzle pulse, O2 keeps detecting the minuscle combustion process changes in exhaust. This also causes small fluctuation in rpm, and you can hear this this change if you keep engine running, say at steady 1500rpm...
This adjustment is going on always except low idle (the ECU/IACV handles the process according ECU data table.) and full wide open throttle WOT.
Utilization:
O2 sensor is only used when engine is warmed. The ECTS temperature sensor gives input to ECU, and based on this O2 feedback will be used. When engine is cold, O2 signal is not used, but pre programmed ECU data -table is used with TPS throttle position signal [open loop -state].
After warmup, TPS signal is not used in engine control. O2 Oxygen sensor is now giving feedback how well the ingnition is succeeding, and this actual feedback [closed loop -state] decides how ECU controls injection.
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Oxygen sensor [only one exists on VG30E] on the exhaust, exhaust ground strap (RH).
Oxygen sensor connector; engine room view, down the firewall; rear engine support bolt seen beside it.
Faulty O2 sensor may even smtimes cause dashboard Engine Check light to illuminate. .
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Measuring O2 Sensor Resistances (engine off) .
Disconnect the sensor electrical harness. On models with a three-terminal connector, measure resistance between the two outer terminals.
For three-terminal connectors, the resistance should be 5.2-8.2 ohms @ 77°F (25°C). For four-terminal connectors, the resistance should be 2.3-4.3 ohms @ 77°F (25°C).
FSM does not help at all in the 'four' pins...
Schema foldout has B, W, & G/B -wires from the O2 sensor (R/B in VE), where B=gnd, W=signal to ECU, G/B(R/B)=+12V
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O2 Heated Oxygen Sensor test:
(ECU leds see p.15, Test using ECU test procedures, see p.21.)
A. 1. Start and warmup engine
2. Run engine 2000rpm, 2min.
3. Keep engine at 2000rpm. Check ECU GREEN led goes on/off
If NOT, cont
B. 1. Stop engine
2. Disconnect O2 connector under hood
--->From ECU side connector, the viewing pins seen are as follows: cba
3. Turn ign sw ON
4. Check for batt voltage between terminal a and gnd; If NOT, Disconnect "Engine Cont" -fuse. Check continuity between pin a and the fuse; If NOT, repair
C. 1. Turn ign sw off
2. Check for continuity between c and ground
If NOT, repair groundings
If OK, cont to D
D. 1. Take batt -terminal off
2. Check continuity between ECU 29 and pin b; If NOT, repair
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Before re-installing connector back, install droplets contact grease on connector pins with a 'toothpick'.
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Note: O2 sensor wiring is shielded to keep this ridiculously anemic signal from distortion... This shield has to be grounded from computer side.
Check page 15 for the ECU pins, Groundings on page 10 .
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Bypassing the O2 Sensor:
If the O2 is found faulty and causes problems, its connector can be disconnected until replacement is done.
Another way is to bypass ECTS sensor (see page 3. ) and cause ECU to see always 'cold engine' -signal. ---> Disconnect ECTS connector, install a bypass resistor on the harness side of the connector ' to simulate a cold engine (just like on KS, see above).
In both cases no harm is done, engine control just drops to open loop -state, and uses TPS in engine control. The only result is light gas consumption increase...
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General Articles From ; OXYGEN SENSOR FAILURES
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volksparts.com: "The normal aging process will eventually cause the oxygen sensor to fail. However, the sensor, may also fail prematurely if it becomes contaminated with lead from leaded gasoline, phosphorous from excessive oil consumption, or silicone from internal coolant leaks or using silicone sprays or gasket sealers on the engine. Environmental factors such as road splash, salt, oil, and dirt can also cause a sensor to fail, as can mechanical stress or mishandling.
The sensor is mounted in the exhaust manifold and generates a voltage signal proportional to the amount of oxygen in the exhaust. The sensing element on 99% of all oxygen sensors in use is a zirconium ceramic bulb coated on both sides with a thin layer of platinum. The outside of the bulb is exposed to the hot exhaust gases, while the inside of the bulb is vented internally through the sensor body or wiring to the outside atmosphere.
A dead sensor will prevent the onboard computer from making the necessary air/fuel corrections, causing the air/fuel mixture to run rich in the "open loop" mode f operation, resulting in much higher fuel consumption and emissions.
An additional consequence of an O2 sensor failure may be damage to the catalytic converter. A rich operating condition causes the converter to run hotter than normal. If the converter gets hot enough, the catalyst substrate inside may actually melt forming a partial or complete blockage. The result can be a drastic drop in highway performance or stalling because of a buildup of backpressure in the exhaust system. ...Keeping the sensor fresh may improve fuel economy as much as 10-15%, to be changed every 100kmiles." See this whole article, voltage levels etc. at: http://www.volksparts.com/o2sensors.htm
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dnd-automotive.com: "Compared to the more common zirconia O2 sensors, titania sensors have three advantages: (1) they don't need an air reference (there is no internal venting to the outside atmosphere to plug up); (2) they have a fast warm-up time (about 15 seconds); and (3) they work at lower exhaust temperatures (they won't cool off at idle and they can be located further downstream from the engine or used with turbochargers). You'll find titania O2 sensors in '86 and later Nissan 300ZX and Stanza 4WD wagons, '87 and up Nissan Maxima and Sentra models, and 1986-1/2 and up Nissan D21 trucks." ...for the whole article clic:
http://www.dnd-automotive.com/tuneup/02-sensor.htm
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Detnews: Cracked O2 sensor? Volkswagen AG agreed to pay a $1.1 million fine for failing to fix or notify federal officials about a faulty oxygen sensor that increased pollution from its Golf, Jetta and New Beetle models.
The Environmental Protection Agency said Wednesday it was the largest fine ever imposed for this type of violation. ...
The faulty oxygen sensor was found on 326,000 VW models from 1999 through 2001.... The oxygen sensor on the affected vehicles could crack in cool and damp environments, prompting the "check engine" light to illuminate...
http://www.detnews.com/2005/autosinsider/0506/16/0auto-217280.htm
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.FYI Local Emission Inspection results Jan/06, at 85k miles.
[allowed maximum Emission acceptance limit at right, in brackets]
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-------- 2488rpm --------
CO: 0,00% ------ [0,30%]
O2: 0,01% ------ [5,00%]
HC: 0006ppm - [0100ppm]
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-------- 0926rpm: --------
CO: 0,00% ------ [0,30%]
O2: 0,02% ------ [5,00%]
HC: 0004ppm - [0100ppm]
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Jan/08 at 95kmiles [spark plugs now 30kmiles]
-------- 2534rpm --------
CO: 0,00% ------ [0,30%]
O2: 0,00% ------ [5,00%]
HC: 0024ppm - [0100ppm]
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-------- 0950rpm: --------
CO: 0,00% ------ [0,30%]
O2: 0,00% ------ [5,00%]
HC: 0018ppm - [0100ppm]
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As u can see, tuneup 'pays'. Also driving on low gear 4000rpm for 5-8 miles, time to time, keeps engine clean:
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"God hath made all nations of one blood ... determined times before ... bounds of their habitation; That they should seek the Lord, if haply they might feel after Him, and find Him." Saul the Tarsite
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