White95Legacy

Thanks people, I made a checklist from all our posts. 1.Verify 12v to injectors is staying on. 2.Verify 12v to TPS, MAF and Coolant sensor is staying on. 3.Check pin 4 of MAF for signal. 4.Disconnect knock sensor and bypass it's wire with 580kohm resistor to ground. 5.Verify pins 2 and 3 of TPS have normal readings. 6.Verify O2 sensor readings are reaching the ECU connector. 7.Verify Coolant Sensor signal is reaching ECU. 8.Use http://legacycentral.org/library/literature/codes.htm green connector trick for engine code tests while driving. All of these tests will be tested before driving, then tested while driving while the hesitation occurs. I came up with a nifty test probe trick, take a sewing needle, put a wire thru the eye, wrap the eye end with gorilla tape to hold the wire on and create a handle, then stab the needle thru a wire you want to test. Just leaves a small hole and allows you to tap into a wire with minimal damage if probing a connector is not an option. We have to take out the engine in a few days to replace the right head gasket cause it's leaking oil, and replace the clutch. Would be the time to replace gaskets and search the intake plenum/PCV/EGR etc for leaks.

MAF pinout: Pin 1 Connects to Batt+ when the main power relay comes on when the ignition is on Pin 2 Connects pin 1 of the TPS and pin 2 of the Coolant Sensor and connects to pin 25 of the ECU Pin 3 Connects to engine ground pin 4 Connects to pin 26 of the ECU, and the shielding jacket around the pin4-pin26 wire connects to pin 54 of the ECU I read the schematic and this appears to be the way the MAF is wired. I'll first check to make sure pin 1 is Batt+ with the multimeter. Then I'll check that pin 3 really is grounded. Pin 2 seems to be either a solid positive or negative charge switched by the ECU so I will investigate that. And pin 4 seems likely to be sending some kind of signal or voltage or current reading.

I looked around the internet and it sounds like all a knock sensor does is notify the ECU that detonation is occurring and the ECU retards the ignition timing. Unless the ECU is cutting fuel pulses to 1% duty cycle for several seconds as a test to somehow diagnose a knock sensor reading malfunction.

I should of described how severely underpulsing the ecu is being in my original post, but read my reply to Numbchux for a better description, it's like 1% duty cycle when it should be like 40% duty cycle. I see tiny pulses, then when the hesitation ends and the engine runs fine the pulses go back to like 40% duty cycle. Pumping the throttle doesn't immediately end the hesitation, so it doesn't feel like a dead spot in the TPS. The hesitation ends several seconds later regardless if the throttle position is changed after hesitation initiates. But i'll try probing the TPS at some point if the MAF checks out fine. Unfortunately my friend doesn't want to fork out the cash for a new MAF, they run between $100-$250, I see one for $35 but who knows about the quality. I'll try probing stuff near the ECU to let us know if there is a loose wire between the MAF and ECU. I'll closely examine the MAF for an integrated circuit, if it looks too simple then the measurement circuit is probably inside the ECU and the MAF connector can be probed with a simple multimeter, if it has an integrated circuit built into the MAF then the measurement circuit is probably inside the MAF and the integrated circuit sends a digital or analog signal to the ECU, like it says in the last sentence of that Wikipedia paragraph I linked. Or the calibrated signal it talks of is voltage based as you say and not a digital or analog pulsed signal. Here is the Wikipedia link: https://en.wikipedia.org/wiki/Mass_flow_sensor Under section named Hot Wire Sensor (MAF) read paragraph 4, it sounds like what is in this car since the white wire from the MAF to the ECU is shielded. I'll probe all the MAF wires for voltage till I understand, then I'll hook the Oscilloscope up if it doesn't make sense, to see whats hiding in the wire signals. Thank you

Do you mean MAF instead of MAP? Cause the MAF is above the right strut tower, I can't find a MAP anywhere. The fuel pulses cut wayyyy down to like 1% duty cycle during the hesitation, as if the ecu thinks we are coasting downhill with foot completely off the throttle, even if foot has the throttle all the way to the floor. Pulses are 1% when they should be about 10-20-30-40-50-60% duty cycle judging by how far we have our foot on the throttle, then the ecu comes back to life several seconds later and we see pulses the way they should be, 10-20-30-40-50-60% etc. The hesitation comes and goes, happens for about 1-5 seconds at random times, then completely disappears for maybe 5-30 minutes and the engine does it's job perfectly, happens when driving fast and maintaining speed, accelerating from a slow speed, maintaining a slow speed. Feels like a loose wire. Thank you, making a list of what to look for when we feel like playing with his car again. When I get a chance to look at my friends car again we will try this trick with the connectors under the steering column http://legacycentral.org/library/literature/codes.htm

Problem: 95 Legacy engine computer is cutting fuel pulses short while foot is still heavy on throttle, causing hesitation while power is demanded by the driver. The hesitation lasts a few seconds then it is fine for tens of minutes. Car is not disabled by this problem but it is an occasional annoyance. Sometimes it stalls while coasting in neutral or clutch is pressed, but doesn't stall while idling while stopped. At first we noticed the problem as a hesitation, but have since narrowed it down to ecu not providing long enough fuel pulses for the amount of air the cylinders are breathing. My friends car: 1995 Legacy AWD 5speed with hill holder. EJ22 MODS: None MAINTENANCE: New spark plugs. Inspected the Mass Air Flow Sensor visually but not electrically. New front oxygen sensor. New fuel pump and sump filter when the pump failed recently, new engine compartment fuel filter as a precaution, the stuttering/hesitation was there before and after the replacements. No check engine lights. We hooked a multimeter to the fuel pump to watch how much current it was pulling to let us know if it was shutting off, current stayed steady while hesitation occurred while driving. Hooked a wire to one of the spark plug wires and ran it inside the car, when the hesitation occurred while driving we brought the wire 5mm away from a grounded part of the car and saw the arcs, meaning the coil was firing just fine during the hesitation, ignition is not the cause of the hesitation. Then we hooked an oscilloscope to one of the fuel injector wires and watched the pulses while driving and sure enough we saw the pulses cut down to almost non-existent when the hesitation occurred. Something is telling the engine computer to kill fuel delivery to a very small amount while foot is still heavy on the throttle. Swapped the front oxygen sensor with the rear one and it didn't fix the hesitation. Then he bought a new oxygen sensor for the front and it still didn't fix the problem. Throttle position sensor? Mass air flow sensor? Coolant sensor? Loose wire somewhere? I don't see a MAP sensor anywhere on the engine or in the shop manual, so vacuum leaks seem unlikely. I have a few ideas of what to do: The MAF seems like it can be probed with an oscilloscope I read this on Wikipedia about MAFS: Hot wire sensor (MAF)[edit] A hot wire mass airflow sensor determines the mass of air flowing into the engine’s air intake system. The theory of operation of the hot wire mass airflow sensor is similar to that of the hot wire anemometer (which determines air velocity). This is achieved by heating a wire suspended in the engine’s air stream, like a toaster wire, with either a constant voltage over the wire or a constant current through the wire. The wire's electrical resistance increases as the wire’s temperature increases, which varies the electrical currentflowing through the circuit, according to Ohm's law. When air flows past the wire, the wire cools, decreasing its resistance, which in turn allows more current to flow through the circuit, since the supply voltage is a constant. As more current flows, the wire’s temperature increases until the resistance reaches equilibrium again. The current increase or decrease is proportional to the mass of air flowing past the wire. The integrated electronic circuit converts the proportional measurement into a calibrated signal which is sent to the ECU. Seems like the white wire of the MAF is the signal wire from the MAF integrated circuit since we see it is shielded from EMI/RFI in the schematic. Anyone have an idea of the frequency range or any advanced knowledge of Subaru MAF? All I have for an oscilloscope is my laptops sound card with 44khz sample rate, "soundcard scope" software and some 1 megaohm resistors to protect my laptop from dangerous current levels.