shae201 Posted June 9, 2009 Report Share Posted June 9, 2009 Is there are way to test your mass air flow and sensor to see if it is bad? Car idles at low rpm and dies after 8-10 sec. Checked fuel pressure and injectors. Sometimes the car backfires through the air filter, my maf is from a 91 eclipse. If bad should I stick with 1st gen eclipse or put stock maf back? Can you test mass air sensor? Link to comment Share on other sites More sharing options...
AlexNYC Posted June 9, 2009 Report Share Posted June 9, 2009 Try unpluggin the mas, and disconnect the battery for at least a minute to reset the ECU. then start the car see if it runs without the mas plugged in. This does work for some 86 not sure if it will work for an 87. Link to comment Share on other sites More sharing options...
shae201 Posted June 9, 2009 Author Report Share Posted June 9, 2009 Try unpluggin the mas, and disconnect the battery for at least a minute to reset the ECU. then start the car see if it runs without the mas plugged in. This does work for some 86 not sure if it will work for an 87. I will try that, appreciate it. Link to comment Share on other sites More sharing options...
hschwartz3 Posted June 9, 2009 Report Share Posted June 9, 2009 What alex said should work for an 87, but i don't think the car will idle afterwards. the reason i say this is, one time when i lost my accordian hose, i did just as alex described, and i was able to drive home with the mas unplugged, but the car wouldn't idle when i came to a light, had to keep my foot on the gas a little. I have an 87 with an 89 ecu. I was also running a 1G mas at the time. If you still have the original MAS that would be the easiest test, other than that i'm not sure. The backfiring through the intake doesn't sound like a MAS though, that sounds more like ignition timing. Hope this helps. Link to comment Share on other sites More sharing options...
patra_is_here Posted June 9, 2009 Report Share Posted June 9, 2009 you can test the MAS but you need a multimeter capable of reading DC Hz at idle should be 40Hz to 70Hz it's usually the white wire, but really, i suppose you could just back probe each wire one at a time until you see a Hz reading in the range, and if you don't, then you know it's not working. Link to comment Share on other sites More sharing options...
Shelby Posted June 9, 2009 Report Share Posted June 9, 2009 while the air mass sends a signal in hurtz it can be read as volts also,, at low rpms the signal volts will be low and increase as the air flow increases,,the exact reading isn't important but the fact it increases voltage is,, by the book 87-89 may idle but be very hard to get any rpms out of the engine because the ecu is not seeing any air flow i have use'd a shop vac to control the air flow thru an air mass and test the read out voltage , not a 100% test but if you have no other option it'l tell you if the air mass is sending a signal or not Link to comment Share on other sites More sharing options...
patra_is_here Posted June 10, 2009 Report Share Posted June 10, 2009 shelby i gotta disagree with you, a voltage output test won't tell you anything worthwhile Link to comment Share on other sites More sharing options...
mikec Posted June 10, 2009 Report Share Posted June 10, 2009 The MAS outputs a "pulse train" signal - a short ON burst followed by a varying length OFF burst. The more airflow you have, the shorter the OFF time so you get a higher frequency output as airflow increases. On a plain old voltmeter set to read DC volts, this will show up as an increasing voltage. The factory service manual suggests using Shelby's test too. It will identify a totally dead MAS unit. This type of pulse train varies both frequency and "duty cycle" - where duty cycle is the ON vs OFF time. A normal "square wave" is a 50-50 duty cycle: 50% on, 50% off. A DC voltmeter would read a constant voltage regardless of frequency for such a signal. But StarQuest MAS units go from a 20% ON/80% OFF cycle to something close to 90% ON/10% OFF so the "average voltage" - which is what the DC voltmeter will read - rises as airflow increases. Sometimes though the MAS electronics get screwy and the ON pulse isn't a sharp-cornered signal (like a square wave)... it gets rounded off. That is no longer a quality "digital" signal that the ECU expects... as a result, the ECU sometimes "misses" MAS pulses and you end up with the incorrect air:fuel ratio. Hooking an oscilloscope to the MAS output will show this - and it's probably the best test of the output you can do. Few folks though have o-scopes. The MAS unit has a few other sensors though; Mitsu kept adding sensors to the MAS assembly every couple model years. Early cars have an airflow sensor, then separate engine-compartment sensors for air temp (like the temp sensor in the over-the-valve-cover pipe on 86s), and air pressure sensors on the firewall. For 87-later cars, the temp and pressure sensors were combined with the airflow sensor in the MAS assembly. The ECU error code for "airflow sensor bad" only tests the actual air counting part - it does not test/monitor the temp sensor nor the air pressure sensor ("barometric pressure sensor" in Mitsu's manuals). But they can be tested with simple multimeters too - the procedure is described in the factory service manual, Fuel System chapter. The FSM for earlier model year cars shows the "ECI Checker" tool (a Mitsu dealer's tool) to check these sensors. Guess what: the ECI checker is nothing more than a glorified multimeter that, instead of having two wires (red & black wires like your multimeter) it has ECU connectors to "tap into" the car's wiring harness. The rotary switches on the ECI checker just pick which ECU connector wires it's going to monitor... you can do the same thing moving your voltmeter leads around. The ECI Checker tool is NOTHING like today's OBD-II scan tools at all. It's dirt simple inside - no computer brains at all unlike OBD-II scan tools/code readers. mike c. Link to comment Share on other sites More sharing options...
Whiplash Posted June 12, 2009 Report Share Posted June 12, 2009 A quick first check we did was to bump the MAF housing with your hand, while the engine is running. If the engine missed or stumbled, then the MAF failed the first check and needed replaced. Link to comment Share on other sites More sharing options...
Shelby Posted June 13, 2009 Report Share Posted June 13, 2009 did you remove the air mass from the car your self , if so was it hit in the frt,, most are thats a quick death for an air mass, also was it from a turbo car,,if not then your wasteing your time Link to comment Share on other sites More sharing options...
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