How to identify and clean a dirty MAF sensor (Subaru)

Рет қаралды 188,153

11 жыл бұрын

In this video, I’m covering the methods I use to quickly identify lean conditions caused by dirty hot-wire MAF sensors, and what you can do to clean them. Hot-wire sensors are used by MANY different manufacturers, including Toyota, Mazda, Nissan, Subaru, Infiniti, Lexus, Mitsubishi, VW, BMW, Mercedes Benz and others.
Engine Performance Diagnostics chapter 12
Symptoms
- check engine light (P0171)
- hesitation on acceleration
Fix
- clean the MAF sensor
Tests shown
- using freeze frame data, live fuel trim data, to identify the type of lean condition
- visually identifying a MAF sensor with an integrated IAT sensor
- how to scope a MAF sensor signal
- using the sensor ground during scope testing
- analyzing a MAF sensor waveform
- understanding how a dirty MAF sensor results in fuel trim changes
- how to clean a MAF sensor, and which designs are able to be cleaned
- understanding short and long term fuel trims countering each other after a repair
Tools used
- scan tool
- lab scope
- brake cleaner
- soft, small brush
Playlist
- (Chapter 12) Mass Airflow Sensor Testing
• (Chapter 12) Mass Airf...
Related videos
- How to identify and clean a dirty MAF sensor (Lexus)
• How to identify and cl...
- How to troubleshoot a faulty MAF sensor (Mercedes Benz)
• How to troubleshoot a ...
- Dirty MAF Sensor Case Study
• Dirty MAF Sensor Case ...
- MAF and lean codes from a missing air filter (P0171, P0174, P0102)
• Cold Air Intake Warnin...
- Low power, lean conditions (cracked air intake tube) GM
• Low power, lean condit...
For more information on this topic, I have written a “field manual” called Engine Performance Diagnostics which is available at www.scannerdanner.com as an eBook or paper book.
Want even more diagnostic training? Whether you are a DIY trying to fix your own car, someone looking to become an auto technician, or a current auto technician that wants to get more into diagnostics, subscribe to ScannerDanner Premium www.scannerdanner.com/join-sc... There is a 14 day free trial.
On ScannerDanner Premium I will bring you right into my classroom at Rosedale Technical College. You will find page for page lectures taken right from my book as well as exclusive classroom type case studies. What is so special about these classroom case studies? I pull live problem vehicles directly into my classroom and we troubleshoot them in real time, using and applying the theory and testing procedures we learn during the classroom lectures. There is no better on-line training of how to troubleshoot automotive electrical and electronics systems anywhere!
Disclaimer:
Due to factors beyond the control of ScannerDanner LLC, it cannot guarantee against unauthorized modifications of this information, or improper use of this information. ScannerDanner LLC assumes no liability for property damage or injury incurred as a result of any of the information contained in this video. ScannerDanner LLC recommends safe practices when working with power tools, automotive lifts, lifting tools, jack stands, electrical equipment, blunt instruments, chemicals, lubricants, or any other tools or equipment seen or implied in this video. Due to factors beyond the control of ScannerDanner LLC, no information contained in this video shall create any express or implied warranty or guarantee of any particular result. Any injury, damage or loss that may result from improper use of these tools, equipment, or the information contained in this video is the sole responsibility of the user and not ScannerDanner LLC.

Пікірлер: 181

@inris2353 7 жыл бұрын

Actually you are the first who gave me some real information regarding the MAF

@mikewatson8739 7 жыл бұрын

you're videos are great. I've been a dealer tech for 15 years with a lot of training under my belt and still learn something from every one of your videos. 171 on a Subaru I was thinking a/f sensor and reflash, had a lot of those. keep up the good work!

@ScannerDanner 7 жыл бұрын

Thank you!

@ryannakama 8 жыл бұрын

Thank you! After 10 years of driving with hesitation/stuttering/missing/leaning out/check engine and blinking cruise light, I sprayed the hell out of the MAF Sensor with Carb Cleaner and my '04 STI is running smooth! Awesome video and explanation! Thanks again!

@ScannerDanner 8 жыл бұрын

Thank you!

@atypical_blk_guy 6 жыл бұрын

Hey when you were having the issues were you having misfires on multiple cylinders? I'm currently having the issues with the addition to my wrx stalling when trying to park.

@Mrjonblakely 6 жыл бұрын

Thanks man, I "cleaned" my MAF by spraying the thermo sensor and not the resistors. Cleaned the resistors and my '05 Forester is running much better.

@jamalmarafi4076 6 жыл бұрын

I came with an idea how to detect leak in the intake manifold by using AC gas and leak gas detector , and I found the leak fast and easy . thanks to you .

@bigbadjohn8207 7 жыл бұрын

My 02 wrk was almost un drivable until I did this. Now it's like a brand new car!!!!! Thank You!!!!!

@jonathanflynn618 4 жыл бұрын

really great video, thanks for the clarity and good production.

@roberthenderson8483 4 жыл бұрын

I had been a bit baffled with this problem. I had cleaned my K&N air filter and changed out my fuel filter, with no real change. After cleaning my MAF, my '98 Subaru is running like a beast! Thanks for the detailed help!!!

@GreenGc8 4 жыл бұрын

What was your car doing prior to cleaning the maf

@roberthenderson8483 4 жыл бұрын

@@GreenGc8 it would run smoothly at idle and most times at speed. Other times it would just die at idle or at speed. Overall power was not good. Poor acceleration.sometimes surging while driving. Thanks again for the help

@Oofsmageroo 11 жыл бұрын

I am just enrolling to take training to be a technician. your Videos are extremely helpful, I use android to monitor my vehicle and my MAF has always read around 3.2G/S at idle. I did clean it with spray, but never with a small brush. I am getting a lean condition with misfire at idle. from what I infer from your video it is more likely a vacuum leak. Thank you for doing these videos and for explaining everything in detail. seriously helps!

@cherepa1992 10 жыл бұрын

Thank you for sharing this video I have absolutely the same symptoms and reaction but with non cleanable maf sensor!

@victor35ma 11 жыл бұрын

Thanks ScannerDanner for your super educational videos. It is always highly appreciated it. I like to add this... in order to determinate whether the MAF is bad or not, techno must do a VE test (Volumetric efficient test), a 7 min test. you got the data at the end.

@CaptainRorke 7 жыл бұрын

Thank you for the outstanding explanation.

@HeAhaBro 6 жыл бұрын

I really like how you summarise what your video covers in the description.

@ScannerDanner 11 жыл бұрын

thanks for the comment and greetings from the US my friend

@AGuysGarage 11 жыл бұрын

I just wanna tell ya, thank you for taking the time to post videos and give us all of this info. I learn a lot from you. =)

@Hellkinglol 5 жыл бұрын

Solid video man, thanks for all the info!

@Pabloman333 Жыл бұрын

You are a sharp Dude! Well done! Thanks for the education!

@Daarispieter 6 жыл бұрын

Absolutely perfect video, thanks!

@ScannerDanner 6 жыл бұрын

Thanks so much!

@glizbane 2 жыл бұрын

Thank you so much for this. I've been trying to diagnose a P0171 in my 07 Forester XT for months now. After watching your video, I checked the freeze frame data, and it was under load when the code tripped. Popped my MAF out, gave it a good cleaning, and popped it back in. Not only has the code not come back, but it seems that my XT hasn't been running at full power for a while now, and I didn't even know it. Now to figure out my P1153...

@ScannerDanner 2 жыл бұрын

Heck yeah! Nice job, always feels good to help others

@matthewmuturi8195 5 жыл бұрын

Very informative. My 2007 JDM 2.0L turbo-charged subaru forester has the duty cycle stuck at 66% and as a result I do not have boost even at WOT. My mech thinks it could be the fuel pump (the relay works fine), however the vehicle starts perfect , runs very smoothly so I ruled that out and now I think it could be the MAF (although I have no codes). Thanks

@ScannerDanner 11 жыл бұрын

I have heard that, thanks for your input Michael.

@johnnok7775 7 жыл бұрын

It does use the built-in IAT sensor as a reference... but it would be a very minimal impact on performance if any. Sweet video :) Very correct on the assumptions for turbo cars. Once the turbo is spinning under load, you're well over 200 g/s

@ScannerDanner 11 жыл бұрын

Great question! It is because there is only one upstream O2 on this engine, so there is technically only one bank fuel control even though there are two separate banks. Hope that makes sense.

@ScannerDanner 11 жыл бұрын

Yes, I look for this initial spike on all of these. Also peak MAF voltage or Frequency at WOT redline. I don't use the VE test. Another guide is to watch O2mv at WOT. It should be 800+ mv the entire time.

@rusty9501 11 жыл бұрын

Very good example. Thanks Paul.

@ozzstars_cars 11 жыл бұрын

Thanks for the video, great diagnostics!

@ammar0alkashif 11 жыл бұрын

Thanks man, lots of useful Information, Thanks again for sharing... Keep it up. Greetings from the middle east.

@AmericanLocomotive1 11 жыл бұрын

Finally starting to see widebands trickling down to "lesser" cars now. The 2011+ Mustangs are all running them now, including the V6s. Would be good to have a video or two, as a lot of people don't know about them.

@tyleri.163 11 жыл бұрын

Man I wish you would come teach in Florida at my school. Great videos!

@relleck2036 4 жыл бұрын

Great video man I learned a lot, hoping this will fix my issue with my 02 wrx. Getting break up around 4k rpms and getting a slight bog right before I give it throttle. Gonna take some brake cleaner to the MAF and I also have to replace my center differential viscous coupler. gonna be a fun weekend

@TinkeringTom91 3 жыл бұрын

Did it Fix your issue?

@careyautorepairs Жыл бұрын

Love simple videos.

@spinacz0z 10 жыл бұрын

ohhh man. It was oddsome. you saved my day. Thanks mate.

@GRUSSNewton 11 жыл бұрын

Great video Paul!

@roofbolt1 6 жыл бұрын

Thanks for this excellent video and diagnostic. I fixed my 2005 Forester XT after numerous visits to the dealer with no luck. Turned out to be a tiny blob of dirt on the hot wire.

@ScannerDanner 6 жыл бұрын

sweet! Thanks for watching

@TinkeringTom91 3 жыл бұрын

What were your Driveability symptoms with the Dirty Maf Sensor?

@roofbolt1 3 жыл бұрын

@@TinkeringTom91 There was a distinct delay in revving when you hot the throttle. As if it there was fuel starvation So if the car was in neutral and you stabbed the throttle the engine hesitated for a second then revved. Also down on power on the road.

@TinkeringTom91 3 жыл бұрын

@@roofbolt1 My Wrx won't seem to go past 4k in any Gear Very Sluggish only reving in Neutral can I get it Higher, 2013 WRX 70kmiles I have changed Air Filter and Spark plugs already, new throttle body w/sensor, Mishimoto Hose, slightly better still Seems Bogged Down... Should I go for the Maf Here, also ordered a Crankshaft sensor before I Saw this Video.

@randhawaj1 11 жыл бұрын

Great video.....lots helpfull info. Thanks

@jctunner 10 жыл бұрын

Great vid and great tutorial keep up with the great work.. also I have a question I have a 07 wrx turbo and for some reason after I drive the car for like 20-30 minutes (warm car) the throttle seems to respond slow when I hit the throttle pedal quick like 10% and I see no respond at all

@calvinchai8455 7 жыл бұрын

Hi Danner: I recently got a P0172 and AFR's were at 10.0 at idle. During driving it was 12.5 or so. I cleaned the MAF and dramatically made things better. It was still bucking on initial acceleration. The MAF is an original OEM Subaru One. Figuring it might possibly be a MAF sensor issue. My friend happened to have one dandy, Part Number 197-6040. So installed that literally 30 mins ago and it seemed to run better with no bucking. Also the ECU has been reset.

@ScannerDanner 11 жыл бұрын

Any small soft paintbrush will work. Just do not push hard. The resistors will distort very easily.

@drewbarker5598 10 жыл бұрын

Thank you!!! You R the Man!!!!!

@jamalmarafi4076 6 жыл бұрын

Thanks so much I found the leak not by Brakleen PRO , or AC telco Carburetor tuneup , but by Starting F lid .

@ScannerDanner 6 жыл бұрын

Nice, just be careful with doing that in the future Jamal. Nice find bro

@MrGetBad4u 9 жыл бұрын

I threw a 0171 last week. I cleaned the MAF and still gave me a 0171. Ran a smoke test, turned out to be a vacuum leak on the PCV. So a 0171 may not always be the case with a MAF. A simple 3 inch 3/8 hose that is cracked will cause your car to idle very very rough. If you have these symptoms with a lean car, you have a vacuum leak somewhere like I did. Thankfully it was fixed quickly but still. The MAF isn't always the case when you throw that code.

@Autofixpals 8 жыл бұрын

+aaf1218 most of the time when you have a p0171 there usually is a vacum leak. but 30% of the time it can be MAF. Fuel trims tell you everything.

@str33trace 11 жыл бұрын

Thank you sir for the education video

@ScannerDanner 11 жыл бұрын

I don't know the VE test. Can you enlighten me? Thanks

@anyheck 11 жыл бұрын

Great video, thank you! What sort of brush are you using for your cleaning?

@ahill007ny 11 жыл бұрын

AWESOME VIDEO :)

@richardbell556 10 жыл бұрын

many thanks saved the day dan after watching your video ford fiesta 1.25 zetec cheers may i add i also had a P0174 with the P0171

@Cattachmore22 11 жыл бұрын

Thank you ScannerDanner that very interesting.

@roro560v8 11 жыл бұрын

You are the man ....

@sidlimp 11 жыл бұрын

nice fix dude

@Hamofasa 10 жыл бұрын

This is very interesting. I took my car in for power loss on cruise. They said it may be the MAF but then they concluded it was a faulty O2 sensor. They changed it but the day I drove it away it played up straight away. I took it back to them and they were baffled (needless to say these guys are "Subaru specialists") . Anyways they are pretty confused and pointing at "possible air flow sensor on its way out". I can check it myself now

@DJDevon3 11 жыл бұрын

Neat, looks like I got all of my info correct whew. I have a video on cleaning a MAF (hotwire type) on the Mazda 626 if you want to show your students a very common Mazda/Mitsubishi design. It's sooooo much easier to clean than the one in your case study. Sorry I didn't take any readings before and after it was purely a cleaning video.

@Cruz0604 4 жыл бұрын

My 02 WRX has that code and did a vacuum leak test and it’s holding decent vacuum,

@TheDavidwaldrop 10 жыл бұрын

nice love it so know you fix it a you going to change the plugs,,

@markharvey1299 9 жыл бұрын

Perfect just what I was looking for had the po171 code for a few weeks and comes on when causing so around the 3000 rpm tried a few things but my maf is ment to have been cleaned 2 weeks earlier. Hoping the new maf I ordered sorts it. But a great video understanding exactly what's happening thanks :)

@MrGetBad4u 9 жыл бұрын

Mark Harvey I had the same issue last week with the 0171 code, turned out to be a crack in the PCV hose. Did you figure your issue out?

@markharvey1299 9 жыл бұрын

Hey yer took agers took everything apart spent heaps of time looking for it. Turned out the mechanic hadn't cleaned the maf correctly :(

@MrGetBad4u 9 жыл бұрын

Damn, I bought a new MAF in hopes that would resolve my issue last week. But ended up being a cracked hose at the PCV. I ran a lean code the week before and it never came back until this past Sat. I hope your MAF is cleaned up properly now and she's running good.

@helloow1234 11 жыл бұрын

thanks for the educational videos. I got question though, the spike on the snap shot, does that apply to all dirty MAF sensors testing or only this vehicle. that looked very easy to graph the MAF to see if its dirty or not. I took that VE class but some how I couldnt get right because my slow scanner

@ScannerDanner 11 жыл бұрын

Thanks man

@94navin 11 жыл бұрын

Great video I learn a lot form your video as i am training to be a mechanic as well. But i was wondering why the computer didn't give a rich condition and why only bank 1 was lean?

@redclift30 11 жыл бұрын

HI Paul, I probably missed it in you other videos but, can you tell us what you used to clean the Hot wire? Thankx.

@ScannerDanner 11 жыл бұрын

that and probably EGR flow diagnostics and back-up

@mlb0611 11 жыл бұрын

MAF failures are very regional, when I worked in the burbs, I called very few MAFs as bad, I now work in Downtown Atlanta and replace alot of misreporting Mafs, I have tested cleaning versus replacement, and have found it not good enough to call a complete repair, fuel trims were better but not right, so I replace rather than clean. But to each there own.

@kuruptprez21 3 жыл бұрын

I'm getting confused with a Subaru I'm having to take over for another tech. So he just replaced a bunch of parts, maf, a/f sensor and 02 sensor. I look at short term and its 22% performed a smoke test no vacuum leaks found. Maybe a guide towards the right direction would be appreciated

@ScannerDanner 11 жыл бұрын

thanks bro

@ScannerDanner 11 жыл бұрын

definitely cleanable on that model. Check your scan data BARO HZ number first. At sea level you should be close to 156-160HZ. If it's there, your MAF is clean

@12vgs8606 11 жыл бұрын

It seems as if the relationship of the MAF output and gm/sec readings is not linear as seen on this car. My experience with the Nissan Maxima MAF was that I thought it was linear but I could be wrong as I am going by the memory and do not have the hard data in front of me. The voltage went fro 1.2V to 4.0V but the gm/sec went from 3 to 180

@serchmarc 11 жыл бұрын

thx for sharing, cheers

@ScannerDanner 11 жыл бұрын

Ok. Start by checking MAP voltage KOEO (no vacuum) and idle (full vacuum). KOEO honda MAPS usually read about 2.8v and around 1v at idle. With engine running as you snap the throttle map voltage should increase. Also check your TPS for glitches or drop outs. Watch my "Section 7 Playlist" for more on TPS testing

@ScannerDanner 11 жыл бұрын

everyone's been asking me to do some wideband stuff, got this Lexus in my classroom right now that I am hoping to shoot a video on. keep watching

@Turbotomass 11 жыл бұрын

I was thinking the same thing. I'd love to see what you used.

@beenselock 11 жыл бұрын

what about a digital maf? do u have any videos on them?

@mike-yp1uk 9 жыл бұрын

The way i got it explained is the dirt on a maf is insulation. Its like wearing a parka coat on a hot summer day standing out the sunroof of the car and that is why you dont get spikes on a snap throttle. The rest is the conveter protection program, nox egr ect..

@ScannerDanner 11 жыл бұрын

Again, the only kind I have ever cleaned is this style and I wouldn't recommend cleaning other types. The housing that holds the actual resistors is not a typical plastic and brake and carb clean will not hurt it. I didn't notice the intake ripples. I need to watch it again. I've seen them on MAP sensors but never on a MAF, but you could be right. Not sure if its chlorinated or not and never cared, it just needs to leave no residue.

@pete1rocks 4 жыл бұрын

Would a dirty maf cause cel P0068?

@cm1251976 11 жыл бұрын

thank good job

@ScannerDanner 11 жыл бұрын

It does and for the most part will not cause a rich condition, but it can at times at idle like I've shown. The main condition with a dirty MAF is under load lean conditions

@Kennethrandallross 7 жыл бұрын

2006 Forester have one of these?

@joegenova51 11 жыл бұрын

Hi i was wondering if you can clean a f 250 4+4 it is a flat box but i can see some wires is it cleanable or not it has 5-6 wire have 171 penting 174freeze frame thanks

@ScannerDanner 11 жыл бұрын

usually lean conditions but they can also cause rich conditions as well

@Randomgearhead 7 жыл бұрын

I was told to clean the maf to test and see if the numbers/ and or drive-ability got better, and then replace it if it did. This was coming from a instructor employed by a sensor company, smart non the less. but cost on these sensors can get real expensive. so i say clean it to see if it numbers improve, and don't replace until code or concern comes back! cleaner is cleaner in my opinion, how can one be more delicate than the other? like fuel injector cleaner, if gas ain't cleaning them enough how the f is some clear juice super concentrate crap going to clean it adding it to a tank of gas going to clean an injector?

@dogburrito 2 жыл бұрын

Would you show the brush you used on the delicate sensor resistor?

@ScannerDanner 2 жыл бұрын

I've used a pocket screwdriver before 😁 Just be gentle

@AmericanLocomotive1 11 жыл бұрын

O2 voltage floating around ~3.7v, is this a wide-band O2?

@atypical_blk_guy 6 жыл бұрын

Would a bad maf sensor cause multiple misfires? I changed my plugs and coils but I'm getting this code as well as misfire codes on cylinders 1,3 and 4

@ScannerDanner 6 жыл бұрын

attack the misfire issue first. most likely your MAF code is being caused by the misfire, not the other way around

@nathanyoung8284 5 жыл бұрын

Video was super informative for my Legacy GT! Is it OK to use throttle body cleaner/intake cleaner on a MAF sensor or is that a bad idea?

@ScannerDanner 5 жыл бұрын

Just make sure what you are using doesn't leave a residue

@nathanyoung8284 5 жыл бұрын

I went safe and bought MAF sensor cleaner, but the CRC throttle body cleaner I use doesn't leave a residue as far as I can tell.

@dingpongchi632 2 жыл бұрын

Is the LOAD _PCT 1.2 % normal, mine having the same value however the workshop manual says is 18% at idle.

@ScannerDanner 2 жыл бұрын

Depends on the data PID, some offer absolute load and calculated load and they will read differently. If you're fuel trim numbers are good at idle, then I wouldn't be concerned

@mygiguser 6 жыл бұрын

Great video. I have a question, how does this MAF get dirty? Where is the carbon coming from? I also thought it is supposed to be self cleaning, is it not? Then if you clean it, how long will it last after that?

@ScannerDanner 6 жыл бұрын

PCV gases primarily. 50k+ before you will see it get dirty again

@kenh5418 3 жыл бұрын

5:10 Look to the right of the MAF sensor. If you look closely at the intake hose with the clank you'll see it's not seated all the way on the intake box. Hose should be more to the left. Someone probably forgot to button it back up. Could have been part of the problem.

@pabloarevalodelaguila8767 3 жыл бұрын

Excelente.

@Portuguese-linguica 11 жыл бұрын

Im talking about im haveing a hesitation with the snaping the trottle . The rpms will fall to about 200rpm them go up . It has a full tune up . The egr ports are cleaned out . New egr valve . No vacuum leaks.

@ScannerDanner 11 жыл бұрын

yep

@redsson6669 11 жыл бұрын

i know you had a map P.I.D. as well as the MAF... is it common for cars to have both those sensors in them? usually you have one or the other ''i thought''.. another great video paul,thx

@bendy113 6 жыл бұрын

04 forester xt ej255...i got a p0172 pending code not stored and no cel but my car is basically almost stalling out at idle and will lag and then jump back up on accel. As well as the fuelsys1 being in open loop-drive whenever i let off the throttle or give it enough gas. Think this would help?

@ScannerDanner 6 жыл бұрын

You've definitely found the right video for your symptoms my friend. Good job!

@bendy113 6 жыл бұрын

ScannerDanner haha thanks I cleaned my maf just like you said and although the problem is still there it's way better so maybe I just need to replace it full on...anyway thank you very much!

@ScannerDanner 6 жыл бұрын

that is possible, but without some data there is not much else I can suggest

@ScannerDanner 11 жыл бұрын

yep, that is the only explanation that makes sense to me. clearly it is a characteristic that happens, so we cannot deny that. low airflow with a larger surface area = more dissipation of heat, which is interpreted as higher airflow, which = more fuel. weird isn't it?

@Portuguese-linguica 11 жыл бұрын

What about a map sensor.for a 1991 accord?

@bmwmsport11 9 жыл бұрын

So what exactly does short term/long term fuel trim tell you exactly? My car keeps throwing po171 and misfire for every cylinder. It is a impreza wrx. My scanner can only show freeze frame data. Short term fuel trim is showing 25.0, long term is showing -3.9. Engine speed is 660rpm and vehicle speed is 12mph. Seems like both times the code was triggered at the same speed. Is there a general direction I should be heading in as to resolving the issue? should I focus on the MAF/O2 or should I be looking for vacuum leaks? Already cleaned the MAF sensor with no luck. Had a shop replace intake manifold gasket last year. Same issue stays and shows whenever it gets cold. Have not checked the 02 sensor yet. thanks!

@ScannerDannerPremium 9 жыл бұрын

Watch my video "understanding short term and long term fuel trim"

@MrGetBad4u 9 жыл бұрын

bmwmsport11 you must of had a vacuum leak somewhere. I had the same issue last week. Misfire on all cylinders, A/F was at a full 25.0. Means it's a full lean. What did it turn out to be?

@bmwmsport11 9 жыл бұрын

aaf1218 turned out the shop ripped me off and never actually changed the intake manifold gaskets(vacuum leak). It was a factory design issue(OE gaskets were too thin to make contact with the block when cold). Spent 5 hours and managed to replace the gaskets with $40 in parts and tools. Legacy GTs and early WRXs(08 and some of 09s) had this issue.

@dmorley100 11 жыл бұрын

Comment #2. At idle RPM was around 600-650, MAP sensor voltage was 1.8-2 volts, calculated air flow was around 4 grams per second, ran worse in closed loop, STFT was -25. Replaced O2 sensor and ran a little better but still ran like crap and fuel trims stayed the same. Tried a known-good MAP sensor, but no change in running or MAP sensor voltage. Spec I found says 0.5-1.5 volt MAP signal at idle. Performed vaccum test and found needle drifting back and forth at idle. More on next comment.

@dmorley100 11 жыл бұрын

This's probably gonna be stretched out over 2 or more comments, but I need your opinion on whether I'm right or not about a diagnosis I recently made. 1996 Chevy Cavalier with a 2.2 engine that has NO MAF sensor. It uses speed density fuel control. Engine was running rough at idle. Ran better on acceleration but still not great. P0300 misfire with cylinders 2 and 4 showing the most misfires but 1 and 3 had some as well. More in next comment.

@kcirremsenoj7870 6 жыл бұрын

Av got a subaru exiga the engine light and the wheel light oon won't Go away needed you assistance please

@ScannerDanner 6 жыл бұрын

you have to give me more than that bro

@dmorley100 11 жыл бұрын

Comment #3. Did not run compression test, but did perform cylinder leak down test on 2 cylinders and heard and felt air coming out of oil fill cap hole. My thinking is that bad piston rings could have not only directly caused some of the misfires, but also have caused the higher than normal MAP sensor voltage, thereby causing a tug-of-war of sorts between the MAP sensor and the O2 sensor with the fuel control being the proverbial rope. More on the next comment.

@michaelovitch 11 жыл бұрын

I thought deposits on the MAF would insulate it from the air.

@dmorley100 11 жыл бұрын

Comment #4 What leads me to believe this is that I was also told years ago when I was in school that almost anything that affected compression would also affect vaccum as well, so bottom line is do you think my reasoning is correct for as far as that the worn piston rings causing a high MAP voltage reading at idle as well as a high calculated air flow at idle and the negative fuel trim numbers. Your opinion is appreciated.

@mlb0611 11 жыл бұрын

Volumetric efficency test, search IATN for more info, it is a program you input all scan tool data and it gives you a score on how the well the system is working, Albin has been testing, he talked about it in his class about fuel trims last time I took it.I personally think it is a wasted step, watching PIDS like load, o2s etc. 5 minute Flat Rate Test Drive and I can call it. FYI, I just replaced the same kind of sensor on a Prizm, rebadged yota, hair ball hanging on the hot wire