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MAF sensor problem on C70 2004 2.4T, car now start but does…

Customer Question
MAF sensor problem on...

MAF sensor problem on C70 2004 2.4T, car now start but does not run properly, new BOSCH MAF fitted, no change. Nearby repairman say MAF reads 1000 kg/s (more than 10 times too much).

Mechanic's Assistant: Does the engine stall right after starting? And what about hesitation or jerking during acceleration?

Car was working with problems for 50 miles, then stoped on motorway, and no more starting. Then two days of sun and car started again. It does handle idle or few meters, no hesitation, no jerking.

Mechanic's Assistant: Are you fixing your C70 yourself? What have you tried so far?

Three repairman did not find the problem, no ODBC2 code. I can do some stuff, I did change the MAF myself, and tried new camshaft and cranckshaft sensor (but did not change anything so have put back the old ones).

Mechanic's Assistant: Anything else you want the mechanic to know before I connect you?

No, I can pay for good advise...

Submitted: 2 months ago.Category: Volvo
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Customer reply replied 2 months ago
I also cleaned the main battery ground point (under battery) but no change.
Answered in 18 minutes by:
5/29/2018
Volvo Mechanic: Danny, ASE Certified Technician replied 2 months ago
Danny
Danny, ASE Certified Technician
Category: Volvo
Satisfied Customers: 4,621
Experience: ASE Master Technician with L1 advanced engine performance, VW Certified, former US Army mechanic
Verified

Do you have a scan tool capable of reading real time sensor values? I'd like you to verify that mass airflow sensor volume for me. I don't think it's possible to read 1000 grams per second, for one it would through a fault for implausible signal, and it'd probably then ignore that reading, for two....yeah I just don't think it's possible for it to read that high, that indicates a potential wiring issue. I can walk you through testing it.

https://www.amazon.com/Scanner-OBDATOR-Wireless-Diagnostic-Android/dp/B074DX2N2Z/ref=sr_1_10?s=automotive&ie=UTF8&qid=1527623024&sr=1-10&keywords=obdii+elm327

These are nifty devices, you use a free app from the app store and you can then get me the MAF readings and other values I'll need to diagnose the problem. Otherwise, if you have a scan tool let me know. We need to verify that maf reading, then unplug the maf completely and see if a reading shows up on the computer then, and let me know what it is at idle, and at 2000 RPM with the vehicle stationary. See if the terminals in the maf connector are splayed, they should be nice and tight, if the prongs are spread open for each wire, it could be causing high resistance and causing this.

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Customer reply replied 2 months ago
Already changed the MAF sensor, a repairman came with two different computers able to read real time sensor, one read before the change and one read after the change - exactly the same reading with the two computers.
Before buying the new BOSCH MAF (with BOSCH security seal), I even tried another second hand MAF (second hand from a working car) which was reading exactely the same crasy flow.
I have myself a small and cheap ODBII reader, but I cannot access real time data. It does not seem any of the MAF are faulty, and the contact/connector look perfect, 12 volts arrive on battery pin. Read of sensor looks like 11 volts instead of what should be arround 2 volts... I was suspecting a ground problem, that is why I cleaned the main battery ground point - no change...
Customer reply replied 2 months ago
If one unplug the MAF meter, the engine stops immediately.
Volvo Mechanic: Danny, ASE Certified Technician replied 2 months ago

I understand that they read it, but here's the thing, they weren't good enough to fix it, so I can't rely on what they told you. We need to actually vertify and test things. When you remove the maf connector, often it should default and insert what the engine SHOULD be seeing for airflow at that rpm and temperature, generally when you disconnect a maf and it dies, it means the Maf is actually good. The MAF is the main sensor used for fueling, the fuel injector pulsewidth is directly calculated from it, your injectors would be stuck open all the time at 1000 kg/sec you'd be trying to fuel something like 10 kg sec of fuel. It doesn't make any sense, in 18 years of experience I've NEVER seen it, it indicates a faulty ECM if that's the case, but I need to know numbers, and not just the MAF, other numbers too.

Are you sure your meter can't read live values? What's the model number of that meter you have? It's pretty standard. If not you'll need to buy that bluetooth dongle.

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Customer reply replied 2 months ago
I was there for one of the measurement, the computer clearly displayed unbelievable value, I know you cannot get that amount of air through that tube, and without any abnormal noise - just at idle (measurement reduce a bit at high RPM). My ODBII is too old and too cheap ($15 few years ago), it would take time to get another one. Anyway it is in accordance with what the voltmeter gives: 10 Volts on the sensor pin (whatever RPM) instead of arround 2 volts (other pins: stable 5 volts, battery and ground, one unconnected). I have just checked and the engine does start with unplugged MAF, engine just stops when you unplug MAF sensor while already running.
Also I think it is important that the car refuse to even start for few days (no a single explosion), it took few very warm days to get it to start (nothing touched in the car during those few days), and now it starts no problem.
Volvo Mechanic: Danny, ASE Certified Technician replied 2 months ago

Right it's not just about only that though, it's also about what happens to other values. I need to see how they react to each other. For example you mention temperature, quite possibly the coolant temp sensor could be at play.

You can buy that ELM327 for $15 dollars, you need to do so. I need to see how the ratings react, it's not about a voltmeter, a the voltmeter isn't specific enough. It's about how other numbers react WHEN certain things are done. What's the short term fuel trims, what's the long term fuel trims, when the values are plugged in by the ECM, do the fuel trims settle down, what do the oxygen sensor values look like, what's the ignition timing. You CANNOT diagnose this with a voltmeter. Amazon prime carries those Elm327 devices you could have one maybe even still today if you get on and order it now or in the morning.

I understand you don't want to bother, trust me 15 customers a day try to do this, but here's the thing, it's not a carburated 74 with points ignition, you cannot diagnose this concern with a voltmeter. Well you could, but its going to cost you a ton of time and money in parts you throw at it. We don't buy scan tools for fun. My BMW and Porsche tool was 25 grand, you think I'd buy that if it wasn't absolutely necessary?

If your meter is reading 10v, but yet the commputer says 1000 grams per second then that would likely mean your engine control module is faulty, but I'm not going to have you find a used module then spend 200 dollars having it programmed to the immobilizer without first seeing the numbers myself and seeing if they look plausible. You simply need the right tool for the job, and in this case that's an EXTREMELY inexpensive bluetooth device and a free app.

Sometimes, a sensor will rea correctly the majority of the time, and the signal will drop out for a fraction of a second, a digitial meter can't catch that, real time values being graphed CAN.

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Customer reply replied 2 months ago
OK, i will order a new ODBII reader, but living in the UK it will take a bit longer. I cannot get that brand here (unless waiting for more than a week), any advise from such a list: https://www.ebay.co.uk/sch/i.html?_from=R40&_nkw=Car+Wifi++OBDII++OBDATOR&_sacat=0&LH_PrefLoc=1 ?
If not I will just get one looking at descriptions...
Volvo Mechanic: Danny, ASE Certified Technician replied 2 months ago

I just went to Amazon.co.uk and typed in Elm327 and there's a TON of them available on prime, you don't need that exact one I showed you. Find the cheapest elm327 bluetooth adapter available on prime and order it on Amazon so you'll have it quick.

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Customer reply replied 2 months ago
OK, got one, tried the first Android app advised with the product, just shows me the codes; tried the second app proposed, do not connect (whatever option). Which app do you suggest in "you use a free app from the app store"?
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