mass air flow sensor - Page 2 - Alfa Romeo Bulletin Board & Forums
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post #16 of 33 (permalink) Old 03-20-2019, 06:23 PM
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A word of warning re: Alfa / Bosch AFM. Each AFM, as it comes out of the factory, is laser trimmed for resistance vs opening angle. This is a pretty precise permanent adjustment to the circuit board trimmer resistors -- The test fixture blows a precise air rate through the opening, and the laser actually adjusts (removes) electrical resistance through the trimmers in a multi-point calibration process. What does this mean in practice? It means that the arm to flapper angular position must be maintained (and therefore the arm/trace relationship as well) as well as the spring force on the flapper must not be disturbed. It also means one can;t swap out flapper springs/circuit boards etc.
The whole thing is dicey. Would have been WAY better to simply put a MAF in that uses heat conductivity. Then everything else (mechanical stuff) becomes somewhat moot.
Yup. I would not adjust or mess withe these, ever. Just asking for trouble. Cleaning it is another story and fairly simple.


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post #17 of 33 (permalink) Old 03-21-2019, 07:30 AM
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So can I swap out mine with a new one with the same Bosch part number but for a Porsche? The used on Ebay from here in the US looks like it has been opened and messed with.

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post #18 of 33 (permalink) Old 03-21-2019, 07:48 AM
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I would think so, but have never tried this. When Bosch made them, I doubt there was different calibration curves for Porsche vs Alfa.

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post #19 of 33 (permalink) Old 03-21-2019, 08:13 AM
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Thanks Goats. That was my thought as well. My thinking is that the fuel injection management system should work with the data the sensors are providing and it will instruct the air flow meter on how to operate. That may be an oversimplification of how things work but seems reasonable. I will discuss this with my mechanic and let everyone know how we proceed and what the results are.

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post #20 of 33 (permalink) Old 03-21-2019, 08:31 AM
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well its kind of like that but not really. The AFM is delivered a fixed, regulated voltage as an input, and it outputs a variable voltage that is proportional to the air flow RATE (volume of air/unit of time). The rate is measured by the degrees of 'opening' of the flap, which in turn wipes the contact, which in turn varies the voltage delivered as an output. So the AFM is an INPUT to the fuel injection system which tells the computer how much air is being sucked into the cylinders, and therefore how much fuel needs to be injected to keep the mixture within reasonable stochiometrics.

If you can imagine an AFM that is 'out of trim' (ie not calibrated) it might tell the computer that at idle, the air going into the manifold (and thus the cylinders) is x. But the true air rate is x-y. Thus, the computer will compensate fuel to the x value, but since the true rate is x-y, it will be rich. The O2 sensor will then measure this, and if its too far out , will flash the CEL for 'sensor out of range' code.

Anywho give it a shake lets see what happens. How much $ is this porsche AFM ? Can you return it if its a no-go (which I dont think is likely at all)

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post #21 of 33 (permalink) Old 03-21-2019, 01:56 PM Thread Starter
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I would think so, but have never tried this. When Bosch made them, I doubt there was different calibration curves for Porsche vs Alfa.
I would think Bosch would have given them different part numbers if the calibration was different - otherwise chaos could result. It would be up to the individual car/brand computers to use the data correctly for their own engines. Production wise, nothing else would make logical sense.
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post #22 of 33 (permalink) Old 04-19-2019, 12:55 PM
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I heard back from my mechanic today about my check engine light issues and the car running lean at idle. I found a used Bosch part for a Porsche that looked to be in great shape and unmolested. He swapped it out but it did not prove to be the issue. He checked and replaced as needed several sensors and checked the fuel injectors as well. Two of the coil packs were intermittent and he replaced those as well. The new air flow meter did not help and he went back to my old one. The check engine light still comes on at idle but it goes away when you start to drive away. I will drive it for a few weeks and see how it performs. I will report more when I see his notes on the invoice so I can see what he replaced. Let me know if anyone has any suggestions.

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post #23 of 33 (permalink) Old 04-19-2019, 02:35 PM
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With my 94LS, I had the engine light come on at idle sometimes but always go out when the car is accelerated away. Turns out there was a small air leak in the fuel pipeline system, mainly, the little air hose (item 5, Fuel Tank Pipeline, https://alfa-romeo.7zap.com/en/164/r...+10201s00+5-0/ going to the spherical air chamber (item 1), located in the left fender area. Small leak, couldn't hear it but the unlit propane torch waved around found it.

Dreaded PO had disconnected that hose because the small valve (item 3) it also attaches to was clogged/stuck one way. Once I cleaned that valve and reconnected the hose, the symptoms such as the engine light being on, disappeared.

You just might check that stuff out, being very easy.

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post #24 of 33 (permalink) Old 04-19-2019, 02:49 PM
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I know I am resurrecting a very old post, but my MAF needs replacement. My mechanic had to set it too lean to get it to work. I get a gas smell when it is idling and the check engine light comes on. The light goes away when I start driving. Has anyone had any luck with replacement MAF's? He has told me that he has done just about all he can with the current one.

Let me know and thanks.

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So what Code are you getting for this check engine light? Turn on key, stomp accel pedal 5 times and count CEL flashes such as 1223 or possibly 1224 for O2 sensor for example.

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post #25 of 33 (permalink) Old 04-22-2019, 07:50 AM
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So what Code are you getting for this check engine light? Turn on key, stomp accel pedal 5 times and count CEL flashes such as 1223 or possibly 1224 for O2 sensor for example.
I will ask that when I go pick up the car this week and report back.

Thanks.

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post #26 of 33 (permalink) Old 05-03-2019, 08:58 AM
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Here is the update. I picked up the car on Tuesday and the check engine light was not coming on, but my mechanic said it might come on periodically if idling for an extended period of time. He put the replacement Porsche sourced Bosch air flow meter on and it actually performed worse than what the existing one did. So that did not solve the problem. He replaced a temperature sensor at the radiator and also two coil packs that were not firing as strong as they should be. He did quite a bit of work trying to figure out what the problem was and he said he has probably gone as far as he can without a new Alfa air flow meter. So, while the Porsche part looked to be in good shape, it probably had been tampered with. The car runs strong and quite. My next task is to get the ATX fluid changed as it is holding on to first year more than it should when it is cold. And cold being not very cold. This is Texas in the spring.

Thanks everyone for your guidance and support.

Cheers

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post #27 of 33 (permalink) Old 05-03-2019, 12:07 PM
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I see code readers for OBD1, are any compatible with the 164 24v?

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post #28 of 33 (permalink) Old 05-03-2019, 12:32 PM
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no, 24V 164 requires a non OBD tester. Do a search here for Marelli tester and you will find a treasure trove of info including some great work by Pinino on making a PC communicate with the Motronic brain

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post #29 of 33 (permalink) Old 05-03-2019, 04:43 PM
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You can pull codes by turning on key and stomping accel pedal 5 times and then count flashes in Check Engine Light to read codes stored in memory.

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post #30 of 33 (permalink) Old 05-04-2019, 07:52 AM
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no, 24V 164 requires a non OBD tester. Do a search here for Marelli tester and you will find a treasure trove of info including some great work by Pinino on making a PC communicate with the Motronic brain
Thanks
downloaded Alfaobd and emailed them for latest see if there is a latest.

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