Car stalls. Hard start. MAF questions

surfbug1 · Post by **surfbug1** » 31 Mar 2022, 21:25

misha wrote: ↑31 Mar 2022, 12:59 Maf or fuel delivery(fuel pump,filter,fuel pump relay).
But...if it runs good with Maf disconnected and not stalling or cutting out...it's bad Maf.

Ok I will check tomorrow.

I did clean the MAF, or do I need to buy a new one

Is this something that has to be Bosch or Volvo, or can I go aftermarket.

And, what about grabbing one out of a wrecking yard?

Al

Post by **abscate** » 31 Mar 2022, 21:26

Bosch or Volvo from a reputable source, not eBay or Amazon. Junkyard part is fine. Look for a wreck

surfbug1 · Post by **surfbug1** » 31 Mar 2022, 21:28

Abscate-- thanks

Now question. Can I drive the car with the MAF disconnected, so I can 'test' the theory that the MAF is bad?

How far can I drive it? 20-30 miles?

Will I ruin anything?

Al

Post by **abscate** » 31 Mar 2022, 21:43

surfbug1 wrote: ↑31 Mar 2022, 21:28 Abscate-- thanks

Now question. Can I drive the car with the MAF disconnected, so I can 'test' the theory that the MAF is bad?

How far can I drive it? 20-30 miles?

Will I ruin anything?

Al

With the MAF dosconnected the ECU doesn’t get the airflow information so it guesses it based on rpm. It deliberately sends more fuel than design because lean running destroys engines.

In modern cars , several things contribute to the fuel / air mix. Disconnecting the MAF isn’t a good diagnostic procedure since the car defaults to open loop running.

Post by **erikv11** » 31 Mar 2022, 23:45

surfbug1 wrote: ↑31 Mar 2022, 21:28 Abscate-- thanks

Now question. Can I drive the car with the MAF disconnected, so I can 'test' the theory that the MAF is bad?

How far can I drive it? 20-30 miles?

Will I ruin anything?

Al

Abscate hates this as a test for the good reasons he mentioned, but yes you can do it. Disconnect the MAF before starting, not while it is running. You can run it for a half hour that way with zero risk to your engine. 20-30 miles is fine. If running it that way removes all the symptoms, 99% chance the MAF is the problem. On the other hand if it runs like crap with the MAF disconnected then you haven't learned anything. You haven't harmed anything either.

Post by **abscate** » 01 Apr 2022, 03:06

A junkyard MAF is a cheap swap and it’s not a bad part to have in stock, cheap.

The place it burns you is when you have an induction leak after the math, so called “ unmetered air”

With MAF ON, the air isn’t detected by the MAF so not enough fuel is sent. The engine runs lean and crappy.

Unplugging the MAF the car suddenly runs decently, so you think the MAF is bad. The car runs well because now the ECU sets it to run on rpm and also rich…usually enough to compensate for the air leak.

You bolt in your shiny new $200 MAF… and you are right back to closed loop poor running.

You are now poorer , but wiser.

See the saga of Sir MAF here…

https://www.matthewsvolvosite.com/forum ... se+failure

surfbug1 · Post by **surfbug1** » 01 Apr 2022, 07:31

abscate wrote: ↑01 Apr 2022, 03:06 A junkyard MAF is a cheap swap and it’s not a bad part to have in stock, cheap.

The place it burns you is when you have an induction leak after the math, so called “ unmetered air”

With MAF ON, the air isn’t detected by the MAF so not enough fuel is sent. The engine runs lean and crappy.

Unplugging the MAF the car suddenly runs decently, so you think the MAF is bad. The car runs well because now the ECU sets it to run on rpm and also rich…usually enough to compensate for the air leak.

You bolt in your shiny new $200 MAF… and you are right back to closed loop poor running.

You are now poorer , but wiser.

See the saga of Sir MAF here…

https://www.matthewsvolvosite.com/forum ... se+failure

Read thru that, and learned more about Sir MAF

Thanks!

Still working on the issue ....

Al

surfbug1 · Post by **surfbug1** » 01 Apr 2022, 09:26

Ok, so I unhooked the MAF. Started right up. Let's see if the CEL comes back (went out for now)

Cel would come on and off for no reason, and wouldn't effect driveability

So, let's see how she runs with the MAF discoed

Funny that cleaning it didn't change anything. (but I just pulled out the element, didn't remove the whole assembly)

Thanks

Al

Post by **erikv11** » 02 Apr 2022, 13:26

Yes, always check for unmetered air (or err!) first. But more often there are codes to send you looking for that (e.g. P0172) when there is unmetered air.

surfbug1 wrote: ↑01 Apr 2022, 09:26 ...

Funny that cleaning it didn't change anything. (but I just pulled out the element, didn't remove the whole assembly)

...

It's not surprising at all. Unless you can see oil smudge of some kind on the MAF filament, "dirty MAF" is almost never an issue. I harp too much on this one but - MAF cleaner is mostly useless!

surfbug1 · Post by **surfbug1** » 02 Apr 2022, 13:40

erikv11 wrote: ↑02 Apr 2022, 13:26 Yes, always check for unmetered air (or err!) first. But more often there are codes to send you looking for that (e.g. P0172) when there is unmetered air.

surfbug1 wrote: ↑01 Apr 2022, 09:26 ...

Funny that cleaning it didn't change anything. (but I just pulled out the element, didn't remove the whole assembly)

...
It's not surprising at all. Unless you can see oil smudge of some kind on the MAF filament, "dirty MAF" is almost never an issue. I harp too much on this one but - MAF cleaner is mostly useless!

Yeah thanks. But had to try!

Do I need to take the whole assembly out to do a throro cleaning?

I have been running it with the MAF disconnected and it is running fine for the last 15 miles or so, about 4 different drive cycles. No issues running it like this , so far

Al

Car stalls. Hard start. MAF questions

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