Yann

Hello,

I need some help to make the good diagnostic and repair.
I have some troubles with my non-sti impreza gt MY 1998. Car is quite stock (like ppp set up).
It began 3 weeks ago, It was normal/cruising driving and during warm up
It started like misfires or cut (fuel or ingition), sometimes engine stalled. I thought it was dust/contamination in fuel as I was low fuel.

This fault disappeared, and came back again, really erratic... but never hard to restart engine...
No CEL on dashboard. Iddle OK

So I checked if there was a fault code (with jumpers/couplers under steering wheel), it was code 23 (MAF).
But I had doubt about it (and no other MAF to try, that's the purple label)
as I was thinking about fuel or ignition issue (and I had some new parts in stock).

So what I did :
- Air filter check/cleaning, MAF as well
- New Fuel Filter
- New Fuel Regulator (it was factory one)
- New Sparks plugs
- 12V Battery check (12.6V =OK, iddle 13.6V)

=> Result : Ok during some miles and again some cut/stops...

So then I did :
- New fuel Pump (Walbro)
- ECU swap (from ppp to ESL with stock map) tp be able to data log.

=> Result : still some erratic behaviuour / misfires / cuts.. but after Ok during 50 kms
When It cut/stalled (war-up, in the traffic)a few times...I saw on laptop the flag (23) MAF.
After It was OK (traffic and road), I think I stayed in CL all the time.
The MAF voltage seems "OK" for me (voltage @ contact ON, Iddle, Driving). But don't know if really consistant.

What do you think ? I can share logfiles I made

Thanks for your help

ossett2k2

iTrader: (9)

If it's throwing maf error it points to the maf sensor.
Check the circuit board on the maf,sometimes take water in and corrode connections.

Post up log file,we might spot something.

Yann

OK thanks
I m going to see if I can open the MAF to clean inside (no screws to open the cover, don't know if clips or glue...).

Here the 1st event I could "catch" : 2019-09-05 - City Traffic
It looks like, I switched off the engine (but with still contact on)
we can see the 3 restart attempts
I had the code 23 here

Yann

After a successful restart, it was OK (or seems to be)...

with MAF voltage oscillations @ iddle :

Yann

After that I could drive :
- about 50 kms without any issue (Mix driving : City / A road )

But yesterday (09/07), it was OK during 35 kms ( City / A Road / B Road) :
Engine had some hard cut suddenly with like pon n bang sounds in exhaust... and motor stalled...
Really, really dangerous as I was on a curve in a B road...
No fault code at all this time, I am going to have a look at the datas...

Yann

On the log (2019-09-07-15h59) between 275 sec and 320 sec
I can see the multiples progressives decreases of the MAF signal (V) in about 2 / 3 sec, same as when I switch off engine with the key...
But the signal comes back in 80 ms ( the mini time step in logger at that time)...
It looks like false electric contact, in MAF or in the power supply to the maf ??
Or it is the/a classic failure mode of that type of MAF ???

also strange datas on this log file :
- Fuel correction cut @ 295 sec...
- 2 Boost pressure "peak" of 0.6 / 1.13 bars @ 2-3 kph / 400 rpm / 0% throttle

MrRtm

So error codes report its the maf and you go no its not and throw a couple of hundred at it? Wut? Try another maf man!
No way there isn't someone with a subaru within 50 miles of you that's a member of here or one of the many Facebook groups that will let you swap to test. Not to mention a maf costs half of what you've just thrown at it while ignoring the one thing the error is telling you is causing the issue!

Yann

Thanks for your help and recommendations
Even if I'm not sure to understand everything... but I think I don't agree with what you say...
In a few words :
- I haven't spent any money on this issue, I had all parts on my shelves (and have to put it on my car asap anyway to run e85)
- Error code gives you sometimes faulty component but rarely the origin... (even on latest 32b scooby ecu)
- None of my friends (imprezas owner) have this MAF (purple label)
- I won't borrow a MAF from anybody just to try (for a few days and 70/80 kms or maybe much more to be sure regarding occurency...) and take the risk to damage it (eg : if electrical problem)
- This MAF costs more than £400...

Anyway, the most important thing is that I like to understand things, how it works, and it is maybe a good exercice (for me) to evaluate MAF State of Health with ESL monitoring...
If this is classic failure mode for this MAF, that's fine, I would only like feedback/confirmation of it...from people who knows
And then either I buy a new MAF (maybe not the same) or go Mafless.

MrRtm

Just because you have the parts on the shelves doesn't mean it isn't a cost.

Put it this way, if I boot my computer and it won't boot with a message stating "nvidia driver missing" I don't assume it's the ram or motherboard and replace them or throw money at other components, I check what it tells me, the nvidia driver, to avoid first checking the very thing its telling you is the problem is moronic.

You don't need to buy direct from the dealer, nor should you with them prices, you'd save 70 just going to icp but tbh I'd be going to a breaker or checking ebay, guaranteed (I've looked and asked) you can get a known working maf for less than 100 from either which costs less than the parts you've already changed, not to mention the time taken.

You can think it's something else all you want but why not first eliminate what it's saying it is before going further or jumping to conclusions plus the fact that your really going to kick yourself if it is and all that time and those parts weren't needed.