Another MAF failure?

[nzflash]

On my 99 Chim 400 rovergauge is showing - 100% long term trim for both banks.

Have tested MAF and spikes to just over 0.6 volts before settling down to about 0.4 after about 10 to 20 seconds.

Firstly, does this sound like a failed MAF?

Secondly, does anyone know of a reputable place to source a replacement?

Other than appearing to run a bit rich the car runs well.

As usual, thanks in advance for the support.

[Belle427]

Maybe let frank here analyse the data for you if he pops up (blaze away), very useful to see it first before spending on a new one.
https://www.pistonheads.com/gassing/topic.asp?h=0&...

Edited by Belle427 on Wednesday 1st May 06:59

[blaze_away]

Belle427 said:

Maybe let frank here analyse the data for you if he pops up (blaze away), very useful to see it first before spending on a new one.
https://www.pistonheads.com/gassing/topic.asp?h=0&...

Edited by Belle427 on Wednesday 1st May 06:59

Cheers Steve....yep here to help if you want it.

I will need a specifically run dataset. Will post how later when I can fire up my laptop..

Edited by blaze_away on Wednesday 1st May 08:15

[nzflash]

blaze_away said:

Cheers Steve....yep here to help if you want it.

I will need a specifically run dataset. Will post how later when I can fire up my laptop..

Edited by blaze_away on Wednesday 1st May 08:15

Awesome, thanks.

[blaze_away]

1. Plug the 14CUX cable into the loom connector on the car
2. Start RoverGauge software
3. Setup RG opions settings as follows
a. COM - COMx (use whatever COM port works for you)
b. Speed - mph
c. Temperature – Celsius
d. Parameters to log – all but not road speed or gear selection

4. Set RoverGauge main screen as follows:
a. MAF – Direct
b. Throttle – Absolute
c. Trim – Short Term

5. Turn on the ignition switch and press ‘connect’ to link 14CUX with your laptop.
6. Preferably start the car from cold.
7. Start logging the data (Start Log F5) and drive the car for 15 minutes on a local roads (eg A or B class to get varying running conditions) then stop the car and allow the engine to idle for a further 5 to 10 minutes. (DO NOT TOUCH ANY OF THE CONTROLSAT THIS STAGE)
8. You can now stop logging data by pressing “Stop Log F7”
9. Send the logfiles (held in a sub folder where RoverGauge is) to me (I will msg you my email address)

[blaze_away]

your profile does not permit me to email you so you'll have to msg me via ph

[nzflash]

blaze_away said:

your profile does not permit me to email you so you'll have to msg me via ph

Can you try now? I've tried updating my profile.

[pmc_3]

I had a similar issue one lambdas was showing -100% on short term and the other was high in the - numbers. I was getting black soot lines when starting the car and you could smell it was rich. Mine did flag an error for injector bank even. I chased it for a while checking injector wiring, had injectors tested, checked fuel pressure. Rovergauge logs didn't indicate an issue with the MAF but like yours mine took a long time for the voltage to come down. In amongst the fault finding I bought a secondhand MAF to keep as a spare, I thought I'd try it to see if it made any difference and suddenly all of the over fuelling stopped, lambdas sat around the middle and no black soot lines anymore. If I plugged the other one back in it went straight back to overfueling.

Here's the thread https://www.pistonheads.com/gassing/topic.asp?h=0&...

Edited by pmc_3 on Wednesday 1st May 12:19

[blitzracing]

nzflash said:

On my 99 Chim 400 rovergauge is showing - 100% long term trim for both banks.

Have tested MAF and spikes to just over 0.6 volts before settling down to about 0.4 after about 10 to 20 seconds.

Firstly, does this sound like a failed MAF?

Secondly, does anyone know of a reputable place to source a replacement?

Other than appearing to run a bit rich the car runs well.

As usual, thanks in advance for the support.

The standby voltage is CRITICAL is it sets the point for scaling across the whole airflow range. It should fall in the region of 0.3-0.34v. Higher than this will cause the engine to over fuel, but If you take Frank up on his kind offer he can analyse the whole airflow scaling against good AFMS

[nzflash]

Thanks all. Frank is reviewing a log for me to determine if anything is amis. I'll provide an update when we have the results.

[blaze_away]

nzflash said:

Thanks all. Frank is reviewing a log for me to determine if anything is amis. I'll provide an update when we have the results.

Had a look and unfortunately I think OP ran the log with MAF set to LINEAR where as I need it run at DIRECT (for comparison to good and bad MAF's).

Good news though all the sensors are working OK, although Idle bypass is low so suspect base idle is not set correctly but will know more when OP does a re-run.

[blaze_away]

Logfile is analysed and I would say the MAF is all good, all sensors are working as they should and are within normal parameters except Idle Contrlol is a bit low at around 18% its better at 25 to 30 and just needs base idle reset.

The MAF is bang on normal at idle rpm showing 0.31 (ie 31%) with Std Dev 0.0027 anything under 0.005 is a good MAF)

Here are the charts for those who like to take a look.

Question remains why is OP's long term trim at 100% ?

Have suggested he looks at ignition and ensures thats in top order switch plugs to 6's and ditch the extenders. what other suggestions ?

[nzflash]

Thanks Frank that's awesome.

Further detail on the car..

Running bpr6es plugs with plug extenders removed.
Full manifold vacuum
Relatively new stepper motor which improved running behaviour

Generally the car runs well and doesn't stall, returning to smooth idle after driving.

I'll try resetting the base idle again to try and lift idle bypass to 30%

Cheers.

[nzflash]

Latest update. Brought the car up to temperature to the point the fans came on and off.

Adjusted idle so bypass is now reading 27%.

Disconnected ecu to perform reset.

Started car and confirmed long term trim was zero.

Over a relatively short period the longterm readings went to - 100% on both banks.

If I clamp the idle bypass hose the revs drop significantly and the engine will stall at about 500rpm....

Would appreciate any other thoughts out there to explain the long term readings.

Thanks.

[Belle427]

pmc_3 said:

I had a similar issue one lambdas was showing -100% on short term and the other was high in the - numbers. I was getting black soot lines when starting the car and you could smell it was rich. Mine did flag an error for injector bank even. I chased it for a while checking injector wiring, had injectors tested, checked fuel pressure. Rovergauge logs didn't indicate an issue with the MAF but like yours mine took a long time for the voltage to come down. In amongst the fault finding I bought a secondhand MAF to keep as a spare, I thought I'd try it to see if it made any difference and suddenly all of the over fuelling stopped, lambdas sat around the middle and no black soot lines anymore. If I plugged the other one back in it went straight back to overfueling.

Here's the thread https://www.pistonheads.com/gassing/topic.asp?h=0&...

Edited by pmc_3 on Wednesday 1st May 12:19

I think id try another Maf personally as above, maybe a kind member will let you borrow one for testing purposes?

[nzflash]

That is my next plan. I've been in touch with a mate to try his on my car once he's confirmed his is reporting correctly.

If anyone has a healthy spare they're willing to part with I'd be interested in buying it. No harm having a few spares as I'm in New Zealand so spares are not readily available.

[blaze_away]

Before you off chasing ghosts that is not how to set base idle.

Fully warmed engine clamp stepper feed and adjust revs to 650 700 ish. Unclamp stepper hose.

See what % you get. Is it at 25%ish ?
No you have a problem eg vac leak.

Setting it the way you did it will result in system being set incorrectly. What you've done is useful because it now does suggest you have vac leak albeit only a small one.

Hope that helps.

Edited by blaze_away on Saturday 4th May 12:41

[blitzracing]

You are limited to why it's running rich. It's down to a wrong fuel map, over high fuel pressure ( check the vacuum to the fuel pressure regulator), temp sensor reading too low or AFM reading high. Also check your inlet pipe is not collapsing. It upsets the plenum vacuum and causes all sorts of weirdness you can't diagnose.

[nzflash]

blaze_away said:

Before you off chasing ghosts that is not how to set base idle.

Fully warmed engine clamp stepper feed and adjust revs to 650 700 ish. Unclamp stepper hose.

See what % you get. Is it at 25%ish ?
No you have a problem eg vac leak.

Setting it the way you did it will result in system being set incorrectly. What you've done is useful because it now does suggest you have vac leak albeit only a small one.

Hope that helps.

Edited by blaze_away on Saturday 4th May 12:41

Have reset base idle again and bypass is back to 20%.

Have gone over all pipes carefully and can't find any leaks.

Have checked plenum and all seems good.

Not sure if running full manifold vacuum affects achievable bypass values?

Trying a friend's MAF soon will help with diagnosis process...

[blaze_away]

OK great that base idle is set. The vac leak if there is one is relatively small so won't be easily seen. Can't remember if I asked this already.....did you check using a smoke generator ? Its the only way to find them.

Just a thought....Do you have an overly thick gasket on the stepper motor ?