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[Nick W]

So - a case of 1 step forward - about 6 steps back..

Reset codes with tool which eventually arrived today and car is now back to the state it was when I started it for the first time after 7 years. Starts, and then splutters to a stop after about 10 seconds. Was running fine prior to the reset (though indicating a bit fuel hungry on the computer - if I believe that).

I have read that it can take a quite a lot of starts to get it running again (would this imply that some parameter in the fuel / air delivery is a long way off from nominal values). I did about 10 starts but battery is weak (it was one I had lying about), so have left on charge overnight for another crack tomorrow.


 

P0170 Fuel trim malfunction bank 1
P0173 Fuel trim malfunction bank 2

The ECU has tried to correct for under (or over) fueling and reached a limit on both banks.

Given the other symptoms it does point to a fuel pressure issue.

Considering how simple and reliable the pressure regulation is, that seems unlikely to me. But it is so easy to check that I would do that first. And then move onto the more likely causes such as air leaks, exhaust faults, sensor faults, and top of the list, the air flow meter.

[Andy H]

So - a case of 1 step forward - about 6 steps back..

Reset codes with tool which eventually arrived today and car is now back to the state it was when I started it for the first time after 7 years. Starts, and then splutters to a stop after about 10 seconds. Was running fine prior to the reset (though indicating a bit fuel hungry on the computer - if I believe that).

I have read that it can take a quite a lot of starts to get it running again (would this imply that some parameter in the fuel / air delivery is a long way off from nominal values). I did about 10 starts but battery is weak (it was one I had lying about), so have left on charge overnight for another crack tomorrow.


 

P0170 Fuel trim malfunction bank 1
P0173 Fuel trim malfunction bank 2

The ECU has tried to correct for under (or over) fueling and reached a limit on both banks.

Given the other symptoms it does point to a fuel pressure issue.

Considering how simple and reliable the pressure regulation is, that seems unlikely to me. But it is so easy to check that I would do that first. And then move onto the more likely causes such as air leaks, exhaust faults, sensor faults, and top of the list, the air flow meter.

I wasn't suggesting the regulator was at fault (but it might be worth checking that the little rubber pipe is still connected to the correct place on the inlet manifold)

All the above checks are worth doing. A code reader that can display 'live' readings will show whether the air flow meter is giving a plausible reading.

[Doctor Gollum]

Fuel pump.

It will deliver enough rail pressure on initial start to prime the rail when you turn the key to 2, but not enough to sustain running.

Low fuel quantity and the car not being level will exacerbate the symptoms. Ensure that there's at least a quarter tank showing and that the car is level.

Extreme low fuel level will eventually kill the pump as it will not have enough flow to cool it.

[arjc1]

Another brief update. I managed to get the thing started by reving it hard once started. If I held the revs up at about 5000 for a few tens of seconds it would sort itself out and then run OK at idle. But drive off and it was clearly not right - quite lumpy (much worse in Drive or 1 than Reverse oddly). This is a car which was driving OK prior to resetting the fault codes to turn off the EML. No sign of a lack of fuel to hold it up there - and when the thing stalls - the instantaneous fuel consumption reading climbs (from 0.5 gal / h at normal idle to 1.2 gal / h as it stalls) - so looks like the system is trying to deliver more fuel under these circumstances - though I wonder if this is just a calculated value based on assumed pressure and time injectors are open for?

BTW - tank is 80% full - all new 99 octane E5 fuel and all the old stuff was pumped out and new fuel filter fitted.

No great sense out of the ELM327 reader in terms of getting a real-time reading of Air mass flow - or much else in real time to be fair. It came with EasyOBD and Proscan 5.9 - but when you look in the comms logs when asking for real time readings - there are just loads of 'unrecognised commands'  - so clearly doesn't properly support the GM command set. I'll have a look for some more software options. Any suggestions for what will work and deliver real-time readings with an ELM327 interface appreciated.

I have also ordered a fuel pressure gauge - so will be able to get to the bottom of that soon I hope soon.

Thanks again for your interest and help.

   

[Andy H]

when the thing stalls - the instantaneous fuel consumption reading climbs (from 0.5 gal / h at normal idle to 1.2 gal / h as it stalls) - so looks like the system is trying to deliver more fuel under these circumstances - though I wonder if this is just a calculated value based on assumed pressure and time injectors are open for?

I think you are correct.
The symptoms are similar to that of a blocked fuel tank breather. Thing is that the pump should be strong enough to collapse the tank if the breather is blocked (or miss connected).

[Doctor Gollum]

when the thing stalls - the instantaneous fuel consumption reading climbs (from 0.5 gal / h at normal idle to 1.2 gal / h as it stalls) - so looks like the system is trying to deliver more fuel under these circumstances - though I wonder if this is just a calculated value based on assumed pressure and time injectors are open for?

I think you are correct.
The symptoms are similar to that of a blocked fuel tank breather. Thing is that the pump should be strong enough to collapse the tank if the breather is blocked (or miss connected).

Would trying it with the filler cap off prove that?

[Migalot]

No great sense out of the ELM327 reader in terms of getting a real-time reading of Air mass flow - or much else in real time to be fair. It came with EasyOBD and Proscan 5.9 - but when you look in the comms logs when asking for real time readings - there are just loads of 'unrecognised commands'  - so clearly doesn't properly support the GM command set. I'll have a look for some more software options. Any suggestions for what will work and deliver real-time readings with an ELM327 interface appreciated.

James V6CDX and I used scanmyopel software (EUR 9.99) and the real-time readings were easy to follow. Download it and read on your phone. Not sure if it will work with an ELM327 reader.

https://scanmyopel.com/

[grifter]

Take it the battery is ok? I know it cranks over but have heard of duff batteries having just enough to churn it over but not enough to run all the gubbins, causing wizardry in the leccy system, had a similar issue and that was on an old 95 cavy with simple multec injection.

[arjc1]

Sorry for the delay folks - lots going on here - but managed to find an hour tonight to work on it again.

I've found some software which gives sensible real-time readings of data - scantool.net v1.13.

Mass Flow Sensor at idle reports as 3.25 g/s, going up to about 13g/s at 3000 rpm and after running for a bit - long term fuel trim on both banks is pegged at +25%

The car got as far as running quite reasonably tonight - but still a little hesitant as you pull away from idle - so doesn't feel right.

Full readings at idle
RPM : 638
Load Value : 2%
Timing Advance (Cyl 1) : 4.5%
MAF Sensor : 3.25 g/s
Short Term Fuel Trim (Bank 1) : -8.6%
Long Term Fuel Trim (Bank 1) : +25.0%
Short Term Fuel Trim (Bank 2) : -13.3%
Long Term Fuel Trim (Bank 1) : +25.0%
O2 Sensor 1, Bank 1 : 0.295V @ -8.6% st fuel trim
O2 Sensor 2, Bank 1 : 0.440V
O2 Sensor 1, Bank 2 : 0.685V @ -10.9% st fuel trim
O2 Sensor 2, Bank 2 : 0.435V
Intake Air Temperature 44C
Coolant Temperature 89C

And at c. 3000 rpm
RPM : 3085
Load Value : 9.4%
Timing Advance (Cyl 1) : 34.5%
MAF Sensor : 13.25 g/s
Short Term Fuel Trim (Bank 1) : +14.8%
Long Term Fuel Trim (Bank 1) : +25.0%
Short Term Fuel Trim (Bank 2) : +18.0%
Long Term Fuel Trim (Bank 1) : +25.0%
O2 Sensor 1, Bank 1 : 0.195V @ +22.7% st fuel trim
O2 Sensor 2, Bank 1 : 0.440V
O2 Sensor 1, Bank 2 : 0.605V @ +22.7% st fuel trim
O2 Sensor 2, Bank 2 : 0.440V
Intake Air Temperature 41C
Coolant Temperature 95C

The intake air temperatures seem pretty high given its about 13C outside right now - but I don't know if the air is drawn through the radiator perhaps.

Now to demonstrate my real level of ignorance in public.... I bought a fuel pressure gauge - but for the life of me, I can't find the Schrader valve to connect it to. Most of the fuel injection system seems hidden under covers - and I'm at a bit of a loss as to what to remove... sorry ;-)

Thanks again.




I also

 

[dave the builder]

Full readings at idle
RPM : 638
Load Value : 2%
Timing Advance (Cyl 1) : 4.5%
MAF Sensor : 3.25 g/s
Short Term Fuel Trim (Bank 1) : -8.6%
Long Term Fuel Trim (Bank 1) : +25.0%
Short Term Fuel Trim (Bank 2) : -13.3%
Long Term Fuel Trim (Bank 2) : +25.0%
O2 Sensor 1, Bank 1 : 0.295V @ -8.6% st fuel trim
O2 Sensor 2, Bank 1 : 0.440V
O2 Sensor 1, Bank 2 : 0.685V @ -10.9% st fuel trim
O2 Sensor 2, Bank 2 : 0.435V
Intake Air Temperature 44C
Coolant Temperature 89C

And at c. 3000 rpm
RPM : 3085
Load Value : 9.4%
Timing Advance (Cyl 1) : 34.5%
MAF Sensor : 13.25 g/s
Short Term Fuel Trim (Bank 1) : +14.8%
Long Term Fuel Trim (Bank 1) : +25.0%
Short Term Fuel Trim (Bank 2) : +18.0%
Long Term Fuel Trim (Bank 1) : +25.0%

long and short term fuel trims are very bad  should be close to zero
have you checked for unmetered air ,air intake leaks 
ambient intake temp is high but was that with bonnet closed ,in the sun 
 

[Raeturbo]

Dais right👍

[Nick W]

MAF.


As I wrote in post #31.


Disconnect it, and see if the car runs better. That will put the EML on, but it will go back out when the MAF is reconnected. Inspect the wiring around the connector while it's apart.

[LC0112G]

Now to demonstrate my real level of ignorance in public.... I bought a fuel pressure gauge - but for the life of me, I can't find the Schrader valve to connect it to. Most of the fuel injection system seems hidden under covers - and I'm at a bit of a loss as to what to remove... sorry ;-)

There is a schrader valve on the injector rail underneath the plenium. You will need to remove the plenium to get at it though - which basically means you can't run the engine and measure the fuel pressure at the same time. However, the fuel pressure will be a maximum when the engine isn't running, so bridge the fuel pump relay with a paper clip, and monitor the pressure. I suspect it should be 3bar above atmospheric - or 4 bar absolute. Then suck on the small pipe to the fuel pressure regulator (or use a MityVac if you've got one). The fuel pressure should drop, but should not go below 3 bar however hard you suck.

I may be wrong, but your readings don't suggest air flow meter to me. With 2% engine load the ECU is reporting 3.25 g/s. With 9.4% engine load it's 13.25 g/s. That's not far off 5 times for both figures, which suggests the MAF is behaving.   

[arjc1]

Thank you all - very helpful. Disconnected MAF sensor tonight - and car runs worse and strong smell of excess petrol.

EML back on - presume because the fuel trims are beyond the end stops again. Car runs OK, but is a a little lumpy and very gutless.

Thank you for the info about the Schrader valve - I hadn't twigged you couldn't measure the pressure with the engine running - so makes sense now. Will remove plenum and check fuel pressure - but not until after the weekend.

[Andy H]

EML is on because someone unplugged the MAF....

I think that the ECU goes into limp home mode when the MAF is unplugged and runs on 'factory' settings which clears the learned fuel trims.

Does your fuel pressure gauge have a flexi hose? Can you refit the plenum with the fuel gauge attached and lying on the cam-cover?