CEL - Check Engine 2.8 V6

Hi all,

Trying to sort out some problems on a 1996 QP 2.8. We get "Air/Fuel Ratio" code - flashes 1-4. Initially we found that both water temp sensors where far out of spec (6K and 15K) and changed those. That didn't cure anything other than better exhaust gasses... Then we found that the left cam sensor lost contact when warm - so we changed that. No cure here either... The air temp and MAP sensors have been tested and found ok.

The engine runs strong until it is at working temp - then the engine lights come on and it will start to misfire slightly - and with noticeable reduced power. A quick on/off with ingnition switch clears it up - but just for a few minutes.

After all these repairs we still get same fault code. As I understand it it's the water-/air- and MAP sensors that can throw this 1-4 code. All other sensors,the lambda/cam/crank/TPS,have separate codes.

Are we missing something ? I know the air conveyor - 571060300 - is a bit loose and the screws have been over tightened and punched holes in the throttle valve body. Can that be the issue ?

Would be very happy for any tips and advise.

Thanks - Arvid

Have I missed something, and it's a bit of a guess. What's the water temp sender saying?

C

CatmanV2 said:

Have I missed something, and it's a bit of a guess. What's the water temp sender saying?

C

Click to expand...

We have changed both as they where both far out of spec - one at 6K ohm and the other at 15K ohm. Should be about 3-4K at room temp.

Arvid said:

We have changed both as they where both far out of spec - one at 6K ohm and the other at 15K ohm. Should be about 3-4K at room temp.

Click to expand...

Yeah, sorry, been at the post car cleaning bottles.

OK, again, a bit of a guess. It's electronic ignition? Is it possible that one or more of the injectors are getting hot and moving out of spec?

C

Try swapping the Map-sensors.

I haven't thought of that. Can they do that ? They might be worn or partly clogged with a bad spray pattern. That can surely result in faulty air/fuel ratio. I'm more curious about the on how the engine is effected by false air from the air intake. How will this engine respond to that with the lack of a modern Mass Air Flow sensor ?

Arvid said:

I haven't thought of that. Can they do that ? They might be worn or partly clogged with a bad spray pattern. That can surely result in faulty air/fuel ratio.

Click to expand...

I don't know, but I'm trying to think of things that would cause a bad fuel/air ratio. Cleary 'something' wrong with the injectors could do that very thing. They are electromechanical (I assume) so moving parts will wear. Heat will change they way things operate and so.....

Totally no assurance that I am even vaguely correct, but if it was my car, that would be where my head would be going.

C

Wally said:

Try swapping the Map-sensors.

Click to expand...

Tested them both this evening. They seem fine although they where not 100% equal. They measured 4.95 volt and 4.85 on pin 1 and 2 volt with 1 bar pressure applied - starting from atmospheric pressure and 1.75 volt. Could that measly 0.1 volt result in a fault code ?

There has been a slight progress today. The aux air screw on the throttle body was shut - and that can't be correct. In the first post I mentioned that the valve body was sucking in false air due to someone overtightening the air conveyor onto it. Therefore they have shut the air aux screw to lower the idle rpm. We'll se later today if these improvements have resulted in anything positive.

When we ran the engine earlier today it idles fine from cold until it shifts into warm condition - then we get the 1-4 code immediately and uneven idle. I believe the aux air valve shuts when the engine is warm enough - and since the aux air screw was shut it will end up with to rich mixture ??

Arvid

Another update. We just found that the left lambda was not regulating - this is something we haven't investigated thorough enough until now. We concentrated on the air/fuel ratio fault code and the way the manual suggest to remedy that - that being the sensors for water/air/cam/crank. Along the way we found faults on three of those but in the end it still threw the code and started idling uneven. As a test we then disconnected the left lambda as this was the exhaust that smelled most rich. The car then idled normal although with a new code 3-1 for lambda

Have now changed to a new lambda and both the 1-4 and 3-1 codes are gone - car runs strong and idles fine. It seems that the air/fuel fault was a direct cause of the lambda fault - and that the system chose to throw a 1-4 code instead of 3-1 for lambda. If it just could have been the other way...

Let's see what the next days of test driving will disclose...

Probably means the lambda value was acceptable, jut making the mixture too far out. Sounds stupid, but there is a *certain* amount of sense.

Glad it's all sorted

C

Good news...fingers crossed for today...and the sun is out too.

safrane said:

Good news...fingers crossed for today...and the sun is out too.

Click to expand...

No sun here though but the engine has seen the light ;-)

The car was run extensively on long trips both yesterday and today without faults. I think it's ready to go back to its owner who was somewhat frustrated of his firts Maserati experience. It now boosts into the orange on the gauge and runs strong and clean smelling. It's puzzling that the engine even ran with so many sensors giving faulty signals.

We used the AG25640 decoder and it helped us a lot along the way. Can this be used on the Evoluzione also ? Who knows I might encounter problems with this one also along the way ;-)

Yes it can, where did you find it? I would be interested in one but they can't be found anywhere. There is a company in Croatia that can provide a software for laptop that can read the ECU's. I was in a discussion with them a couple of years ago but didn't pursue it because they would have needed a chipdump from the ECU. I didn't dare do it even if the local contact said he could do it, chip needs to be extracted from the mainboard for the dump.

aaw said:

Yes it can, where did you find it? I would be interested in one but they can't be found anywhere. There is a company in Croatia that can provide a software for laptop that can read the ECU's. I was in a discussion with them a couple of years ago but didn't pursue it because they would have needed a chipdump from the ECU. I didn't dare do it even if the local contact said he could do it, chip needs to be extracted from the mainboard for the dump.

Click to expand...

Sadly the decoder belongs to the owner of the QP 2.8 - lucky for him as I can't find one for sale. I should want one too now that I know it fits the Evoluzione. I read somewhere that it is no big deal to make your own. It is very uncomplicated with simple switches that breaks or closes circuits. I need to find that article again