Lean/rich rough idle issue

2006 4.2 v8 s/c

So…driving last week I started getting lean bank 1 and 1. This week I’ve started getting rich back 1 and 2. Looking at the ltft it’s -20% ish gets back to zero when I rev it. If I take it a run it runs perfectly. When I sit on idle after it it’s a bit lumpy but get gradually worse until it stalls (unless I rev it).

MAF it’s idling between 5 and 6gs o2’s up and down stream are fluctuating when rev’d upstream going back to zero when held at 1000rpm etc and downstream sitting around 7v falling and rising when rev’d. I’m also getting a low fuel rail pressure code? Low fuel pressure but running rich so in my head someone is not holding back the pressure for the fuel rail but then why does it run perfectly off of idle.

Im still getting a cat efficiency bank 1 and 2.

It’s got me completely confused any suggestions for me to poke at?

check for air leaks. unmetered air will make it run rich, but less obvious at higher engine speeds

But my fuel trims would be + not - it would be adding fuel to compensate the unmetered air not taking it away? I’m going to smoke test the intake to make sure. Unless my upstream o2’s are giving false signals

if you've unmetered air then it will add fuel, making it too rich. if i recall the fuel trim values are upside down to what you think they should be

I’m even more confused now . So my understanding of vacuum leaks would be the o2 sensor sensing a lean sate from the unmetered air throwing up a lean code. The ecu has been adding fuel to compensate hat lean mixture giving a +value .

I have the opposite…a rich code which it’s trimming down that gets better with revs .

I’ll smoke test for vacuum leaks tonight

yes you're right, and wrong. the o2 sensor sees more o2 than it expects based on the input from the maf and more fuel is requested which causes the fuel trim value to deviate from the fuel map because its running rich

unless i'm getting brain fog from all the diesesed fumes since falling to the dark side

FraserW said:

a rich code which it’s trimming down that gets better with revs .

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idles at rich, from unmetered air.. which at higher revs goes back to normal because an air leak is insignificant when compared to the higher air flow with an open throttle and a lower vacuum

My life is a lie thank you, this has been a beneficial conversation

I hope I'm not talking bollox!! Wouldn't be the first time

Me too! . Still no idea how unmetered air at idle creates a rich code at the o2. But I’m happy to be proved wrong if it fixes my range

kermit_rr said:

idles at rich, from unmetered air.. which at higher revs goes back to normal because an air leak is insignificant when compared to the higher air flow with an open throttle and a lower vacuum

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Unmetered air usually results in a lean mixture.

Datatek said:

Unmetered air usually results in a lean mixture.

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i thought a manifold leak/unmetered air means the 02 sensor sees more than expected oxygen (thinks its lean) and adjusts the fuel trim to add more fuel?

kermit_rr said:

i thought a manifold leak/unmetered air means the 02 sensor sees more than expected oxygen (thinks its lean) and adjusts the fuel trim to add more fuel?

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You could well be right, I predate O2 sensors.

Vacuum leak is good. I have new 02’s here but I’m reluctant to fit them just yet. I’ve just filled the cats with foam to clean them over night, I’ve directed my attention to the MAF, in my head it can be the only thing that could cause it at the moment, MAF could be telling the ecu the wrong amount of air which it’s adding the fuel for…but that doesn’t explain the improvement under load. Unless I have a small vacuum leak that I’ve missed and a fudged MAF. Thoughts?

Spent a few hours going over the codes and seeing what the diagnostic tool is telling me.

Currently I have 4 codes

Rich on Bank 1 and 2
Low fuel rail pressure
Fuel rail sensor range/performance

So this is leading me in another direction. Car runs perfectly and fuel trims sit around 0 when under load but idling is another mater particularly starting it’s really rough until you give it a few revs and then it will idle.

Given that’s it’s rich and I can see it’s rich I can presume the pump is good.

Anyone any thoughts on this? About to lose the will the live

Forgot to add my fuel rail pressure sensor is sitting at a constant 1.47v it does not change when rev’d anyone know what the voltage should be?

Found the issue. Broken pin on the fuel rail sensor. I have a new sensor coming but the plug is pretty goosed and I’d like to replace it ratting that just put spade connectors on it like a bodge it monkey. Any idea where I’d find a 3 pin connector to suit the frp?

FraserW said:

Found the issue. Broken pin on the fuel rail sensor. I have a new sensor coming but the plug is pretty goosed and I’d like to replace it ratting that just put spade connectors on it like a bodge it monkey. Any idea where I’d find a 3 pin connector to suit the frp?

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Nice find

pwood999 said:

https://www.ebay.co.uk/sch/i.html?_...313&_nkw=3+pin+power+timer+connector&_sacat=0

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looking at those plugs they aren’t right. Any other info