Testing MAP sensor with vac gauge - due to rough idle

[Pete30nz]

Kaiapoi NZ, on Google it says we are 6 meters above sea level.

Could I still be chasing a bad intake manifold gasket?
I do have one here to replace.

Could it be a Crack in the exhaust manifold that's playing a part?

Having a sniff at the exhaust end, it smells a bit rich.

Today I also swapped over to the after market adjustable fuel reg. Didn't seem to be alot different.

[vlad01]

Generally the intake gaskets only leak coolant into the intake ports or externally, also oil can get sucked into the coolant via the PCV ports. I personally have never seen a vacuum leak on these gaskets and I had some catastrophically bad ones.

It could be the engine is getting tired or a mechanical issue and the VE table no longer matches the actual VE of the engine. I found that was the case with my current daily yesterday, VE was down 15-20% compared to all the other engines using my dyno tune, I have seen max 1-2% difference, not around the 15-20% mark.this engine has. So I just reduced the injector rate by negative 20% and the VE was pretty bang on for what the engine wanted. I already ruled out fuel reg, O2 and MAP. Even the engine vac was pretty good at 30 Kpa idle but was a bit higher than usual at cruise. I suspect a damaged head gasket from when the intake gasket flooded the intake with coolant and probably hydro'd the cylinders. Never idled or drove the the same after the intake flooded with coolant, down on power and a slight miss on 1 or 2 cylinders and it's not fuel or spark related, not really a miss but rather a weak firing. I haven't got a comp test kit to check the comp but the car has driven 10s of 1000s of Ks and over a year like this already.

[Charlescrown]

With a manifold vacuum reading of 21 @ idle your engine is in top condition with no intake leaks. I do know these engines have an issue as the O2 sensors get old they get slow in response which will cause a rich mixture. You should be able to view the O2 sensor activity with TunerPro. Not sure what model your car is but from memory one used 2 O2 sensors one in eack bank and they has an earth problem. I'd have to dig through my old notes on that one.

[Pete30nz]

Hi

This is the VR V6 just the one oxygen sensor. Brand new 2 weeks ago.

The oxygen sensor data is in the most recent data logged a few messages above.

Cheers

Yea the VS v6 has the sarth problem from memory.

Edit: photos of sensor data attached

[vlad01]

VR only has 1 heated o2 just before the cat and they didn't have any grounding issues, that was VS onward. Anywho, o2 isn't even used at idle as that is open loop. The stock AFR for idle is 13.0. However, even if vac is good there can be a shift from actual VE to the VE in the cal as I found out 2 days ago in my daily and that effected the fueling everywhere including idle and is worth looking at. This could be the reason why some healthy cars use way more fuel than others which are otherwise the same and have no sensor issues or alike.

I just drove to work (100km, city and highway) and the fuel reduction in the cal made a big difference in idle drive and stop/start, the car no longer bunny hops in idle and doesn't want to stall when stopping. All because it was running too rich. So far on the fuel gauge it appears to be getting better economy by I will know on the next fill. Last fill was 11.8L/100 which is way too much for this car.

[Pete30nz]

I could swap back to the factory memcal, and see if that makes a difference. But from memory, I don't think it will.
How would I go about checking the VE ?

Cheers

Edit: my last tank of fuel I got about 570 to 580kms highway and city

[vlad01]

All I did is warm up the car by driving around for 20 min or so. In N or park I rev and hold the engine rpm over a number of spots at random and wait for the target AFR to go 14.7 and closed loop indicator to go green. Then hold there and see what the integrator does while watching the O2 voltage and cross counts to confirm. For my engine the 02 was pegged at 900+ mV and the cross counts were 0, the integrator crept negative until it was maxed out at - 20. This confirmed it was way out to the rich side. I repeated in other rpm/load areas that use 14.7 and it confirmed without a doubt it was out.

I also checked while cruising at 80-100km/h, same thing. integrator was anywhere from -15 to max of -20. So I subtracted the injector rate by the same range until the integrator was as close to 0 with good 02 readings and high cross counts in as many test rpm/load areas with 14.7 as practical.

Also watch out for lean cruise. I turned it off in the tune for the cruising tests so I could see the integrator working as in lean cruise it's disabled.

You want a wide band ideally but I used the 02 as my tune was done on a dyno/road for this combo and is spot on for all my other cars with this combo of mods, just this engine is way out as it's probably worn/damaged. The VE is close enough just needed moving down to get it in the ballpark and not miles out. It's a band aid as mentioned for a mechanical issue or maybe a factory variance from the typical engine.

Just goes to show, every single engine in an ideal world should be tuned individually.

[vlad01]

First work run on the lowered injector rate. 9.3L/100km. Very substantial improvement. I expect in the 8s on a good run as the weather and traffic was bad today. Basically it's back to how it used to be economy wise.

[Pete30nz]

I'll post up my log later on, I logged on the drive into work today. I saw the oxygen sensor in double digit yellow and 3 figures in blue and red. But I didn't see the calculated VE change, if it should?

[antus]

calculated VE is designed to be used with the histograph. its an interesting attempt at a way to tune but in practice didnt turn out to be very effective and made smooth maps more spikey (which is sign they are incorrect) as you tuned. You can still chart it on the monitor to get an idea, but its not the best way and you need to manually account for its limitations.