TOPIC: 2007 Buick Rendezvous 3.5litre V6

Kyle - I've been pretty diligent in updating this thread about my successes in achieving gains with Wendy.
Yes, it's a 3.5L v6, and yes, for short times in the summer when it's humid and the atmospheric pressure is low, I've hit 50 MPG for brief stretches before the computer jumps in and takes it back up into the upper 30s/low 40s.
the 3 three things this tells me are:
1 - low manifold pressure (high manifold vacuum) does indeed aid in making fuel vapourize...remember, the injectors themselves only atomize fuel; vacuum rips those atomized droplets into the gasoline vapour the engine can burn. Further, the MAP sensor does play a part in determining fuel delivery in that it plays a part in adjusting fuel injector pulse duration, so there's some messing around with that par of the computer we can do.
2 - humidity: not only does water vapour displace air in the intake air stream, making for a gasoline rich exhaust (if we're believers in 14.7:1 air-fuel stoichiometry, which we're not), but it also cools the combustion event, keeping the computer from seeing above average coolant temps and delivering more fuel to quench the burn. All the YouTube videos you see with water bubblers attached to intakes with people saying how it has improved their mileage are onto something, like they were in WW2 on bomber engines when oil/fuel supplies were key to winning the war. (I've thought about putting the BMW cyclone seperator back on Wendy, with the catch can also being the bubbler, but I haven't gotten around to thinking about the plumbing of that yet - it would likely be a closed loop, so that it wouldn't need refilling with water, instead using the condensed water vapour from PCV blowby. My only concern is winter and freezing)
3 - o2 sensors work as designed/implemented at the factory to balance the air-fuel ratio the computer is programmed to adhere to, so if there's a lot of oxygen in the exhaust from a complete burn of fuel, the computer will add more fuel to make itself feel better about how well it's running the engine. this is probably where most groove "failures" occur, so we really need to make sure we can either fool the computer or make it think a bit differently. I've bought an EFIE from George Wiseman at Eagle Research that I've been trying to find the time to install that I'm sure will be a big help in my quest to make Wendy a 60MPG+ vehicle.

So, tell me this, then...

If the fuel burns more completely, how does that INCREASE the O2 content in the exhaust?

The answer (in fact) is that it DOESN'T. The O2 levels actually drop. Most fail to consider that in the combustion process, it is actually rapid oxidation, as the O2 molecules bond with whatever substance is there acting as fuel for the fire. As the system IS designed to adapt to this condition, the answer (at least in the Winter time) is to be found in the TEMPERATURE DIFFERENTIALS.

As the ambient (atmospheric) temperature drops, heat loss from the engine and the exhaust increases. The ECU will force over-fueling of the engine to compensate, as the temperature of the catalytic converter is considered an omnipotent command, overriding all other fuel delivery parameters.

Gentlemen, please. Read the manual... It's also all over the forums in different locations, about all the different ways engines fail to get mileage.

My "failure rate" is less than 3%. There's a reason for that.

After modifying over 4,000 engines, you'd think I might ought to be someone you pay attention to...

Ron

Ron, I also intuitively thought this about O2 in the exhaust. I'd think that more complete combustion ought to cause reduction in O2 in the exhaust. Not to poke at the good Dr. Dude here- your contributions are most valued, Greg!

So, Ron, if I am catching your drift here--then the exhaust insulation mod ought to be particularly valuable to us Norte Americanos, just now. I did my Subaru Outback Shiela already as posted in the forum. Unfortunately, I don't have any pertinent data to share. Mostly 'cause I don't drive it that much yet. but I will, I will...

Tracy G

Re-read that, Ron. I never said the word Increase, I said (well, I was hoping to IMPLY; giving the benefit of the doubt to the smart people here that they's get my gist and follow my stream of thought) there was more oxygen in the exhaust than the computer was programmed to see because we're using less fuel more completely. To clarify: The amount of oxygen drawn in at the induction stroke is metered by the MAF - the o2 determines if enough of it was used making power and changes fuel delivery to compensate; this we're quite sure of by now. And same thing for IAT- I'd bet if the computer in certain vehicles doesn't see enough of an increase in the exhaust temps at the o2 sensors, fuel delivery is also probably adjusted, making the exhaust wrap an important thing. Fact of the matter here is we're not completely aware of the logic and decicion making going on by the computer, but we have learned some (LOTS!) things. What makes this a bit of a trial-and-error process is that every engine and it's computer, from each different manufacturer, complies to the the broad OBD2 standard, but each manufacturer applies it slightly differently to each of their engines. This is why we have to be aware of all the possibilities and how to address them, in my opinion.

I figured it was time to post an update here, as it has been a while and I've recently made a change based on something I saw in another thread, and that change has had positive mileage results.
That's right, Wendy's still gaining mileage..

I saw a reply in another thread that got me thinking about the PCV re-route. I figured it made sense, so I decided to give it a shot, and it seems to be paying off so far.
scroll to the second last post here: Re: No improved gas mileage - Page 2 - Groovy Forums

what I did was plug the factory breather intake into the back bank of the engine with a bolt in a vacuum cap, and then simply routed the stock PCV outlet on the front bank into the intake snorkel (between TB and MAF). It eliminates the T as shown in previous posts here, but it keeps the blowby flowing out in the direction the factory intended; while the vacuum source varies with throttle angle, I'm sure with me opening that hose up to 3/4" ID from the 5/16", the flow has improved, as does system evacuation at wider throttle angles/higher demand.

The result? well, I was cruising along a route I use often and glanced down at the instantaneous Fuel consumption readout in my instrument cluster, expecting to see the usual number or close to it. Instead, I saw a lower one. thinking it was a fluke, I disregarded it. when I checked again a while farther down the road, it was still reading that earlier number: 2.2L/100km at 60km/hr (that's 106.9 MPG(US) at about 40mph)

I know what you're thinking. and believe me, I share those thoughts. But the gas gauge is dropping more slowly, the power feels no different, the tailpipe still doesn't smell...
the ONLY thing I could think of that might contribute to this is that we're still on winter gas (stuff that vaporizes more easily), and that day was about 16 degrees Centigrade(61 F). maybe both this new re-route and the weather/fuel are all factors, but something special was happening.
I still haven't put the EFIE on, I did re-locate the MAP sensor to the factory PCV location, and I did cut down the hose I used to be shorter so the sensor is closer to the manifold. If I could get that type of result year round as an average, I'd be a very happy camper. Even if I could get a consistent 60MPG I'd be happy. I'm getting closer...that's all that matters.

keep grinding away, gadgetpeople!

Well done Greg! If you keep that mpg you will have the championship belt! Keep us informed please. Keep groovin!

Tracy Gallaway wrote: Ron, I also intuitively thought this about O2 in the exhaust. I'd think that more complete combustion ought to cause reduction in O2 in the exhaust. Not to poke at the good Dr. Dude here- your contributions are most valued, Greg!

So, Ron, if I am catching your drift here--then the exhaust insulation mod ought to be particularly valuable to us Norte Americanos, just now. I did my Subaru Outback Shiela already as posted in the forum. Unfortunately, I don't have any pertinent data to share. Mostly 'cause I don't drive it that much yet. but I will, I will...

Tracy G

I was just re-reading the thread and caught a slight failure on my part to FULLY inform on O2 levels. You see, it is the MASS of oxygen that diminishes due to the enhanced combustion. but the RELATIVE values increase.

This means that the O2 is converted into other substances (such as water), and as the formerly waste fuel by-products(CO, CO2, HC and NOx) are diminished, the percentage value of O2 in the exhaust increases.

Sorry. An unintentional omission, gentlemen.

Ron

GregK wrote: I figured it was time to post an update here, as it has been a while and I've recently made a change based on something I saw in another thread, and that change has had positive mileage results.
That's right, Wendy's still gaining mileage..

what I did was plug the factory breather intake into the back bank of the engine with a bolt in a vacuum cap, and then simply routed the stock PCV outlet on the front bank into the intake snorkel (between TB and MAF). It eliminates the T as shown in previous posts here, but it keeps the blowby flowing out in the direction the factory intended; while the vacuum source varies with throttle angle, I'm sure with me opening that hose up to 3/4" ID from the 5/16", the flow has improved, as does system evacuation at wider throttle angles/higher demand.

keep grinding away, gadgetpeople!

Greg, would you mind posting pics? And for all you OTHER guys out there, pictures say a thousand words... So please start posting pics or diagrams to show your modifications so we visual learners stand a better shot at comprehending your efforts!

Ron

Here's what I came up with... Correct me if I'm wrong.
(with my apologies. I used Paint, and I'm no artist.)

And the modified version:

Ron

That's exactly it, Ron, except the breather plug and PCV are reversed in yours compared to mine, so the hose is short. Also, the plug on the manifold for the PCV is where the MAP sensor lives now...probably the location of the deepest vacuum.
I'll shoot some pics...It seems the ones I had posted previously didn't make the transition to this new server, unfortunately.

the only thing I'm concerned with is stuff building up in the back (plugged) valve cover. as long as it's liquid/vapour, it SHOULD migrate to the crankcase, but the heavier stuff might choose to stick around. luckily, we have a fix for sticky valves, if necessary.

I believe you may be correct on the MAP sensor location, Greg. The key is to look at the location as flow. The HIGHEST flow rate provides the LOWEST pressure point.

And most usually, they do it EXACTLY opposite for max economy. MAP in LOW pressure, PCV in HIGH pressure zones.

There are some rare exceptions, as in the FWD Passenger Car Chevy's, but it's "normally" bad for us.

We should start a thread on relocating the MAP (if we don't already have one!)

Hope that helps.

Ron

Just so people can see the difference, here’s a pic of the original (factory) breather/PCV tubing diameter and what I’ve replaced it with. Left is factory, right is mod. To get a seal on the nipple on the valve cover, I used Tracy’s “hose in a hose” trick to match diameters. If I ever have cause to replace the gaskets, I plan on machining the nipple off and replacing it with a fitting for the larger hose, which will hopefully help evacuate whatever vapours are in there.