Falling out of lean burn on 94 VX

[jeffcat]

I bought a new 94 VX a few weeks ago and I'm getting acclimated to how it drives and what things need serviced on it, but I have been driving a few times around 65mph and cruising. I don't feel the "lean burn" plummet in power some people refer too, but I'm just presuming it's in lean burn, because I'll be cruising at 65mph and then out of nowhere, you can feel a pickup in power and it begins to accelerate faster than 65mpg...presumably falling out of lean burn and getting more power because of it. Is that typical of the VX to fall out of lean burn at such a low speed, or what would be the cause of that?...EGR issues? Excuse me for being stupid...I just noticed it yesterday while driving a distance and was curious how to keep it in lean burn at those speeds or even up to 75mph as I'm only at around 2100rpm or thereabouts at 65mph.

[firehawk618]

I can't speak directly of the VX but can tell you how my HX works.

From what I understand the VX is much faster to go in LB vs the HX.

With my car it's much easier to get it into LB when you meet the following conditions:

RPM's ~2700. It will go in at lower rpm's. I have watched it kick in just under 2000 before but it's much harder to do it below 2700 rpms. It will kick out of LB at 3100 on the dot.

Throttle position must be 20.9% or lower but above 10%. On my car 10% TP is foot off throttle, so you must be on the throttle a touch but never above 20.9% to engage it. Once it is in LB I can roll into the throttle and at that point I watch engine LOAD. Once the load hits just north of 90% it will kick out of LB.

Engine load: It must be pretty low for any hope of LB. I have not figured out the lower / upper threshold that must be met to engage LB yet.


Speed: Mine will engage as low as 28 mph but will kick out at 75 mph. THis is because at 75mph I am at 3100 rpm's. I'm confident if I had taller gears I could go faster.

I am very happy with the gearing in my DX transmission. I don't need to exceed 75mph. 65 mph puts me at the sweet spot to get LB engaged. ~2700 rpm's.


I know if I have engine codes then LB will never engage. I am battling EGR issues right now * to be fixed today* and have a persistent pending P401 code. Low EGR flow. I can still get LB because the code is pending and not a hard code yet.

O2 sensor is another touchy one. If yours has never been replaced I would suggest to pony up the $$$ and just do it. O2's can test fine, look fine on a scope but not be fine. Especially our super sensitive Lean o2 sensor.

Maybe for giggles try cruising the highway in 4th gear for a day and see how LB goes. I bet you have an easier time keeping in LB because 5th is so super tall which puts your engine load higher and throttle position higher.

It sounds like you do not have MPGuino. I highly recommend one if you're serious about really monitoring what's going on.

That bump in power you experience is most likely what you think it is. LB dis engaging. It could also be issues with your EGR system. The only way I can think of to tell for sure is an MPGuino.

[Chrysler kid]

Lean burn feels like you are dragging a parachute at 65mph. The car requires a steady pedal to stay in lean buburn

The kick in power you are describing does sound like it's coming out of lean burn

Start with the basic tune up items like wires cap and rotor and plugs and see if you notice more improvement

[firehawk618]

"dragging a parachute at 65mph" That's a great way of putting it. lol Very true.

When this parachute deploys do not hammer down on the throttle or it'll kick right back out. Ease into it to maintain your speed if needed.

[OG VX]

Hey, I got to go right now to work. But real quick, basically it sounds like you're right. Get yourself a vacuum gauge as soon as possible. Basically, with the VX, I found that if you stay at 1.7 bars or more, you're in Lean burn.

[jeffcat]

I've only had the car for a couple weeks now, and I'm just getting around to routine maintenance right now, but after that, I'm going to get into aero mods, and guages like MPGuino, scanguage, vacuum, etc. after I research them a bit, but I know little about hooking them up for the VX or what each one specifically reads, so I'll have to look into it more.

I changed the engine and trans fluid, so next up, I have a new air filter, and I might just take the entire intake off to clean out the EGR valve, IACV, and entire intake assembly where the EGR ports are. What about the spool valve? Does that ever get dirty or need maintenance done to it?

It just seems odd to me that with the tires at 50psi and cruising at 65mph, that I'm popping in and out of lean burn on level ground. I figured it probably wouldn't do that until 75 or so, but I'm not experienced on that matter. On level ground, how fast can you guys go before you fall out of lean burn in mph and RPMs?

[firehawk618]

Originally Posted by jeffcat

I've only had the car for a couple weeks now, and I'm just getting around to routine maintenance right now, but after that, I'm going to get into aero mods, and guages like MPGuino, scanguage, vacuum, etc. after I research them a bit, but I know little about hooking them up for the VX or what each one specifically reads, so I'll have to look into it more.

I changed the engine and trans fluid, so next up, I have a new air filter, and I might just take the entire intake off to clean out the EGR valve, IACV, and entire intake assembly where the EGR ports are. What about the spool valve? Does that ever get dirty or need maintenance done to it?

It just seems odd to me that with the tires at 50psi and cruising at 65mph, that I'm popping in and out of lean burn on level ground. I figured it probably wouldn't do that until 75 or so, but I'm not experienced on that matter. On level ground, how fast can you guys go before you fall out of lean burn in mph and RPMs?

Pull your intake and clean the EGR, passages and the ports under that plate. If it's like the y5 they'll be clogged. Do not miss the little holes that feed EGR into each cylinder. Chances are those are clogged and are easy to miss.

Test your EGR valve also. Use a VOM and make sure the position sensor is actually working.

It seems my car is very sensitive to a PROPERLY functioning EGR for LB to happen more. When my position sensor was faulty I always had one of two pending EGR codes. I would still get LB but it seems MUCH easier now that I have resolved those issues.

The IACV will also be dirty. Pull it and clean it out + the screen.

I think you're going in and out of LB because your VX gears keep your rpm's soooo looowwww. My car LOVES 2700 rpms for LB. Once it's in LB I can let the rpm's go down to as low as 1800 rpm's at times and as high as 3099 rpm's. Anything above 3100 and it immediately kicks out of LB.

You can't use a Scangauge or Ultragauge. Your only real option that I can think of is MPGuino. The first 2 gauges require OBDii which you are not and they really don't work to calculate MPG on a LB vehicle either.

Try cruising in 4th gear at highway speeds, make note of your RPM's. See if LB is easier to engage and keep engaged.

I'm not sure if it's better to cruise in LB at a higher RPM or shift to a lower one and never get LB.

Once I have my MPGuino in hand I will be testing this kind of stuff.

I have a hunch that I will be better off at a higher RPM in LB vs lower RPM and no LB when cruising.

Keep in mind, all the LB talk I mention is how the HX behaves. I can't see the VX being that much different.

I am running a DX geared transmission so 60-75 mph in 5th keeps me ~2400 to 3100 RPM's. Perfect gearing for LB at highway speeds for me.

[firehawk618]

Good reading for your VX here.

If this guy's accurate then the logic in the VX vs HX ecu is totally different.

http://ecomodder.com/forum/showthrea...nfo-18050.html

[jeffcat]

Alright thanks, I'll look into that. I actually took the car on it's 1st distance cruise today. I did the 1st fill up and it was at about 35mpg since purchase. Obviously horrendously low, but I also drove the car about 70/30 city and drove it really hard a few times, just to see how the car behaved and what's it's limits are. I also had it idling for the better part of 3 hours probably through warming it up in the cold, dealing with fluid changes, and playing around with things while inspecting it.

Anyways, I drove across Ohio today, but before the trip I put in Shell 93 V-Power fuel. I'm not expecting anything beneficial from the octane rating, but I wanted to run their cleanest fuel and presumably least ethanol content fuel(still waiting to hear back on that verdict). At any rate, it ran fine on it...couldn't really say for better or worse, but maybe a little smoother, but it probably had nothing to do with octane, but the additives. I stopped in Akron at a BP, just to see how much fuel I went through driving from across the state and it came out to 52mpg, which was commendable as I drove 65-75mph the entire way there, but I was bouncing in and out of lean burn, but was in lean burn maybe 4/5ths the trip.

I've only had the car 2 weeks and of course a snowstorm hit Mansfield and my tires are at 50psi and the car slid off the road and had to be towed out. Luckily, I don't think anything was damaged or hurt and neither was any of the 7 other vehicles that slid off in the same spot...go figure...just my luck that a new vehicle has this happen.

At any rate, I drove back from Akron and I noticed something a little odd. Earlier on the trip and since I have owned it, I was pulling 2100rpm at 65mph. On the way back, I was pulling 100rpm less at 2000rpm at 65mph. I know that seems like a trivial difference, but to just suddenly decrease 100rpms for no reason seemed quite odd to me. This was on perfectly level ground. At any rate, it seemed to be able to stay in lean burn a little longer around 70mph, instead of 65mph.

Perhaps, the previous owner just had it sitting too long and it just needed ran...or maybe the Shell V-power actually cleaned up some bits of the engine from running through it long enough....hard to say, but we shall see. On the way back, I probably averaged about 40mpg, but I also drove through the Akron city more and we were idling off the side of the road for almost 2 hours, AND battling treacherous snow at lower speeds in lower gears for quite a while, so that was actually commendable.

[firehawk618]

It's physically impossible for your RPM to MPH correlation to have changed without any modifications *transmission* or clutch slipping *which would not be a consistent 100rpm difference*.

I would place the blame on either the speedometer or tachometer being inaccurate.

Considering the weather you describe and a massive amount of idle time 35Mpg seems pretty good to be honest.

I believe these guys who get north of 50Mpg in their VX or HX are very careful drivers.