Lean Tip In

[Tom @ Fast Forward]

I have a customer who is experiencing a problem with the A/F going lean just before it reaches boost. Before the PC-Pros can do anything about it. Are any of you with 94-97 (or other years) experiencing this? I have a 99 and an 05 and both of those glide in and out of boost so easy that you wouldn't even know it was going in and out of boost if I didn't have a gauge.

Doug says that as he starts to depress the pedal, the A/F goes lean and the car bogs a bit. Then enters boost, gains fuel and all is well.

He purchased an O2 clamp and it appears to fix the problem. I think it is a bandaid and the real problem needs to be fixed.

Any ideas?

All that comes to mind is either a bad O2 or a MAF problem?

[Mark]

My 95 transitions very smoothly going into and out of boost. Unless you're looking at the boost guage, you don't even know you've made the switch. My problem is when cruising along in any gear with RPM's around 2700. It wants to cut full to full lean and then back to normal. So if I'm making my way through the subdivision, it want to drive real jerky. Makes you look like some kind of goof until you can get to a gear/rpm combo that gets you away from that spot.

[Tom @ Fast Forward]

Steady 27oo RPM and off boost it just goes lean?

[BlownMX5]

My '94 does this (the "lean then rich" behavior). I don't have any Zeitronix data logs with me that show this, but I'm sure I do at home. Question: is this happening when just slamming the gas pedal to the floor, or during a quick but gradual opening of the throttle? Mine does it when doing a dyno-like run (quick flooring of the throttle).

[Mark]

Yep. Steady 2700 RPM. Off boost. Goes full lean. My AFR gauge drops to 15.1 and then right back to high 13's/low 14's. Just enough that the car lurches from the stumble. And if you had your foot "light" on the throttle, it lurches enough to make your foot bounce on the throttle to make it lurch even more.

All is fine while accelerating from a dead stop on up through the gears. Just when I'm motoring along trying to keep an even speed steady speed.

[Kyp J]

My 95 transitions very smoothly going into and out of boost. Unless you're looking at the boost guage, you don't even know you've made the switch. My problem is when cruising along in any gear with RPM's around 2700. It wants to cut full to full lean and then back to normal. So if I'm making my way through the subdivision, it want to drive real jerky. Makes you look like some kind of goof until you can get to a gear/rpm combo that gets you away from that spot.

Is this even after warm? Probably a case of apples and oranges but my 2001 does something similar when cold. If I let it warm up a while before leaving the driveway it doesn't do it. I blame it on the big TB exceeding the ability of the ECM to make small enough changes to keep it smooth. (I also don't know anything, I just made that excuse up.) Someone else blames it on the 2001, & 2 ECM recall but that wouldn't apply to you. I have to take my foot completely off the gas to keep from looking like a 16 year old girl trying to learn to drive a stick.

[Tom @ Fast Forward]

The 01-05 has the problem of the VVT oil control valve no wanting to move easily until the oil gets a little heat in it. This was originally corrected by the VTCS but that went with the old manifold. Typically it is a 30-60 second problem on a cold start.

[Mark]

Is this even after warm? I have to take my foot completely off the gas to keep from looking like a 16 year old girl trying to learn to drive a stick.

Warm or cold, I feel the same way... Not that 16 year old girls learning to drive a stick is a bad thing :) My wife won't even think if driving the Miata! I wish she had tried to learn back when she was 16!

[Kyp J]

The 01-05 has the problem of the VVT oil control valve no wanting to move easily until the oil gets a little heat in it. This was originally corrected by the VTCS but that went with the old manifold. Typically it is a 30-60 second problem on a cold start.

On topic: Do the 94-97s have the adjustable TPS?

Off topic: sorry

If I drove like a guy I worked with many years ago it wouldn't be noticeable. He would crank up his 900 cubic inch (or whatever they were in the 60s) Dodge challenger, immediately burn rubber backwards out of the parking space and hit the road out of the parking lot in a drift, burning rubber for a block up the road. Everyone else just stayed back until he was gone.:driving:

(He was in a hurry to get to the first beer of the afternoon :cheers2:).

He also did this after a bunch of beer at a company summer picnic and backed over a bunch of boulders so bad he had to tow it off them. If he had hit them like normal drunks it would have just bashed the bumper.

[mx5jmcb]

Yep. Steady 2700 RPM. Off boost. Goes full lean. My AFR gauge drops to 15.1 and then right back to high 13's/low 14's. Just enough that the car lurches from the stumble. And if you had your foot "light" on the throttle, it lurches enough to make your foot bounce on the throttle to make it lurch even more.

All is fine while accelerating from a dead stop on up through the gears. Just when I'm motoring along trying to keep an even speed steady speed.

same here even though its less of an issue when warm

[Tom @ Fast Forward]

Have any of you tried a new front O2 sensor?

[Mark]

I'll let you know tomorrow or the next day as I just installed a new O2 sensor up front. I'll probably get the car out on the road at lunch tomorrow.

[Tom @ Fast Forward]

Just curious if those who have the lean problem have a narrow band O2 gauge? We found once upon a time that the O2 sensors don't always like things across them. Especially during cold start.

[Mark]

Nothing on the stock location narrow band sensor other than the ECU. I've got an Autometer wide band with the sensor about a foot downpipe from the stock sensor location.

[Mark]

Have any of you tried a new front O2 sensor?

Went out for a short drive at lunch time today. First chance I've had to drive since replacing the narrow band o2 sensor for the ECU. It stumbles both when cold and when warmed up. :(

[Tom @ Fast Forward]

Vacuum leak? Only other thing. You could be getting air into the system someplace after the MAF. Mark in Kentucky used one of those long butane lighters to find his. Flick your BIC but don't let it light. Then move the end of it all over the kit with the engine idling. If it comes near a leak, the idle will increase. Start at the outlet of the MAF. Run around all of the seams where one device bolts up to another.

[bogey]

Or use a propane torch... Just don't light it off!

[Tom @ Fast Forward]

Yep. lighting either one and testing around the 3" hose will result in huge leaks whether there were any there or not. :)

[Kyp J]

Or use a propane torch... Just don't light it off!

I was going to make a joke about making sure the garage door was closed but thought better of it.

Is propane or butane heavier or lighter than air? When I was using the ether, it would drop down into the air filter and speed up if I got near the front of the engine. Coincidently the front of the manifold is also where the leaking was occurring. Had me confused for awhile until I saw all the broken studs.

[Mark]

I tried both butane and propane with zero effect on the idle. I tried watching the boost gauge to see if I could see a difference in the vacuum between idling and cruising down the road. Nothing discernible. I'm going to try and spend some time over the weekend going over all vacuum connections to make sure they're all good.

[Tom @ Fast Forward]

Mark, At idle you should see around 18" vacuum. At cruise, you should see around 10" vacuum.

[bogey]

Just curious if those who have the lean problem have a narrow band O2 gauge? We found once upon a time that the O2 sensors don't always like things across them. Especially during cold start.

I have a narrow band. I see a little bit of lean at tip in also, but it then goes rich. I have not been concerned. Should I be?

[Tom @ Fast Forward]

Somewhat normal. remember, when you first step on the pedal, especially part throttle, you add air by opening the throttle plate. Then the MAF, O2 and ECU need to react to what they just saw. It takes a finite amount of time.

[ckkcmx5]

Somewhat normal. remember, when you first step on the pedal, especially part throttle, you add air by opening the throttle plate. Then the MAF, O2 and ECU need to react to what they just saw. It takes a finite amount of time.

ususally it takes less than 0.5 second to react, my car has serious delay and go lean (about 1-3 seconds) since few weeks ago and i have thoroughly checked the car. All sensor are alright and re-adjusted the TPS to the right position (this is important) but with no success.

Finally I found that is a grounding problem. All the grounding of important sensor measured ~ 20mV which should be 0V. And I found the voltage is leaking from the ECU 2D pin (94 car), I tried another ECU but it's the same. 2D is wholly a "ground output" for sensors like TPS/CAS/MAF... Then I cut the wire near the ECU and feed a good ground to the wire going to those sensors directly and the car running fine now! anyway dun understand the cause of how the 20mV building up... :surrender:

[Tom @ Fast Forward]

Great choice. I'll post my V1 story someday but I know mine was paid for on one trip. :)