Ok, plain and simple, could a vacuum leak cause a car to run rich??

Symptoms are running extremely rich, verified on dyno and on datamaster. From a cold start, car idles up then to the programmed 800 fine. After about 45 seconds, IAC starts to drive shut from 40, all the way to 0. Vacuum takes a slight dip to the tune of about 2-3 In Hg. O2's Mv starts to take a climb. Stumble starts to happen at fast throttle movement.

Mind you, this is all in open loop.

I'm just wondering if I've got a massive vacuum leak, possibly internal intake, that could be causing all of my problems.

 

Nope it would cause the car to run LEAN because the o2 sensors would see all this extra air that the MAF didn't see and in turn think that your running lean.

Wait ok just saw you said its all in open loop, well open loop doesnt use the o2 sensors. So what are you using to judge that your running rich? Wideband??

 

Verified it on the dyno and datamaster. The dyno tip in was 10.5 at 2800 RPM and leaned out gradually to a 13.0 at about 5800 rpm. IT'S NOT A TUNING ISSUE.

Datamaster verified it by the O2 millivolts in open loop. When the issue starts, the mV starts to drive up from 450, indicating a rich condition. Once closed loop hits and I get a full view of the fuel trims, the LTerms dump to 108 (bottom) and the STerms dive to the 40's. Extremely rich, and I haven't been able to find why. No leaks, pressure is good, ect. ect. I've got a couple of other pretty lengthy posts on it.

So now the question becomes why would I get a vacuum leak indication (IAC shutting, idle coming up above the target anyway, vacuum drop) and an extremely rich condition with an associated stumble/miss fire/hesitation associated with it??

 

How so? I thought under this condition, that the extra air woudl pass by the O2's making them think they need to add more gas. Since the leak isn't being monitored if it is after the MAF, the car would conitually keep adding more and more fuel, since the O2's see the passing "extra" air from the leak, and think you're running lean.

I don't know though -I would swear everything I've read is the opposite of what you've said though.

Oh, and anywhere the engine opens to any fitting there could be a leak. Someone was saying that even a bad HVAC valve or tubing can cause air to be pulled into the engine unmeasured.

 

My only problem with this theory would be this: I don't think the computer is adding the fuel in, reason being, if you look at my datamaster log, the LTerms are showing 108, bottomed out. Meaning the computer is trying to lean out the mixture, not add fuel in to it.

*Unless, datamaster only shows what it's reading, and not what the computer is doing. Can anyone verify this thought??*

 

Yup your right, long night last night

Your BLMS are at 108 meaning it's subtracting a $hit load of fuel cause the car is running rich. Just as you said you were on the dyno (10.5:1) So I would start checking for leaky injectors, leaky FPR etc

 

Yeah, I've been all over that. No leaky injector. Done the pull the rail check and there's absoluetly no hesitation on start up. FRP is a brand new Hypertech Adjustable which made no difference.

 

So have you never had tuning??

 

Can you post a list of things you checked?

 

List:

Opti
ICM
Plugs
Wires
Coil
O2's
Grounds
Fuel Pressure
FPR
Canister EVAP system
IAC
IAT
Coolant Sensor
TPS
EGR
Can't find any vacuum leaks
and EXTENSIVE tuning....

Can't think of anything else, but it's early.

 

Is it possible your enrichment tables are incorrect? or do you think it is more likely a mechanical issue?

 

Mechanical. Have done a total of 11 tunes, three of which were started from scratch.

Also for reasons being that when started cold, the car is FINE. After about a minute, it starts to degrade. By the time it hits closed loop, it's full blown.

Cliff notes: As something is warming up, it's causing problems.

 

I think your confused.. Your car starts off in OPEN LOOP and then SHOULD be going into CLOSED LOOP.. Can you verify?

 

Why, whatever are you talking about?? Why did you change my post in your quote??

I love the edit feature.

Yeah, I meant closed loop. My bad.