shaky motor at idle need help

[Taz]

Confused yes. I am just now trying to get into the tunning and how it all works. But you explained it very well. So I shouldn't have anything to worry about then? I have not done any datalogging at WOT yet because I just got the car back from the bodyshop. I hope to do some this weekend. When i do so what should be my main focus point to really watch? How does the short and longterm fuel trims work at idle? The PCM will still add fuel just like if I was giving it gas? Of course it wouldn't dump as much fuel. You have been very helpful so far. thanks.

It looks like you're okay as far as fuel trims are concerned. Personally, I never pay much attention to the STFT's. They're constantly fluctuating in response to sensor inputs and even the PCM's programming. (See, the PCM is programmed to fluctuate the fuel trims between slightly rich and a bit lean. Why? Because that's how it monitors the health of your O2 sensors and can tell when one is becoming slow to respond. If/when that happens, the PCM will set a trouble code.)

The LTFT's are where I focus my attention when I'm looking at closed loop (cruise mode) fuel trims. They reflect the overall averages of the STFT's, and they change quickly enough to enable you to dial in just about any adjustments you'd care to make. (If you change something in the fuel system, the LTFT's will immediately begin to change, and it takes only about 30 seconds for them to stabilize at their new values) These are the fuel trim values the PCM uses to maintain a stoichiometric A/F ratio during the engine's closed loop operation.

As far as what to datalog, "FRPGL" (fuel pressure) is one good data point. "SPARKADV (timing) is another. Then, "IAT" (intake air temp), "EGT" (exhaust gas temp), and "KS1/KS2" (knock sensors). You could also look at the voltage from your MAF meter("MAF" data point). Those will tell you quite a bit about how your motor is doing, but there are a zillion different monitors. Whatever else you monitor is up to you.

 

[aaron427]

It looks like you're okay as far as fuel trims are concerned. Personally, I never pay much attention to the STFT's. They're constantly fluctuating in response to sensor inputs and even the PCM's programming. (See, the PCM is programmed to fluctuate the fuel trims between slightly rich and a bit lean. Why? Because that's how it monitors the health of your O2 sensors and can tell when one is becoming slow to respond. If/when that happens, the PCM will set a trouble code.)

The LTFT's are where I focus my attention when I'm looking at closed loop (cruise mode) fuel trims. They reflect the overall averages of the STFT's, and they change quickly enough to enable you to dial in just about any adjustments you'd care to make. (If you change something in the fuel system, the LTFT's will immediately begin to change, and it takes only about 30 seconds for them to stabilize at their new values) These are the fuel trim values the PCM uses to maintain a stoichiometric A/F ratio during the engine's closed loop operation.

As far as what to datalog, "FRPGL" (fuel pressure) is one good data point. "SPARKADV (timing) is another. Then, "IAT" (intake air temp), "EGT" (exhaust gas temp), and "KS1/KS2" (knock sensors). You could also look at the voltage from your MAF meter("MAF" data point). Those will tell you quite a bit about how your motor is doing, but there are a zillion different monitors. Whatever else you monitor is up to you.

ok great. That is all my little brain can handle today. I will study some notes and things tonight, and let what you have said sink in. This gives me a great starting point for the weekend. Thanks

 

[green99_svt]

20% is too high on with ltft or stft. take the predator and spray carb clean on the intake and hoses. if the fuel trims drop you have a vacuum leak. also if your runnning a breather on one sie of the engine and not on the other you are sucking in unmetered air. thats what the small hose from the air inlet duck to the pass side cover is for. the pvc air comes in there and through the crank case in to the pcv. with only that one breather you engine is not counting that air coming iinto the intake as its after the maf. notice how the inlet tube to the crankcase is after the maf. that air is metered and WILL cause a reading what your seeing. and no +20% at idle is not within specs. long term and short term ft's should stay under 10% in most conditions

 

[aaron427]

20% is too high on with ltft or stft. take the predator and spray carb clean on the intake and hoses. if the fuel trims drop you have a vacuum leak. also if your runnning a breather on one sie of the engine and not on the other you are sucking in unmetered air. thats what the small hose from the air inlet duck to the pass side cover is for. the pvc air comes in there and through the crank case in to the pcv. with only that one breather you engine is not counting that air coming iinto the intake as its after the maf. notice how the inlet tube to the crankcase is after the maf. that air is metered and WILL cause a reading what your seeing. and no +20% at idle is not within specs. long term and short term ft's should stay under 10% in most conditions

I know it isn't good to have one breather on, but I had to for the time being. I just got the pipe so I can hook that back up. I have always wondered how much that little bit of unmetered air coming in would effect things. Well I should find out this weekend. I understand that the 20% is not good, but it does mean that it isn't allowing me to run lean at least at idle? I will check for a vacuum leak on Sat. and post up if I find anything out. Also if my settings change any when I hook the stock pcv back up. Thanks.

 

[Taz]

You were running a breather on the passenger side and the PCV on the driver side???

Oh, ya, I went back and found that in one of your earlier posts.

:nonono: :nonono: :nonono: :nonono:

Wrongo!

T-

 

[lemosley01]

good catch green99_svt - I didn't even see that.

 

[aaron427]

I just put the pcv back on last week. Just got my catch can, and the tubing that I need to get everything hooked up right. I have only driven the car a couple of times with it like that. About 10 miles if that. So I should have some hard data about how much unmetered air is really getting in.

 

[green99_svt]

its actually quite a bit of air if you put your finger over the valve.

 

[aaron427]

well finally got a chance to hook up the pcv valve and stuff. So for all of the people who say having a breather set up will not let in alot of unmetered air well it does. I put the stock stuff back on, and plugged up the predator and I have no lean condition anymore. That is all I changed on it also. Didn't mess with anything else. I guess that answers the age old question.