408-99-f

I apologize in advance if I'm posting this in the wrong Forum. Now I have a full forged 408. My fuel trims intermittently. Go from around 10% to 20% at idle hot I'm a mechanic, and undestand what all the sensors do. Also how they work together. What I am not is a tuner. I know the bigger the cam the more vacuum I lose and can cause fuel trim Issues. I have checked I do not have any vacuum leaks. Now should my trims be high all the time (due to the low vacuum) or should the pcm have been recalibrated so they should be whithin the + or - 10% the pcm is supposed to run in? My cam is 247/251 623 111 lsa, heads 215 TFS, With a fast 90/90 no egr, cats, Air and tuned by RPM in D.E.

ddnspider

iTrader: (26)

Does the car currently have a tune in it? I assume the car has longtube headers? A setup like that likely needs some help compensating at idle due to the exhaust and overlap. Some people even disable STFT idle trimming so it doesn't create large LTFT swings. You should be able to get closer LTFT's though with a good tune.

408-99-f

It was tuned by RPM (race proven motorsports) has long tubes, with o2s before the collectors. No leaks. 42lbs injectors. I have smoked tested it sevral times. And is rich as hell idleing. Booster and all that is ok. So what you suggest sound logical thanks, Ill research it.

ddnspider

iTrader: (26)

It wasn't tune in the winter by chance was it? Also, are you sure you have no intake/vacuum leaks? Just some other things to think about.

ctd

iTrader: (1)

That's a good size cam, I had a 243/247 & the only way it idle decently was OL. I don't think you will be able to idle decently in CL. OL idle is easy to do, then back to CL above 1200 rpm.

moosifer

iTrader: (1)

The tuner should have been able to get the tune closer than 20% fuel trim. One of the main reasons to tune a vehicle is to make sure you have plenty of room for the fuel trims to keep the engine running safely. You say the vehicle is rich as hell idling. That is something the tuner should be able to get in line. Sounds like you need a new tuner. If the vehicle was running rich open loop I would say mess with the OLEQ. Since it is closed loop I am thinking later injection timing could help get things in line. Bottom line is a good tuner knows this stuff. I am just a weekend warrior...

408-99-f

Long story but I believe it was tuned during the winter. I trust it was done right. Also I took the intake off just to re seal everything on the off chance pressure in the intake would show no leak but vacuum will. If I split this intake a old fast 90/90. I have herd to throw out the old rope seal, and use just blue rtv or "the right stuff" or should I get the rope. I ve heard both. And having an OL idle sounds Like a good idea thank you. Now I know vehicle control systems pretty well. And diag them on a daily basis. I want to learn to tune my own stuff. What system should I start with? Hp tuners?

ctd

iTrader: (1)

OL idle lets you determine the happy AFR for idle area. Sounds like are aware of all the factors that cause the grief with NB, if nothing else you need to find the happy spot. You can't do that in CL.

If you want to get very fussy about now the car runs, drive ability & idle take forever to get right. Then you always want to try something to make it better or another mod Best to have your own tuning software understanding there has to be large commitment on your part to learn. Many dive into it trying to short cut the school of hard knocks no short cuts.

I went with HPT only for the reason I was lucky enough to have a mentor along the way.

Slowhawk

iTrader: (12)

Just needs the tune checked over. Could be bad 02's too.

408-99-f

Have 2 new 02s went with bosh because it was what was in it after it was tuned. What do you rec? Also are you in the shop in mass. I live in NH. Was thinking of calling after I get it my intake seals and intake on. You are prob pretty busy now?