Fuel trims and consequences

[sweet97]

I have searched several sites and posted also. My trims are all lean on my 1G. 140.118 and 120. What are the effects of this? Would I be better to bring them closer to 100% and if so, why? I use a MAFT and with a leaner base I can lean WOT for a leaner A/F without getting too much timing and knock. An 11.x:1 makes so much more power than a 10.x:1. Is there a better way to do it? Thanks, Mark

 

[TURFNNSURF]

I have searched several sites and posted also. My trims are all lean on my 1G. 140.118 and 120. What are the effects of this? Would I be better to bring them closer to 100% and if so, why? I use a MAFT and with a leaner base I can lean WOT for a leaner A/F without getting too much timing and knock. An 11.x:1 makes so much more power than a 10.x:1. Is there a better way to do it? Thanks, Mark

Im guessing that your LOW=140, MID=118 and HI=120.
Your LOW is maxed lean, the ECU can't compensate for changing conditions. one click richer on the MAFT might help that a little bit. IMHO, this trim can be lean without doing any damage, It is basically only for idle and there is minimal load on the motor at this time.
Your MID trim is mildly lean 118 is not bad, and the ECU can still compensate for changing conditions somewhat. This trim is for low rpm cruising 20 to 45 mph. Again not alot of load on the motor but more than at idle, so a trim closer to 100 is better for the car.
Your HI trim is about the same as your MID, The ECU can deal with it. HI trim is for highway speeds 50 to 85 mph and there is a fair amount of load on the motor to keep you moving forward. IMHO, I keep this trim a little on the lean side to help my fuel economy a little. Since 75% of my driving is done on highways I have tuned my HIGH trim for about 109 to 112 and this gets me about 2 more MPG for a tank full of gas.

PLEASE keep in mind that these trims only affect closed loop driving. ANY, pulls of 50% throttle or more including WOT will make the ECU go into OPEN LOOP mode and a whole new fuel tuning curve is used. I would reffer you to Kyle's (KPT4321) tuning guide in the tech section for more detailed tuning.

 

[sweet97]

Thanks Brad, that's the first info I have received. The odd thing is my car idles so rich it waters my eyes when I stand next to it!! My muffler outlet is very sooty also. I can get the high closer to 100 but the low stays pegged at 140. I am also trying to run a leaner A/F under WOT. I think I will lower the boost and try tuning again. Thanks, mark

 

[Burnett03]

Thanks Brad, that's the first info I have received. The odd thing is my car idles so rich it waters my eyes when I stand next to it!! My muffler outlet is very sooty also.

because the ecu is dumping in fuel to try and get the trim back to normal

 

[sweet97]

So proper trims should result in better mileage?

 

[StyleElements]

So proper trims should result in better mileage?

yes

 

[Burnett03]

So proper trims should result in better mileage?

yup!

 

[sweet97]

Well I had a spare TB refurbished this winter and same problem. Low trim is 140. I am just idling the car now in the garage and will not have it on the road until April but am still not getting these trims and their purpose. I can often get a low trim of 140 and a high of 80. How do I adjust that with a MAFT? If I richen the low I make the high worse!
I also have another problem. The car will not idle cold and the BISS is all the way in when warm but if I back it out it will idle cold. This is a summer car and I have no coolant going through the TB. Why will it still run well with the BISS closed all the way when the car is warm? I hope it runs OK when warm weather gets here so I don't have to sit and feather the throttle until it warms up! I heard about a cold idle valve on the bottom of the TB but would hate to pull this off. Mark
PS: high trim is the most important? If it would be off 10% should I have it rich or lean for better mileage? Thanks, mark

 

[Newlogics]

First off, getting fuel trims closer to 100% doesn't improve your gase mileage. Not directly anyway. As long as fuel trim is not maxed out or at a minimum, your gas-mileage won't change. The whole point of fuel trims is to keep certain A/F ratio, which ECU deems best for power/economy. That means if one car has 90% low trim, and another 120%, given everything else is the same, they actually run same AFR, and will get same gas mileage.
It is still a good practice, however, to try and bring your trims close to 100%, to give ECU the most wiggle room.

Secondly, just because running too lean at idle won't kill your engine on the spot, doesn't mean it's good for the engine. If you un like that for long enough, you will start seeing white residue on plugs, valves and piston tops. Eventually, it will hurt your performance, and may even cause piston slap (rare, but I've seen a case)

Running 140% trim at idle indicates you're VERY lean. It's impossible to say exactly how lean, but it's enough to cause headaches later. Don't leave a problem like that unsolved. Check base timing, and make sure it's where it should be (5btd). Log and see if your O2 cycles. Turn idle knob on MAFT untill you see O2 start cycling. (It may be bad in the first place, reporing mixture as too lean, while actually running rich). Then see where your low trim moves to, and adjust more if needed. Neither low nor mid adjustment knobs will affect your high-throttle runs, so don't worry about hurting performance by adding fuel there. You probably spend 80% of driving time under the control of low/mid adjustment knobs, so tune them as well as you can.

 

[sweet97]

O2 is new and wideband reads 14.xx but I always seem to have the low trim at 140, perhaps a side efect of the KEYDIVER chips which in my case is compensating for 950cc inj's. According to MAFT instructions on fullthrottletech they say to set the high trim and don't highlight the low/mid very much. I can usually get mid and high near 100 but low will not move from 140 much at all, puzzled! mark

 

[Newlogics]

O2 is new and wideband reads 14.xx but I always seem to have the low trim at 140, perhaps a side efect of the KEYDIVER chips which in my case is compensating for 950cc inj's. According to MAFT instructions on fullthrottletech they say to set the high trim and don't highlight the low/mid very much. I can usually get mid and high near 100 but low will not move from 140 much at all, puzzled! mark

I think at this point, your strategy here is to at least get it to move. Make sure your coolant temp is about 194* (that's when trims start moving).
What does your O2 read at idle (not wideband) ?

 

[Newlogics]

Well I had a spare TB refurbished this winter and same problem. Low trim is 140. I am just idling the car now in the garage and will not have it on the road until April but am still not getting these trims and their purpose. I can often get a low trim of 140 and a high of 80. How do I adjust that with a MAFT? If I richen the low I make the high worse!
I also have another problem. The car will not idle cold and the BISS is all the way in when warm but if I back it out it will idle cold. This is a summer car and I have no coolant going through the TB. Why will it still run well with the BISS closed all the way when the car is warm? I hope it runs OK when warm weather gets here so I don't have to sit and feather the throttle until it warms up! I heard about a cold idle valve on the bottom of the TB but would hate to pull this off. Mark
PS: high trim is the most important? If it would be off 10% should I have it rich or lean for better mileage? Thanks, mark

By the way, High trim is important for freeway cruising (up to about 65mph). It does NOT affect high-throttle runs.
If you richen Low knob, it will not affect your high trim (provided RPM wire is hooked to the MAFT properly). If you're running 140% low and 80% high trims, that means your idle is too lean, and cruising is too rich.

as for your car running fine with BISS screw all the way in, it's because you're letting air in through cold-idle valve (since you have no coolant in TB, and it always in 'cold' mode, letting air through). However, when it's cold outside, the air passing through cold-idle falve isn't enough. It needs to work in conjunction with BISS to provide enough air to keep the car idling when cold. In addition, since your ICS only controls passage with BISS, by having BISS screw all the way in, you're taking away ECU's ability to control idle at all. Not good.

Block off Cold-idle passage and use BISS screw, if you really want to keep coolant out of the throttle body.

 

[unclesam099]

I'm having a problem with the low at 139% also... I have a MAFT set up for blow-thru, it's all zereoed, set up for 450s, and I have a Walbro 255HP. I also have an SAFC which I have been playing with. If I put the idle (1000rpm on the AFC) up to +20, the trims come down to the 115 range, but why in the world would I need to make it +20 for it to idle correctly??

My WOT runs are pretty good with a max of 6 counts of knock, and I am just under 100% in the Mid and Hi trims.

Any help is appreciated, thanks!!

 

[sweet97]

Kevin you must also have a KEYDIVER chip as that seems to be the common denominator here. I can get the mid and high trims OK but low is usually pegged at 140. Mark

 

[unclesam099]

I think that my ECU is stock though... How would I tell if I have a keydiver chip? It's not an EPROM ECU, I do know that. I don't know much of the history of the car, it was already modded when I got it.

 

[sweet97]

NO EPROM then NO CHIP! So it has the MAFT with stock injectors? Mark

 

[unclesam099]

Yes, I have 450s in it now and I have a set of 550s to install. But I'd like to get this fixed before I put in the 550s.

Or would it be easier to put the 550s in and go from there??