I have a buddy that has a 99 Formula. He has a 402 in it and runs with the MAF and the narrow O2's. At wide open throttle NA his AFR is ok (at about 12.5). The problem is that he has a direct port nitrous setup and whenever he sprays the 250 shot, he is seeing 10.8 AFR. We are trying to get it to 11.5-11.8 range. I have HPTuners. He is already running his fuel jets 2 sizes smaller than recommended. He is using a fuel cell for the nitrous and the pump is down to 9 psi (running low pressure jets). Here is the stumper though. We hooked up a 50hp dry shot to his car and guess what happened. 10.8 AFR . Could a maxed out MAF do this? Open to suggestions.

 

I'm assuming this is LOSLS2, like I said on need2speed, with the directport it would have nothing to do with the maf, the directport gets it's own fuel from the standalone and is after the maf, so the maf does nothing with it. Just gotta keep playin with the jets and fuel pressure till you get it right. My tnt always ran pig rich, put the 150 fuel jets in with the 200 nitrous jets and dropped pressure from 60 psi to 50 psi and that got the o2's down in the 960 - 970 range from over 1000, not sure what that would be on a wideband, but I didn't go less than that to be safe till I get myself a wideband and can actually keep an eye on the real a/f.

 

Narrow O2's are worthless. MAF measures airflow. When you add 250hp you increase airflow. This can max out the MAF.

 

Ok you are a bit off here.
1- The oxygen sensors are out of the equation here because they no NOTHING at WOT in terms of fueling (you are in power enrichment mode, not closed loop)

2- Since direct port sprays after the MAF, the only air that the MAF is measuring is the air that the motor is sucking in thorugh the intake. The other 250HP are being sprayed directly into the cylinder, so MAF is out of the equation with the direct port setup. And you already know the MAF is doing Ok because the AFR NA is good.

What fuel jets are recommended and what size are you using?

 

What style direct port?

Fogger or under-the-injector style?

 

Exactly what I was sayin, since the direct port is after the maf, the maf is out of the equation!

 

I'm pretty sure he's running a fogger, if i'm not mistaken it's an nx direct port that he got from nitro dave.

 

Ok, but my car also dipped off the chart (under 10.1:1) on the dyno with the wideband. I know you think the regular o2's are worthless, but they do get you close, I have always tuned off them, but will eventually pick up a wideband just to get everything perfect.

 

OK guys. The MAF can be maxing out because the additional power is causing the engine to suck more air. I understand that you are saying that the nitrous is going in behind the MAF but the engine uses more air with more power. I really need to hook it up to the scanner. I just wanted to get some ideas. Also, the dry shot is going in ahead of the MAF and he is having the same rich condition. This is why I believe that the problem is in the MAF or some other sensor that is causing the injectors (not the jets) to dump an excessive amount of fuel.

 

How much power did the car put out with the dry shot hooked up?

 

Ok, if a maf maxes out, doesn't that usually cause a lean condition?

 

Yes. I have only been able to get my MAF up to like 9200 MHz out of 12000 MHz that you can use. It takes a lot of airflow to make it to 12000 MHz.

How much power does this car make NA??

 

The additonal power from the shot does nothing to the MAF. Go hook up a scanner and scan MAF frequency and see if the range if different from a NA run and then a nitrous run. The range will be the same, which means that the airflow is the same both NA and on spray.

 

If anything putting a lot of nitrous in after the MAF may cause less air to go through the MAF not more. Did you check to make sure there was a siphon tube in the bottle? I've seen bottles that didn't get siphon tubes in them do this. No matter how much fuel you seem to take away or nitrous you add it always runs rich. Not a real common problem but easy enough to check just in case.

 

Thats correct Srsnow. A large shot after the MAF will displace some airflow. That can be measured with a sanner setup. It can be so bad at times...that if you have dry nitrous retard programed in (programed to retard timing when the maf sees more air flow due to the dry nitrous)...it can cause the maf reporting to be lower and kick it out of retard if you have a dry/wet 2 stage combo and are relying on the dry kit to retard timing via tuning. So spraying after the MAF will never increase reported MAF flow...and if the shot size is big enough it will decrease it.

Unless your MAF reporting is screwed up NA forget about the MAF. If its screwed up NA youll need to figure out the issue before you spray again.

But IMO its just a jetting issue on your DP.

Did you get close to 250 hp on your pulls when you sprayed?
Also...there is nothing wrong with 10.8 to 1

I like 11.0 to 11.5 on a larger shot but Id take 10.8 over 11.8.

What is the recomended fuel pressure from NX on the low pressure systems?

 

Well, he hasn't sprayed on the dyno. I just can't understand why he would be just as rich on the wet shot (which adds fuel) as he is on the dryshot (which doesn't). I am not talking about him being rich using it in 2 stages. I mean, he is just as rich spraying one or the other.

 

I remembered that I had a copy of his tune in my laptop and have been looking at it. I noticed that his commanded PE is rich to begin with so this could be part of the problem. I guess I need to dig into the tune and do some logging to see what his VE table is doing.

 

Your first job is to get actual AFR to equal commanded AFR. Let us know how it goes.

 

keep jeting down. if you are maxing out the maf. car would go lean because it can only measure that certain amout of air then stay there. the car shouldn't get richer. i would keep jeting down on the fuel side. i have jeted the tnt wet down before and it only drop a little bit. but i was really close to where i wanted to be already