duty cycle at 100% - boost leak?

[chrisAWD]

car info: 1g with 660's, 2g mas, 255walbro rewired, pte 50trim, stock FPR, unmodified 1g BOV, BC 272's, keydiver chip for the 660's and 2gmas, safc, pocketlogger, built 6bolt.

This past Friday I went to the track to see how my new BC 272's are doing. Ended up running a 12.51@110 which bested my previous best af 12.70@110. Obviously I was looking to pick up some MPH though and didn't achieve that goal. Before going to the track I have been trying to tune out some knock that i've picked up since installing the 272's. Getting frustrated with little success, while at the track I decided to run race gas to take care of the knock problem.....which it did almost entirely.

New questions have arisen however after looking at my logs of the runs.

First and foremost, I'm seeing 100% duty cycle from about 6k up on the 660's. I'm surprised i'm maxing out these injectors already and I believe the stock BOV must be leaking alot of air at 23psi(boost at track), and causing the cpu to run the injectors more. Additionally, I'm starting to wonder if my stock FPR w/ the 255 is causing some of the tuning problems i'm seeing as well. I did not log 02's since i was running leaded gas and the 02's get nutty when doing so.

First, is a 1g unmodded bov most likely leaking enough air at 22-23 psi to cause the injectors run a considerably higher duty cycle? If so, then the car wasn't most likely running lean even at 100% duty cycle, since it was really a "fake" 100%, no?

also, would overrunning my stock fpr cause the fuel pressure to rise as well, resulting also in a richer then measured charge?

I'd like to get one more track day in before the end of the year, but i'm concerned about the duty cycle of the injectors and the fact that i've picked up no mph with the cams and my mph doesn't change much going from 21 to 23 or so psi.

I realize this post is a little disjointed, but any insight into these issues would be appreciated.

 

[kahl23]

I'd say first thing's first: Do a BLT before anything else. That will tell you if you actually have a leak. If you do, fix it, then see if your IDC are still high. Next, get an AFPR. It's been said thousands of times on here: the 255 will outflow your stocker. Between possible boost leaks and no fuel pressure control you have a lot of variables going on, and something is not right. Did you lean out your tune at all on race gas? When going from pump to race I usually lower global settings by 10% and still run rich. Race gas requires far less fuel than pump. Do you have a wideband or are you just relying on the narrowband? I've never really found that leaded gas does anything that alters the readings of the O2, it just kills them in my experience. Go do a BLT and see what happens, then report back.

 

[JayRolla]

Like mentioned do a boost leak test. Not having an AFPR will not cause your issue. 1g's usually dont have overrun and if you do its hurting lo throttle and idle, not WOT. Sounds like you have a boost leak. Most likely your knock is happening when you hit 100% IDC.

 

[chrisAWD]

Alright, first thing friday i'll take another stab at doing the boost leak test. Got to go home depot tonight and see what I can put together. I tried an expanding rubber insert last time and was only able to test up to 5psi, before it would fly out. The only leak i found at that level was in part of the Hallman BC.

to be continued....

 

[JayRolla]

Yea you need to do a test to at least 25psi, I do mine to 30.

 

[steve]

First, is a 1g unmodded bov most likely leaking enough air at 22-23 psi to cause the injectors run a considerably higher duty cycle? If so, then the car wasn't most likely running lean even at 100% duty cycle, since it was really a "fake" 100%, no?

If the BOV is recirculated the air is not lost so the leak doesn't cause a major change in AFR. Keep in mind that a boost leak causes the car to run rich not lean. It will raise the IDC because the ECU thinks more air is reaching the cylinders that it has to provide fuel for.

A leaking BOV will raise the intake air temps because the turbo has to work harder to build boost and the air leaking past the BOV is going to be hotter than the air from under the hood (usually).

also, would overrunning my stock fpr cause the fuel pressure to rise as well, resulting also in a richer then measured charge?

FRP overrun happens when your not running WOT. The overrun is caused by more fuel being pumped than the return port/line can send back to the tank. When the engine is using the extra fuel the overrun stops. So usually the problem is with part throttle tuning.

 

[Car Cannibal]

As long as you know the pressure is 1:1 at WOT 110mph could be a low 12 E.T. and if it's a 3400lb car the 100% DC doesn't seem too odd.

Also what's your Air Fuel Ratio? If you're in the 9's or 10's then it makes even more sense.

 

[chrisAWD]

Well, I'm not sure on the weight of the car. Whatever a full weight 1g AWD is minus, the back seat, back seat belts, all spare tire stuff and ABS is....+plus my 185 lbs.

My AFC settings for the runs were +6 from 4k up (to combat a bit of knock I'm running into on pump gas). I might try bringing these down on race gas a bit from some of the comments above. That should lower the IDC some as well.

In preperation for discovering my 1g BOV is probably leaking at 23-24 psi, I've been researching possible fixes for it, mostly the dodge garage mod method. I might just plug the bottom reference hole and drill out the atmosphere reference for now(I'm really just planning 1 more track trip and this car see's very little street action, this might help for my last track trip.) Then when I have more time, go back and add the "brake line" portion of it when I have more time.

Longer term though, would getting an AFPR and bumping fuel pressure to 43psi ( i would have to have my keydiver chip reprogrammed), be a signifigant way to lower IDC's as well? Or would stepping up to 850's or so be the wiser choice? or both?

 

[chrisAWD]

Also what's your Air Fuel Ratio? If you're in the 9's or 10's then it makes even more sense.

I don't know, wideband is first up for next year. I do know that I was catching a little knock though, so I don't think I was running too rich. Also my EGT's stay below 1550 F, maybe even lower, as I don't watch the EGT gauge much anymore.

 

[xdxoxuxgx]

I would definitely recommend a wideband A/F gauge, that will help you with whether or not you're running rich.

 

[JayRolla]

You may be trying to combat knock from to much timing. So when you add fuel your running real rich and that may be the reason. What timing do you see at wot?

 

[chrisAWD]

You may be trying to combat knock from to much timing. So when you add fuel your running real rich and that may be the reason. What timing do you see at wot?

My last run, which was at about 23-24psi, 3rd gear kept between 13 and 15 counts of knock from 5200(beginning of gear) to shift, and held between 12 and 14 deg of timing. 4th gear had no knock at first but from 5500 to 5800 knock went up to 15 and tapered off to 11 by end of pass(6500rpm)....timing went from about 12 degrees up to 15 during that time. resulted in 110.61 trap.

second to last run which was about 22psi. i had pretty much no knock, 1 count or less for entire run, with timing staying around 18degrees. resulted in 110.13 trap.

 

[JayRolla]

You may look into a meth injection kit to help out with the knock!

 

[chrisAWD]

indeed, that's on the block for spring, along with a new 3" turboback to replace by leaky 2.5".....and wideband.


so boostleak test went well i guess. went to Lowes on Wednesday night and put a new tester together. Ran it up to 22 psi. I caught 1 intercooler hose leak that would only show its face at about 12psi.....no leak under that. Also, it seems my throttlebody leaks a bit of air through the center shaft section......don't know what to do about that. Someone make rebuild kits for these TB's? BOV had the tiniest trickle at 22psi....so little I can't imagine it makes any difference.

I'll post some specific info on my logs from tonights track outing. I did manage to duplicate my 12.51@110 run and also had a 12.59@111 run. This was on a little less boost than before...only about 21-22 or so. I believe IDC's came down a few ppoints as well...but not much.

update tomorrow.

 

[Car Cannibal]

You're running too much boost, you shouldn't see that much knock and with an EGT around 1550 it's fat with the lower timing altering it to be lower than normal.

 

[chrisAWD]

You're running too much boost, you shouldn't see that much knock and with an EGT around 1550 it's fat with the lower timing altering it to be lower than normal.

If i'm running that fat, why would I want to lower the boost? You think lowering the boost a little and leaning it out will result in a more powerful mix? damn I need a wideband.

 

[JayRolla]

If i'm running that fat, why would I want to lower the boost? You think lowering the boost a little and leaning it out will result in a more powerful mix? damn I need a wideband.

No dont lean it out. I would rather run 10.3:1 at 20psi than 11.1 at 15psi. More boost always makes more power. First boost, then timing and last afr. So I tune to a rich afr, add as much boost as possible with a low timing map. Then add timing till I knock. After that lean it out as much as possible.

A boost leak at 12 psi can be pretty bad. I have one at 15psi and It elevated my IDC's from 64% to around 69%.

For the TB your best bet is to get another used one or buy one from this guy on ebay, not sure if he still sells them. They usually worked pretty good, and if it leaked he would replace it.

 

[kahl23]

Visual Frequently Answered Questions - Home Page

Under intake, go to throttle body shaft seal replacement. It will tell you how to do it and what you need to get it done. It is kinda a PITA, but I'd say its worth it. What kind of BOV are you running?

 

[Car Cannibal]

You need to lower the cylinder pressure, period. You have too much knock and the easiest is to lower boost, making it run 9:1 won't allow you to run 35psi so your current tune is done on pump.

Not only is the car pulling timing but it's fat making even less power. On my car every .5 leaner in AF/R netted a 9awhp gain almost throughout the powerband on the dyno at zero knock.

It's hard to drive fast when you're replacing headgaskets all the time so lower cylinder pressure and run a safe/powerful AF/R.

 

[JayRolla]

You need to lower the cylinder pressure, period. You have too much knock and the easiest is to lower boost, making it run 9:1 won't allow you to run 35psi so your current tune is done on pump.

Not only is the car pulling timing but it's fat making even less power. On my car every .5 leaner in AF/R netted a 9awhp gain almost throughout the powerband on the dyno at zero knock.

It's hard to drive fast when you're replacing headgaskets all the time so lower cylinder pressure and run a safe/powerful AF/R.

This is true. His issue I think though is since the injectors are maxed, they become unstable and when I had maxed injectors I would see all kinds of knock.

 

[chrisAWD]

Thanks for all the help so far guys.

a little info from my logs on Friday night. This is with 2 gal of sunoco purple(110 leaded) added to almost empty tank(warning light on).....not too scientific, but I mostly use the race gas to control the knock I'm receiving.

I'll keep this short as possible and only put info of my last run, which had the most knock of all.

22psi; only knock in 4th gear starting with around 12 counts at 5800 and the knock came on all at once....tapered of to 8 counts by 6500 rpm through traps. Duty cycle goes over 90% by 6k rpm and max's around 97-98%. This is an improvement from before, probably due to the moderate IC leak I found and fixed. Obviously though way higher than I want.

Curiously on pass before this I only had knock in 3rd gear, none in 4th. I think this was 21psi. hit new high trap of 111 here.

maybe my knock is related to my IDC's. I'm amazed I'm maxing these 660's already though. If it wasn't for the fact that my keydiver ecu was compensated for the 660's and it runs them great at part throttle etc, I would have thought I got 550's by mistake. Also maybe it has to do with running them at 37psi fuel pressure.

So, I guess an FPR would be in order for next year.....along with some 850's and a new keydiver chip. Wish I had ethanol in jersey...I would start getting the fuel components for that instead.

 

[Car Cannibal]

You're getting the stock reg with the 255 hotwired to give you a base pressure of 37psi?

Your 110 mix with the warning light might have been around 100 octane if it's with 93 octane so it still has too much cylinder pressure/load for your 4th gear pulls.

I'd get the FPR so you can up the pressure into the low 40's and go from there. I actually run 5 gallons of 110 with 6 gal of 93 as my daily driver mix. I run 24 degrees and 24psi with no knock on a 11.5ish AF/R, my FMIC helps but I'd run the 110 mix all the time and tune around it.

 

[chrisAWD]

well, stock fuel pressure of 37psi, keydiver chip setup around that. At idle I register 37psi on gauge I have mounted off filter.

I guess you run dsmlink? I have no control over timing.

 

[JayRolla]

Since you have more load in 4th you run out of injector easier. I would run out of my 550's in 3rd and up only.

That 50 trim should beable to run 22psi on pump no problem with timing around 16*.

I run 30psi spike holding 24psi by redline and 25* timing with no knock on my 16g with e85 and its only rated at 105 octane.

 

[Car Cannibal]

Huh, well only read the liquid filled gauges when the car is just started and cold, the liquid will not read accurately as the gauge heats up.