I think that you are running lean. I have an AFM Link and did some data logging - see the attached file below. The O2 sensor shows lean >90. I am running the latest Guru 18 psi chip and have non-stock equipment so it needs to be dialed in. Car has AFM Link and Lindsey Sport Turbo, 55 lb/hr injectors, Lindsey manual boost contoller and Lindsey dual port wastegate. Stock cam, ignition, and exhaust. Car made 290 rwhp @ 15 psi and mixtures were good wtih ver 8 chip. Chugging started with ver 9 chip and 18 psi. Car feels very stong and when mixture is right guess that I will be @ 330+ rwhp.

Think problem may also be partially plugged fuel filter, or weak pump. Also see some evidence of boost spike so manual controller may be the problem or bolw off valve (stock).

Danno, feel free to comment.


0 4 16 20 118 0 25 255 0 0 0 0 0 10 213 15



0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0 +2 +2 +9 +27 +41 +45 +30 +40 +40 +40 +43 +43 +40 +40 +40

+4 -1 +2 +3 +3 +5 +5 +6 +4 +7 +4 +4 +4 +4 +4 +4

0 +3 +5 +6 +3 +5 +3 +5 +5 0 0 0 0 0 0 0

+5 +4 +4 +10 +10 +10 +7 +7 +5 0 0 0 0 0 0 0

+6 +6 +6 +5 +15 +15 +12 +15 0 0 0 0 0 0 0 0

+8 +7 +7 +7 +5 +20 +25 +20 +20 +5 0 0 0 0 0 0

+2 +2 +2 +2 +2 +5 +25 +25 +20 +20 +15 +15 +15 +15 +15 +10

+2 +2 +2 +2 +2 +2 +25 +30 +35 +30 +30 +30 +25 +20 +15 +15

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 +2+127 0 0 0 0 0 0


3168 58 51 77 0 133 123 54

3228 103 162 1 0 168 161 102

3305 118 182 85 0 182 176 102

3420 136 182 92 0 201 197 118

3550 156 182 94 0 213 210 119

3724 173 182 95 0 223 221 135

3944 212 182 92 0 245 243 151

4201 231 182 89 0 255 255 152

4452 221 182 90 0 255 255 152

4669 217 182 90 0 255 255 153

4915 223 182 89 0 255 255 153

5152 222 182 89 0 255 255 154

5390 217 182 90 0 255 255 154

5600 212 182 90 0 255 255 155

5809 207 182 92 0 255 255 155

5485 68 24 79 0 203 198 91

4358 25 24 0 0 77 64 40

RPM MAP TPS OXY AFM VECU GAIN ZON

4249 22 24 0 0 65 50 40

4206 22 24 0 0 69 55 40



3895 54 53 68 0 146 137 55

3895 56 53 9 0 145 136 55

3891 54 53 23 0 149 141 55

3928 113 162 7 0 181 175 103

RPM MAP TPS OXY AFM VECU GAIN ZON

4109 210 182 88 0 255 255 152

4259 220 182 84 0 255 255 152

4384 218 182 84 0 255 255 152

4489 221 182 82 0 255 255 153

4617 225 182 83 0 255 255 153

4915 219 182 76 0 255 255 153

4895 229 182 83 0 255 255 153

4987 179 74 86 0 255 253 138

4947 24 24 1 0 77 60 41

4807 22 24 0 0 61 50 41



2487 99 80 5 0 148 145 84

3014 109 182 83 0 167 161 102

3750 135 182 88 0 205 203 119

4687 187 182 90 0 252 251 137

5938 208 182 90 0 255 255 155

5685 49 24 70 0 168 149 59

4073 117 182 0 0 190 185 104

4132 169 182 90 0 223 227 136

4681 228 182 86 0 255 255 153

5253 219 182 86 0 255 255 154

RPM MAP TPS OXY AFM VECU GAIN ZON

6236 228 182 89 0 255 255 156

6093 101 23 75 0 255 206 108

4776 24 24 0 0 74 60 41

4244 131 182 3 0 204 205 120

4561 198 182 88 0 249 253 137

4838 221 182 84 0 255 255 153

5089 239 182 85 0 255 255 154

5711 212 182 82 0 255 255 155

5550 212 182 85 0 255 255 155

4426 28 24 1 0 94 78 40

4055 36 41 0 0 111 99 40

4132 127 182 10 0 191 197 120

4132 171 182 88 0 233 228 136

4244 229 183 84 0 255 255 152

4394 217 182 83 0 255 255 152

4577 42 24 77 0 143 135 57

4298 24 24 0 0 77 64 40



3046 39 45 0 0 110 99 38

3007 45 46 5 0 118 107 54

3000 46 46 7 0 118 107 54

3000 52 48 31 0 119 109 53

3022 96 140 3 0 160 153 86

3019 113 182 82 0 173 166 102

3064 130 182 88 0 198 193 118

3084 155 182 90 0 203 199 118

3144 175 182 88 0 205 201 134

3217 195 182 89 0 218 215 150

3282 203 182 87 0 223 221 150

3386 229 182 85 0 231 229 150

3446 216 182 85 0 224 222 150

3550 226 182 84 0 250 249 151

3591 215 182 85 0 242 240 151

RPM MAP TPS OXY AFM VECU GAIN ZON

 

I've seen what you are talking about from both lean and rich conditions. If you've seen both and are familiar with your car you can pretty much tell which is which. With lean my car feels likes it struggling to go up a hill (I think I can, I think I can) and with rich it feels like it's bogging down and almost like the engine is gonna die (oh, why did I eat all that turkey I should take a nap kinda deal). The lean condition also has more violent stumbles and is more of a sputtering. I've got a wideband O2 sensor installed so I can see the numbers to back up the butt diagnosis - highly recommend that if you plan on modifying and tweaking your car.

 

I'd pull the plugs and check them (for the couple $ replace them) and check the cap and rotor. If they are okay, then check the AFM voltage at idle. I've seen some cars set at .45v at idle, some at .6v, and mine is now closer to .8v. I can run 18psi at the current AFM setting. The exhaust pops a bit when cold, but it's a SFR 3" so that may be part of it.

 

it's the chip, not the plugs.

the PO had APE chips, no stumble.

i put in of guru chip v.9 and had erratic idle, and a bad stumble.

i changed them to 18 psi guru chip and it is much better but still has a small stumble

the thing is i have no way to fine tune my car, other than the LBE.

I'd like a MAF kit, but no one makes on using the stock aibox. my insurance doesn't allow modifications and if someone made a MAF kit but utilized the stock i'd probably get it, because it would still look stock.

 

Hmm, this sounds similar to an issue Matt Sheppard had. It only chugs at partial-throttle right? Like brisk acceleration with 50-75% throttle? What if you were to go full-throttle, like from 3000rpm onwards? Does it stumble the ? It might be an issue of switching back & forth between the partial-throttle and full-throttle maps.

 

I think that the answer lies in your signature. Is that stock wastegate shimmed? Your symptoms sound like the typical tired wastegate issues.

 

how do you alter the voltage going to the AFM??

 

Danno writes

Hmm, this sounds similar to an issue Matt Sheppard had. It only chugs at partial-throttle right? Like brisk acceleration with 50-75% throttle? What if you were to go full-throttle, like from 3000rpm onwards? Does it stumble the ? It might be an issue of switching back & forth between the partial-throttle and full-throttle maps.

YES, that's correct. 50-75% Throttle is where it is. I was hoping to get a dyno at PCA Dyno day but couldn't make it.

 

In general terms only, and nothing to do with the Chip matter, but to answer the original question, chugging is from a Rich condition just before backfiring happens. A lean engine will not chugg, but will "lay down" on power. A Rich engine will backfire thro' the Exhaust, and a Lean engine will backfire thro the Intake. This is why on lean engines, the Intake Valves, or that side of the Combustion Chamber, sometimes see's the damage

 

If I had to pick between rich and lean, I would def say you are lean, I still get a little chugging at times on cruise cos I am trying to be too economical.

 

Have you closely checked your throttle position sensor lately? I adjusted mine along with adjusting the throttle stop and setting the idle with the idle control valve disabled and the car idles and drives better than ever. I'm stunned at the difference. (It previously popped out the exhaust often, now much much less.) See Lindsey Racing's site or Clark's Garage or search the archives here for the procedure. IMO, there are many variables besides the chips that can cause driveability problems to surface when you crank up the boost to 18psi. HTH

 

I have not messed with TPS. There is no chugging with my original chips, a dramatic chugging with my second set, and the chugging described with my current chips. I hope to get a dyno and figure from there, but I do not have backfires or pops.

 

In general, stumbling is absolutely an indication of a lean condition or at least an on/off lean condition. When an engine is running rich it will be down on power but it will be smooth, unless it's crazy rich or on/off between crazy rich and just a little rich like a bad carbureted setup.

In your case, I think it's something else. I, and like danno said, a few others here have experienced the same thing. I had it on a previous 951 that I owned and unfortunately to this day I haven't for sure figured out what it was. With my current 951 I don't have this problem.
I bet if you disconnected your O2 sensor the problem will go away, however this is not a good solution because your car will always run in a rich mode at part throttle causing bad gas milleage and, if your extremely unlucky, a little cylinder washing.

I have only one theory of what the cause may be, but like I said before, I wasn't able to prove it:
It's a combination of north american chip maps (which run a richer baseline) and the O2 sensor constantly pulling out fuel to get to stoichiometric. In stock form it seems to be okay, but as soon as you do some fuel mods like higher fuel pressure, there was more of "swing" in fuel delivery caused by the O2 sensor trying to do its job, causing this stumbling. For me, the problem got worse when I did mods that increased mid range air flow (like an exhaust upgrade). I think this is because then there was even more of a sensation that the car wanted to accelerate at part throttle, yet there were even more contradictions within its own engine management. I think, really the part throttle maps need to be remapped when doing mods. I guess, a really good test would be to get an adjustable FPR, set it really low, like 2 bar, and see if the problem goes away.

Although I don't have this issue anymore, I also wouldn't mind to hear any other possible reasons for this.

 

I have had the very same thing, the BEST it has ever been is with my current chips (TT programmer of Vitesse's Chips) But it is still slightly there.
I tend to agree, I can feel the surging in time with the led swing of the autometer A/F gauge. I tried copying the ROW maps to the USA location just as a test, still felt the surge. Its also less noticible on cold days than warm.
I just run the ROW maps and be done with it. The USA set up is just to protect the cat and meet emissions anyway. TT programmed my ROW maps to run with my mods so its safe, I dont know if other chip tuners bother with re-mapping the ROW maps so you might want to check before you run them.

 

"It's a combination of north american chip maps (which run a richer baseline) and the O2 sensor constantly pulling out fuel to get to stoichiometric. In stock form it seems to be okay, but as soon as you do some fuel mods like higher fuel pressure, there was more of "swing" in fuel delivery caused by the O2 sensor trying to do its job, causing this stumbling."

TurboTommy, I think you are on to something there. The GURU chip-kits come with a higher-pressure 3.0-bar FPR. I've scaled down the fuel-maps to compensate for the higher-pressure, but not fully in all areas. Some people who've dyno-tested the partial-throttle mid-ranges have mentioned that the chips are really rich above 3500rpm and lean from 2000-3500. This has to do with a blending of the WOT fuel-curve into the partial-throttle ranges.

Blueman33, I just had another guy this past week solve this problem on his car. I'll get you guys in touch.