Fueling DOES make a difference.... lean surge...

[Jinxmutt]

Got back to the dyno to do some tuning. I changed around my setup a bit and decided to put the car on the dyno for an hour to dial in fuel and timing.

I must say the car is making MUCH more power, but I think I have some misfires or something. We ended up cutting my dyno session early so I can look things over. I pulled the plugs at the dyno and they all looked mint. The car ran fine when I drove home, its still making good power on and off boost, but it does seem like there is a bit of 'roughness' to it under load. The knock sensor voltages aren't crazy, and I can't 'hear' anything as far as pinging, popping, etc. One thing I 'have' noticed is that it seems I'm getting a very slight lifter tick, or maybe exhaust leak. That is my only guess as of right now.

These two pulls are on 17psi. Both logs show the car holding 17psi nicely, but the fueling was leaned out as you can see. The two runs are of 463hp and 481hp peak numbers. The only change between the two was fueling. I know its still PIG rich below 4500, but I didn't make enough pulls to clear that up.

For reference, I made ~519hp on 24psi before. As soon as I get this sorted out, and crank the boost up, I'm expecting some mid 500s. These runs were made on the same dyno as last time.



(It appears to spool slower than last time because of the way I had the boost controller setup. I usually use electronic closed loop feedback to get quicker response, but it was overshooting, then correcting, so I just set it to a constant DC for tuning)

[Shaun41178(2)]

I am guessing when you said the plugs looked mint, you meant the ceramic wasn't bright white? A nice light brown color?

Whats your plug gap?

When you say roughness, it just does not feel like its pulling right? The dyno isn't showing a misfire as that would be a big dip in power. What gas did you use? Pull a plug or two, and look into the bores at the tops of the pistons. You will see if anything doesn't look normal.

what rpm does the roughness occur at? Does it clear up? Does it do it at lower boost levels?

Being a dyno dynamics you could have changed the load rating and created a higher load for the car, to see if you could recreate the roughness in say 5th gear rolling into it at a lower boost.

its hard to say right now, but if you bumped the timing up, you will have higher cylinder pressures, which could cause ignition problems That or you had a smidge of detonation. The plug might not show that if it was light enough

you got a log of your aem wideband vs the dyno wideband? I got a bad tank of gas once and my car ran like shit under load. Normal driving was fine but ran super rich. Basically my o2 sensor got messed up from the gas, and screwed up all my fuel trims. I emptied the gas, put in a new o2 and been good since. Basically I am saying it could be fuel related or a sensor.

I think a test at a lower boost would be a good way to help determine the prob.

[Jinxmutt]

The "misfires" occur in the upper rpm region where the power kinda flattens out. The lean spikes in the AFR graph are representative of the roughness. I hadn't touched the timing at all at this point.

The ceramic was not bright white, it looked nice. I have the plugs in the car still, since I swapped them at the dyno, so I'll bring them in to take pics. I dropped my plug gap to .036. My O2 sensor logs showed the same lean spikes the dyno dynamics did. I considered playing with the dyno some to see which conditions caused it, but I really didn't want to break it. The reason I was running at these boost levels is because this is 'low' for me. I typically run over 21psi to and from class, I beat the shit out of this car. It has seen consistent beatings at 25+.

I run just the run of the mill corner gas station 93, so I'm hoping its just bad gas. I typically get it at the same gas station near school, but my last fill up was in the city, since I was running low and had no choice.

I have since turned the car back down to 10psi (basically open gate) so I can drive it around. It has been fine since, but I'm not takin many chances until I look other things over.

I was planning on doing a timing sweep but didn't get that far into the dyno session. I wanted to get my fuel somewhat close, set the timing maps, then finalize my fueling.

I checked the spark plug wires they all look good. (They're only like 8" long). If the problem persists, I'll try changing out 1 coil at a time (I have 2 spares from the v8) and see if it changes at all. I'm also going to look more into that lifter tick. I just upgraded to 130# springs not too long ago and maybe its related...

i have another dyno graph that got messed up, but shows the lean spikes much more peaky if I can dig it up.

[Shaun41178(2)]

plug gaps seems kind of high to me. I have mine gapped at around .020 Whats stock on a 3800 S/C?

A serious misfire would show a hp drop of close to 80 hp based on what each cylinder is roughly making. I don't see any such drop so if a cylinder was completely losing spark you would see a huge dip in power.

if you are down to 10 psi I would see if the problem occurs at that boost level or not.

Here is a misfire on a dyno on a 4 cylinder so the results are more dramatic with less combustion proceses overall, but it still shows just how power it drops when it happens. Your graph isn't experiencing that, so I am thinking it might not be a misfire.

[Shaun41178(2)]

you can hear this. sound like your car? Like I said a total misfire would lose a bunch of power.

http://www.youtube.com/watch?v=ivPPYu9yr54

starting around 2:10 for this vid,
http://www.youtube.com/watch?v=3CCtE50NVcM

[Jinxmutt]

Okay, I looked at my other graphs that had worse lean spikes, and the power still isn't dropping off that bad. It does fluctuate slightly, but that must be due to the afr (roughly 5hp).

Another thing could just be that the cal corrupted. We noticed some of the logging parameters were being weird and had to restart the program. We uploaded a fresh cal before the drive home, and this too could have perhaps fixed something.

So many routes to take, and so little interest in breaking something. The track season is just about to start and I need to get this thing down the strip a few more passes before I take everything apart for auto.

(I really don't want to go auto, and this allows me to procrastinate a bit more. Although going auto I'm going to be on X's heals...)

[Shaun41178(2)]

when driving home were you running the same boost as on the dyno and did you get into it all at all see if the problem still felt like it was there? Or did you just cruise it on home?

yea 5 hp dip here and there on a dyno is nothing. Thats what the smoothing is for. 5 hp when making close to 500 could be a slightly out of balance tires.

I am guessing your aem is controlling boost? If so, adjust your solenoid while driving slowly raising the boost from pull to pull on a straight flat road like a highway. After each pull if it all seems fine, bump it up 2-3 psi and do another pull. Would be good to know if the problem is boost related.

[Jinxmutt]

I watched my vids, I don't have that noise like the NSX. I'm gonna have to just take it easy and keep upping the boost little by little to see when it starts and what causes it. The AEM is controlling my boost and everything else. The plug gap is .036 right now, which I don't think should be out of line with the LS1 style coils. I've run more boost with this gap and no issues.

My main concern from all this is that my afr is usually a lot more flat and doesn't have spikes like it does now. Even when I ran it lean or rich it was usually consistant, and it wasn't rough. Both my aem and they dyno show the same spikey afr reading.

[Series8217]

I had a bad PROM socket a while back that was causing all sorts of strange misfires and even throwing trouble codes sometimes at high RPM.

[The Dark Side of Will]

An intermittent misfire would show up as lean spikes on the AFR readout.

Tell us more about your valvesprings... what was the old spring load? Have you done a compression check? How are your valves doing? New springs have dampers? Tapered/beehived/Ovate wire?

[Jinxmutt]

I was running comp cams 105# springs before, now I'm using 130# comp cams "918" springs. They are both LS1 style behive springs. I also use their OE-R lifters, but I'm using stock rockers and pushrods, which could be causing the problem.

I haven't checked compression or leak down,etc. Next week is spring break and I have some reports and some stuff due by friday. I'll be busy these next few days with school, then I'm going away for a week. This saturday would have been the first track night, but I'm gonna skip out.

[Jinxmutt]

I had a bad PROM socket a while back that was causing all sorts of strange misfires and even throwing trouble codes sometimes at high RPM.

I've just been reading that the prom chip can vibrate loose in these AEM boxes too. I'm gonna pull it apart and make sure its seated fully. Good suggestion.

[Jinxmutt]

Ok well I was finally looking over the car to try to get this figured out and I realized that nut on the stud I was using for ground had come loose. I welded a stud to the frame and connected 'all' my ground points to this one stud. I have a ground from the block to this stud, from the battery to this stud, as well as many other electronics such as the AEM, my coils, etc. At the time, I didn't have a lock nut, so i used a standard nut that I had. Well it turns out this nut was only held on by 2-3 threads and looked like it was about to come right off. I tightened that nut back down and with it tight, about 1/8" of thread actually sticks through the nut. I am going to be replacing this nut with a lock nut as soon as possible.

I haven't beaten on the car yet, but with the car on wastegate spring, it seems to be running a lot smoother. No surprise there.

[Shaun41178(2)]

lets hope the prob was that simple.

[Jinxmutt]

Nope, that didn't fix it. I raced a camaro tonight and took a log. I can feel the car surging but stayed in it anyway so I can see what the data was doing. The car is 4.0 bore iron block, bla bla, i didn't listen. It has a big cam, headers, cut out, and I didn't care what else. He was willing to run, so I was ready. I pulled on him like he never started. Twice. His friend with a lightly modded C5 Z06 wouldn't go...

In anycase, the problem is still there!!


Very top line is TPS, then Boost, then the crazy AFRS. The two slopes are mph and rpm.

Next thing on the list are my fuel filters and then then fuel pressure regulator. At this point, I don't really think its software related.

[KurtAKX]

Can you use an open channel in the PCM to log fuel pressure? I think DarkHorizon was doing this with an AC pressure channel or something... might help.

[fieromadman]

Have u looked over your wires carefully to see if they are arching out? Have you looked at your plugs? Have you checked to make sure all electrical connections are tight (such as injector clips ect, I had a problem last summer that just turned out to be a loose injector clip)? Also, just because your plugs and wires are good doesn't mean your coilpacks haven't gotten weak. The stupidest little things can cause issues...

Nice kill BTW!

[The Dark Side of Will]

Nope, that didn't fix it. I raced a camaro tonight and took a log. I can feel the car surging but stayed in it anyway so I can see what the data was doing. The car is 4.0 bore iron block, bla bla, i didn't listen. It has a big cam, headers, cut out, and I didn't care what else. He was willing to run, so I was ready. I pulled on him like he never started. Twice. His friend with a lightly modded C5 Z06 wouldn't go...

In anycase, the problem is still there!!
http://i13.photobucket.com/albums/a260/ ... 38d856.jpg

Very top line is TPS, then Boost, then the crazy AFRS. The two slopes are mph and rpm.

Next thing on the list are my fuel filters and then then fuel pressure regulator. At this point, I don't really think its software related.

Nice kill.
So the bumpy line is AFR? Are the high points on the AFR trace lean spots? Do you have any sort of traction control function on your ECU enabled? Have you talked to AEM tech support about this?
Looks like it could be an intermittent misfire. You've ohmed out your wires and changed plugs, right? Have you checked coil primary and secondary resistance?

Intermittents suck to diagnose... but if you keep running it hard, it'll turn into a dead miss and be easy to find!

[Jinxmutt]

Good suggestions guys! I haven't talked to AEM about it because I'm not sure its software related. There ECU does have traction control, but I don't have it enabled. Rather than use the traction control setup, I have a switch retard. The switch is a momentary one, and upon release, it pulls 15* of timing and ramps it back in over a second and a half. This is usually enough to not spin my all-seasons...

I will ohm out the coils and the wires. A bad coil wouldn't be a bad thing. I bought the whole set from the v8 so I do have 2 spares around here somewhere. The wires I'm running are just basic NAPA brand ones I got when I first put it together.

The car only does this on high boost levels. Cruising around its fine and if I just get to like 5-10 psi at like 1/2 throttle its fine too.

[The Dark Side of Will]

The car only does this on high boost levels. Cruising around its fine and if I just get to like 5-10 psi at like 1/2 throttle its fine too.

Sure sounds like a weak ignition.