Tip in bog, O2's read lean, lots of fuel added by pcm

[mecanicman]

Because of the size of your cam and resulting lack of vacuum, you hit atmospheric pressure before the throttle is fully open. It has essentially taken away some resolution in the table for lower rpm ranges. The 95/100 kpa cells are having to do the job that would normally be spread out over a few more cells. As such they have to be a made higher value initial tuning would show. Increase the ve values in the 400/800/1200 columns at 95 and 100 kpa buy 20% each try until this lean tip in goes away. You can fine tune it once closer.

[GHuggins]

Yeah, I have no experiance really with the conversion of the 24 vs so on counters. I'm just going off of what is being stated and what I know plays with things from my own experiances with not only having to fix my own screw ups but the more funner mess ups of other shops. Really leaves you "chasing your own tail" for long periods of time only to have your literally beating your head against the wall once you figure it out and see just how simple it was.

I know he's not running or atleast shouldn't be running a cam profile big enough to really need a different setting from say something like the 04 Z06 Vette (cam is very close to stock cam of this car), but really wasn't sure how the counts difference was playing into the equation. BUT to have that lean of a tip in is leading me to believe something is wired wrong (02's hooked to wrong connectors) or we indeed are seeing something weird with the count conversion. I don't know off hand, but is there somewhere in the tune to change the pickup counts?

[mowton]

Because of the size of your cam and resulting lack of vacuum, you hit atmospheric pressure before the throttle is fully open. It has essentially taken away some resolution in the table for lower rpm ranges. The 95/100 kpa cells are having to do the job that would normally be spread out over a few more cells. As such they have to be a made higher value initial tuning would show. Increase the ve values in the 400/800/1200 columns at 95 and 100 kpa buy 20% each try until this lean tip in goes away. You can fine tune it once closer.

So based on previous observation and your comment M'man above, I went back and looked at my VE which is developed around a similar cam spec and the 70-100 kPa area's are abit higher than Jasons...I provide it as a sample for you Jason to try some of the values in the 400-1800 rpm areas.

Ed M

eds VE.xlsx

[JasonS5555]

Yes, the harness does change the firing order, and in conjunction with the changes to cylinder bank assignment get to a setup that generates a traditional SBC firing order. If you screw that part up, you end up chasing LTFT since the cyl bank assignments are not right and the pcm can't adjust fueling closed loop. I'm not having that issue at all. So I'm pretty sure all that is good.

If any of you guys need info on the subject in the future, I do plan to keep this thread as up to date with 24X conversions as possible.

http://www.hptuners.com/forum/showth...se-step-inside

GHuggins, thanks for the thoughts on the injector timing. I had changed the normal and makeup, but not the boundary. I'm still learning about all the injector parameters. The cam has a lot more duration than the Z06 cam. The heads don't flow as well at high lift as the later style heads do so to get higher end power for RR/autox I was willing to sacrifice a little low end drivability. So specs are below: 230/238 @50 .565/.565 on 114+2.

Thanks guys. I had tried increasing the airflow in those areas, but not nearly enough apparently. I'll give that a shot and report back.

[xrelapse13]

I haven't had a chance to look at the logs since I'm at work, but going off of mecanicman's point about the vacuum.

If the cam is that big that you're hitting 100kpa at low throttle openings, upgrade the os to 1 bar sd. You'll see a modifier table next to the VE table for TPS vs. RPM, (effectively an Alpha-N table).

You can use this in conjunction with your standard ve table to increase your resolution.

I've used this on cars with huge cams that hit 90+ kpa almost instantly on throttle opening.

You can set up a histogram and filters to only populate that table on KPA readings over 90KPA and to only populate your standard VE histogram on readings lower than 90KPA. I don't have my HPTuners in front of me right now but when I get home I'll look for the config I made for these kind of set ups.

With some polishing up, you can have it running with 0 issues. Have done this on a several cars with 347-383 c.i. motors and cams in the 250+ duration range.

[ElecTech]

I haven't had a chance to look at the logs since I'm at work, but going off of mecanicman's point about the vacuum.

If the cam is that big that you're hitting 100kpa at low throttle openings, upgrade the os to 1 bar sd. You'll see a modifier table next to the VE table for TPS vs. RPM, (effectively an Alpha-N table).

You can use this in conjunction with your standard ve table to increase your resolution.

I've used this on cars with huge cams that hit 90+ kpa almost instantly on throttle opening.

You can set up a histogram and filters to only populate that table on KPA readings over 90KPA and to only populate your standard VE histogram on readings lower than 90KPA. I don't have my HPTuners in front of me right now but when I get home I'll look for the config I made for these kind of set ups.

With some polishing up, you can have it running with 0 issues. Have done this on a several cars with 347-383 c.i. motors and cams in the 250+ duration range.

That's just it though, that cam is not big. I would suspect either a vacuum leak, misfire, poor valve adjustment, or possibly the O2 sensor connectors got switched left to right. Very easy to do on an LT car (seen it several times) and it causes the trims to go stupid the wrong way.

[ElecTech]

What's your TPS voltage at idle?

[mecanicman]

That's just it though, that cam is not big. I would suspect either a vacuum leak, misfire, poor valve adjustment, or possibly the O2 sensor connectors got switched left to right. Very easy to do on an LT car (seen it several times) and it causes the trims to go stupid the wrong way.

All of your points are worth checking. I believe that cam is big enough to cause this issue, especially if the throttle body is the big mono blade used on the lt1. Don't think o2s are switched from log.

[ElecTech]

Don't think o2s are switched from log.

I agree. Once I was able to open and view the actual log, I scratched that one out.

A large monoblade I can understand, but I've dealt with many cams like this and also some with larger duration and tighter LSA's without this type of behavior. I definitely feel its not normal behavior given the specs.

[JasonS5555]

Hey guys,

Thanks for the thoughts. I will certainly look for a vacuum leak, and possibly valve adjustment, but it ran fine with the valves adjusted this way on the LT1 PCM.

The richer tune did help the tip in bog, but its still there. So Jamie and m'man are likely right that there is some other issue. I'll post a log and tune when I get a chance.

Thanks a ton,
Jason

[JasonS5555]

One other question occurs to me after looking at the logs. Why does the PCM spend so much time in cell 22? It seems like it shouldn't be there as much as it is. Shouldn't it be in other cells based on the RPM and MAP boundaries? Thoughts?

Thanks,
Jason

[JasonS5555]

Just wanted to let everyone know, that extra fuel and timing has at least made it driveable. I searched everywhere for a vacuum leak with starter fluid etc and found nothing. So the cam may act a little bigger than everyone here is used to because the LT1 heads don't flow nearly as well as LS1 heads. I'll post a log when I get a chance.

Thanks!!!

Jason

[GHuggins]

Yes, the harness does change the firing order, and in conjunction with the changes to cylinder bank assignment get to a setup that generates a traditional SBC firing order. If you screw that part up, you end up chasing LTFT since the cyl bank assignments are not right and the pcm can't adjust fueling closed loop. I'm not having that issue at all. So I'm pretty sure all that is good.

If any of you guys need info on the subject in the future, I do plan to keep this thread as up to date with 24X conversions as possible.

http://www.hptuners.com/forum/showth...se-step-inside

GHuggins, thanks for the thoughts on the injector timing. I had changed the normal and makeup, but not the boundary. I'm still learning about all the injector parameters. The cam has a lot more duration than the Z06 cam. The heads don't flow as well at high lift as the later style heads do so to get higher end power for RR/autox I was willing to sacrifice a little low end drivability. So specs are below: 230/238 @50 .565/.565 on 114+2.

Thanks guys. I had tried increasing the airflow in those areas, but not nearly enough apparently. I'll give that a shot and report back.

When you stated you had changed the injector normal and makeup tables, which way did you go with them? Sorry, but I don't have my laptop with me to check this out at the moment. Left it at work... Injector pulse widths are another good tell tell of this. I personally don't like seeing much above 2.5ms at hot idle and try my absolute best to achieve around or less than 1.7ms. If I'm thinking correctly yours has the "volts" tables. Try setting your normal and makeup tables back to stock, then raise your boundary table to 6 or 6.1 and see what your fuel trims and injector pulse widths do. Datalog hot idle, then immediately change this and reflash while still hot and see what you get. If it's better, drive about 7 to 8 miles then recheck. If it's not or you see no improvements, then you can simply return it to what you had before.

Hope this helps you out.

[flame]

To those not familiar with the LT1 intake/tb
Twin 58mm throttle blades and the map sensor is only 2 inches past the tb. The intake is also known for reversion with larger cams causing the o2 sensors to get confused

[GHuggins]

To those not familiar with the LT1 intake/tb
Twin 58mm throttle blades and the map sensor is only 2 inches past the tb. The intake is also known for reversion with larger cams causing the o2 sensors to get confused

So, other than the reversion part, is it possible to plumb in the map somewhere else on the intake manifold? Would this take care of his problems or does he just need to do the 1bar map OS conversion and set it up to add fuel only in the 90 or 100 kpa zones as I believe was previously suggested? AND if this is really that problematic, I think the transitional tables should be addressed to the standard thinking principles of this being forced induction. In other words multiply out the 100kpa line by 1.5 then 90kpa line by 1.25 then perhaps even the 80 and 70 kpa lines by stepped down values from there in both the impact and evap factor tables with the most highest multiplied percentages being in the evap tables. Of course if FI, I would use values slightly higher than that, but that's me.

I'm really curious now myself. Really think the injection timing will help especially knowing these intakes are known for reversion issues, but now knowing the above forementioned, kinda find myself going back to the very basic discussed fueling problems and if it were me, I would correctly set timing and "tweak" in the transient tables to elliminate the final "lean tip in" stumble.

Your thoughts?

[JasonS5555]

Hey GH,

Both normal and make up went up to 6.29 from 5.55 in the normal operating temp area. The stock value for boundary is 6.5 so should I increase that? I am seeing idle inj pulse widths of 3.2 or so. "volts" tables? Oh, and I don't think it would be that easy to move the MAP sensor.

flame,

Thanks for clarifying that. I should have done so as part of the LT1 differences discussion.

Thanks for the help guys. I knew there were folks here with way more experience than me. If I do go the way xrelapse suggested and the 1 bar SD tune, I loose the MAF functionality?

Thanks,
Jason,

[ElecTech]

To those not familiar with the LT1 intake/tb
Twin 58mm throttle blades and the map sensor is only 2 inches past the tb. The intake is also known for reversion with larger cams causing the o2 sensors to get confused

Ls2 and LS3 MAP sensors are directly behind the throttle body also.

[flame]

Ls2 and LS3 MAP sensors are directly behind the throttle body also.

My point was more that the original calibration was designed around a 75mm tb and map sensor at the rear. Composite intake vs aluminum, alum block vs cast, there are so many things different. How many hours does gm spend building the calibration? I'm no expert by any means but have tuned a bunch of LT1s over the years and moved onto LS1 since doing my swap. I screwed around with a 24x a couple years ago and spent countless hours trying to get rid of issues that were not there with the LT1 pcm. Kudos to the people that figure it out but Im keeping the opti on my 96!

[GHuggins]

Hey GH,

Both normal and make up went up to 6.29 from 5.55 in the normal operating temp area. The stock value for boundary is 6.5 so should I increase that? I am seeing idle inj pulse widths of 3.2 or so. "volts" tables? Oh, and I don't think it would be that easy to move the MAP sensor.

flame,

Thanks for clarifying that. I should have done so as part of the LT1 differences discussion.

Thanks for the help guys. I knew there were folks here with way more experience than me. If I do go the way xrelapse suggested and the 1 bar SD tune, I loose the MAF functionality?

Thanks,
Jason,

OK, had to go and actually look at the tune. Should have done that to begin with. I seem to remember the boundary being 5.55 for some reason. I guess it's been too long since I've worked on one of these. As for what you did to your injection timing. You kinda went 180 to which way you needed. Other's can chime in on this, but that's how I've found is the best way to adjust it when medium to large cams are involved. You basically want the fuel being shot in while the intake valve is open and exhaust closed so your no longer "short circuiting" the fuel, which is what I really believe you have going on. Set your normal and make up tables back to stock and just increase the boundary "upward" about .2 at a time until you stop taking away fuel. As for the "volts", I was referring to the referrence tables you have been adjusting. This is if you see fuel being taken away and your injector pulsewidths coming down. If not, you can always reload what you currently have and take another approach.

THEN - if you still have a "lean tip-in", adjust your transient tables as I mentioned above. As for the SD OS, someone else can correct me on this, but I believe you can still use your maf. The OS just gives you a lot more to "play" with, as far as tuning capabilities goes.

[JasonS5555]

Kudos to the people that figure it out but Im keeping the opti on my 96!

After going through 6 of them and the last one only lasting 2500 miles, I'm done with them.... Yeah I know, may not be as easy tune to completely sort out, but the tune won't go bad and leave me stranded either....

Jason