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Some tuning issues...and I just want to learn

Old 01-11-2019, 02:55 PM
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turabo87
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Default Some tuning issues...and I just want to learn

Hi folks,

Brief background first:

I just finished my "big C5 project" last weekend. This involved going from basically bone stock to installing a mild cam (JEGS .585/.585/228/230 112LSA), top end rebuild with my stock 853 heads (rocker arm trunnion upgrade, BTR pushrods, LS7 lifters, dual valve spring kit, cleaning valves and piston tops), new Melling oil pump, resized 42#@58PSI injectors, LS6 intake, K&N Cold air intake and airbridge, and full catless exhaust with Texas Speed long tube headers 1-3/4 with X pipe and Magnaflow XL mufflers, among other "while youre there" things. Did it all myself too . Anyhow, finally took it to tuning to a reputable local tuner and he did a great job and making torque, power (397WHP), good idle and very good cruising drivability, BUT I have two issues. I already contacted him and he's going to take care of it but he's not the talking type nor to give a lot of details while I'm the learning and curious type. Anyway, I want to post my issues and understand what features, settings, and tables are responsible for this behavior. Maybe I'll get HP Tuners one day and fine tune things little by little:

1) As I coast down on slow speeds (5-20mph) and I press down clutch, the RPM's raise up to 1400 and won't settle unless I come to a complete stop, then it settle to idle at 850RPM which is my set idle speed. Although it helps not to stall, but it's a little bit too high for my taste and gets annoying to hear such high RPMs when coasting, when all I want is to hear that choppy idle.

2) On a morning cold start, somewhere between 50-60F of ambient air temp, the car would struggle to start unless I throttled the gas while cranking. Seems to be a like a temp related fuel enrichment table or setting is off for this temp, but I don't know about the HP Tuners software and what tables and settings it accesses. I was able to recreate it again this morning on another true cold start. It was around 55F this morning and did the same thing. I made sure the pump primed the injectors before cranking. It cranked and you could here a couple of combustion events but not enough to start. Then again I tried cranking and cranking without throttle and nothing happened. Then, I tried priming fuel with key on again and this time I throttled maybe 25% or more in pulses while I cranked. Took a couple of seconds and started, and I had to keep it alive by keeping it throttled at 2k rpm for a couple seconds, until it could keep itself from stalling. Once it warmed up for a couple of seconds, I was good to go and had no issues afterwards.

Just trying to learn here of the process and how the C5 ECU functions. I have some tuning experience I had once with a Megasquirt project (fully programmable ECU) on a 600cc engine, so I can understand basic tuning concepts and ECU parameters.

FYI: My C5 was tuned with HP tuners on MAF strategy, for 93 octane.

Last edited by turabo87; 01-11-2019 at 03:02 PM.
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Old 01-11-2019, 03:09 PM
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aaronc7
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1.) Sounds like "throttle cracker" table. I have similar mods and since I moved to high elevation this suddenly became an issue on my tune too.

2.) Sounds like cranking VE table, Car runs in open loop for xx amount of time depending on CLT or CLT temp.... surely at 55F it's going to be open loop for a while. There is an open loop fueling table, but I doubt many people mess with that, which is why I would suspect the VE table-- values need to be lowered with a more aggressive cam since it is not as efficient at low rpm now.

I had a turbocharged miata that ran on megasquirt 2 that I built and tuned, sounds like we have a similar background. I have EFIlive for my car and kinda tinkering and learning as I go. I would recommend HPtuners though, they still continue to develop a bit for the LS platform and have some neat new products. I got EFIlive only for a convenient handheld flash tuner and black box logging at the time.

Last edited by aaronc7; 01-11-2019 at 03:09 PM.
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Old 01-11-2019, 06:35 PM
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turabo87
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Thanks. Iím a mechanical engineer and back in my college days via Formula SAE I got introduced to learning about tuning for port fuel injection with Megasquirt. It was a 600cc high output race bike engine. I learned about about the basics of tuning and I got the friggin thing to run from scratch. No base table to start with.

Anyway, thanks for the info. Iíll let my tuner do his thing and pretend not to know much for now. It can be annoying for him and anyone for that matter to tell him what to do when heís the pro and Iím not.
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Old 01-11-2019, 07:03 PM
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aaronc7
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BTW you can download the HPtuners or EFILive software and install, look at various stock tunes for free. You can begin your learning before purchasing anything or tuning your actual car. Both softwares actually have pretty good table descriptions and lots of great info on both site's forums (much more active DIY community on hp tuners).

Throttle cracker "cracks" the throttle open by X amount when above Y speed (tables for both).

Last edited by aaronc7; 01-11-2019 at 07:05 PM.
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Old Today, 10:18 AM
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turabo87
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Originally Posted by aaronc7 View Post
BTW you can download the HPtuners or EFILive software and install, look at various stock tunes for free. You can begin your learning before purchasing anything or tuning your actual car. Both softwares actually have pretty good table descriptions and lots of great info on both site's forums (much more active DIY community on hp tuners).

Throttle cracker "cracks" the throttle open by X amount when above Y speed (tables for both).
Hey Aaron, so I took my car back to the tuner and he fixed the throttle cracker as best as he could. It's pretty good now, however he believes I might have a small vacuum leak somewhere that's keeping the car from being at idle when coasting. Only a few hundred RPM higher so it doesn't bother me. Anyhow, he also said car needed more airflow on cold start on cold temps so he tweaked some values. Made it better, but still needs my throttle to keep it from stalling in a cold 50-60F morning for first 10-15 seconds or so of the cold start.

I figured it would be easier and more of a learning experience to get HP tuners and an OBDII dongle. How much is the HP tuners download? Then what is it that I need besides the software and the dongle that actually costs?

Last edited by turabo87; Today at 10:18 AM.
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Old Today, 12:01 PM
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aaronc7
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I don't have hptuners so I'm not really an expert, but I have been looking at the website out of my own curiosity... The MPVI2 is the new dongle/interface. There is standard and Pro.... standard is $300, Pro if $550. Pro adds blackbox logging (no laptop), bluetooth connectivity, expander hub which allows external analog and serial inputs (think Wideband). Then credits are $50 per.... you either need or one or two for a GM vehicle, not sure.

The pro is a decent price jump, but I would get that if you have the desire to wire in a permanent wideband to the car. Also the BT connectivity would be convenient at times for me and works with their own "track addict" app etc. If you get standard, but still want a wideband, there is a workaround via routing analog signal to the unused EGR port on the PCM. I used to do that, but now I have wideband connected via serial cable and have fuel pressure going into EGR port.

https://www.hptuners.com/mpvi2/

Hope that helps
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