Unwanted IDC cut

[smokeshow]

I've searched high and low on this forum for an answer thinking someone else has to have had this problem before, but I found nothing. The car is a 99 camaro ss, manual transmission and absolutely stock save for cat-back exhaust. Not even a tune. A friend asked me to look at it and tune out a problem he is having, but I don't understand what's wrong with it. Every time the engine gets between 5500-6000rpms, it reduces injector duty cycle for some reason.

I'm not sure how else to explain it. Have a look at the log in that RPM range. Anybody have a clue what this is?

[c.u]

Have you scanned any of the fuel cut pids.

[smokeshow]

Have you scanned any of the fuel cut pids.

I've never seen any fuel cut PIDs, least not on this car.

[c.u]

So nothing in insert pids, engine-general fuelcut TgMgt. Or under fuel system-injecctors fuel cut type?

[smokeshow]

So nothing in insert pids, engine-general fuelcut TgMgt. Or under fuel system-injecctors fuel cut type?

No, nothing of the sort. I suppose I could log "TCS Desired Engine Torque" and see if it is indeed the torque management somehow pulling the injectors back. Whats interesting about this problem is that my truck does it too when I start turning the boost up. Unlike this car its far from stock, but the effect is similar. My truck isn't limited to a particular RPM range though, as the camaro is.

[Chris@HPTuners]

if i had to guess i'd say it's valve float.

[smokeshow]

if i had to guess i'd say it's valve float.

I considered something mechanical, but I just can't get there seeing as pulse width and injector duty cycle decrease when it happens.

[c.u]

After looking at the log this looks normal for a stock tune. For the first two shifts he`s bumping the fuel cut off rpm vs gear limt. For the rest just looks like dfco kick in when he shifts. ask him if has gone to a smaller tire.

[smokeshow]

After looking at the log this looks normal for a stock tune. For the first two shifts he`s bumping the fuel cut off rpm vs gear limt. For the rest just looks like dfco kick in when he shifts. ask him if has gone to a smaller tire.

Here's the file. The fuel cuts happen long before the actual desired fuel cutoff at 6200.

[Chris@HPTuners]

I considered something mechanical, but I just can't get there seeing as pulse width and injector duty cycle decrease when it happens.

when the valves float the airfow into the engine drops and the IDC drops too. You should be able to hear it misfiring. It's definately not a rpm limiter or anything like that. Stock LS1 springs very common to float @5600 - 5800 RPM as you grab higher gears and load up the engine more it gets worse.

Also, i assume you aren't seeing any codes. But its a good idea to set the MAF codes (P0101/2/3) to MIL on 1st error.

[smokeshow]

when the valves float the airfow into the engine drops and the IDC drops too. You should be able to hear it misfiring. It's definately not a rpm limiter or anything like that. Stock LS1 springs very common to float @5600 - 5800 RPM as you grab higher gears and load up the engine more it gets worse.

Also, i assume you aren't seeing any codes. But its a good idea to set the MAF codes (P0101/2/3) to MIL on 1st error.

Interesting... Well I'll let him know. I wonder what the issue is with my truck then? It has new PRC 675 springs, can't imagine that would have a similar issue.

[Chris@HPTuners]

post tune and log of your truck, the LS1 PCM is a lot simpler in operation compared to the newer PCMs. People have supercharged and turbo'd just about every combination you can think of without problems.

[jimmyblue]

The "fuel cut" seems to track perfectly the MAP and TPS.
And some of those TPS-drops go all the way to idle range,
which will drop him out of PE and properly cut fueling to
match the in-the-moment air mass flow, only problem
being that the filtering will make that a day late & dollar
short.

What ever happened to "mat it and row it"? Or is there
some fault that makes TPS drop out every time he shifts?
And take the MAP with it? Electric throttle on a '99 stock
F-body, can't be.

Now I have to say that the wideband reading is too damn
consistent to be credible.

[smokeshow]

The "fuel cut" seems to track perfectly the MAP and TPS.
And some of those TPS-drops go all the way to idle range,
which will drop him out of PE and properly cut fueling to
match the in-the-moment air mass flow, only problem
being that the filtering will make that a day late & dollar
short.

What ever happened to "mat it and row it"? Or is there
some fault that makes TPS drop out every time he shifts?
And take the MAP with it? Electric throttle on a '99 stock
F-body, can't be.

Now I have to say that the wideband reading is too damn
consistent to be credible.

Lol the wideband isn't plugged in, so yeah thats not useful data. As far as the shifts go, he lets off the throttle every time he shifts. I'll have him no-lift shift net time I get a log though

post tune and log of your truck, the LS1 PCM is a lot simpler in operation compared to the newer PCMs. People have supercharged and turbo'd just about every combination you can think of without problems.

Here's the latest. I just switched to E85 (most of the tank is, anyway) so the commanded AFR doesn't match the actual. Haven't begun using lambda yet.

[Chris@HPTuners]

Ok firstly, it looks like you are trying to run in SD mode, but you haven't set it up right.

Set the MAF fail freq to 0 (if you are not using a MAF it doesn't really matter). Set DTC's P0101/2/3 to "2 - No MIL Light" this is very important. MIL on 2nd does very weird things.

Also, put normal numbers in the PE table, setting it to zero is a bad idea. The Boost Enrich table is meant as a fuel safeguard to enrich the fuel if the engine enters boost when the PE table didn't kick in at low throtttle. Don't use it as your primary fuelling, use the PE table.

The VE table also looks very,very agressive, even running 16psi on my 408ci LS1 i had numbers only like 105-110 in the VE table and the big jumps by 10% or more between 200-220kpa etc. are causing the g/cyl to jump around wildly with small MAP changes.


Hope that helps,

Chris...

[david_viny]

The INJ duty % looks like its following the MAF flow. The MAF Hz goes kinda wacky in frame 263. Just an observation.

[smokeshow]

Ok firstly, it looks like you are trying to run in SD mode, but you haven't set it up right.

Set the MAF fail freq to 0 (if you are not using a MAF it doesn't really matter). Set DTC's P0101/2/3 to "2 - No MIL Light" this is very important. MIL on 2nd does very weird things.

Also, put normal numbers in the PE table, setting it to zero is a bad idea. The Boost Enrich table is meant as a fuel safeguard to enrich the fuel if the engine enters boost when the PE table didn't kick in at low throtttle. Don't use it as your primary fuelling, use the PE table.

The VE table also looks very,very agressive, even running 16psi on my 408ci LS1 i had numbers only like 105-110 in the VE table and the big jumps by 10% or more between 200-220kpa etc. are causing the g/cyl to jump around wildly with small MAP changes.


Hope that helps,

Chris...

Hm, I was aware that setting those codes to "No error reported" does weird things, cause it doesn't really run. Didn't know it had a similar effect just disabling the light.

Why do you recommend using PE as the primary enrichment? I always try to add fuel with boost, in essence adding fuel with cylinder pressure/heat. I can't see why you should richen the mixture the maximum amount as soon as it hits boost because the extra fuel isn't really necessary. Can you elaborate? Also, since the operating system is custom from you guys at HPT, I assume you are the ones who determined the high-value priority between the BE and PE tables (as I understand, picking the richest commanded value). Why not use a more complex mixing function between the two enrichment tables? For example, stacking the fuel multipliers to better represent enrichment for cylinder pressure. Just a question I've had for a while.

As for the crazy VE on the high end, I haven't turned the boost up that much so those were just rich guesses from when I initially set up the table. As you can tell I've leaned it out quite a bit at lower values The PCM does interpolate between cell values though, right?

I always find myself wanting to figure this stuff out with a software flow diagram. Feels like I'm missing a huge chunk of valuable info without one lol. I'll try those settings though, and let you know how it turns out. Thanks for the extensive help!

[Chris@HPTuners]

the PCM will choose the richest of the PE and BE, the issue is the BE doesn't operate as quickly as the PE table becuase it was meant to be a safety feature rather than the primary fuelling. It's up to you, but as the person that actually wrote the custom OS, all i can do is give you my opinion I've had supercharged and twin turbo LS1's and never actually used the BE table!

Yes the VE table is interpolated between cells just like any other, however, keep in mind that the GM VE table is not a regular VE table is the true % style. You will find the numbers need to be a lot lower. The inconsistency in the fuelling is being caused by the big changes to g/cyl which is a consequence of the VE calibration.

[DrLoch]

the PCM will choose the richest of the PE and BE, the issue is the BE doesn't operate as quickly as the PE table becuase it was meant to be a safety feature rather than the primary fuelling. It's up to you, but as the person that actually wrote the custom OS, all i can do is give you my opinion I've had supercharged and twin turbo LS1's and never actually used the BE table!

Yes the VE table is interpolated between cells just like any other, however, keep in mind that the GM VE table is not a regular VE table is the true % style. You will find the numbers need to be a lot lower. The inconsistency in the fuelling is being caused by the big changes to g/cyl which is a consequence of the VE calibration.

Good info to know

[smokeshow]

Chris, I applied the changes you suggested and there was no change for good or worse in the inconsistent fueling. MAF fail frequency to 0, P0101/2/3 to "2 - No MIL Light", put values in the PE table, and did a bunch of smoothing to the VE to make it less aggressive in general. It still has those erratic 10-20% dips in injector duty cycle. I was considering your input regarding the fueling and it would seem that duty cycle should increase if it were pulling from extremely rich adjacent cells in an aggressive VE table, rather than decrease duty cycle. It seems like there is something else going on here.

On a side note, concerning the BE table not operating as quickly as PE, is that a delay in commanded enrichment or actual enrichment? The commanded BE in all the logs I've seen appears to respond right when it should. I do have oversized turbos for my application, so it won't enter boost as abruptly as a supercharger. Perhaps that is why I don't notice any BE delay?