Engine stumbles and knocks on acceleration

[pghalcrow]

This only happens on the first and sometimes second time after a startup when accelerating. The motor will stumble like it can't get fuel, then hit some pretty good KR, recover, then be OK after that. This usually goes away after it happens the first time when attempting to repeat the issue - until next startup. WOT throttle has no fuel starvation issues, so delivery to the fuel rail is not the issue. Aside from this issue, the drivability is spot on.

6.0 E38 LSA
850cc Fuel injector Clinic
47 psi base fuel pressure with boost reference (works properly, can verify 1:1 increase from fuel pressure sensor)

Logs and tune provided.

20240402_1.hpl
20240401_2.hpt

[Alvin]

It wasn't going into PE in the situation where you saw all this knock even though it was 7psi maybe up to 15psi of boost. Looks like the TPS enable for PE needs some help.

Also I wouldn't take fuel pressure for granted. Until you put a gauge on it and see that it has fuel pressure when this happens you don't know.

[blindsquirrel]

In the FIClinic datasheet, what pressure delta column did you take the data from? 328kPa column will be closest to 47PSIG.

[pghalcrow]

In the FIClinic datasheet, what pressure delta column did you take the data from? 328kPa column will be closest to 47PSIG.

It's been a while since I put that data in, but I believe that was the column I used, or should I say, would have used.

[pghalcrow]

Regarding fuel pressure, I was watching it when it went into this mode and I was somewhere in the 50-something psi.

Looking again at the PE settings, I guess I'm unclear as to what dials would need to be tweaked to get into this mode under this condition.

[Alvin]

The TPS enable likely is the culprit. Works by accel pedal %

[Lakegoat]

How about this?

[Alvin]

How about this?

That's awful but first priority is its asking to be at EQ = 1 with significant boost. Needs to be in PE with boost.

[sgod1100]

I've always had good results with using map instead of pedal position. Especially in higher gears where a very small amount of pedal movement can result in large change in engine load. Where I have the 15 circled change that to 80-90 kpa. Then change the pedal enable to all 5s or a very low number. That way you will have the map sensor be the main trigger. I have my map trigger at 90, but it's really up to you as long as you have PE coming before 100 kpa (aka boost).

PE.JPG

[pghalcrow]

I've always had good results with using map instead of pedal position. Especially in higher gears where a very small amount of pedal movement can result in large change in engine load. Where I have the 15 circled change that to 80-90 kpa. Then change the pedal enable to all 5s or a very low number. That way you will have the map sensor be the main trigger. I have my map trigger at 90, but it's really up to you as long as you have PE coming before 100 kpa (aka boost).

PE.JPG

Thanks for the info. After changing the petal position table, the issue is gone. While waiting for some responses on this, I sort of figured it out and decided <3500 RPM, 10 was "good enough", but I'll lower it to keep out of the corner case where it may still happen. Regarding the Min MAP value, I guess it's still confusing. I read this as "PE will enable when your MAP shows manifold pressure above this value", meaning that if I raise this number to the suggested value of 85 kpa, this condition will be met at a higher manifold pressure - which seems opposite of what I want. I'm sure I'm just interpreting this wrong.

Final question: is the "Min MAP" and "Throttle Hot" tables an AND condition to meet PE enable? Not sure I understand the logic under the hood here.

[pghalcrow]

That's awful but first priority is its asking to be at EQ = 1 with significant boost. Needs to be in PE with boost.

I'm glad we pointed this out. I attempted to do a bunch of VE tuning a while abo using Goat Rope's method, but apparently I suck at it. I always wondered if I am even using the VE tables because my Dynamic Airflow numbers appear to turn it off. High RPM Disable =1000 and High RPM Re-enable = 0. If I look at the HP tuners sample file for the 2010 Camaro E38, these are 4000 and 3900, respectively. If I set my values to match this, this thing runs like absolute garbage, so I keep it (what I believe to be) off.

[Alvin]

In my opinion you'll have a far better driving car with less issues with idle and other things if the VVE is tuned in well. I'm a advocate of disabling the MAF sensor, tuning VVE, then re enable MAF if you wish.

[pghalcrow]

Can you verify that VVE is disabled currently on this tune? I believe it is based on the High RPM enable/disabled values. I can go through the VE tuning steps again and try to get this looking better, but just need to understand the logic as to when it is enabled vs disabled.

I'm assuming it is currently disabled since (A) VVE tables are garbage and (B) when I set High RPM enable/disable to stock values, the drivability is terrible.

[blindsquirrel]

VVE is never fully disabled, it's still used for transients even with "MAF only".

[Alvin]

Can you verify that VVE is disabled currently on this tune? I believe it is based on the High RPM enable/disabled values. I can go through the VE tuning steps again and try to get this looking better, but just need to understand the logic as to when it is enabled vs disabled.

I'm assuming it is currently disabled since (A) VVE tables are garbage and (B) when I set High RPM enable/disable to stock values, the drivability is terrible.

I consider that a hack way of tuning so I don't know for sure. I believe the VVE stuff is always in play at least to some degree.

[07GTS]

just zero out the VVE table and u will know exactly when it is being used no matter the rpm enable/disable settings, *** do not recommend and i take no responsibility for this being tested ***

[pghalcrow]

just zero out the VVE table and u will know exactly when it is being used no matter the rpm enable/disable settings, *** do not recommend and i take no responsibility for this being tested ***

Did just that, instructions unclear, engine exploded. LOL..

[edcmat-l1]

just zero out the VVE table and u will know exactly when it is being used no matter the rpm enable/disable settings, *** do not recommend and i take no responsibility for this being tested ***

There was actually someone on here in this section with a tune file with the VE zeroed out and he said it ran well. I'll see if I can find it.

Here you go. Guy says it ran like this for year and a half and it ran pretty well.

https://forum.hptuners.com/showthrea...rged-Silverado

[sgod1100]

Thanks for the info. After changing the petal position table, the issue is gone. While waiting for some responses on this, I sort of figured it out and decided <3500 RPM, 10 was "good enough", but I'll lower it to keep out of the corner case where it may still happen. Regarding the Min MAP value, I guess it's still confusing. I read this as "PE will enable when your MAP shows manifold pressure above this value", meaning that if I raise this number to the suggested value of 85 kpa, this condition will be met at a higher manifold pressure - which seems opposite of what I want. I'm sure I'm just interpreting this wrong.

Final question: is the "Min MAP" and "Throttle Hot" tables an AND condition to meet PE enable? Not sure I understand the logic under the hood here.

In regards to changing your min map value to 85kpa, your engine is still in a vacuum condition at that point. Yes you are raising it but with your current pedal settings I can almost guarantee that you are higher than that 85kpa setting before PE kicks in. For example when I had my 2.55" upper pulley on and I had those exact same pedal settings (those are what the stock cts-vs are set to) I wasn't getting into PE until around 120kpa. So you are essentially "lowering" when you get into PE even though you are "raising" that value.

Yes, Min map and throttle hot is an AND condition. Both need to be met in order for you to get into PE. I just find it much more simple to take the pedal out of the question and use map (personal preference of course).

Keep in mind that you changing the pedal position 10 may be too low as you may be getting into PE all them time (i.e. just normal part throttle acceleration from a stand still). Going to have to get a log so you aren't eating up fuel unnecessarily

[07GTS]

There was actually someone on here in this section with a tune file with the VE zeroed out and he said it ran well. I'll see if I can find it.

Here you go. Guy says it ran like this for year and a half and it ran pretty well.

https://forum.hptuners.com/showthrea...rged-Silverado

crazy maby it was using the predictions coeff or something like that, cos then u have the goat rope silverado that he had maf only with meth spray and he found out that the vve not being populated in the boost areas when he did a throttle stomp it took all fuel out and only the meth was left and went lean and killed the engine, its in one of his videos, interesting tho, he could launch just fine but it was end of track zero to a full mash throttle that caused it so might need a large movement to force it