Vijay Rajendran

I suspect my car has a problem with the thermostat resulting in low rpms immediately after throttle. Is the correct procedure to replace the relay on the thermostat and to use a obd2 tuner to make sure the pressure on the fuel rail is less than the flow on the intake.

ChopperDoc

I'm having trouble understanding your question. Would help to know your mods, if you changed any parts like TB, intake, cam, etc. One thing I can say with confidence is that Injector Pressure should NOT be less than your Manifold Absolute Pressure (MAP). Like not even close. Injectors run at 4 BAR or 58-60 PSI, whereas your MAP will not exceed 1 BAR (105 kPa or 14.7 PSI) for N/A engines. If for some reason you have more boost than injector pressure (60 PSI), then I'm simply impressed, and I would like to know more about this build lol.

Vijay Rajendran

The misunderstanding I think is in Pascals Principle. I indicated fuel rail and you are indicating injector. Injectors have a very small aperature so pressure there is different from the fuel rail right. At least that is what is intuitive. Another problem I indicated intake which is usually variable and you are indicating exhaust. Your interest has been noted and I would like someone with experience solving the problem to comment. Have you seen this problem before or are you just having a good time. The car in question has a funny exhaust setup so be careful in your response. It may destroy the corvette industry. Ha Hs hsadfa

Vijay Rajendran

From my understanding mods make pressures variable and the thermostat is vital to controlling heat which alters pressures. Adding a new relay will reset the system and sometimes delimiting the ecu will make the relay and the computer auto-handshake or jas and the systems will correct. Correctness or apparent determination of correctness is practically impossible. So the electronics are given incorrect information at the start and left to their own devices and after a few cycles the desired result is guaranteed

Darth_V8r

iTrader: (4)

You are overthinking it.

Pressure at the injector orifice is identical to pressure in the fuel rail. Pressure differential is based on fuel rail absolute pressure vs intake absolute pressure. Injector flow rate increases as the differential increases. This is represented in the controller as a table that dictates injector flow vs manifold pressure in some form. That is all there is to it. This info is always provided with the fuel injectors.

In the controller, temperature is used for three major factors - commanded idle airflow, fuel air mixture (usually richer with lower temperature), and spark timing changes.

If a lower temperature thermostat caused idle surge you need to first look at your commanded stoich vs temperature, and your base idle air flows.

Also your exhaust could be causing your oxygen sensors to read false lean, causing the ECU to add fuel, and rich idle will surge - especially in a cammed car.

All the other stuff about temperature influencing injector flow is a distraction. There is. Or much more I can do to help without knowing basic details like say the year, make and model of the car, engine size, cam, intake, electric vs cable throttle, basic exhaust details. Now if you have some super secret ultra gonna break the internet Uber exhaust design, and want to keep secret, that is fine, but still Knowing basic info such as long tubes, x pipe, open headers with extensions is necessary to be of any help.

ChopperDoc

I did nothing but teach hydraulics and flight controls on multi-million dollar helicopters for 2 years and here we are talking about Pascals LAW.... Which if memory serves me correctly states:

Any force applied to a body of fluid is transmitted equally and undiminished in all directions; the force acts perpendicular to anything in contact with the fluid.

Or something along those lines, but that conveys the basic law of fluid pressure. It's literally how hydraulics work, and how we use it for hydraulic multiplication (again in hydraulics) so as Darth correctly pointed out, injector pressure is exactly the same as the rail, the fuel line, and anywhere else beyond the source of pressure. Where do you think we check the pressure anyway? The injector?

But that's off topic and wasn't the point of my first post. I was asking about mods, parts, etc, same as Darth, because we can't help at all with your issue with so little information.

ChopperDoc

And yes, I've seen a lot of problems when mods are done without a tune. Don't assume the computer is just going to relearn everything. It won't. Temperature can be accounted for, and is. It's in the Charge Temperature Bias table. Two factors influence calculations for dynamic air (based of VE table): Intake Air Temp (IAT) and Engine Coolant Temp (ECT). The reason for these two factor is simple: air cools down when it moves. So when you are sitting still, heat soak occurs faster than when you are going 50 MPH. So lower airflow is biased towards ECT for heatsoak, and higher airflow is biased towards IAT. Makes sense right?

When in closed loop, the MAF also plays into this calculation, but is also biased. Under 4000 RPM down to 0, VE is biased more and more for Airflow calculations. Above 4k, MAF is used (stock settings). So at idle VE is biased and used for the majority of airflow calculations, and has a huge affect on your idle.

Mods to the engine change ALL of these things to some degree, which is why we the tune for the mods made to account. We don't install relays and pray the computer just makes up for it.

Darth_V8r

iTrader: (4)

One of the things I do at work is design spray cooling systems. Imagine trying to convince people if pressure issues are on the pumping side or the nozzle size. Especially when you operate with VFD on the wrong side of the pump curve.

Spray cooling systems as I design them are remarkably similar to fuel injection in that regard.

BUT.... understanding of the engine controller is far more important than understanding of physics. I do not really care if temperature slightly changes fuel flow due to viscosity changes, thermal expansion of orifice, etc. I care about knowing how to tell the controller what to do to get the engine to do what I want. You and I are in the same boat.

This is why I think the OP is overthinking it. Trying to apply physics to the engine controller does not always help because you cannot tell the controller fuel viscosity and density vs temperature. What you can do is tell it how much extra fuel to spray while the engine is warming up and do iterative testing to get it right. Or pay someone who knows what they are doing.

ChopperDoc

Couldn't agree more. Knowing the physics is nice, but knowing what to do with that information is another story. I believe both of us are quite versed on how heat and pressure work. But we also know what to do with that information too.

I like the physics and curiosity to know more drives me to learn it, however I would still be okay if I didn't for most of the tune, because of simply knowing what to tell the controller. Knowing why something does what it does (theory) isn't necessarily going to be a deal breaker. Just knowing the right direction to take it and why (out of limit or running like ****) is though. If I'm lean I need fuel lol. Do I really need to know why? I do though, but I see your point perfectly.

Vijay Rajendran

The reason I am unhappy is because other members of the forum are per se calling me electrically conduit like. I thought operating without some constraints and letting the computer do the work was a tried and true paradigm. Examine the case of engine idle. In a GM car idle parameters are designed never to be changed unless sore need of a correction is present. Even if you change the idle dramatically the system and obd2 will adjust itself. I have seen this before. So why isn't this champion of an idea extended into rpm's while in gear. Not a far cry from the truth. Maybe Spark Advance fouls the whole idea. So changing plugs and relay together combined with ecu delimiting will work. Ha HS hahaha IM right sure of it but I have no intention of being dead right.

ChopperDoc

The computer won't adjust itself if you don't want it to. You can simply turn the trims and learning off. In fact that is recommended for large cams with lots of overlap. You can set the RPM to whatever you want, really. You'll hit the mechanical limit before you hit the computer limit. Spark advance produces efficiency, and is a careful balance of "timing" the ignition of a compressing mixture.

Too early and the mixture will over pressurize, which adds heat and other ignition points, aka, detonation. If you set it too late, then you miss the opportunity for maximum pressure in the cylinder (mind you under the knock threshold) and lose lots of power. Think of the cylinder pushing into a big spring and being shot back down (advanced) vs trying to push a falling object to make it fall faster (retard). The optimum full burn should be complete no later than 14* ATDC regardless of engine. After that it is wasting potential energy. It's actually rather complicated.

So basically you want to pull all the limits off the computer then? I'm not going to be a part of attempting to circumvent something that has absolutely no advantage whatsoever over simply running a good tune. What you are saying makes no sense at all.

Vijay Rajendran

Maybe enough info about the car was not given. The check engine lights are not present. What I am saying is a normal car will rev and move rpms through the gear cycle and acceleration. Is there something I'm missing where the rpm's move to idle immediately after applying throttle. Transmission gearing is designed to save fuel and provide a smooth experience. The ecu comes into play resetting parameters and with constraints. NO LIGHTS Present but problem is evident. Is there a mod present that is causing this behavior. Relay exchange usually negates ecu mods right. Something has to be redone. But what? The generational learning curve I suppose. How to put it in terms everyone can understand is difficult at best. Try Xoutalpha.

ChopperDoc

Is it a cable or wire driven throttle body? Does it STAY at low rpm or does it just hesitate? This sounds a lot more like a mechanical issue than a tuning one.

Vijay Rajendran

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Darth_V8r

iTrader: (4)

Correct not enough info. Lack of CEL is unimportant. Year make model and modifications please.
Nothing negates ECU changes. It is the ECU. The ECU tells the relays what to do. However It is not artificial intelligence. It does not learn. It uses feedback from oxygen sensors to refine fueling calculations. Called fuel trims. Beyond that it can store commanded air offsets for various conditions called idle trims. It does not self optimize timing and even what it can somewhat optimaize is a very narrow range. Move the oxygen sensors it throws the calibration off. Change almost anything related to hardware and you need to edit the ECU tables. Called tuning. Your problem is likely either a hardware failure or a hardware change that has not been tuned for in the ECU. And a common one at that.
That something is to take the car to a person who knows how to tune the ECU by properly editing the tables.

No clue what that last statement meant.

Darth_V8r

iTrader: (4)

The computer is not capable enough to do what you are suggesting. It needs the tables modified. And FYI, idle is often the most difficult thing to get right, and the ECU rarely does this without human intervention in a modified car.