Huge idle hunt under high electrical load.

[wrenchdad]

Oh, yeah, post up a new tune file too when you get some more logs done.

wd

[MaxxAction]

34 degrees of timing at 900 rpm !!!! That just doesn't sound correct to me, sorry. I don't have cams in my engine but with that much timing, I would feel that it would Knock like crazy as soon as the load comes up off idle. Do you have a knock sensor? If not I would suggest getting one before I tried that much timing at idle, in fact I would never try that much timing at idle, cams or not.

What is your static timing set to? You know, the base timing? 10 degrees? 8? If so then I still go with what I said before about trying 15 degrees. Think of it this way, if you add timing at idle, the idle WILL GO UP !!! BUT if you get it too far advanced then the spark is firing way too soon as the piston is coming up to TDC and trying to reverse the engine, that is a lot of unneeded stress on the rotating parts, IMHO BUT DON'T DO IT !! Yeah if you go far enough advanced it will lower the idle RPMs but at what cost?

IF at 15 degrees you still can't get your idle to come down, then start looking for air leaks, somewhere its getting air, a quick check, block off the idle control valve inlet hose and see if it will keep running, even if its at a reduced rpms. If is does then you have air coming in somewhere. IF not then maybe your ICV is not closing off? I had leaks around the base of my ICV, it kept me from lowering my idle below 900, and it gave me lots of trouble going into fuel cut.

later wd

EDIT, I just noticed that you are saying you want to adjust the timing to get the steps number to come down for a idle under 1000, correct? Then why don't you just change the step curve so that is has a lower number of steps, that's kind of what the curve is for, ok? The step curve controls the valve which controls the amount of air which sets the RPMs. later wd

Right now...

when I start pulling steps, the idle becomes unstable, and reintroduces oscillation. The further I drop the timing below twenty, the more it wants to oscillate.

All the gaskets on the motor are new, but I will do a leak test just to rule that out.

[MaxxAction]

Oh, yeah, post up a new tune file too when you get some more logs done.

wd

Will do.

[MaxxAction]

Just an FYI...

I spoke to the guy who built this engine about this issue. He builds motors for several SCCA race teams (which use a cam grind similar to mine, a little more aggressive), and various other motorsport applications. Most of what he does is carbuerated stuff, but, he said the majority of these guys run their motors "locked out" on the distributor which is giving them 32 degrees at idle.

[DaveEFI]

Must admit I can't see any reason to use a fixed ignition setting. Unless the engine is running at constant RPM.

[MaxxAction]

Must admit I can't see any reason to use a fixed ignition setting. Unless the engine is running at constant RPM.

If i understand it correctly, "locked out" means full advance at idle, and the timing varies through the RPM range based on vacuum advance.

[wrenchdad]

Are you saying that you still have vacuum advance? Then I have another question, have you put a timing light on this engine and verified the timing matches what the MS unit is commanding it to be?

wd

[DaveEFI]

Must admit I can't see any reason to use a fixed ignition setting. Unless the engine is running at constant RPM.

If i understand it correctly, "locked out" means full advance at idle, and the timing varies through the RPM range based on vacuum advance.

Given that's more simple than combined centrifugal and vacuum, why wasn't that used by car makers if it is effective? Would have saved a buck or two in production.

I've not come across an engine which would start well on full advance (or idle properly) - it would tend to kick back. Maybe not a problem if it's just used for racing.

[MaxxAction]

Must admit I can't see any reason to use a fixed ignition setting. Unless the engine is running at constant RPM.

If i understand it correctly, "locked out" means full advance at idle, and the timing varies through the RPM range based on vacuum advance.

Given that's more simple than combined centrifugal and vacuum, why wasn't that used by car makers if it is effective? Would have saved a buck or two in production.

I've not come across an engine which would start well on full advance (or idle properly) - it would tend to kick back. Maybe not a problem if it's just used for racing.

Carbuereted racing motors. In the SCCA Trans Am Series, which this guy builds motors for, they have to be carbuereted, have to have identical bore, stroke, valve size, cam, etc. It may not be as effective, but by doing it the way they do, no one can cheat.

[MaxxAction]

This is driving me insane!!

Sorry, no new log to post, you can see this phenomenon in the log I posted previously, but I f'd around with this thing for two hours last night trying to get the idle dialed in to no avail. More timing, less timing, more fuel, less fuel, longer pulse width, shorter, nothing makes much difference. I also did a leak test, and found one small one in the PCV system, fixed it, no difference. It is most steady at about 24 degrees timing, but as soon as the fan kicks in it starts oscillating all over the place. If I watch the AFR, it goes lean, the ECU tries to compensate, and the oscillation between lean/rich begins and the ECU is chasing it's tail.

I am fairly convinced by now that there is something else going on, and I think it has to do with voltage variation. I say that because if I have been out driving the car, and the battery is fully charged, the oscillation is almost non existent. If it is oscillating bad, and I rev the motor up to 6 k 5 or 6 times, the oscillation gets better, but the longer it idles under electrical load, the worse it gets.

I am using a bosch style injector that I bought from TRE Performance. The injectors are all ohming out at 12.2 to 12.4, the alternator is a 90 amp stock alternator, and tested good right before I put the motor in the car.

Anyone ever seen this issue before?

[Matt Cramer]

You may want to adjust the injector battery voltage correction curves.

[wrenchdad]

Looking at your log again , I don't see your battery voltage changing very much, pretty steady, between 13.4-13.8. So you may want to put a meter on your injector 12vdc supply AT the injectors and see just what they are getting and if its as steady as your logs show. Could be a bad connection feeding your injectors.

Just my 2 cents worth.
later wd

[MaxxAction]

Had a bit of eureka moment tonight...

and realized I was being an idiot. I had been running the FPR on vacuum reference. Derp.

Anyway, when I realized what that was doing, I pulled the vac from the regulator, set it at 40 psi, the flow rated pressure of the injectors, and it smoothed out greatly. It will stay steady now with a partial load, fan and headlights. But if I turn on anything else, heater, crank the stereo, it will hunt again after idling awhile.

Where do I find the voltage correction curves?

[wrenchdad]

Hey, where's the new log and tune file, it's really hard to see what you are seeing without something to actually look at, OK?

Later wd

[DaveEFI]

Had a bit of eureka moment tonight...

and realized I was being an idiot. I had been running the FPR on vacuum reference. Derp.

Anyway, when I realized what that was doing, I pulled the vac from the regulator, set it at 40 psi, the flow rated pressure of the injectors, and it smoothed out greatly. It will stay steady now with a partial load, fan and headlights. But if I turn on anything else, heater, crank the stereo, it will hunt again after idling awhile.

Where do I find the voltage correction curves?

Can I ask a basic question? Is this a race engine with a cam etc designed to give maximum power at high revs, and not for road use?

Did you re-fit the vacuum fed to the FPR (from true manifold vacuum) after setting the pressure?

[MaxxAction]

Had a bit of eureka moment tonight...

and realized I was being an idiot. I had been running the FPR on vacuum reference. Derp.

Anyway, when I realized what that was doing, I pulled the vac from the regulator, set it at 40 psi, the flow rated pressure of the injectors, and it smoothed out greatly. It will stay steady now with a partial load, fan and headlights. But if I turn on anything else, heater, crank the stereo, it will hunt again after idling awhile.

Where do I find the voltage correction curves?

Can I ask a basic question? Is this a race engine with a cam etc designed to give maximum power at high revs, and not for road use?

Did you re-fit the vacuum fed to the FPR (from true manifold vacuum) after setting the pressure?

It's a daily driver...

the cam isn't huge. 228 duration, 575 int/574 exh total lift.

No, I left the vacuum off. I think this is the proper way to run this system. The injectors are rated to flow 410cc per minute, or 39 pounds per hour, at 40 psi.

When it is vacuum referenced, the load slows the motor down, which decreases vacuum, and therefore forces more fuel pressure, throwing off the AFR. As the fuel pressure would increase, the ECU is trying to compensate for the additional fuel, raising the speed of the motor, increasing the vacuum, and lowering the fuel pressure, and I believe that is why it would oscillate so badly. The variable vacuum was adding to the "chasing it's tail" effect.

I did a little reading last night, and ran across this article.

Often times the term fuel pressure is used with little understanding of what it really means. This leads to confusion with respect to injector flow rate, and people lose sight of how their injectors really work. Understanding how fuel pressure works and is applied in both returnless and return style fuel systems is important if a user wants to properly set up their injector characterization and get predictable fueling. Knowing what to expect also allows a user to diagnose problems with their fuel system and ultimately make the vehicle function as intended.

There are two pressures that people need to consider: rail pressure and effective (or differential) pressure. For the purposes of the rest of this article, it will just be called effective pressure. Rail pressure is self-explanatory; it is the pressure inside the rail. When you stick a fuel pressure sensor on the end of a rail, it is reading the pressure inside of the rail. While this number is important, it is only half of the story.

Effective pressure is the actual applied pressure for the injector, and is the pressure differential ACROSS the injector. Effective pressure is what injector flow rate is ultimately based off of. When an engine is idling, there is a vacuum in the intake manifold. This vacuum pulls fuel out of the injectors, and increases the effective pressure across the injector to a pressure higher than the rail pressure itself. When a supercharged or turbocharged vehicle is in boost, the pressure inside the manifold is trying to push fuel back into injector, resisting the flow and decreases the effective fuel pressure below that of the rail.

This concept is important because it changes how the fuel system needs to be set up in the PCM. There are two generic types of fuel system setups: returnless and return style. A returnless system does just as the name implies and doesn’t return fuel to the tank. Return style systems will bleed excess fuel back to the tank through the regulator. Return style systems hold a big advantage in that with a vacuum/boost referenced fuel pressure regulator, the system can maintain a CONSTANT effective fuel pressure, which can extend the range of fuel injectors and help them function at lower fuel demands as well.

With a return system, the base pressure is set with the engine off, but the pump running. For a GM, this pressure is usually set to 58psi (factory fuel pressure in the rail). The vacuum/boost referenced regulator will help to change the pressure in the rail based on the pressure in the manifold. When an engine is idling, it may be pulling 20 inHg of vacuum, which translates to roughly 10psi. The reference to the regulator will allow it to adjust and lower the pressure in the rail to 48psi, resulting in 58psi effective pressure, which is the same as the base pressure. When the engine is making 10psi boost, the regulator will adjust and increase rail pressure to 68psi, again resulting in 58psi of effective pressure. The regulator will constantly bleed off pressure inside of the rail to maintain the same effective pressure at all operating conditions. This helps to prevent a loss of effective pressure during wide open throttle, and also helps to prevent injectors from having to run extremely low pulse widths to fuel at idle. A downfall of return systems is the fact that they circulate fuel through a very hot engine bay, ultimately carrying that heat back into your fuel tank.

A return style system that isn’t variable will maintain a certain pressure inside the rail, regardless of what is happening in the manifold. For instance, take a GM system with the standard 58psi in the rail (usually there is a mechanical regulator near the pump to bleed pressure back into the tank and keep the rail itself at 58psi). No matter what operating condition (short of demanding more fuel than the pump can supply), pressure in the rail will always be 58psi (or pretty close). When idling at 20 inHg, this means effective pressure will rise to 68psi because the vacuum in the manifold is adding 10psi to the rails 58psi. This requires injectors to pulse shorter so as to not overfuel the engine and cause a rich condition. By contrast, when a naturally aspirated engine is wide open throttle, the manifold pressure is not in vacuum or in boost, so the effective pressure is the 58psi of rail pressure and nothing more. However, a boosted engine at 10psi will be resisting the fuel, causing effective pressure to drop to 48psi from the 58psi in the rail. This lowers the ultimate output of the injectors.

Some returnless systems will actually vary the pump output to emulate a referenced system, or to offer more fuel pressure at higher demands and less fuel pressure at lower demands. Ford fuel systems modulate the pump in an effort to maintain effective fuel pressure at 3 bar. The Corvette ZR1 runs fuel pressure in the 30s until an increased demand is on the system, at which point it will ramp the fuel pressure up to 88psi in the rail. Systems like these use sensors that record the fuel pressure, and when combining that pressure with the manifold pressure, the PCM knows what the effective pressure is and will determine a pulse width for the injector accordingly. Systems like these offer the best of both worlds.

Ultimately, what we need to know is the effective fuel pressure in any given situation though. GM uses manifold pressure to subtract away from the rail pressure (which it always assumes is 58psi) to calculate pulsewidth. By referencing the flow rate table, in which the flow rate at various effective pressures is programmed in, the PCM knows what flow the injector is capable of at any given operating system. To convert a GM vehicle to work with a boost referenced return system, one must simply populate all of the various pressures with the same flow value, since the effective pressure (and consequently injector flow rate) will remain constant, regardless of manifold pressure. Word to the wise, when you see injectors advertised to flow X amount of fuel at a certain pressure, if you have a boosted vehicle, they will actually flow less while in boost unless you have a boost referenced system!

Dave Steck
DSX Tuning

[MaxxAction]

I wanted to add:

I am using the MS3 "Gold Box" which has a built in fuel pump control module that runs the pump as needed for the demands the ECU is seeing.

[wrenchdad]

So are you saying that the ECU varies the speed of the fuel pump based on load? If so is that loggable?

And if the above is true, then why do you need that when the manifold references regulator would and can do the same thing?

Later wd

[DaveEFI]

Had a bit of eureka moment tonight...

and realized I was being an idiot. I had been running the FPR on vacuum reference. Derp.

Anyway, when I realized what that was doing, I pulled the vac from the regulator, set it at 40 psi, the flow rated pressure of the injectors, and it smoothed out greatly. It will stay steady now with a partial load, fan and headlights. But if I turn on anything else, heater, crank the stereo, it will hunt again after idling awhile.

Where do I find the voltage correction curves?

Can I ask a basic question? Is this a race engine with a cam etc designed to give maximum power at high revs, and not for road use?

Did you re-fit the vacuum fed to the FPR (from true manifold vacuum) after setting the pressure?

It's a daily driver...

the cam isn't huge. 228 duration, 575 int/574 exh total lift.

No, I left the vacuum off. I think this is the proper way to run this system. The injectors are rated to flow 410cc per minute, or 39 pounds per hour, at 40 psi.

When it is vacuum referenced, the load slows the motor down, which decreases vacuum, and therefore forces more fuel pressure, throwing off the AFR. As the fuel pressure would increase, the ECU is trying to compensate for the additional fuel, raising the speed of the motor, increasing the vacuum, and lowering the fuel pressure, and I believe that is why it would oscillate so badly. The variable vacuum was adding to the "chasing it's tail" effect.




Dave Steck
DSX Tuning
[/b]

The idea of the vacuum controlled reg is to compensate for the 'suck' applied to the injectors by varying manifold vacuum. On my 3.5 litre V8, if you disconnect the vacuum feed to the reg at idle it will over fuel and stop. Mine is designed to run at approx 36 psi with no vacuum connected, and at idle this reduces to approx 28 psi. IIRC, MS assumes the fuel pressure will be controlled in this way - and although it might be possible to tune round it, why bother?
I have no idle control at all - only a non ECU controlled fast idle for starting and warming up. Once warm, it idles at a steady 700 rpm regardless of electrical load on the 100 amp alternator.

[MaxxAction]

So are you saying that the ECU varies the speed of the fuel pump based on load? If so is that loggable?

And if the above is true, then why do you need that when the manifold references regulator would and can do the same thing?

Later wd

Yes...

that is how it works.

As to being loggable, I am unsure. The stock fuel system on my car operated similarly. It had three speeds in the controller based on throttle position voltage, but also had a vacuum referenced regulator.

The guy who sold me the box told me that non boost/vac reference is the way to run this setup. The newer GM LS fuel systems are run the same way. The LS2 for example is fed a constant fuel pressure of 52 PSI with a return-less system. I didn't really mess with the car this weekend as I had a lot of other stuff going on, but it does ilde much better without referencing vacuum on the FPR, and AFR's are still exactly where they are supposed to be at higher RPM and WOT loads.