Chrysler "fuel sync"
Chrysler "fuel sync"
(OP)
I am looking for someone who "UNDERSTANDS" the fuel sync concept in Chrysler efi. Why? I am calling BS on virtually everything I read on the net about how the fuel sync "precisely" establishes when the injectors fire in relationship to intake valve opening. If that was so, the factory spec of +/- 8degrees would be in relationship to the stock camshaft opening point. Since there are three different v8 cams used from 93-98, it seems the sync would be at a specific number of degrees based on which specific cam was installed. All Chrysler says is "...These distributors are equipped with an internal camshaft position (fuel sync) sensor. This sensor provides fuel injection synchronization and cylinder identification ..." Nowhere can I find that the amount of sync degrees correlates with the amount of degrees related to intake valve opening. Additionally, any aftermarket cam or a different rocker ratio would alter the intake opening point. Add 20-30 degrees of duration to the cam and the intake opening is significantly earlier. I don't see any discussion of increasing fuel sync an amount equally proportional with the additional intake opening. In actual practice, +4 to +6 degrees seems to be the normal setting, regardless of camshaft. Consequently, I am not buying sync is based on valve opening but rather, something else. Could someone explain to me what fuel sync establishes? I have found posted by bigpaul "...Fuel sync is the overall injection start point delay measured in internal units." I don't really understand "start point," in relationship to what? I could accept the notion that the sync is tied to piston TDC but not valve opening. I would really like to understand this. Regards, dan...





RE: Chrysler "fuel sync"
The ignition timing and fuel injection timing in most new cars is controlled by a computer.
The computer looks at a number of values that may include;
Engine temperature,
Oxygen in the exhaust,
Pre-ignition, (knock sensors)
Mass air flow,
Cam or crank position,
Ambient air temperature,
Throttle position.
The computer determines the optimum timing and then controls the ignition and injection timing.
Note that the computer may not provide ignition nor fuel injection on the until after the first cam timing signal is received.
Some of the first computer controlled diesel engines would make up to two complete rotations before the computer knew for sure where everything was and started fuel injection.
The signal from the cam shaft provides a reference for following ignition/injection cycles.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Chrysler "fuel sync"
If someone later modifies the engine with a different cam and/or rocker arms, then that may call for an ECU software modification to re-sync things, if required.
I don't know for sure, but it's not something that's obviously "BS".
RE: Chrysler "fuel sync"
RE: Chrysler "fuel sync"
It may be tied to the leading or trailing edges produced by the flag on the cam position sensor. How that's related to the "valve opening" ... is built into the design of the camshaft.
A common setup, which is likely how this system really works, is that the CRANK position sensor has a ring with many teeth on it which actuate the CRANK position sensor so that the CRANK position is accurately known ... but the CAM position sensor is just one flag, the "accurate" timing of which is not important, as long as the cam position sensor is "on" during (for example) cylinder #1 passing through the version of TDC that is in between the end of the exhaust stroke and the beginning of the intake stroke, and "off" during the version of TDC that is passing through the end of the compression stroke and the beginning of the exhaust stroke. This is because the crank position sensor alone cannot know which "version" of TDC is approaching, being that there are two of them through the four-stroke cycle that both look identical to the crank position sensor.
When the engine first starts turning, the electronics won't immediately know whether a particular cylinder is on the intake or power strokes, until it gets proper signals from both the crank and cam sensors, and only then can it be "in sync".
Dunno how Chrysler in particular does it but I do know that Suzuki EFI motorcycle engines give an initial untimed fuel injection squirt when the system gets a non-zero crank position signal of any sort, then once they establish a TDC they operate in wasted-spark (a spark on every revolution, only half of which actually ignite something at the end of a compression stroke) and a fuel shot on every revolution until they figure out which version of TDC is the right one, then they operate with proper sequential fuel injection and ignition once it is in sync. It also allows the engine to continue to run in wasted-spark mode with a half-shot of fuel on every revolution if the cam position sensor fails.
If the engine has variable valve timing, THEN the cam position signal needs to be accurate with respect to the valve opening time, because then the cam position sensor is not only used for establishing which version of TDC is "intake" or "power", but also for feedback of actual cam timing.
But again, the phase relationship of the cam position sensor to intake valve opening is something built into the camshaft; the electronics have no way of knowing the actual motion of any of the valves.
It may perhaps be of interest that Honda single-cylinder EFI motorcycle engines don't have a cam position sensor. They figure out which version of TDC is the correct one by monitoring the crank sensor and figuring out when the crankshaft is slowing down due to the compression stroke. It again operates in wasted-spark with half-shot of fuel each revolution on initial start-up until the computer figures out what's going on. This doesn't work on multi-cylinder engines.
RE: Chrysler "fuel sync"
I learned from this experience that the ECU is keeping track of such tiny details, which is very nice. It even had something to say about a thermostat being out of tolerance, which was also replaced.
RE: Chrysler "fuel sync"
You listed as a possible measured parameter "Pre-ignition, (knock sensors)"
I don't think pre-ignition is the same as "knock" (detonation) although both are aberrant combustion, and when severe can coexist or trigger the other.
regards,
Dan T
RE: Chrysler "fuel sync"
----------------------------------------
The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.
RE: Chrysler "fuel sync"
In many cases the duty cycle of the injectors at full engine load is considerably longer than the entire intake stroke, and there will be fuel injected against a closed intake valve.
There is always fuel wetting the intake port walls which hangs around from one cycle into the next.
In many cases the injection timing is deliberately against a closed intake valve, because it's better for the (rather hot) intake valve to vaporize at least some portion of the fuel prior to the actual intake stroke than it is to inject fuel as a liquid during the intake stroke.
Bottom line, unless you are concerned with meeting Tier 2 bin 5 EPA emissions, on a port-fuel-injected stoichiometric-operation engine, the injection timing is not important.
RE: Chrysler "fuel sync"
On new EFI systems, the crank and cam sensors tell the PCM where the engine is quite accurately. The PCM's are quite powerful and can do a lot of computing. So, it's not a small stretch for the programming to tell the PCM how far before TDC the intake valve opens. Given the right programming, the PCM can calculate when to fire the injectors very accurately.
If you have more adjustment then why don't you try adjusting it? I've read about the injector timing making enough of a difference on LS engines that some tuners will adjust it. It's been a while since I've read anything about it, but I recall the LS engines matching the closing of the injectors to the engine rotation meaning the opening moves forward in time depending on the injector duty cycle.
RE: Chrysler "fuel sync"
RE: Chrysler "fuel sync"
There were a couple of detailed SAE papers on the subject, and I think maybe some patents, and some actual products, all associated with Harmon Electronics of Grain Valley, MO, USA.
The resulting systems did work, but suffered from durability problems associated with the mechanical components, as for instance a classical distributor's vacuum advance mechanism would not last long cycling at many tens of Hertz.
Where I'm going is that it's not quite trivial for microprocessors to dynamically adjust and optimize the things they can control electronically, without wearing out, and to infer quite a lot of information from the limited view provided by their sensors, so assertions of modern ECUs being able to adjust themselves to deal with a fairly wide range of engines without reprogramming or any sort of intervention (other than not being confused by driver input shortly after first start) are quite credible.
Mike Halloran
Pembroke Pines, FL, USA
RE: Chrysler "fuel sync"
je suis charlie
RE: Chrysler "fuel sync"
Does your engine have valve position sensors?
This should be clearly obvious. The PCM can't know about any change in valve timing unless the PCM has sensors for valve motion or the PCM is in control of the valve motion.
The PCM actuated valve designs by the Koenigsegg spin-off company Freevalve would be a case where the PCM knows when the valve is open and closed.
There is nothing wrong with the statement " fuel sync "precisely" establishes when the injectors fire in relationship to intake valve opening". IF you have both rotational angle and valve timing then you can precisely match injector firing to intake valve opening.
RE: Chrysler "fuel sync"
But it turns out that you don't need sensors for everything.
Simple example; modern ECUs can infer that the fuel tank cap is off or leaky, by watching the behavior of the evaporative emissions system. No 'fuel cap loose sensor' is required.
Beyond that, a modestly fast microprocessor can easily measure the time interval between ring gear teeth using a simple magnetic sensor, and from that can infer the instantaneous crank speed. Using that and the crank and/or cam reference signals, it could compute the position of any given piston with reasonable certainty. Just from the time trend of the ring gear teeth, it can detect a misfire event. ... and it can make adjustments. ... and then it can watch and see how much the adjustments change the ring gear time pattern and in which direction, and make further adjustments.
In other words, a modern ECu can learn, and remember what makes a particular engine run best.
It can also apply an offset of sorts and run closed loop at a condition other than 'best', e.g. for emissions reasons.
Mike Halloran
Pembroke Pines, FL, USA
RE: Chrysler "fuel sync"
From what has been explained here, I have to conclude that sync is tied to piston position rather than specific valve opening. I think BrianPetersen and LionelHutz have nailed it, inferring to the lack of sophistication at that time. As has been stated earlier, "It's not tied to actual "valve opening" ... for the simple reason that the computer has no way of knowing it." I have to agree. The issue I have is I am looking for an absolute answer as opposed to believing it's piston position based on common sense. Sync could be something else entirely. One Mopar enthusiast insinuated it was tied to fuel quality, meaning burn rate. I don't accept that but it does have a small bit of merit, (I suppose it could change timing by a given amount for the quality of fuel, sort of like an software knock sensor, but that's a far reach.) Unfortunately, I do not KNOW what fuel sync adjusts and I'm hoping to find a Chrysler engineer or someone similar who really knows. If not that, I'm open to additional theory or opinion.
RE: Chrysler "fuel sync"
The 4.7 (which is OHC) and Hemi (pushrod, but a modern engine design) use distributorless ignition. The 5.2 and 5.9 are holdovers from the old days and used a distributor well into the EFI era although I'm not sure if it remained right to the end of production of that style of engine.
Ignition timing on these engines is based on the crank position. Because the cylinder ignition sequencing is handled by the distributor, the electronics know to fire the coil four times per crank revolution and the distributor takes care of which cylinder the spark goes to. But the ignition getting to the correct spark plug is contingent on the arm inside the distributor actually lining up with that cylinder's terminal inside the distributor. If the distributor is too far out of position, it may simply be that the arm inside the distributor is getting too far away from that terminal, giving weak ignition at best, and potentially it may even be firing the previous or next cylinder in the firing order instead of the one that it's supposed to fire.
The fuel doesn't have anything to do with it; the engine won't much care. The spark getting to the correct cylinder, it sure will care ...
This doesn't affect the engines with distributorless ignition, correct??
RE: Chrysler "fuel sync"
RE: Chrysler "fuel sync"
----------------------------------------
The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.