Timing advance processor

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Budgetbond
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Re: Timing advance processor

#21 Post by Budgetbond » Sun Apr 04, 2021 9:34 pm

Looks interesting anyway they seem to cover a wide range in vehicles, have you got a simple strategy of how you mite initially trial and test it, looking at a petrol/Lpg advance graph I don't know whether it's universal, approx 3-3500 rpm the plots merge whereby advance is the same for both fuels, above that it looks like retarding would be optimal.
So I suppose up to around 2500 rpm + high degrees of over advance could be effective.
I suppose knowing the rpm s you usually operate at and tweaking those especially if that falls into the low/mid range could be effective, and yeah they look easy to fit.

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Re: Timing advance processor

#22 Post by CNG » Thu Apr 08, 2021 1:28 am

I always make a point to read LPGC's posts. It's not often on forums that I get to learn too much. And that's not because I know all that much. More because, sadly... most times, I'm found reading mindless mis-information?

LPGC... thank you.

Back in the day, or in my case the present... I've gone thru' AEB Joker and AEB Wolf TAPs. But running a 1960s Land-rover on CNG, we're talking old skool stuff here. A TAP is essential!

disco stu
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Re: Timing advance processor

#23 Post by disco stu » Thu Apr 08, 2021 4:30 am

He's certainly proved himself time and again. Lots of good info, so I find I'm having to reading it later on again.

I've heard the TAP makes much more difference on CNG, but I figured it was still worth trying on LPG.

Just managed to fill with lpg again to check consumption. It's down to 14.3l/100km now, which I'm much happier with (12.5 on petrol, so under 15% difference). Will probably get the TAP running next week and see how it goes for me. Will post results
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LPGC
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Re: Timing advance processor

#24 Post by LPGC » Thu Apr 08, 2021 9:54 pm

Cheers @CNG and @disco stu :-)

Yes a TAP will make a lot more difference on CNG, necessary for CNG.

Look forwards to your results Stu.
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Pinger
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Re: Timing advance processor

#25 Post by Pinger » Thu Apr 15, 2021 3:24 pm

disco stu wrote:
Thu Mar 25, 2021 6:48 am
I recall reading in the manual for my car that ignition timing is based on the crank sensor angle and injection based on the cam sensor, or something to that effect. I still can't understand why, as they both do the same thing so why not just base it all off the one sensor (cam would be logical).
LPGC's comments re VVT are valid but it's more basic than that I think.
The cam sensor is the only sensor that knows 'where' the engine is in the cycle. The crank sensor can't tell a compression from an exhaust stroke so the cam sensor has to be there for start up (unless like my smart (the only engine I've ever heard of that is so configured) it employs another method). Once running, cam sensors aren't really needed as the crank sensor can provide enough info for the ECU - once it's been primed by the cam sensor. Some engines however may continue to use cam sensor data for sequential fuel injection. Cam sensors also pinpoint misfires to relevant cylinder(s).
The crank sensor though will be more accurate for ignition timing which will eventually stray with wear in the cam drive - which is why I think, it is the primary source of data for ignition timing.

What might be useful for those messing around with timing is data logging software. I'm looking into TunerPro software (free downloads available from their website) that runs on a laptop via an appropriate interface to the OBD port.
One of the parameters it can measure is 'knock counts''. The guys on my Chevrolet truck forum adjust (via TunerPro) their timing in particular speed/load bands then subsequently monitor the knock counts. If overly high, they then retard a touch.

I agree with LPGC that advance isn't everything. The aim is to burn as much of the fuel at the most favourable piston position relative to TDC. 50% of mass fuel fraction burned by 10 degrees ATDC seems to be the norm. Over advancing will promote detonation and the contained (un-expanded) heat will exacerbate the tendency in the extreme but negative work can accrue long before that. A good indication would be exhaust gas temperatures if they were easily monitored. When they cease to cool with advanced timing - that's probably optimum timing.

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Re: Timing advance processor

#26 Post by LPGC » Thu Apr 15, 2021 6:33 pm

We broadly agree mate but I would repeat that some engines with hydraulically controlled VVT do compare cam position sensor pulses to crank position sensor pulses to know how far cam timing is advanced/retarded. Might have an electrically controlled hydraulic master solenoid that feeds oil to a remote slave hydraulic cam timing adjuster, cam timing adjustable by controlling the duty cycle of electric pulses to the master... But with this type of setup the ECU cannot assume that (say) a 50% duty cycle pulse on the master will give X degrees cam advance, it has to measure the cam advance and control duty cycle to achieve the cam advance that is aimed for (or otherwise cam timing might change when viscosity of oil changes). Like you say the crank sensor cannot tell the difference between a compression and exhaust stroke but plenty crank sensors have gaps in teeth so do have reference points for crank position which can be compared to cam position data. Plenty engines will give 'cam timing too advanced' type errors if a cambelt/chain is fitted a tooth out.
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Re: Timing advance processor

#27 Post by Pinger » Thu Apr 15, 2021 7:00 pm

LPGC wrote:
Thu Apr 15, 2021 6:33 pm
We broadly agree mate but I would repeat that some engines with hydraulically controlled VVT do compare cam position sensor pulses to crank position sensor pulses to know how far cam timing is advanced/retarded. Might have an electrically controlled hydraulic master solenoid that feeds oil to a remote slave hydraulic cam timing adjuster, cam timing adjustable by controlling the duty cycle of electric pulses to the master... But with this type of setup the ECU cannot assume that (say) a 50% duty cycle pulse on the master will give X degrees cam advance, it has to measure the cam advance and control duty cycle to achieve the cam advance that is aimed for (or otherwise cam timing might change when viscosity of oil changes). Like you say the crank sensor cannot tell the difference between a compression and exhaust stroke but plenty crank sensors have gaps in teeth so do have reference points for crank position which can be compared to cam position data. Plenty engines will give 'cam timing too advanced' type errors if a cambelt/chain is fitted a tooth out.
My comment was based on simpler engines such as my Vortec that has no VVT but still times the ignition from the crank and not its cam sensor.
I'd say driving the ignition from the crank began there when the cam sensor being used was theoretically possible - but impossible on the engines you describe for the reasons you give.

The discussion has got me thinking about tackling timing from the other end - EGT. If setting up from scratch, measuring EGT with known to be retarded timing and then advancing the timing until the EGT ceased to drop that would represent an ideal as combustion was early enough not to miss the expansion event and wastefully through heat down the exhaust pipe. And without having to push the timing into negative work territory.

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Re: Timing advance processor

#28 Post by disco stu » Thu Apr 15, 2021 11:08 pm

That's a good point regarding timing belt stretch etc and ignition timing, and now you say that it does seem much more logical. I was thinking too simplistic about that sort of thing (for probably the first time ever-chronic over thinker!)

EGT is another really good point also, and not sure if I have come across anyone discussing monitoring that for optimising timing. That also lines up with things that I mentioned in another thread, where the Russians kept mentioning advancing the timing to save exhaust valves, as apparently the lpg mixture is often still combusting on the exhaust stroke leading the valve/seat issues. I'm not certain of the correctness of that info, but it seems to line up with info from Mitsubishi Australia.

Problem with my car is its pre obd2 for Australia (2005), and also lacks knock sensors. Fairly poor I thought for a 99 model

I did try some different timing yesterday and testing acceleration times with the software. I saw no real difference with up to 9deg extra advance. The car did feel a bit better with some advance, not as jumpy, but feel is very subjective. I emailed the seller and he gave me some things to try which I'll look at today
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Re: Timing advance processor

#29 Post by Gilbertd » Fri Apr 16, 2021 9:06 am

On some engines, those that use a wasted spark ignition system, cam sensor won't be needed as the sparks fire on both the compression and exhaust strokes. So as long as the crank sensor is working the timing can be calculated from that alone.
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Re: Timing advance processor

#30 Post by LPGC » Fri Apr 16, 2021 10:13 am

On my last post I meant to include a bit at the end to say there are other ways some ECUs can detect incorrect cam timing besides direct comparison between cam and crank sensors but direct comparison is one way.

I think it's the norm for ignition and even point at which each injection pulse begins to be crank sensor referenced (as opposed to cam sensor referenced), the cam sensor only purpose on a less advanced engine (without VVT) is so the ECU knows which part of the 4 stroke cycle each cylinder is on, but we approached this subject with TAPs in mind so I raised the point about some VVT engines using cam sensor info to read cam timing and how on some engines fitting a TAP to just the crank sensor could make the ECU incorrectly read cam advance. For sure there are simpler engines where fitting a TAP to just the crank sensor will affect ignition timing without messing any other aspect up.

I like the theory of measuring EGT to set ignition timing, not sure if it will work but would be interesting to see how such tests go. Slightly different subject but I know some piston engine'd aircraft pilots set mixture using EGT. They may all watch EGT to make sure the temp isn't too high but some take things a bit further - to save fuel instead of backing off the throttle in a relatively low speed cruise they keep the throttle relatively wide open but lean the mixture, which at first sees EGT soar, but then leaning the mixture further sees EGT fall again. They reckon this method helps save fuel partly because the engine isn't losing as much to intake throttling losses (inlet manifold pressure still relatively high) and partly because the leaner mixture burns slower in the cylinder giving a more average pressure push on the piston on it's power stroke (more like a diesel) rather than have a big push closer to TDC, which at lower RPMs helps give more torque for less fuel use. There is argument between the minority who use the mixture method to control engine power / airspeed / EGT and those who more conventionally use the throttle, those that use the throttle reckon it's risky to use the mixture method for the very small gains and that a lean exhaust mixture is more likely to cause valve damage at any given EGT because there will be a lot more unburned oxygen in lean mixture exhaust gas.

We often think in terms of changing one aspect but there are some very complicated interactions between aspects - If we have a fuel injected car and advance timing by fitting a TAP we may also have advanced the point at which the fuel injection pulse starts.. which on the face of it should make less difference on LPG (which has no chance of wetting the manifold) but can make a difference to engine response particularly in transient (changing throttle / rpm) conditions if for example pipes between injectors and manifold are a bit long (and definitely on an engine which has VVT and runs a pseudo Atkinson cycle). Another difference between LPG and petrol is LPG is injected as vapour, petrol as liquid, they have slightly different stochiometric ratios anyway, petrol will take up less volume in the intake and have a cooling effect as it evaporates.. For any given MAF reading MAP reading will be very slightly higher on LPG than on petrol (because the vapour LPG takes up a bit more volume in the manifold raising it's pressure slightly) and this can affect throttling losses. I've recently converted a lot of the same type of engine and have noticed that at warm idle the MAF voltage reading seems to drop by 0.01Volts on LPG compared to running on petrol, which (if a true reading) means the engine idles using less air than it uses to idle on petrol. On the basis of the engine using less air to idle on LPG than on petrol it could be that the engine idles more efficiently on LPG than on petrol, which could be due to a tiny bit less throttling loss, could be something more complicated such as speed of the burn, or could just be a rogue reading (e.g. the petrol ECU has slightly different reference voltage for MAF due to not having the load of petrol injectors). Often discussion about making adjustments to timing and fuelling is about flat out power.. which is an easily repeatable condition for testing purposes (driver just puts his foot to the floor) making it easy to compare results between different tests, making it easy to find the ideal advance and fuelling... If we were to look at the idle situation I just mentioned should (or how would) we factor the difference in MAF reading into results we should aim for? Then it gets more difficult to find the ideals to dial in for all the various combinations of part throttle and mid RPMs?
Last edited by LPGC on Fri Apr 16, 2021 10:54 am, edited 6 times in total.
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Re: Timing advance processor

#31 Post by Pinger » Fri Apr 16, 2021 10:27 am

disco stu wrote:
Thu Apr 15, 2021 11:08 pm

EGT is another really good point also, and not sure if I have come across anyone discussing monitoring that for optimising timing. That also lines up with things that I mentioned in another thread, where the Russians kept mentioning advancing the timing to save exhaust valves, as apparently the lpg mixture is often still combusting on the exhaust stroke leading the valve/seat issues. I'm not certain of the correctness of that info, but it seems to line up with info from Mitsubishi Australia.
Thinking about it more, by the method I outlined the most retarded acceptable timing could be found. Then, by pursuing knock, the earliest acceptable timing could be found. Somewhere between those two points must lie optimum timing. To do that over the entire load/speed range is a massive undertaking though.

Late timing hammers exhaust valves - I have the burned ones from my smart to prove that!
EGT is ignored by 4T (4 stroke) guys (with the exception of aviation perhaps) but 2T guys employ to monitor in-cylinder temps not least because of the piston's susceptibility to heat. When looking for knock they observe cooler EGT - after an initial increase. What this tells them is the heat they expect to see in the exhaust is being transferred to the piston crown because detonation has scoured it's protective boundary layer. They then either drop the throttle or lose an engine.
disco stu wrote:
Thu Apr 15, 2021 11:08 pm
Problem with my car is its pre obd2 for Australia (2005), and also lacks knock sensors. Fairly poor I thought for a 99 model

Are you absolutely certain of that?
The generation of truck I run began in 1988 and even those with early OBD systems had knock sensors. They aren't always located in the head. On my engine there is one and it doubles up as a coolant drain plug on one side of the block.

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Re: Timing advance processor

#32 Post by Pinger » Fri Apr 16, 2021 10:41 am

LPGC wrote:
Fri Apr 16, 2021 10:13 am


I like the theory of measuring EGT to set ignition timing, not sure if it will work but would be interesting to see how such tests go. Slightly different subject but I know some piston engine'd aircraft pilots set mixture using EGT. They may all watch EGT to make sure the temp isn't too high but some take things a bit further - to save fuel instead of backing off the throttle in a relatively low speed cruise they keep the throttle relatively wide open but lean the mixture, which at first sees EGT soar, but then leaning the mixture further sees EGT fall again. They reckon this method helps save fuel partly because the engine isn't losing as much to intake throttling losses (inlet manifold pressure still relatively high) and partly because the leaner mixture burns slower in the cylinder giving a more average pressure push on the piston on it's power stroke (more like a diesel) rather than have a big push closer to TDC, which at lower RPMs helps give more torque for less fuel use. There is argument between the minority who use the mixture method to control engine power / airspeed / EGT and those who more conventionally use the throttle, those that use the throttle reckon it's risky to use the mixture method for the very small gains and that a lean exhaust mixture is more likely to cause valve damage at any given EGT because there will be a lot more unburned oxygen in lean mixture exhaust gas.
Our posts were written at the same time and you have confirmed that aviators monitor EGT and given the reason why.
If they had the capability to advance the timing while leaning the mixture it would be beneficial as the closer an engine runs to the 'constant volume' model (vs the 'constant pressure' model) the more efficient it is as more of the expansion stroke can be utilised. (See diesel 'cut-off ratio' and how it hurts efficiency - probably the biggest advantage common rail brings to the party is its reduction).
In essence they are pursing 'lean burn' technology with the associated lowering of combustion temperature (and thus reduced heat loss in conjunction with the reduced throttling losses you allude to).

This is also what the guys (well one at least!) on the Chevrolet forum pursue. They call it HLC (Highway Lean Cruise) and can enable some very lean mixtures. They are however attending to timing requirements in every load/speed range to achieve this.

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