Megasquirt vs 14CUX

[WernerVC]

I am glad I started this post. I didn't realized there was such an interest in FI and MS. There will be much more questions asked in the future about this .
Thanks Nigel for the info. Where exactly is Costa del South in the UK ?
I'll be coming to the UK next year for 6 weeks so I might make some time to visit if work schedule allows.
I'll be working at Sizewell. Got in touch with RPI but had complaints about the way they treat customers.( Never got the VAT back for parts imported in the USA).
I am going to stick with MS1 for a while.
Werner

[NigelB]

RPI ....Oh yes I tried dealing with them a couple of times

Spoke to one of the guys - Chris - a Legend in his own mind, Like Adolph Hitler - but without the charm
I couldn't believe the attitude and unhelpfulness sprouted down the phone at me.

Dealt with John Eales (JED)  instead - and gave him my money for top servic and support  :O)

Nige

[Moderator]

I actually prefer the Ford IAC which is PWM controlled and needs only 2 wires. I like the configuration and mounting better too.

Jim, I'm curious to know which Ford throttle body / IAC you're thinking of?

I've looked hard at some of the Mustang throttle bodies - there must be a dozen companies making aftermarket versions and some of them are appealing - but I'm leaning toward a Chevy 4.3L V6 (72mm) throttle body because I think its form factor might work a lot better for my installation. It's only 56mm thick (flange to flange). Chevy mounted it as a downdraft, but I'd mount it vertically with the throttle linkage on driver side. (I prefer a linkage to a cable, and its design appears to suit that better than most.) Its IAC is tucked-in pretty neatly to the body, side by side and about the same size as the TPS, both on passenger side.

Anyone have a comment about using the GM 4-wire IAC with MS2 or MS3?

Here's what I don't understand about the Chevy throttle body: they put a "diffuser" on the back of the throttle plate that blocks a lot of airflow, particularly at low throttle openings. Even at wide open throttle the diffuser probably blocks 25% of airflow! Aftermarket throttle plates are available without diffusers... although removing the diffuser is as easy as grinding off two rivet heads. The diffuser is in addition to a "nautilus" shaped cable connection - so why did they do both?


(by the way... the diffuser is shown here in a video about how to remove it: http://www.youtube.com/watch?v=Gy0_ecIof7M )

[MG four six eight]

Curtis

The GM 4 wire IAC works well with MS2/3. For the most difficult part for me was tuning the IAC for my application. Since there is no position sensor in most IAC motors, they are controlled by steps or voltage applied for a certain amount of time. (step size). Since some IAC motors can react more quickly then others, its up to the tuner to set the step size and other values based on how the idle speed responds during warm up.
Normally the default settings in MS are pretty close, then it just requires some tweaking.

In MS2 your options are warm up only. In this case you set the idle speed with the throttle stop screw and the IAC is used as a fast idle device for cold starts/warm up. Once the engine is warmed up the IAC pintle is fully extended or closed.
With MS3 you can have either "warm up" or "closed loop" idle control. With closed loop idle control, the throttle stop screw is adjusted to a "minimum" idle speed which is slower then what your "target idle" speed would be. Then MS3 extends or retracts the IAC pintle based on desired idle rpm/engine load.
Most all newer vehicles are closed loop idle controlled.

Link to MS3 idle control page http://www.msextra.com/doc/ms3/Idle_Control.html#SECTION00055000000000000000

Currently I'm still running my IAC set up as warm up only, with the same settings as I had while the car was using MS2. I haven't tried using the closed loop IAC feature in MS3 yet. Its one of those back burner projects that I may play around with in the future when I have the time. I would think that the GM 4 wire IAC should work for closed loop as well, since GM does it!

The diffuser is there to direct air flow in relation to how the EGR gases are distributed within the stock GM Vortec intake plenum. It also allows GM to make one throttle body for the different engine displacements. The 4.3L has a larger diffuser then the 5.7L.
I have seen the diffusers fall off before. We had a truck in a couple of weeks ago that the diffuser came loose and was getting caught in an intake valve, the motor didn't like that so much!
I removed the diffuser on mine by drilling out the rivits and installing solid rivits (instead of pop rivits) in the holes. I'm not a big fan of cutting the diffuser, since there is still a chance that the left over piece could still come loose.

Bill

[cgill]

This is a great topic!!! Thanks for posting Werner.

I have the 14CUX system and I can't seem to get the car to run well at low RPM (engine misses between 1000-2000 rpm) or get the (new NGK) oxygen sensors to go into closed loop (the two are probably related. Wiring checked out okay). It might be because I am running a fairly agressive cam and have it set at 104 degrees. So I am curious to know if the MS might be the solution to my EFI woes...

[Moderator]

Very helpful comments, Bill. Thank you!

I think I might leave the throttle plate's diffuser in place through initial development, on the theory that a 4.3L (72mm) throttle body is probably larger than ideal for my 3.5L engine anyhow.  Last night I mocked-up a plenum design, and today I visited my local machine shop and got them started on machining a custom plenum base. The proposed plenum top is extremely simple in form... still not sure if it will be carbon fiber, aluminum, or satin black powder-coated mild steel. As designed, the whole plenum will be so narrow that Rover's steel fuel rail will be removable without disturbing the plenum top or throttle body. I might end up fitting an extrusion-based fuel rail, but my initial plan is to simply rework the two ends of the one-piece tubular rail.

So here's my next question:

For MS2/MS3, how helpful is it to fit an adjustable fuel pressure regulator? Is an OEM style regulator more robust? Is there much real utility to having a gauge, or will I only need one for initial development?  (Aesthetically, I'd prefer to keep things simple and monochromatic...)

[BlownMGB-V8]

The main disadvantage of the Rover fuel rail is that due to the injector angle it is a pain to install. This can be fixed by replacing the big bend with a braided hose though. If you are using the Rover lower Intake,  keeping the trumpets is probably a good idea sin e they tune the runners.

If someone comes up with a particularly good fpr I would like to know the details. I've been using Ford but they are not that easy to add to a custom rail. I tried an adjustable but went back to stock for simplicity and ease of replacement. I feel it is better to use a standard rail pressure and match injector size and pulse width to the engine. Fpr's generally are a band aid for systems that aren't adjustable.

A gage is handy for tuning or troubleshooting but otherwise is a potential leak. Rail pressure rarely changes once the system is stable.

A midrange surge is an extremely common problem in modified OEM systems. Frequently it cannot be cured using the stock controller,  even if there is axway to tune it,  and it doesn't seem like anyone wants to discuss it. I got rid of it on my car only when I ditched the Ford controller, which with a tweecer add on was very tunable if you only had access to Ford's secret files. With MS-II it worked just fine.

Jim

[MG four six eight]

I would agree with Jim on this. Generally its best to use a stock pressure regulator if the horsepower levels are close to stock levels and the stock injectors are being used. ECMs have a useful range of pulse width control. If the injector is to large then the pulse width becomes to narrow and the engine becomes difficult to tune at idle and low rpm cruise. If the injector is to small the pulse width can be maxed out at WOT and cause a lean condition.

Adjustable fuel pressure regulators can be handy if the engine is highly tuned/modified and there is not a suitable sized injector avilable for the horsepower levels.
An adjustable fuel pressure regulator allows the tuner to move the "pulse width window" up or down slightly by changing the fuel pressure. Often times simply changing the pressure by 5-10 psi will be enough to bring the pulse widths into the ideal range for the ECU. Once the ideal pressure is found, normally it is left alone since changing the fuel pressure will change your entire tuning requirements.

There are calculators on the MegaSquirt web site and these will get you close for injector sizing. However you won't know where your pulse widths are until the engine is up and running/tuned. If the engine's horsepower was over/under estimated, or the horsepower level has been increased/detuned, then an adjustable regulator may be an option instead of buying 8 new injectors. (been there done that)!
The main thing is you want to stay in the fuel pump's ideal working range which is usually 30 to 60psi for most pumps. If the pressure has to be adjusted out of this range in order to bring the pulse widths in line, then the  best option is to change to a different flow rate injector.

An advantage  MS3 has over MS2 is the finer fuel table resolution .1% compared to 1%, this can be helpful when tuning for very short pulse widths. With the finer resolution I've noticed that the MS3 is a little easier to tune at idle and low load (city driving) conditions. For a car driven on the race track, it won't make a huge difference. For a street car, driven in the city that has larger injectors and other mods MS3 and an adjustable regulator are probably worth while investments.

Bill

I copied the following from the  MS manual that explains the effect of pulse width at low load/idle.

Idle Pulse Width

You have to select your injectors based on the maximum horsepower your engine can produce to prevent the engine from running lean at wide open throttle. But why not just pick the biggest ones you can find?

The answer has to do with idle and cruise pulse widths. If you use very large injectors, your idle pulse widths get very short. This can drastically reduce the mixture ratio control that you have during idle and cruise situations, and lead to very poor driveability and seemingly strange tuning behaviour.

To illustrate, suppose you have established that your engine produces the lowest MAP reading at an idle pulse widths of 1.2 milliseconds, and your opening time is 1.0 milliseconds (considered the 'standard opening time'). Recall that MegaSquirt can only change fuel by 0.1 milliseconds at a time.

And also recall that MegaSquirt assumes NO fuel is injected during opening (which is close to true, since the injectors remain closed until the coils charge, then they snap open at the end of the opening time). Now if the net effect of the enrichments change by 2%, the pulse widths don't change at all. Even if they change by 49%, nothing changes. But once they change by 50%, the pulse widths suddenly changes to 1.3 seconds.

So the next leaner possibility is 1.1 seconds, and the next richer is 1.3 seconds. However 1.3 milliseconds is not 1.3/1.2x100% = 8.3% richer, instead it is (1.3-1.0)/(1.2-1.0) = 50% richer! The mixture becomes very, very rich, and the engine runs poorly.

To confuse your tuning efforts further, it may be that you are already near a threshold, so that a small change in one parameter makes a very big change in the air/fuel ratio in one direction, but no difference at all in the other direction!

But doesn't the EGO correct? Actually, it can't. Even if you set the step size to 1%, nothing happens until the 50% (i.e. 1.3 milliseconds) threshold is reached. That is, the step size only takes effect once the 0.1 threshold of PW is reached. And if the number of ignition events between steps is large, the engine may stumble and die before it recovers and leans out. So in fact you may be better to set the O2 step high (50%), and the number of ignition events low (say 2) so that the average over just a few injections is correct. It is a band-aid approach, however, and likely to induce ignition related problems.

Obviously the converse is true if the engine goes lean. It has to go at least (1.1-1.0/(1.2-1.0)=50% lean before anything happens. If does go lean, it may back fire and die before it gets a chance to become richer.

You might think you can get around this by decreasing the injector opening time (to get a larger "adjustable time") and increasing the VE (or req_fuel), but that doesn't work because the 'ideal' injection time is still 1.2 seconds, and the permissible step is still 0.1msec, regardless of the way you add the components of the pulse width up.

And making matters worse is the fact that many high-performance engines will want even lower pulse widths at cruise than at idle, compounding the tuning problems and introducing more driveability issues. A system with a very short pulse widths like this will be difficult to tune. It will appear not to respond at all to enrichments over a certain range of a parameter (say IAT), then suddenly it will seem to change so drastically that you seem to require an entire new set tuning values.

Now even if your engines idles perfectly at a very low pulse widths, changing load, speed, and other variable (EGO, IAT, etc.) will demand slightly different air/fuel ratios. However, none of them are likely to need exactly the +50% you have to choose from!

This is why several aftermarket ECU manufacturers recommend an idle pulse widths of not lower than 1.7 milliseconds. If yours is lower than this, you need to address it before you will be able to tune your engine for all operating conditions. Ultimately the best solutions are appropriately sized injectors or staged injectors.

[BlownMGB-V8]

Very good reference Bill. I see someone has been working on the manual. Could you post a link please?

Jim

[Moderator]

You guys are so incredibly helpful. Thank you!

Since I have two Rover fuel pressure regulators, I guess I'll try to make that style work. I like the price!

---

Now I've turned attention is on what should probably be even simpler... the intake air temperature sensor (IAT).

Q1: for a normally aspirated engine, is there any reason to prefer mounting the IAT either before or after the throttle body? (My intuition is that upstream of the throttle body is cleaner, especially if PCV is ported in nearby. Downstream may be warmer.)

Q2: should I try to arrange it so the airstream flows over the IAT sensor, or is it fine if the sensor is just in near proximity?

Q3: do you expect there's any significant performance to be gained by putting a phenolic spacer between the lower manifold and the plenum in an effort to reduce intake air temperature? (Some of the UK performance shops sell spacers for this purpose. I could make my own if it truly makes sense, but I'm skeptical.)

[MG four six eight]

Jim

Sure! Link to main menu for MegaSquirt manuals http://www.msextra.com/doc/index.html

When searching through the manuals/links, I've found that most of the basic information such as injector sizing, fuel, ignition tuning, etc can be found in the MS1 manuals.
Then for more specific features or advanced topics, the information can be found in the MS2 and MS3 sections.

Curtis

I've found that locating the IAT sensor as far away from the throttle plate as possible works best. The issue is with heat soaking the sensor on re-starts.
For example I had the IAT located fairly close to the throttle body and when I would shut the engine off for 20 minutes or so. Then do a re-start the engine would run lean for a short time until the sensor cooled down to ambient temperature. When I would check the data the IAT could be reading 115*F when the ambient temp was only 70*F.
In theory the in rushing air should cool the sensor down right away. If I started the car and headed out on the highway right away, the sensor would indeed cool to ambient quickly. However if I started the car and was just doing stop and go driving, the sensor would take much longer to equalize to ambient temperature. At the lower RPMs/throttle openings there isn't as much air flow across the sensor to cool it.

I ended up moving the sensor to the air inlet at the cowl. In this location the sensor dosn't get as hot during a hot soak condition and the sensor responds to ambient temps much more quickly.
There are correction tables in MS3 to help compensate for heat soaked sensor as well. I've played around with the settings some and they can make a difference. Ultimately I found experimenting with different IAT locations gave me the best results though. Depending on your air intake set-up, usually its pretty easy to move around the IAT sensor!

It is best to have the sensor directly in the air stream.

Not sure how effective the spacers are. I would think that they could help somewhat, as a lot of the OEMs are now going to plastic intake manifolds in order to reduce air intake temps.
Bill

[BlownMGB-V8]

Interesting. Sort of makes me wonder if a location in front of the radiator and not in the intake at all might not work well.

Jim

[MG four six eight]

For those who draw they're air intake forward of the radiator and behind the grill, I would think that it work quite well.
The main thing is to locate the IAT sensor in a position where it can measure true incoming air temps. So for installations that have no cold air intake set-up, that most likely would mean locating it the air stream near the air filter.

There are also MAT (IAT) correction tables in MS2 and MS3. So for example once the engine is tuned you find that the engine runs slightly rich in the morning and maybe a little leaner mid-day when the ambient temp is hotter. You can use the correction table to automactically adjust the VE table up or down as the ambient temperature changes.

MS3 takes this one step further by offering both the correction table and an additional setting (MAT correction value) that allows you to change the percentage to which the physics of gas law is followed.

The method I use to tell if I need to use correction table is to first get the VE table, ignition timing table, etc tuned so that the engine runs well. Then drive car on a cold morning with auto-tune on and in the "hard or very hard" setting. Then check to see if auto-tune wants to change most of the bins richer or leaner. (It's easy to tell because the numbers will be either blue or red) Then leave the VE as is (don't allow Auto tune to change the VE table). Next drive the car with auto-tune on during a hot temperature day. If auto-tune wants to correct the VE in the opposite direction as the cold morning drive, then I'll use the MAT correction table.
Normally its best to do this test several times, to account for changing weather conditions etc. Also its best to start out with a small amount of correction and work your way to higher correction values if needed.
The goal is to get to the point where auto-tune wants to change as few VE bins as possible whether the ambient temp is hot or cold.
http://www.msextra.com/doc/ms2extra/MS2-Extra_Conversion.htm#matcor

Bill

[BlownMGB-V8]

Very good tip Bill. That is something I haven't tried yet, but I will now that you have explained it.

I will consider mounting the IAT just behind the grille. That will eliminate more wires up to the Enderlie style scoop/TB. Both should be at the same temperature as both are at the leading edge of the car in terms of airflow.

Jim