Paul_H

The comparator output would need to be normally low during defend zone; and high during new fuel cut (inputs transposed?)

I presume the zener would flow like a signal or rectifier diode when comparator output goes high? There may be a voltage drop across the diode (same goes for my circuit above) so supply to comparator would have to take this into account. If fuel cut is about 1.25 Bar on my car (I think it's actually less) this translates into about 4.14V required at FCD output to trigger a new fuel cut.

That 1K resistor may need to be a trimmer to fine tune the output voltage so that is matches the input. Altering this would also change current through the zener, I don't think it will cause a problem.

How about taking the input to the comparator from the buffer output, to maintain high input impedance? Are you going to build it and tell us?

john banks

The 7221 is an open collector comparator. When MAP signal is below that set by the pot the output is "on" and it connects the anode of the zener to ground leading to regulation. When the MAP signal is above the setpoint, the anode is left floating (as long as the 1M ohm resistor for hysteresis does not draw too much - I don't think it will).

Connecting the inverting input of the 7221 to the output of the 7111 would result in the comparator reading a clamped signal all the time I reckon. The input impedance of the 7221 is incredibly high anyway.

I do intend to build it after any more input from you guys.

Does the zener setup make sense or am I talking crap? A variable sounds a good idea for initial testing. It is a nice idea to just have one potentiometer I think, as a suitable zener cuts down the component count considerably.

How are you progressing Paul with the design you were trying?

Paul_H

I'm going to order parts today - LMC7221BIN comparator, and looking at LMC6462 or LMC6482 op amp. Incidentally power consumption really is micro-power isn't it! we may well get away with powering it off the ECU. I'm using a regulator until I'm sure.

Do know where I can order these online? RS don't seem to stock them.

The zener sounds feasible - one way to tell for sure, isn't there. I think the RF filter & spike protection is a good move.

I've brought the MAP sensor wires & Lambda sensor wire up onto a plugblock which I've fixed under the plastic trim around the gearlever - so I can change the options more easily - fed up of lifting the carpet and stuffing my head into the ECU footwell.

Have fitted your AFR this morning, CO is 7% @ WOT. I'm going to fit the defender (not lifter) while waiting for the lifter chips, seeing as how it is sat there.....

While taking measurements of MAP sensor output, a while ago, I used a syringe to apply air pressure....and blew off a hose at about 1.4 Bar. So failures can happen and I think it is important to have a new fuel cut in place. Every pressure hose is secured on my car, and I'll be keeping an eye on the boost gauge in the interim.

I think we're very nearly there

john banks

LMC6462AIN from Farnell £4, so a bit more expensive.

The comparator and op amp I showed are both available from Farnell - it takes a long time to find a suitable IC in an 8 pin DIL and then find it from the supplier.

When you search on Farnell it needs the BIN or AIN bit as well otherwise doesn't find it.

I would suggest a few different zeners to get the right value- the ones from Maplin are 5%, 3.9V + 5% could take you to fuel cut.

I really think we are nearly there. Are you using a Dawes to alter your boost or another sort of valve?

Is it worth you ordering double quantity for me too given the postage rates these guys charge for only £2 of components?

john banks

Is it also worth ordering the LM317 regulator and a few simple diodes so we could try Xavier's design at the bottom of the last page if this one doesn't work? The op amp and comparator would be OK.

On second thoughts, how about ordering a few spare of everything -the postage is far more than the bits, and the habit I have of smoking things.... we'll obviously square up as appropriate as we have done so far.

It will be the zener if anything that uses the power depending on what resistor it is mated to.

[Edited by john banks - 3/3/2002 12:07:36 PM]

Paul_H

Sure, drop me a mail with exactly what you want

Paul_H

Just when you thought it was safe to go back in the water....

The fuel cut defender (no lift) sometimes triggers a check engine light. This happened the second time I started the engine...the check engine light came on. As it is powered separately from the ECU, I thought that the supply to it might be being interrupted while cranking the engine and that the ECU was detecting no MAP signal for a micro-second - and that the FCD might need a smoothing capacitor on the supply.

Switching the ignition on and off a couple of times cleared the check engine light. Might be a clue here?

2 minutes down the road, check engine light on again. Continue driving....2 minutes later, light goes out. This was while below defend point, so it can't have been the diode switching to close the feedback loop.

I'm not sure why this happens. Output impedance of the FCD is 680 ohms, I assume the input impedance of the ECU is much higher.

Any ideas?

john banks

It gives a CEL if the MAP sensor is disconnected, so the power theory seems a reasonable one, assuming all the connections are good.

Possible solutions might be to take power from ECU supply so they power up at the same time, or perhaps to consider a design where the MAP sensor wire is not cut, but clamped in-situ - ie a simple zener diode as many of the MR2 people have done - just connect the zener from ground to MAP and that is it. There are two issues - load on the sensor - which is probably not an issue as I heard it doesn't mind being grounded (but have not tried it), but also the comparator would always be reading a clamped signal so wouldn't work properly - there would never be a fuel cut.

I haven't checked to see whether my uC circuit with big cap and 7805 resets (brown outs) during cranking. I was powering it off the cigaratte lighter socket so far.

There has got to be 5V at the ECU during cranking, but presumably the main relay box disconnects non-vital circuits?

[Edited by john banks - 3/3/2002 6:44:38 PM]

Paul_H

John

Bits arrived from Maplin today, will post tomorrow (Thursday)

This is working on the bench.



This is the plot



I've had the defender part (not lifter) on my car all day today. It sometimes - not always - triggers a check engine light when cranking the engine. I think it needs to be wired into the ECU supply - I think the supply is being interupted when cranking. The light goes out on its own after a couple of minutes when the ECU decides there is a MAP input after all.

More difficult to understand is that the first time you give it some, the check engine light comes on. Again after a couple of minutes it goes out - then stays out for good. No matter how hard you try it doesn't come on again. I was a bit puzzled by this and measured the current that flows from the MAP sensor to the ECU. I thought my meter was broken - I could only get a reading on the 2mA scale - and the reading was 0.002mA. Absolutely tiny.

What I speculate is happening is that the first time you boot it and the MAP sensor output rises, it is charging the capacitor on the input - i.e. the low pass filter. Hence I've removed it on the circuit above. That's my best guess anyway. Sound possible?

The circuit above draws 7mA in total.

My vote goes for getting this thing finished quick because I'm pissed off working on it!

dowser

Sounds good Paul - give it a try in the car

I finally got all the bits to start playing.....but the chips are 'out-of-date' now, lol!

Richard

john banks

Sounds good Paul. How about a smaller capacitor?

I await the bits and will try the simple one I posted last. But glad to know we have a working design above that we can "trim" as much as is sensible.

I am wondering whether we need all this protection - if we are using a MAP sensor and the circuit powered by 5V from the ECU I can't see an issue with spikes or whatever. My microcontroller circuit hasn't complained with inputs straight from ECU sensors.

Paul_H

Richard - it IS looking good & you should see what I've got left in the way of parts! I will try it as soon as I can.

John - bits posted but no zeners, Farnell have discontinued the ones I ordered for you.

I agree, the protection diodes are probably unnecessary - so D1 and D2 could be removed. They would of course take the spike into the 5V supply rail anyway, necessitating further protection. Also that filter on the input could go too, particularly as the capacitor seems to load up the sensor - I'm assuming this is what's happening, I haven't had time to remove it yet. I think it's probably better removed entirely.

The pull up resistor on the comparator output is needed to get the output to go high. The 0.1uF capacitor on the comparator stops it oscillating - I watched it going all over the place on the voltmeter, stuffed in the capacitor and bingo. That breadboard is really very useful

What has surprised me is how little power is actually required to run the MAP sensor. I've not taken a risk with the ECU, I've powered it from an LM7805 - only 49p. It would be a good idea to put an ammeter in the 5V regulated output to the TPS and see what it's drawing. I wouldn't be surprised if its much less than the 7mA this circuit draws.

Paul_H

This circuit works very well on the bench.

The circuit is now built & wired into the ECU supply. I've just started the car - NO check engine light. The ECU is powered from a relay which I can hear clicking on & off under the dash - my improvised arrangement was causing the problem - now resolved.

All that remains is a test drive tomorrow!

john banks

Sounds great please keep updated.

Parts received with thanks Paul.

Paul_H

A good result. It's stunningly effective.

When powered off the ECU supply it powers up with the ECU, and the ECU is happy. I tested it as follows:

I wound my Dawes up to 1.25 Bar, set defend point at 3.85V and new fuel cut at 4.3V...went for a drive. Works great - 1.25 Bar held, no fuel cut.

To test the new fuel cut I lowered the setting to 3.9V, watched the boost gauge rise to 1.25 Bar, a few seconds later hit fuel cut. The switch works (break before make) and is so fast that it does not trigger a CEL. Reset the level to 4.3V and normal service was restored.

So we have a working fuel cut lifter, with fully adjustable defend and fuel cut points, that draws only 7mA and is powered from 5V.

I think it fulfills all the criteria we set

It would probably be useful if I open a new thread for RESULTS. We could keep this thread going for development of the other circuits - assuming you want to do this John - the other circuits have fewer parts - and have the results thread for tried and tested, working circuits, to save people trawling through this thread with all its ups and downs on the way.

Richard - go build it

john banks

Fantastic achievement Paul!

As we said, now we have something that works we can trim as necessary. I am going to try a few of the ideas with the components availabe.

You are quite happy drawing 7mA from the ECU then? Does the voltage drop at all?

Paul_H

Yes it is an achievement - but it is OURS, not mine. We have both contributed!

I've powered it from an LM7805, not from the ECU - don't know what the ECU can safely supply. I think it's cheap insurance.

dowser

Well done, and thanks

Richard

Paul_H

Just for completeness I thought you would like to know that the car goes rather well at 1.25 Bar

No error codes logged by the ECU; car fuelled correctly; no fuss, no bother. Just faster

john banks

Very nice isn't it?

Paul_H

Yes, a real improvement, as long as you can resist the temptation to turn the boost up Keep it reasonable and it will be OK, go silly and it won't!

The little box of tricks is tucked away neatly. It's very satisfying knowing how it works, too.

This project has got me back into electronics. I like being able to make something useful and have already started the next project - a DIY anti hijack system using an electronic security lock IC, keypad, 555 timer and a relay. I might have it done by Christmas

john banks

Good isn't it! I have done the same too with this and the EBC. Before all this all I could do was flashing LEDs.

I am planning K-thermocouple inlet temp sensor converter to allow DVM connection. Knock display. And fuel computer - remap the MAF sensor by RPM/load, but only after the others! And all this after I finish the EBC. So that is me for a long time then.

john banks

Unless I want to run 20PSI which I don't, I don't need it John. But I could test it on my car if you want and then we could put it on yours and see how your car with FClifter and mine with PPP at the same boost compare - say 18PSI? We could get AWD to run a Select Monitor as you suggest. I think we will break 260bhp at Star no problem on your car, and probably see 270lbft. Are you game when you have your lambda and knocklink? I have no intention of blowing anything up and would not suggest it if I did not think it was safe? Hell, if it really is that good I will be selling my PPP ECU if you equal me at Star with the same boost. Have you got the Knock and Lambdalink and Dawes yet John?

Please send me the assembled board Paul and we'll work it out. Someone will buy it off me and I'll send you the cost of the bits.

John me thinks you should sort your exhaust bits out and get in the running so we can make your car into a monster - at least by TD04L standards but keep it safe - that is a real priority for me in all I am doing.

[Edited by john banks - 2/8/2002 6:44:28 PM]

john banks

You don't NEED a FMIC. We have quite a decent intercooler on our cars for the sort of boost we run IMHO. Remember Dave was running 25 PSI - makes you a bit happier to run 17-18 IMHO. Loads of people run remaps or whatever with 17-18 PSI without issue. The PPP runs over 17 sometimes and seems very safe. Are you game or not? If you want 17 with no risk of fuel cut when overtaking a bus it would be very nice and we could set your fuel cut to 19PSI.

I don't think my or your car as I am planning it for you will eat gearboxes!

[Edited by john banks - 2/8/2002 7:06:51 PM]

john banks

The three setups on the same car would be tricky. Stephen Done's multiple ECU test was tricky for errors because of time allowed for bedding in the ECUs - the differences between the ECUs looked significant, but the errors could have been a substantial part of it - same with a rolling road for small differences. Also tests of three setups on the rolling road could get very expensive - ie £180 if it is £60 a run as quoted to me!

If we setup two cars with the same boost, similar exhausts and induction - ie yours and mine, both with Dawes at the same boost, but one with MY99 ECU + 19PSI fuel cut and the other MY00 PPP, both at 18 PSI I think this would be most practical.

If your results are as good as mine and it drives as well on the road, and I suspect they might be I might source a MY99 ECU and sell my PPP ECU!

Obviously we can install the FCD and check on the select monitor immediately for safety - would need to get Dave Brown involved in this. I don't have any way of logging ignition timing like Stephen did as I don't have the protocol for reading the select monitor port and cannot get it.

Small differences in fuelling and timing are unlikely to affect safety at higher boost for MY99 vs MY00 ECU I don't think, but we need to check it on the select monitor.

[Edited by john banks - 2/10/2002 12:18:29 PM]

T-uk

I would think that the same car would have to be used,for it to be fair.

I was thinking along the lines of fitting the ECU,set and check with select monitor,once happy reset and run car on a dual carriage between junction to the next junction or r/bout to r/bout,basically a set circuit for all three tests of about 10"bed in" miles,then using a bridge or similar as a test start point in 3rd for 2000 to 7000rpm.

edit to add:if the MY00 802 ECU runs more retard and fuel,I think temps should be kept lower and safer.the MY99 ECU may give the best performance but as we know performance has a price.

[Edited by T-uk - 2/10/2002 12:34:56 PM]

john banks

Yes OK. Are you going to get the car select monitored and rolling roaded?

[Edited by john banks - 2/10/2002 3:10:47 PM]

john banks

I'll try and get intake temp monitor set up on my car then and see before going on track.

Did the MY98 have a smaller intercooler than the MY99/00?

I wouldn't plan to do more than 5 laps anyway - seems like too much for a road car to me unless you start upgrading everything.

How many laps do you usually do? Does your car drop off in performance? If so I don't think you want any increase in boost on track. How do PPP or Link cars with TMIC and TD04L go?

Surely everything will wear worse if you stress them and heat them up and keep pushing them lap after lap as well? Why not buy a track car to do that or restrict the number of laps?

If you buy a FMIC you will only transfer the problem to the next weakest link? Would a new turbo be more rational than an inefficient turbo with a good intercooler? Don't know just a few thoughts....

I know all about Dave's injectors.

What other things do we need to account for for engine safety on the track?

[Edited by john banks - 2/10/2002 4:17:53 PM]

cube

Hi all,
Does anyone have a complete part list for the final version of this project?

Cheers,

Cube.

Scott.T

iTrader: (2)

I think I posted a partlist on this thread somewhere. Also included the differences required for a Pre96, as the map sensor voltages are different.