Hi There,

Been out playing with the megajolt maping to try to get the engine running better this morning.

Noticed something funny......as soon as I plug in the laptop, the engine is transformed. without the laptop, it pops and spits, has a reluctance to rev and is very difficult to drive

With the laptop connected it cures everything....

Cant realistically drive round with a laptop permanently connected so need to sort it out ASAP.

Anyone got an clues what could be causing this strange phemomenon.......?

Any ideas gratefully recieved, the sun is out and I am itching to get out.

The engine is a 2.0 pinto running on DHLA 40's. I've had the carbs in bits for a damn good clean recently to try to get rid of the symptoms, valve clearances are bang on and compressions are all good.

Im pretty sure the problem comes down to the megajolt instalation but where.

Also not been able to get the VDO rev counter working yet despite a collection of diodes, resistors, could this have something to do with it ?

Totally out of ideas now, and looking to all my locostbuilder buddies for inspiration

Whats going on....???

What version MJLJtune are you using. I know that for V3 you have to press another button to commit the map in the laptop to the MJLJ chip, otherwise when you switch off and restart it will use the old saved map in MJLJ.

Just a thought.

do the following and report back:

1. plug the cable in on its own

2. plug cable in with lap top on other end but lap top dswitched off

3. as 2 but lap tio switch ed

4. as 3. bupt tap top switched on and running yer tuning program.

5. is lap top powered by its own batteries or are you taking power from the car battery?

in all cases you drive areound or whatever it is you are doing to monitor performance.


could be a simple earth wiring thing, or not.

sounds like the megajolt is not saving the map and reverting back to safety mode, hence when you plug the lap top in its reading the map from the laptop.

With engine running on its own (ie no laptop) have you tried connecting a strobe and observing the advance changing in line with whatever map you are expecting to be in the mJLJ unit?

As said before if it is running in safe mode you will get a fixed 10deg across the rev range. Assuming your expected map is variable (and not fully populated with 10deg) you should see the advance change. Advance timing lights are good for checking this.

Have you had the laptop connected before and proved the comms to be working fully or is this a new install?


The simplest thing to try first, asuming comms are good is to check you are uploading the maps correctly.

My God....that was quick, onlywent for a brew and loads of replies.

So in response to the questions.

Darren, I have Megajolt Lite JR V 3.0.0 beta 4, according to the help button on the program. I have been hitting the 'Commit Configuration to Flash' Button, but I'll go and give it another go.

O2GF74

1. Plugged cable in on its own....runs like crap, pops an spits, doesn't want to rev.
2. Plugged in with laptop switched off....runs well, revs and no popping and spitting.
3. Same as 2
4. Same as 2 and 3
5. Laptop is running on its own batteries, not connected to the car (or even mains at the moment) other than via the serial cable.

I'm just running it on the drive at the mo, and revving it, trust me no need totry and rive it the difference is obvious.

Tim,

Could be, but even with the cable connected and the laptop off there is a difference.

Keep the thoughts coming, really I have no clue with this one.

John

That is a strange one. I cant explain why it runs better connected to a laptop that is switched off.

Has it always been like this or has something changed / been changed?

I think i will have to direct you to the Autosports lab for this one. Too strange for me. Brent may have the solution.

Did you build the unit yourself from Kit? I assume its a new install and hasnt been running faultlessly before. Could it be a dry joint on the board that is making a connection as a result of the plug being inserted.

Are you using the serial port? Does anyone know if these are powered up on a laptop even when its switched off??? Could it be theres a power supply problem on the board hence crap running and attaching it to the serial port is powering that part of the board up? Sounds strange.....

It is a new install, done over the winter.

I didnt build the board, I got it from someone on here at the Donnington show.

I think its a V2 board but stand to be corrected.

I wasn't running that well when it was on a dizzy, I was hoping that Megajolt would cure it. When it still didn't run as I had hoped I turned to the carbs and head. Just finished these and still the same....



Like I said, compressions are all in order, and with the laptop connected, it seems to rev like it should.

I'm disconnecting the serial cable at the laptop end, not the megajolt end.

John.

Ben,

Do't think the serial port is powered until the laptop i switched on, but do stand to be corrected.

Damn right it sounds starnge......I was at there for 10 minutes connecting and disconnecting the serial cable thinking to myself...this cant be right....

John

Almost tempting to get a serial break-out box and start connecting / disconnecting wires to find out which one it is!!!
Looking at how power can be taken from a serial port it looks like its possible current output is pretty piddly... and it also looks like the serial port is switched off when the computer is off....

Confusing!!

The megajolt website says * Verify you have an adequate power supply, correctly connected to the MJLJ unit. See the Vehicle installation guide
* With the unit powered up, check to make sure the correct voltage (+5v) is present at all of the power input pins of the integrated circuits and oscillator.

I'd try monitoring the voltages whilst connecting / disconnecting the serial cable....

I'd monitor the voltage across the

Try using a db9 connector with a 1..10k resistor between pins 2 and 5 and the same between pins 3 and 5, could be that the serial port is picking up static and the jolt might not like it.

(pin 2 and 3 are the TX and RX pins and 5 should be signal ground)

Other possibility is that you have grounding problems inside the jolt and then try connecting the same DB9 with pin 5 connected to the outer shielding (laptop might have this internally done)
If this is the problem, you can do it internally off course. But db9 is a quicky.

As I think of it now, might try last one first. Could explain why even a turned off laptop could cure the thing.

All i can say at this stage is that i had some confusing comms problems and was messing on for 2 days with it. A quick post on Brents site got a reply within 30 mins and problems solved. Defo worth a try on there. If Brent cant fix it then no-one can.

If it is V2 board then it is quite old but presumably worked for the guy you bought it off. Again on Brents site there are guides on how you can identify them.

If its a V3 board then the V3 config software works very well indeed and doesnt need Java which is the root of problems for a lot of people.

If you load up Brays terminal you can enter C and S commands (NB Capitals)and get a string of hex code returned to confirm the comms are good and the board is functioning ok. I put up a link to this prog recently in the EFI section.

You can of course test what map is installed when you first connect the laptop to confirm the upload is working good.


Here is a link to Brents main page.
http://www.autosportlabs.net/index.php?title=Main_Page

The only difference with the cable connected to the laptop and the cable not connected is the serial port on the ecu will be grounded.
I'm wondering what would happen if you grounded pin 5 to the car.

quote:

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Originally posted by chockymonster
The only difference with the cable connected to the laptop and the cable not connected is the serial port on the ecu will be grounded.
I'm wondering what would happen if you grounded pin 5 to the car.

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Right, been back out to make some more tests based on your thoughts.

So currently with the laptop connected it idles better and revs cleaner, no laptop, idles rougher, and spits and coughs when held at revs.

Left the serial cable connected to the Megajolt and enlisted the services of a paperclip to 'test'

If I connect 5 an 3 or 5 and 2 together there is no change, however if I connect 5 to the actual metal body of the plug, idle revs lift and the engine revs cleanly.

Also had to try connection touching pin 5 to the chassis (out of curiosity) and again the engine idle get better and the engine revs cleanly.

Now what.........?????
God this is strange

John

Sounds like you may have an earth problem or poor connection in your MJ then that is overcome by joining 5 to the body of the unit.
A diagram of the unit should highlight the problem joint.
Time to visit here and compare against your board. I suspect a badly soldered joint.

strange!!

pin5 is ground

pin 3 / 2 are Tx and Rx on MAX 232 side..

pin5 normaly is connected to the max pin 15 pin 15 should be connected to the car body ground or the ground of the 5volt reg wich supplys the MAX 232..

in the event of no ground the max 232 it will generate all sorts of rubish wich your megajolt tries to interpret and then its spark is comeing late etc...

the error clearly lies in the zone of the MAX 232 in your PCB.
make sure pin 15 is connected to any ground pin the board.
also pin 5 is connected to pin 15.

the laptop and the megajolt nead to have the same ground in that way they both interpret the signals the same.

your max232 is floating (if you ask me) and generates by itself some RS232 signals wich then hold on the megajolts wich tries to untherstand them.

Tks

[Edited on 5/4/07 by tks]

on the pic you see that pin 15

isn't drilled/etched sow i gues you only need to drip a bit of solder on there..!!

pin 15 is the second from the right side of the dot. with rs232 facing to you..

Tks

Guys,

Sorted it I think, (fingers duly crossed and they will remain so for the next month or so....)

It does seem to have been an earthing problem, as so many of you diagnosed.

The earth pin in the molex connector at the megajolt box had been partially pushed out, shoved it back in again tried it.

Big shouts of YES were heard in the next street !!!

Just for the hell of it I connected it up to the laptop again and the engine note stayed the same. Its revving properly and all seems well with the world.

As for why it was gettng an earth from a powered off laptop I have no idea. My only guess is the laptop was acting as a conductor between one of the pins (possibly pin 5) and the metal body of the plug.

Thanks again for the suggestions, you have done me proud, all hail to Locostbuilders, a truly great national institution.

John

quote:

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My only guess is the laptop was acting as a conductor between one of the pins (possibly pin 5) and the metal body of the plug.

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If you get enough suggestions some of them will be right!!!

Glad to hear you sorted it!!!

I hate electrics, if I can't see it then I don't trust it....

quote:

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Originally posted by John22000
I hate electrics, if I can't see it then I don't trust it....

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