Rev limiter problem!

dangerousdave · Post by **dangerousdave** » Sat Oct 17, 2009 10:34 pm

Hi guys any help is much appreciated,

Have been running mj on my car for a few years now and all has been well, when the hard rev limit board was released i fitted one, fantastic thing it is scaring people with the rev limiter of death shooting flames etc

The problem started today, finally got round to wiring in the switchable map feature. Did it, t'd into the 5v tps vref and put that to a switch, then into the option pin from the switch. All tested with the tuning software, copied map 1 across and tested with a 2500rpm limit and working fine popping away. Packed up the laptop and tools after raising the 2nd limit to 4500rpm to use as launch control (main map is 6200) and headed out for a drive. Went to hit the 1st map limiter thats always worked perfectly, and no bangs.....felt the car slow as the limit was reached but no bangs to let me know i was on it. Switched the map over to map 2 the lower rev limit and same again, no bangs but car slows at the rpm limit. It feels like its switched itself to soft cut...but i didnt think/know it existed as far as i understand its bangs or nothing!!

Have taken the mj out the car and taken it apart, both boards seem fine, no visually burnt components all wires connected still and verified with the multimeter. The limiter board is earthed through the mj earth pin so no bad earth unless the main body one has suddenly turned bad after all this time!?

Im completely stumped as to what it could be so just wondered if anyone has any advice to offer?! Need it fixed asap as the car is really boring to drive now im used to it sounding like im doing a drive by everytime i hang it out

Thanks in advance
Dave

NITROPIXIE · Post by **NITROPIXIE** » Sat Oct 17, 2009 11:06 pm

Hey Dave, who sounds dangerous

What motor have you been scaring people to death with??? lol Get some pics up in powered by section

I'm guessing you have a V3 with map switching option. It sounds like you have wired in your Map Option and is working correctly.

Double check your connection to the hard rev limiter from the rev limit ouput to the rev limit board. It sounds like this isn't connected somewhere as the coil pack is still powered through the rev limiter board but the board isn't getting the signal to reduce power to the coil pack.

If you have a ohm meter you can check that there is actually a solid connection between rev limit pin of mjlj to the rev limiter board.

If this is good there could be a chance you have fried the uln2003an. A replacement chip isn't at all expensive but i would recheck your connections first.

dangerousdave · Post by **dangerousdave** » Sat Oct 17, 2009 11:41 pm

Lol, not very dangerous...just an old forum name that is easy to remember! Cars a ford escort mk2 harrier with a xflow on 40's, will get some pics up when i get a chance!

Yep v3 with tps, firmware upgraded to 3.2.1 as far as i can make out, it was a while ago i added the board and did the firmware!! Map switching was working fine, got the message pop up when switching with the laptop plugged in and the rev limiter that seems to be there now does change in respect of the map that is switched on at the time. Il get it hooked up to the laptop again tomorrow and see what the ignition value is at the rev limit as it feels like it is definately cutting the power, just not with the harshness i have grown to love!

Just double checked the connection and moved the wire about and it keeps continuity so it would seem its wired in fine. As i say its worked fine for 6 months or so since i have had the car on the road again after fitting the rev limiter board and its only today that its messed up right after i fitted the switch and enabled switchable maps in the tuning software! Its odd that it still runs fine as it would seem the limiter board is working fine otherwise it would cut out if there was a problem on that board right?!

Any idea what may have caused the uln2003an to fry if it is that which is blown....is there any way to test it?!

Thanks for your quick reply

NITROPIXIE · Post by **NITROPIXIE** » Sun Oct 18, 2009 12:00 am

If we think logically about the wires which go to the rev limiter board. You have:-

+12v, without this you wouldn't get power to coil pack therefore no running engine

Gnd, without this connected it would fry U1 and would be obvious in smell, smoke and general mess

Coil, again no power to coil pack and no running engine.

Trig, without this no hard rev limit.

You could test the operation of rev limit output by connecting a Lamp/LED as in

http://www.autosportlabs.net/MJLJ_V4_ve ... hift_Light

If the lamp/led doesn't come on then you have a good indication the uln2003an chip is fried.

If it works there is the possiblilty that Q1 on the hard rev limiter board could be at fault.

dangerousdave · Post by **dangerousdave** » Sun Oct 18, 2009 12:04 pm

Just out testing it now, with the engine off i have battery voltage 13.4v at coil wire terminal, 13.4v at +12v terminal, 12.7v at the trigger wire terminal and good earth. With it running i have battery voltage again of 15.2v at coil, 15.2v at +12v and 14.4v at trigger. At the rpm limit of 2000rpm (for testing) the advance gauge goes to 0 on the tuning software and the engine holds back, but more throttle will let it rev up to 4k probably more (i didnt want to go too mad!) At the rev limit of 2k the trigger terminal drops voltage to read 2.2v suggesting that its working?

From searching the forum it would seem i have a similar issue to this post http://www.autosportlabs.org/viewtopic.php?t=2458 only problem is that it has no answer

With that in mind i followed brents advice in the post.

In it's current state, when you're trying to activate the rev limiter, do any of the components get hot? nope

During normal operation the MOSFET is "on", bypassing the resistor array. When the limiter is activated, the MOSFET is turned *off*, routing coil power through the array, attenuating the spark energy.
When activating / deactivating the rev limiter, what voltages are you seeing into the gate of the mosfet? It's that lone trace that goes to the mosfet device, viewable from the top. test from the vantage point of Q1.

Into the gate of the mosfet (i think i have the right point i have added a pic from the site, its the trace that comes up from r11 tested where the soldering iron is on in the pic.) with the engine running at idle im seeing 11.8v and when activating the limiter i see 15-15.2v. This says to me that the mosfet is not turning off as brent says it should and therefore not routing the coil power through the array? Right?! With this in mind which component am i looking at needing to change is it the mosfet or something else? Also wondering what would have caused it could it be the map option switch?

NITROPIXIE · Post by **NITROPIXIE** » Sun Oct 18, 2009 12:34 pm

At the rev limit of 2k the trigger terminal drops voltage to read 2.2v suggesting that its working?

It should really read 0v. 2.2v sounds like there is a bit of a voltage leak somewhere. Try disconnecting the trigger input to the rev limiter board with wire still attached. Then with the engine running, ground the trigger input to the board an see if this makes a difference.

If it does then it could be 2003, if it doesn't work then its either Q1 or U1 on rev limiter.

dangerousdave · Post by **dangerousdave** » Sun Oct 18, 2009 1:33 pm

Just tried that, unsoldered trigger from the pad, ran it up and it holds back at 2k as before with the wire disconnected. When reconnecting (holding it at 2k where its limiting/holding back) it does nothing at all, so would point to it being a problem with Q1 or U1 on rev limiter as you suggest. Is there any way to test these components individually or is it just a case of changing them in turn to see if it cures it?

Thanks very much for your help so far

NITROPIXIE · Post by **NITROPIXIE** » Sun Oct 18, 2009 1:50 pm

How did you mean reconnecting?? As in reconnecting it back as it previously was and should be.

Try running the engine just at idle or fast idle and connecting the trigger of the rev limiter boad straight to a ground. Engine should die if limiter works properly.

If it doesn't, replace the easier of the 2 semiconductors first Q1, as well its easier obviously. The price of the components aren't expensive. Are you in England? Might be able to find you a UK supplier if needed.

To remove the components it maybe easier to snip each leg of the component with some small side cutters and then use soldering iron to de-solder legs.

Thinking about it, it shouldn't be too difficult to setup a little test bed for this circuit with some lateral thinking.

NITROPIXIE · Post by **NITROPIXIE** » Sun Oct 18, 2009 1:58 pm

U1 - FDS6681Z - http://uk.rs-online.com/web/search/sear ... &R=6710618

Q1 - SMBT2907A - http://uk.rs-online.com/web/search/sear ... &R=5449438

Hope this helps

dangerousdave · Post by **dangerousdave** » Sun Oct 18, 2009 2:13 pm

I see, sorry got a bit confused there its been a long day already!!!

Just did it again and grounded the trigger input and the engine carries on running so it must be a problem on the board. Im in the uk so i will get some ordered up asap and go from there.

Thanks again, will update when i get it working again (fingers crossed!!!)

Post by **brentp** » Mon Oct 19, 2009 8:02 pm

Thanks for hanging in there with the troubleshooting. If you're grounding the input to the rev limiter and still nothing works, try replacing the transistor, then the mosfet- would be good to know where the failure was.

dangerousdave · Post by **dangerousdave** » Mon Oct 19, 2009 11:20 pm

No problems brent, it will be good for the forum to know the fix as i couldnt find anything about the problem on here. Just wondering what might have caused it as i had been playing about with it earlier in the day but that could just be a coincidence!

Just waiting for rs to take my order/deliver the bits! I processed the order and clicked ok but havnt had the email to say they got it!!

dangerousdave · Post by **dangerousdave** » Thu Oct 22, 2009 10:18 am

All sorted thank god!!!!

Changed the transistor first and tested, seemed to hold back a lot stronger but could still over rev the limit with more throttle (although a lot harder to achieve than before) so id imagine there was something up with that, it also sounded like anti lag (kinda like a jet noise when held on the limit) but without the bangs! Then changed the mosfet, and hey presto the ak-47 is back in my tailpipe!!

Thanks for the help guys much appreciated

Ps if anyone else in the uk has any similar problems and needs the parts but without having to order 5 mosfets min order from rs then let me know as i have 3 left (keeping one for spare) and 2 transistors (i lost one when i got it out the packaging....the thing is tiny and fell through my fingers and god knows where its ended up!)

NITROPIXIE · Post by **NITROPIXIE** » Thu Oct 22, 2009 2:24 pm

Good to hear you have it all sorted now fella. And you can get back to enjoying your rev limiter again, lol.

dangerousdave · Post by **dangerousdave** » Thu Oct 22, 2009 3:52 pm

Just had to take it out for a drive, im in love again!! Now to just finish off the new rev counter install into the old clocks!

By the way when i say "had" i mean, i went to go to the local motorfactors for some bits in my other escort (1998) and i got 5 mins down the road and the clutch ratchet snapped!! It was all good i picked up a new ratchet for the heap and the other bits, but more importantly all the blokes at the motorfactors were wetting their pants with excitement over the car when i came out, so what better way to toast them but firing the engine off the now fixed limiter as i left