with the help of some po.com guys, i made this lil' gadget :




if it works as designed, it will pass through the map signal essentially unchanged, until it reaches 2.8v (adjustable with the pot), at which point it clamps it. it's three resistors, a voltage regulator, and an op-amp. i don't really understand how it works except in the most basic principle.

i'm going to solder on and heat shrink some proper wires with bullet connectors and then put it in a 3/4" x 1/2" x 2 1/2" housing. i made another one based on a much more complicated design, with a relay, but i think this one is nicer!

hope it works.

 

I used to use one in my Civic, but it wasn't home made, it was produced by Link called "ClampLink" which did practically the same thing, and could be adjustable. They work well, no more damn checkvalves!

 

sweet - i'll have to check that out. how much was it?

 

damn thats pretty tight....post up some prices.


Yager-

 

click on the "link engine management" link in my signature, its somewhere there on the site.. probably under accessories or options.

 

That's pretty neat Schwett! I'll bet you test satellite equipment too huh?

 

Cool, could you get a diagram of that? I want to make one but it is hard to sort out the conections, and I can't read the third color band on one of the resistors.

-Dustin

 

do you have a sketimatic for that? i want to build one!!

 

thats a nice little voltage clamp circuit. i bet thats very similar to what the J&S v2 has in it.

 

i checked the link site... didn't see it... but i do see it on the one in your sig. what does it look like? $70 isn't too bad i guess. same as a missing link.

the one i made cost about $5-10 though, but i have yet to see if it works. here's the schematic, but nobody go build one until i can test it! it would be a bummer if 4 or 5 of us built the same non-working voltage clamp. heh.



notes from the designer : The op amp is set up so the output follows the input 1:1. R1 and R2 set the reference of the TL431 so that when + input on the op amp reaches 2.8V, the TL431 will start to conduct and limit the voltage to 2.8V. R3 drops the voltage when the TL431 is conducting, otherwise R3 would drop a maximum of 9 microvolts. Also, if the input in the ECU is high impedence, you probably wouldn't even need the op amp in the circuit I drew. I really doubt the op amp is even needed.

If the input inpedence of the ECU were not high enough, you would have voltage drop on R3 even when the TL431 is not conducting. That would mean the ECU would always see slightly less voltage than what the MAP is sending.

Also, replacing R1 with a 20K pot would make this circuit adjustable.


[Modified by schwett, 10:06 AM 5/21/2002]

 

http://www.carmodifications.com/Link...ink-tuning.htm

its the last device listed on the page, "MAP sensor ClampLink" - same thing that I had running in my Civic. Works brilliantly, and voltage is adjustable by using a screwdriver and multimeter).

probably the schematics to your own version would work well.. just get it tested, and let us know of the results!

 

So, whats the point of this thing? What does it do? Sorry I'm dumb.

 

If the MAP sensor "sees" boost, it will cause the ECU to throw a code. The map limiter circuit allows the sensor to see boost, but it will clamp the voltage going to the ECU so that a code will not be thrown. Adjusting the max voltage seen by the ECU from the MAP sensor is also a way of controlling injector duty cycle at WOT.

Sonny

 

So is something like this pointless with a standalone?

 

for the most part, yes.

hondata, for example, modifies the ecu program to see and accept boost.

the pms, on the other hand, uses a separate 3 bar map sensor to adjust fuel for boost, and just passes the original signal along to the stock ecu unmodified.

 

so when are you goning to test this out

 

with some batteries and a voltmeter, tonight... for real, next week some time. built motor getting dropped in in a few days. [fingers crossed]

 

Your using a 7805, which is a 5V regulator. You make no mention of this in the schematic (although you do mention it in your initial post).

Care to fill us in?

 

yep, that's a mistake. i thought the tl431 was a 5v regulator. it's not. i need to switch that piece out.


[Modified by schwett, 4:03 PM 5/21/2002]

 

Yeah, the TL431 is defenitely not a 5V regulator. Thanks for the clear up.

EDIT: But it is a regulator no less.

EDIT 2: Perhaps a better Vref for the TL431 would be the output of the BARO sensor. From what I've read, to generate a MAP code (from boost), really means to exceed the BARO output. Just a thought.


[Modified by EE_Chris, 7:53 PM 5/24/2002]


[Modified by EE_Chris, 7:57 PM 5/24/2002]

 

bump.
want to see how its going

 

looks like one of Gabes ideas!

 

yeah me too. i have some oscilloscope traces of the J&S map limiter circuit. i would like to see some traces from this circuit also. someone wire it up and take pics with a scope!

 

haven't had time to check it - work sucks.

i will definitely be testing it out this weekend though. very interesting idea hooking it to the baro circuit for a reference.

 

i replaced the 5v regulator with the specified regulator. (used an nt999, equivalent to the tl431. first i tested it with a 3.15 volt input. adjusting the pot, i got the output to 2.83v. so far so good. tried it with 4.35v input, got out the same 2.83v. tried it with 8.11v, got the same 2.83v.... all good!

but then i tried 1.21v, and the output was.... 1.38v! WTF! i tried 1.57v, and got 1.44v. i have no idea what the problem is. i don't have anything that will supply a <1v input, so i don't really have a good range of results for the "1:1" condition.