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Fuel enrichment - was: (RE: Semi O/T: Got a pickup with 2.0 16V, doI need Motronic?)



> > > No, stay away from the fuel enrichment modules.  Almost
> > > everyone I've ever heard of having one eventually
> > removes
> > > it because it ends up causing running issues, either
> > with
> > > the 1.8 or 2.0.
>
>  Daun, any recommendations
> > for an expose' on
> > those?  I shall have to look at that more carefully...
>
> No expose, just an observed thread that pops up on the list
> every now and then, and at least three friends off the top
> of my head have had issues.

I too have had issues with my homebrew TT-style (relay+resistor) module,
as well as my brother with his..

In both cases, replacing the relay fixed the problem. A dissection
revealed that water had gotten inside and corroded the relay terminals,
adding a significant amount of resistance.

A better solution would be to use a watertight relay, or design a
solid-state FET circuit to do the switching (without a relay).


On another note..

I have an Autotech module (due for installation Real Soon Now) and I took
it apart to see what's inside. I found an LM311 (voltage comparator)
driving a small relay, a rotary switch and a bank of resistors.

It appears to be bringing in the tach signal, running it through a
half-wave rectifier to produce a dc signal, then comparing that to a
reference voltage (corresponding to ~3000 rpm) and when the comparator
output turns on, activating a relay to switch one of the resistors
(the one selected by the rotary switch) in series with the DPR to change
the current. A lower DPR current corresponds to a richer mixture, so this
makes sense. Oh yeah, and there is also a BJT that prevents that device
from activating unless the full throttle switch is closed.

I might be able to post pictures and schematics at a later time, but
unless you want to build it on a wire-wrap board or etch a PCB, it's
probably too "busy" of a circuit to build your own (lots of components).


To be honest, I was expecting better (from autotech?! i know, i know..)
Granted, you're getting a lot more than the TT module (it's adjustable,
it doesn't activate below 3000rpm and cause bogging, it modifies dpr
current directly which doesn't suffer from the same problem as tricking
the ecu with the coolant temp sensor.. that the enrichment lasts only as
long as it takes the o2 to detect and undo it), but the circuit they
used is primitive. I thought maybe they would use a current amplifier to
do a linear enrichment based on rpm, or something along those lines.


Since the module housing has no grommets or seal sealing whatsoever, I
suspect that the reports of failure with the autotech module are due to
the same thing as the others.. water getting inside the relay.

-Toby