400 Pre cat too lean? How to make it richer?

[huggy59]

My 92 Griffith 400 pre Cat no other modifications AFIK): Car suffer between 1500/2500rpm of hesitations/misfiring (start/idle OK and pull like a train up to 2500rpm)

MOT guy said yesterday CO value at idle is similar to catalysed cars so too low for a pre CAT so too weak: This could explain hesitation before wide opening for butterfly. Is there a way to adjust richness?

Is AMM adjust air flow so indirectly AFR? And do you think AMM adjustment could by a way for a richer mixture? And if it is if 1V is less air so more richness ? or up to 2.3v more air so weaker ratio? Or vice versa

Who can I try to get it richer to check if hesitation desapear ?

What I have done yet without success:
- Grounds checked/cleaned
- Throttle pot adjusted by elongated holes (was out)
- Air mas meter adjusted (was very out at 2.3V with normal value at 1 to 1,5V for pre cat)..but I don't know if 2,3 make it leaner than 1V

Thanks or your help !

[blitzracing]

The mixture gets richer as the CO trim voltage goes up and You should have been running too rich at over 2 volts . Listen to the engine as you alter the setting and it should be clear if its actually working. A rich engine should like it's running on choke and smells of fuel and has a sooty exhaust. A lean engine will rock with a poor idle and the exhaust is really acrid. There should be a sweet spot between these two settings which is the 1.4 to 1.6 volts on a stock engine.. Having said all that if the CO trim is actually working then I'd be looking for an air leak in the plenum area somewhere.

[lancepar]

Might be worth having a read of this.......

Setting Air Mass/Flow Meter & Throttle Pot......

http://www.v8engines.com/carbs-2.htm#setting-up

AFAIK AFM and AMM are the same.

Blazeaway has done a lot of tinkering with AFM's BTW.

[huggy59]

blitzracing said:

The mixture gets richer as the CO trim voltage goes up and You should have been running too rich at over 2 volts . Listen to the engine as you alter the setting and it should be clear if its actually working. A rich engine should like it's running on choke and smells of fuel and has a sooty exhaust. A lean engine will rock with a poor idle and the exhaust is really acrid. There should be a sweet spot between these two settings which is the 1.4 to 1.6 volts on a stock engine.. Having said all that if the CO trim is actually working then I'd be looking for an air leak in the plenum area somewhere.

Blitz, Following Steve_D answer below could you help about an OBD cable with canon D connector / RoverGauge ?
Is rover gauge of interest for a pre cat ?

blitzracing said:

Hi again.
That cannon 'D' connector has been fitted by some previous owner replacing the original connector for OBD. If you don't have it yet you should get yourself a copy of RoverGauge (from Blitzracing). You will need a special cable but with the other half of that Cannon connector again Blitz will be able to help you there.
470 ohm is the correct resistance for non cat vehicles also know as the green map.
Steve

[blitzracing]

RoverGauge is of less use on a pre cat as you dont get any lambda feedback or trim values but you still get sensor data and CO trim values. You could quite easily wire a programmed USB cable and dropper resistor directly into the loom and forget about D connectors completely. All the info you need is here on how it needs connecting to the loom down towards the page bottom. . Drop me a line if you want a pre programmed cable with resistor you can join to the. Loom.

https://github.com/colinbourassa/rovergauge/blob/m...