Lean idle. Rich cruise.

Dave999 said:

Modern gauges should all read the same to within a tolerance that is small. A modern wideband sensor comes paired with a calibration module in the plug connector. they etch off a chunk of some resistor or chip in the plug connection section to get it calibrated
that connector and sensor are now paired for life

usually a warning sticker saying do not disconnect this bit disconnect the wire at the other end of this part with the flip up clip weather proof connector

what happens is someone then takes 1 sensor ignores the warning sticker or it comes off and then swaps the connector bit along with the wire to another sensor and you end up with something that is way way out
i.e you have 3 parts
the wire harness
the plug bit
and the sensor that bolts into your headers

The majority of the plug bit is married to the sensor and is there to provide calibration BUT can be removed if you are persistent enough

most of the screw in wideband sensors will be bosch or similar these days and they do put effort into getting it right. when they make the sensor they don't know if its going into a aftermarket kit or its going into a box of 5000 to be delivered to Peugeot/FIAT for the challenger production line, they all need to be calibrated correctly because the ECU they usually connect to, expects them to be.

AEM and similar all use a chip and LED based gauge, again the tolerance stack up in the circuit will be tiny and inconsequential.

in the past or with unknown history, or cheap knock-off/fake ..... ????

new stuff as in last 10-15 years should be pretty accurate

Dave

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Modern doesn’t mean good. Just like anything electronic, it has a wide range of acceptable tolerance.

Tuning to a number, any number is a fools errand

I agree

my use of modern was to cover lambda sensors produced for OEM use by big players in the supply chain

rather than the older narrow and wide band sensor that were produced to work with a very specific ECU or gauge system which were quite rightly bespoke jobs for the application in hand.

since then they have become almost universal fitment and its a damn sight easier to just standardise the sensor than it is to tweak the software on every ECU

its a bit like the original OBD set up with its manufacturer specific plug and codes and the eventual closer standardisation of OBDII

every car has its own unique codes but the majority applicable to all cars in the range or indeed across car companies using an ECU from a supplier common to both will have a reasonable amount of standardisation. you can now buy a code reader that works reasonably effectively across a wide range of manufacturers rather than having to get one for each.

Economics and the need to "Plug n Play" on the production line, drives standardisation

a modern wideband sensor is a 3 or 4 wire unit 1 signal 2 heater and on the 4 wire job the 4th is earth for the signal partner wire

Dave

aaronk785 said:

12.3 cruise and 14.5 idle after opening the idle mixture screw about a 1/4 turn

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aaronk785 said:

Idle screws are at 7/8 out now. Turning them out makes cruise richen up.

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Changing the idle mix screws changes the cruise AFR means the speed your are calling cruise is still mostly on the 'idle circuit'. It should really be called low speed or low throttle circuit, and in fact that's the term Chrysler often used.

aaronk785 said:

91 pump gas. Pump says contains no ethanol. Thanks

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Only reason to avoid the ethanol is if you're not using the car much. Even avoiding the E, using pump fuel you still are dealing with relatively poor lifespan and the seasonal changes. On the other hand, if your car can run WOT in top gear on 91, then that's working out with timing curve on the engine, fine.

There's a sequence to tuning the carb that is useful. It reduces the iterations and dead ends in chasing (changing) because its based on the circuits interact. For example, fuel level effects everything. Next, all fuel exits the bowl through the main jets until enrichment is needed (PV opening). However, the restriction of the main jets is very large (or should be) compared with the idle restriction. So when we work on the idle circuits we can ignore the main jet. Without going further I think you get the idea.

1. Focus on getting the idle to run strong. This is defined as lowest reasonable rpm it will go into gear with the minimal drop in vac and rpm. Easy to test with an automatic transmission. With a manual trans to some degree you'll have to trust the automotive engineers - idle should be relatively rich - especially compared to emmissions era stuff. I wouldn't trust the WBO2 AFR number too much at idle but anything from 12 to 13.5 is at least in the ballpark. As long its not soot up the spark plugs it can even be a little richer if that's what's needed. The reading will change when placed in gear because of the loss of manifold vacuum = less pressure difference on the idle circuit.
1a. I'd work on the primaries as much as possible. The secondary fuel mix is helpful with low manifold vac but don't be afraid to restrict those screws further in that the others, becuase fuel distribution on the idle circuit is more about vacuum than air velocity. On the other hand the primary side is critical in getting the off-idle correct.
1b. Off - idle and idle is going to be controlled by IFR, IAB and the transistion slot exposure. So measure the primary transition slot exposure and make some adjustments with that to see the effect on idle.
2. Check the impact of the idle tuning on off-idle. Should be able to slowly accelerate from closed throttle to 35-45 mpoh without hesitations or sluggishness.
3. Main circuit. Depending on the car and gear ratios, Cruising on the primaries will be interstate speeds. At least 55 mph in my experience, at 60 - 65 mph should be enough load and throttle that most of the fuel is coming through the boosters.
4. Enrichment is full load/max acceleration in at least 2nd gear, preferably 3rd. This is 1/4 mile time (mph) or chassis dyno time.

PS. Even when cruising, when there is a slight downhill and we lighten up on the throttle, a high vacuum is created under the mostly closed throttles and guess what happens.



There's less air mass coming through and more vacuum at the idle port and transition slot so the 'idle circuit' starts supplying fuel again.
I've posted some data tables showing that if your interested.

The better we can get the idle circuit to work at idle, the closer we can get the idle vacuum to where the idle system will choke. Choke in this sense is the pressure difference where increasing pressure no longer pushes more fuel through.

Going to rework my distributor and start over. I rechecked my timing and things aren't right. Think it has a broken spring or something. Very inconsistent. I'll let you kno×what I find.