Air to Fuel Ratio Gauge for fine tuning Weber in 78' 20R Questions (2 Viewers)

[HS44]

My questions are based on installing, (or not?), an Air Fuel Ratio Gauge Kit so I can both fine-tune the Weber carburetor and also monitor the AFR when I am driving.

Note 1: If the exhaust system was like more common ones, I would definitely install one, so I am questioning if I should get one with what I have, the CA "Legal" 1978 Toyota Pickup Mini RV with 20R.

Note 2:
In most cars and trucks there are no air pumps and/or exhaust air pipes going into the exhaust manifold like at least some of the Toyota 20 series motors do.

Note 3:
I am sure that the added air into the exhaust stream will skew the AFR reading to a lean condition.

The Situation:
I have a Weber 32/36 DGEV-33B carburetor using a CA "legal" Weber 'Kit' Part# K 8747 installed on my 78' that is now having issues with high fuel consumption.

The Weber 32/36 has been installed for years.

Also, for the installation, I installed the adjustable Holley Fuel Pressure Regulator that adjusts down from ~ 6 - 7 PSI to between 1 and 4 PSI; Holly PART# 12-804.
I have fuel pressure @ ~ 2.5 PSI.

I also added a fuel return line pipe to the gas tank for the required CA "Legal" as per the Weber's instructions which also made it so the fuel pressure would not creep up at idle.

When I first installed the Weber, with the jetting that came with it new in the box, it ran too lean so I got a jet kit for re-jetting it.

Before the Transmission upgrade, (mentioned below), the fuel consumption had already started increasing from ~ 16.2 MPG @ ~ 65 - 68 MPH, (mostly 68 MPH), on the1,000 mile mostly Freeway trip to ~ 15.8 MPG on exact same route and very similar road conditions.

I had the L42 4 Speed Transmission when I first did the Weber install. Since then, I upgraded to W56 5 Speed Transmission.

At first, the W56 was getting about the same MPG as the L42 on same 1,000 mile mostly Freeway trip, (~ 15.8 MPG) @ ~ 65 - 70 MPH and was getting about 15.8 MPG which was same, + or - a couple of 1/10ths fuel consumption as with the L42.

On the last 1,000 mile trip, (same exact route), very similar conditions it averaged 14.7 MPG!... ...which is less than I would get with a 30 MPH headwind @ as fast as it would go up to 68 MPH, usually between 55 and 65 MPH in 30 MPH headwind with L42 Transmission... ...Even hauling the Trailer with headwind, it never got below 15 MPG on that same trip.

Note: 1- For accuracy, I used google maps to calculate the miles traveled for those particular trips because the speedometer and odometer readings read different from actual miles traveled.
I used Google Maps when I had the L42 4 speed also, so I know it is not the odometer reading differences between the different transmissions.

2- I also always use Top Tier Gasoline and for these trips, I used only Chevron Gas.

Below are my notes from after getting the Redline Weber Jet Kit and doing some experimenting and re-jetting:
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Weber re-jetting 04/28/2011
@ 2800 ft above sea level:

Also, Timing must be advanced to get correct idle.
on 78' timing set between 10° and 13° BTDC.
I got it @ ~ 10 1/2° BTDC.

It is good there all year here in CA (winter and summer fuel) between sea level and 6,000 above sea level without adjusting the carburetor.
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Note: I was doing the driving same as I had done and used power to keep with traffic and was not feathering gas pedal for maximum vacuum pressure, which would yield about 17.2 MPG going between 58 and 63 MPH just after install and re-jetting the Weber when keeping vacuum pressure to between 7.5 @ low end and 10 or more when cruising.

In essence, I could plan for my fuel expenses for where I needed to stop using 15 MPG as the minimum MPG and always got more than that until recently.

Anyway, I checked all the usual suspects and gave it a tuneup:
Air Filter, Ignition Timing and Distributor, Plug Wires, Spark Plugs, adjusted Weber as per Weber instructions, (adjustment ended up same as before, no change of adj. was needed).
There are no vacuum or fuel leaks, Valve Lash is spot-on, Exhaust System is free flowing and no exhaust system leaks, there is no misfiring and power is about the same as far as I can tell.

At This Point I have acquired a major carburetor rebuild kit and will be rebuilding the Weber before going on any long trips.

I will also be removing Intake manifold and replacing manifold gasket, (no vacuum leaks now but there is a very slight coolant leak on the cover plate on the underside of the I/M that has been there for a very long time that I did not want to mess with previously that I had used Radiator stop leak to solve in the past...

...However, I have flushed-out the cooling system recently because I installed a new radiator which reopened the seeping leak so now I am going to seal the leak.

While I am at it, as a preemptive, I will also replace the ABV because it is so hard to reach with the intake manifold on. It has been on there since before I got it in 2004, so it is bound to be leaking now or fail soon.
I will also do a check of EGR Valve and ports.

I could, in theory, install the AFR Kit and take and note of the readings as it will be after rebuilding and doing the usual tuneup and adjusting the Weber first to get a baseline under all conditions from Idle to no load @ low-speed, cruse and high RPM in the 'shop' first, then drive @ slower town speeds, cruse conditions/ /both in town and Freeway Cruising and full open throttle with load to get the range of the AFR readings for each condition individually. I will be doing that with the exhaust Air system connected as is normal first if I do install the AFR Kit...

...At which point...
...Then completely disconnect the air pump and plug the air induction circuit to the exhaust manifold so there will be no air going into the exhaust manifold to skew the actual AFR reading and take notes of the actual 'true' readings so I can accurately compensate, (my brain), for the difference for when the air pump air induction system is reconnected.

Then, before reconnecting exhaust Air Induction system, make the final adjustments and jetting for the fine tuning to get it as close as possible to what is correct for how I want it to be before reconnecting the exhaust air induction system....

...Then after reconnecting the Air Induction system, and going through the same test situations I will take notes of how lean the AFR readings are and get used to knowing, (compensate my brain), for what the 'lean' readings are and know how much to compensate to so I can know what they actually are out of the combustion chamber.
I will put a label with the AFR reading offset on the dash or somewhere on or near the gauge mount.

Furthermore, FYI, other than the testing for the initial AFR Reading compensation, I will not be removing the Air Pump or defying the Exhaust Air Induction system, therefore, suggesting that I do that is not a viable answer for me and is not an answer for the questions that I would consider doing.

The final Questions:
1- Will the method I stated for compensating for the air induction into the exhaust system difference be reasonably close enough to use when the air pump exhaust air induction system is connected permanently?... ...If not; why, what did I miss?... ...Or is there something else an experienced AFR tech here can say I should consider that would be of good use or is a critical issue?

2- Because of the fact that if it were not for the air induction system situation on the 78' 20R motor I would definitely get the AFR Kit that is linked above... ...So do you think I would benefit from getting and installing it on my 78 pickup with 20R that has the Air Pump Air Injection system to both make fine-tuning adjustments and monitor AFR?

 

[MoaByte]

I'm sorry you have to keep it smog legal. I got the same carb on my 80 pickup, 20R, 4-speed, 4x4, I get up to 19 mpg on the freeway and about 16 around town and trails. Desmogging was the best thing that ever happened to that truck. It pulls grades with 31's better than it did new with 235's.

 

[HS44]

I'm sorry you have to keep it smog legal. I got the same carb on my 80 pickup, 20R, 4-speed, 4x4, I get up to 19 mpg on the freeway and about 16 around town and trails. Desmogging was the best thing that ever happened to that truck. It pulls grades with 31's better than it did new with 235's.

That is close to the same MPG I was getting with the 4 speed before the MPG began slowly decreasing. It was getting about 16.6 - 17.4 MPG on Freeway depending on headwind and when I was careful to keep vacuum pressure as high as possible while traveling @ reasonably fast speeds for road and traffic conditions. Around town it would get about 16 MPG average and on very slow, steep, minimally deep sand and gravel, etc. the MPG would vary anywhere from 15.6 MPG and 8.8 MPG if I had to keep it at a low vacuum and 1st gear most of the time it would guzzle gas, but compared to my friend's 1 ton Ford van with 360 CI engine, 4bbl carb and automatic on same roads that got 4 MPG at best, it was a sipper.

Rear drive tires are BF Goodrich BF Goodrich T/A KO LT235/75R15 and front tires are General Grabber 27X8.5R14 LT which is now off the market in 14" wheel size. General now went to a Grabber A/TX for the 14" wheel size.

There is allot more rolling resistance with the AT's than street tires.
With street tires, I was getting about 18.8 MPG Highway with the same 4.56 gear ratio diff.

All the MPG stats is with same tires and all the same mandatory Federal Emissions equipment installed and functioning as it was when it was manufactured for Federal emissions standards.
At least it does not have to have all the CA crap as a 100% CA standards vehicle would. No CAT and fewer vacuum and thermo-vac control gizmos.

 

[MoaByte]

Curious, but how old is your timing chain? Have you checked your valve lash lately?

I installed A/F ratio meter on my type IV VW with dual carbs. It wasn't hard to do, just weld a O2 sensor port in the exhaust and wire it up.

I recently install a Holley Sniper on my FJ60, I like it so much that I was looking into installing one on my 20r.

 

[HS44]

This 78' 20R motor has the 2 row timing chain with about 60K miles on it.

I always check and adjust valve lash every other oil change and sometimes more frequently and when I do, it usually only needs a very slight adjustment on one or 2 valves. I do valve lash adjustment very carefully and use a go/no-go technique, I use a 0.001" thicker feeler gauge for the no-go instead of the 0.002", which is the way a go/no-go feeler gauge is if you go to the auto parts store and get a go/no-go type of feeler gauge.
Also, I installed a Ford 90° oil filter adapter just so the oil pressure comes up right after startup even if the flapper check valve were to leak back into oil pan. Oil pressure gets to the top end ASAP.

I have used AMSOIL 20W-50 because of the High-zinc formula for the last few years.

I removed the oil pan to repair the gasket; I was in a pinch and needed to get oil right away and I wasn't going to wait for the AMSOIL to get shipped, so after reading the various test results that I could find and comparing the data, I ended up deciding on Shell Rotella T6 15W-40 Full Synthetic Motor Oil.

I know the Shell oil is not the low MPG issue I am having because; 1, The difference between the oils is not significant enough for that much difference in MPG. 2, the MPG was same as it was just before the change and 3, The increase of gas consumption came after going over 1,000 miles of freeway driving and just kept steadily increasing to the high rate it is now.

Transmission and Differential oil are fresh and the rear wheel, (axle), bearings were just replaced.... ...Yes even the U Joints were inspected and greased.

The center driveshaft bearing does need to be replaced soon because the rubber dampening part of it's mount is worn and it has a bit too much movement, but the bearing is still good with no leaky seals or end-play and it turns normally as if new, plus there are no major vibrations that I can tell coming from the driveshaft.

There are no fuel line or gas tank leaks and it has new fuel filters; (I added a primary fuel filter after I changed to an external fuel pump which I did years ago so I know it is not that).

Distributor is fairly recent rebuilt and timing is same at all RPM's as was before the MPG went down so I doubt it is timing related, but I am not 100% sure that timing is not contributing somewhat. Timing is not the major low MPG issue either.

Tire air pressure is same as before.

Bottom line, it is at least mostly engine/fuel delivery issue.

Anyway, I am still wondering if the way I was saying to remove air input into the exhaust system to get a baseline for the AFR Meter so I could compensate for the air injection into the exhaust manifold would be close enough so as I would 'most likely' be able to make carburetor and whatever distributor/timing adjustments using it to fine-tune 20R engine for best results and maybe get better performance and higher MPG and afterwords, after I reinstall the exhaust air injection, I could monitor the AFR so I can better keep it tuned.

I guess I may end up trying it before I get any definitive answers to that.