79 CA bus - poor fuel economy

[airkooledchris]

ok, so I have been posting to threads here and there while testing various FI and other bits on the bus trying to track down the cause of my poor fuel economy.
Im starting to clutter threads related to specific systems with my issues and figured it was time to put this into one place.

To summarize:

Fuel Pressure Test
I disconnected the vacuum hose from the pressure regulator and plugged the hose
fuel pressure at idle (1000 RPM) was 40 PSI, which is 5 higher than spec and 3 higher than the tolerance listed
With vacuum hose connected, at idle (1000 RPM), fuel pressure was 32 PSI, which is 4 higher than spec and 2 PSI higher than the tolerance listed
At full throttle and with the vacuum hose connected, I saw exactly 30 PSI

I run slightly larger than stock tires, there was some concern this was throwing my MPG numbers way off:
I went on a longer drive to really make sure the odometer was on and in the end I need to add .0414 to every mile
On the most recent fill up, the worst one, instead of 9.41 MPG it would have been 9.8 using 10.488 gallons in 102.818 miles VS 98.7
I think I can rule out overstock tires for now, or grossly inaccurate odometer

Temp 2 sensor
I installed a new one, so we'll have to wait and see if this helps on the next fillup.
Couldn't confirm one way or the other that this was faulty, so I just threw that one at it to be sure.

Microswitch
The Microswitch failed the Bentley test, so I swapped in a good used one (I MAY have failed testing it properly, but like with the Temp 2 sensor, if I have a good working one that I can bench test properly, I may as well put it in. I think it had failed open, which theoretically means it wasn't overriding the O2 sensor at WOT, though that also means it would have been running leaner than it should have.

Running the proper 79 CA parts?
Yes, ive confirmed thus far that I have the correct electronic ignition, coil,, oxygen sensor, AFM, and 13 prong DoubleRelay
STILL NEED TO CHECK THE ECU
My Bentley does not mention anything about an Idle Stabilizer, though on page 34 of the AFC FI troubleshooting manual they show this unit.
Where your supposed to connect it to itself when adjusting the ignition timing, then plug it back into the box when your done.
I don't have this on my bus. I can't see anyplace on the firewall where something WOULD have been and where something is now missing.
Maybe some 79 CA models didn't have the idle stabilizer, or perhaps they meant that it's 79+up only, meaning starting with the aircooled CA Vanagon for the model year 1980 but began production in 1979?

On the opposite side of the firewall is another relay looking thing and it has one un-accounted for wire coming out of it, black with a white stripe:




What do the plugs look like?

Look OK.

Compression:
#3 = 120
#4 = 115
#1 = 114
#2 = 120


What's next on the list for stuff to test?
Condition of catalytic converter? - though without removing the whole exhaust and pulling this from the system, I don't see how you could actually check it.
The connections between it and the bits it's connected TO, are pretty rusty looking. It doesn't have any holes and it feels solid, but I think disconnecting it from everything else just means replacing it. That sounds pricey if it doesn't end up being something I needed to do.

More FI testing probably, Thermo Time Switch, Auxillary Air Regulator, Injectors, Series Resistance Block, Cold Start Valve, Thermostatic Valve (though Bentley is a little vague on what exactly this looks like, unless the EEC Valve replaced it? - my EEC is working correctly.)


All of the details of this saga are now in one place, and thanks to those who have been helping by replying to my posts in other threads.

[vwlover77]

Is the engine totally stock, particularly the camshaft?

[airkooledchris]

Is the engine totally stock, particularly the camshaft?

As far as I know, it is. The case is original to the bus, the heads are AMC.
Hydraulic cam/lifters. I can't guarantee it, but I know the shop where it was built (about 6+ years ago at least) and they don't do anything other than stock factory spec builds, and will send you elsewhere if there's something you want other than that. I don't like them for not even considering other parts in a build, but at least you know (generally) what to expect from it.

Im lucky, I suppose, in that if I really get stuck on this I could take it to them and see what they think, but im not totally thrilled with the shop (they always have this 'were SO busy' attitude, like you should be grateful they will speak to you) and would rather discover and correct this on my own if possible.

[dingo]

I use Bosch electronic ignition without idle stabilizer...and it is not a problem, so i would eliminate that from your investigation. Also the extra wire on the alt/reg harness is non-issue.

Seems like if more fuel was being used than was required by the engine then the plugs would show it. Otherwise, some obstacle in the drivetrain is causing the engine to work harder and require more fuel............does that sound logical ? maybe not ?

if it was me, i would first dial in the idle and eliminate that....then clean the plugs to a shine, then do a road test at open throttle, shut down, cool and inspect plugs. All that only if you dont have access to some a/f device.

longshot: switch the exhaust segment of your Vanagon with the 02 sensor. Then drive around with voltmeter reading the 02 signal...poor man's a/f meter

[airkooledchris]

I couldn't update my original post, so ill add it as a reply:


UPDATE 1/16 - The replacement Temp 2 sensor didn't look exactly the same as my spare or the one that came out of the head. It was every so slightly longer. Also, the hole that the T2 sensor screws into by #3 was completely cross threaded/stripped when I pulled the old, so the new was equally painful to try and drive it there tightly enough.
Today I noticed that since I have the AMC heads, there is a hole over by #2 cyl, and thankfully the tinware was CLOSE to being aligned to gain access, so with a little loosening of tin here and moving this and that out of the way, I now have a nice clean T2 sensor install over on this side instead.

I set the AFM to 1.5 turns out from max rich at the idle bypass, set the idle to 975 RPM and reset the timing to 28* max advance. This AFM had been nearly at full rich, which I had originally set to 4 turns out to get to halfway before setting the idle, but the bus *seems* to like this setup better. I'll try it the other way again when it's stone cold if it's more ideal for a starting point.

Update 1/17 - The above steps seems to have helped quite a bit with the morning routine. This morning on a deal cold startup it sounded very happy and healthy, but once warm my idle was 1150 RPM, so I backed the idle down (not the idle mixture) 1.5 turns and that put me closer to the 975 I was shooting for. Ideally it'll still be happy in the morning when dead cold and won't stumble and hunt ..

oh yea, and maybe my next MPG readings won't be soo bad. I re-filled the tank, averaged 9.8 MPG, but there was quite a bit of time just idling in the driveway while setting things right and gas overflow. looking forward to my next real MPG reading to see where im at now with a few changes made, before moving on to the rest of the testing and fiddling.

[Amskeptic]

I couldn't update my original post, so ill add it as a reply:


UPDATE 1/16 - The replacement Temp 2 sensor didn't look exactly the same as my spare or the one that came out of the head. It was every so slightly longer. Also, the hole that the T2 sensor screws into by #3 was completely cross threaded/stripped when I pulled the old, so the new was equally painful to try and drive it there tightly enough.
Today I noticed that since I have the AMC heads, there is a hole over by #2 cyl, and thankfully the tinware was CLOSE to being aligned to gain access, so with a little loosening of tin here and moving this and that out of the way, I now have a nice clean T2 sensor install over on this side instead.

I set the AFM to 1.5 turns out from max rich at the idle bypass, set the idle to 975 RPM and reset the timing to 28* max advance. This AFM had been nearly at full rich, which I had originally set to 4 turns out to get to halfway before setting the idle, but the bus *seems* to like this setup better. I'll try it the other way again when it's stone cold if it's more ideal for a starting point.

Update 1/17 - The above steps seems to have helped quite a bit with the morning routine. This morning on a deal cold startup it sounded very happy and healthy, but once warm my idle was 1150 RPM, so I backed the idle down (not the idle mixture) 1.5 turns and that put me closer to the 975 I was shooting for. Ideally it'll still be happy in the morning when dead cold and won't stumble and hunt ..

oh yea, and maybe my next MPG readings won't be soo bad. I re-filled the tank, averaged 9.8 MPG, but there was quite a bit of time just idling in the driveway while setting things right and gas overflow. looking forward to my next real MPG reading to see where im at now with a few changes made, before moving on to the rest of the testing and fiddling.

Find a dead-level bit of asphalt. Set the car rolling with a good push at the driver's door pillar. Does the car slow to a stop imperceptably, or do you feel it stop? Repeat in reverse. Report back.
Colin

[Amskeptic]

so, to answer the question "which brakes are dragging, the front or rear?"

YES.

Im not familiar with what a sticking front brake means (new caliper, or adjustment of some sort?)

Unstick caliper, replace brake hose, replace caliper.

Those are the usual culprits in order. Hey man, we're on top something here, heh?
See ya in BRAKES.
Colin

[airkooledchris]

to FINALLY update this thread with some numbers, for anyone wondering what stuck brakes will do to your fuel economy.....

last 3 fillups prior to repair netted 9.4, 9.6 and 11 MPG. the 11MPG was suprising as that was higher than most id had seen so far...

anyway, with 94.4 miles on the clock since the brake repairs were finished, nearly every single one of those miles in town and short distance driving - im getting 14.1 MPG now.

looking forward to seeing what I get on the highway now, and the next test is to drive it some highway miles and find a good spot to kill the motor and coast into a parking spot to check the plug colors.

[Amskeptic]

to FINALLY update this thread with some numbers, for anyone wondering what stuck brakes will do to your fuel economy.....

last 3 fillups prior to repair netted 9.4, 9.6 and 11 MPG. the 11MPG was suprising as that was higher than most id had seen so far...

anyway, with 94.4 miles on the clock since the brake repairs were finished, nearly every single one of those miles in town and short distance driving - im getting 14.1 MPG now.

looking forward to seeing what I get on the highway now, and the next test is to drive it some highway miles and find a good spot to kill the motor and coast into a parking spot to check the plug colors.

Thanks for the update. You fuel economy was getting better because the brakes were burning themselves away.

[airkooledchris]

the MPG hadn't improved any since the above posts, though most all of my driving is very short and in town, so ive been seeing around 11-12 lately. my head temps have been pretty high since I started tracking them, at highway speeds, so on a whim I disconnected my O2 sensor. It was my understanding that the computer would go to full rich with this disconnected and I wanted to see how it would effect my temps.

it was a drastic difference. I just did 2 full days of driving, climbing to 3000 ft and back down a few times, up and around bends, and all loaded to the gills with people, dogs and camping gear.

I got 17MPG and my head temps never went over 424*, with the max usually happening at about 418*.

Sure, it's not ideal to find a solution by disabling something the factory (as well as the engine and the computer) have come to expect, but it's an interesting thing to come across.

between fixing the faulty AAR and now this - the bus seems SUPER happy at all temps, speeds and inclines.

[dingo]

17 mpg whilst loaded to the gills...? not too shabby.

still, if you want to find out what your 02 sensor is up to...run a wire from it up to the cockpit..attach to pos lead of voltmeter, neglead to ground and keep driving....on 1V or 2V scale..see what it is spitting out

[Amskeptic]

on a whim I disconnected my O2 sensor.
I got 17MPG and my head temps never went over 424*,

In my CHT/LM-1 write-up, I found a very similar result.
When I finally adjusted the AFM to the IAC "ask the engine" method, I got a "pig rich" 11.5 that yielded the best CHT temps AND the best fuel economy 17.5 mpg 406CHT at 70-75 mph highway cruise?????
Colin

[Bleyseng]

ok, I get that kind of mpg when I set the AFR to 13 but I get 21mpg with it set to 14.3. CHT are cooler by a bit at 13-385F but at 14.3 they can hit 410F on a steep loong ass hill going on the Freeway at 70-75 in hot 80F weather. So I am fine with getting 21 mpg and seeing 410F on occasion.
Now I have forgotten what the AFR was before you started adjusting it Colin?

[Amskeptic]

Now I have forgotten what the AFR was before you started adjusting it Colin?

I did not have a CHT gauge all the way across the country, and probably am glad I did not see what I did to that poor engine.

http://itinerant-air-cooled.com/viewtop ... f=3&t=9460

[airkooledchris]

another interesting fact is that this happy rich running situation is with a NOS AFM, specific to the CA model.

this AFM is set from the factory with a near perfect match to the computer when deprived of the O2 signal it expects.

it would like it to be leaned out at least a hair, as when climbing hard I could take my foot out of the gas a little and it would respond better than pressed all the way (which wasn't ALWAYS reproducible, but it worked enough times to take note of the behavior) - but around town and during light driving it's perfect.