Mystery fuel consumption on v345 scout 2

[Bob Prohaska]

My '72 Scout 2 with v345, tf727 and Holley 4412 carb and Pertronix
ignition turned in about 13 mpg in mid-July and ran beautifully. This is
about the best mileage it's delivered in sub-100 mile trips. In mid
October it turned in 11 mpg and ran very badly, missing, stumbling
and stalling off-idle when warm, with a very rich smell to the exhaust.

Close inspection revealed a dislodged vacuum advance hose
and a vacuum leak at the carb flange (loose bolts). Timing was at
15 degrees BTDC, idle a bit slow at ~650 rpm. Idle mix screws were
within a couple turns of correct and not very sensitive to adjustment.

The faults were corrected, timing set to 10 degrees BTDC and an identical
~40 mile test run taken. The mileage dropped to around 8 mpg. Idle was
good, no stumble off-idle, but a subtle hunt could be heard (not felt) on gentle
acceleration. The tailpipes have light soot, I can't find any visible fuel leaks.
Hard acceleration is smooth and brisk. These results baffle me.

I looked for threads related to gas mileage and found "My Scout drinks fuel" but
I couldn't follow the link suggested by Scoutboy74. Any suggestions appreciated.

Thanks for reading,

bob prohaska

 

[Scoutboy74]

The Holley List 4412 isn't necessarily the best choice for any SV8 engine. It's intended to be a performance carb. That being said, it's what you have and it should be capable of doing a little better than it seems to be doing at the moment. What choke design does this carb have? Is it functioning properly? More specifically, is it opening fully once the engine has reached operating temp?

 

[int77345]

did you tune the carb jets any ever ? i bet your rich to start with .

this new even worse rich condition, sounds like a leaking or blown power valve.

is your distributor car tight ? loose wires ?

 

[Robert Kenney]

Does it seem to have the same power that it did when it pulled 13mpg?
First verify that the air filter is clean. Fuel contamination in the oil could easily be a leaking fuel pump diaphragm. Check for fuel smell of the oil.
If the truck is in it's stock configuration, one side of the exhaust will have a temperature controlled exhaust valve that should be closed when cold and open as it warms up. This is designed to aid in quicker warming of the intake manifold by forcing exhaust through a passage in the manifold under the carb by creating a exhaust pressure difference between one side ant the other. If that valve is staying shut, the backpressure will kill gas mileage.

 

[Bob Prohaska]

The choke is automatic and works correctly.

The main jets were tuned when I bought the carb in the
late 1980's. The car has run well enough since that it
seemed pointless to replace the 4412.

Good call on the air filter. It can't be the whole problem,
since the problem emerged while sitting in the garage between
drives two months apart, but it surely doesn't help.

WOT power seems reasonable. It's never been a rocket, but
performance is decent compared to the last time it ran right.

No hint of trouble with dist cap or wires. No signs of sparking
on the wires when examined in the dark.

No smell of gas in the oil. An extra gallon of gas in the
sump would be pretty obvious on the dipstick

Power valve has been on my suspect list, but wouldn't it
interfere with idle/slow running also? Idle is very good.

One puzzle is how sensitive the idle speed should be to
adjustment of the idle screws. They can be rotated a couple
turns either side of what seems to be best with a noticeable
but slight change in average speed. The idle has always hunted
10-20 RPM even at the best of times. I always tuned the idle
a roughly per the emissions procedure, but not quite so lean,
for the sake of fuel economy.

Another puzzle is the slight "warble" in the exhaust note on
gentle acceleration. It's fast, a few cycles/sec, and not enough
to feel, only to hear.

The choke is automatic and works correctly.

The main jets were tuned when I bought the carb in the
late 1980's. The car has run well enough since that it
seemed pointless to replace the 4412.

Good call on the air filter. It can't be the whole problem,
since the problem emerged while sitting in the garage between
drives two months apart, but it surely doesn't help.

WOT power seems reasonable. It's never been a rocket, but
performance is decent compared to the last time it ran right.

No hint of trouble with dist cap or wires. No signs of sparking
on the wires when examined in the dark.

No smell of gas in the oil. An extra gallon of gas in the
sump would be pretty obvious on the dipstick

Power valve has been on my suspect list, but wouldn't it
interfere with idle/slow running also? Idle is very good.

One puzzle is how sensitive the idle speed should be to
adjustment of the idle screws. They can be rotated a couple
turns either side of what seems to be best with a noticeable
but slight change in average speed. The idle has always hunted
10-20 RPM even at the best of times. I always tuned the idle
a roughly per the emissions procedure, but not quite so lean,
for the sake of fuel economy.

Another puzzle is the slight "warble" in the exhaust note on
gentle acceleration. It's fast, a few cycles/sec, and not enough
to feel, only to hear.

Would these symptoms be consistent with plugged/restricted air
jets? I tried squirting carb cleaner in the four air jets in
the front of the choke box. None seemed plugged, at least not
up top in the choke cavity. Maybe down below in the metering
block? Carb cleaner got into the barrels, but maybe it should
go elsewhere too.

There's no thermal valve on the exhaust, but there is a thermostatic
control on the air intake horn. It works correctly.

Thanks very much for all the replies!

bob prohaska



Would these symptoms be consistent with plugged/restricted air
jets? I tried squirting carb cleaner in the four air jets in
the front of the choke box. None seemed plugged, at least not
up top in the choke cavity. Maybe down below in the metering
block? Carb cleaner got into the barrels, but maybe it should
go elsewhere too.

 

[int77345]

"Power valve has been on my suspect list, but wouldn't it
interfere with idle/slow running also? Idle is very good."

I dont think the power valve leaking would affect idle much if at all. because the power valve comes in to function with the jet circuit, i think fuel would have to be flowing through the jets to to put any pull on the power valve system.

this problem came on after the scout say a while correct ? wonder if your float and needle valve is stuck open. some times needle valves get dirty gummy and done close good. and some times floats leak, or saturate and sink keeping the needle open.

 

[FDChappie]

Loosing timing advance might cause what you are seeing. If you have access to a good timing light, check your total advance.

 

[Bob Prohaska]

I'm under the impression that the power valve diaphragm has fuel on one side and manifold vacuum
on the other. If the diaphragm leaks, rather than the valve itself, it would deliver fuel direct to the intake
manifold all the time. Is this mistaken?

It looks as if fuel comes out of the left-hand venturi booster when the engine is revved a little above idle.
Considerable additional revving does not cause fuel to come out of the right-hand venturi booster. This
all with choke open, engine warm and idling nicely. That looks very wrong to me. I've probed the main air
bleed jet on both sides, they seem clear. Aerosol carb clean squirted into either main air bleed comes out
at the both venturi boosters, a bit more on the side I'm squirting. That's a surprise, I thought the two circuits
were totally separate.

Regarding timing, I'm using a strobe and the advance looks reasonable at least when I'm measuring it.
Given the fuel delivery mismatch side to side this doesn't look like a spark problem to me.

Others may differ and I'd be curious to know if that's the case.

Thanks for reading and all your help!

bob prohaska

 

[Bob Prohaska]

It looks as if some portion of the trouble was a fouled sparkplug:

http://www.zefox.net/~bp/scoutplugs/IMG_0023.JPG

I've never seen a plug look like that. It's #7, rear driver side.
A very casual (sloppy) compression check showed 90 PSI in
the cylinder, so I chipped off the crust (dry, brittle and only a
little hard), checked that the plug would spark on a lawnmower
magneto and reinstalled it. The cylinder appears to fire (exhaust
seems to warm up) but it still idles poorly, probably because of
earlier misguided adjustments.

Does anybody have an idea what might cause that sort of fouling?
The other plugs look relatively decent, photos are in the same place

Index of /~bp/scoutplugs

The plugs are early Bosch platium plus, with only about 30k miles
on them, though they're around 20 years old.

This all feels like a small mount of progress, but I'm not very confident
of the direction....

Thanks for reading!

bob prohaska

 

[Scoutboy74]

With 30k on them, I'd say your entire set of plugs is due for replacement. You got the goodie out of them. I know new plugs are far from cheap these days, but I think it's that time for you. I recommend NGK 3332 for these engines. See what, if any difference is made. If it runs well enough to go for a drive, get it warmed up good and take it for a rip. Get yourself to a location where you can safely switch off the engine while at part throttle cruise @ 40 mph and safely coast off to the side of the road. Have your plug wrench handy and pull some plugs at random, but most especially #7 and see what they look like. This will get you your most accurate visual of how the combustion situation is going. Also, getting back to the original post, a 40 mile trip probably isn't long enough to make definitive fuel consumption conclusions.

 

[Bob Prohaska]

With 30k on them, I'd say your entire set of plugs is due for replacement. You got the goodie out of them. I know new plugs are far from cheap these days, but I think it's that time for you. I recommend NGK 3332 for these engines. See what, if any difference is made. If it runs well enough to go for a drive, get it warmed up good and take it for a rip. Get yourself to a location where you can safely switch off the engine while at part throttle cruise @ 40 mph and safely coast off to the side of the road. Have your plug wrench handy and pull some plugs at random, but most especially #7 and see what they look like. This will get you your most accurate visual of how the combustion situation is going. Also, getting back to the original post, a 40 mile trip probably isn't long enough to make definitive fuel consumption conclusions.

Are there any longer-life type plugs compatible with the v345? Changing plugs is difficult enough to be worth at least
some extra expense. Getting matched reach isn't too hard, but finding a heat range match for the wr9fp in a
different brand seems more difficult.

It looks as if there were several problems. The fouled plug was one, but there turned out to be a few vacuum leaks that
had accumulated over the years (carb mounting bolts, brake booster hose and maybe PCV valve). A new air filter couldn't
have hurt, either.

Cleaning the fouled plug by flaming the insulator with a plumber's torch seems to have got it firing, at least for a slow
putt around the block. I'll test it a bit more seriously tomorrow.

One odd thing is the amount of RPM drop when the auto trans is put into gear at standstill. Idling in neutral at 740 RPM
the tach drops to around 540 RPM in gear. That feels like more than usual, though I've never actually measured it before.
Timing is at 15 degrees initial, throttle response is slightly hesitant but there's no off idle bog or misfire, it just doesn't pull
instantly. Idle vacuum is about 18 inches, which seems good.

Response to idle mixture screw adjustments is much clearer at low speeds. I balanced the idle mixes at 500 RPM and
then set the idle speed to ~740 RPM. The cylinder with the fouled plug compression tested at 150 PSI on the starter, a
very pleasant surprise.

Thanks for your help!

bob prohaska

 

[Scoutboy74]

Heat range matching seems akin to over thinking for this application. I've personally had great performance from the NGK plugs I mentioned and I know they've become a pretty popular choice within the IH community over the past decade. @ 150 rpm drop into gear is pretty normal. 200 is a bit on the high side. How does the engine run while in gear with your foot on the brake? Stumble at all? The brake booster check valve and even the brake booster itself can be a source of leaky vacuum. Compression testing without all spark plugs removed and the throttle not blocked wide open doesn't provide useful results.

 

[Bob Prohaska]

Heat range matching seems akin to over thinking for this application.

I'm commonly accused of over thinking and usually guilty

I've personally had great performance from the NGK plugs I mentioned and I know they've become a pretty popular choice within the IH community over the past decade.

That's very helpful to know

@ 150 rpm drop into gear is pretty normal. 200 is a bit on the high side. How does the engine run while in gear with your foot on the brake? Stumble at all?

Stepping on the brake doesn't do anything drastic. Shifting into reverse or drive with a foot on the brake it slows a lot and gets
rougher but doesn't seem to outright miss. I tried increasing the idle to near 800 RPM, which helped a bit but feels and sounds
slightly frantic.

The brake booster check valve and even the brake booster itself can be a source of leaky vacuum.

Aye, there's one rub. Looks like the booster is leaking. Funny thing is that it still seems to work correctly.
Capping off the booster-to-manifold port didn't drastically change the idle, opening the port to air promptly
kills the engine. Clearly the booster leak isn't good but it does not seem to dominate the situation. It could
be old news.

I tried capping off the booster port, thinking that would lead to a rich idle. To my surprise, it didn't. The other
fuel-related oddity is the left-hand booster venturi dripping gas over about 1500 RPM. The right-hand
side doesn't drip at anywhere near that speed. Fuel level is just even with the sight port threads, correct
at least by the book. Both booster venturis dripping would suggest a high fuel level, but just one?

I started out thinking this was a carb issue until the single fouled plug turned up. Maybe it still is a carb issue.

Compression testing without all spark plugs removed and the throttle not blocked wide open doesn't provide useful results.

But doesn't 150 PSI under any circumstances suggest the rings and valves are functioning? That's all I meant to check.

Thanks for reading, and all your counsel!

bob prohaska

 

[Scoutboy74]

I'm commonly accused of over thinking and usually guilty

LOL! I suppose most of us are guilty of it at one time or another.

Stepping on the brake doesn't do anything drastic. Shifting into reverse or drive with a foot on the brake it slows a lot and gets
rougher but doesn't seem to outright miss. I tried increasing the idle to near 800 RPM, which helped a bit but feels and sounds
slightly frantic.

Aye, there's one rub. Looks like the booster is leaking. Funny thing is that it still seems to work correctly.
Capping off the booster-to-manifold port didn't drastically change the idle, opening the port to air promptly
kills the engine. Clearly the booster leak isn't good but it does not seem to dominate the situation. It could
be old news.

I'd be curious to see what your Vac reading is in Park, both with the brake booster hose connected and brake applied, and also with the hose capped off. Back in my Scout's former auto trans days, (T-19 now), I often had my park idle speed bumped to @ 800 just so my in gear with brake applied idle could be a bit higher. I never felt like the engine was frantic or frenetic at that slightly higher idle speed. My ear could never tell that much difference between 725 and 800 revs while idling in Park. I relied on the tach readout to know for sure. I agree that this is most likely some sort air/fuel delivery issue. Perhaps some internal orrifice has a blockage. Still several variables that haven't been completely accounted for.

 

[Bob Prohaska]

LOL! I suppose most of us are guilty of it at one time or another.


I'd be curious to see what your Vac reading is in Park, both with the brake booster hose connected and brake

Idling in park near 600 rpm the vacuum reads 21 inches and doesn't change when I step on the brake.
If I engage reverse while holding the brake vacuum falls to 18-19 inches, the gauge zeroes at 2 inches.
It really doesn't appear that the booster leak, though unhelpful, is the main problem.

applied, and also with the hose capped off. Back in my Scout's former auto trans days, (T-19 now), I often had my park idle speed bumped to @ 800 just so my in gear with brake applied idle could be a bit higher. I never felt like the engine was frantic or frenetic at that slightly higher idle speed. My ear could never tell that much difference between 725 and 800 revs while idling in Park.

I guess it's the bang into gear that makes me cringe when the idle's high.

I relied on the tach readout to know for sure. I agree that this is most likely some sort air/fuel delivery issue. Perhaps some internal orrifice has a blockage. Still several variables that haven't been completely accounted for.

Any idea what a reasonable plug wire resistance should be? On #7 (fouled) I got about 16 kohms. #3 (clean) showed
about 10 kohms. I was expecting less than half that much but haven't been able to find any credible numbers. The plug
wires were put in when the car still had points and condenser. Like the plugs, they're probably due for replacement. Still,
I hesitate throwing parts at a problem I don't understand. The single fouled plug seems significant but I can't guess how.

I keep hoping there's something simple I've forgotten to check, but the easy list is getting short.

Thanks for your patience!

bob prohaska

 

[Robert Kenney]

SAE recommends 12kohm/foot. This is only for the carbon infused glass core resistance wires. The mag core / wire wound wires should be much lower. Check all of them and see if that one is an outlier for it's length. If it is significantly higher resistance, change them all.

 

[Robert Kenney]

IMHO, that fouled #7 plug seems to represent water contamination. I have never seen that formation or color on anything other than an engine that was eating water. I certainly hope I'm wrong. I have never had issues with Champion sparkplugs in boats, race cars, street cars or aircraft. Nor have I experienced problems with AC plugs. All plugs can fail, only one I've ever had that did fail out of the blue was an old set that was in my 68 Travelette after a run to Mammoth and driving around pig rich. Went out to start it and one hole was dead. just slapped another one in and down the road I went.

Just install new traditional plugs all around and drive it some number of miles (20?) recheck.

 

[Bob Prohaska]

IMHO, that fouled #7 plug seems to represent water contamination. I have never seen that formation or color on anything other than an engine that was eating water. I certainly hope I'm wrong.

By water do you mean coolant? A head gasket leak would certainly explain the single plug. However, there's no hint of coolant
in the exhaust and no noteworthy loss of coolant in the reservoir. If there's a coolant leak it's not big..

I have never had issues with Champion sparkplugs in boats, race cars, street cars or aircraft. Nor have I experienced problems with AC plugs. All plugs can fail, only one I've ever had that did fail out of the blue was an old set that was in my 68 Travelette after a run to Mammoth and driving around pig rich. Went out to start it and one hole was dead. just slapped another one in and down the road I went.

Just install new traditional plugs all around and drive it some number of miles (20?) recheck.

For the moment I'm tempted to put the spark plug question aside and go back to fuel as the culprit:
This morning on a cold start the engine fired, revved up and as the choke plate opened there could
be seen a cascade of fuel from both booster venturis. The engine started to stumble, so I shut it off and
took out the fuel level sight plug. Fuel ran out, indicating a clearly too-high level. It wasn't coming out
of the bowl vent standpipe, so the valve wasn't stuck wide open.

Took out the needle & seat, could find nothing visibly wrong, put it back and readjusted the fuel level.
The engine ran, turning the level down sufficiently stalled the engine, suggesting the valve did have
control of the fuel level. So I reset the level, adjusted the idle screws and for a little while the engine
idled as in the "good old days". A shift into reverse with brake on produced a ~150 RPM rev drop
and the engine remained smooth, much better than before.

A one-mile test drive at residential speeds rather quickly repeated the rough idle and sluggish throttle
response, but by the time I got the car home and removed the sightplug the level looked roughly where
I set it, certainly not over the lower edge of the sight hole.

An intermittent problem in the float valve seems more plausible than an intermittent overpressure from
the fuel pump, so I'll study the valve more carefully. If intermittent pump overpressure is a possibility
please let me know. I can't imagine how it might come about.

Thanks for writing!

bob prohaska


bob prohaska

 

[FDChappie]

It sounds like there maybe some water in your fuel. It doesn't flow through the idle circuit due to having a higher surface tension. You could try some denatured alcohol to emulisify the water. Or burn the rest of the tank and try some fresh quality gas.

 

[Robert Kenney]

Some thing like one plug having the odd look points to that cylinder as the culprit but with out installing a new plug and retesting it would be very difficult to say for sure.
Verify no water in the fuel by either pumping some into a clear container, water will be clearly visible at the bottom. Or by draining some from the tank if the tank has a drain plug. Water should push past the threads once loose.