Carbed 2.3l n/a ... quite a bad mileage

[TuxStang]

Ok, it has automatic transmission (C3) and 3.08:1 axle, not the most economic set-up, but can't get better than 12mpg city, neither highway nor country side, same mileage whereever i drive, which is a bit too low for such an engine
That car had a better mileage before (well, in a way 'cause it was already ~16mpg) ... even with a dead PCV, vacuum hoses plugged at random, 0 initial timing, EGR left open, dist advance to intake vacuum (was running hot at idle when using timed-vacuum), dead dist cap, 30yo spark-plug wires, brittle spark-plugs (broke two only by sliding the socket on them), idle at 1400rpm in neutral ... every bit i did enhanced the way it ran except for mileage which got worse.

Status of the fuel hog :

• ~84.000 miles old
• vacuum hooses (new) reduced to minimal : distributor advance (timed vacuum), transmission modulator, brake booster, and vacuum gauge
• EGR blocked (thin aluminum plate with exhaust gasket material between valve and spacer) and disconnected (port plugged on carb)
• carb : rebuilt '77 Holley 5200 with new fuel filter, all vacuum ports blocked except timed-vacuum (distributor advance), electric choke installed but disabled (full open), new EGR to carb spacer
• initial timing set to 10deg
• PCV valve changed (hoose to oil separator a bit brittle but no leaks)
• almost new spark-plugs (NGK TR55 gapped to .040)
• new spark-plug wires
• new distributor cap, rotor, pick-up coil
• new ignition coil
• new air filter
• new thermostat : 180deg
• smog pump : removed (was dead), remaining check valve plugged
• cats : still one (close to exhaust manifold)

Carburetor setting :

• Primary
  
  • idle jet : 60
  • main jet : 140
  • air corrector : 195
  • emulsion tube : (hard to read) 95
  
  
• Secondary
  
  • idle jet : 50
  • main jet : 132
  • air corrector : 195
  • emulsion tube : (hard to read too) 05
  
  
• Idle mixture screw set to 1-3/4, vacuum drops ~1-1/2
• accelerator pump set to middle hole

That's way leaner than factory carb (had way bigger main jets) but didn't enhanced mileage.

While tuning the carb, engine hot (normal) in Neutral, can't lower idle rpm better than 1200rpm (~800 in Drive) with 20-21inHg (15-16 in Drive).
Vacuum is quite stable while driving but fluctuates a bit at idle (1inHg variation either in Neutral or Drive).
Exhaust fumes doesn't smell rich at idle. Oil doesn't smell gas. Clean coolant.
There's some fresh gas smell when under a bit more than moderate acceleration (climbing a hill for ex.) but didn't notice any cloud at exhaust (a minor grey one at full throttle however) neither detected any fuel leak.

Have check all vacuum leak sources i could think of with WD40 (don't have better) ... from what i can tell, cat is not clogged (vacuum doesn't drop to 0 when accelerating), vacuum doesn't seem to show a sticky, leaking or burned valve nor bad valve guide, don't see blow-by at the intake to air-filter nor at the PCV valve, oil pressure was good last time i checked (factory gauge already dead, aftermarket gauge dead since but indicated correct pressure when i used it, waiting for another one) ...
There's some knocking when cold that i haven't located yet but seems to disapear when hot (maybe my ears are not sensitive enough).

When i changed the pick-up coil of the distributor, i noticed the springs were a bit rusty ... are they the same as on V8 dist ? Haven't checked the timing curve as i was alone last time my buddy lend me his timing-light ... but if they are the same, i can use the two clean V8 springs i have from a spare dist.

Any idea where to look now ?

[ethangsmith]

Man, this is a real puzzler. You are running basically the same setup I retrofitted my 86 capri to. I have the 1977 5200 carb (only jetted quite a bit richer!) and all. I get about 18mpg around town out of my setup. I also have a C3 automatic but with 3.27 rear gears. Are you getting any pinging or sluggishness on acceleration? Does the engine seem to have power or does it feel weak? What do the spark plugs look like when you pull them out? Have you done a compression test? Also, what are the internals of the carburetor like? Is the enrichment system working properly and is the float adjusted properly? Your timing is set correctly as is your idle.

[TuxStang]

Haven't checked compressions yet ... will be for next month, don't have the tool.
Internals of the carb are great ... all passages plugs are new so it looks like a good, professionnal rebuilt. Float was set a bit conservative to prevent flooding (hate those copper floats but can't fit nitrophyls from original carb which are easier to adjust).

Will remove the spark-plugs tomorrow to look their color. Previous ones, with same mileage and factory carb, where brown on the isolator (so a bit rich, that's why i switched to the '77 carb), but show no sign of oil (compressions shouldn't be bad), detonation or flooding.

No pinging on acceleration ... a bit sluggish just when i floor (not on moderate acceleration) but i guess it's because of my conservative float setting and i don't do it often.

[FoxChassis]

The 'SVO/2.3 Turbo Specific' forum is not for natually aspirated 2.3L engine tech. This thread has been moved to the appropriate forum....

[TuxStang]

sorry

[TuxStang]

Here are the spark-plugs ... Thought i used the ones gapped to .040 but installed the ones gapped .060 instead.
They don't look running too rich ... but what's funny, is that all 4 dual colored on the isolator ... one half is quite white while the other half is brown. But it may be because those spark-plugs were used previously on a flooded 5.0 (we removed them before identifying the problem) so they were all black when installed on the 2.3l last week.

Installed the ones gapped to .040 this morning ...
This afternoon, i did again my EGR block-off ... removed the old gasket and installed a new aluminum plate with exhaust mounting paste (don't have better) on both sides. Will buy a better block-off once i've identified the thread of the EGR cross-over tube.

[SRM351]

Your plugs look to be in great shape, your fuel mileage figures are almost so bad I would make sure your calculation method is correct before I got bent out of shape about this. When I was getting 12mpg with my 351w, it was running quite rich and you could tell as much from the black, sooty plugs. A 2.3l getting 12mpg would have to be a super rich pig- your's obviously is not. Nobody's stealing your gas are they? Could be the transmission starting to slip too, have you noted any change in the cruising rpm?

[TuxStang]

Converter doesn't seem to slip as far as i can tell ... a bit slow to answer compare to the C4 of the Pace Car but according to a friend more usual to C3s, there's nothing wrong ... may require a band adjustment as i guess it has never be done (automatic transmissions were not popular here in the 80s so mecanics didn't always maintain them perfectly). Fluid is not old, it was changed less than 2000miles ago and still good color/smell ... wouldn't last if transmission was slipping.

Fuel needle is at the same level i left it when i stopped every time i start again ... plus one of the first things i bought was a locking gas cap ... so no gas steal.

Plan to do an oil change next week-end ... doesn't smell gas so pump not leaking inside the block but starts to turn black and i don't know what viscosity was used as previous change was done by previous owner, and as soon as possible, change all rubber fuel lines.

Mileage calculation i use is (added fuel volume in liters * 100)/kilometers since refill
Last refill was 6.34gal for 87miles ... so ~13.7mpg (best mileage since weeks).

[etc1006]

Just a thought.. Did you put the jets in the right hole? I did a carb on a beater Plymouth Horizon(someone put sugar in the tank of the P.O.) I had years ago and got the jets swapped when I put it back together. It ran like a raped ape with the secondary jet in primary, but the gas mileage sucked like all hell.

[TuxStang]

On the factory carb, which was rebuilt some years ago and that i rebuilt when i bought the car this year, primary and secondary jets seemed strange with the bigger jet on primary so i inverted them (was 223 pri/179sec and is now 179 pri/223 sec) ... it didn't changed the mileage.
On the actual carb, which is professional rebuilt, i haven't changed anything ... just removed one part at a time when i received it to get the numbers ... this carb is jetted way leaner than the factory carb.

[ethangsmith]

Lean mixes can cause poor fuel economy as well because the engine must work harder to produce power. However, your spark plugs look like your fuel mix is about right. I would definitely consider a compression test.

[TuxStang]

A compression problem should be visible at the exhaust tip and/or at the vacuum gauge ... none show any sign of piston ring or valve failure ... but i plan to do one as soon as i can buy the tool.

[SRM351]

Mileage calculation i use is (added fuel volume in liters * 100)/kilometers since refill
Last refill was 6.34gal for 87miles ... so ~13.7mpg (best mileage since weeks).

So your last fill up you averaged 17 liters per 100 kms? That's Hummer territory!

[TuxStang]

Yep ... 17l/100 against a usual 19l/100 (this week, the way the needle drops means i'll be closer to 19 than 17).
That's a bit better than the Pace Car on the same usage (20miles a day in city) ... but the Pace Car is a 5.0 and has a 2.47:1 axle.

[gr79]

While tuning the carb, engine hot (normal) in Neutral, can't lower idle rpm better than 1200rpm (~800 in Drive) with 20-21inHg (15-16 in Drive).
Vacuum is quite stable while driving but fluctuates a bit at idle (1inHg variation either in Neutral or Drive).

Mine was like that one day. Ran fine but sucked up fuel like a old musclecar. The per mile fuel cost was like paying a taxi.
I was playing with the vac hoses, nothing else. Its now 20+ again. Conclusion: engine and carb are sensitive to vac routing.
Go back over the vac hoses and routing. When they are connected right, the engine will idle with a rock steady 18+ vac reading and rpm. Should be able to set warm idle under 1000 rpm. Disconnected, broken, plugged stuff somehow messes with the calibrations.
When you disconnect the dist. vac line, does the engine rpm pick up or want to stall? This was where i started after setting the timing.
Advanced timing till she spark knocked under load then backed it down so it never knocks. Locked it down.
Time consuming, but worked for me and one less variable to deal with. Change one thing at a time and keep posting notes.

[TuxStang]

All remaining vacuum hoses are brand new ... they are multi-fuel hoses.
I've routed minimal vacuum hoses ... timed-spark to vacuum advance, manifold to transmission, manifold to brake-booster and manifold to vacuum gauge (this one is silicon). There are still some plugs that are factory ... i'll order a plug assortment next week and compression tool, that mileage is running me out of cash quicker than expected
There's also a hose from fuel-tank to charcoal canister. Charcoal canister has no other hoses on it so that might play on tank vent ... try today to drive with the tank cap un-seated to see if it helps.

Now that i think of it ... this week-end, i unplugged the vacuum gauge while the engine was running to help tuning the carb of a friend's II ... idle didn't change, neither up or down ... but shut the engine and forgot that ...

[KevinK]

I bought a 79 Mustang with a blown 2.3. After rebuilding the motor, it started to run poorly. Checked the timing etc. Turns out the new spark plugs were bad. While yours pictured looked ok, is it just me or do the electrode tips seem pretty tiny on you plugs? Motorcraft plugs are the best and Champions were the ones that went bad on me.

BTW, you did verify the choke is opening right?

[TuxStang]

Choke is inactive ... upper flap always vertical. I have hard times starting sometimes and need to compensate with throttle for about 1-2min before getting a good idle but it's ok ... i drove the Pace Car that way for months without any loss of mileage.

Electrode tip is small but it's because those are NGK TR55 IX ... a bit overkill but that's to drive while i order the right plugs.

Nobody knows if the springs for mechanical advance are the same as in V8 distributors ? as they are pretty rusty, i can change them.
Made a partial (was interrupted) note of the actual mechanical advance curve this Sunday :
Idle => 10
1000 => 10
1500 => 13
2000 => 14
2500 => 17
3000 => 19
3500 => 24
Don't remember which slot is used neither its value.

[SRM351]

Now that i think of it ... this week-end, i unplugged the vacuum gauge while the engine was running to help tuning the carb of a friend's II ... idle didn't change, neither up or down ... but shut the engine and forgot that ...

You mean you basically created a massive vacuum leak and it didn't affect the idle or you unplugged the gauge and then plugged the hole?

[TuxStang]

Well ... yes ... i unplugged the gauge from the inside of the car with engine running and idle didn't changed.
Will check that again when back home so the engine will be at temperature.

[TuxStang]

Just checked and yes, when i unplug the vacuum gauge engine running, idle doesn't change at all ... so there's still a massive vacuum leak somewhere.

Shopping list :
_ vacuum plugs of various sizes
_ EGR delete plate
_ EGR to intake gasket
_ transmission vacuum modulator (doesn't seem to leak but ...)
_ spark-plugs (Motorcraft AWSF42CF4)
_ fuel hoses (hard to tell the sizes as there are not accessible so if someone knows)
_ cylinder compression tester

[gr79]

It should at least run roughly i suppose. Mine does if i pop off a vac hose like that.
This one has stalled on the first stop since day one.
The charcoal canister to carb was one area i reconnected.
One of the plastic return lines, canister to tank, was cracked (leaked fuel)
Mine is a turbo, thus has some added and different vac routings.
Yours is in Europe-different emissions specs? Man, how can you guys afford gasoline?
Hose size? Slice off a very thin cross section sample to take with you.
Still, a gas hog is a gas hog even if its on the moon.

[TuxStang]

Yours is in Europe-different emissions specs?

No real emissions specs in France when in vintage category ... at least less restrictive than todays. I just have to meet the emissions of the years of the car and as in the '80s, we didn't know anything about unleaded and cats, let alone EGR ... i can remove all emission items and still be below the emissions limits with a good tune-up.

Man, how can you guys afford gasoline?

we are accustomed to its price and we don't have much choice. Could be worst for me ... gasoline in England is even more expensive than in France.

[SRM351]

Just an idea- take another look at your PCV system. Even though you've replaced the valve and checked the hose, you could be flowing too much air through the crankcase. You should be pulling some vacuum in the crankcase to help with the ring seal, however there must also be fresh filtered air source to help flush out the byproducts of the combustion process for the system to work properly. Unplug the PCV valve and seal it with your thumb and see if the engine rpm drops. If it doesn't drop your leak is elsewhere, if it does drop (and it should) you may have found your problem depending on how significant the drop is.

Another possible problem could be that your vacuum advance module is leaking. That would explain the crappy mileage yet clean plugs. The vacuum leak causes a lean mixture while the lack of a functioning advance causes poor mileage returns. The engine will run fine with just the mechanical advance working, the vacuum advance is what gives you economy.

[TuxStang]

Was a bit too dark to check exactly but tried to plug the PCV valve with my finger.
I needed to turn it to put my thumb (not much space to do it with the valve vertical) which it did a bit to easily to my taste ... while doing this, it seemed the idle rpm droped a bit (maybe ~50rpm, hard to tell alone) but when i plugged the valve, it didn't drop more as far as i can tell. So there's a small leak at least on the hose. Thought i already changed it ... will check tomorrow and maybe try using a collar to make it tighter.

Would a leaking vacuum advance still act ? Because until two weeks ago, it was on intake manifold and when i played with throttle, i saw the backing plate linkage moving.