CARB or EFI and WHY??????????

85_SS_302_Coupe said:

So you're right but only by the one chance that two guys would meet up on a hot humid day. LOL that's a lot of factors that have to fall into place just for the sake of being right. Practicality, yeah sure. Efficiency? Absolutely, why not. None of that equates to any reason that EFI makes more power than a carb setup. You're also thinking that the weather has some kind of astronomical effect on the carb's ability to make power, but that's just not so. If the weather is bad enough to make my carb run crappy then the EFI is going to be sluggish as well. That's just a plain simple fact of weather and air quality vs. the internal combustion engine, and a/f delivery isn't going to change that enough to make a win or lose difference.


This debate comes up like every other month, and no offense to anyone in particular but it just gets so tiring hearing the same thing over and over from people that i suspect have 0 carb tuning knowledge (again not directed to the quoted person, just an observation). People tend to be biased to what they know, and i'm just as guilty of that as anyone because i honestly know more about carbs than EFI, but i do know how EFI works in relation to a carb, and i do know that it all comes down to the tune on the carb...plain and simple. It'll take more work, sure, but the reward is the same...it's all horsepower and torque at the wheels, it just depends on how you want to get it and what you're willing to learn and do to make it.

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25thmustang said:

What about gas mileage... I know carbs these days are much better than in years past, but will they get the mileage an EFI car gets. I recently went to SC (800 miles each way) with my car. At 15 degrees of timing and 38-40 psi of FP, I got 26-27 mpg cruising at 65-70, and 23-24 mpg cruising at 80-90. This was also with an easy 400-500 lbs of luggage (3 guys luggage for a week, 1 guys luggage for 4 months overseas) and 2 passengers (me at 190, friend at 230).

Would a carb car (not tuned for gas mileage, as mine isn't) see similar mpg as the EFI? Also would the swing in weather, from 100 degree and muggy to 55 degrees and dry, affect the carb a good amount?

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Boss 351 said:

I admit the carb checklist is shorter, but the EFI can run for 20 some years without any problems. CFI is even better, my dad's 84 Lincoln 5.0L NEVER has needed the air filter cover removed besides to change the filter. He has so few problems with his engine that the hood is almost rusted shut

This is my second EFI Mustang and it's VERY reliable. My carb'd one needed adjustments every once in a while. My 650 double pumper (first carb) gave me headaches (it was used). I eventually bought a new vacuum carb for the street.

Case and point: My cousin's 454 powered pontiac had some dirt fly past the fuel filter, he had huge problems with his carb, the car would stall and he needed a tow truck to get it back home. I had a simular problem with my coupe. The fuel filter hasn't been changed, in what seemed like, 10 years. I had brown dirty fuel leak out of the filter (with filter particles to boot). You know what? My car brought me home, it had a weird problem when I floored it, but it drove back home without too many problems. I changed the cheap fuel filter, put some injector cleaner in the tank and I was off. I didn't need to rebuild a carb.

After having both carb'd and EFI, I'm sticking to EFI. Now that I understand our EFI systems, it's a piece of cake.

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85_SS_302_Coupe said:

So....rebuild the carb maybe? In reality you wouldn't even need that...just clean the dang thing out. Let's say you get something REALLY nasty through your filter and you ruin an injector....what's that going to cost you?

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85_SS_302_Coupe said:

Carbs are cheaper and more simplistic. Anyone who says EFI makes more power, i'll match you dollar for dollar and we'll build an engine from scratch and lets see who makes more power.

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86bluecobra said:

hands down carb would win.

I went the carb route because I had to upgrade so much to stay EFI. Since my car was a 86 and it was speed density. The carb route was cheaper. It isn't all that friendly before it warms up but after it has it's a beast.

Another pro to having a carb is the sound of the 4 barrels. Nothing quite like it.

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FBD said:

All of the people arguing gas mileage... you bought a performance car to start with, who cares about gas mileage.

The debate could go on for years, but this is what made me decide to go to carb:

Crank but no start checklist for carb:
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1. Look in carb, are you getting gas?
2. If not, get your screwdriver and make adjustment.




Cranks OK, but No Start Checklist for Fuel Injected Mustangs
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Revised 29-Jun-2007 to update TPS testing procedure for 94-95 Mustangs

All text applies to all models unless stated otherwise.

Note: 94-95 specific changes are in red

1.) Remove push on connector from starter solenoid and turn ignition switch on. Place car in neutral or Park and set the parking brake. Remove the coil wire from distributor & and hold it 3/8” away from the engine block. Jumper the screw to the big bolt on the starter solenoid that has the battery wire connected to it. You should get a nice fat blue spark.
Most of the items are electrical in nature, so a test light, or even better, a voltmeter, is helpful to be sure they have power to them.
No spark, possible failed items in order of their probability:
A.) MSD or Crane ignition box if so equipped
B.) Coil
C.) TFI module
D.) PIP sensor in distributor. The PIP sensor supplies the timing pulse to trigger the TFI and injectors. See paragraph 5A - a noid light will tell if the pip is working by flashing when the engine is cranking.
E.) No ECC or computer power - ECC or computer relay failure
86-93 models only: ECC relay next to computer - look for 12 volts at the fuel injector red wires
94-95 models only: EEC or PCM power relay in the constant control relay module. Look for 12 volts at the fuel injector red wires.
F.) No ECC or computer power - fuse or fuse link failure
86-93 models only: Fuse links in wiring harness - look for 12 volts at the fuel injector red wires. All the fuse links live in a bundle up near the starter solenoid.
94-95 models only: 20 amp EEC fuse in the engine compartment fuse box. Look for 12 volts at the fuel injector red wires.
G.) Ignition switch - look for 12 volts at the ignition coil red/lt green wire. No 12 volts, blown fuse link or faulty ignition switch. Remove the plastic from around the ignition switch and look for 12 volts on the red/green wire with the switch in the Run position. No 12 volts and the ignition switch is faulty. If 12 volts is present in the Run position, then the fuse link is blown.
94-95 models only: Check inside fuse panel for fuse #18 blown – 20 amp fuse
H.) Computer
J.) Engine fires briefly, but dies immediately when the key is released to the Run position. Crank the engine & when it fires off, pull the small push on connector (red wire) off the starter relay (Looks like it is stuck on a screw). Hold the switch in the crank position: if it continues to run there is a problem with either the ignition switch or TFI module. Check for 12 volts at the red/green wire on the coil with the switch in the Run position. Good 12 volts, then replace the TFI.

See the following links for wiring diagrams...

http://www.autozone.com/servlet/UiBr...3d8016713c.jsp for 79-88 model cars
Computer/fuel pump/ignition wiring diagram, 86 model http://www.autozone.com/images/cds/g...3d80167158.gif
Computer/fuel pump/ignition wiring diagram, 87 model http://www.autozone.com/images/cds/g...3d8016715e.gif
Computer/fuel pump/ignition wiring diagram, 88 model http://www.autozone.com/images/cds/g...3d80167162.gif

http://www.autozone.com/servlet/UiBr...3d8019595a.jsp for 89-93 model cars
Computer/fuel pump/ignition wiring diagram, 89-90 cars http://www.autozone.com/images/cds/g...3d8019595f.gif
Computer/fuel pump/ignition wiring diagram, 91-93 cars
http://www.autozone.com/images/cds/g...3d80195960.gif

http://www.autozone.com/servlet/UiB..._us/0900823d/80/1d/db/3c/0900823d801ddb3c.jsp for 94-98 model cars

2.) Spark at coil wire, pull #1 plug wire off at the spark plug and check to see spark. No spark, possible failed items in order of their probability:
A.) Moisture inside distributor – remove cap, dry off & spray with WD40
B.) Distributor cap
C.) Rotor
D.) Spark Plug wires
E.) Coil weak or intermittent - you should see 3/8" fat blue spark with a good coil

3.) Spark at spark plug, but no start.
Next, get a can of starting fluid (ether) from your local auto parts store: costs a $1.30 or so. Then pull the air duct off at the throttle body elbow, open the throttle, and spray the ether in it. Reconnect the air duct and try to start the car. Do not try to start the car without reconnecting the air duct.

Two reasons:
1.) If it backfires, the chance for a serious fire is increased.
2.) On Mass Air cars, the computer needs to measure the MAF flow once the engine starts.
If it starts then, you have a fuel management issue. Continue the checklist with emphasis of fuel related items that follow. If it doesn’t, then it is a computer or timing issue: see Step 4.

Clue – listen for the fuel pump to prime when you first turn the ignition switch on. It should run for 5-20 seconds and shut off. To trick the fuel pump into running, find the EEC test connector and jump the connector in the Upper RH corner to ground. The EEC connector is near the wiper motor and LH hood hinge.


If the relay & inertia switch are OK, you will have power to the pump. Check fuel pressure – remove the cap from the schrader valve behind the alternator and depress the core. Fuel should squirt out, catch it in a rag. Beware of fire hazard when you do this. In a pinch, you can use a tire pressure gauge to measure the fuel pressure. It may not be completely accurate, but you will have some clue as to how much pressure you have. If you have any doubts about having sufficient fuel flow/pressure, rent a fuel pressure test gauge from the auto parts store. That will tell you for sure if you have adequate fuel pressure.


4.) No fuel pressure, possible failed items in order of their probability:
A.) Tripped inertia switch – Coupe & hatch cars hide it under the plastic trim covering the driver's side taillight. Use the voltmeter or test light to make sure you have power to both sides of the switch
B.) Fuel pump power relay – located under the driver’s seat in most stangs built before 92. On 92 and later model cars it is located below the Mass Air Flow meter. Look for 12 volts at the Pink/Black wire on the fuel pump relay.
C.) Clogged fuel filter
D.) Failed fuel pump
E.) 86-90 models only: Blown fuse link in wiring harness. Look for 12 volts at the Orange/Lt Blue wire on the fuel pump relay.
91-93 models only Blown fuse link in wiring harness. Look for 12 volts at the Pink/Black wire on the fuel pump relay.
The fuse links for all model years 86-93 live in the wiring harness near the starter solenoid.
94-95 models only: 20 amp fuel pump fuse in the engine compartment fuse box. Look for 12 volts at the Dark green/yellow wire on the constant control relay module.
F.) Engine seem to load up on fuel and may have black smoke at the tailpipe. Fuel pressure regulator failed. Remove the vacuum line from the regulator and inspect for fuel escaping while the pump is running. If fuel is coming out the vacuum port, the regulator has failed. Check the regulator vacuum line for fuel too. Disconnect it from the engine and blow air though it. If you find gas, the regulator has failed.


5.) Fuel pressure OK, the injectors are not firing.
A.) A noid light available from any auto parts store, is one way to test the injector wiring.
The noid light plugs into the fuel injector harness in place of any easily accessible injector. Plug it in and it will flash if the injector is firing.
B.) I like to use an old injector with compressed air applied to the injector where the fuel rail would normally connect. I hook the whole thing up, apply compressed air to the injector and stick it in a paper cup of soapy water. When the engine cranks with the ignition switch on, if the injector fires, it makes bubbles. Cheap if you have the stuff laying around, and works good too.
D.) Pull an injector wire connector off and look for 12 volts on the red wire when the ignition switch is on.
E.) No power, then look for problems with the 10 pin connecter (salt & pepper shakers at the rear of the upper manifold).
F.) No power and the 10 pin connections are good: look for broken wiring between the orange/black wire on the ECC relay and the red wire for the 10 pin connectors.
G.) TPS voltage exceeds 3.7 volts with the throttle closed. This will shut off the injectors, since the computer uses this strategy to clear a flooded engine. Use a DVM, a pair of safety pins, and probe the black/white and green wires to measure the TPS voltage.
On a 94-95 Mustang, probe the black/white and grey/white wires to measure the TPS voltage
It should be .5-.99 volts with the key on, engine not running. Note that if the black/white wire (signal ground) has a bad connection, you will get some strange readings. Make a second measurement using the battery post as the ground to eliminate any ground problems. If the readings are different by more than 5%, you may have a high resistance condition in the black/white signal ground circuit.

6.) Spark & fuel pressure OK.
A.) Failed IAB (no airflow to start engine). Press the throttle ¼ way down and try to start the car.
B.) Failed computer (not very likely)
C.) Engine ignition or cam timing off: only likely if the engine has been worked on recently).
D.) Firing order off: HO & 351 use a different firing order from the non HO engines.
HO & 351W 1-3-7-2-6-5-4-8
Non HO 1-5-4-2-6-3-7-8
E.) No start when hot - Press the throttle to the floor & try starting it if you get this far. If it starts, replace the ECT.


Ill give up the troubleshooting headache for the ease of maintenance.

And sure, carb technology is old, but there is a reason ALOT of racers still choose carb over EFI

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Modular2v said:

This is the exact reason i went carb.... i have less than 7k dollars invested in my whole car (including the price of the car) and i run 10s.... efi takers?

by the way dan...have your distributor re-curved and that warm up problem wont be an issue!

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millhouse said:

Head on over to the TM forums and you'll find guys that could smack you around with less invested on EFI setups. I'm not sure I see your point…once you start getting into forced induction the carb vs. EFI argument becomes much more blurred. The EFI setups typically will still have better drivability though…get better fuel economy and many will still pass emissions.

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Modular2v said:

my point is FOR DOLLAR TO DOLLAR PERFORMANCE YOU CANT BEAT CARB
And ...i thought this had already been covered but ill say it again....Who cares about fuel economy in a performance car???????????? buy a honda hell

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