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carb or fuel injection

9K views 98 replies 31 participants last post by  STJP 
#1 ·
New to the thread, just bought an 86 CJ7 last month and wondering about a 2100 carb or a Mopar fuel injection? Any thoughts, suggestions and/or advice would be welcomed.


I apologize in advance if this topic has already been worn out in the forums.
 
#2 ·
Well there are definitely 2 sides in this camp, but I went fuel injection and you couldn't pay me to go back. I just look at the key and it starts. No pumping to set a choke etc etc, reliable offload performance and breezed through smog.

If you do consider injection, look at Howell too. Lots of happy peeps running their Chevy based TBI system, and half the price of Mopar. You do give up timing control however, but some have added it in.
 
#4 ·
New to the thread, just bought an 86 CJ7 last month and wondering about a 2100 carb or a Mopar fuel injection?
If you're going to compare a fuel injection system to a carburetor, at least go with something new and of known quality like a (genuine) Weber 38. Yes, you can get a new MC 2100, but what's the quality of those?
 
#15 ·
I'm curious what makes you think that a new MC2100 wouldn't be a quality product?

The reliability of EFI is at least 100x that of a carb, so the comments about fixing a carb with a screwdriver are about as relevant as dinosaurs eating humans. Yes, we see threads here from people having problems with their EFI kits, but for every problem there are countless more that aren't a problem.

I would agree that the expense of EFI isn't going to be re-couped for a long time, even if it does result in better fuel mileage.
 
#5 ·
just out of curiosity, what exactly don't you like about your existing set up?

My thought is change for change's sake is simply a waste of money.
 
#7 ·
And fuel injection has proven itself to be unreliable and in efficient, automakers have gone back to carbs...oh wait...nevermind. :wink:
 
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#8 ·
Thanks for all the comments. First off, Jeepdaddy, no problem with existing system I was just looking at increasing gas mileage. Ken, I hadn't thought of a Weber 38. I will definitely look into that. ECJ you are correct about the warnings. My first ride was a 70 Chevy pick up and I spent many 15-30 minute sessions on the side of the road working on carb or points and condensor to get it running.

I guess bottom line is I m looking for a good solution for best performance and gas mileage.

Thanks
 
#10 ·
I guess bottom line is I m looking for a good solution for best performance and gas mileage.
IMHO, that would be an upgrade to EFI. Cold starts and drive-ability should improve. Fuel economy? I guess that all depends on what your CJ delivers now (with a properly tuned carb). And what your expectations would be.

The 'bolt on' systems available are pretty straight forward. And there are several choices: Howell, MoPar, DIY JY (I'd do the complete 4.0L head and everything swap).

I'm running a 'chipped' Ford EEC-IV A9L computer on my EFI 5.0L. Basically a 'plug-n-play' system that has a long history of reliability.



I like carburetors, but they have several drawbacks. And for the most part they are 'simple'. But once you take the time to educate yourself on EFI, you'll find they aren't that complicated either. Biggest PITA, is going to be putting an electric fuel pump into your Jeep. But there are several options for doing that.
 
#9 ·
no problem with existing system I was just looking at increasing gas mileage.
OK, first, what gear ratio's are you running? Tall gearing is responsible for more fuel and performance loss than virtually any other issue.
What is your existing fuel mileage and under what conditions? City and urban driving, short hops, or a lead foot will kill economy. Given Jeeps are aerodynamic bread boxes, even on the highway, you aren't going to see much over 18MPG on the best of days.
What other mods have you done to the engine?

There are a couple of things you can do to the existing motor to bump up the economy. A good tune up, including insuring the vacuum advance is working, bumping up the timing, inspecting the choke, opening the plug gap slightly,etc...

Not trying to be a nay sayer, it is just that while the step to an MC swap is relatively inexpensive ( I actually like the MC swap), an FI swap will set you back a bit of coin. Either way, the question is will the possible difference of a mile or two to the gallon (3 to 6 bucks a tank) offset the cost and effort involved in the swap.

Just a couple of things to think about.
 
#11 ·
It's a trade-off. Pros and cons to both. Gas mileage won't change significantly, assuming both system are operating well.

Reliability can be debated, too. We see proportionally large numbers of FI problems as we do carbs.

Personally, I like the simplicity of a carb. It seems to match the nature of a CJ, to me. And most carb problems can be fixed with a screwdriver and some carb cleaner. Not so much with FI.

Matt
 
#14 ·
.. And most carb problems can be fixed with a screwdriver and some carb cleaner. Not so much with FI.
Yeah, break out a laptop PC and start reading the logs.

.. it is a stock CJ running 2.73 in the rear end and it has the good old Carter carb on it...Looking under the hood I am sure that if I got rid of all of the emissions garbage it would probably see a tremendous gain in both power and mpgs!
Those 2.73 gears are really working against fuel economy with your 31x10.5 tires. Going back to the stock 29" tires would bring back power and maybe a bit of fuel economy.

Removing the emission control hardware will not create a "tremendous" gain in performance or fuel economy. At best, you'll get a small increase. The more logical approach is to remove the components from the feedback carburetor system, and ensure all of the remaining vacuum and vent lines are not leaking. There's no reason not to have a correctly installed PCV valve and a catalytic converter. Your 258 was only making 110 HP from the factory, and the cat isn't doing anything to hamper that.

From personal experience, I can say that installing a genuine Weber 38 and a DUI HEI ignition really woke up my 258. Also, moving from 33" to 31" tires (I have 3.31 gears) made an improvement too, and I will probably move to 30.5" x 9.5" tires after these are done. My fuel economy isn't any better than before, but I have much more power and the Jeep is more quick and fun to drive.
 
#12 ·
If you're doing it solely for the sake of fuel mileage, you need to do some math at roughly 2 mpg difference to see how many years it's going to take to recoup your funds and decide if it's still worth it.

You can get a lot of stripper glitter and blow for $1,500 and your carbed Jeep will get you there and back ;)


Shawn
 
#13 ·
Jeepdaddy, it is a stock CJ running 2.73 in the rear end and it has the good old Carter carb on it. I have only had it about a month and this thing called life, job, etc keep getting in the way so no mods yet. It is going to be my mostly daily driver and occasional mild to moderate trail jeep. Looking under the hood I am sure that if I got rid of all of the emissions garbage it would probably see a tremendous gain in both power and mpgs!

swatson as far as the coin is concerned, yeah it would take me a while to save up for a Mopar system. :)
 
#17 ·
I'll throw in a vote for EFI. I went the junkyard route and am all in at ~$900 for a complete system including pump, surge tank, computer controlled HEI dizzy and the ability to write my own tunes.

I had a Holley 2150 before the EFI. I liked the carb quite a bit. It did well off-road and tuned up alright. I went EFI primarily because I was tired of trying to source parts and the never-quite-right exhaust smell while out crawling. My wife was pregnant and we were scheduled to drive the rubicon that summer, so, to avoid exposing my wife and kid to nasty fumes, I went FI and ran the whole trail in closed loop. As an added bonus, I went from 12 MPG avg to 16.25 (as taken on my way to the con fully loaded with gear). And the "stall saver" feature in the code makes you look like a pro off-road in a manual ;)

To wrap it up, I like the 2150 (very similar to the 2100). It's a good carb, but waiting a week for mail order parts sucks (to be fair, not the case with other carbs). While a carb can be good, FI is great, I have no substantial complaints. It's the stuff of dreams for rock crawling. If you want to build a junkyard system, you'd better have a lot of time and patience. The learning curve is steep.
 
#18 ·
Jeepdaddy, it is a stock CJ running 2.73 in the rear end and it has the good old Carter carb on it. I have only had it about a month and this thing called life, job, etc keep getting in the way so no mods yet. It is going to be my mostly daily driver and occasional mild to moderate trail jeep. Looking under the hood I am sure that if I got rid of all of the emissions garbage it would probably see a tremendous gain in both power and mpgs!

swatson as far as the coin is concerned, yeah it would take me a while to save up for a Mopar system.
My quick take:
First, as stated, your gearing is poor. even with the auto, it is going to suck performance out of the engine. Equate it to a guy riding a 10 speed with the bike stuck in 7th gear. It is slow to start, hard to pedal, strains the drivetrain, and almost impossible to get up a hill. The option is to either lower the gearing or work out to get stronger (build the motor). The same analogy applies to your gearing.
This leaves you with a decision. Lower gearing or smaller tires. You will have to do either one to truly get the most out of your power plant. Given your set up and usage, I would probably stay with the 33's and replace the gears with ones in the 3.50 range. This will not only up your final drive RPM's, but close the shift points and take some of the strain off the drivetrain. This will result in a much snappier engine and should increase mileage to boot. The downfall is the swap isn't cheap. If you bring the gutted housings and the R&P's in to a shop, you can look at about 3 hours labor per axle to install. Dropping the Jeep off will increase that to about 5 for the rear and 7 hours for the front. This doesn't include the cost of the gears and the rear carrier.

Upgrading the carb and exhaust (just a free flowing muffler, I despise headers) will give a bump in performance. A lot of folks like the Webber, however, the MC is a super super simple carb that is relatively cheap to get.

As for the "smog junk", you can pick up some reliability by removing it, but it's absence won't effect your performance much.
 
#19 ·
12 years ago I adde the MOPAR FI kit and have never looked back nor had any problems with it. The reliability factor is off the charts and it is still the best upgrade I have made to my CJ...
 
#23 ·
That's a number I'm very comfortable with. C'mon, you grew up in the age of points and carburetors just like I did. I'm sure you remember the smell of exhaust back then from most carbs that weren't tuned correctly.

How many millions of TBI Chevys ran the roads in their heyday without ever so much as a tuneup?
 
#22 ·
How's that carb working on your Toyota truck Matt? Better than ever cause ifs Fi, and has been for two decades. :wink: All things considered, it probably is 100x better. There are 3 carb threads in the 1st 20 here alone. I know your heavily invested, in your carb, but you understand it, you tune it, you've learned its nuances , but your the exception, not the norm. Most folks wanna turn the key and go.

I put a used YJ Howell system on my CJ, started and drove away. Didn't have to set the idle, dick with a choke, nada. And outside of taking out my TPS while pressure washing, it's been perfect. And the system gave me a code and told me what failed. Yer carb will never do that. There is just no comparison. The manufacturing practices of every major automaker would support that statement as well.
 
#24 ·
If you go to the Cherokee forum you will find a lot of threads concerning unreliability of the injection system, sensor failures being very common. A "No start HELP" thread is started every few days. Injection was not universally accepted by the motor industry when it first came in. OK, few people understood them at the time but it was then emissions regulations that made them a "no brainer" for the motor industry along with engine management systems. When working, they are more precise than a carb and at angles they are hands down the better option. No doubt they are smarter and better at running the average engine.

The question here is whether adding fuel injection in place of a 30 year old Carter BBD will improve fuel economy. Maybe. Will it reduce the running costs? No way, that it is a huge outlay to gain a small improvement.

Will it improve general driveability? Probably. Better starting, less maintenance are offset by greater complexity to an extent.

A rebuild kit for the BBD runs $15 and will usually work if the throttle shafts are not worn. Add in $20 of vacuum hosing, $30 of service parts and a day to sort out the engine bay and Nutter the electronics and change the distributor advance and most emission 258s will be dancing like it was 1981 compared to how they were, as the previous 30 years of poor maintenance and tired components are stripped away. That is money you could actually recoup in the short term, over say 3000 miles.

Beyond that a few hundred more for a new and genuine Weber 38 would have you delighted.
 
#25 ·
As an ownerr of GC and previously, a TJ, i spend a lot of time in those forums lurking. I respectfully disagree. The most common issue with the no start is the CPS, and that's a timing issue.

And as some one who roiled a 74 k2500 after loosing drive up a hill due to a flooded (carbureted) engine, the only argument for having a carb is they are cheap, and you can work on one with basic hand tools...if you know what your doing..,,and the fact is the majority don't.

And it's more like 5 carb threads lol. Not counting the air pump one, which would be eliminated with injection.
 
#26 ·
With respect the CPS feeds into the injection system through the PCM which controls the ignition and injection. Without the CPS it is a no-go for the injectors.

The complexity of the 4.0 HO multipoint injection (which is not especially complicated by FI standards) is that the Powertrain Control Module (PCM) requires the following inputs:

Generator output
Auto shutdown (ASD) sense
Intake manifold air temperature sensor
Battery voltage
Brake switch
Engine coolant temperature sensor
Crankshaft position sensor
Ignition circuit sense (ignition switch in run position)
Manifold absolute pressure sensor
Oxygen sensor
SCI receive (DRB scan tool connection)
Camshaft position sensor signal
Throttle position sensor
Vehicle speed sensor
Sensor return
Power ground
Signal ground

The PCM then provides the following outputs:
Idle air control (IAC) motor
Auto shutdown (ASD) relay
Generator field
Malfunction indicator lamp (Check Engine Lamp)
Fuel injectors
Fuel pump relay
Ignition coil
SCI transmit (DRB scan tool connection)
Tachometer (on instrument panel, if equipped)

The CPS by itself is there for timing but that timing is used for both ignition AND injectors. The inputs determine the time and length of grounding of the injector on each cylinder.

Chap on the Cherokee forum only today dealing with a misfire, injector was stuck open. ahha hah , a carb would not do that. 0:)
 
#30 ·
CSP said:
Who said anything about the number of threads regarding problems Matt? I don't believe that threads on the internet are representative of anything other than threads on the internet. It's certainly no measure of reliability. :confused:
Skip,

I was commenting on Crash's earlier post. He mentioned 3 threads in the top 20 about carb problems, implying that was evidence they are less reliable.

I agree, the web is no measure.

My measure is a carb has never left me stranded on the road. I can't say that about all the FI vehicles I've owned.

Matt
 
#31 ·
That part is sure true, Matt. If a carb starts going South, it at least gives you plenty of time to sort it out. Fuel injection just quits.

My mother called me one afternoon while sitting at a stop light and said the car (Mercedes SUV) started running rough and smoking like a pig out of nowhere. She was able to limp it home but it was $1,500 to replace 3 bad injectors and 16 (yes, 16!) spark plugs.

Now granted, it had 150k miles on the clock but that certainly wasn't a $20 carb rebuild that gave you a couple of weeks to prepare for.

It sure is nice to be able to knock the snow off the door, reach in and fire it up and go back inside to finish your coffee though.


Shawn
 
#33 ·
This is likely one of the hardest choices to make on an engine there is. Both have their appeals. After deciding to go with the factory EFI on my Ford 5.0 and in reading everything I can find it seems to biggest fail on EFI is either a bad ground or faulty connection. Unless the connection is severed the engine will run. There are censors to go bad and rarely do they just stop sending info to the ECM and even if they do there's a factory installed mode that lets the engine run enough to get you home. With that being said I would not let the fear of being stranded deter me from EFI. It hardly ever happens and usually when it does it's the pump, but pumps go bad with carburetors too.

What would deter me, and almost did is the cost. EFI demands more fuel pressure in most cases and that means you need to update the fuel lines, they're likely needing it anyway, you'll likely be going with an electric fuel pump and those can get pricy. So if you're on a budget I'd go with a carburetor.
 
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