Setting Expectations for TBI

[Lumpskie]

So, I've read a lot of conflicting information on the performance increases that result from going to TBI. Some people say that you'll get 0 hp and 0 mpg difference, with the only benefit being altitude compensation. Other people claim that you can see 20-30 hp and 2-3 mpg increases.

I've got a stock carb on my Wagoneer, and it works great. I've never had vapor lock. It will run my rig just fine from 5,000 ft (my house) to 13,000 ft up in the mountains. I've never taken it to a lower elevation, so I don't know how it would do there. (if you have information on that, pass it along, please!)

So, based on what you see here, do you guys think a TBI setup is worth the effort for me, in the long run? Do you think I'd see any difference in performance in any way? What's your opinion overall?

Thanks for the info,

[will e]

I would say you would just be creating issues for yourself and spending money while you do it. If your stock carb works great and you have never had any vapor lock issues I wouldn't mess with what works. Going from a stock carb to a TBI you might see some performance improvements. The TBI will probably have a larger CFM capacity but if your engine isn't matched to the extra flow it won't add as much as you might think. Throttle crispness might be lost a little with the higher flowing TBI.

I ran a Holley Projection and it was great for altitude changes and it did awesome wheeling.

I now run a holley truck avenger. I did have some vapor lock issues with it (which I recently solved). I got tired of the electrical gremlins with my projection unit.

Tuning wise, you might get a little better gas mileage out of your TBI if it is tuned properly. The fact is both your carb and TBI use a 'wet manifold' where the gas and fuel travel together through the manifold. Since the path to each cyl is different you end up tuning to the leanest cyl. That is, you tend to run the others a little rich so the leanest doesn't run too lean.

Port fuel injection uses a dry manifold system and the fuel is shot into the air right at the valve. It is more tunable than a carb or TBI. On more modern engines the head/manifold design placed the injectors into the optimal position. We don't have that option. The most modern cars inject the fuel right into the cyl during the compression stroke. This is, by far, the best method but again, not available to us.

I hope this helps. Again, if it was me and my truck was running fine and I was happy with it I would leave it alone. If you find you need more power for towing, decide you want to go offroad more at more crazy angles and it's stalling on you or the carb finally wears out then I would toss around my options.

There will, of course, be different opinions. I know some people who went TBI and have become part of the faith and will never look back (Blake) as well as folks who tried it and, for whatever reason, couldn't get it to work for them (Kevin).

[90supra]

Comparing apples to oranges here: The biggest difference for me from the carb'd truck to the TBI'd GW is that, when I leave them sitting for 2-4 weeks, the GW starts right away and the truck takes a few tries

[Lumpskie]

Thanks for the responses, you guys. One quick question is jetting... If I'm fine at 5,000-13,000 ft, do you all expect that I'd have to change out jets to go down to 2,000 ft?

[AwesomeJ10]

Here are my thoughts, all based upon experience.

MPG's - ya, if you spend a lot of time tuning, then ya, you might get a little better MPG. I only use my rigs for 'wheeling, so I don't really know what kind of MPG I get. Although I did recently drive up Hwy 14 (the Poudre) from Ft Collins to Walden and the old Honcho got about 14MPG. That was not towing and it's running 5:38 gears and 42" tires (aired up, which does make a positive difference) I was hauling @$$ too. I don't know that any carb guys can HONESTLY say that. Most people with TBI have reported little to no gain and maybe even a little loss, again, depending on tuning.

Power - well I have mine tuned for rock crawling. I have it running a little rich at idle and a little lean at the top end for MPG. I really think that a carb may actually have a little more power, but again, it depends on tuning. Carbs are VERY good at dumping lots of fuel into the mix.

Now here is where a decent TBI system literally blows away ANY carb on earth:

Drive ability and overall performance.

I'm the kind of guy who wants my machine to run. Hot, cold, upside down in a pit, sideways, off camber, etc. I don't wanna have to deal with the 'anomalies' of carbs in 'wheeling situations. Example: say I'm 'wheeling in Moab on Hells Revenge, more specifically, on Hells Gate where it's a real possibility to die. If I stall the engine while in a precarious situation (off camber, vertical, etc) I want that thing to start right back up and continue my line. The last thing I wanna do is have to deal with that stupid freaking carb spitting and sputtering all over the place and not wanting to run. I don't wanna die.

Cold starts. I've always had lots of junk sitting around my house (residential neighborhood) and it's embarrassing to go out there and have that carb do what it does best; not start. I want it to start right up and run perfect no matter how long it's been sitting or how cold it is. I know there are 'carb whisperers' who claim they can make their carb start right up, but honestly, the fact remains: I've not seen it in person.

The only real downside to TBI (in Colorado) is probably emissions. They simply aren't 100% legal unless to get it inspected by one of those referee places (one in Ft Collins and one in Littleton IIRC). I believe that is a one time process. Now most people at the emissions place don't know the different between a car and a truck, so they aren't gonna notice anything other than 'wow, that thing runs clean huh?'. The unfortunate fact is that you will need a charcoal canister and air system connected to pass. I don't play that game and have Collectors plates on my junk.

So in the end - if you carb is running fine and you aren't 'wheeling, then go with the tried and true old saying: if it's not broke, don't fix it.

But... If you want to learn how your engine ACTUALLY runs and want to learn some cool stuff about engines, timing, fuel, etc, then TBI is a GREAT way to do so.

[will e]

It will probably run okay. It might run a little rich but if you are just visiting down low it should be fine.

[AwesomeJ10]

oh and I don't think you can take much account from those running that Holley ProJection JUNK. Cause that's exactly what it is: 100% JUNK. their experiences with TBI are incomplete and inconclusive.

(sorry guys, but as you know, that thing really is junk and should not be compared to GM TBI)

[Lumpskie]

So, because I don't have any complaints about the way the waggy is running, it sounds like TBI shouldn't be a priority. Blake, if you ever have some time, I'd love for you to take a ride in my rig, just to tell me if you think power levels are where they should be. My guess is that I'm getting about 14 mpg on the highway, if I don't go faster than 75-80 mph. But, power is just ok... not great. It certainly won't spin the tires if I stomp on it from a stop.

[AwesomeJ10]

Sure thing man. I'm probably about 3 weeks away from ripping the TBI AMC 360 out of the honcho in favor of the GM 496, so if u wanna hear that thing run and play with the moates tuner, you better make some plans soon. I'd be happy to look at your junk too.

[Lumpskie]

^Sounds good. I left you a message on your cell last night. Give me a call some time and we'll set something up.

[tgreese]

Let me point out that EFI is significantly more reliable and durable than carburetion. Modern electronics has mechano-vacuum-power beat all to heck in that area.

[AwesomeJ10]

yep.

The only issue I've had with my TBI was I lost a TPS once. The engine wasn't responding to throttle correctly and wasn't idling correctly. the CEL came on so I connected the Moates and saw the code. Threw in a spare TPS (takes a whole 2 minutes) and was 'wheeling again.

On another occasion the engine wasn't running correctly while I was 'wheeling. Popped the hood open to investigate and discovered that the vacuum line for the MAP sensor was disconnected. Reconnected and was on my way.

In both of those cases, I still able to drive and not stranded.

[will e]

Let me point out that EFI is significantly more reliable and durable than carburetion. Modern electronics has mechano-vacuum-power beat all to heck in that area.

I do not agree with this statement. Carbs don't usually just fail. TBI can. A loose wire or a bad component like a TPS (as blake said) can ruin your day.

[AwesomeJ10]

Not really.

the GM TBI stuff is pretty darn reliable IMHO. Ya, the TPS, MAP or ECM could fail, but they usually fail in a 'still running' condition. I think I went on a couple of 'wheeling trips after the TPS 'failed' before I actually replaced it.

Heck the ECM on my honcho is missing the inspection cover which is exposing the SF512 chip, zif socket and daughter board to the elements. I know it get's snow, dirt and sand in there all the time. I was kinda curious to see what kind of failure condition it would have, but alas, it never failed.

[Lumpskie]

Where did you locate you ECM?

[AwesomeJ10]

If you don't have A/C, there is a GREAT spot on the passenger side firewall in the cab. There are two heater box bolts that you can use to build a strap to hold it in there perfectly.

If you do have A/C, then there really isn't that great of a place to put it without doing some work. Under the passenger side seat is good, but you have to lengthen a ton of wires. On my '88 GW, I had it under the passenger side carpet, towards the firewall. Worked great there, but I do think it got a little hot.

[will e]

Not really.

the GM TBI stuff is pretty darn reliable IMHO. Ya, the TPS, MAP or ECM could fail, but they usually fail in a 'still running' condition. I think I went on a couple of 'wheeling trips after the TPS 'failed' before I actually replaced it.

Heck the ECM on my honcho is missing the inspection cover which is exposing the SF512 chip, zif socket and daughter board to the elements. I know it get's snow, dirt and sand in there all the time. I was kinda curious to see what kind of failure condition it would have, but alas, it never failed.

I had both an ecm and injector fail. Also a loose wire (my fault of course). It ran with the bad injector but barely. The ECM went into limp home mode which was awful. The loose wire took a bit to track down.

[AwesomeJ10]

LOL

I wonder how many injectors are in your driveway now?

Every think about converting your DD to a carb? No, didn't think so. Heck, it wouldn't even be legal to do.

[shimniok]

I did mine for emissions, not MPG. To say it helped is a massive understatement.

I have struggled with carb emissions EM240 tests on FSJs since 1997 and have tweaked and fiddled with several carbs, 2150, AFB/Performer, Qjet. Every single time the FSJ failed 1, 2, 3, or more times, except the Qjet which passed the first time. Every tie it passed, it just squeaked by. Colorado AIR program lists FSJs as a "Gross Polluter" meaning most of the time they not just fail, but bomb the living crap out of the test. (Search for it... it's kind of funny)

But, after I installed the TBI, the truck "fast" passed meaning it was running *so* clean they didn't need to do the full EM240 test. 8-O -- and that is with a catalytic converter that blew its guts out all over my driveway months before the test! I know this also happened with my friend Scott R (the red WT Waggy "Super Chief") too. And probably the TBI would rock the emissions test no matter the temperature or weather or altitude.

As for MPG, my city mileage still sucks but I suspect drivetrain problem, exhaust problem (that jacked catalytic converter), more tuning needed, or who knows what else. My highway mileage seems to consistently run 13mpg or above, quite a bit better than any carb I've run.

If you're trying to fix a major problem it could be worth the expense and significant effort of installing and tuning. If you can make it with the carb you have, in the long run that's probably simplest/easiest.

Driveability and power is the best I've experienced versus any carb, excepting a few glitches I'm still working to tune away.

Hope this helps.

[shimniok]

PS: I see you're local. You're welcome to come by and drive mine and see what ya think.

As for reliability, we used to go back and forth on carb vs. efi on cfsja years ago. I've witnessed more than a few carb failures, some of my own too. Anything can fail, especially since we are talking about Jeeps here

It's like anything. Just learn how it works and you can troubleshoot it. Although carbs don't provide error codes or let you plug in a laptop to view sensor readings and diagnose problems. And GM TBIs, particularly the 7747, aren't *that* complicated.