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TBI: How Good Is It?

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jim burke

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I've got Edelbrock MPFI on my ('89) 350. It starts and runs okay (no hesitation, stumbling, etc.), but when I went though emissions last week I was about 400% over the limit(s). I just started to look into the problem (checked fuel pressure and it seems fine), so I haven't really exhausted my possiblities for figuring out what's wrong. That said, I'm thinking of taking off the Edelbrock system and re-installing the TBI. (The Edelbrock FI was on the truck when I bought it). Question: how well does the TBI work on a pretty much stock engine? Would I be giving up much power if I go back to TBI? If the air/fuel mixture with the TBI is a lot closer to where it should be, I'm thinking I might actually pick up some power instead of losing it.

TIA,

Jim

P.S.: I searched around for about an hour, but couldn't find the answer. The search function doesn't seem to like sort words like "tbi".
 
multi point is a way better system then the tbi. It has a lot to do with fuel atomizing better. You might want to look in to computer tuning to help with the emissions problem
 
what he said.

As far as tbi goes it will work better with no computer mods than the mpfi but if you spend a little money on the mpfi it will blow the tbi out of the water. I currently run a holley manifold and holleys 2bbl 670 cfm tbi with high pump pressure and it will support roughly 400 hp with proper tuning. the mpfi kit will support well over 500 hp with correct injectors and probably even more than that but you still have to tune the computer. mpfi gives better off idle torque and better gas mileage and will support larger numbers than tbi unless you want to spend a grand on a 4bbl kit. I think that kit your running costs about 1200 bucks... the stock tbi system would go for 150 if your lucky.

spend some time tuning the mpfi system and you will be glad you stayed away from the tbi. I think the mpfi kit uses the stock computer so all you need is a labtop, an aldl cable, and a prominator and you can monitor air fuel and make changes as needed.
 
I've heard edlebrock support sucks, but they are the first place I'd go. See if they've got any troubleshooting literature.

If you can't figure out what is wrong with MPFI, TBI is not going to be any better for you.
 
dirtwarrior17 said:
the mpfi kit will support well over 500 hp with correct injectors and probably even more than that but you still have to tune the computer.

spend some time tuning the mpfi system and you will be glad you stayed away from the tbi.
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I'm sure you're right about the 500hp, but I've got a pretty stock 350 (that's going to stay that way).

Sounds like I need to spend some more time on the MPFI before I give up on it. I'm kind of surprised it's so far out of whack (high on the emisssions). It looks like the previous owner did a good job on the install and the system I have is definitely not some type of "race" system (that could be expected to run rich); it's a a 50-state emissions-legal system.
 
dyeager535 said:
I've heard edlebrock support sucks, but they are the first place I'd go. See if they've got any troubleshooting literature.
Click to expand...

I spoke with them once already; they're the ones who suggested I check the fuel pressure. I'm trying to get back in touch w/ them now.
 
dirtwarrior17 said:
What state do you live in? 400 percent is huge numbers for smog.
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Colorado (I don't think emissions tests are particularly strict around here). Yeah, maybe being so far out of spec. will make it easier to find the problem...:dunno:
 
see if it has the correct chip for the cam when on the phone. you might need to get the # off the chip first.
 
1) Make sure the rest of your emmissions equipment is functioning properly, especially the catalyctic converter.

2) If it is the MPFI system causing your problem WHEN you figure it out not only will you pass emmissions you will probably pick up some power if it's that far out of wack.
 
The converter looks almost new. It's definitely crossed my mind that the ignition could be a contributing factor. But, I installed new spark plugs the other day. After about 15 minutes of running (granted, it was mostly at idle) I took one out and it looked like it had quite a bit of raw gas on it. The old plugs were a really dark brown/almost grey, which would also indicate it's running rich.

So, is the general consensus that a *good running* Edelbrock system will be "a lot" better than TBI on a stock motor?
 
Okay, I just got off the phone w/ Edelbrock tech support. According to them, the cam is the problem. There are only two different chips that they (Edelbrock) provide: one for stock; the other is for their performance package. The cam I have in the truck is a Comp Cams Xtreme Energy w/ .480/.487 lift and 206/212 duration @.050. This is supposedly way beyond stock (or at least far enough beyond stock) to "confuse" the hell out of the computer (the Edelbrock chip I have in there is for a stock cam). It's even too much for the Edelbrock "performance package" chip, which is calibrated for a 194* cam. Seems I have two choices: install a stock cam or have a custom chip made. Edelbrock does not do this, they recommended Command Peformance here in CO. Apparently, the cost is $400-500 (Command Performance was closed when I called, so I have not verified that price is accurate). Anyone know of a less expensive place to get a chip made? At this point, I'm definitely leaning toward installing the stock cam. It's pretty lame the Edelbrock system doesn't have a bit more "flexibility" :mad:.
 
The cam I have in the truck is a Comp Cams Xtreme Energy w/ .480/.487 lift and 206/212 duration @.050.
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Whats the part number on this cam? That seems like a lot of lift with that amount of duration....are you adding in a 1.6:1 rocker arm to that figure? I'm not criticizing you, I'm just curious on what cam that is. ;)

I am suprised Edelbrock couldn't do more than that for you. I JUST was over at a friends house where he fired up his new built 454 for the first time that is equipped with the Pro Flo MPFI system and, as far as I know, Edel. burned him a chip to match his cam. Infact, in my Edel. catalog they list a chip will be included that is custom burnt to match the cam and rest of the engine. I would bet they just don't want to build two chips for one system. :rolleyes:

Jet also burns chips but they are 400-600 bucks too. :mad:
 
rjfguitar said:
Whats the part number on this cam? That seems like a lot of lift with that amount of duration....are you adding in a 1.6:1 rocker arm to that figure? I'm not criticizing you, I'm just curious on what cam that is. ;)

I am suprised Edelbrock couldn't do more than that for you. I JUST was over at a friends house where he fired up his new built 454 for the first time that is equipped with the Pro Flo MPFI system and, as far as I know, Edel. burned him a chip to match his cam. Infact, in my Edel. catalog they list a chip will be included that is custom burnt to match the cam and rest of the engine. I would bet they just don't want to build two chips for one system. :rolleyes:
Click to expand...

Comp Cams part #12-408-8, grind # CS XR258HR-10. I'm going off the numbers provided to me when I bought the truck (I didn't build the motor, so criticize away :) ). The rocker arms are 1.5s

I'm kinda surprised about the lack of flexibility, too. But, keeep in mind this is the $950 emissions-legal system and I can see why they won't/can't burn a bunch of different chips (they probably wouldn't be in compliance w/ CARB, EPA, etc.). Was you friend's system the $2,000+ model?
 
i know the cam was going to be the problem. and for the chips from edelbrock thay enly offer 2 for the tbi to mpi setup. and for the pro flo units ( $2000 ) its a lot more for adjustibility. because thay use a different computer based on a tpi motor setup. but it to is limited to the certin range of cam specs. but hase more choices of chips. thay told me no less than 112 lobe seperation and min vac of about 16 at idel and as smoth as possible.
 
the 1 piece seal blocks are setup for roller but truck and plain motors come flat tappet setup. you can get the roller parts and just bolt in.
 
Searching

jim burke said:
P.S.: I searched around for about an hour, but couldn't find the answer. The search function doesn't seem to like sort words like "tbi".
Click to expand...

I don't post here much but do a lot of searching. Usually with short three-letter words like that I'd put an asterick at the end, i.e., tbi*. Not many words start with tbi so you'd probably have a good chance of finding tbi-related results. Just a thought.
 
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