I have a 85 iroc with the tpi 305 and im sick of it really never running right, and i want to change to carb. I heard though that if i do i will loss some power, mostly on the lower end. Is that true?
THANKS

 

Yes it's true, your MPG will go down the drain too. No way would I ever dump a TPI for a carb unless it was just for racing.

 

You will loose some lower end torque but will gain a ton of horsepower in the upper rpm range. The factory TPI setup is not a performance setup it should have been put on trucks.

 

You'll be able to pull past 5K with ease.
I did the exact opposite though, carb to TPI. I wanted a more up to date looking engine bay.

 

Well, i don't realty want to change but this car just wont run right no matter what i have had done to it. It always runs hot even though the fans run all the time, half the time the power isn't there, like i cant burn the tires when acouple days ago it would, it does this all the time. Then it has a low rpm stumble, and the gas mileage isn't all the good anyways it gets like 9 to 13 mpg, and it has a rough idle. I just dont know what to do with it. Im so tired of fuel injection.

P.S no codes

 

I did the switch when I replaced the LB9 with a L98. There where many reasons for my decision. I am using a higher rpm cam, new injecters are expensive as well as new runners and Throttle body. I mean your talking about spending just as much money on the fuel system as the engine and heads put together. But the biggest benifit for me is the ease of tuning and running a carb from day to day. I know a lot of people like tinkering with chips and don't mind troubleshooting sensors. But I need my car to run every day, and if something goes wrong I need to be able to fix it fast. And that is the biggest benifit I have had.

I am using a Q-jet and with a 269HR cam and performer RPM manifold I am averging between 18 and 20 mpg. 75% of my driving is highway. And thats with gears that cause me to spin 3000 rpm at 75mph. I think they are 3.73s. Not sure, I bought the car with them in there.

 

If i change it what would i have to do with the extra wires, the intank fuel pump and the computer.

 

You'll probably need a mechanical fuel pump and you might have to pull the electric one out of the tank.
I have a working mech pump as well as the carb intank pick up and fuel level sender, Edelbrock carb, air cleaner, valve covers, and distributor. Only thing you would need is an intake.
PM me if you need any of this.

If you have dual fans, you will have to either install a manual fan switch for the primary fan or wire it up to the secondary and get a lower temp fan switch.

You should be able to pull out the entire TPI Engine harness with no problems.

 

OK thank you very much, but i have all that in the garage, if i dont though i will pm you. With the harness where do i unplug it and will it mess anything up. like does it connect to anything else besides the wires for TPI.

 

The main connection is under the dash on the pass side. The harness comes in from the engine bay, down into the fender and then into the pass side compartment.
Not sure how many connections are on the 85 TPI, but the 91 TPI I had had 3 ECM connections and 2 connections that went to the IP harness (Instrument panel).

The harness comes out from the top of the fender, right next to the heaterbox blower motor.
It should be able to come out as one piece with out cutting anything.

 

So the Ecm harness is separate from like the starter wires and ignition wires and alternator wires. So when i take the harness out everything will still work normally just there is no computer to control the motor and fuel pump.

 

Jimmy_mac probably knows more about that than I do.
I've haven't taken a stock TPI out, just put one on my car.
I can't remember if the alternator was on the TPI harness or not, I don't think it is.

If you are commited to doing the conversion, start it and let us know if you have problems.

 

OK will do, im going to give it one last try to get this thing to run right and if it wont hello carb.

Zepher
thanks for the help to understand things and very nice car.

 

Let's look at it this way....

A Vette L98 and a ZZ4 are the identical same long block as far as power output is concerned. The difference is a mild carb cam and a 50-state-legal smog dual-plane intake manifold, compared to TPI.

The Vette TPI was "rated" at 240 to 250 HP. The ZZ4 is "rated" at 345 HP.

Now of course the ZZ4 is "rated" with headers, while the L98 had manifolds. Let's be generous and say that the manifolds are costing the L98 40 HP. Sounds to me like that little street intake and a carb are still a 50-60 HP upgrade to a L98.

So how much horsepower will you lose by putting a carb on a L98?

 

The L98 factory ratings are "net HP" ratings. The ZZ4 is rated as gross flywheel hp. The factory takes into consideration parasitic loss from install accesories such as alternators, ps pumps, etc. The difference in peak hp would be a lot closer considering this. Carbs generally have a higher peak hp than TPI. Peak hp is just that, "peak", it dosen't indicate what happens in the rpm scale leading up to the "peak".

 

That's why I gave the L98 the benefit of the doubt, and allowed it a 40 HP gain from headers which is far more than the real world will experience. And the 2 HP "ratings" are obtained similarly: both are net HP at the crank, the main difference in the way they are obtained is the exhaust, and the fact that the ZZ4 is not 50-state legal as it comes, since it isn't computer-controlled. IIRC it was rated for something like 285 HP when it was part of the "HO conversion kit", which was the ZZ4 motor with a Q-Jet on it. SO let's look at it that way instead... you can take that long block, stick a computer-controlled carb and virtually identical exhaust manifolds as the L98, and come up with 285 HP; or you can put TPI on it and come up with 240-250 HP.

So how much horsepower will he lose under that comparison?

 

No problem, just helping out where I can.
Thanks for the compliments on my car, but right now the car looks like crap,

 

I believe the ZZ4 conversion, with log exhaust manifolds and the dual cat setup, was rated at 308 net hp at the crank. Or thereabouts if memory fails... I want to say it has a hotter cam than the factory 250ish hp Vette L98s though...

 

Yeah, the cam is a little hotter. Not 60 HP hotter though. The answer for TPI's poor performance lies elsewhere.

Face it, the problem is TPI. It's just simply not a performance system. It should have been used in trucks, not sporty cars.

Bottom line: he's not going to lose anything. Not even fuel mileage, if he's a good carb tuner. There's no reason that a well-tuned carb setup can't get at least 90% the fuel mileage that TPI does, especially if the cam choice is conservative.

 

no need to switch to a mechan fuel pump with a carb swap all you need its a decent pressure regulator.. do a search this topics been gone over many times, but no you dont need to change your fuel pump

 

If i dont have to remove the intank pump will i have to keep the computer in to run the pump or would i have to hook it to a toggle switch or something.

Zepher

Your car still looks better then mine. i need new rear quarters, they are rusted out and there is a dent from the owner before me. Also the silver paint is faded in the back where the rear quarters are bad.

 

I guess you can wire the pump's relay to the ignition so that it comes on when you turn the key.

How much does a regulator that drops 45psi to 6psi cost?
Mech pump is only $12-15. I know it will be a lot less hassle to just run the electric pump, if you can find the right regulator.

 

a regulator costs around 70 bucks or so.. i got mine for free from a friend so it was cheaper for me to do it that way.. yes you wire the pump to come on with the ignition.. i remember reading some posts on here before where people said they just hooked up a mech pump and used the electric pump as the pickup.. sounds easier and cheaper.. not sure of all the details though maybe someone else will post or just do a search

 

I wanted to do the same thing to my IROC when I bought it about two years ago. A carb, I figured, would give me gobs of simple power and I could ditch the complex, sensor-ridden TPI fuel injection.

They say that the factory TPI shuts off at 4500 RPM and really doesn't make any more power after that. That's exactly correct; TPI was designed to produce TONS of low-end torque. That makes it really fun to drive around town and you can light up your tires very easily (if that interests you ). People commonly replace their TPI setups with other port injection systems, like an Accel SuperRam. Those aftermarket systems not only cost lots of money, but they extend your power curve well past 4500 RPM, assuming that it's matched correctly to your engine internals. What Accel doesn't tell you is that you can extend the power curve of your stock TPI with little trouble, simply by doing some mild porting or more radical siamesing of the intake runners and intake base. I recently port-matched my plenum and runners and I'll be doing the rest of the intake next winter. I can't mention any performance gains, as it's still off the car.

Fuel injection adjusts a lot better to atmospheric differences than a carb. It'll usually cold-start a lot easier than a carburetor, and it'll even adjust for changes in air density and altitude. I'm not sure if computer-controlled carbs can do that, but your TPI already has the feature.

You might have heard of people talking about reprogramming their car's computer chip, or PROM. That's the beauty of a fuel injection system -- you can fine-tune your engine so much better (in my opinion). Plug a laptop into your car, log your dragstrip runs, compare the sensor readings, and make your changes. There's really no limit to what you can do, and a properly tuned FI system will usually run better than a properly tuned carb. Check out the DIY PROM board and see what they're up to; it's really cool.

Any bets as to what induction I'm currently running on my Camaro? Don't get me wrong, I still respect carburetors. In fact, I just purchased a new Holley 750 cfm carb for my father's 1967 SS-396 Camaro. Partially for nostalgia, but also because it's not daily driven (14,000 miles on the odometer) and the car doesn't require an emissions test.

When was the last time you performed a tune-up on your car? Your symptoms sound ignition-related. Might want to check the plugs and wires, along with flushing the coolant and replacing the thermostat, before you decide to go with a carb. Think of it this way... it's not running properly, right? Say you did everything that you could and it's still not running the way it should be. With FI, hook up a laptop and monitor the car's sensors and see what's wrong. Not everything will trip a code.

I hope that I was helpful, and I apologize for being a little biased .

 

i am also considering swapping to carb on my car due to tpi gremlins and the cost of upgrading the system. my tpi has been a real nightmare. mine is a daily driver so i am looking for something that will be easy and cheap to work with. i only drive 7 miles a day so gas mileage is not a concern. i have asked around and 90 percent of the people that did the swap didnt look back, and i doubt i will either. i am hoping to score some good deals at super chevy show next month so i can get this project done sometime this summer. good luck with your swap man

 

Here are two articles in the tech area for doing the conversion:
https://www.thirdgen.org/newdesign/tech/carbswap.shtml
http://5finger.8m.com/tpi2carb/tpi2carb.html

I pulled the fuel pump from the tank and replaced it with a rubber hose to pick up fuel. I have heard of people leaving it in and just diconnecting it. I didn't want to take the chance of it blocking the flow. I am using the carter 5psi inline pump near the tank. You don't want any more than 5 psi going to a Q-jet. It's a good idea to use the mallory 3 port pressure regulator whether you use the TPI fuel pump or a low pressure inline one from Holley or Carter. But I am currently not using a pressure regulator.

I got a used ZZ3 HEI distributor off ebay for 100 bucks, a Q-jet that was rebuilt off ebay for 30 bucks, and a performer RPM off ebay for just under 100 bucks. Yes I know I rely on ebay to much, but I havn't been burned yet.

As far as wiring goes most of the stuff from the ECM comes from the passenger side. The stuff you need to run a carb set up come from the driver side. Things like the coil and tach wire, the temp sending wire, and oil pressure wire.

Those two articles are great and are what I used. But keep in mind your emision laws and re-sale value. I don't plan on getting rid of mine so I don't worry bout things like that. If mine ever stops driving on the street it will just become a gutted trailer queen.

 

thanks man!! i plan on using the mallory 3 port regulator with my stock fuel pump. anyone had and probs with it?

 

blue86iroc

I have tried everything on getting it to run better. Everything checked out ok, there are no codes and everything is set to where it is supposed to be. I don't know maybe it is just because the 85's computer sucks or what. I don't have a hard time starting it when it is cold, it starts with one crank but after it warms up it takes a lot of cranks and then it will start. The car has always ran the way it has even if i give it a tune up. Could it be the distributor, because thats the only thing i haven't changed for the ignition. Or could the TPS and IAC be warn out, I have a new mass air flow sensors and O2 sensor.
THANKS

 

My car usually takes a long time to start, anywhere from 5-8 seconds of cranking. Other times, it'll start right up after one turnover. I think I've narrowed down the problem to the ignition module, which is located in the distributor underneath the cap. A local auto parts store tested the module and it intermittently failed the "low RPM" test -- which I think may be related to initial start-up. My engine is apart right now so I haven't had an opportunity to test it.

You bring up a good point about the TPS and the IAC. A malfunctioning IAC is the equivalent of a vacuum leak, and we all know that vacuum leaks are detrimental to engine reliability and performance. The TPS could cause some problems, too. A friend of mine recently replaced the throttle position sensor on his Jeep Wrangler after trying a host of other things. His symptoms were stalling and hesitation; a new TPS fixed it. It's interesting that you aren't throwing any codes, though. You might want to check this article and see if you're IAC and TPS are functioning properly: https://www.thirdgen.org/newdesign/tech/tpimod2.shtml.

It's possible that the car is in "limp-home" mode (though I've never actually experienced this). Limp-home mode is enabled if the ECM's PROM chip fails... it runs the car off a set of pre-programmed parameters and doesn't compensate for anything. After checking the IAC and TPS, pull the PROM out of the car's computer and see if it runs any different. If it runs the same, it's possible that the chip is bad.

 

Well, I was throwing a mass air code for the longest time, anytime i stopped at a light it would idle really low and then the light would come on. And when i would check the code it was always the mass air, so i cleaned out the throttle body and it solved that problem. But my other problems are still there, so do u think i should take the cap off and take the ignition module in somewhere to get tested. Cuz its weird that sometimes the power is there and other times its not and the way it idles and stuff like that.

 

It certainly wouldn't hurt to get the ignition module tested; most places will even test them for free. If you have a GM, Haynes, or Chilton's manual they will explain how to remove it if you don't already have experience with removing one.

Is the car still stalling on you? A dirty throttle body could theoretically throw a code, but that sounds a little shaky to me. If the MAF isn't hooked up properly or isn't working, the car will be a bear to drive. You might want to flash the codes just to make sure the Check Engine light isn't burned out (sounds stupid, but anything is a possibility). Maybe you're still throwing a code and you don't know it.

 

There is no stalling and no codes. But today it ran great so i dont now whats its problem is.

 

bubbz89 i've been using one for 3 years now, no problems yet!

 

thanks man, are you using the stock tpi pump?

 

since i will have the motor somewhat apart, i am also thinking of going ahead and doing a few other things and get it all knocked out at once. i am looking at a set of protopline vortec heads, but what would be a good cam for that setup? my car is a daily driver, but only like 7 miles a day. i am looking for a setup that will haul *** and be a good daily driver too. i dont know alot about cams, so any suggestions are welcome. my motor is a L98 with 22k miles on a .30 over rebuild. what would be a nice combo? also remember i am going with a carb. what all parts will i need? has anyone ever ripped off a tpi and threw together a vortec/cam combo and a carbed L98? thanks guys!!!

 

i agree with this 100%. you arent going to go to carb and get 3 MPG, not if the carb is tuned correctly. also you do not need a new fuel pump; just get the mallory AFPR with return port. cam choice is fully up to you and your driving needs. some will say .525 lift on a flat tappet cam is perfectly streetable and fine. some might go crazy with a much tamer camshaft. 7 miles a day is barely anything, so if you want to go somewhat radical i would think it would be ok...

 

Well now, I could talk for days on this topic. Why are you going to throw away fuel injection for carb? If you aren't throwing any codes then there is something wrong with either fuel, or spark and not your injection system. Yes, it is a hassle sometimes of changing sensors, but when it is running right you can just get in it and go, you don't have to go and adjust things on a carb to get it to run right. Maybe it's just me, but lots of people out there would love to run a TPI system on their car, I'm one of them. Right now I have TBI, and have been messing with it forever to get it to run right, but now that it does it is a fun car to drive. I'm sure if you would just diagnose your problem and fix it, you'd be very happy with your car. Oh and by the way, carb does make you lose around 3-5mpg as far as I can tell with people who have swapped in either direction. Fuel injection is more efficient, and while it may not create the biggest hp or tq numbers, it still creates power and streetability. Well, that's all I have to say, it seems like you're pretty set with a carb and I wish you luck on the swap. Let us know how it goes.

 

Well, i have found out that some of my injectors are really bad, so iam going to swap for some new ones and see how that goes. Maybe that was the sorce or my problems.

 

Actually, as I was reading through the thread the injectors are what kept coming to mind. Also, my friends 89 5.7 tpi Iroc was having problems when it would first start and a lack of power. It turned out to be the iac. It wasnt throwing any codes either.

Ben

 

My Iroc is an 85 TPI also, and i had the same Maf code related problems you had for a long time. It wasn't the maf, swapped those out. wiring all tested out okay. I dunno what was going on with it. the 870 ecm's that are in the 85 tpi setups suck ***. I converted to speed density and it made a world of difference. Definately no maf codes anymore In my case, i ditched the maf and never looked back. Also, with my stock maf setup, my car took like 7 or 8 seconds of cranking to start when cold and 2 or 3 when warm. when i converted to SD, it fires right up warm or cold. Not to mention that if you do hook a scan tool up to the 870 ecm, the baud rate is so slow that the scan tool updates too slowly to be real useful. (I have alot of chalkmarks on my "I hate MAF" list)

oh yeah, ditto on the injectors. that could be what's causing you some problems. also, have you set your minimum air and tps voltage correctly per the tech article? I know from experience with my car that those make a HELLUVA difference. if your tps is not set correctly, it can cause stumbling on takeoff, surging idle, lack of power, surging on acceleration, stalling, etc. In my experience, never helped a rough, ****ty idle though. i'd suspect fuel injectors or something. changed fuel filter lately?

 

Ya my AIC, and TPS are set to where they are supposed to be. i checked my injectors more today and the one farthest on the passenger side is almost completely dead. SO iam just going to order the injectors and replace them and see what happens from there.