C.F.I. Performance tips. - Are their any?

[B.H.K.]

I have a 85 gt top AOD transmission.
Car runs and drives but I have to give it some gas to start, their is some surging at about 35 Mph and after a heavy accel and during heavy deceleration... well it blew up my muffler (this happened after i removed my cat).
im trying to fix the problem as i think it can be done and if all else fails i will be putting a carb onto it.
I would rather keep it all stock for bragging points and maybe get a collectors plate in future.
I have changed coolant temp sensor, map sensor, tfi modual,
Act sensor on order in mail... i hope that solves my issue...
After i get it running well again is anyone familiar with changing cams on a cfi engine? how radical can i go; does it care?
Any performance tips they can offer?

[Walking-Tall]

... welcome to the forum.
There are, lots, of tips, that is, but establishing basic good stock function of everything as is first is more important. Blowing the muffler to hell indicates all sorts more raw fuel in the exhaust system than should be. Stop hoping, and throwing good money after bad at expensive replacement parts that might not have needed to be replaced. After learning about and running it to look for EEC-IV trouble codes, if you want to do things yourself with that system, you need to do some digging and reading and learning how it all works in order to whip it's a$$ and make it work as is acceptable to you. You might be satisfied at that point, because most people are happily surprised at how well something works when it is simply working right. Otherwise, and after the above, there are things that can be done to wake that lazy inside the box conundrum up. Otherwise 2.0, I would HIGHLY recommend going with traditional carburetion and ignition to rid yourself of ALL of the hair-pulling frustration and road blocks that electronic fuel injection can be.

[cb]

After installing 1.94 valves and porting intake a little, mine wouldn't smoothly accelerate past 3500 RPM. CURE, I installed a couple of injectors under the
throttle body and a pulse modulator. In other words any mods to CFI would be i'll advised. How ever mine does run quite nicely.

[Matt J]

An important piece of information we need is how long you've had the car, and when the problems with it running started. If it was fine and suddenly started doing that, then it's a totally different deal than if you just got the car and it's not right.

I had a CFI car ('84) that ran great. Regarding performance mods, well, I never bothered as there are so many things about that engine that limited it, and frankly most attempts I've seen resulted in a lot of expense for marginal results. That said, if it's a cruiser, then the CFI not only performs fine, but it's got the benefit of having a computer give you hints about things when it's not right. I'll say as well that the CFI system is old-school computer controls...lots of vacuum lines and analog tech controlling a digital brain. I found it pretty fascinating, actually, when I figured it all out. They didn't have the benefits of all computer controls like they to today when everything can be controlled via wire.

If it's always been that way since you bought it, then you're going to have to start from the basics and work your way up. You'll have to make sure that all the gremlins are worked out one at a time as any of them can cause a problem. Start with checking all your vacuum lines, one simple leak will make the whole thing run like junk. Also keep in mind that a lot of those controls (choke heater/kickdown, dashpot, cruise control module and others) all have vacuum lines running into them and have rubber bladders in them that can break down and leak as well. It's at once frustrating and rewarding, you really will gain an appreciation of how it all works as you go through it.

Someone else suggested reading the computer codes...do that right away! I bought a code reader for 30 bucks, you can use a test light if you want. I think the code reader was a good investment as it allowed me to store codes and also reset the onboard computer when I was comfortable that I didn't need the old codes anymore. It will tell you if sensors are out of spec, which can cause trouble. Run some injector cleaner through it to make sure the injectors are working right. Make sure all the plugs and wires are firing, another way to get raw fuel dumped into the exhaust.

Start with the simple stuff, and work your way up. It's not a bad idea to replace a lot of the stuff you've bought, as it's all 30 years old at this point, but I'd bet a lot of it is probably still working fine. Start with leaks, check the computer codes (keeping in mind that a problem might be indicated, but it's really from something else causing it). Those codes will at least steer you in the right direction. Well, be prepared for a lot of directions, there's most likely more than one thing wrong.

Finally, keep in mind that these cars, even the CFI ones, were considered serious performance cars at the time, and cheap too...that means a lot of poorly thought tinkering by well- intentioned amateurs who most likely made things worse. Don't assume that because you haven't touched it that it means that what you have there is stock. For instance, if the idle is rough from a vacuum leak that they couldn't find, they "fixed" it by kicking up the idle instead of replacing the leaking hose. You'll find plenty of stuff like that. If it's a hobby for you, well, all the stuff in here is bolt-on and you'll feel like a hero when you fix it. If you need the car to get to work every day, well, you might want to trade it for a Honda...

Good luck!

[emerygt350]

my 84 cfi has been a slow lesson in making everything run like it should (as mentioned by others above). This car was completely stock, completely untouched. Really a single owner before I got it (I have all the receipts too). First thing I did was rebuild and hook back up the EGR system. Engine ran better and cooler. One of the most obvious issues that took forever to actually figure out was my original ignition coil was going and that would randomly result in the surging you mention. After 20 bucks at the local parts store that was fixed. My most recent find was a PCV system that really needed new hoses and parts (25 dollars for everything). The computer has been a god send. Helped with some little things like temp sensors etc and also alerted me to lean conditions (which led to the PCV system). Last night I finished off the last two motor repairs to bring it to 'brand new', a new clutch for the fan (mine was completely shot) and new hoses for the air filter housing (the big black tubes that hook to the fenders). Now the car runs perfect(knock on wood) throws no codes, idles perfectly, cruises like a champ, gets about 17mpg city/highway mix. All of the repairs on the motor have been cheap bits. The expensive items have all been 'aftermarket'.

My AOD also has a shift kit in it and I know that helps a ton. I would definitely suggest that. Really makes it fun to drive.

I added hooker super comp headers to the thing and full dual exhaust. That made a big difference in power, particularly up high but noticeable down low (https://www.youtube.com/watch?v=r5_UZ8ponYY this before I fixed the PCV so the idle is a little high). Although I didn't really want to mess with the 'stock' draw of a gt-350, it was so uninspiring performance wise that I wanted a little more from it. I am now dreaming of a 3723 edelbrock. I don't think the intake will change too much although I did see in another forum an LTD CFI that added the 3723 and had good results (particularly at mid street rpms).

The way this thing starts and runs is just so nice and I don't drag race it (I have auto-crossed it for fun) so I think I may just stick with the CFI. It takes two minutes to rebuild, they are simple, interesting, and sound cool.

[erratic50]

Blown up muffler eh? Fun.

Thinking back to nobody gives a crap about this old carbureted motor fun here.....

We used to wait for the converter to lock up then shut the key off at highway speeds and pump the ever loving bahjezus out of the accelerator pump then turn the motor back on while also dropping the trans into low....... if we were lucky it would blow up the muffler. If we were damn lucky it would blow up the catallitic converter too. Would sound like a cannon going off. If the cop was parked on the edge of town it would wake him up and he'd stop us for a muffler violation and give us a fix-it ticket then the cop on duty the next day would always just sign them without inspecting anything. Couldn't sneak up on it's shadow after that but....small town fun!

Worked even better on the old 3 on the tree cars and trucks. Laugh a minute on those.

Then we figured out to put an injector in a spark arrestor and put that in a Y after the motor with a spark plug and a coil..... then we could prime the pipe with fuel and light it off and throw fire out the exhaust any time we darn well wanted to -- practically on demand.

Absolutely horrible gas mileage the first night. Lol.

It's a wonder we didn't start that old piece of crap on fire because the exhaust was white hot at one point.

Anyway - back to your post...... I suspect it's running rich and loading up then exploding. Don't blow out any church windows!