tssteph

93 TBI 350 automatic, engine idles fine, revs fine when not in gear, under slow accleration it runs fine, under hard acceleration it does not, it has a lot of hesitation, no backfiring or popping it is just not smooth. New parts, fuel filter, 12 lbs of fuel pressure even under acceleration, EGR selonoid, GM crate engine, two sets of injectors, two different chips, new cap and rotor. Mods, headers, stock cat, flowmaster exhaust, tbi spacer and stack. All of this was done when I bought it so I don't know when the problem started.

Any thoughts? I looked through all the archives, man there is a lot of good information, but I did not see anything that sounded like my problem.

Thanks in advance.

RGZWS6

The only thing I can take a stab at would be the "stock cat". Check to make sure its not plugged. Or, take a crow bar and make it hollow. I had a friend have his 84 Z28 plug up on him and the car ran slower that an Escort when WOT.

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89 Formula 305 TBI
160* stat, 200* fan switch, K&N, Headers, 3in Flowmaster (hollow cat) back, pullies, 1.6 full roller rockers, B&M trans cooler, home-made ram-air
3.73 Richmond gears and SLP Zexel Torsen Posi (waiting for install)

burnoutrpm

i know this is out there but question 1 does it cut off about 4500??
#2 does it get to about 3000 rpms and seems to kind of...runout of engine??

if the answer is 1 then its the stock ignition

if 2 then you are experinceing valve float


these are just guesse mine did that to and it was the ignition and lots of valve float, the springs were matched to the cam but, they went weak fast!!

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89 firebird formula


356 10.5:1compression
comp cams xe262 cam
performer rpm intake
#1405 edlebrock 600
434 casting completely redone with bronze guides and 202/160 valves 64cc chambers. decked .0005 thousandths. 3 angle valve job
msd 6al
h.e.i. proform 50,000 volt vac. advance ditributor
700r-4 with 3.08 first gear and 3.23 posi 7 5/8 rear end.
b trans shift kit(will kill shifts...suck dong!!)
shorty heddman hedders with custom 3" pipe y-pipe back(no damn cat!) with 40 series flowmaster!

future mods: 406 roller REALLY REALLY REALLY RADICAL!!!!!

Bort62

To sort of extrapolate on what the Burnout Said...

Hesitation During acceleration leads me to belive Dirty plugs, Faulty wires, Or a bad Cap/Rotor situation. Has all this been replaced ?


If your getting Valve Float at 3000, Then you are either using Way to big of a Cam, Way to weak of springs, Or you have your rockers adjusted Improperly, Too Tight.

I really dont think Its valve Float.

Check the Ignition, and let us Know. Once We know that is good it will help us get to the bottom of it.



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60 Ranchero - Project ( Money Hole )
85 Sport Coupe LG4 - Daily Driver

Just another Hot Rod kid, or thats what they all tell me.
Livin' the Stereotype

Bort62

Ahh ****, Just realized You are using TBI on a 350.

All sorts of possible problems there, Ill Have to let one of the other guys who has more experiance with this take a shot.



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60 Ranchero - Project ( Money Hole )
85 Sport Coupe LG4 - Daily Driver

Just another Hot Rod kid, or thats what they all tell me.
Livin' the Stereotype

gruveb

I had a similar problem in a Volkswagen Type 1. I didn't everything possible to it, ignition, carb, even changed the valves and springs.

Turned out that one of the cam bolts had worked itself loose and was rubbing on the case.

No trouble at idle, or under a light load, only when you got on it.......

With problems like this, it's just good trouble shooting techniques, start with the simpliest, check it thoroughly and move on until you've covered all of the bases. Eventually you'll find it, but it can be a real pain.

Worse thing is, you usually find some other problems which contribute, but don't entirely cause the problem.

Good Luck.

tssteph

The engine is a Gm crate engine with no intenal mods, thus the valve spring issue can not be the problem. It has had a new cap and rotor nut not wires. New plugs were used when the engine was installed, and the old motor (383 stroker with alum heads) had the same problem. The engine revs to the moon if not under a load so this does not point to the converter. Any other thoughts? I am surprised noone pointed to the map sensor, I may pick on up tonight and see what happens, my reasoning is that it only happens under a load, the map sensor essentially measures the load and provided data to the ECM for mixture maps.

Any other ideas?

TransAm182

have your tranny checked out...my friends camaro did the same thing cause his tranny was slipping.....