ATAY383

Alright, I have a 383 stroker LT1. When I first bought the car, it ran 11 flat on street tires, and about 3 weeks after i ran it, it lost a lot of hp. (currently running a 13.5 or so) we've checked almost every sensor on the car and cant seem to find the problem, does anyone know what would case that big of a decrease in hp so rapidly?
Details about the car it is a 1994 Camaro Z28 with a LT1 with a 383 bottom end, cc 306 cam, 1.6 rrs, mid length headers, morso air intake, ported intake, 3.73 gears, and a built 700r4 transmission. one unusual thing ive noticed with this car, is there are no o2 sensors in the headers. another problem I have been noticing: when im at a stoplight and my foot is on the brake, it tends to jerk forward a little bit. fuel pressure is still fine, and theres no knocks. i just had new plugs wires and coil put on, as for top end rpms, it doesnt sputter or miss at all no ses lights come on. could the problem lie in the lack of o2 sensors? ok well that day that i got the car the oil light came on and we checked the oil and it was okay. then it came up agian, and then the next day it wouldnt start. so we had to jump start it. 5 times in a row we had to jump it and then it was fine. thats when we noticed a hp loss. anyone know the problem?

Alex94TAGT

I take it you weren't the one who originally performed these modifications, so this is going to be a little bit of a guessing game. Have you determined whether this setup is using a factory computer or aftermarket engine management system?

Few thoughts:

1) I'm not sure of what purpose removing the oxygen sensors would serve, unless the previous owner didn't intend on running unleaded fuel. Otherwise, oxygen sensors are relatively vital for proper fueling, imo.

How did the old spark plugs look when they were removed? Were they white-ish or carbon-fouled?

The idea is that the oxygen sensors provide feedback to the PCM in closed-loop mode, which then ultimately makes corrections to the long-term fuel trim (aka "block learns"). With this information, the computer can generally add 25% fuel or subtract 15% (by controlling injector pulsewidths), in order to achieve the target air/fuel ratio. As I understand it, this is also the information the PCM uses to calculate fueling at wide-open-throttle. Without this system, there's really no guarantee that you're not running ultra rich or lean, which could easily affect horsepower (or kill the engine).

2) Without more information, my only other ideas would be to check valve lash, and perhaps run a compression test. Since you're apparently experiencing some electrical gremlins, you might also consider testing your battery (obviously), as well as double-checking your primary grounds (from factory, there's typically one on the front driver's side of the engine block to the frame, and one of the negative battery cables connects to a passenger-side engine mount bolt).

Alex94TAGT

Another quick thought on the no-start condition:

I don't recall if the low oil sensor has the ability to prevent the engine from starting, but if you're sure the oil level is ok, you can pull the electrical connector and jumper it with a paper clip for the time being. That will prevent the low-oil light.

If you could describe what happened when you turned the key, that might provide some more insight. Did you have a flashing SECURITY light on the dash (VATS)? Starter solenoid clicking n' all?

ATAY383

well when i step on it theres alote of smoke that rolls out and all my freinds say that my car is running to dam rich. cause i can smell that **** when i start it and it makes me like high because of smelling alot of ****. see when i start it it would crank but wouldnt start so had to jump it. and i had a guy from kansas city that some times fixes pcm 4 less pcm and he told me that they deleted the oxegen sensors on the headers. and he tried the best he could with the tune.

IH8FORD

iTrader: (6)

If the problem is not all electrical , you could have a head that is lifting or blown head gasket. Also possibly a broke ring. I would check your oil dipstick for coolant and if there isn't any then do a compression check.

9sec93

iTrader: (67)

sounds like it was tuned to rum in open loop all the time. i would check the coil. i had alot of LT1 cars and had to replace the coil on almost all of them. is it an MSD coil. i have had a few of them go bad. if the coil is ok, make sure all cylinders are getting spark. it could be smoking and smelling like fuel becsuse it may not be firing on all cylinders and puting unburned fuel out of the exhaust.

96capricemgr

iTrader: (1)

Am I the only one that is going to say that setup running 11 flat on street tires is a pipe dream worthy of Snoop Dog himself.

The jerking is the surge from a poor cam choice and poor tuning.
The lack of O2s sounds as if it has been wrenched on by some truely ignorant folks.
If it has a 700R4 in it instead of a 4L60E that would just backup my suspicions of complete incompetence from whomever built the car.

I will go out on a limb and say the car was built by an idiot who messed up everything he touched and then sold the basketcase to you.

Probably a good time for an oil change as if it is that rich, it is likely diluting the oil which will do a lot of damage to bearings.

If you ran it and the slip said 11.0 or hell 11.9 for that matter I strongly suspect that was the car in the other lane, because the setup you are describing is NOWHERE near capable of that sort of ET on street tires. If running well high 11s on slicks might happen.

ATAY383

well i drag raced a trans am that ran 11.04 and i beat him.

Formula350

iTrader: (3)

Reason for 700R4 could be it was converted to SD, Cap.

If it ISN'T a SD motor, maybe replace the MAF?

IH8FORD

iTrader: (6)

I have a CC306 in my 383 and run low 11's all day long. Not to say that he has what I have . But the cams are the same.

96capricemgr

iTrader: (1)

What was his reaction time?

Formula, the MAF pcm is perfectly capable of running in speed density just turn off the MAF in the tune, if someone swapped back to the 93 setup just to run speed density that would be further proof of the incompetence I suspect, the 306 should not need to rev high enough to go beyond the MAF pcm rev limitations either.


IH8FORD, sure the rest of your car is VERY different. I am sure you were commenting on my comments and not suggesting it is vaguely possible on street tires as he claimed

IH8FORD

iTrader: (6)

It depends on his definition of street tires.Definatley not a Z rated radial. If it had enough power to run those times it would never move on a radial.Maybe an ET street or a drag radial "street tire".

ATAY383

its on z rated tires but id have to buy new tires the next day cause my car will burn the tires in first second and third gear.

ATAY383

i dont know much about my car but im learning cause my freind knows a **** tons about f bodies. and he has the same 383 as me but he has a supercharger that is running 16lb of boost. and hes been helping me out.

ATAY383

wheres the cheapest place to get a head gasket fixed.

FASTFATBOY

iTrader: (23)

If the car has no o2's and is on factory electronics thats a problem, anyone that would tune a streetcar to run in open loop is a dumb ***. Or ANY EFI car with stock electronics for that matter.

You come here asking for help and have not answered BASIC questions asked to you.

Does it have stock electronics, stock ecm, opti, maf?

Are you SURE it has a 7oor4 and NOT a 4L60E, does it have a throttle valve cable on the throttlebody? Is there a barrel electrical plug on the top passenger side of the trans pan?


A blown head gasket will not slow a car down like that. Of course you dont KNOW for a FACT the car runs 11.0's

Is the trans slipping? This will cause stuff like this.

Is the car slow to rev? Does it labor like it is pulling an F-150 behind it on a trailer?

Sitting at a stoplight, is it missing?

When it will not start, is it slow to spin over? ECM has a minimum RPM requirement to start the car.


Sounds to me like you bought a problem child.....good luck.


David

ATAY383

yes its stock

FASTFATBOY

iTrader: (23)

I give up.


David

pyronotic138

iTrader: (1)

i am ashtons friend. and i work on this car here and there till the ******* thing works like it used to. one day it was able to burn all through 4th gear and yes did run 11s on street tires. one day he called me up and it wouldnt start. come to find it was the coil. replaced that and started up but had codes thrown. we did a check and there were no codes present. (fucked up). now as it sits we are playing the guessing game that everyone describes while they work on other people problems that they built up. this car now has. new knock sensor. new MAF, new MAP. new coil, new wires, new plugs. the plugs when we changed them looked like dogshit got on them and burned. but all in all it smokes terrible when he takes off. barely will burn the tires off the line. and WILL NOT run in speed density mode. it starts and dies right away. we thought about trying 02 sensors and keep playing the guessing game. the bad thing is this is getting costly to him. just like all other fbody owners. the reason i am led to believe its 02 sensors is becuase it gets about 5 gallons per mile. not really but honestly 6mpg in town. cant take it out of town becuase there isnt a gas station on the on ramp. and another reason is lack of power. but i understand there are many other factors. i just dont know anything but something electrical causing this. becuase it just happened overnight. i remember the night before i was in it and it would spin for ever wherever. the next day the thing was sluggish. i checked the vacuum and has about 28-30 at 1000 rpm. i just would like to figure out why it doesnt run in speed density. why the hell it lost that much power. my stock WS6 can almost stay right next to it and that thing has 254rwhp. his used to have 410 rwhp. PLEASE HELP.

96capricemgr

iTrader: (1)

410rwhp does not equal 11s on steet tires, 12s yes, 11s no unless the suspension is REALLY dialed in perfect but if the engine is this much of a basketcase I see no way the suspension works that well.

On the vacuum, 28-30 what??

Obviously something is causing a gross rich condition, I repeat change the oil NOW. That rich will do damage quickly.

Here is a wild guess, does it have Accel injectors on it? If not what does it have?