ok here is what i got, its a chevy 350 with speed pro pistons running 10:1 compression, i have a set of 041 casting heads, full length headers with custom y-pipe and exhaust, lt4 hot cam running 1.5 full roller rockers, and a holley stealth ram set up with a non-adjustable fuel pressure regulator, its got the stock prom, and stock injectors.

i jut finished puttin git in the car, i also put in some new things like
new knock sensor, wires and ac delco plugs, the car runs rough, back fires like crazy, boggs out off the line, running rich as hell, and sluggish, some one help me whats wrong with the motor, why is it acting up, does any one know what i can do to fix it?

 

I have just a few suggestions. been there done that.
I personally wouldnt take it out the drive way untill you have confidence that everything is right.

If it back fires out of the throttle body your timing is way off make sure you set it with the ecm wire(brown with blk stripe) above the ac reservoir disconnected. set the timing then reconnect it.
If it back fires out of the exhaust make sure you have the firing order correct.

Get a chip burned or burn one your self usually a stock chip wont take to weel to all those mods.

just a pointer when you install the knock sensor dont over tighten it and dont use any tape or sealant on it, it should stay sensitive to knock.

 

ok, i mess withthe timing and it gets to a descent point, still boggs off the line, but its better than nothing, and then i drive it and after like 30 mins of driving it start bogging and back firing out the exhaust and now its giving me a code 33 and 42, some one please help me i dont know whats wrong....

 

you're going to need computer tunning you're going to need to up the pump shot ALOT to get rid of the bog off the line..

 

Personally I think his MAF died sometime during the conversion to the new motor. Back when I was young and dumb, I ran a maf setup. I had a MAF sensor go bad at the track, and the car behaved very similar. Almost didn't make it home.

But your advice is correct. I mean.. Even with working components, his tune will be farther off than John kerry in this election.

-- Joe

 

Come on, keep politics out of this. Try unplugging the MAF and see how it runs.

 

your stock prom is not even close to what you need!! just changing the cam in a stock setup can give the ecm fits, you changed much more than that. get a prom then worry about whats broken, probably nothing.

 

When was the last time an incorrect load table gave a check engine?? I think he needs prom tuning, but I think somethings broken too.

What he SHOULD do is get a scanner and see what everything is reporting.

-- Joe

 

i'm not particularly knowledgable when it comes to tuning stock ecm's but i have seen engine mods cause check engine lights. low vacum gives map sensors fits and can cause an overly rich idle that may give a code, also the O2 sensor will further confuse things. What i'm saying is, he has a very limited ability to diagnose bad parts if the parameters they are seeing are so far from the stock engine. If low vacum causes a rich condition is the MAP actually bad? or is the ecm giving it the fuel the tables say it should. Basically stuff like that. Seems to me that if everything is working the engine shouldn't run well at all.

 

Low vac (high kpa) would give more fuel because VE is higher, true. In closed loop, the o2 should detect the difference and provide correction. (and issue a low BLM).. It shouldn't give a code, unless we're talking 80-90kpa at idle. Even then, i'm not so sure.

He's running a MAF setup. Basicly at idle he's looking at a load table, which is based on MAF voltage.

I really wish he was local, cuz i'd like to hear the car running. I had some issues with my "tpi" tune when I switched to a singleplane EFI intake. The fueling and timing requirements are soo different its not even funny. My setup was backfiring through the intake, and bogging out. This was because it wasn't getting enough pump shot. (AE).

Also, ramping out timing a little quicker really helped.

On a TPI setup, the injector angle seems to work well with lower fuel pressures. On my single plane, with the injector straight up, it likes to idle around 50psi. (this is with the tune to 128 blm either way).

First thing I'd do, is look at the setup with a scanner. See what the maf is outputing at idle. then snap the throttle. Might need more spark. Post scan results. I'll be glad to help.

-- Joe

 

Actually i'm thinking maybe the opposite. I'm thinking back off the pump shot, and more spark advance. I think maybe high load at idle, then AE adds too much fuel dump.

-- Joe

 

ok yesterday i ran the car and took it about 60 miles on the open highway, it ran descent but was back firing under load till about 2500 rpm, and it picked up pretty good till about 3800rpm then it wouldnt pick up any more, on the way back the check engine turned on and it ran like it was going to blow up, i stoped turned off the car and started it back up and it was fine agine, still back fired till about 2500, ran pretty good till about 3800.


i took off the maf and it ran a little worse, i also disconnescted the iac and it ran a little better so i then reset the iac and it stayed running a little better, the timing seems a little bit off still, its at about 6* advanced right now, and i checked for vacum leak y spraying starting fluid around the intake and i found none.

i'm gonna try and cahge the plugs again to see if it helps, if some one with a similar set up out there has a prom that they made there selves please help me, i'm really not good at the DIY prom thing and one of you guys could be kind enough to gimme a hand i would appreciate it.

 

The chip is not the problem. I had the LT4 cam, SR and TF heads and ran stock chip injectors and converter. All ran perfectly smooth with 25 MPG and passed e-check. Maf cars can take the changes. I'm thinking something is out of tune.

 

Sounds like maybe one or more of the old stock injectors has gone tango uniform (went bad..leaking/sticking).

 

i checked the resistance of the injectors and they were all at around 18 to 19 ohms, could they still be bad?

also is there anyting else that can casue the problems which i am having?



if anyone out there has any injectors for sale i maybe interested...

thanks guys if any one has any othere suggestions please let me know

 

Those ohm readings are good, which means the windings in the injectors are good...could still stick open/closed though.

Can you beg, borrow/steal a fuel pressure guage to check your pressure? I know you said it was the stock regulator but something may have gone wrong with it or maybe the pump and the injectors may be getting too much fuel or too little.
You may also have to take apart the distributor and see if something has come loose in it (reluctor ring maybe) and is causing erratic ignition timing

 

are the valves adjusted right? i had the same problem once with tight valves.

 

ok, well tomorrow we are expecting a hurricane, i live in miami florida, so i wont be able to check for at least one o two days, but i'll let you guys know after i check everything

thanks again, if any one else still may have an idea of what it could be please keep on informing me, thanks again

 

Did you re connect all of the ground wires on the back of the motor ??

Did you install your cam straight up and down?

and also try having a chip burned running in open loop all of the time.

 

Isn't there someone on this board with a similar setup that can e-mail you a copy of their EPROM for you to try, that would at least address the tuning question.

10:1 CR seems a bit high for a 350, unless the heads are alum, other wise higher CR requires more octane.

I would definitly check the fuel pressure especially at part throttle, the stock regulator is calibrated for 18" of vacuum at idle, too high, or too low may make it difficult for the ECM to supply the required fuel. That's all I can think of for now.

 

well i changed the tps and the check engine light hasnt came back on, code 33 is gone, the car idles so much smoother now, but as i accelerate, the car back fires, and its sluggish out the hole. i dont know what causes this, but if any one has any other ideas just feel free to let me know

 

You just need to chase down the steps others have already posted.

Get a timing light, disconnect the EST, and check your advance. Adjust as necessary.

Get a fuel pressure gauge, disconnect and cap the vacuum feed to the fuel pressure regulator, and check your fuel pressure at idle and while revving the engine a bit.

 

i already checked the timing , its at 6 degrees, the fuel pressure i still have'nt checked.

 

Fuel pressure specs for 86-90 5.7Liter 350
Full vacuum (idle) 30.5-44psi
Key-on/engine-off; no vacuum (same as WOT) 40.5-47psi

 

ok i still havent checked the fual pressure, but its still backfiring, and now its smoking blue, the engine is new but the heads were never redone, so i don't knwow if its the valve seals or the oil ring, it smokes as i accelerate after i stop at a light, or as it revs down after i rev the motor, i took off the valve covers to see if i can see anything, but theres smoke every where , could this be bad heads ( heads were never redone) or could it be the rings gone already, everything but the heads are new. thanks for your guys help

 

Go measure your ring tension and end-gap, and report back.


*since you can't check fuel pressure, I'm guessing that you actually fixing whatever you eventually find wrong ain't gonna happen anyway...

 

You should have at least replaced the valve seals as motors get old they usually get brittle and crack allowing oil to get passed them, the real tell tell in valve seals is when the motor sits and you start it it smokes real bad on start up.

But you kinda goofed by just replacing the whole bottom end neglecting the top.. I guess you can say you rebuilt half your motor, the heads are just as important as the bottom end your going to wish you had because your prolly going to have to go back and tear the top half off and do it right the second time around..

 

its smokin more and still back firing, i'm thinking of just getting a new set of after market heads, what do you guys think, i was thinking something like bow tie heads, or something like pro toplines, or fast burns, i dunno... and also when i take off the valve covers there is smoke everywhere, is that normal for heads to do when they have bad valve seals?

 

Fastburns need a Vortec-compatible intake manifold.

If the smoke you're seeing is actually coming from inside the engine...emanating from the pushrod holes or oil drainbacks...it's more likely blowby from the rings. Combustion gasses get blown into the crankcase, they have to go somewhere.

I'd do a leakdown test on it before pulling the heads. Then again, I wouldn't have put used heads on without new springs, seals, and a good valve lapping.

 

ok, i'm really hoping that its not blow by, everything is new except the heads, and i am still hoping that maybe one of the seals is really gone and maybe its smoking alot cuz of that, i pulled out my oil dipstick and it wasnt smoking from there so i hope i am not gettihg any blow by, also i think the back firing maybe caused by a bad valve seat, on the exhaust valve.

any ideas get back to me. also is there any ways o run fast burn heads with a stealth ram, if any one can help me with that i'd be real grateful, also if not does any one know of any good but not to expensive heads that i may be able to buy

i am running lt4 hot cam, 10:1 cr and HSR

 

ok also i noticed that on one of the heads where the seal goes over the valve there is a small crack around the area where the seal meets the actual head( the seal covers it when it is set in place)

would this cause it to smoke, and if so y didnt it do from the begining?

also my friend just informed me that when the exhaust valve was closed u could see a littl gap where the valve meets the seat, what would this cause, would it cause the back firing?

 

I have one idea...get ahold of a leakdown tester and check all 8 cylinders. Bring each piston to TDC (firing) and test it at 100psig, report back what you find.

 

You never mentioned what happened with your spark plugs? Are you sure the gap is good? Similar problem tuning my TPI for first time, shop manual read gap to .045".

I replaced the plugs as I was putting a fiberglass hood on.

After minutes of scratching my head, (and a miserable ride to work in my new toy, i got beat by a VW!!) I paused and read the emission label on the stock hood which indicated the gap @.035".

Re-set and all is well, just a thought.