Mark305TBI

Didn't think this site was ever coming back up...

I just finished (well, about 2 weeks ago) installing a set of SDPC ported L98 heads, Torker II intake, Holley 670cfm throttle body, and double roller timing chain. Now, I can't get the damn thing to run right. When you quickly open the throttle (note: it doesn't do it if you slowly open the throttle) the car sputters, shakes, and backfires through the intake.

I'm about to the end of my rope. The firing order is correct, the timing is correct, the TPS is properly adjusted, I've tried a new ECU (3 different PROMS), the MAP sensor is working properly, as far as I can tell there's no vacuum leaks, the fuel pressure from the pump is good, and the valve timing is correct.

Is there anything else that I'm missing? This thing is driving me crazy. Please help me!

-Mark W.
<A HREF="http://www.angelfire.com/al3/thegreycar">'88 SC Camaro w/ 305 TBI</A>

[This message has been edited by Mark305TBI (edited September 11, 2000).]

Pablo

iTrader: (1)

You need a custom chip
whats happening is that the pump shot on your current chip is not big enough and this causes intake backfires on sudden throttle openings

are these chips custom?

with the single plane and big throttle body you are letting ALOT of air in suddenly.. so you need aLOT of fuel in the pump shot

btw did you change cams? and are these heads the aluminum l98 heads?

your setup can scream when tuned right (provided you did the cam too)
nice manifold choice

[This message has been edited by Pablo (edited September 10, 2000).]

Mark305TBI

No, none of the chips are custom. Two are stock (one from the old computer, one from the new) and the other is a Stage II Hypertech.

No, unfortunatly, the stock cam is still in the engine (I did however add a set of Crane 1.6 roller rockers that I hope will help make up for it some). And yes, they are the aluminum L98s .

Who/Where should I turn for a custom chip (I've seen alot of custom TPI people, but not TBI) and how much should I expect it to run me?

-Mark W.
<A HREF="http://www.angelfire.com/al3/thegreycar">'88 SC Camaro w/ 305 TBI</A>

FastBroker

Custom chip can cost anywhere from less than $50 (if you send them the "data" to burn it) to over $250 if the person spends alot of time w/you and/or your car.

I agree that you need a much bigger cam than stock (even w/1.6's) for your combo. Try the Crane Compu Cam w/either 210deg intake or the next one up (216deg???). Unfortunately, this may make your existing promlems worse and you will need a new chip almost before you drive the car (not start it). You may be able to crank up Fuel Pressure a little as a temp. band-aid...

I am in the process of doing some similar tuning myself with the help of a Snap-On scantool and will post my spark/fuel/etc curves on this site if anyone is interested... Anyone really care for this much info???

Pablo

iTrader: (1)

it will be driveable with a larger cam just run real rich

imho you should burn your own chips
buying a chip from someone is a waste of time they dont know how your car performs they have no idea how much fuel to add or subtract and where

dont be afraid of the computer stuff its real easy

Mark305TBI

What do you need to get into chip burning, and what does it cost? Software, a burner, chips, am I missing anything? Where can I go to look at this stuff? Advice required...

-Mark W.
<A HREF="http://www.angelfire.com/al3/thegreycar/">'88 SC Camaro w/ 305 TBI</A>

[This message has been edited by Mark305TBI (edited September 11, 2000).]

Pablo

iTrader: (1)

Patience! there will be an article posted on this very thing shortly, its allready written up just needs some fine tuning. Theres a little bit more ot it that can be explained in just one post but its not hard at all. So just wait till the article goes up. Start visiting the prom board and soaking up information

DSouthern

Pablo,
I'm intrigued by your comment that with a larger cam the engine will run real rich. Will this also happen on a TPI running a bigger cam and a stock PROM?
I have a 87 GTA, 350 TPI that I rebuilt using ported stock heads, an Edelbrock intake and a ZZ3 GM performance cam. I know this is the TBI tech board but I'm having a real rich running condition.
In fact I am fouling plugs and I thought I had three leaking injectors, but so far have not been able to confirm this. I have not found any leakage with the system under pressure and the fuel rail lifted up to observe the injectors. These injectors were serviced and balanced by Cruzin Performance.
Appreciate any comments/suggestions.
DS

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87 GTA, 350 TPI, TPIS fastpack, ZZ3 cam, ported heads and plenum, modified MAF

812MANY

DS, I'd say check the fuel pressure and replace the O2 sensor...

EFI rarely runs rich unless a sensor is bad or the FP is too high...

Check the codes too (FIRST)....

Pablo

iTrader: (1)

i dont know MAF setups too well, but to hazzard an educated guess, i dont think its your problem

the Map setup for instance uses an RPM vs MAP KPA (vacuum)table to look up how much fuel is added
So say your stock car idles at 600 rpm and dles at 30 kpa which i think is around 19-20 inches of vacuum. The ecm looks up on the chart how much fuel is added and adds it accordingly. When you cruise the vacuum is gonan be a little higher since its just light throttle cruise and more rpm so your ecm looks in that area of the table say 23 inches of vacuum, 1400 rpm to see how much fuel is delivered. So the ecm is assuming how much air is entering the motor based on vacuum.
Now with a larger cam, your car pulls less vacuum at idle (because its moving less air), and at part throttle. So for instance in my case my car idles at 50 Kpa which is around 15 inches of vacuum. if i still had the stock chip the computer is gonna look up in an area of the stock chip that would only have been looked up on the stock motor had it been under acceleration (moderate throttle= low vacuum.. and at low rpm)
So at idle my stock chip was giving me way too much fuel since it was the equivalent of my stock motor under load.

The TPI MAF setup is different in that it actually measures the amount of air coming in so it can adapt to changes much easier. The fact that the ZZ3 cam isnt that big also increases its computer friendlyness. It shouldnt be SO rich that it fouls plugs, but i would advise on starting on your own custom chips youll extract every last ounce of that combination. are you pulling any codes? could be a bad maf and it could definately be a bad o2

DSouthern

Pablo,
Hey, thanks for the info. Very interesting. I'm not getting any codes and I replaced my O2 sensor. I'll have to check the MAF a little closer.
I read the draft tech article an burning custom chips. This sounds like good stuff. When I get my problem fixed, it should be time for a custom chip.
Thanks again.
DS