unprdictable1

iTrader: (2)

Ok, I'll start with some brief history. It's a 85 Z28 with a 305 to 350 conversion tpi. Every thing was converted correctly, including all sensors, ECM and chips. Runs GREAT!! accept for 1 small issue. From a dead stop, if you floor it, the car pulls hard and strong all the way to about 4800 rpms and shifts fine and keeps on going. But if you are rolling at about 25mph then floor it, it stumbles and hesitates around 3500-3800rpms like it's not getting enough fuel.

Before everyone tells me to go putting a Holley Stealth ram on it, or other intake. I want to keep the stock set up. I just want this to be a fun weekend street car.

Here are some of the settings:
IAC relearn base idle at 500 rpms
AFPR set to 50psi (holley)
Base timing set at 6 degrees
22lb BoschIII fuel injectors (South Bay)
BLM count at 129-131 (idling in my driveway)
INT at 129 (idling in my drive way)
IAC steps 34-47 (idling in my drive way)
Closed loop
Engine temp 210 degrees
o2 sensor is switching rich to lean, just fine
TPS 0.56v
Idle at 950rpms
MAF 9gps
stock 195 degree thermostat
(yes the motor has a cam in it, Not to radical, slight lope to it, have no clue as to what cam??)

Mods:
Mallory Ignition
Flowtech ceramic headers
"Y" pipe, Flowmaster cat back system 40 series "No Cat"
SLP Air Foil
Stock Cast Iron heads
Stock intake and runners

Now, the odd thing is that while monitoring the fuel pressure and power braking the car. The pressure drops to around 35psi when it starts breaking up and stumbling. The previous owner told me that he had installed a new high performance fuel pump from Summit racing. This may be true (then again it might be a lie, due to all of the parts I had to change that he said he already did. Which he didn't) The fuel filter is brand new.The fuel pump is pretty loud when the car is running. In my experience usually when a pump is that loud, it's on it's way out the door. I have gotten a code 43 when it stumbles and found out that my BLM count was at 154 (lean) when this happened. ( I know it is not the "knock sensor" ohms out just fine) My question is, has anyone ran into this issue? And do you think the fuel pump is not sending enough fuel when it's under certian load conditions? He may have installed a high volume fuel pump that works great under regular load but can't handle the pressure needs when rolling and then hitting WOT. Any thoughts and advise are welcomed. Thanks for your time

Tom

old z mzn

iTrader: (1)

stock chip

Tony89GTA

iTrader: (7)

I wonder with the cam in there that the car requires more acceleration enrichment in the chip or could be to much, basically your pump shot is off if you understand carbs more.

I would tape the fuel pressure gauge to the window and do a couple full throttle runs and make sure your fuels in line. Check your BLM's all over and see what the general fuel trim looks like. Also record what's going on with your scantool then go over your data later and see if something shows up like a dead spot in the TPS or whatever. Might want to invest in a WBO2 as it's a great tool for tuning and figuring out problems like this.

Guess once you checked all that out and there is nothing physically wrong you will probably need your chip tuned.

DAVEY420

When I swapped my 350 in, I kept getting that code 43. with known good knock sensors. After searching about it I read that the knock sensors from the 305's were more sensitive. I swapped to a 350 ks and esc module and haven't seen that code again. Maybe worth a shot.

watajob

iTrader: (29)

+1 on the WB O2 and a proper tune. A datalog session will have the answers.

DAVEY420

Can u datalog an 85 computer? When I hook mine up it says Do Not Drive all over it, damage can result. I'm not sure thats y Im askin?

1989GTATransAm

iTrader: (3)

"I wonder with the cam in there that the car requires more acceleration enrichment"

That would also be my first thought. You need a custom tune as stated above.

unprdictable1

iTrader: (2)

This custom "tune" that you all are speaking of, refers to the the "chip" in the ecm being re-programmed correct? Where or how do I go about getting this done? Should I just give "Jet Performance" or "Hypertech" a call and tell them what I have and get a chip from them?
Just to let everyone know, since the 305 was swapped out to a 350. The ECM and Chip are for a 1985 Corvette with cast iron heads. The camaro and the corvette for that givin year use the same ECM but different PROM chips. I am going to be installing a set of 3.73 gears with a posi unit in the next few weeks. I already have the parts (ordered them from JEGS) more gear may help or make the problem worse, we'll see. I'm gonna do a few fuel volume tests to see what the pump is actually putting out.

I also have WinALDL with a cable that hooks up to my DLC to my laptop. I have recorded some of the data and found the file and tryed to look at it, but it shows up in "note pad" and it is really hard to make out each set of figures. I have not tried to drive the car with WinALDL hooked up and running. Is this possible to do, with getting acurate results? As when I have the program hooked up to the car the cooling fan runs constant and the rpms increase by about 300rpms kind of like a "Test Mode"

Tom

Jaxom

Do yourself a favor and do NOT call Hypertech or Jet. Mail order tunes are bad. If you have the patience and the time to learn to do it yourself, it's by FAR the most rewarding and cost-effective way to go. It just takes time to learn how everything works. Bury your face in the DIY-PROM forum for an hour or two, read the stickies especially, and decide if you want to tune it yourself. If not, call some performance shops in your area and ask about custom tuning. Be sure to tell them it's TPI as some shops don't tune EFI on anything this old.

The guys on the PROM board can answer your WinALDL question too. I would if I could, but don't have any experience with that particular datalogger.

Street Lethal

iTrader: (16)

Doesn't sound like injector pulse width in the chip because fuel pressure should remain either constant and rise, not decrease w/load. Check injector ohm to make sure they are all opening, check your fuel lines, filter and regulator for signs of any leakage under higher pressure, then finally replace your fuel pump. At WOT from a dead stop your immediately in Open Loop so the ECM simply dumps fuel into the engine, but at part throttle from a roll your INTegrator has averaged a calibration based on an already decreasing fuel pressure, which may be causing a stumble when you blip the throttle from a roll just until the O2 can catch up and correct. It sounds like you have a fuel leak somewhere, or bad pressure....

ninetyone

iTrader: (2)

you may not like a 373 gear in that car, you will be faster with a 342. 373 may throw you out of your usable powerband too soon. i think your 323 gear is just fine.

ninetyone

iTrader: (2)

i would try lowering/leaning out that fuel pressure a little.

unprdictable1

iTrader: (2)

I used to have a 82 Z28 305 back in the day with 3.73 gears, I loved it!!! Thats why I'm putting 3.73's in this car.

unprdictable1

iTrader: (2)

By lowering my fuel pressure the problem gets worse, my BLM's stay in the 147 range (lean) and the stumble comes on quicker in the power band. I'm almost positive that it's a fuel issue. Just gotta figure out if it's the pump, or the tune that is causing the issue.

unprdictable1

iTrader: (2)

No fuel leaks anywhere, short of me rebuilding this car from the ground up. I have installed a new fuel filter, new injectors, new AFPR, and new fuel lines. All of the injectors are brand new and firing, you can hear them really well with an automotive stethascope. I am thinking you are right with the fuel pump not delivering on demand from a roll. I'm gonna install a new Holley in tank fuel pump that has a max output pressure of 110psi, and use the AFPR to dial in the correct pressure to keep my BLM's near the 128 range. Hopefully this will solve the issue, so I don't have to start messing with doing custom tune stuff.

Street Lethal

iTrader: (16)

It really isn't as hard as it seems, but then again it doesn't sound like your tune is the problem. All we really do is tune fuel consumption, as we bring pulse width as close to and to achieve 128 BLM (0% correction) as possible, which simply makes the ECM's job easier in averaging stoich. That is all that it really is, aside from tuning the spark tables of course. I agree though, with a new fuel pump and adjustable regulator, just raise or lower your fuel pressure until you can average close to 128 BLM across the boards, and if you can't, then I would look at and consider a new prom....

ninetyone

iTrader: (2)

no, no,no, Your 82' was not a tpi car nor was it a 700r4 trans was it? Tpi will not like a 373 gear. You may get thrown right out of your usable powerband. Where your car really shines and just end up at the end of the powerband too quickly where the tpi runs out of breath! Your 700r4 is also geared very low in 1st gear. How are you going to launch that thing now?

unprdictable1

iTrader: (2)

Read the begining of my post, "Before everyone tells me to go putting a Holley Stealth ram on it, or other intake. I want to keep the stock set up. I just want this to be a fun weekend street car."

So the 3.73's will be just fine for driving around town, or cruising. It is not a drag car, or anything hardcore at all.

DENN_SHAH

iTrader: (1)

the computer system GM used on TPI thirdgens in 85 was trouble prone at best. if they used the same ECM on the vettes, then it isn't any better.
they also have a very slow update when data logging.
86 and later MAF systems are much better.

like was said, the fuel pressure should not drop during WOT. if it is, then that will be the first thing you'll need to take care of. no amount of chip tuning can help if the fuel pressure isn't right.

with 3.73s and a 700, first gear will be pretty short, it should make for some fun off the line takeoffs

myzblubyu

I have 3.73s in my '90 IROC with the L98 and I love it... I'm also getting 24mpg on the highway with 27.6" tall tires. Peace..

unprdictable1

iTrader: (2)

The fuel pump was the problem!! I installed a new Racetronix system w/ a Walboro 255 pump, fuel pressure set to 50psi unregulated, and she hauls ***!! from a dead stop or rolling, punch it, and she flies!! Now for the gears & posi unit!!

88irocz28bwj

just bought a 350 carb engine, i have a 305 tpi, i was wondering can i use my parts off the 305 to make the 350 a tpi engine, if so what do i need to do/

utilityguy2

iTrader: (1)

It would bring more results if you start your own thread, This one is on different subject. put it in the Engine swap forum would bring most responses. Good luck.

TPIVette

A steeper gear will definitely feel faster, but with a long tube runner set-up the car will be slower at the track compared to a 3.42 or 3.23.