Jaxley

As the title says, I'm running out of ideas as to why it's doing what it's doing.
When I set off, the initial surge is there, but as I press the gas it falls on it's face until the gas pedal gets down to maybe 80%. At that point, it feels like it picks back up again, but I'm going to slow to make effective use of the excess throttle.

Things I've done:
New Plugs, rotor, cap, coil, ICM, fuel filter, fuel pump, IAC, Serpentine.
Checked Fuel pressure static and moving.
Checked/Set timing.
Checked ohms on injectors.
Checked for fuel in Regulator vacuum hose.
Checked for vacuum leak by spraying starter fluid all around connections.
Checked Ohms on TPS.
Checked Ohms on pickup coil.
Checked air filter.
Added Lucas fuel treatment
um.. possibly others...

Looking for more directions. Anyone have anything? Tricky part is, it doesn't do it all the time and there's not much rhyme or reason to when it decides to act up. But it acts up far more than it acts normal.

Thanks in advance for the suggestions.

-Jason

Corvette40

Check your Cats to see if they're clogged.

Joe C

did you clean your throttle body?

ex-x-fire

What was your fuel pressure readings?

Jaxley

Pretty sure cats are just bumps in the pipes.
Cleaned intake and throttle blades.
Fuel pressure was 41 with vacuum and 48 without. And stayed somewhere between the two when driving. (Possibly higher, test rig was leaking a little at test connection after driving)

Jaxley

Tried driving with EST wire disconnected, no effect, just more sluggish.
Tried disconnecting MAP, would barely idle so I assume it's working.
Battery tested good but at 30% charge. Could faulty alternator cause issues? Not smooth DC?

rhyno

did you put all these parts on in pursuit of the issue? if so, wonder if you got a bad optispark

does it do it cold / warm? also wonder if coolant temp sensor could be bad, makes car run too rich and likely bog until air leans out mix at higher RPMs

Jaxley

Dont believe I have an Optispark, but the suggestion is still valid. But most of the parts replacement was because of the issue and the fact that it needed done anyways. I will take a hard look at the coolant sensor. Didnt realize it had that much control on the mix.

Jaxley

question: With timing set at 6* with EST wire disconnected, what should it be at with the wire reconnected? and if it stays at 6*, what does that mean?

chstitans42

Could be a possible computer issue, but that would be an expensive part to throw at the car. Any check engine lights?

Jaxley

So just went out and took the ECM off the plugs and ohmed out everything that comes to the ECM that can be ohmed. Everything checks out. coolant temp, manifold temp, tps, manifold pressure, knock sensor, injectors (i know it's bank, but just wanted to check, 11.9 if anyone cares), ecm grounds and battery feeds.

Chstitans:
no CEC.... but.... I'm beginning to wonder if the light is disabled. Going out to read codes now....

Jaxley

no codes....

tunedport85inject

If you don't have electronic timing advance the circuit need a check,when you reconnect the EST plug you MUST have advance,way more than 6 degrees, at least 20 degrees at 2000 rpms, this means that the timing mark on balancer should disappear beyond the visible part from your point of view when you shot the light gun over it.

Jaxley

it does not.... it moves maybe to 12.... perhaps this is all computer related... PO mentioned changing out the computer to make the radiator fans work...

tunedport85inject

here the spark advance table in your ECM calibration (1990 8$D),this is the amount of timing advance vs rpms

Jaxley

Thanks for the table. my current idle is just above 900 according to the A/C display (31*25). My dash tach is a little higher than that, but i'd rather reference the display. Suddenly wishing my timing light had a tach on it. Currently I'm working down the path of finding either a computer with a serial port, or a serial-USB adapter so I can do a data log.

But based on the table, 20* should be me at idle and it's no where near that. so is it stuff feeding the ECM not working? or is it the ECM itself... May be better off taking it into someone who knows more what they're doing. I know just enough to be dangerous, and have enough pride to make up the rest....

tunedport85inject

this is from my 85 FSM, you need your 90 FSM

Jaxley

Agreed. The FSM would be great... I tried to datalog but the usb-serial cable I have isnt supported by Datamaster apparently.

Jaxley

If I wanted to get a spare computer to test (Gm Ecm 1227727), the part number there shows that other vehicles made by GM have the same one. Can I get one from a different type if it has the same part number and then just transplant the PROM?

Seems that putting the word "corvette" on the ecm doubles the price.... if not more

tunedport85inject

in your 727 ECm calibration and calpack are built into the same Prom so you can use a 727 ECM and slide in your $8D prom.

...Vette TAX...