my 85 corvette is still having a missing problem past 3500RPM.
But the thing i have recently found out is that if you don't go past quarter throttle and just let the rpm's build without shifting, it will go out on the rpm's as far as i want it to without any missing. But if i go anything past quarter throttle it does it. I can even feather the throttle and get it to miss and not miss when it on that quarter, over quarter teetering point.

Seems electrical to me.

Things that have been done to the car, only has about 20,000 miles. Sat most of its life.

Open Air Box Lid
Header back exhaust, no cat
High performance coil
High Performance ICM
New cap, rotor, plugs, and accel wires
High Flow air filter
New FPR diaphragm and adjusted cap
Replaced fuel pump, and pulsator, new pump screen
Fuel Filter wasn't plugged and looked new so i didn't replace that

I have no check engine light, but i went and had the it scanned anyways to check for codes, heres what came up:

25 : Manifold ait temperatur circuit low
32 : EGR Failure
42 : Electronic Spark Spark Timing
43 : Electronic Spark Control
45 : Rich Exhaust
54 : Fuel Pump Circuit low

Since i've checked the codes is when i replaced the spark plugs,and the ICM

I was wondering if i got the fuel pump and air temp codes from unplugging those two item when i did the fuel pump and the FPR. The Rich exhaust could have something to do with the missing, if the spark is cutting out it will be throwing all the unburnt fuel into the exhaust, and also i turned up the FPR a bit above stock setting so that could exacerbate the problem. Those are just my thoughts, that might not be correct

So, anyone have any advise, thoughts, help, anything at all?

 

Could be a number of things, but the throttle position sensor sounds like a possibility.

 

TPS was my gut feeling but then with all of the codes im wondering of you ecm is acting up.

You can ohm out you tps off of the car and you can do it on the car by backprobing two of the wires with the ignition on and you can read volts. Look the the procedure on here for more info.

Mike

 

I left my EST wire unplugged by accident one time on my 85 Corvette and it was like hitting a rev limiter at 4000 RPMs. And I have a Miniram... it also set an EST code, I believe 42.

You have 2 EST codes there... I'm just wondering if the timing is not advancing.

I would clear out the codes, take it for a drive and see which ones come back. That way you know which ones are current.

 

I will look that up and test it as soon as I get a chance.


Where is the plug for the EST located at?

 

Right next to the drivers side exhaust manifold by the firewall.

 

Reset the ECM and see what codes show up afterward. Do you have this connector on your car?



If you do, then open the connection for a second or two. If not then you'll have to disconnect the negative battery terminal.

 

I believe I found the plug, was it like a tarnish color with a black strip. A bit hard to tell the exact color from black gunk on the wire. It was next to a big cluster of wires on the firewall. If that is what it was then the plug looked good. No corrosion of any sorts.

 

With the coil I have on it, the high output, I think its like 65,000 volts, I believe. Would this cool need more heavy duty plug wires? I got the accel' from autozone, cut to fit. Could they not be adequate enough to handle the voltage of the coil? Just me thinking here.

I haven't had a chance to go et the codes checked again. I have to drive 25 minutes to the closest o'rilleys, they are the only ones around that can scan this thing. Everyone else doesn't scan anything before 1996.

 

That voltage is the OPEN CIRCUIT VOLTAGE. That's what you would get if the wire were not connected to the spark plug. In real life on a real car you will get about 10,000 volts at the spark plug. It doesn't matter what kind of coil you have. The cylinder pressure and spark plug gap determine what the voltage will be, NOT the coil. The HEI system can put out 50,000 volts, which is more than adequate.

You can check your own codes:

http://forums.corvetteforum.com/1574918379-post18.html
http://corvettephotographs.com/c4vettes/codes.htm

What they mean:

http://forums.corvetteforum.com/1576116036-post35.html