High RPM miss...only when hot
 

Hey all,

I posted on this many months ago and still have not resolved the issue.

Here are the rules to help me: you must think beyond the obvious. Why? Because I have done it. Fuel pressure checked, valve spring change, EVERY (and I do mean every) electrical component changed (battery to plugs baby). all grounds checked and confirmed. On top of this, I have completely rewired the car except for the stock engine harness wiring. Don't say opti or something noob like that...you will only embarrass yourself.

The car will start to miss above 195 F coolant temp and 5500 rpm. It slowly gets worse as the temps increase until it is just impractical to run it on the course at 220 F.

Give me help because I am stumped!

Ben

opti

opti or icm

2 opti's and 2 different ICM's and still the same problem. You gotta do better than that!

HOWEVER, the 2 optis were NOT AC Delco but the exact same issue? That seems odd.

Get a LS1: Just joking, Could be a sensor?

have u checked the fuel pressure when engine is above 195F on WOT?

No but how does temp difference at the coolant affect the flow of fuel and pressure? Pressure is fine at WOT when checked at 180-190 range.

Too much money stuffed into this engine already so no. It is the only remaining issue I have.

What sensor?

clean the fuel injectors?

These are new injectors and the O2's show no leaning out at high rpm. Further this would be an issue no matter what the temp, right?

You guys are trying but you need to stretch the brain and help a frustrated LT1 owner.

The harness to the opti could be intermittent. Have you checked for good connections on those wires. I've had luck by just moving the wiring harness around on an engine while running to see if anything causes a problem. Your problem is temp dependent, which points to an electrical component that gets overheated and starts to malfunction. Do you have the ability to datalog when it messes up?

^my thoughts as well, check the opti harness all the way along the intake. I've seen enough harnesses in these cars just rot away over time due to heat exposure.

Opti harness is fairly new with only about 5K miles on it.

I can datalog but we cannot datalog the signals from the opti. up top, the rpms just seem irregular (of course because it is missing) and nothing else is prevalent. No voltage variability,etc.

Opti pulses can be diagnosed with an oscilliscope. Here is a link to a thread with a description of how to do it. It helps if you know someone who has experience with a scope. I would also try the engine harness trick while running to look for problems.

http://forums.corvetteforum.com/c4-t...-of-codes.html

Update: put in my old harness (that was giving me no problems before) and tested the car. Same exact issue this was not a solution.

Let's keep trying...