Hi fellas. Have a 1998 Cobra. Had it since new with 33 miles on it. It has 5,550 miles on it now. 2 yrs after I owned it I put a 6 psi KB blower unit. Been running great, but after getting out of storage this April I have this high rpm stumble. Runs great right up to red line in 1st and 2nd gears, but in 3rd gear at 6000 rpm it and a load on it the engine stumbles and stutters.4th gear its about 5000 rpm when stumble shows up. Does not feel like a rev limiter though. Changed plugs, fuel filter, o2's, new GMS coils. Still there.Running VP unleaded 101 race fuel in it right now. I have Motorsport 9mm wires on order. Did ck fuel pressure and it is 56 psi under boost. Have not had a problem for the past 10 yrs then this spring I have an issue. What gives? Any ideas?Thanks!

 

Put the the new wires on today.Concern still there. I put new coil packs on last week. Rechecked fuel pressure. When this stutter ocures under load fuel pressure is 52psi and as this stutter is happening at 6000 rpm the fuel pressure goes down to 48psi. Data logged the MAF 4.2 volts. The o2's are at .16 and .22. I am running oxygenated VP MS-101 unleaded racing fuel. I want to say that this situation started eversince I started using higher octane racing fuel. Filled my tank full with race gas when I put it away for the winter. Put a fresh 15 gal of MS-101 a month ago.

 

Do you use a fuel stabilizer when you store the car for long periods of time? Bad fuel can clog fuel lines and injectors.

 

drain the whole fuel system and try again. Pretty sure you have bad gas.

 

Yeah.. Bad gas can cause a lot of problems, especially when you're on a date

 

If your not tuned for that high of octane you will have problems too.

 

try putting in pump gas 93 octane, see what it does.

 

Thank you guys. I am in the process of going through the race gas then I will run 93 octane and see what happens.