Since my last post I've driven the car moderately since the misfire problem under higher power has not been solved. Until Today. Thinking it was a fuel pressure problem I hooked up my OBD2 reader and set it for live data. The fuel pressure most of the time was about 44 PSI and occasionally it hit 56PSI. This told me that the fuel pump was not the problem. With other things to do I mostly ignored it. I've mostly ignored my honey-do list for six months and have quite a backlog. I needed to drive over to Spokane a couple of weeks ago and took the freeway. At highway speeds the same problem came up only at a much lower throttle position. Passing other cars was just not possible without misfire. Could it be exhaust flow restriction? I thought that was the only thing that had changed since I cleaned up the wiring and finished the exhaust in October (unless I made a wiring error).

This week it began to snow and stick so I decided this would be a good time to change the oil & filter, swap wheels, tires, brake rotors and install the inner wheel tubs. So while I was under there I chopped off the resonator tips and finished the other work. One thing I needed to fabricate were the splash guards covering the sides of the engine compartment below the wheel tubs. Last time I made them from a thick gasket-type material. It really didn't hold up very well. Debbie & I drive (her Venza) over to Spokane to get some tonneau cover snaps from Tandy Leather. And the light went on. Why not make them from leather? So $50 later I had some 8 ounce per square foot leather about 1/8" thick, some leather dye and some mink oil. I used the old shield as a pattern, cut the leather to shape, applied the dye and then the mink oil as waterproofing to both sides. Some new plastic push-in fasteners and they fit nicely. Since they are exposed I'll re-treat them with mink oil in the spring.

Using the old shield as a pattern. Then cut out with a sharp utility knife.


And the resulting leather part


Why did I swap brake rotors? My snow tires are on original 14" rims and those won't work with Corvette rotors. So back to the originals. Today has been mostly clear and warmer so the snow melted and the roads were dry - and full throttle acceleration was back to normal with the exhaust tips removed. Those exhaust tips had a tail pipe diameter of 2.25" but the resonator reduced that to about 1.5", cutting the cross section by 50% and giving more back pressure.

The inside diameter of the tips is much smaller than the outside causing the misfire.


So if you are considering an LFX swap then keep the exhaust free flowing. Now I'm going to need to find a replacement that fits and keeps the same inner diameter. Both Vibrant and Borla look like they have resonator parts that could fit. Solving this has made me much happier since with an unsolved misfire issue I was concerned about driving in the winter. Also with the smaller diameter snow tires the motor hits the redline quicker and then sits at 7,100 RPM making very little power. Need to upshift when it hits 6700-6800. The ECU does not want you to kill your engine.

[This message has been edited by MikesFirstFiero (edited 12-09-2021).]

[This message has been edited by MikesFirstFiero (edited 01-10-2022).]

Just a quick update. I was planning on making the Impala Cruise Control work but after investigation that may prove difficult. According to the Mitchell 1 online manuals the CC needs the parking brake controller and the ABS controller to function which I don't plan to install. I don't know if there is a work-around for the Body Control Unit which talks to them and decides it is okay to engage the cruise function. Since it is CAN bus I might try to figure out what data those two modules send and program a small computer to respond with the correct signals.

The Borla exhaust tips with resonators are in and reduce the idling & low power sounds quite a bit (maybe 6-8db). I'm happy with that. They are big with a 4" outer diameter but they were the only thing I could find that fit and reduced the noise at cruise. They have little muffling effect above 1/4 throttle which is cool so it snarls nicely. Still looking at the DTCs to eliminate high rpm misfire. Got a deal on AC Delco OEM iridium plugs for $3.50 each and swapped them, made no difference, old plugs worth keeping. I think the rebate is good until end of Jan on all AC Delco plugs, check RockAuto.com. I may buy a new coil pack and try it one cylinder at a time. I'm also going to bypass the fuel pump controller and tie the pump to the Hot-in-Run power feed to eliminate that as a cause too. In the end I may need to take the car to someone who understands the LFX and can provide a solution.

Those tips are 4" OD and 13" long and just fit


It's been snowing and the car is covered with dirt. But at least I can keep it in the heated garage and not worry about removing the snow.


Also mounted the key fob detector ring where the old OBD plug was. Looks good and works to hold the fob securely in position. If the correct fob is installed it will start otherwise it won't. The steering column key now does nothing and does not need to be used.

The open hole where the lighter went will be used for a USB connector to the Sony receiver. The red switch is to turn my Escort 360 radar detector on and off.

[This message has been edited by MikesFirstFiero (edited 01-11-2022).]

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" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

[This message has been edited by Dennis LaGrua (edited 01-11-2022).]