Hello,

I did a pretty good search on this forum before I posted this but I cannot find any simple answer to this question since most people are swapping the L67 into an N/A vehicle rather than swapping parts in the in other direction. I have 5 Grand Prixs from '97 to '01 in various states, 4 are parts cars at this point, 2 I purchased for the engines or trans and parts. I drive over 100,000 miles annually and the 3800 engines have been absolutely the most reliable engines for me. I have 1 SE 3800, 2 GT 3800s and 2 GTP 3800SC as well as a '00 SSEI Bonneville, all with over 200,000 miles and most with near 300,000 miles. I cannabilize parts from them to keep my remaining '99 GT running and I currently have 454,000 miles on it with it running great.

Before my tranny went out on my last GTP I replaced the fuel pump. Since I'm swapping the newer parts onto my current GT and the original fuel pump had almost 450,000 miles I decided to pull the new pump from the GTP and put in into the GT before it went out. It has run great the last 2 months, until the weather warmed up and now anything over 80 degrees and the car with randomly sputter and die. Not like the CPS (which I've changed a number of) the tach doesn't drop and the car feels like it's running rich. I can even smell a fuel rich smell if it happens a few times. I have an HPtuners and the LT B1% goes out of whack right before it quits, telling me the fuel pressure is in question. The car will start back up and run fine, and usually won't repeat the issue until I'm cruising on the highway and let off the throttle, the engine will stumble for 10 seconds or so, so I put it in neutral and let it quit, turn the ignition off and back on, start the engine, and put it back into drive and it may run for several hours or 5 minutes. It gets worse with more heat and does it continually if the car is let sit idle hot in any weather over 82 degrees. On my last trip from Michigan to Florida, it made me laugh because the issue started for the first time in Kentucky right at 80 degrees, was the worst in Florida and as I got back into cooler climates under 80 degrees back through Kentucky went away completely. It only came back today in Michigan because it is 82 degrees out today. I started trying to research the difference in pressure between the 2 pumps without any luck.

I may be answering my own question, but does the 2-speed SC pump possibly create too much fuel pressure in the system, in which the stock PCM of the N/A causes the engine to run rich? This would worsen as the temperature gets higher as less fuel is required with the warmer air mixture. I'm going to swap another stock N/A pump with an unknown mileage out of one of my parts cars and see if the issue goes away, but I'm curious if anyone else has had a simular situation with the difference in the two fuel pumps. I should have just waitied until the eom fuel pump died, but after 450,000 miles I figured it would go at some point soon, usually at the worst moment possible so I thought I'd be proactive, only to create this issue. Any feedback would be greatly appreciated.