stalling in high rpms.

2000 ssei 3.8 supercharged. starts fine, idles fine. new plugs, wires, fuel filter, pcv valve, k&n air filter cleaned. It pulls good until about 5k rpms and then it just kinda falls flat on its face. I am a mechanic myself so this is kinda irritating!!!:banghead: Its got good fuel pressure and no codes have came up. I don't know if an injector would do something like this? Im really hoping someone has had this problem and can help me with it. I don't care if its just and easy fix or a hard one. I just want to fix it. Being i fix cars all day it sucks when your own runs like crap. Thanks to any help!!!

Good fuel pressure at the point it fades? How about back pressure from a partially restricted cat? Does it loose power or just stop at 5k how about in low gear, same thing? Is this a supercharged engine?

My fuel pressure tester dosent reach far enough to see what its doin when it does it. Yes its supercharged. It still gains speed but just alot slower than when i hammer on it at lower speeds. Its very noticible. Yes it does it in low gear to. U think a cat would effect it at high rpms rather than at all rpms. Ive felt what plugged cats feel like and normally as far as what i have seen, they wont even have much power with it in park or neutral. This car dosen't really have that many miles on it for a 2000 either. Its got 109k. Most of them are highway miles.

I don't know if the cat will cure the problem but its worth a look for sure and a back pressure test.. It was very common for a lot of the 2000-2001 Bonnevilles to have a Cat failure and cause problems such as you have..

Remember tho, when you get into the Boost that 3.8 flows more than a Chevy V8.. If that cat is restricted a little it will make a difference on the top...

As Well, Make sure you are not loosing fuel pressure up near the top of the rev range, if you are dropping pressure causing a lean condition you could chip the pistons...

Let us know what you find..

I had the same problem with my Ultra last year after installing a 3.4 pulley on my SC & doing a PCM re-flash. Fuel pressure checked 45-48 psig on prime & 45 @ idle & increased when burping the throttle! I soon developed a clogged cat, so I removed it and installed a bypass pipe. That helped regain the HP, but I still had the 'drop dead' feeling @ 5300-5500 rpm.

About a week later, I found a hire-line crack in the plastic return fuel hose, so when I fixed that problem, I was hoping that was the solution. It did help somewhat, but did not totally resolve the problem. At that point I was thinking the fuel curves were off on my tune, causing a lean condition and hitting KR. We modified the fuel curves again & did another flash on the PCM. Next, we recorded KR on the scanner @ 5500 rpm and found retard @ 2-4 deg, but I knew this was not enough to cause the engine to fall flat on it's face.

I had a lot of other things going on during this time, so I was forced to live with the problem for about 2-months. Then one day I was driving to the our shop & the engine just shut off. I was able to coast into a side street & called my son to bring the trailer & a fuel pressure tester. When he arrived & tested the pressure, it had 10-lbs, so we loaded it on the trailer & towed it to our shop to replace the pump.

I ordered a Carter pump which arrived with "Walbro" stamped on the side of the pump. When discussing this with Carter technical group, they informed me that they use 'Walbro' as a supplier for their pumps. (Which was fine with me) After removing the tank and old pump, I noticed the electrical connector was different, the Walbro pump had larger spades, so I had to make the terminal connectors using female spade connectors. You can order the correct terminal for the Walbro, but that would take several days to arrive. When I finally had the pump ready to install, I noticed the fitting in the pulsator was not very tight, but out of desperation, installed it anyway. Everything went back together as planned and fuel pressure was restored to 46 psig prime. I thought this was a little low and suspected the pulsator was leaking!

I drove the car for about a week. I did notice some improvement, @ 5500 rpm, but still had some 'drop-dead' felling now @ 5800 rpm. The next day, I called Walbro seeking advice and they asked me if I eliminated the pulsator & installed the rubber hose supplied in the kit. Of course, my answer was NO! They said that the Walbro pump was designed to operate without a pulsator & advised me to remove the pump & install the rubber hose in place of it. I do have a rack, so removing the tank again was less than a 30-min job, and once complete, fuel pressure jumped to 52-psig @ prime # 48-psig @ idle & with throttle burp, it jumped to 60psig. Now I was ready for a test drive knowing my fuel pressure was much better than before. Bingo, problem resolved and full power every time up to 6000 rpm!! (Yes my PCM fuel shut-off was moved to 6200 rpm during the reflash)

In summary, check the cat first and if that checks ok, you are starving for fuel @ high rpms!

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