Engine Dies During Downshift

I was out having a little midwinter therapy session in my 1999 F355 GTB. I had been driving the car (not aggressively) for about 15 minutes after letting it warm up for about 10 minutes. Everything seemed normal, so I decided to get a bit more aggressive. I did two 8500 RPM shifts (first and second gears.) By this point I was coming up on a stop sign, so I put the transmission (manual transmission) into neutral and stepped on the brakes. As I stepped on the clutch to put the car in neutral and let off the gas, the RPMs dropped off (obviously) and subsequently the oil pressure dropped off as it normally does. But this time the low oil pressure light inside the oil pressure gauge came on and the engine died. The oil pressure gauge was indicating somewhere between 70 PSI and first thick line on the gauge. (The oil pressure was not anywhere close to zero when the light came on.) My car has never done this before. I stopped at the stop sign, and turned the ignition key off. I checked the oil level in the engine, and according to the dipstick, the oil was well between the min and max lines. The oil appeared nice and clean still, and it's been less than 2,000 miles since my last annual service (oil change.) I was satisfied that I still had oil in the engine so I got in and started my car up. The engine started right up and the oil pressure came up right away to where it normally does after the car is warm and the low oil pressure light and buzzer inside the oil pressure gauge extinguished right away after the engine started. (When the car is warm and the engine is at idle, the oil pressure normally is between the first thin and first thick marks above zero.) [Sorry, I haven't been able to figure out what PSI each hash mark on the oil pressure gauge is supposed to indicate.] So I drove off wondering what just happened. I decided to take it easy on the car and go home. This problem of the low oil pressure light coming on and the engine dying as I started to decelerate and downshift persisted every time I would come to a stoplight or stop sign. Basically, if I stepped on the clutch and let off the gas, and the oil pressure started to drop, the engine would die. (I'm assuming that this is some sort of computer protection system that shuts down the engine if low oil pressure is sensed.) After cycling the ignition key off, and then back to start, the engine would start right up and run normally. This happened probably 8-10 times on the way home, but then magically things went back to normal. I would come up to a stoplight, and step on the clutch while letting off of the gas, the oil pressure would drop to where it normally does (the first hash mark above zero PSI,) no lights or buzzers would come on, and the engine would continue running normally. I decided that it still was best to cut my therapy session short and continued home uneventfully with no more abnormal issues. So Fratelli, what gives? Can you help me out on this one? When I start my car up cold the oil pressure normally goes to the hash mark just below 140 PSI and then it progressively drops off as the engine warms up. (I'm assuming that is normal.) Once the engine is warm the oil pressure at idle power usually resides between the first thin and first thick hash marks above zero PSI. (I'm assuming that is normal as well.) At 70 MPH in 5th gear on the highway, the oil pressure indicates usually between the 70 PSI hash mark and the next thin hash mark greater than 70 PSI.

 

The battery in my car is less than one year old. Back in November/December I had the factory headers replaced with a new set of Tubi headers (which I might add are fantastic!) The job of replacing the headers took a bit longer than anticipated, and the battery was drained while the car sat in the shop. That's the only time recently that the battery went dead. I always keep the car hooked up to a battery tender when it is parked in my garage. After driving the car I'll hook up the battery tender, and the solid red light (charging) will come on for a few minutes and then extinguish, followed by the steady green light (fully charged.) Electrically speaking, everything seems normal with the car. Like I said, this problem with the engine dying upon deceleration didn't start until after I did a few redline shifts and then the problem seemingly corrected itself. Does the F355 ECU have a rev limiter? Could I have hit the rev limiter, activated it, and then for some reason have the rev limiter not "reset" itself after the RPMs go below redline?

Upon cold start up, the car will idle at about 1000 RPM and the idle is very stable. Today was no different. After the car was warm today, and after each time the engine died even upon re-start up the engine would idle at about 1000 RPM and it was a stable idle. I didn't have to toe the throttle to keep the revs up.

 

It's a 1999 F355 GTB 6-speed.

 

I certainly believe that I found the problem. On the driver's side air intake, the tube that feeds air into the air filter box, had slipped off the air filter box completely. So that bank of cylinders were being fed with air being taken in from around the engine bay instead of through the intake at the base of the C-pillar. I'm assuming that would cause the problems that I described to you all. My next question is this- now that I've driven the car in such a state, do I need to be concerned with potential engine problems as a result of driving without that tube connected? I'm thinking that spark plug fowling might be an issue due to an excessively rich mixture or something along those lines. Also, there don't appear to be any clamps holding those tubes onto the air filter boxes on either side. On my engine they appear to just slip onto the flanges on the air filter boxes on both sides without any clamps. Is this the way it's supposed to be, or am I missing some clamps or other fasteners back there?

 

Thank you Dr_Ferrari. I took your advice and turned the battery switch off for one minute and then turned it back on. I then let the car idle for 10 minutes. At first the idle was pretty rough and fluctuating, but after about 5 minutes or so, the idle smoothed out and everything seemed normal. After letting the car warm up, I decided to take it for a drive. I drove about 50 miles before I stopped for lunch. The car ran fine (it never died while downshifting.) There was one downshift where I stepped on the clutch and the oil pressure warning light came on momentarily and I thought that the engine was going to die, but it didn't and the light extinguished. So, I thought that the problem was fixed. I stopped for lunch and let the car sit in the shade for about 45 minutes. After lunch I jumped back in and off I went- seemingly everything was copasetic. I was on a two-lane highway and everything was fine- no warning lights, no engine dying, no engine rough running, nothing to make me think that anything was wrong. I came up on a small town and had to slow down for some stop-and-go traffic and that's when the problems started. The "SLOW DOWN" light started flashing, so I pulled into a parking lot and shut the car down thinking that I would let the cats cools down and see what happens. I sat there for about 20 minutes and then started the engine back up. The slow down light was still flashing, so I shut the engine back down immediately. I sat there for about another 20 minutes and then started the engine back up. The slow down light was out, so I proceeded to drive home gingerly. Back out on the highway things seemed normal again. Then I came up on another small town and some more stop-and-go traffic. This time when I slowed down, the "CHECK ENGINE" light illuminated. All engine parameters looked normal: Oil pressure about 105 PSI at 4,000-5,000 RPM, Oil Temperature about 190 degrees, Coolant Temperature at about 170 degrees. So nothing was out of the ordinary on the gauges. At this point I figured that the problem is probably an oxygen sensor with the check engine light on, and the previous "SLOW DOWN" light on. I continued home (about 50 miles) with the check engine light on (the only abnormal indication on the dash at this point) and continued to monitor all other parameters. Nothing else gave any indications that anything was wrong- no loss of power, no rough running engine, no funny noises, no smoke, nothing. So what do you think now? I'm assuming that a mechanic with the right diagnostic computer can plug in and isolate what made the CEL come on.

On a side note: Like I said before, I recently had the factory headers (which were just beginning to leak) replaced with new Tubi headers. I didn't have any problems before I had the headers replaced. I have Hyper-flow catalytic converters, and Tubi exhaust on the car. The Hyper-flow cats, and Tubi exhaust with the factory headers were on the car when I purchased it about a year ago. I figured that the factory headers were on their way out, so as a preventative measure I decided to put on the new Tubi headers. The Tubi headers were put on the car less than 200 miles ago.