My car has a weird problem: the engine falls on its face at 4,000ish RPM at WOT. I can walk it past 4k under partial throttle but as soon as I open it up it's like it looses fuel/spark. The car will actually decelerate in gear with the gas all the way down. I drove around with a fuel pressure gauge tied to the fuel rail for a little while and the needle didn't drop off when it happened. If I unplug the MAF (to make it run in open loop?) it's perfectly fine and I can run all the way to redline at WOT. No codes, etc. This makes me think it’s a sensor.

I replaced the MAF 3 times with three different remain units (from the same company). The first time it worked fine - for a day. Then it rained and the next day it was back to more of the same. The next two times I replaced it the problem never got better, even temporarily.

I decided to datalog to see what was happening with my car. I bought the Moates cable and downloaded winALDL and hit another bump in the road: data only refreshes every half second or so (no clear before and after data) and the log file is fairly hard to read. It’s easier watching the screen than reading the log, but I can’t watch the screen while driving on public roads. I don’t have access to a dyno (read: I’m trying to fix this myself instead of taking it somewhere).

I can say this: MAF readings make sense. They’re pretty high under acceleration (100+) then drop to around 40ish around 4,000 rpm when the engine dies (no longer accelerating). They increase more or less linearly with engine RPM with much higher increases when the engine is accelerating (ie acceleration @ 3,000 rpm means a higher MAF reading than just holding it at 3,000 RPM). The O2 readings jump around a lot. I can read .04 at one reading and then .6something the next. More often than not it’s generally a higher number but I do get an occasional low number. I’m not sure how much this would impact the car’s performance. The TPS sensor is properly adjusted and has no dead spots. Recorded some knocking reading in the 2,000-2,700 RPM range. Nothing higher up.

I also discovered that the problem is progressive today thanks to traffic on the road I was testing on. I was in first gear @ 4,000 RPM trying to get some data from the dead spot when I saw a car behind me. I shifted to get the RPMs down and met the same problem in second at a much lower RPM (it accelerated for about .1 seconds than died again). I immediately shifted into third and met the same problem at around 2-2,500 RPM. I got off the gas some more (wasn’t on it all the way to begin with) and the car started to do a surging acceleration thing.

Anyone have any ideas as to where I should start looking? The car drives fine otherwise as long as I shift around 3,500 but I would like to be able to shift higher than that when I need to (merging, etc).

 

Rubber intake collapsing? Seen it happen.

Is it cutting out completely? Look at fuel

Is it stumbling, on/off type of sensation? Look at spark

Up top its usually fuel related or igntion.

Since the pump seems to be flowing well at the speeds, I would look towards ignition or other engien causes...

Also grounds on back of pass head can cause similar conditions..

later
Jeremy

 

I had the upper intake apart a half year ago to swap injectors (accell 24#) if that matters. I’m not sure what else you would mean with the rubber intake collapsing.

The motor is a flat out dying sort of sensation (no bucking, etc), which does lead to suspicions about spark and/or fuel. With the fuel pressure gauge hooked up I didn't see any spikes in pressure (ie the injectors shutting off) or drops in pressure (the pump not being able to keep up) so it's a safe bet that the injectors are still firing. It almost has to be ignition related. Plugs, wires, and cap/rotor are both relatively new (sub 7,000 miles) but the ICM and coil (remote coil on my car) are both of unknown age.

Could it be the ICM, coil, and/or the fuel pressure regulator? Sometimes the car has a hard time starting when the engine is cold. I also know that the valve on the brake booster is leaking as it looses all vacuum in a few hours.

It's just weird that the problem goes away when the MAF is unplugged?

Grounds are more than adequate. I’ve got a 2 gauge run going straight to the frame and another one going from the frame to battery negative.

 

When was the last time you replaced spark plugs rotor dist cap and wires?

 

By the last post, everything was replaced aside from the coil and ICM about 7,000 miles ago

 

Some more information. Occasionaly right before the engine is about to fall on its face I can hear a winding metallic sounding noise. Maybe spark falling off? I have no idea.

 

I'm having a similar problem,been fighting it all summer.Checked the TPS,MAF.plugs,cap,rotor,distributor replaced.I only does it at the track at WOT on hot days,sometimes throwing codes,ecs 43,maf 34,or egr 32.All codes will clear and not return on the street,but it acts up at the track.It may just be the rubber intake tube by the maf sensor collapsing,because of the heat of the day and high under hood temps.