Porschefile

As the title says, I'm having a WOT cutout issue on my '87 Carrera. I have sort of a hybrid Protomotive Stage 3 turbo kit on it. Currently I'm only running .6bar, but the car is reacting exactly how it did at 1bar. Basically, at 1/2 to 3/4 throttle the car will run perfectly fine, will generate full boost, etc etc. It's only about ~3-4 seconds after I go WOT, the car will cut out violently like I slammed on the brakes. I've been doing the shotgun approach and replacing various components, however nothing has eliminated the cut out. I've come to the conclusion that it is not a fuel issue, and is some sort of electrical/ignition cut out. I've replaced all of the following:

Injectors, plug wires, dist. cap/rotor, plugs (NGK BP7's, one step colder which is proper for this setup), DME relay, Cylinder Head Temp Sensor, all relays and fuses, both fuel pumps, fuel filter, throttle valve switch (made sure it's adjusted properly), and that's about all I can think of at the moment. I've come to the conclusion it's not a fuel issue as I'm seeing ~6 bar at the fuel rail, which is normal for this setup and the rising rate fpr. I'm not seeing any fuel pressure drop at WOT or high rpm. I should be hooking a wideband up in the next few weeks just to verify my a/f's, but I'm almost positive it isn't a fuel issue. I had considered the ignition coil at one point, and haven't yet replaced it however, the cut is so abrupt and under specific circumstances whereas a worn coil should cause a bit more of a broad or random problem and not just at WOT. The problem is also not rpm specific, and will do it under pretty much any rpm if I stay WOT for more than ~3-4 seconds. Here's what doesn't make any sense though. Occasionally when it is fairly cold outside (say ~40-60deg F), the car will run absolutely perfect under WOT for at least a few runs.

The only other things I can think of is the AFM is malfunctioning in some way or that the DME itself is somehow damaged. I looked the DME over and couldn't find any obvious cold or corroded solder joints, or any other damage. I'm also skeptical that the AFM could be the issue because according to Todd @ Protomotive, this type of setup ignores the AFM under WOT. Anyone have any clues? I'm about to throw an aftermarket EFI at the car to rid myself of these issues, but if there's something simple I'm overlooking, it sure would be nice to know about it.

84_Carrera

Do you have a blow-off / wastegate on there?

Also, on my S/C'd SHO, ~1 bar (15 psi on mine) could actually extinguish the spark and I needed to drop the gap on the plugs considerably. Didn't cause a complete ignition failure, but did cause rough / stumbling. How's the fuel pressure?

Jaws911

I've no special or even average knowledge of these things, but i had a similar problem after going WOT -i wrote about in a thread of 4-08-2007 titled "had to be towed". (sorry, not sure how to post the thread location).

Anyway, turned out to be the throttle body sensor, which was replaced , now no problems ...

(i have an n/a '86 cab)

Porschefile

Well, I replaced the TPS and messed around with the adjustment and that had no effect. I originally suspected the plug gap might not be tight enough, but I've double checked and that isn't the issue. The thing is, it isn't a misfire or misfire due to a weak spark, wide gap, etc etc. If that were the case, it would be a bit more progressive and would generally be present at partial throttle and boost pressure as well. The problem I'm having is very abrupt and only at WOT. It feels almost like hitting ignition cut or fuel cut on any more modern car as it is pretty violent. My fuel pressure is ~6bar at full boost, which is right considering the rising rate fpr. Using a fuel gauge with a sender off of the fuel rail, the pressure does not drop on the top end, so it's not a fuel supply issue and is definitely something electrical.

J. Brinkley

which injectors do you have?
edit, that's probably a dumb question no that i re read it

I've read that afms do fail when sooner when boosted, though mine hasn't, and they do still send a signal to the dme at the point where the WOT switch is closed.
there is a off idle switch and a wot switch on the T body, did you change/check both? make sure wot switch engages somewhere around 80%
try afm swap and check
then swap dme
what did Todd say about it?

Mike Murphy

Take this with a grain of salt, since my car is nothing like yours, but I noticed cutting out and attributed it to bad gasoline. My car always did this on Shell, and as a test on a camping trip, I filled up with BP. Actually, that test is reproducible in my car, so it wasn't a fluke. I tested 3 times.

84_Carrera

Silly question but with the turbo heat back there, could your coil / ignition box be baking? On the V6 SHO, the (3) coils are electrically isolated, but in the same module. When the coil pack insulator cracks, (heat expansion??), you get arcing across.

Just a thought.

Edgy01

I assume that you don't have any blow off or pop-off device in the 3.2 system (like we had in the 3.0 liter CIS systems). Once boost gets above a certain value it will blow that thing open. (I had to GE Silicon mine closed on my 1981 which had been turbocharged with a Rajay turbo kit--270 hp!)

Porschefile

Well, the car unfortunately doesn't have any type of bypass or blow-off valve in the turbo system, although I can tell the turbo is well worn and needs to be replaced anyways so I haven't been too worried about that at the moment. Running without a BV/BOV is most definitely bad for any turbo as compressor surge can quickly wear one out. I will be installing an aftermarket BOV once I replace the turbo in the near future. Running without one isn't causing my issue though. The only negative effect of running without the BV/BOV is I get compressor surge quite often, however there is nothing that it can really "blow off" due to the backpressure. I can't even count how many times I've checked all of my intercooler/intake piping to make sure there isn't any boost leaks. It's not quite like SC's where a backfire on the intake can blow the airbox off or anything.

84_Carrera, that's a good thought but I'm about 99% positive the coil isn't the problem. The turbo is outside of the engine bay and at the very bottom. Although it is located on that side, it isn't nearly close enough to the point where it could be causing the coil to overheat. I'm going to replace the coil anyways, however I'd tend to think that if the coil truly was the issue that I would have intermittent misfiring at various throttle levels and boost pressures. The thing is. even at 1/2 or 3/4 throttle, I can still build full boost and the car will run just fine. If the spark wasn't strong enough and the boost was blowing it out under high load, that amount of boost even at partial throttle should still cause a cut out or misfiring at the least.

The injectors I'm running are Siemens #3102 55# injectors. They're low impedance and the impedance is almost identical to that of the stock injectors, so there really shouldn't be any problem there. I'm also running twin Bosch 044 fuel pumps, which is more than enough fuel flow capability for a good 700+whp. Personally I prefer a single pump as a single 044 is more than sufficient. I will eventually remove one of them, but I must confess I'm lazy and haven't gotten around to it yet. I had Todd re-tune the chips for these injectors. Honestly, at this point I'm giving serious though to buying a Wolf 3d aftermarket ems from Lindsey Racing as it's not too terribly expensive for an aftermarket ems, is apparently plug and play, will work with most of the factory sensors, and at least I could give this car a proper tune.