Thread: Pulley drop, now bad miss at WOT

Dropped to a 3.6 today, now at WOT the engine cuts out and sounds like it is starving for fuel. It has done this before the drop but never to this magnitude. I'm not completely ruling out ignition but it seems like it's leaning out to me. With my minimal mods I can't see that I have exceeded the factory fuel system. Anyone have any experience with this? I'm nearing 130k miles on the factory pump and injectors. No codes. I suspect a weak pump but I have nothing to base that on other than age. One of the things I am also looking at is the returnless fuel system on the 05, and the fact that I can't change the fuel filter without changing the whole fuel module in the tank for $300. Facepalm. Anyone know what the fuel pressure should read at idle?

Do you have a way to scan your car at all? I doubt it's a fuel issue.

you need to be able to read your fuel trims to see if there maxed out. If not then it's probably your igntion system

Originally Posted by Aeroheadcww

Dropped to a 3.6 today, now at WOT the engine cuts out and sounds like it is starving for fuel. It has done this before the drop but never to this magnitude. I'm not completely ruling out ignition but it seems like it's leaning out to me. With my minimal mods I can't see that I have exceeded the factory fuel system. Anyone have any experience with this? I'm nearing 130k miles on the factory pump and injectors. No codes. I suspect a weak pump but I have nothing to base that on other than age. One of the things I am also looking at is the returnless fuel system on the 05, and the fact that I can't change the fuel filter without changing the whole fuel module in the tank for $300. Facepalm. Anyone know what the fuel pressure should read at idle?

Should be 60psi. What you need to do is get a scanner on it. Then you need to look at KR, Fuel trims, Misfire, and Bank 1 Sensor 1 o2 MV. You should be seeing 0 or at least less then 2* of kr. Your fuel trims should be whiten 5% of 0. Missfires should be 0 but at least you can potentially see if it is one cylinder in particular giving you issues. Could be a burned wire on one cylinder. Finally if your exhaust isnt leaking and your 02 sensor is good you should be seeing 800mv or higher on the 02 at full throttle in most cases. Yes the narrowband is a horribly inaccurate way to read it but I have used it to diagnose lean conditions before on other cars by watching it start out at ~800mv and by the time they get to the end of a pull it is reading ~200mv and has massive kr / missfires.

Originally Posted by indygrandprix

you need to be able to read your fuel trims to see if there maxed out. If not then it's probably your igntion system

Fuel trims could very easily be perfect at idle and it could still be fuel starved up top. In fact that is usually what happens with a weak pump. Remember that the fuel trims are guessed up top because there is no way for the pcm to actually read afr at wide open.

Thanks for all of the good info. I don't have a good scanner but I might be able to borrow one. I'll check the fuel pressure at idle tomorrow. Of course I run premium fuel, 93 octane. When it starts missing it feels like I hit the rev limiter except the miss is erratic, the power loss is similar. It misses any time I'm at WOT, but worse at high RPM. It only missed at high RPM before the pulley swap. I really don't see how I could be getting KR with all of my mods,and like i said, it started doing this recently on the stock pulley as well. I'm running 3 year old plugs and wires, I'll check the plugs and maybe replace the wires too, but I doubt they are the culprit.

Just because I wish it to be very simple,

pull your plugs and close the gap on them to about .050, and see if it persists. Even though it's only a 3.6" pulley, my guess is with the older plugs (assuming they are the AL104's in your sig) and stock gap, you're probably getting some spark blow out.

Also, check the condition of the plugs while their out, and replace if necessary.

Check your ICM and the coils as well.

x2 on the spark plugs... my car used to feel like it was studdering when it got above 5k rpm... put new plugs on and it fixed it.. I would also check out your coils

Update: Got Torque Pro working and scanned the car. I couldn't duplicate the miss to the same extent today, (23 degrees outside, icy and can't get traction). Fuel trims seem okay, 02 voltage is all over the place so no help there, very rarely did I ever register any KR (maybe twice in a 10 minute trial). However, I am registering several misses on cylinder 4. I will be going through the ignition on cyl 4 when I can stand to be out in the cold again.

AL104's are only like $10 a set. Just change them all and gap them a little tighter and it will likely run fine.

I run 103's and change them out every other oil change

I'd run 605's on your setup. Check the plug out and see how it looks if it's not that check out the wire. If that does nothing swap the coil to another cyl and then finally swap injectors.

I would stick with AL104's, and replace them, gapped about 053. Are you by chance running ZZP wires?

You sized down your pulley, did you swap belt? You may have belt slip. Check your boost for consistency. It will be hard to tell, because at high RPM, it happens quick. You can move coil packs from one to the next and see if your misfire moves.

02's all over the place? Or are they switching like they should be?

Ended up being the plug gaps. They were gapped correctly when I put them in. I've heard of them expanding on their own before but I've never seen it until now. Some of them were over .065. Closed them to .050 and it runs like a champ.