Resolved 2004 Mach 1 WOT fuel/spark issue?

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May 23, 2022
Hello all,

I am in the process of recording datalogs for my tuner to get my Mach 1 dialed in. The base tune is dialed in according to my tuner, so he requested some 3rd gear 2,000 to 5,000 rpm pulls. On the first pull at WOT it felt like I hit the rev limiter at ~5,000 rpm. I am not sure if it is actually hitting some sort of limiter but it feels that way, if that makes sense. My tuner explained he obviously does not have the rev limiter set that low. He explained on the datalog that around ~4,800 to ~4,900 rpm he sees the fuel pressure spiking. At idle the fuel pressure is around 39~40 psi. He said everything else on the datalog looked good. I 100% trust my tuners word, as he tunes my friends cars and has tuned one of my other mustangs. He recommended I check the spark plug gap. I have basically brand new NGK TR55 plugs gapped to 0.052 inches. I rechecked the gap, same issue. It has a basically brand new Walbro TU229HP-2 fuel pump. This is supposedly 255lph. Could I be running out of fuel/have a bad pump? It is hard to start. It will never start the first try. It will only build up 5-10 PSI with one cycle to the run position, but I have been told this is common with fuel pump assemblies that come with the PPRV already removed. It seriously feels like I am hitting the rev limiter whether I am or not. It will not climb over 5,000 and has that thumping sound/feel of a rev limiter. I still need to physically verify the fuel pressure at WOT when the problem happens. What else should I look at here? Any help is appreciated.

24 pound ford injectors
Walbro TU229HP-2 fuel pump
Stock MAF
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Weak fuel pump, clogged filter, bad return line, and or injectors. Maybe a possibility of the two. Also check coil packs.
Quick update. I ditched the Walbro setup and went to a stock oem fuel sending unit combined with a Deatschwerks 340 lph pump. No luck. The car still hits 5k and acts like it's hitting the rev limiter. Fuel filter is good. Coil packs next I suppose.
Fuel Filter Direction? They have to go a certain way as indicated by the arrow, also just because it would be a new filter doesn't mean it's not defective or clogged. Also check intertia switch and Fuel Pump Relay on CCRM.
Fuel Filter Direction? They have to go a certain way as indicated by the arrow, also just because it would be a new filter doesn't mean it's not defective or clogged. Also check intertia switch and Fuel Pump Relay on CCRM.
It is confirmed the right direction. Inertia switch is good. I've read through it with my multimeter. Fuel pump relay is good. Getting 12v to the fuel pump driver module in the run position. Car runs amazing until it hits 5k in any gear or in neutral. It has a constant P1233 code. I have changed the fuel pump driver module already for this reason but it never goes away. Ground is good for the FPDM, all the wiring shot good regarding the FPDM. Only things I question now is the actual PCM itself or the tune somehow
It sounds crazy but check the battery and alternator they are more important than you think at WOT and also the Crankshaft Position Sensor, Camshaft Position Sensor, and Transmission Speed Sensor.

Another thing is maybe a fuel injector at the rail is losing pressure or leaking through a bad gasket. Fuel Injector o rings are cheap and can be replaced easy.
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You know what, Nightfire has a point. Go back and re trace your steps.
I have plenty of times. I ohmed the crank position sensor and cam position sensor after your recommendation. Crank position sensor was 325 ohms, cam sensor was 330 ohms. Seems like a fairly normal reading according to a quick google search. Also the battery is good. The battery voltage in my data logging stays between 12v and 14v. The alternator is a good idea. Probably worth getting it tested. I will check the transmission speed sensor as well, but it also has the same problem in neutral. Any gear including neutral. And checking the injectors is a good idea I will check out as well.
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Also, check o2 sensor wiring - make sure the wires are zip tied clean and not ripped or exposed, or arcing. And exhaust leaks.
I’ve made sure they’re tied and out of the way previously but always worth another look. Over the next couple of days I’ll look at them again. I do get the codes P0141 and P0161. Which are for the rear O2 sensors if I’m not mistaken. Might be onto something there. What do you think about a knock sensor? I’m not getting a code for one but it’s worth looking at. I haven’t looked at the one below the intake manifold yet.
Well intake manifolds heat up at the top of the 5k range, as do hoses to them. And like I said the o2's or anything shorting to ground could cause a jitter. I'm sure you will find out whats going on.
UPDATE: Replaced the crank position sensor, cam position sensor, and changed all 8 COP's, used ford oem of course. Still ran into the 5k issue. BUT as I was driving, all of the sudden my odometer read dashes for a few minutes and it would rev completely free. It would rev beyond 6 or 7k no problem. It was driving fine with the dashes displayed. I stopped for a bit and turned the car off. The mileage came back and it again would not rev beyond 5,000. What are we thinking here?
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There is a ground to the ECU I have taken that off before and cleaned it, also, you could try this.

Try disconnecting the negative battery terminal for 2-4 hours then letting the car do a full re learn. Don't mess with any adjustment screws or idle screws.