98 cobra cuts out and bogs at wot?? Bad fuel pump? What fuel psi at wot?

[1998jeremy]

My 98 cobra cuts out and bogs at wot runs fine just normal driving. I don't know why.
I changed plugs and fuel filter and cleaned maf and cps no vacuum leeks.
I was having voltage problems fixed it with a new alternator hoping that would fix it.
I'm leaning towards fuel pump. I'll be checking it this weekend.
What should the fuel pressure be at wot?
If it is a bad pump what is a good replacement?

 

[ZeroDCX]

Fuel pressure should be the same at WOT and KOER w/ the FPR vacuum line removed. Around 39 psi IIRC. KOER and FPR connected should be around 29 psi. This is of course on a naturally aspirated engine.

Forced induction cars at WOT, fuel pressure should increase to 39 psi plus 1 psi of fuel for every increase in psi of boost/intake restriction. So if you're vehicle produces 8 psi of boost at WOT, the fuel pressure should be 39 + 8 = 47 psi.

Standard Walbro 255 LPH fuel pump is a great replacement if you're running a stock-ish setup. It's also good for some small boost setups w/ supporting mods.

 

[1998jeremy]

I hope it's just the pump wearing out and its not sustaining enough fuel pressure. I'm running out of options on what is causing my cut out and stumble.
I'm running dual walbro 255 with kbbp on my 03. They seem to work good.

 

[ForcFed93]

Deatschwerks DW200 is a great pump for a very inexpensive price.

 

[deadernie]

Have you scanned for codes? They can be present even without a CEL.

Do you still have your IMRC? It might be stuck closed.

 

[006]

My 98 cobra cuts out and bogs at wot runs fine just normal driving. I don't know why.
I changed plugs and fuel filter and cleaned maf and cps no vacuum leeks.
I was having voltage problems fixed it with a new alternator hoping that would fix it.
I'm leaning towards fuel pump. I'll be checking it this weekend.
What should the fuel pressure be at wot?
If it is a bad pump what is a good replacement?

It's most probably a voltage problem.

Check your alternator pulley. If it's smaller than your original one, the alternator is over spining and causing the voltage to cut out at higher rpms.

Also, if the alternator is not suited for your vehicle, you may experience this as well.

Your stock alternator pulley should be ~2.25"

When the alt overspins, it begins to cut voltage.

To calculate the alternator shaft speed, which should be no more than 16,000 RPM do the following:
Alternator pulley size (ie 2.5")
Crankshaft Pulley Size (ie 5")
Ratio is 2:1 (5 / 2.5 = 2)
Max engine Speed = 5800 RPM
Multiply Max RPM x Ratio (5800 x 2) = 11,600 shaft RPM Max
Idle RPM = 1000
Multiply Idle RPM x Ratio (1000 x 2) = 2000 shaft RPM @ Idle
An alternator needs 1800-2000 at idle to make power and will make maximum output at 6000 rpm, and will start to fail at 16,000 RPM.

 

[1998jeremy]

My voltage is good now. My imrc plates are wired open. I did fuel pressure check it's good under normal driving but when I go wot the pressure starts to drop then spikes back up. I'm pretty sure the pump is just weak. It does have 202k miles on it.

 

[98-svt-stang]

My 98 cobra cuts out and bogs at wot runs fine just normal driving. I don't know why.
I changed plugs and fuel filter and cleaned maf and cps no vacuum leeks.
I was having voltage problems fixed it with a new alternator hoping that would fix it.
I'm leaning towards fuel pump. I'll be checking it this weekend.
What should the fuel pressure be at wot?
If it is a bad pump what is a good replacement?

My cobra would randomly cut out at wot. I replaced the crank and cam sensor. I haven't had a problem since. Maybe theres a way for you to test yours.