I have a 98 GT with a engine from a 2000 GT. Swap went well and runs and drives great but have a slight issue when under WOT at high rpm ranger from 4-5K. Seems like combustion isn't good under load at high rpm as if it's stumbles ever so slightly.
So first the full story of the history of the car and just a small list of mods. Bought the car from a guy who drove it up until sometime in mid 2018 when he spun a bearing and created a bad knock on the bottom end. The car was parked for however long for the remainder ( the guy never said how long it had been sitting) until I bought it in January 2019. The car did have about half a tank of fuel sitting in the tank since he had parked it.
I replaced the engine with a 2000 GT with 157K used engine with a new PI intake manifold, new NGK plugs, new alternator, clutch, rear main seal, new stock flywheel, adjustable clutch cable and quadrant, water pump, a used SVE plenum and 75mm throttle body and a cold air intake with stock MAF sensor. Also have a Bama tuner running on the 93 octane tune right now. I will mention at this time that the stumble has always been present before changing the tune and after changing the tune the stumble may be slightly worse than before the change but the stumble is always present regardless whether it has the tune or not.
Now here's where I'm at presently.... I've ran about 3 or 4 tanks of 93 fuel through it from driving it in hopes to clear out any of the old gas that I'm thinking has been in for 6 or more months thinking maybe the old gas is giving me trouble. I feel like the old fuel should either be gone by now what is left has mixed enough with new fresh fuel would even it out some but still has a stumble. So this morning I finally got a chance to slap a fuel pressure test gauge on and went out for a small drive.
Idle I'm at 28-29 PSI... Casual driving 30-34 PSI.... WOT spikes to 39 but drops back to 37-38 PSI. I'm taking my readings off the port on the fuel rail on the driver side
I've looked around for information on what's to be considered normal for WOT and seen where some have said around 40 or a little higher but I'm not hitting 40 at all. I've been having issues with the fuel sending unit as gauge on the dash is always fluctuating even when I know it has a full tank. My first thoughts is replace the whole fuel pump assembly and then move forward from there if the stumble persists after that.
My question is what do you guys think? Do you think that the old fuel with the ethanol sitting in the tank for months took away some of the performance of the fuel pump causing not enough air/fuel mixture when at high engine speeds? Or is the old gas still in tank somehow and causing problems with combustion? I've also have this stumble to occur going up steep hills now which makes me think more the fuel pump isn't up to par and not providing enough fuel when under a heavy load.
My next steps before I pull the tank and change the pump is simple things such as clean the MAF sensor and change the plug wires as they are some cheap knock off brand I've never heard of and while I'm changing the wires I'll pull each plug while I'm at it to see what the plugs look like and maybe get a clue to what's happening during combustion. I also plan on changing the fuel filter. I still feel like the pump isn't pushing enough fuel but I would like some input to see if those numbers are ok and should start looking elsewhere before pulling the tank.. Thanks for any info!
So first the full story of the history of the car and just a small list of mods. Bought the car from a guy who drove it up until sometime in mid 2018 when he spun a bearing and created a bad knock on the bottom end. The car was parked for however long for the remainder ( the guy never said how long it had been sitting) until I bought it in January 2019. The car did have about half a tank of fuel sitting in the tank since he had parked it.
I replaced the engine with a 2000 GT with 157K used engine with a new PI intake manifold, new NGK plugs, new alternator, clutch, rear main seal, new stock flywheel, adjustable clutch cable and quadrant, water pump, a used SVE plenum and 75mm throttle body and a cold air intake with stock MAF sensor. Also have a Bama tuner running on the 93 octane tune right now. I will mention at this time that the stumble has always been present before changing the tune and after changing the tune the stumble may be slightly worse than before the change but the stumble is always present regardless whether it has the tune or not.
Now here's where I'm at presently.... I've ran about 3 or 4 tanks of 93 fuel through it from driving it in hopes to clear out any of the old gas that I'm thinking has been in for 6 or more months thinking maybe the old gas is giving me trouble. I feel like the old fuel should either be gone by now what is left has mixed enough with new fresh fuel would even it out some but still has a stumble. So this morning I finally got a chance to slap a fuel pressure test gauge on and went out for a small drive.
Idle I'm at 28-29 PSI... Casual driving 30-34 PSI.... WOT spikes to 39 but drops back to 37-38 PSI. I'm taking my readings off the port on the fuel rail on the driver side
I've looked around for information on what's to be considered normal for WOT and seen where some have said around 40 or a little higher but I'm not hitting 40 at all. I've been having issues with the fuel sending unit as gauge on the dash is always fluctuating even when I know it has a full tank. My first thoughts is replace the whole fuel pump assembly and then move forward from there if the stumble persists after that.
My question is what do you guys think? Do you think that the old fuel with the ethanol sitting in the tank for months took away some of the performance of the fuel pump causing not enough air/fuel mixture when at high engine speeds? Or is the old gas still in tank somehow and causing problems with combustion? I've also have this stumble to occur going up steep hills now which makes me think more the fuel pump isn't up to par and not providing enough fuel when under a heavy load.
My next steps before I pull the tank and change the pump is simple things such as clean the MAF sensor and change the plug wires as they are some cheap knock off brand I've never heard of and while I'm changing the wires I'll pull each plug while I'm at it to see what the plugs look like and maybe get a clue to what's happening during combustion. I also plan on changing the fuel filter. I still feel like the pump isn't pushing enough fuel but I would like some input to see if those numbers are ok and should start looking elsewhere before pulling the tank.. Thanks for any info!