I was really hoping the 155 was a typo as i didn't know they really made them that small. DEFINITELY upgrade it. A 255 walbro is cheap insurance, and the install isn't that bad (drop in).
V3 Install Under Way Finally
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My son had it out at a car meet last night. He knew to keep it limited to 5k rpm until we figure out the stumble, bla bla bla..... He calls me from the meet and says the car is cranking fine but wont start. I go out there and run through the usual, spark at the coil, spark at the plug, fuel pump running. All that was good so I'm stumped for a moment until I find the harness connection at the MAF sensor had backed out. Shoved it back in and the car starts fine. He later reports to me that the 5100 stumble is no longer there. It's raining now so I can't do further testing today but as soon as I can I'll verify if the loose MAF connector was the problem.
So, is it possible that a loose connection at the MAF could cause higher rpm stumble I've been talking about?
So, is it possible that a loose connection at the MAF could cause higher rpm stumble I've been talking about?
I suppose it's possible, I had a loose connection at the salt and pepper connectors one time. Talk about chasing a gremlin!
1990Coupe
Founding Member
That pump is way too small, thats a must upgrade IMO. She's not getting enough fuel.
You all are starting make me realize I might be in for a pump upgrade. No biggie, I can do that. Meanwhile I'm changing to Autolite 24's and gapping at .032.
I was thinking about the stumbling issue. At 50psi rail pressure it was giving me 12:1 AF WOT and getting to 5900 rpm. At 53psi it was giving me 11.5:1 AF WOT and only getting to 5100 rpm. It now make sense to me (I think). The richer mixture demands more from the pump so its hitting the wall at the lower rpm.
Does that make sense?
I was thinking about the stumbling issue. At 50psi rail pressure it was giving me 12:1 AF WOT and getting to 5900 rpm. At 53psi it was giving me 11.5:1 AF WOT and only getting to 5100 rpm. It now make sense to me (I think). The richer mixture demands more from the pump so its hitting the wall at the lower rpm.
Does that make sense?
Correction, the Autolite 24's are going back because they don't fit. They fit the E7 heads but not my GT40's. 764 is my number and they are among the colder of their group already. They had been gapped at the stock spec of .054. I'm just going to re-gap them to .035 and put em back in.
1990Coupe
Founding Member
Makes perfect sense. Exactly what happened to me. Stumble on high RPM, the motor was starving for fuel
As the demand for volume rises the pump cannot keep up hence the flat spot
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I'm gonna take a test drive before I change the pump to see if the plug gap adjustment changed the situation. The stumble feels more like an ignition flutter than a nose dive fuel starvation thing.
The 155 lph pump is 40% more volume capacity than a stock 110 lph. Hard to believe my moderate setup would need more than that. Maybe.... We shall see.
The 155 lph pump is 40% more volume capacity than a stock 110 lph. Hard to believe my moderate setup would need more than that. Maybe.... We shall see.
Duty cycle on a forced induction engine brings down the horse power rating on pumps greatly coupled by pump being rated to run at x psi when raising pressure changes the rating as well.
Page 3 and read the part in red
http://fordperformanceracingparts.com/download/tipspdf/properlyselectingeficomp.pdf
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Calculator says at 6psi of boost with your 50 lbs of fuel pressure you're at with a .65 Bsfc (typical for supercharged application ) for 350 flywheel hp as a guesstimate that you need a 30 lb injector which you have and a calculated pump of 213 lph minimum which puts the reccomeded pump size at 255lph .....
Fuel Injector and Fuel Pump Calculator
Just some food for thought
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Fuel Injector and Fuel Pump Calculator
Just some food for thought
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Here's the Walbro GSS340 255lph on amazon for $65. It's pump only.
I just installed the 155lph Walbro not long ago so can use the pick up sock and harness that's already on the car with this higher volume pump?
Amazon product ASIN B002ERGI7QView: http://www.amazon.com/Walbro-GSS340-Fuel-Pump/dp/B002ERGI7Q/ref=sr_1_1?ie=UTF8&qid=1445991021&sr=8-1&keywords=gss+340+walbro
I just installed the 155lph Walbro not long ago so can use the pick up sock and harness that's already on the car with this higher volume pump?
Amazon product ASIN B002ERGI7QView: http://www.amazon.com/Walbro-GSS340-Fuel-Pump/dp/B002ERGI7Q/ref=sr_1_1?ie=UTF8&qid=1445991021&sr=8-1&keywords=gss+340+walbro
- Dec 19, 2010
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Wow. That's cheap. I don't remember what I paid for my 340, but it was waaaay more than that.
Yes. The gss340 pump uses the stock sock, wiring, and metal housing. I have this pump in my hatch.
First test runs after reducing plug gap from .054 to .035 are in.
Still running 155 lph pump.
3rd gear pull WOT straight up to 6000 rpm before letting off the pedal. No stumble, no hesitations.
Boost exceeding 8 psi approaching 6k rpm but took eyes off boost gauge to monitor tach.
Looks like the pressure was blowing the spark out!!
Still running 155 lph pump.
3rd gear pull WOT straight up to 6000 rpm before letting off the pedal. No stumble, no hesitations.
Boost exceeding 8 psi approaching 6k rpm but took eyes off boost gauge to monitor tach.
Looks like the pressure was blowing the spark out!!
I'm glad it's running great . One last thing on the pump and I'll stop breaking balls - I wouldn't want that pump maxed out all the time like that Even if it's working . Takes one lean pull to hurt it bad . If the pump gets to hot etc that's all it takes esp if it's at its peak . I'd consider the 255 or the 340 for piece of mind
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