The Top DSM Community on the Web

For 1990-1999 Mitsubishi Eclipse, Eagle Talon, Plymouth Laser, and Galant VR-4 Owners. Log in to remove most ads.

Please Support ExtremePSI
Please Support Fuel Injector Clinic

Closed loop stumble

This site may earn a commission from merchant
affiliate links, including eBay, Amazon, and others.

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

inthemidst

10+ Year Contributor
363
23
Aug 25, 2009
PALMDALE, California
I have 96gst with afc fuel psi at 80 and as soon as it hits closed loop I get this stumble for a second almost like all the cylinders misfire at least once. I do have the 6 bolt cas sensor don't know if that's normal?
 
I get misfires for a second and gos away only when it gos into closed loop
 
I think he was referring to the 80psi fuel pressure. Think it should be around 42 psi.
 
Yes, the base fuel pressure for a 2G 4G63 Turbo should be 43.5 psi. So what's the story?

Most fuel pumps have relief valves that open at about 80psi, by the time you account for the pressure drops from the tank to the pump an 80psi pressure at the FPR will be several psi higher at the pump and flow rate will be impacted.
 
I'm saying that IF your running 80psi base fuel pressure you need to fix it and then work forward.

At that base pressure the FPR isn't going to be able to raise the fuel pressure to match the manifold changes and it's likely that most of the fuel is cycling in the tank not going to the injectors. The inability of the fuel rail pressure to track manifold pressure CAN cause tuning issues.

So why are you doing it (or is your measurement incorrect) and how are you tuning for the almost double fuel pressure at idle? It's hard to debug people issues when they are so far out of whack as a starting point.

What does "AFC" have to do with your fuel pressure? Since the car idles and cruses in closed loop but runs open loop when warming up, during acceleration and deceleration I'm wondering when the stumble is actually happening. A few more details would assist in thinking through the problem.

Your other posts don't seem ignorant so there must be some reasoning behind what your doing that eludes me.
 
Last edited:
Uh Hmm.
80 psi? If you're on here and have somewhat idea cars, do you think open and closed loop difference in 40 psi may be doing it?

Even so, once in closed loop, your right back in open when you floor it. So the 80 psi is only aiding the open loop scenario.

Right?

Unless you run ecm link and change your tables for open loop, to accommodate the higher fuel pressure.
 
Ok I'm a put the psi back to stock.i did it because higher psi give you better fuel atomization therefore better mpg.
 
Fixed pressure to 43 lbs still getting a stumble now its a Lil more often than before..
 
Are you running ECMlink? And do you have a wide band? And if you do run a wideband, is it simulating o2 sensor values for ecmlink, and where is it located in the exhaust? Im still very new to tuning, but i believe open loop is mostly to do with readings from your o2 sensors so that is probably where i would start looking. Maybe they got carbon fouled from over fueling from having base fuel at 80?
 
Last edited:
No ECM link just safc and robs facile to log my stft and ltft along with othe sensor values.
 
In terms of atomization I actually spoke to some guys at FIC and he said the amount you'd gain is very little relative to how much more strain it puts on the fuel pump (and the extra fuel pump required to maintain double the pressure). Unless you're running a really balls to the wall track only car, the tradeoff isnt worth it. You can bump it a bit to gain a bit of headroom on injector duty cycle but only as the rest of the fuel system allows.
 
Support Vendors who Support the DSM Community
Boosted Fabrication ECM Tuning ExtremePSI Fuel Injector Clinic Innovation Products Jacks Transmissions JNZ Tuning Kiggly Racing Morrison Fabrications MyMitsubishiStore.com RixRacing RockAuto RTM Racing STM Tuned

Latest posts

Build Thread Updates

Vendor Updates

Latest Classifieds

Back
Top