my car misses at low rpms/boost

B0B · August 14th, 2008, 01:10 AM

ok, i took my car back to the tuner because it "trailer hitches" at constant speeds when i'm cruising with no load on the engine. we determined that its likely the injectors misfiring when there isn't very much fuel pressure. it runs fine when i step on the gas but when just cruising normally it misses every second or so and its annoying. so my question is, is there any way to increase the fuel pressure? it goes down to about 30psi when i'm not on the throttle hard, and whenever it dips below 30 is when it misses a little bit. if i could raise my mininum fuel pressure up to about 40 i think it would run fine. anyone know what i can do? it has 42lb injectors by the way with a procharger. will different injectors like ford lightning injectors run at lower fuel pressures? my tuner said that if all else fails just sell my injectors and buy a set of green top 42's. but i'd rather not tear it apart and waste the money

RyanGT · August 14th, 2008, 01:29 AM

He can change the fuel pressure. At rpms he can change fuel pressure to different rates. At least he should.

Trick tuners used a complete different fuel pressure function. And the tune i got from MPH had the fuel pressure edited also to higher. Someone else could chime in.

Also i heard draw through mafs with the centri blower sometimes causes drivability issues.

Drgnracin72 · August 14th, 2008, 04:24 AM

yes he can change fuel pressure at different rpms, loads, and boost levels

Drgnracin72 · August 14th, 2008, 04:25 AM

and if he cant fix it, put 42s in it and go to a different tuner

~C~ · August 14th, 2008, 09:04 AM

what color are your injectors? I thought the 42s were green tops!

Trick Tuners · August 14th, 2008, 11:45 AM

Originally Posted by B0B

ok, i took my car back to the tuner because it "trailer hitches" at constant speeds when i'm cruising with no load on the engine. we determined that its likely the injectors misfiring when there isn't very much fuel pressure. it runs fine when i step on the gas but when just cruising normally it misses every second or so and its annoying. so my question is, is there any way to increase the fuel pressure? it goes down to about 30psi when i'm not on the throttle hard, and whenever it dips below 30 is when it misses a little bit. if i could raise my mininum fuel pressure up to about 40 i think it would run fine. anyone know what i can do? it has 42lb injectors by the way with a procharger. will different injectors like ford lightning injectors run at lower fuel pressures? my tuner said that if all else fails just sell my injectors and buy a set of green top 42's. but i'd rather not tear it apart and waste the money

Are you talking about rail pressure? If so, that is correct. The FP should be 40psi + boost, or - vacuum. So at 10psi boost it should be 50 and at 20"Hg (~-10psi) is should be at 30. It sure sounds like the tune is not complete and is too lean at part throttle. I have seen this problem so many times, caused from dyno tuners that only tune for WOT. You should have a wideband on there to protect your investment. If you did, i'm betting you would be seeing 16+ AFR at part throttle.

August 14th, 2008, 01:10 AM	#1
B0B Boost gets you laid 2001 Mustang GT 12.93@113.7 (on the 18's) Join Date: Dec 2006 Location: Milton, WA Posts: 2,601 iTrader: 2 reviews	my car misses at low rpms/boost ok, i took my car back to the tuner because it "trailer hitches" at constant speeds when i'm cruising with no load on the engine. we determined that its likely the injectors misfiring when there isn't very much fuel pressure. it runs fine when i step on the gas but when just cruising normally it misses every second or so and its annoying. so my question is, is there any way to increase the fuel pressure? it goes down to about 30psi when i'm not on the throttle hard, and whenever it dips below 30 is when it misses a little bit. if i could raise my mininum fuel pressure up to about 40 i think it would run fine. anyone know what i can do? it has 42lb injectors by the way with a procharger. will different injectors like ford lightning injectors run at lower fuel pressures? my tuner said that if all else fails just sell my injectors and buy a set of green top 42's. but i'd rather not tear it apart and waste the money __________________ '01 GT. Just a couple Bolt-ons. 0rwhp 0rwtq. Epic Turbo build in progress 2003 Rubicon (wheelin rig) 2008 Silverado 4x4 (towin rig/road queen) 2009 KTM 450 XC-W (Brap Brap!)

August 14th, 2008, 01:29 AM	#2
RyanGT MM Fanatic 2000 GT Join Date: Dec 2006 Location: Lynnwood, Washington Posts: 4,258 iTrader: 4 reviews	He can change the fuel pressure. At rpms he can change fuel pressure to different rates. At least he should. Trick tuners used a complete different fuel pressure function. And the tune i got from MPH had the fuel pressure edited also to higher. Someone else could chime in. Also i heard draw through mafs with the centri blower sometimes causes drivability issues. __________________ 2000 Black convertible GT: KB 15psi, and other goodies... 1971 Datsun 240 z: Header and rebuilt motor. (The DD)

August 14th, 2008, 04:24 AM	#3
Drgnracin72 I Post Entirely Way Too Much Join Date: Jan 2006 Location: somewhere in oklahoma Posts: 10,638 iTrader: 2 reviews	yes he can change fuel pressure at different rpms, loads, and boost levels __________________ RIP ΜΟΛΩΝ ΛΑΒΕ Political Correctness is a doctrine, fostered by a delusional, illogical, liberal minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a turd by the clean end. One Big Ass Mistake America SHEEPDOGS

August 14th, 2008, 04:25 AM	#4
Drgnracin72 I Post Entirely Way Too Much Join Date: Jan 2006 Location: somewhere in oklahoma Posts: 10,638 iTrader: 2 reviews	and if he cant fix it, put 42s in it and go to a different tuner __________________ RIP ΜΟΛΩΝ ΛΑΒΕ Political Correctness is a doctrine, fostered by a delusional, illogical, liberal minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a turd by the clean end. One Big Ass Mistake America SHEEPDOGS

August 14th, 2008, 09:04 AM	#5
~C~ ~C~, The Other White Meat! Y2K YellowJacket GT ~TBD~ Join Date: Jun 2008 Location: West side B-More Posts: 1,710 iTrader: 2 reviews	what color are your injectors? I thought the 42s were green tops! __________________ BLOWN Bumblebeast! 370 rwhp / 381 ft lbs ~Tuned by JJ at WMS "Like the blind man says......We shall see...."

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