Bucking under no load

289 · 09-28-2005, 07:40 PM

Hi
My 89 5.0 is having troubles it wants to buck under low RPM no load situations. And then other times it does fine it just does it when it wants like something is turning on and off it might do it for 10min or 5 at any time, but its really getting old and I don't even know what would cause it to do this. please help
thanks

mpj76 · 09-29-2005, 08:07 AM

I just had the same thing happen to mine. There are probably a few different things that could cause this, as in most cases. In my car, for the past couple of years, I noticed that every now and then when I started my car, it would cough and struggle to stay on for the first two or three seconds after start up and then surge up to 1100-1200 RPM for one second and then immediately drop to normal idle. I would keep the plugs, wires, cap and rotor new and the MAF and idle air valve clean and this problem would still occur randomly. Then one day it started to do exactly what you described. It would buck and hesitate under low load in high gear. I popped the hood and noticed a slight hissing sound. I traced the hissing sound to a very small crack in one of my vacuum hoses. After replacing the hose, all the above problems went away and the car idles smoother than it has it two years. Sometimes these kind of problems come and go. In my case the hose must have moved slightly during engine vibrations and movements and ulitimately the crack grew more permanent. In my case it was the hose going from under the upper intake manifold to the evaporative emmisions canister. Good Luck

DZEE'S LX · 10-13-2005, 12:08 AM

I agree with the vacuum leak theory.
Had the same bucking problem and then found the vacuum leak in one of the lines under the intake.
It was a PIA to take the intake off but it was a big relief to find the culprit.
She runs great now - and best of all - NO MORE bucking!!!!!!!!

HoodStrype · 10-14-2005, 01:35 PM

I three had the same problem, however fixing my vacuum leaks didn't work- I had just put a 1" spacer on my intake and it started. Turns out she wasn't getting enough fuel. If you haven't added anything it would most likely be a vacuum leak or kink in a vacuum hose.
The main ones on my car that were bad were the one going to the Fuel Pressure Regulator, the one going to the charcoal canister, and my intake gasket had broken when I put the new one on. If you do hear a hissing noise, spray carb cleaner around with motor running until you hear it stop... that's your leak!

PS: Carb cleaner and paint DO NOT MIX...

289 · 10-14-2005, 02:36 PM

Really I have a 1" spacer on
I will try upin the Fuel Press cause I have a adjustable reg
I will also check the hoses
Thanks
Everyone

09-28-2005, 07:40 PM	#1
289 Registered Member Join Date: Jan 2000 Location: Mount Joy, PA , U.S. Posts: 198	Bucking under no load Hi My 89 5.0 is having troubles it wants to buck under low RPM no load situations. And then other times it does fine it just does it when it wants like something is turning on and off it might do it for 10min or 5 at any time, but its really getting old and I don't even know what would cause it to do this. please help thanks

09-29-2005, 08:07 AM	#2
mpj76 Registered Member Join Date: Sep 2002 Posts: 158	Re: Bucking under no load I just had the same thing happen to mine. There are probably a few different things that could cause this, as in most cases. In my car, for the past couple of years, I noticed that every now and then when I started my car, it would cough and struggle to stay on for the first two or three seconds after start up and then surge up to 1100-1200 RPM for one second and then immediately drop to normal idle. I would keep the plugs, wires, cap and rotor new and the MAF and idle air valve clean and this problem would still occur randomly. Then one day it started to do exactly what you described. It would buck and hesitate under low load in high gear. I popped the hood and noticed a slight hissing sound. I traced the hissing sound to a very small crack in one of my vacuum hoses. After replacing the hose, all the above problems went away and the car idles smoother than it has it two years. Sometimes these kind of problems come and go. In my case the hose must have moved slightly during engine vibrations and movements and ulitimately the crack grew more permanent. In my case it was the hose going from under the upper intake manifold to the evaporative emmisions canister. Good Luck __________________ 91 Coupe: FMS 1 5/8 unqual shorty's, BBK off road X-pipe, Super Duty T5, Pro 5.0 short shifter, 2.73 rear, G3 alt, MSD coil, dist, no smog pump, oil cooler, 195K miles, 14 deg timing, 23 mpg city/29 mpg highway @ 65 mph.

10-13-2005, 12:08 AM	#3
DZEE'S LX Registered Member Join Date: Jan 2001 Location: Salt Lake City Posts: 117	Re: Bucking under no load I agree with the vacuum leak theory. Had the same bucking problem and then found the vacuum leak in one of the lines under the intake. It was a PIA to take the intake off but it was a big relief to find the culprit. She runs great now - and best of all - NO MORE bucking!!!!!!!! __________________ Spec Service (UHP), BFG G-Force KDW's, Turbo Coupe 3.55 rear w/disks, 73mm calipers, Stg 1 Twisted Wedges, TFS Street Intake, 70mm TB, E cam, Crane 1.7's, Aeromotive FPR, BBK 1 5/8 shorties, elec fan, FMS Al Radiator, Moroso Wires, Kenne Bell Ramair, March pulleys, Race Magnums, 190 lph Walbro, FMS Al Dshaft, D/S loop, MM 4point rollbar, FMS C spngs, strut tower brace, Tokico Illuminas, Prothane bushings, MM Lwr Conrol Arms, KB welded subs, Cervini Mach 1 hood/valence/side skirts/wing/airdam.

10-14-2005, 01:35 PM	#4
HoodStrype Rearview Mirror Haze Join Date: May 1999 Location: Huntsville, Alabama...a.k.a. "HuntsVegas" Posts: 387	Re: Bucking under no load I three had the same problem, however fixing my vacuum leaks didn't work- I had just put a 1" spacer on my intake and it started. Turns out she wasn't getting enough fuel. If you haven't added anything it would most likely be a vacuum leak or kink in a vacuum hose. The main ones on my car that were bad were the one going to the Fuel Pressure Regulator, the one going to the charcoal canister, and my intake gasket had broken when I put the new one on. If you do hear a hissing noise, spray carb cleaner around with motor running until you hear it stop... that's your leak! PS: Carb cleaner and paint DO NOT MIX... __________________ 93 lx Notch 01 GT ...the epitome of Murphy's Law

10-14-2005, 02:36 PM	#5
289 Registered Member Join Date: Jan 2000 Location: Mount Joy, PA , U.S. Posts: 198	Re: Bucking under no load Really I have a 1" spacer on I will try upin the Fuel Press cause I have a adjustable reg I will also check the hoses Thanks Everyone

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