motor cutting out????? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Rhino · 04-04-2003, 03:36 AM

ok here is the situation at about 55-60 mph and starting around 2700rpms my truck will start cutting out and will not go any faster, but if i put it in 2nd gear it will runn fin all the way up to 4000 rpms and easily cruise at 55 mph....so my question is (having little knowledge of transmissions) is this a tranny prob or a motor prob....i have done about as much as i can to the motor filters, wires, cap and rotor and it still does this it is a 305 and a 400 tranny.......thanks for the help....

tom hand · 04-04-2003, 09:11 AM

It's hard to trouble shoot from hundreds of miles away but I will give it a shot. From what you describe I would say it is a fuel delivery problem, the reason it will rev up in second is the gear muitplcation. Check your fuel pressure...a lot of vacuum gauges will also check this if you don't have one ,buy one they are not that exspensive. If it is not up to par change the rubber hoses first and don't forget the one under the cab, they can get rotton on the inside and block the fuel flow. If that is not it check the "sock" filter on the pickup tube in the tank. The reason I say this is usally machanical pumps either work or they don't, but there are exceptions so as a last resort change the pump. Good Luck

*Randy70C-10* · 04-04-2003, 10:24 AM

Valve float could cause this too. (weak valve springs)

Blue68 · 04-04-2003, 04:21 PM

When did it start? Did you change something? Suddenly began?

Once you check the fuel delivery, check the distributer advance mechanism. In 2nd gear at 4k you can easily have 32deg of advance and run fine. But say your advance is still at 32deg in 3rd at 2700, your engine is fighting itself to turn over. See if you have a busted or weak springs.

Set up your timing light and tach to see when full advance is coming in and see at what rpm it drops.

Just a thought.

Rhino · 04-04-2003, 10:17 PM

well i checked out the fuel system and everything seems to be in order.. i have yet to check the timming, but in the process I fliped the lid on the air cleaner so and so far today it seems to be running much better........could this my problems possibly be from a starvation of air????????

04-04-2003, 03:36 AM	#1
Rhino Registered User Join Date: Mar 2002 Location: carthage, tx Posts: 108	motor cutting out????? ok here is the situation at about 55-60 mph and starting around 2700rpms my truck will start cutting out and will not go any faster, but if i put it in 2nd gear it will runn fin all the way up to 4000 rpms and easily cruise at 55 mph....so my question is (having little knowledge of transmissions) is this a tranny prob or a motor prob....i have done about as much as i can to the motor filters, wires, cap and rotor and it still does this it is a 305 and a 400 tranny.......thanks for the help.... __________________ 1968 C20 long bed http://home.earthlink.net/~yup00

04-04-2003, 09:11 AM	#2
tom hand CCRider Join Date: Feb 2000 Location: Olive Branch,MS,USA Posts: 2,232	It's hard to trouble shoot from hundreds of miles away but I will give it a shot. From what you describe I would say it is a fuel delivery problem, the reason it will rev up in second is the gear muitplcation. Check your fuel pressure...a lot of vacuum gauges will also check this if you don't have one ,buy one they are not that exspensive. If it is not up to par change the rubber hoses first and don't forget the one under the cab, they can get rotton on the inside and block the fuel flow. If that is not it check the "sock" filter on the pickup tube in the tank. The reason I say this is usally machanical pumps either work or they don't, but there are exceptions so as a last resort change the pump. Good Luck __________________ 72 GMC Sierra SWB almost finished---- 84 Softail Olive Branch MS

04-04-2003, 04:21 PM	#4
Blue68 Registered User Join Date: Apr 2000 Location: Frisco, Tx, USA Posts: 606	When did it start? Did you change something? Suddenly began? Once you check the fuel delivery, check the distributer advance mechanism. In 2nd gear at 4k you can easily have 32deg of advance and run fine. But say your advance is still at 32deg in 3rd at 2700, your engine is fighting itself to turn over. See if you have a busted or weak springs. Set up your timing light and tach to see when full advance is coming in and see at what rpm it drops. Just a thought. __________________ http://home.comcast.net/~r.landrum/w...tos.html-.html '68 C-10 LWB, '98 Z-71 350 w/accessories (Serpentine), Edelbrock Performer, Edelbrock 1405 (600cfm) carb, GM HEI, CompCam Extreme 4x4 roller cam, Thorley Headers, Carter Electric Fuel Pump, Vintage Air, 700r4, 3.73, disc brakes and power steering upgrades.

04-04-2003, 10:17 PM	#5
Rhino Registered User Join Date: Mar 2002 Location: carthage, tx Posts: 108	well i checked out the fuel system and everything seems to be in order.. i have yet to check the timming, but in the process I fliped the lid on the air cleaner so and so far today it seems to be running much better........could this my problems possibly be from a starvation of air???????? __________________ 1968 C20 long bed http://home.earthlink.net/~yup00

04-04-2003, 10:24 AM	#3
Randy70C-10 Account Suspended Join Date: Mar 2001 Location: Virginia Beach, Va. U.S.A. Posts: 15,320	Valve float could cause this too. (weak valve springs)



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