Chevy truck bucking/mis-firing?

Question

Anyone have an idea why my chevy 350 would buck and missfire under load? Wires/cap/rotor/plugs less than a year old. No check engine light either. Ignition module? It's a 1994 Chevy 2500 P/U with a TBI 350. Any help would be appreciated.

Answer 1

I own a shop, build engines, and own a race car & truck. I have found this one real simple. I'll try not get too technical here, but your spark plugs are breaking down. Replace them, and the problem will go away. Guy's, the real "clue" here is; It breaks down under a load. A bad temprature sensor can make the computer think the engine is still cold, and stay in closed loop, thus cause this. A cracked insulator on one of the spark plugs is quite often the cause. My race car will run fine until I slam it to the floor, and if the spark plugs are bad, it will pop, crack, and just not go at all. If it has a lot of miles on it, check to see if the cam is worn out. A vacuum test can find many problems, so I would advise you have this done too.
Glad to help out, Good luck!!!

Answer 2

Normally the most probable reason would be an ignition misfire due to a bad plug wire or two for example, but you've replaced your wires. You could raise the hood at hot idle on a moonless night and when your eyes get accustomed to the dark, see if you notice any ignition sparks jumping off the plug wires when you punch the throttle from under the hood. If so, you've got some high resistance wire paths to the plugs to be corrected. In addition, review other owner complaints and manufacturer's TSBs at these websites for your vehicle. The GM throttle body injection requires higher fuel pressures like 65 psi maybe, so measure the pressure with a shop fuel pressure gauge (link below).

http://www.edmunds.com/maintenance/MaintenanceServlet
http://www.mycarstats.com

Answer 3

I'd remove the ignition module clean it off and add silicone ignition grease between the module and distributor housing. Tighten it securely.
Now that's attack the the red rubber silicone washer between the coil and distributor cap. MSD has a new spring loaded low resistance rotor button that goes inside the cap the distributor and ignition coil. The red silicone rubber washer must be coated on both sides with the same ignition grease as the module. Try that first.
If you still notice a misfire replace the coil with a genuine MSD unit. At the same time replace the distributer cap and rotor with red MSD parts. If all else fails replace the module with a MSD replacement.

Answer 4

I had a suburban that was acting up sort of like that, and the fuel pump was in the process of going bad. It was still pumping, but not enough to do the job when pulling a trailer.

Also, have you replaced the fuel filter in the last 40 or 50K miles? If not, you better do that too.

Answer 5

does it got a 350 vortec in it well i would check the oil and the gas might have some watered down gas in it check ur plugs i got a 67 wit a 350 chevy it runs fine well email me for further questions [e-mail]

Answer 6

TBI's sometimes have a knock sensor (located behind the starter) that sometimes goes bad on high mileage cars, and also, how is the O2 sensor?? was that replaced when the tune-up was done??????

Answer 7

you need to check the timing chain and gears in it small block Chevy,s was good for that ,also check the knock sensor they will cause one to do this also,the most common thing i see on those is the chain and gears worn out,if its got well over 100 k on it id be replacing the timing chain and gears,other wise you may never get it to smooth out,you may also want to check the plugs in it,they can go bad,good luck with it.

Answer 8

did you try high octane gas or maybe put a gas additive in it.