Bad running 1989 s-10 4 cylinder

I have a 1989 s-10 that starts and idles fine But the truck stumbles in every gear.It has no code lights I have changed the plugs , the carb , the fuel filter , EGR valve, adjusted the timing. But nothing changed Has 109k on it

Does the stumble feel like a miss fire? Inspect the cap, rotor and wires. If it is surging and stalling check the fuel pressure. You said carburetor but it may have throttle body injection.

It has trottle body injection Don,t feel like miss fire Runs fine until you step on the gas

Check the fuel pressure. It may be easiest to connect a pressure gauge at the bottom of the fuel filter which is likely a 3/8" rubber hose. It should be 12+ psi.

When you set the timing did you trigger the CEL on? If not the timing needs re-setting.

I do not know what CEL is we just turned the distributer and advanced the timing a few degrees at a time

You mentioned code light. That is the CEL, check engine light-service engine soon light- etc. Generically it is the CEL.

+No the check engine light never came on. But if it did I have a scan tool

To set the timing you must get the test light on which will indicate that the timing will be fixed at base. You need to get the timing corrected and test fuel pressure.

How do you make the check engine light come on. The fuel pump is what I thought but I never had one let the truck start and run every time But The pressure test will be my next step Maybe the pickup on the sending uint has a problem

probably a low fuel pressure situation,has enough to idle but thats about it,should be 8-15 psi. this fuel pump has a rubber hose on the suction side of the pump that often over time will develope a hole or split. it may be that it has a hole and you are losing some of your fuel pressure.and dont go into the gas tank and just replace the hose with the age of this vehicle put a new pump in it, it comes with the rubber hose. i have seen the map/baro sensor cause a similar situation on this particular vehicle but only one time out of all the ones i have worked on. and before some one says that would cause the check engine light to come on, i agree it should but on the one occasion i ran into that problem it did not.

Going to drop the tank Replace pump , filter sock , take a good look at the sending unit make sure it don,t have any cracks or kinks. The only other thing I was thinking is What if my timing chain is badly worn would it cause this stumbling problem.

The 2.5L 4 cylinder has a timing gear. They have been know to fail but when they fail the engine dies. They don’t jump one cog and run “out of time” and stumble. But weak fuel pressure will surely cause the truck to surge when trying to accelerate.