Attn: Wrenchheads, help me diagnose my truck's lack of power.

[Baby Tats]

1989 Chevy small block V8 350 with TBI and 250,000 original miles

Recently noticed a drop in power. It is most noticeable when I "step on it"- like when passing at highway speeds. Less noticeable in around-town driving. Also seems to crank longer when starting than it used to.

All fluids are regularly checked/changed and are fine.
No unusual noises.
No noticeable engine miss.
No knocking or pinging.

I replaced the plugs, wires, distributor cap, and rotor button about 1.5 years ago.

I am thinking that it may be a clogged fuel filter. I found a filter along the frame under the driver's side door and it looks pretty old. Is that the only fuel filter?

Also, if a new fuel filter doesn't work, should I change the plugs again?

Any other ideas?

EDIT: Is there anything special about the fuel filter or should I just get whatever generic brand they have at Advance Auto?

[Carm]

fuel filter (EDIT: car specific) and or air filter.

For a truck that old, you should have a repair manual/chilton or hayes.

Carm

[davester]

If you had a clogged fuel filter then I'd expect that you'd experience stumbling/misfiring, not simply less power. Also, that would probably have no effect on the ability of the vehicle to start. Is it fuel injection or carburettor? If the former, then there isn't a whole lot you can do to diagnose the fuel system at home. I would not replace the electrical stuff again. That stuff generally lasts many years and failures would show up in misfiring, not low power.

[jimbrady]

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[wolfcry911]

My God, Baby Tats,
are you driving my truck?

I have the same type truck - GMC 350 TBI 200,000 on truck but only 120k on the engine. Just last Friday I started having a similiar problem. It's starting to get a little better though. I was leaning towards a clogged catalytic converter, but I already bought a fuel filter for replacement anyway. I too have replaced the electronics about a year and half ago.

[Carm]

The fuel filter was my first choice.
Other possiblilities

Fuel injectors dirty - run an injector cleaner. - Should have injectors in most cars after '86
Fuel pump, going bad or not getting enough juice.

Did you gap your plugs or did someone do it for you? Or did they come pre gapped.
Id recommend platinum tip. They last longer then regular plugs.

Also since your truck has such high miles, the catalytic converter might be clogged.

more change :
Carm

[Harbourmaster]

I can not believe that you have made it this long without a FFilter change!

With the crap they sell around here for gasoline I have to change the one on my Dads 85 TPI Astro van about every 15,000 miles.

You need ot get the correct filter for your vehicle and it must be installed in the correct direction, look for a little arrow on the outside to indicate direction of flow.

[Big Daddy Cool]

250,000 miles–
maybe losing compression?
could be cat– how old? after many miles, they can fall apart internally.

Is there a squirrel living in the intake?

[BigGuynRusty]

TBI = Throttle Body Injection. Yes, fuel injection.

Should be at least two fuel filters, one on the frame, one in the fuel tank. The one in the tank can be a major pain, it looks like a sock and it stops water, the water gathers around it like jelly stopping the fuel. Winter conditions can cause lots of water to get in your fuel tank.

But, it sounds like your plug wires, 1.5 years on cheap wires is a year too long.

BGnR

[OWC Jamie]

Last time I worked on an engine (ancient history)
to check fuel supply one removed the house to the injectors , ran the pump and measured GPM or cc/sec.
Sure beats just throwing parts at something like a dart board.