Sputtering '95

[Guest Friz]

I had to drive to Central Fl on Wednesday and notice a very mild miss at part-throttle. Idle is good, fairly hard acceleration is good, and no miss when coasting.

However at part-throttle maintaining highway speeds (50-75mph) and light acceleration, it has a very slight roughness to it. Just enough to aggravate me.

I threw a set of plugs and an air filter at it yesterday, no joy, so I drove on home today.

Here's my plan; full tune-up(plugs are in, get cap, rotor, and wires), timing check, and a fuel filter.

There was not enough tool support and my sister's house to delve further.

The motor has 22,000 miles on it. Am I missing something?

[Shaners]

Friz,

Wires, cap and rotor along with a new air filter would be a great place to start.  

 

It is possible you just got some bad fuel too...  but if the other stuff is original, then it is about 7 years old and needs attention.  Especially living in a Southern Climate.

[Guest Friz]

Almost nothing is original, I replaced the motor two years ago. The fuel filter was changed just before the motor. I ran almost three tanks of gas through it this week, so I pretty sure it's not bad fuel.

I'm avoiding the dreaded "fuel pump" idea.

Here's another idea, should I think about replacing the injectors themselves? They ARE original. I do always buy good gas (name brand), but I'm kinda slack when it comes to running cleaner through the fuel system.

[Stepside Z]

I would try the injector cleaner. It couldn't hurt. It seems that if the fuel pump or injectors were bad or going bad then it would have some symptoms all the time.

[Shaners]

Do you have any idea how many miles are on the throttle body?

[Kansas Kid]

I think I would try the injectors as a last resort.  My truck has 155xxx miles on the original injectors and I'm not sure if they are bad or not.  I might try replacing them this weekend because my truck seems down on power and gas mileage.  But I've never heard of anybody replacing the injectors on a TBI truck before 100k miles.  Anything after that it might be a good idea.  (The injectors are about $50 a piece, so its not too bad cost wise)

[Guest Friz]

Do you have any idea how many miles are on the throttle body?

The truck has 84,000 on it. When I replaced the motor, it was a GM crate "long-block".

[Guest Friz]

Here's the latest.

Full tune-up; plugs(.035), wires, cap, rotor, air filter, PCV valve, fuel filter, timing check. The timing is advanced about 2 degrees, but I need a new distributor wrench to get to it.

The last two tanks of gas had FI cleaner in them.

Between 2000-2500 rpm there is still a slight miss. It doesn't matter what gear I'm in or if the TC is locked or not.

I'm stumped.

[bassdog]

Have you tried disconnecting the battery? Something may be stuck in the memory at that range. Just a thought....

[Guest Friz]

Have you tried disconnecting the battery? Something may be stuck in the memory at that range. Just a thought....

Yep, it was disconnected for about an hour while I changed the fuel filter and did the tune-up.

[95Yukon]

When you say "missing" does it seem to drop a cylinder and missing, or just general power loss or surging? I'm thinking coil or fuel injectors. If you have a timing light, you can check the spray pattern of the injectors if you point it in there. The strobe will give you a nice look, but you may not see anything if it only does it under load conditions.

The check engine light hasn't come on at all? Make sure that's working and check it for codes. Could be your throttle position sensor or O2 sensor, but usually that will set a code. The timing should be fine. I think the zero setting is GM being conservative and I have found that a few degrees improves power over factory settings on all the vehicles I've owned. I'm running 4-5 degrees on my '95 but I also always use only premium gas. Make sure the check engine light is coming on momentarily when you turn the key on to be sure the bulb isn't burned out. There may be something there you just don't see it. (?)