Driveability Issues with 5.7

[inscarguy]

ok here is the issue. I have a 98 sierra with a 5.7. it has not run well in years. I have changed everything(some things more than once). upgraded spiders, intake gasket, full tune up, trans service, fuel pump, pressure is where its supposed to be, etc.... this thing has never run right. it uses a lot of gas, no power, slightly rough idle, pings. I have run higher octane but I should not have to. once in a while I get codes from the O2 sensors but I changed them recently with Delco sensors. I clear them and no codes for months.

mods done: Volant CAI, magnaflow cats and exhaust, vmax spacer.

I barely drive it due to this.

any thoughts?

 

[skylark]

How many miles are on it?

 

[Ironhead]

Like Skylark is saying, we need more information. Ignition: has distributor been looked at, also cap, rotor, wires, and plugs. Fuel: fuel filter, fuel pressure. Have you checked the vacuum? Finally, the engine: compression and leak-down test? Crankshaft position sensor? Cam drive (is camshaft timed correctly in relation to the crank?)

With enough info, the forum may be able to come through for you.

 

[inscarguy]

it has 136000 miles, I had the dist out to do the intake gasket but it ran the same before, cap, rotor, wires, plugs are all new with AC delco parts. no vacuum leaks, compression test was done a few years ago and if I remember correctly they were all within 2 psi. of each other. have not performed a leak down test. not sure on the cam drive.

 

[Ironhead]

Sounds like you've looked after all the basics, so it's something more obscure. The magnet in the distributor is notorious for developing cracks that seriously affect the running of the engine. Might be worth a try, although I know the distributor is awkward to get at.

The computer itself is fairly trouble free, but there are a lot of sensors for things like coolant temp that can affect the fuel delivery. I realize you've done the O2 sensors, but crankshaft position and the cam position in the distributor can cause poor running if they are not right.

Or, you could get rid of your troubles and buy another truck ;-(

 

[superdave]

Distributor drive gear?

You've thrown a lot of parts at it, but I'd be tempted to throw a new distributor at it.

 

[inscarguy]

Ive thought about it but I can see spending over 45,000 on the truck I want. plus I like my truck even with its quirks.