'99 bogging down until warmed

[MikeD266]

1999 Z71 5.3 4x4 Ext cab. 250k mostly highway miles.

I know this one will be tough due to high miles and a lot of OE still working but I'll give it a shot anyway. Truck is due for plug and wire replacement. Planning on knocking that off when it stops raining. K&N air cleaner was just cleaned yesterday.

Truck starts perfectly fine cold or hot. Idles fine. Cold running slow acceleration is fine but it's next to impossible to step on the gas with any kind of significance w/o the engine bogging and stuttering. Let up on the gas it comes back fine. Eventually clears up gradually with warming of engine until 65 mph is possible. Once warm STILL not possible to floor the pedal and barely able to get it to drop into passing gear.

Feels like a spark/timing issue. Original timing chain. Little baffled by things running "better" (but not normal) as the engine warms up. I'm also getting either an 0446 or an 0449 Evap code. Have it written down just not handy. Replaced the canister, etc. a year ago but the code didn't clear after a computer reset.

Other than plugs, wires which absolutely need to be replaced and/or maybe an ignition coil - thoughts? Or is this too much to guess at with so much original equipment still involved?

[j cAT]

Originally Posted by MikeD266

1999 Z71 5.3 4x4 Ext cab. 250k mostly highway miles.

I know this one will be tough due to high miles and a lot of OE still working but I'll give it a shot anyway. Truck is due for plug and wire replacement. Planning on knocking that off when it stops raining. K&N air cleaner was just cleaned yesterday.

Truck starts perfectly fine cold or hot. Idles fine. Cold running slow acceleration is fine but it's next to impossible to step on the gas with any kind of significance w/o the engine bogging and stuttering. Let up on the gas it comes back fine. Eventually clears up gradually with warming of engine until 65 mph is possible. Once warm STILL not possible to floor the pedal and barely able to get it to drop into passing gear.

Feels like a spark/timing issue. Original timing chain. Little baffled by things running "better" (but not normal) as the engine warms up. I'm also getting either an 0446 or an 0449 Evap code. Have it written down just not handy. Replaced the canister, etc. a year ago but the code didn't clear after a computer reset.

Other than plugs, wires which absolutely need to be replaced and/or maybe an ignition coil - thoughts? Or is this too much to guess at with so much original equipment still involved?

fuel filter every 30,ooomi ??? measure fuel pressure 60-65psi ???

then remove the UPSTREAM O2 sensors, go for a test run ..if it has power the cat converter[s] are plugged..

[MikeD266]

Thanks, jC. Figured you'd be right there...

Fuel filter is also on the list to replace. Hoping like hell that it's NOT a clogged cat. Still raining here so things are on hold for the moment.

DID stop by an AZone and pulled codes. Have the persistent 0446 Evap that has been there for awhile.

Also have a new 0336 in the mix - Crankshaft Position Sensor. Seems to me that this would be the obvious choice to go after for short money ($46 +/-) to throw at this before really digging in and diagnosing with fuel pressure, etc.... PITA to pull the starter to get to it but I supposed it could be MUCH worse...

Wise/unwise?

[MikeD266]

Now that I have a possibility I did some digging.

Found this to be be a relevant thread and one that you had commented on re: CPS jC.

Think I'm going to go with this for the moment...

[MikeD266]

New crankshaft position sensor in. Problem solved. $46 part AZone. Thanks for the earlier post jC.

[j cAT]

Originally Posted by MikeD266

New crankshaft position sensor in. Problem solved. $46 part AZone. Thanks for the earlier post jC.

thanks for the report . these sensors when they go bad can trick even the computer for defect causes..you had the code to reveal this with your problem...

cheap fix good luck//