Strange white smoke exhaust

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missouritig

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Not to beat a dead horse but still dealing with this issue and I beleive it is unburnt fuel.

Today I checked the plug wires and found they were in very poor shape, going to do the "tuneup" with plug wires cap and rotor. Also going to check the condition of the ignition coil.

i tested the fuel pressure and its at 50psi key turn on and i am not leaking any fuel pressure. Thats thanks to a new mpfi set i installed.

Driving it now i get loads of backfiring. Reviewing the factory manual I looked at the ignition system and that led me to the bad wires.
 

Erik the Awful

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White smoke is not fuel, it's either water vapor or coolant. Black smoke is fuel. Grayish-white smoke is oil. Are you losing coolant?

You are fighting multiple issues, and you may still be running rich. Definitely do the tune-up and then report back.

50 psi is a little on the low side for a Vortec. On the old poppet system that would cause a dead miss, but with the MPFI it should abide. Still, it could be running a bit lean, causing the backfiring. What does your data stream say, especially the O2 sensor?
 

Schurkey

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The engine has been run cold, and with a failed O2 sensor. Good chance that the catalyst(s) are damaged. So again...run that thing long enough to get EVERYTHING warmed-up. Maybe the catalyst(s) can come back to life again.

Replaced the two before - cat o2 sensors.
Good. Now replace the downstream sensors...they're almost certainly past their prime.

I had less white smoke after letting it run but still smells a little rich.
"Rich" does not have an odor. "Rich" mixture promotes carbon monoxide (CO), and CO is colorless and odorless. Which is why it kills people. Makes 'em sleepy with no obvious signs of being poisoned.
"Misfire" smells and has eye-watering hydrocarbon (HC) fumes.
"Failed Catalyst" smells kinda bad, has some eye watering fumes, but not nearly as bad as outright misfire. It's what all cars in good condition smelled like in the days before catalytic converters.

First Guess: You're smelling uncatalysed exhaust because the cat was damaged from previous engine problems--running cold, running rich.

Drove the truck around for about 45 minutes and not one bit of steam came out the tailpipe.

it was warm out today but I know I drove it before in warm weather and had tons of steam coming out a few months ago.
Seems like that problem is history.

Im going to throw my hat on a bad fuel filter and perhaps some bad gas?
Unlikely.

Not to beat a dead horse but still dealing with this issue and I beleive it is unburnt fuel.
If your eyes aren't watering, it's not unburnt fuel (HC).

Today I checked the plug wires and found they were in very poor shape, going to do the "tuneup" with plug wires cap and rotor. Also going to check the condition of the ignition coil.
Will the coil fire a spark-tester calibrated for HEI?

i tested the fuel pressure and its at 50psi key turn on and i am not leaking any fuel pressure. Thats thanks to a new mpfi set i installed.
As said...50 psi fuel pressure with no vacuum in the intake manifold is kinda low. Is your gauge accurate? Does it increase with multiple "priming" cycles?

Driving it now i get loads of backfiring.
Backfiring in the intake manifold is not the same as backfiring out the exhaust. Which is it?

Did you get the wires routed properly? Lots of space between #5 and #7 wires? Preferably routed EXACTLY like the service manual shows, using all the original plug-wire looms?
 

RoscoCDN

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where i live, old vehicles smoke like crazy until the exhaust is hot. weird about the temps though. when my buddies showed similar symptoms (97 c1500 350ci) it was a bad thermostat.
 

missouritig

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Good. Now replace the downstream sensors...they're almost certainly past their prime.


"Rich" does not have an odor. "Rich" mixture promotes carbon monoxide (CO), and CO is colorless and odorless. Which is why it kills people. Makes 'em sleepy with no obvious signs of being poisoned.
"Misfire" smells and has eye-watering hydrocarbon (HC) fumes.
"Failed Catalyst" smells kinda bad, has some eye watering fumes, but not nearly as bad as outright misfire. It's what all cars in good condition smelled like in the days before catalytic converters.

First Guess: You're smelling uncatalysed exhaust because the cat was damaged from previous engine problems--running cold, running rich.


Seems like that problem is history.


Unlikely.


If your eyes aren't watering, it's not unburnt fuel (HC).


Will the coil fire a spark-tester calibrated for HEI?


As said...50 psi fuel pressure with no vacuum in the intake manifold is kinda low. Is your gauge accurate? Does it increase with multiple "priming" cycles?


Backfiring in the intake manifold is not the same as backfiring out the exhaust. Which is it?

Did you get the wires routed properly? Lots of space between #5 and #7 wires? Preferably routed EXACTLY like the service manual shows, using all the original plug-wire looms?

I dont have a spark tester, the shop manual mentioned an OHM test that might suffice

Yes the wires are correct to the cylinder and HEI plugs. I removed the 1 3 5 7 plugs prior to the update and found some were wet with what looked like engine oil.

When I rear the factory manual (should have done that in the first place) it said to check the ignition system first when having serious exhaust backfiring, which is what I have.

The spark plug wires felt very floppy and weak, kind of like an old rubber hose that lost its elasticity strength. The #7 plug wire broke off the boot connector with little effort...so my initial thought there was these plug wires were hanging on a thread.

My guess on unburnt fuel was that the exhaust smells like gasoline, it doesnt remind me of a coolant smell. However it still could be coolant..but im leaning on it not being that because I don't lose any coolant and with that rate of vapor coming out it would be noticeable.

Either way the lower intake gasket is surely not doing great and needs to be on my repair list once it gets warm out again.
 

Schurkey

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I dont have a spark tester, the shop manual mentioned an OHM test that might suffice
An ohmmeter can tell you that the coil is bad. It cannot tell you that the coil is good.

Passing the resistance tests--primary resistance, secondary resistance, and having no continuity to ground--AND being able to reliably fire a spark tester especially with the coil warm and misted with water from a squirt-bottle is the only way to know for sure short of amazingly expensive electronic test equipment.

There's many kinds of spark-testers, including a heaping pile of junk that makes a light-bulb glow when it senses spark. You want one that has the spark jumping an actual gap. My favorite style is:
www.amazon.com/dp/B003WZXAWK/?coliid=I3S98D7T1J0RLJ&colid=2VLYZKC3HBBDO&psc=1&ref_=list_c_wl_lv_ov_lig_dp_it

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My guess on unburnt fuel was that the exhaust smells like gasoline,
That's what you'd expect from MISFIRE and/or a failed catalytic converter.

As said...overly-rich mixture primarily produces CO which is colorless and odorless (unless the mixture is so rich that it results in misfire.)

Either way the lower intake gasket is surely not doing great and needs to be on my repair list once it gets warm out again.
Seems reasonable, although are you sure you want to wait that long?
 

missouritig

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So decided to take the truck out the country road and give it the beans. After a few passes at 55-60mph the exhaust vapor cleared up, absolutely no white smoke now that truck is completely up to temp! Also no more popping from exhaust at full throttle.

Transmission is shifting great, power feels awesome for what it is, reminds me close to my old 5.3 LM7.

Its possible my lower intake gasket still needs redone and just seals better when hot, but I do find it odd the white smoke is gone and also gone is the backfiring.

The sealing when hot doesnt quite make sense because ive got engine plenty hot before, i just never hit the highway with it.

Anyway, i think it desperately needed a full range drive to help the computer relearn the fuel delivery.

Now engine is running great, on to fixing the other stuff
 

missouritig

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Thanks again for everyones input. Im sure I will have other issues pop up but Im super happy where it is right now. This was a beat up about to be parted out truck I got at auction and now its going to have another shot at life.

Here are the results

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For what its worth on the shifting. At regular driving speeds my 1-2-3-OD seem to occur at expected intervals. When I gassed it in the video I got a little concerned it reved up as it did and let off the gas a little as it shifted, then hit the gas again at 50mph and it still had tons of guts left in it. I didnt have it pegged to the floor the whole tome.
 
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