Misfire and bluish white smoke from Engine at startup

[jahworks123]

Ok, this is the second time I've had this happen to me in about two years. I stop the truck after about a 10 mile trip, restart it after about 5 minutes, and I get a loud bang..like a backfire..only, bluish shite smoke billows from the engine compartment. I have not idea why. I checked what I could, but nothing seems to stand out. After that, the truck just starts and runs. I'll admit that the truck has been running kinda rough for a while, but it does not miss. I only drive the truck 1-2 times weekly, about 40 miles a day. Any ideas?

[2000CAYukon]

Originally Posted by jahworks123

Ok, this is the second time I've had this happen to me in about two years. I stop the truck after about a 10 mile trip, restart it after about 5 minutes, and I get a loud bang..like a backfire..only, bluish shite smoke billows from the engine compartment. I have not idea why. I checked what I could, but nothing seems to stand out. After that, the truck just starts and runs. I'll admit that the truck has been running kinda rough for a while, but it does not miss. I only drive the truck 1-2 times weekly, about 40 miles a day. Any ideas?

My neighbor's 97 Yukon did the same thing. On his, it was a bad fuel pressure regulator. I hooked up a fuel pressure gauge, started the engine, then turned the engine off. The pressure dropped to 0 in a few minutes. It should hold pressure after the engine shuts off.

On your 97, the regulator is located under the upper intake (plastic) cover.

//2000CAYukon

[jahworks123]

Thanks. Based on another post, that's what I suspected. The truck does have 107K. Does the fuel pressure regulator have anything to do with the fuel gauge? Whenever the truck goes below half tank, the gauge flutuates between 1/2 and full while driving. Sometimes, it will say it's almost empty, but then I only takes 10 or so gallons to fill up. I had a shop supposedly replace the fuel pump and sending unit, but it did not fix the problem. It was not my regular shop, so I'm not even sure if the work was done (long story). I'm wondering if I should just replace the regulator, pump, sending unit and fuel filter all at once. Any ideas?

[2000CAYukon]

The regulator has nothing to do with the fuel gauge. The sending unit, the gauge itself, or wiring is most likely the issue with the gauge fluctuation.

To replace the pump and sending unit, you need to drop the tank so that is up to you if you want to replace those.

//2000CAYukon

[jahworks123]

I may have to drop the tank anyways. There's a sound that appears to be coming from the tank that I can hear from the outside of the truck under idle. It sounds like there's something loose and rattling around in the tank. I may do it myself (waiting on the Factory service manual for the truck). It doesn't look like it's too hard. I just have to run it until most of the fuel is out. My list of possible items to change when I drop the tank are:

1. wiring harness (it's even listed on the Advanced auto parts site, that it's highly recommneded that the harness is replaced when the fuel pump is serviced)
2. Fuel sending unit
3. Fuel pump
4. Fuel filter

I may take it somewhere to have the regulator done, I just need to get a fuel pressure tester (and again, the FSM as guide) to check the fuel pressure.

By the time I get done, the entire fuel systems (sans the hoses) will have been replaced :-)

[glenncof]

I had the same problem with my 1997 Tahoe. Exactly the same. Sounds like a fire cracker. As I recall this started after 100K miles.

AFTER carefully thinking about it I concluded the white smoke must have come from combustion chamber. But how does it get out?

Also note: The sequential sequential fuel injection has documented problems with sticking. (I use techron as specified by GM for this.) This may be a contributing factor. The firecraker effect would usually go away after injector cleaning with Techron. I though it was the problem but could not understand the smoke coming from the hood. Then at about 130K it didn't fix it.

I concluded some ignition crossfire is occuring with the plug wires and causing ignition at a time when the intake valve is open. I assume the smoke is coming out from around the injector nozzle.A GM tech pointed to some possible arcing when he replaced fuel pump.

I have replaced the plug wires a few month ago and have not had a problem.
Yea, 133K miles on wires is enought. I suggest changing them at 100K when doing rotor/cap and plugs.

[stonecold454]

Originally Posted by jahworks123

I may have to drop the tank anyways. There's a sound that appears to be coming from the tank that I can hear from the outside of the truck under idle. It sounds like there's something loose and rattling around in the tank. I may do it myself (waiting on the Factory service manual for the truck). It doesn't look like it's too hard. I just have to run it until most of the fuel is out. My list of possible items to change when I drop the tank are:

1. wiring harness (it's even listed on the Advanced auto parts site, that it's highly recommneded that the harness is replaced when the fuel pump is serviced)
2. Fuel sending unit
3. Fuel pump
4. Fuel filter

I may take it somewhere to have the regulator done, I just need to get a fuel pressure tester (and again, the FSM as guide) to check the fuel pressure.

By the time I get done, the entire fuel systems (sans the hoses) will have been replaced :-)

It is fairly simple....the noise you may be hearing is the fuel pump itself, we had many Tahoes and Suburbans come into the service drive witht he whining noise....they (Gm) were repalcing them under warranty if you were still under the 3/36 then in 98 they stopped and said it was normal...lol (just like the leathewr steering wheels peeling, they would start peeling due to the salts in your hands but were replacing them under warranty, made alot of money replacing those)..they are not cheap, i would recommend going back with an AC Delco....just be sure you have some sort of trans jack with some sort of support, and be sure you put the rubber tank seal back in and make sure it does not pinch the rubber o-ring, it will start leaking fuel when you go to fill it up if it gets pinched, replace the old one with the new one for sure! The pump and sending unit come as a whole unit....last i checked they are over $400....definitely replace the fuel filter as well, it is a simple repalcement