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Sputtering and backfiring

Tiny
TRUBLUROOKIE
  • MEMBER
  • 1993 CHEVROLET SILVERADO
  • 5.7L
  • V8
  • 4WD
  • AUTOMATIC
  • 263,000 MILES
I have a Z71 TBI. I let it run for about forty five minutes to charge the battery before a big snow storm. After forty five minutes I tried to drive the truck away and it stalled out. It took a few times before it turned over again and once it was running any time I pushed on the gas pedal more than just slightly the engine would cut out and almost stall. The next day it seemed to run just fine. A few days later it started to do act the same and when I gave it more gas it would backfire. I checked the distributor cap and the injectors and they seem fine. After I put everything back together it ran perfect, but four hours later when I tried to drive it it would cut out or bog down when I pushed on the gas but never backfired again. I have been told it is a head gasket or timing or bad plugs. I do not know where to start or what to do. This is my dream truck and I do not want to take it to a auto shop if it is something I can fix.
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Friday, February 3rd, 2017 AT 12:52 PM

7 Replies

Tiny
STEVE W.
  • MECHANIC
  • 13,573 POSTS
Take the distributor cap off. Look at it closely for any signs of carbon tracking. If you find any inside or out, replace it. If it looks okay wipe it out with a towel with some alcohol on it.

Next, take a spray bottle filled with plain water, wait until it gets dark or you can pull into a garage or similar so it is dark under the hood. Start the engine and lightly mist the water over the plug wires. If you see any arcing between the wires or around the coil or cap. Replace the wires. Pull the plugs and check them for gap, carbon tracks, fouling, or cracks.

When was the fuel filter changed last? If you do not know, change it.
Get a fuel pressure test gauge and test the pressure.

Highly doubt it is a cylinder head or gasket as these generally give other symptoms of overheating or constant misfires that do not fade away.
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Friday, February 3rd, 2017 AT 1:09 PM
Tiny
TRUBLUROOKIE
  • MEMBER
  • 48 POSTS
When I took off the distributor cap there was a build up of green substance on every contact. I wiped it all out. I do not know when the fuel filter was changed last. Where do I tie in to the fuel line to test the fuel pressure?
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Friday, February 3rd, 2017 AT 1:58 PM
Tiny
STEVE W.
  • MECHANIC
  • 13,573 POSTS
Green is not good. That is brass corrosion and takes a while to form. Looks like an old fashioned tune up, cap, rotor, wires and plugs along with a fuel filter is in order.

For the pressure test, you can fight to get the line off the back of the TBI or just put it inline as you change the filter. Put it on the engine side of the filter so you get an accurate reading.

If you want to be able to do your own repairs you might look into getting a good manual on that truck. The factory paper set by Helm is expensive unless you get lucky on eBay or similar.
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Friday, February 3rd, 2017 AT 5:43 PM
Tiny
TRUBLUROOKIE
  • MEMBER
  • 48 POSTS
I have ordered everything for a tune up. Once everything is in I will check back to let you know how everything is going. Thank you so much for the help.
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Sunday, February 5th, 2017 AT 4:28 AM
Tiny
STEVE W.
  • MECHANIC
  • 13,573 POSTS
You are welcome.
Thank you for using 2CarPros. Com. Tell your friends, family and anyone you like about us and please return with any auto related questions, we are here to help.
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Sunday, February 5th, 2017 AT 6:17 PM
Tiny
TRUBLUROOKIE
  • MEMBER
  • 48 POSTS
FANTASTIC! The tune up worked. While waiting for the weather to warm up so I could do the tune up the rear main seal started to leak and left about 2 quarts of oil on the ground. Everything is fixed and she is running like a top. Thank you so much for your great advice and helping me to learn so I can work on this truck with my son's. I would like to donate but does it go directly to you or to the website?
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Thursday, April 20th, 2017 AT 4:03 PM
Tiny
STEVE W.
  • MECHANIC
  • 13,573 POSTS
Great job on the repairs. Rear main made it a long way. At least the new engines use the one piece seal. You don't need to tear the oil pan off, the rear main cap and then play with installing the old 2 piece rope seals.

It's always something. I just went through a friends vehicle fixing misc. Issues, rear pads, rotors, calipers, parking brake parts, two front hubs, new steering rack and pump, rear upper control arm, and rear wiper motor.
Get it all done and the strut for the rear glass hatch sheared off and it has a leak in the exhaust.

Great memory maker, especially if they want to learn, and a 93 isn't so loaded with computers that you need to spend a ton of money on diagnostic gear.

Donations go to the site.
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Thursday, April 20th, 2017 AT 6:01 PM

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