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1998 Chevrolet Silverado 5.7 feels like a engine miss with no engine code

Tiny
JAYDHEAT
  • MEMBER
  • 1998 CHEVROLET SILVERADO
  • 7,000 MILES
I have a 1998 k1500 with a reman. 5.7 with about 7000 miles on motor. Before I replaced the motor had a engine miss with p0300 code. After engine was replaced still had code so put new wire, cap and rotor, miss and code went away. Now I have miss back but no code. Also replaced intake temp sensor, throttle pos. Sensor, map sensor, cat. Convertor, engine coolant temp sensor. Tried plugs and wires again, went away for 1 day then come back. The intake gasket is new, I think I have rule that typical problem out, (issue doesnt go away when warmed up). Please give me any ideas, I love my truck but am starting to get frustrated. Btw engine was replaced with 210,000 miles and had developed a knock in the bottom end
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Saturday, December 31st, 2011 AT 7:03 PM

15 Replies

Tiny
SATURNTECH9
  • MECHANIC
  • 30,870 POSTS
Did you reuse your old intake manifold?Did you also reuse you injectors?Also did you ever straight edge the upper and lower intake manifolds to make sure they wernt warped before putting them on?
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Saturday, December 31st, 2011 AT 7:19 PM
Tiny
JAYDHEAT
  • MEMBER
  • 7 POSTS
Yes old intake and spider injection were reused, with new gaskets for lower intake. I have never strait edged intake, but I have tried the starter fluid trick and noticed no change in idle
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Saturday, December 31st, 2011 AT 7:33 PM
Tiny
SATURNTECH9
  • MECHANIC
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Using starting fluid to look for a leak I would never do I like to use carb spray. Just because you couldnt find a leak by spraying doesnt mean there isnt a leak and the manifold isnt warped. Its so common for those to warped you must always check them for warpage upper and lower. That has been a issue with those for a while.I would rule that out since you seem to have replaced a lot of the most common reasons for your issues. Also because the problem followed from the old engine. Also how are the spark plugs?Non of them are cracked miss gapped etc?
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Saturday, December 31st, 2011 AT 7:50 PM
Tiny
JAYDHEAT
  • MEMBER
  • 7 POSTS
Plugs are new, gap set not required. Bosch platinum 3 I think, may be wrong, cant remember
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Saturday, December 31st, 2011 AT 7:57 PM
Tiny
SATURNTECH9
  • MECHANIC
  • 30,870 POSTS
The most over looked causes for strange missfires are those intake manifolds there junk and warp often.
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Saturday, December 31st, 2011 AT 8:05 PM
Tiny
JAYDHEAT
  • MEMBER
  • 7 POSTS
Shouldnt I be getting some kind of p. Code
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Saturday, December 31st, 2011 AT 8:07 PM
Tiny
SATURNTECH9
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If its a slight enough missfire the computer doesnt always set a code for it. So your sure you have a missfire?
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Saturday, December 31st, 2011 AT 8:13 PM
Tiny
JAYDHEAT
  • MEMBER
  • 7 POSTS
Just going by feel, and what it felt like before I changed the plugs rotor cap and wires. I forgot to mention that it happens when im barely on the throttle, say just to maintain cruising speed, or if the cruise is set. If im driving 65 on a flat road in overdrive and just barely have accelerator pressed to maintain speed is when I notice it
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Saturday, December 31st, 2011 AT 8:25 PM
Tiny
SATURNTECH9
  • MECHANIC
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So how did it run before you changed the plugs wires cap and rotor driving under those conditions?
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Saturday, December 31st, 2011 AT 8:40 PM
Tiny
JAYDHEAT
  • MEMBER
  • 7 POSTS
Drove the same, but I was getting a p0300. Right after I replaced everything it drove great, didnt miss a beat. The a couple weeks later it was back, with p0300 code, I found that I had a bad rotor (again), replaced with a better rotor and went away. Now its back but this time with no code
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Saturday, December 31st, 2011 AT 8:51 PM
Tiny
SATURNTECH9
  • MECHANIC
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Did you check the rotor again?Maybe you have a worn disributor?Thr p0300 code didnt come back after the second rotor replacement did it?
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Saturday, December 31st, 2011 AT 9:21 PM
Tiny
JAYDHEAT
  • MEMBER
  • 7 POSTS
Noand I still have no code, I check it regularly with my own scanner
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Saturday, December 31st, 2011 AT 9:24 PM
Tiny
SATURNTECH9
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So no you never checked the rotor and cap again after the problem returned?Also you dont have a worn distribtor?
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Saturday, December 31st, 2011 AT 10:31 PM
Tiny
JAYDHEAT
  • MEMBER
  • 7 POSTS
It very well could be a worn distributor, I am going to start with that and another new rotor, and ill get back with you, thank you for your advice, and have a happy new year
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Saturday, December 31st, 2011 AT 10:41 PM
Tiny
SATURNTECH9
  • MECHANIC
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Your welcome keep me posted you have a safe and happy new year as well.
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Saturday, December 31st, 2011 AT 10:46 PM

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