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99 Suburban 5.7 P0300


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Raslinmaster
Novice

Sep 15, 2017, 2:45 PM

Post #1 of 10 (372 views)
  post locked   99 Suburban 5.7 P0300  

Was getting a code saying the number five cylinder had a misfire. I chased that problem by installing new plugs, wires, cap, rotor, and new fuel injector to number five cylinder. Now I am getting a random misfire code. The truck barely runs, will backfire when I try to give it gas, and will not go over thirty mph. Could I have a bad distributor, coil, maybe a bad timing chain? Please help!


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Sep 15, 2017, 3:57 PM

Post #2 of 10 (365 views)
  post locked   Re: 99 Suburban 5.7 P0300  

Did you move the distributor at all when you did this work?

Do you have any other codes beside the misfire code?



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Raslinmaster
Novice

Sep 15, 2017, 5:17 PM

Post #3 of 10 (361 views)
  post locked   Re: 99 Suburban 5.7 P0300  

No I didn't but it acts like the timing is off. I heard a clunk a couple of time when I tried to crank it over. I am losing my mind lol. No, no other codes, just the misfire code. Sometimes I have to hit it w carb cleaner to get it to start but once it starts it seems to be running rich. Sure wish I knew what I was doing lol. My dad was a machanic, I wasn't lol


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Sep 15, 2017, 5:23 PM

Post #4 of 10 (359 views)
  post locked   Re: 99 Suburban 5.7 P0300  

There's really only one thing that could have happened here. Either the wires are installed out of order, not inserted into the cap correctly or the cap got damaged by the rotor.






~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Raslinmaster
Novice

Sep 15, 2017, 6:10 PM

Post #5 of 10 (355 views)
  post locked   Re: 99 Suburban 5.7 P0300  

lol I ran and double checked but they are correct. Also, tried my old cap and still same issue


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Sep 15, 2017, 6:11 PM

Post #6 of 10 (353 views)
  post locked   Re: 99 Suburban 5.7 P0300  

What is the fuel pressure?



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Raslinmaster
Novice

Sep 15, 2017, 6:16 PM

Post #7 of 10 (349 views)
  post locked   Re: 99 Suburban 5.7 P0300  

I haven't checked it but I did replace the filter. The pump is probably 15 or 20k miles old, maybe 2 years. I will go get a gauge tomorrow and check. Thank u for ur help, I have run out of things to try and I'm sick at throwing parts at it w no results. At least tools I can use in the future


Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

Sep 16, 2017, 1:27 AM

Post #8 of 10 (322 views)
  post locked   Re: 99 Suburban 5.7 P0300  

As Hammer Time said do check fuel pressure this engine super counts on that staying high and in range.
See if you can rent the tool as the full set of adaptors will be costly or just the one for the threads for this.
Just noted you suspected timing chain. So would I except exactly NONE on the real Chev block V8s have ever jumped on me but have been found quite loose still running fine tossed because if close to the thing just do those.


New fuel pump even 2 years and not so many miles? These really don't tolerate running low on fuel - even once! Strong guess is these don't tolerate ethanol in fuel well even in a couple years never mind now at this age. Beware of new parts - not up to par IMO,
T



Raslinmaster
Novice

Sep 18, 2017, 12:07 PM

Post #9 of 10 (293 views)
  post locked   Re: 99 Suburban 5.7 P0300  

Full pressure goes up to a little over 50 when I turn on the key but then drops a few seconds later when the pump kicks off. While cranking the pressure is in the 40s


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Sep 18, 2017, 12:28 PM

Post #10 of 10 (291 views)
  post locked   Re: 99 Suburban 5.7 P0300  

There's your problem. This engine needs a minimum of 55PSI to run right.

The actual spec is Key On Engine Off 60-66 psi



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.







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