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1997 Chevy 1500 4.3 V6 won't start, backfires, code p300
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gumb63
User
Dec 29, 2015, 6:08 PM
Post #1 of 23
(2825 views)
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1997 Chevy 1500 4.3 V6 won't start, backfires, code p300
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 I have an issue with my 97 Chevy truck, it ran last week ,but rough, left sit a week, now won't start and is back firing, all new tune up parts and ignition coil, but still won't run, seems to be getting g fuel, any suggestions ?
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Hammer Time
Ultimate Carjunky
/ Moderator
Dec 29, 2015, 6:45 PM
Post #2 of 23
(2817 views)
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Re: 1997 Chevy 1500 4.3 V6 won't start, backfires, code p300
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All "crank, no start" conditions are approached in the same way. Every engine requires certain functions to be able to run. Some of these functions rely on specific components to work and some components are part of more than one function so it is important to see the whole picture to be able to conclude anything about what may have failed. Also, these functions can ONLY be tested during the failure. Any other time and they will simply test good because the problem isn't present at the moment.
If you approach this in any other way, you are merely guessing and that only serves to replace unnecessary parts and wastes money.
Every engine requires spark, fuel and compression to run. That's what we have to look for.
These are the basics that need to be tested and will give us the info required to isolate a cause.
1) Test for spark at the plug end of the wire using a spark tester. If none found, check for power supply on the + terminal of the coil with the key on.
2) Test for injector pulse using a small bulb called a noid light. If none found, check for power supply at one side of the injector with the key on.
3) Use a fuel pressure gauge to test for correct fuel pressure, also noticing if the pressure holds when key is shut off.
Once you have determined which of these functions has dropped out,
you will know which system is having the problem.
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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.
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Discretesignals
Ultimate Carjunky
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Dec 29, 2015, 10:44 PM
Post #3 of 23
(2811 views)
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Re: 1997 Chevy 1500 4.3 V6 won't start, backfires, code p300
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If it is backfiring while your attempting to start it, you probably have an ignition timing problem. Without the fancy equipment to see if an ignition event is occurring close to the cylinders' peak pressures it will be difficult to figure out what is going on. Some of those distributors would get corroded up pretty badly inside causing your symptoms, so that is something to look for. Crank sensor signalling issues can also cause the ignition system to fire at the wrong times. Best tool to use to troubleshoot a crank sensor signalling issue is a lab scope, which most people don't have laying around.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Dec 29, 2015, 10:47 PM)
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gumb63
User
Dec 30, 2015, 5:00 AM
Post #4 of 23
(2800 views)
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Re: 1997 Chevy 1500 4.3 V6 won't start, backfires, code p300
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Thank you for your insight, however, I am getting spark, as tested with a spark tester, although it was visibly weak so I replaced ignition coil, seems to be getting fuel as well , can smell the fuel with air intake tube off, before the engine stopped running, I had a code scan done as it was running rough, and the code came up as P300 random misfire, all other ignition components are new(ie;, plugs, wires cap & rotor etc..).
My concern is whether fuel pressure or filter blockage can cause this issue, I can hear fuel pump run up when key is turned to on position, but have no idea where the test port is for fuel pressure test. Also this engine is equipped with the "Spider" type of injection system and the injectors are not accessible to test without removing the intake plenum, I'm trying to avoid major surgery !
Thank You for your response !
(This post was edited by gumb63 on Dec 30, 2015, 5:04 AM)
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Hammer Time
Ultimate Carjunky
/ Moderator
Dec 30, 2015, 5:36 AM
Post #5 of 23
(2793 views)
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Re: 1997 Chevy 1500 4.3 V6 won't start, backfires, code p300
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I think you're wrong about that. If you are getting backfiring, there is an issue with the spark.
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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.
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kev2
Veteran
Dec 30, 2015, 7:25 AM
Post #6 of 23
(2790 views)
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Re: 1997 Chevy 1500 4.3 V6 won't start, backfires, code p300
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first check the eng oil for excess fuel- overly cautious but to easy to ignore.
there is a test port for the fuel pressure - back of engine on the fuel lines.
you will want to check pressure AND then with KOEO observe the fuel pressure drop - drops Xpsi in 3-5 min.
did you use AC Delco plugs? some aftermarket will = misfire.
the "backfire" was there before the plugs,cap, rotor?
you did NOT move the distributor- yes, no?
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Hammer Time
Ultimate Carjunky
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Dec 30, 2015, 7:34 AM
Post #7 of 23
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Re: 1997 Chevy 1500 4.3 V6 won't start, backfires, code p300
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Low fuel pressure is never going to cause backfiring on a Vortec. There is an issue with the spark, possible crank sensor (doubtful), cracked dist cap, wires crossed, distributor disturbed, etc
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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.
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kev2
Veteran
Dec 30, 2015, 8:02 AM
Post #8 of 23
(2786 views)
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Re: 1997 Chevy 1500 4.3 V6 won't start, backfires, code p300
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HT the concern was not overall pressure...BUT leak down, a simple (basic) test for overfueling- flooding.
There is a logic to the questions. step by step.
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Discretesignals
Ultimate Carjunky
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Dec 30, 2015, 9:00 AM
Post #9 of 23
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Re: 1997 Chevy 1500 4.3 V6 won't start, backfires, code p300
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HT is right. You might have a spark, but for some reason it is occurring out of time. Also the spark should be able to at least jump a 3/4 inch air gap.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
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Hammer Time
Ultimate Carjunky
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Dec 30, 2015, 9:05 AM
Post #10 of 23
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Re: 1997 Chevy 1500 4.3 V6 won't start, backfires, code p300
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Yes, and that was part of my original instructions.
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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.
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gumb63
User
Dec 30, 2015, 10:21 AM
Post #11 of 23
(2769 views)
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Re: 1997 Chevy 1500 4.3 V6 won't start, backfires, code p300
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Wouldn't backfire if spark was absent, thus back FIRE, I'm not a novice, I do have 30+ years in auto mechanics, I'm seeking usable advice and the obvious conditions have been checked,
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gumb63
User
Dec 30, 2015, 10:34 AM
Post #12 of 23
(2767 views)
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Re: 1997 Chevy 1500 4.3 V6 won't start, backfires, code p300
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As stated previously, I'm no novice, seriously guys, I have checked those obvious conditions, now I don't have a 9k$ computer to check it with, but I can still check most conditions you have mentioned, I have, fuel & spark, the distributor has not been disturbed & the truck ran a week ago until parked, but battery (also new) was dead when I returned home, can ignition module be the culprit, or maybe clogged fuel filter? ,,
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Hammer Time
Ultimate Carjunky
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Dec 30, 2015, 10:38 AM
Post #13 of 23
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Re: 1997 Chevy 1500 4.3 V6 won't start, backfires, code p300
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As soon as you think your smarter than the experts you are going to get yourself in trouble. An engine will backfire because it built up fuel without spark and suddenly has spark or the spark is occurring sporadically or at the wrong time. One way or the other, there is an issue with spark not working properly.
The issue Kev refers to is an injector leaking and building up fuel but with poppet injector, the leak would have to be the fuel pressure regulator and then it would likely hydrolock one of the cylinders. The injectors won't let fuel by without pressure applied.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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.
(This post was edited by Hammer Time on Dec 30, 2015, 10:40 AM)
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gumb63
User
Dec 30, 2015, 10:40 AM
Post #14 of 23
(2764 views)
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Re: 1997 Chevy 1500 4.3 V6 won't start, backfires, code p300
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AC Delco plugs? Really? Man I have top of the line Bosch Iridium plugs and all are gapped and installed properly, the truck was misfiring before plug, cap, & wire replacement, and ran afterwards, 
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gumb63
User
Dec 30, 2015, 10:46 AM
Post #15 of 23
(2762 views)
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Re: 1997 Chevy 1500 4.3 V6 won't start, backfires, code p300
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Are you smarter than the technician? I am the technician, and I have my big boy pants on! No need for useless comments, I am retired from mechanics but not an idiot, I have been in this work for over 35 years kid, play nice or go home !
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Hammer Time
Ultimate Carjunky
/ Moderator
Dec 30, 2015, 10:54 AM
Post #16 of 23
(2759 views)
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Re: 1997 Chevy 1500 4.3 V6 won't start, backfires, code p300
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Bosch in a GM. Those are about the very worst plugs you could have used.
PS, don't run your mouth with me. You'll be gone faster than you can hit the enter button. I'm probably older than you and am still in this business.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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.
(This post was edited by Hammer Time on Dec 30, 2015, 10:56 AM)
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gumb63
User
Dec 30, 2015, 10:56 AM
Post #17 of 23
(2757 views)
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Re: 1997 Chevy 1500 4.3 V6 won't start, backfires, code p300
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Would that crank sensor need a relearn if replaced? I don't have that equipment, and I'm on a fixed income (retired) so cost wise I need a cheaper solution or dynamite maybe!
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Discretesignals
Ultimate Carjunky
/ Moderator
Dec 30, 2015, 10:57 AM
Post #18 of 23
(2756 views)
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Re: 1997 Chevy 1500 4.3 V6 won't start, backfires, code p300
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ut oh 
Even with lots of years and experience in the field, your bound to run into something that will humble you. It happens to me all the time.
We are just trying to give you some advice based on what we have ran into on those. Could be an ignition module or any number of things, but you got to run some tests to see what is going on. Personally, I'd start with the ignition system and make sure you have good spark and it is firing at the correct time. One way or another you have to start somewhere and give us some test results.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
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gumb63
User
Dec 30, 2015, 11:02 AM
Post #19 of 23
(2751 views)
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Re: 1997 Chevy 1500 4.3 V6 won't start, backfires, code p300
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You sure like to criticize people's parts, guess what , I've had great results with Bosch plugs, are you an AC Delco rep ?
Really, how about some usable advice, and quit being critical of my parts manufacturer, If Delco was so great, maybe they would still be US made !
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Discretesignals
Ultimate Carjunky
/ Moderator
Dec 30, 2015, 11:14 AM
Post #20 of 23
(2748 views)
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Re: 1997 Chevy 1500 4.3 V6 won't start, backfires, code p300
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Believe it or not sometimes one brand and design of spark plug isn't compatible with a certain ignition systems. In the field to stay away from creating issues with a customer's vehicle, our shop always uses the brand and model of plugs the vehicle came with from the factory.
When the GM engineers, or any automotive manufacture, designed the ignition system, they built it around the characteristics of the spark plug they had chosen. I've seen all kind of troubles with vehicles that had different brands of plugs installed other than what the manufacture called for. Of course, that probably won't cause the problem your having, but keep in mind that certain other drive-ability problems could show up using plugs other than what the manufacture specifies.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Dec 30, 2015, 11:16 AM)
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gumb63
User
Dec 30, 2015, 11:15 AM
Post #21 of 23
(2746 views)
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Re: 1997 Chevy 1500 4.3 V6 won't start, backfires, code p300
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Who is running who's mouth here ! Don't piss on my back and tell me it's raining, I've read your posts for a while now and you seem to have a huge chip on your shoulder, how's that working for ya, I'll go to a different site where the people have humility and patience, as well as intelligence! Get a clue moron, you aren't helping by being a smart ass!
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Discretesignals
Ultimate Carjunky
/ Moderator
Dec 30, 2015, 11:22 AM
Post #22 of 23
(2744 views)
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Re: 1997 Chevy 1500 4.3 V6 won't start, backfires, code p300
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Really? I don't care if you take or leave my advice, but this isn't the place for name calling. If you have a problem with someone, take it to the private messaging system and settle your issue there.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
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Hammer Time
Ultimate Carjunky
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Dec 30, 2015, 12:07 PM
Post #23 of 23
(2736 views)
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Re: 1997 Chevy 1500 4.3 V6 won't start, backfires, code p300
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OK, I've had enough of this idiot.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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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