Question about Chevrolet Astro

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Put new plugs, wires,cap & roter on a 1996 chev astro 4.3 vortec, all a/c delco parts, ran great for two days now have a miss fire on #6 took to a small garadge with a hand held read out, computer says all fine, they tried a few things but couldnt fix it, what can i try.

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  • mdorosz Jul 08, 2010

    I will check all the mentiond and see if any of then are the reason for the misfire. Thanks.

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Mis fire on cylinder 6 or on any cylinder is related to this possibilities. As you mentioned you have replaced the wires and parts but for this problem get the voltages checked on each cylinder also interchange the cylinder connectors and check if the cylinder 6 is properly firing.Also check the voltage at each coil one by one.The spark plugs gets power to spark from the coil pack.If the coil pack is not providing proper power that cylinder will misfire.

  • Faulty spark plug or wire
  • Faulty coil (pack)
  • Faulty oxygen sensor(s)
  • Faulty fuel injector
  • Burned exhaust valve
  • Faulty catalytic converter(s)
  • Running out of fuel
  • Poor compression
  • Defective computer.
Thanks. Keep updated for any more query. You can rate this solution and show your appreciation.

Posted on Jul 08, 2010

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1994 chev 4.3 vortec 6 cyl truck back fire and not want go and when idle up they back fire


backfiring is ignition when there is a inlet valve open. check for incorrect firing order or HT leads touching each other.. Check for dirt and carbon tracks inside the distributor cap or cracks in the cap.

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My 97 Chevy 5.7 vortec is missing on cylinders 3, 4, and 5, changed distributor cap and truck ran great for about two hours. Changed fuel filter and there was no change. New plugs and wires summer of 2012....


Well its not exactly ignition or fuel injectors, since cylinder 6 in in the firing order. 1-8-4-3-6-5-7-2
Could be something with the intake again, or the pickup in the distributor. I suppose if you have the multi-port injection inside the plenium it could be some of the spider valves or lines.
You would need to know if those cylinders are firing, and if they have normal compression.

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1996 5.7 vortec misfire cyliner 4 and 6


have you cleared the codes between fault reads
clean the maf first .....replace the maf if faulty
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I have a random mis fire code and a mis fire code for all six cylinders what could this be?


Since you have replaced all of the usual tune-up parts, it could be a fuel problem, or something going on with the distributor.
Also could be a vac leak but I doubt that would cause a problem on all 6 cylinders.
I would check fuel pressure next.

Dec 12, 2012 | 1996 Jeep Grand Cherokee

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I have a ramdom miss ive changed the cap n roter plugs plug wires coil and fuel filter ,,it has 151000 miles on it still runs real roof dont know what els to do


Sounds like you have pretty-much eliminated most of the ignition system. Now all you have to do is eliminate the fuel delivery, fuel injection, and engine mechanical systems. Doing this by parts replacement can be very expensive. I recommend doing some diagnosis so it does not end up costing you as much as a new engine.

Mar 24, 2012 | 1996 Chevrolet Astro

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NO SPARK PUT A NEW COIL ON DID NOT FIX TOOK IT TO A GSRAGE SAID IT NEEDED A CRANK SENSOR CAM SENSOR WIRES PLUGS DIST CAP AND ROTER RAN ONE DAY NOW THEY SAID A HOLE DISTRIBUTER AND A TIMEING BELT.I REALLY...


If you are sure they said, a distributer cap a roter and a distributer, there is a problem! Because on a 1998
plymouth, there is no distributer or cap or roter.
Your cam sensor along with the crank sensor-temp sensor and a few other sensors, send a signal to the
powertrain control module, that sends a signal to the
coil pack(that you said was replaced) that fires the
spark plug. I would hold off from having any further
work done there, until you can check out what they
say they have already done. Ask if you can have the
old parts they replaced so far. You will want to have
an OBDII scan test done, to see what codes come up. It should have one of the first tests they did.
If I have read your post correctly, have them write an
estimate for what they will replace next. This info. is
based on the car being a 1998 plymouth and not a
1988 I would not wan't to acuse somone of anything
based on a typo. Hope this helps. Good luck.

Jan 25, 2010 | 1998 Plymouth Voyager

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1996 chevy 4.3 vortec multiple missfire p0300 i have replaced the engine harness computer and a complete motor which i heard run and drive no problems in that truck.compression is good idles good give it...


How much fuel pressure do you have? Also did you use the injectors from your old engine or from the new ones? How old is the gas in the tank? Plug wires can cause a miss. Timing can be off causing a miss. There are lots of things that can cause it. Those are just a few to go and test before you throw more parts at it.

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3 Answers

1997 chevy cheyenne c2500...i get a popping noise when i press the accelerator...help meeeeee please...197,000miles i frustrated


Does it idle smooth or rough? Steady loping miss at idle? Loses power as rpm's increase? I'm a shadetree mechanic, and even though your engine is a vortec, it still uses these parts, so you may find this useful.

Make sure your plug wires are good, start it after dark, raise the hood, in darkness you should see tiny sparks jumping from the wires if they are bad.

Most likely cause of my intake backfiring was #5 & #7 plug wires switched. Bad plug wires can also short onto each other and cause the wrong cylinder to fire while it's intake valve is still open, igniting back into the intake. 350 chevy firing order is 18436572. #5 & #7 are on the driver side, the closest to the back. #7 fires right after #5, by switching them I had caused #5 to fire too late / #7 too early hitting the accelerator causes the spark timing to advance, firing #7 while the intake valve was still closing, sending flame up into the raw fuel charged intake, causing the explosion or POP under the hood. The symptom I had was rough idle, stumbling / popping on acceleration, which got much worse as it warmed up.

OTHER PROBLEMS TO LOOK AT:
replace fuel filter, and have a mechanic check the fuel pressure. He can tell you whether the pressure regulator or the fuel pump is bad. Low fuel pressure will lead to engine damage as you'll see below. It causes the combustion gases to run too hot, warping valves.

I have a 95 c2500 with 350 Throttle body injection(not vortec), the problem I had was multiple. The timing chain was extremely worn out, causing erratic timing. The fuel pump was bad( causing loss of power as rpm increased)( letting that continue for 6 mos caused several intake and exhaust valves to overheat, warp and burn). The Throttle position sensor was bad, causing transmission shifting / slamming at odd rpms, and possibly contributing to the popping(backfiring up through the intake). The temp sensor on the intake was bad(cold temp fuel mixture control), and the oxygen sensor on the exhaust pipe had the wires pulled out of it(warm temp fuel mixture control). The spark control module also was bad(causes misfires). Later I also had 2 spark plug wires that were on the wrong plugs(the main cause of the intake backfiring). It is an old work truck, 190,000 miles, many parts/gallons of sweat later, now it runs strong. These motors are worth repairing, as long as the oil-pressure is good and the compression is still decent. I've had 3 vehicles before this one, same motor, great mileage, power and reliability. I've heard the vortecs are even better, as long as the oil gets changed regularly.

Start cheap. Try each item, if that is not it, go to the next( or spend a hundred or so on a full diagnostic by a well established mechanic(not a tire installer who just started his ASE studies. good engine diagnosis requires years of experience and teardowns to be able to determine the causes while running) :
1.) While engine is running in park, use plastic pliers(shock protection, be careful!!!) to remove and reconnect a plug wire at the coil. Listen for a change in the idle speed and smoothness. Move to the next if you hear a change, this means that that plug and wire are working properly(disconnecting them causes the motor to idle up, run rougher). If unplugging them doesn't cause a change: That wire or plug is likely bad. take both to an autoparts store to be tested. Replace the problem part, if that does not fix a miss, see #2 below.
2.) Do a cylinder compression test, to see if you have any valve issues. I bought a $40 compression tester kit. It takes about an hour, but it will tell you alot about the engines health. Mine had a range of 140-170 psi, except for #1( 0 psi, cracked and torched valve) and #7(120 psi, warped valve), I had to pull the intake and that head off for replacement valves(got lucky, cast iron head was not warped)
3.)pull, test(a mechanic can do this) and if necessary replace the throttle position sensor($23 part on tbi motors). This tells the computer how much gas pedal you are using. If it is bad, you fuel mixture will be erratic and can cause misfires, and your transmission may be shifting weird / hard.
4.) Replace the spark plugs with original AC Delco, use good wires, cap and rotor. Cheaper parts can have too much resitance to electric flow, causing poor running. I switched from autolite platinums--> to Delco = huge difference.
5.) If the timing chain is original. It is time, trust me. Mine had so much slop, I was amazed it had not jumped a tooth. This will cause poor power / erratic idle / possible backfiring if really advancing / retarding ignition. Unless you are a mechanic, this is not recommended for do it yourself. The upper radiator housing, fan, waterpump, timing cover and oil-pan have to be dropped and regasketed afterwards. Hours of fun.

my truck sequence of events:
Bought spring '08, noticed poor power / slight miss, replaced plugs wires cap rotor, repaired rear brake line rust-out, new tires, mechanic replaced fuel filter, advised fuel pump was not putting out enough pressure, tried ignoring and drove till fall--> developed REALLY severe miss( no intake backfiring), barely made it home.

Starting this spring: Compression test --> valve issues, removed all front engine components(alt, P.S.(pressed on pulley will need a puller kit to remove)), intake manifold and driverside cylinderhead(found a hole in #1 exhaust valve big enough to slide pencil through), had 4 valves replaced at machine shop, reassembled engine, dropped gastank, replaced fuelpump assembly and fuel-lines(rusted), replaced oxy sensor on exhaust manifold, started motor and set timing(while computer timing wire was disconnected under dashboard), ran rough / intake backfiring upon any acceleration, erratic timing, replaced timing chain = steady timing, still ran rough/backfire though, replaced temp sensor(no change), tested barometric pressure module = ok, replaced distributor(unnecessary), replaced throttle position sensor = ran a little better/still backfiring/ transmission problem fixed too, ran resistance check on wires with ohmmeter-->found #5 & #7 plug wires were switched, fixed that, ran great, replaced exaust system behind the converter, sounds great / runs great / lesson learned. If a mechanic advises a repair, get a second opinion... but don't ignore it, it creates bigger problems, like torched valves.
Good luck.

Apr 28, 2009 | 1995 Chevrolet C2500

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