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1990 chevy pickup 350 plugging in the advance timing wire causes truck to backfire thru exhaust lose power miss badly timing is set at zero with wire disconnected when wire is connected it causes trouble truck is turned off when timing set runs ok with wire disconnected disconnected bat to clear the computer no avail I am running it on eight degrees with wire disconnected has new coil plugs wires distrubutor plugs and cap what can cause this would love a call if you could number is 7313355392 my name is donald

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6 Suggested Answers

6ya6ya
  • 2 Answers

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Posted on Jan 02, 2017

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alicantecoli
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SOURCE: 98 chevy 1500 loses power

sounds like an ECU fault.one of the chips is breaking down when the units warms up

Posted on Nov 04, 2008

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  • 16 Answers

SOURCE: s10 pickup after warming up truck starts missing

You might have computer problems.

Does the check engine light come on when it starts to miss?


Posted on Nov 30, 2008

lovelle40
  • 26 Answers

SOURCE: 95 chevy truck 4.3 motor has like a miss in high gear after warms

The fault could be in the ingnition module in the dist.I had a car one time that did the same thing but when it was cold,try replacing the the ignition module.

Posted on Jan 02, 2009

michigan man
  • 3533 Answers

SOURCE: 1989 ford bronco 302 fuel injected timing

on the bad gas part I would recommend to get some STP gas treatment with injector cleaner to put into the gas tank
try a salvage yard that has a 302 engine like yours and change the whole distributor because the shaft could be bad on that end

Posted on Jan 20, 2009

  • 90 Answers

SOURCE: 1989 ford bronco 302 fuel injected timing

To set timing on these you have to disable the electronic timing control.The engine emmissions/tune label should explain how to do this.Change the fuel filter and replace injectors , be sure to change fuel tank and pump if a corroded/rusty tank is the reason for the injector plug issue. Just had one in shop that was a couple years newer but sat to long with a nearly empty tank and old fuel and original fuel filter that pluged every injector.Hope this helps some.

Posted on Jan 20, 2009

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Why is my truck Backfiring what can I do to fix it


Without knowing the make, model, year, and engine, all I can do is guess.

Could be timing set wrong. Could be valve timing slipped. Could be fuel problem.

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According to my book, the first code is the brake control rough road sensor, and P0302 is a cyllinder #2 misfire. Check the gap on your plug, and make sure the plug wire is on all the way. Give the boot an extra good push. Backfiring or misfiring under load is always caused by poor ignition. You may also have a faulty plug or wire.

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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

1 Answer

1988 chevy pickup 4.3 V6 that has constant backfire


bad dis cap or rotor maby a bad plug wire or valve sticking or out of adjusment

Mar 17, 2009 | 1988 Chevrolet C1500

1 Answer

98Eclipse 2.0 nonTurbo 5speed 180,000 miles ,code PO301


The po301 is a misfire code. The backfire can be caused by a excessive amount of fuel, bad valve timing etc.
My guess is you have damage to an exhaust valve that may have occurred when you had the timing belt problem.A compression test will indicate if you have a leaking exhaust valve.The reason for the backfire is the exhaust valve is still partially open when the spark plug fires.

Jan 03, 2009 | 1998 Mitsubishi Eclipse

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