Question about 1991 Ford F150

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Backfire through the intake

I have a 1991 f-150 that smeels of raw fuel ,runs very rogh and the fuel pump will not cycle off.This problem happened insantaniously.If there is any ideas it would be helpful

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This problem sounds like a fuel pump relay that is stuck and will not magneticly release rule out relay cheapest fix

Posted on Sep 11, 2008

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1 Answer

1990 ford bronco idles fine when you accelerate the gas loses power and backfires through the intake


Fuel delivery problem, not enough fuel on acceleration could cause backfires. Many things cause backfires, mechanical and electronic. I need more info to give a better diagnosis. Did the problem happen all of a sudden or has the vehicle been running crappy for awhile.

Nov 20, 2013 | Ford Bronco Cars & Trucks

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Fuel not getting to engine


fuel filter clog or fuel pump weak.

Feb 22, 2013 | 1997 GMC Sierra

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Why does my truck backfire thru the carborater when it is hot outside?


A backfire is caused when your intake valve/s aren't closing completely before ignition in the cylinder. This ignites any fuel/air mixture left in the intake manifold. Fine tune your timing.

Aug 15, 2012 | Cars & Trucks

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It quite after backfiring has fire but it's like it isn't getting gas.


if you spray intake cleaner into the intake with the air snorkel off and it starts then i would say you have a fuel pump problem.the backfiring was probably caused by the motor all of a sudden going lean.you will have to check the fuel pressure with a gage it should be about 35lbs pressure to run the car.if the pump needs replacing change the fuel filter.

Sep 16, 2011 | 2002 Chevrolet Venture Passanger

1 Answer

Starts quickly cold. must crank 5-8 seconds when warmed up. I let fuel pump run before cranking. Get faint gas smell but no visable leak. New plugs wires cap and rotor. 165k


At that mileage, it's possible that you have one or more injectors that are beginning to leak. When that happens you need to crank the engine over longer in order to clear the raw fuel from the intake and re-pressurize the system as well. Also check the ballast resistor (white ceramic block with two wires going to it) on the drivers fender back near the firewall. I can't remember exactly what it does but do remember that it alters the way the pump operates after warm up.

May 23, 2010 | 1992 Jeep Cherokee Sport

1 Answer

My 1999 isuzu rodeo ran out of gas and now it won't start even with 4 gallons of gas. It cranks, the lights don't dim, but it does not even sputter or anything.


Many times when the tank is empty, the fuel pump draws the sediment up into the fuel strainer that is there to protect the pump.

This can clog or plug the strainer so much that it prevents fuel from being pulled up into the fuel pump.

The fuel pump can be damaged by the debris that is pulled up, causing it to fail.

I suggest a pressure test. You can spray a small amount of wd40 or carb cleaner into the intake while being careful, if the vehicle tries to run, then more than likely it is your fuel pump.

Be careful for backfires, you are spraying a flamable product into the intake and any timing problems could cause sparking to create a backfire. Just stand to one side and be careful.

good luck

Mar 11, 2010 | Isuzu Rodeo Cars & Trucks

1 Answer

I have a 1993 chevy blazer 4.3. We replaced the fuel filter and fuel pump. When I start it up it starts okay. Once I drive it and let it sit for about 30 minutes or so it takes a couple of times before it...


Is it a vortec engine if it is your fuel injector may be the problem. Chevy ran one injector on the vortech engine it is under the upper intake manifold, it has 6 plastic hoses running to each cylinder under the manifold. if one of these hoses are leaking its dumping raw fuel into the manifold during hot soak. that fuel is getting picked up by intake air when trying to start. and flooding it out hence hard to start. gasoline evaporates rather quick so what fuel was in the manifold when you park for the night has evaporated by the next morning so no raw fuel for intake air to pick up easy start. Seen this problem many times. pretty easy fix but a bit pricey around $200

Oct 17, 2009 | 1993 Chevrolet S-10 Blazer

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

1 Answer

Fuel injectors are dumping fuel


Sounds like the fuel pressure regulator diaphragm has ruptured. When this happens fuel is drawn in from the manifold vacuum and if the leak is severe enough the fuel pump pressure will push it in as well. The unit is a small component that resides on the fuel injector rail and will have a vacuum hose running to it. Remember you are working with GASOLINE and lots of it so be careful!

Dec 31, 2008 | 1999 Chevrolet Suburban

1 Answer

Turn over but well not stay running backfires though air intake


When is the last time you replaced your fuel filter? Check your fuel filter. If it's plugged you may have taken out the fuel pump. This happened to me. (2000 Chevy Silverado 1500)

DC

Jul 29, 2008 | 2000 Chevrolet Silverado

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