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08-20-2003, 06:53 PM
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backfire in carb? help?
I got a stock 305 in a 95 chevy van. And out of no where it just started hesitating at speeds above 45 and backfiring. I took out all the plugs and cleaned them, and they all fire. i have no problems untill u hit about 45 to 50. even at higher RPM's. I thought it was just a bad plug or some wires, but they are all fine. It has no noises coming from the timing chain, or head. So i am kind of stumped. Abd suggestions or help would be appreciated. thanks
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08-20-2003, 06:59 PM
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Spark plugs can look good and still be bad. Yours sounds like bad plugs or the fuel filter is stopped up.
What year and model.make van is it? Troy 
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08-21-2003, 06:15 AM
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Does it backfire once or repeatedly, thru carb. or exhaust? Don't think fuel filter's bad, it should be tbi injection, low fuel press. will cause hard starting, and low speed hesitation. For my 2 cents, I'd check wires, cap and dist. module, if ok, maybe there's a sensor out of range, is there a check eng. light on?
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08-21-2003, 06:24 AM
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The advance unit may have stopped working or is this ignition all electronic? It may be wise to take to a Auto Zone (free)or someplace reliable to test it on a machine instead of jumping all over and save some money.
__________________
Luv the smell of NITRO in the morning.
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08-21-2003, 06:33 AM
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Hey '80' Autoclone can only read codes, and if the check engine light isn't on, there won't be any to read. I think they can check some modules though?
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08-21-2003, 08:30 AM
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Is this a repeated backfire thru the carb? AND as you continue to drive this car, you notice the speed at which it backfires get lower and lower? ...Bad cam! Good Luck! ...Mark
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08-21-2003, 11:18 PM
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Its a 95 chevy santa fe G20. it has Tb fuel injection. Its bakefiring thru the TB. Not just once but a lot if i keep the pedal down. This only happens as i accelerate. and its a hot condition only, its fine for the first ten minutes of driving. i took it to auto zone and they got no codes. but they cant run a koer test. i put a new cap and rotor on it, but that didnt help.
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08-22-2003, 04:06 AM
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How about checking the engine ground, its worth a shot. Maybe its causing some type of computer/sensor signal malfunction.
Ive been going through this same problem and havent been able to solve it. Ive tried a lot of stuff.   Im VERY interested in finding out what it takes to cure the problem. Last edited by Greg Latvala; 08-22-2003 at 04:12 AM.
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08-22-2003, 05:37 AM
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Echo may be right, bad cam lobe, but i'd check that cap and module, could also be a broken valve spring on an exhaust valve, I did have a chevy act kind of the same way, was a bad knock sensor, located on driver side, lower block, but it should turn on light! If theres no light, it almost has to be mechanical, or in the ignition, not a sensor.
Does the engine actually backfire, or is it more of a popping, which increases in relation to engine speed? If it's more of a short popping noise, I'd check the valve springs and valve lift! Last edited by Wrencher; 08-22-2003 at 05:37 AM.
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08-22-2003, 07:35 AM
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Im starting to agree with the others. Start looking at your valve train, tight valves, broken valve springs, sounds like a valve not seating during compression. I advise taking a compression test and a leak down test for a base line to start with, and then go thru a process of elimination. The spark control module under the coil pack can cause it to miss. With a TBI setup for a fuel delivery it sounds more like the valve train or a head gasket. Also you mite want to look for any service reports on your van. I cannot remember the site rite now. I will look for it when I have some time, unless someone else can help that may have the site.
Pull the oil filter and tip it upside down for a while and look for metallic in the oil, if none is present the cam should be OK, if there is metallic start looking at the cam & lifters.
__________________
Luv the smell of NITRO in the morning.
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08-22-2003, 08:04 AM
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Another note on the compression test, a weak or broken spring may not show up, it might close at slow speed but close too slow for higher rpm, same for a worn cam lobe. If you can, pull the valve covers, PAIN, check all the springs for a cracked one. Then unplug dist. crank engine and watch for a rocker that's not coming up as high, or moving as far as the rest on the pushrod side.
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08-22-2003, 08:30 AM
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1BAD, are you talking about CARFAX.com? If so, I have a subscription, so if you pm me your VIN # unibrow, I can run it for you (and anyone else that would like it done, it's free right now for me).
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08-22-2003, 08:47 AM
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TSB's
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08-23-2003, 07:06 AM
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Wrencher whats TSB's?
This is a TBI unit and starts to backfire when hot. It sounds more like a sticking valve or carbon deposits. Remove the oil filter and check it for metallic particles, and replace the oil with some Marvel Mystery Oil to clean the inside of the motor and add 4 Oz. of the MMO to each 10 gal. of gas. This should clean the carbon in a tank-full. If this has a AC oil filter PF25 or PF35 go to a 2 qt filter PF 932. unibrowarrior please read the post from gt2betubbed.
__________________
Luv the smell of NITRO in the morning.
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08-23-2003, 07:37 AM
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If its a hot condition only and runs ok cold as stated I would hav to rule out mechanical conditions. I would think more along the lines of ignition coil, or possibly fuel injector pulse width when the computer goes into closed loop operation.If you disconnect the O2 sensor you should be able to retain open loop operation and then see if you can drive it and have it still run ok past the 10 minutes you now have.
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