HELP! Pops and Backfire

J

Joes Mark

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I could use a little help from you guys.

For the past couple of weeks, the engine in my 90 LSC pops and backfires (thru the carb) when its first started.

It starts up fine and Idles great. But once you start giving it gas, it starts to hesitate, pop and backfire. Sometimes it wants to stall but does not. After the cars warms up about 10 minutes, everything seems fine.

Is there some valve that might need changing.

Hopefully somebody has an answer.
 
Joes Mark said:
I could use a little help from you guys.

For the past couple of weeks, the engine in my 90 LSC pops and backfires (thru the carb) when its first started.

It starts up fine and Idles great. But once you start giving it gas, it starts to hesitate, pop and backfire. Sometimes it wants to stall but does not. After the cars warms up about 10 minutes, everything seems fine.

Is there some valve that might need changing.

Hopefully somebody has an answer.
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Assuming that you don't have a carb but rather FI, and you haven't been working on the motor and gotten the plug wires crossed up, I'd start checking for a vacume leak! Sucking extra air will sometimes make it backfire. Otherwise you might have a look at the idle control valve which may be sticking.;)
 
Thanks for the reply. Motor is Fuel Injected and the backfire is in the motor. I have not done anything to the motor. Except for the battery, the alternator and changing the oil every 3000 miles everything else is original. The car only has 43,000 miles. I will check the idle control valve and replace it.
 
Joes Mark said:
Thanks for the reply. Motor is Fuel Injected and the backfire is in the motor. I have not done anything to the motor. Except for the battery, the alternator and changing the oil every 3000 miles everything else is original. The car only has 43,000 miles. I will check the idle control valve and replace it.
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Joe,
Another thought!
My 90 Mark VII with about 155K on it at the time did mysteriously start missing and would occasionally backfire under sudden acceleration. Problem = one plug of a set with less than 8,000 miles on them went bad and would only fire occasionally. Never happened before. What a PITA to discover without various testing equipment. Good luck!
 
You cannot rule out the plug wires unless you physically check the firing order between the dizzy and the plugs.

Even professionals switch the 1 and 2 at times.
 
This is a classic symptom of a malfunctioning MAP sensor. (Manifold Absolute Pressure)

Black thing mounted on firewall, vehicle left. One vacuum hose and one elecrtical connector. Have someone hold throttle at an objectionable RPM and tap in the MAP sensor with a screwdriver handle. If nothing happens, pull the vacuum hose off and cover the hose with your finger. If there is no, or little change in the engine condition, replace the MAP sensor.

Art
 
Joes Mark said:
I could use a little help from you guys.

For the past couple of weeks, the engine in my 90 LSC pops and backfires (thru the carb) when its first started.

It starts up fine and Idles great. But once you start giving it gas, it starts to hesitate, pop and backfire. Sometimes it wants to stall but does not. After the cars warms up about 10 minutes, everything seems fine.

Is there some valve that might need changing.


hey Joe!
Did you solve the problem? What worked? :confused:
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Still have the problem but not every day. I changed the cap and rotor. I plan on changing the plugs this weekend and see what happens. I will also check the MAP.

Thanks for all the help. I will let you when iis resolved.
 
might of jump timing..,plug wires crossed,...cats clogged,...improper plug gap...,bad valve,...cam rounded out a lobe,...pull the plugs and read them and replace and if you can do a compression test at least you will know how healthy your motor is if all else fails pull the vavle covers and turn the motor over and watch the rockers open and close
 
Well here is the latest, the plugs and wires were changes along with the fuel filter. STILL have the same problem! After the car warms up everytiong is fine.

I took it to a shop and after they did some tests, they determined that the intake manifold is all sludged up and some of the airways are clogged. They are suggesting that unit comes off and be boiled out. With a cost of $700-$900, I'm not so sure I want sink more $$$ into the car. The MAP checked out OK.

Any opinions regarding the manifold being the problem. The motor only has 43,000 miles on it.
 
Pull codes. It's probably not the manifold, and if it is it's a simple job you can do as opposed to $700-$800. A can of Seafoam would probably clear most of it out anyway.
 
JoshMcMadMac said:
Pull codes. It's probably not the manifold, and if it is it's a simple job you can do as opposed to $700-$800. A can of Seafoam would probably clear most of it out anyway.
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how good does that sea foam work id really like to give it a try on my lincoln
 
Mulletoffury said:
how good does that sea foam work id really like to give it a try on my lincoln
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Worked pretty well on mine with 160k on it. Made it idle smooth again, Not bad for a $6 investment. Do it a night so the neighbors don't get upset with all the smoke that it creates.
 
Well after driving the car for over a year with the continuing problem, I went to a different mechanic. After running a few tests, he had determinded that the coolent temperature sensor was bad. Upon inital start up the sensor was telling the computer that the car was at 178 degrees. According to the mechanic this caused the fuel mixture to be too lean causing the backfire. The sensor has been changed. After a two minute warm-up after the car is started, it runs like normal.

One other thing the mechanic noticed was the my fuel pressure was only 40lbs. Should I be concerned? What effect can low pressure cause.
 
Joes Mark said:
Well after driving the car for over a year with the continuing problem, I went to a different mechanic. After running a few tests, he had determinded that the coolent temperature sensor was bad. Upon inital start up the sensor was telling the computer that the car was at 178 degrees. According to the mechanic this caused the fuel mixture to be too lean causing the backfire. The sensor has been changed. After a two minute warm-up after the car is started, it runs like normal.

One other thing the mechanic noticed was the my fuel pressure was only 40lbs. Should I be concerned? What effect can low pressure cause.
Click to expand...

Thanks for the heads up!
 
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