# Backfire through the carb???



## mwilliams (May 24, 2011)

Hey everyone

I just replaced the engine in my son's 87 pathfinder, we can get it up to about 2500 rpm's and then it starts popping back through the intake. It won't rev any higher and it just stays there and keeps popping and running. Can anyone give me an Idea where to look from here, oh it has a throttle body not a carb. lol I'm lost>:newbie:


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## SPEEDO (Jun 9, 2003)

sounds like it is in "fail safe" mode... check for any codes... V6?


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## mwilliams (May 24, 2011)

No Z24 four cylinder with 8 plugs?


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## smj999smj (Jan 1, 2006)

Fail-safe will limit the RPM's to 2500RPM, but shouldn't cause it to backfire. Recheck the firing order of the ignition wires, check the distributor cap and rotor (rotors had a tendancy to "burn through" causing crossfire) and ignition timing.


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## mwilliams (May 24, 2011)

Thanks, stay tuned . I wont be able to check until I get back from work.


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## mwilliams (May 24, 2011)

We put a new cap and rotor on and it still is popping back through the intake, checked the other engine to make sure the firing order was correct and it the same. This is starting to really make me want to drive it over a burning piec of sage brush!!!!!!!!!!


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## smj999smj (Jan 1, 2006)

For testing purposes, try swapping the the wires to the ignition coils (intake coil wire to exhaust coil and vice versa) and see if it changes. If it doesn't, swap the wires back and do a compression test.


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## mwilliams (May 24, 2011)

What compression am I looking for???


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## smj999smj (Jan 1, 2006)

128-171 PSI. Lowest cylinder pressure must be 80% of highest cylinder pressure.


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## rogoman (Dec 16, 2004)

Backfiring out the intake is either a valve stuck open or a lean mixture or spark plug wire(s) connected to the wrong cylinder(s). Check compression on all cylinders and then look for vacuum hoses loose, cracked, or misconnected. Check the mass air flow electrical connection and see that it is tight.
Sticking valves: If a intake valve is bent, has a bad spring or is misadjusted, the engine will sometimes backfire through the intake. Use a vacuum gauge connected to any convenient spot on the intake manifold. Run the engine at 1000 RPM & look for 18-21 inches of vacuum with a steady needle. A problem intake valve will make the vacuum gauge needle sweep 5-10 inches.


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