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Missfire/ backfire


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Okay guys so I need a bit of help, I recently got my Mj back up and running after rebuilding the motor. It was running great for about a week... however it has now started missing at higher RPM's. After it misses a couple of times it will backfire. i have a new crank sensor and new distributor, new plugs and wires, new injectors and new fp regulator. suggestions?

 

I had the thought that maybe I am getting too much fuel dumped in too fast and flooding the cylinders? I'm not sure that is even possible but its the only conclusion I keep returning to. I installed 5.0 mustang injectors after my build 

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Get a set of gauges and check the fuel rail pressure. When exactly did the backfiring start? When you swapped the injectors in?

ill see if i can borrow a set at the shop today. ii would ultimately like to put that permanent fp gauge in from the cruiser renix tips, i may just use this as an excuse to do it.

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Just had a discussion with one of the guys from work, he postulated that the MAP isn't going to start regulating fuel until the engine is warmed up, which may be causing my excess fuel dump that I think may be occurring. No proof though

if so, is there any way to tune these ECM's like more modern cars, or should i just go back to factory injectors. I have seen many people go with 4 port 5.0 injectors so I don't really see why I'm having a problem.

 

thoughts?

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Check the FPR first. If okay (31psi w. and 39psi w/o vacuum). If okay, pull and read the spark plugs for rich and/or lean operation. You may have a regulator(s) stuck open or one that's not working at all, and reading the plugs will give you an idea. If they all look good and are uniform, I'd swap the old injectors back in.

 

An A/F meter is very helpful in diagnosing problems like this. I've been running one for years and can tell at a glance if the air/fuel mixture is within specs from idle to WOT. I don't know if FL has emissions inspections, but they can check the mixture for you.

 

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Check the FPR first. If okay (31psi w. and 39psi w/o vacuum). If okay, pull and read the spark plugs for rich and/or lean operation. You may have a regulator(s) stuck open or one that's not working at all, and reading the plugs will give you an idea. If they all look good and are uniform, I'd swap the old injectors back in.

 

An A/F meter is very helpful in diagnosing problems like this. I've been running one for years and can tell at a glance if the air/fuel mixture is within specs from idle to WOT. I don't know if FL has emissions inspections, but they can check the mixture for you.

 

Is that your doll collection in the background? 

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Had a similar problem with Ryan's after rebuild. After trying everything we could think of we finally hooked it up to an oscilloscope to check the wave pattern. When cold the pattern was fine, but when warmed up the timing went 30 degrees out....and the only thing that solved the problem was a CPS from the dealership - original OEM part.

 

It solved the problem because the aftermarket CPS would read the tone wheel (flexplate) erratically when it got warm.

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Check the FPR first. If okay (31psi w. and 39psi w/o vacuum). If okay, pull and read the spark plugs for rich and/or lean operation. You may have a regulator(s) stuck open or one that's not working at all, and reading the plugs will give you an idea. If they all look good and are uniform, I'd swap the old injectors back in.

 

An A/F meter is very helpful in diagnosing problems like this. I've been running one for years and can tell at a glance if the air/fuel mixture is within specs from idle to WOT. I don't know if FL has emissions inspections, but they can check the mixture for you.

 

Is that your doll collection in the background? 

 

 

Yuk yuk. The wife does ceramics..........

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Had a similar problem with Ryan's after rebuild. After trying everything we could think of we finally hooked it up to an oscilloscope to check the wave pattern. When cold the pattern was fine, but when warmed up the timing went 30 degrees out....and the only thing that solved the problem was a CPS from the dealership - original OEM part.

 

It solved the problem because the aftermarket CPS would read the tone wheel (flexplate) erratically when it got warm.

Well my issue is similar but opposite, Also there was no change in the condition of the misfire between original crank sensor and the replacement BWD sensor.

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