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Help Please Pinto Misfire At 4000Rpm


Iang
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Hi All,

I need some help please. I have a 2.0L pinto with a fast road kent cam with twin 40 webers with a megajolt electronic iginition, The engine runs fine up to 4000rpm then misfires (almost a cough and back fire 2 or 3 times) then carries on until 5,500 rpm with no issues.

So far I have changed the coil pack and plugs, changed the settings on the megajolt, re jetted the carbs (mains and airs), checked the webers for air leaks which appears ok. but I still cant find the issue.

I did change the setting on the megajolt and the issue went away during a short drive but after leaving the car for an hour the issue came back. The megajolt appears to be keeping its settings as far as I can see.

I am running out of ideas. Any help comments greatly appreciated,

Thanks Ian

 

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Crank position sensor, probably the wiring in the plug.

I ended up having to replace the plug and support the plug and wire with a short ally bar.

 

With the Crank position sensor bolted to the bracket the plug does not move but the wires which only connect to the plug by the inner 2 wires. You will have removed the outer cover to wire the plug. The wire will flex like hell, took me several goes to figure it out.

Edited by Snapperpaul
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Hi All,

Thank you to everyone that replied with advise.

GREAT NEWS I have now fixed the issue thanks to SnapperPaul :) it was a broken wire going to the crank sensor, Thanks mate I owe you a beer or 2 I have spent a long time looking for this issue.

She now rev's up to 6000rpm no problem.

Thanks Again,

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Glad this has been sorted! Can anyone explain why the crank sensor faulty wiring would only show up at 4000rpm but is ok below and above that figure? I ask because I've got similar symptoms with my engine but the wiring has tested out ok with the engine not running

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cb750,

On the crank sensor wiring did you pull the rubber boot back as well, My wiring looked fine and appeared ok with a meter however when I pulled the rubber boot back and pulled it the connector came off with a short length of cable in my hand,

I don't know why It only showed up at 4000 rpm but glad SnapperPaul suggested it. :)

Good luck with finding the fault.

Best Regards, Ian

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My misfire was a little more random but essentially there is a break in the cable but not a clean break so the 2 ends of the wires are in contact, sometimes there are a few threads of cable still connected.

A vibration can happen at a specific harmonic that pulled the wires apart and/or the signal is to weak for the ECU to register.

The signal required is a square wave if that is degraded into a confusing signal the ECU may disregard it.

I often had a backfire which turned out to be a non ignition event followed by normal ignition that ignited unburned fuel in the exhaust.

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Thanks. My misfire started off random throughout the rev range. My wiring to the crank sensor comprised of a length of new wire from the edis soldered onto the last 100mm of the old wiring going into the sensor plug. I stripped the boot and the insulation off the old wiring but found no problems but replaced it anyway. I replaced the edis module and whether it was coincidence the misfire stopped being random and only appeared at around 4000 revs. If I accelerate slowly though that point the misfire doesn't happen so I put it down to a car problem (running Fireblade carbs with one of the air corrector jets blocked off).

 

Snapper, I never thought of the square wave requirements so I'm going to change both the sensor, plug and screened cable and see what happens. Hope I can get this done before sorning it in October!

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  • 4 months later...

Aftermarket ecu just gives flexible injection and ignition control which makes it more suitable for tuning if the engine is modified.

Standard ecu is perfectly OK on an unmodified engine and should give better fuel control than a carb. It's a basic system by modern standards but Ford put a lot of effort in to developing it and it works well. 

Edited by richyb66
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