Intake backfire, rough running help.

I just posted this over on jeepforum also but figured I'd try here as well.

Engine Code 27 is all that comes up. The Jeep backfires through the intake and has major loss of power, feathering the throttle and going WOT helps but still much lower power.
New parts:
Catalytic Converter
Muffler
Upstream O2 (Bosch)
TPS (currently BWD may swap to OEM have replaced with another just to check and resistance sweep says it's good)
MAP (currently BWD, OEM will be here Tuesday)
Ford 4 hole injectors
Spark plug wires
Cap
Rotor
Water Temp Sender (back of block OEM)

Yesterday after recrimping the connectors and installing the MAP I reset the computer then also reset the adaptive driving module through the headlight on/off sequence. Jepo drove almost perfect for roughly 10 miles. Pulled over and got gas and when I restarted it drove like crap again.

This morning I pulled the ECM connectors and tested resistance to each injector lead while shaking the harness, 0 ohms. Tested resistance from pin 5 ASD relay to injectors while shaking harness, 0 ohms. Tested ECM ground pins 0 ohms. Tested Map, TPS, IAC, IAT to ECM all 0 ohms.

I have also opened up the ECM and replaced the 3 capacitors and resoldered a few of the pins leading to the connectors. I spliced in new injector leads as the old ones where dry rotted and exposed.

I am so stumped as to what to try next. Only thing I've come to the conclusion on is internal in the ECM, but don't want to buy reman.


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Backfiring is only caused by a couple of things. The most common would be getting the sparkplug wires in the wrong order. The firing order is cast into the intake manifold.

A burnt valve can also cause the same problem.

Running too lean can cause excessive combustion chamber temps and cause the mixture to explode while the valve is still open. That is what a back fire really is.

My first thought is what old_man said.
Next thought went to cam position and distributor, then maybe ecm/pcm.
I wonder why it drove fine for the next shut off then failed.

If the wiring is bad maybe.

You might be able to find a JY ecm to have on hand just for testing.




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Fuel pump? Bad injectors/ wiring?


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Bad coil?

Thanks for all the replies guys! I actually took a leap of faith and swapped the ASD relay with the ABS relay and what do you know the ABS light is now lit but no check engine light and it has so far (fingers crossed) been running better. Put about 25 miles on it yesterday and not one hiccup, this was after resetting the computer and the learned driving. I do believe I had many issues all at once so replacing some of those parts were neccesary while others were just overdue as it's got 170k.

Also looks like I forgot to add a few things to my list of parts that I'll update, I had also put in a new bosch fuel pump, new regulator and new inline fuel filter.

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Won't let me edit the original post so here's and updated list
New Parts:
Catalytic Converter
Muffler
Upstream O2 (Bosch)
TPS (currently BWD may swap to OEM have replaced with another just to check and resistance sweep says it's good)
MAP (currently BWD, OEM will be here Tuesday)
Ford 4 hole injectors
Spark plug wires
Cap
Rotor
Water Temp Sender (back of block OEM)
Bosch Fuel Pump
Fuel Pressure Regulator
Inline Fuel Filter

fonzi03 said:

I just posted this over on jeepforum also but figured I'd try here as well.

Engine Code 27 is all that comes up. The Jeep backfires through the intake and has major loss of power, feathering the throttle and going WOT helps but still much lower power.
New parts:
Catalytic Converter
Muffler
Upstream O2 (Bosch)
TPS (currently BWD may swap to OEM have replaced with another just to check and resistance sweep says it's good)
MAP (currently BWD, OEM will be here Tuesday)
Ford 4 hole injectors
Spark plug wires
Cap
Rotor
Water Temp Sender (back of block OEM)

Yesterday after recrimping the connectors and installing the MAP I reset the computer then also reset the adaptive driving module through the headlight on/off sequence. Jepo drove almost perfect for roughly 10 miles. Pulled over and got gas and when I restarted it drove like crap again.

This morning I pulled the ECM connectors and tested resistance to each injector lead while shaking the harness, 0 ohms. Tested resistance from pin 5 ASD relay to injectors while shaking harness, 0 ohms. Tested ECM ground pins 0 ohms. Tested Map, TPS, IAC, IAT to ECM all 0 ohms.

I have also opened up the ECM and replaced the 3 capacitors and resoldered a few of the pins leading to the connectors. I spliced in new injector leads as the old ones where dry rotted and exposed.

I am so stumped as to what to try next. Only thing I've come to the conclusion on is internal in the ECM, but don't want to buy reman.


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Click to expand...

Running great then running poorly right after shutting down to say buy gas is a sign of vapor lock, injector getting super heated by say an exhaust leak, or low fuel pressure. Only time I ever had backfires was from a loose vacuum connection to the MAP sensor.

Still crossing my fingers but looks like the ASD relay was the culprit. Don't understand why it was intermittent but it's running much better now. Just need to get this slight overheat problem taken care of and I can install my lift!

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