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Discussion Starter · #1 ·
Ok so yesterday we did a major upgrade to a friend's 2003 Rubicon 4.0(62mm throttle body, Bosch 4 hole injectors, rear cat delete, flow master muffler, and banks torque tube header) after install noticed a misfire in the engine checked for vacuum leaks also checked didn't find any vacuum leaks but still has a slight miss to the engine. Also checked plug gaps and they were all set to .35(they were at .45). Please has anyone run into this issue? Engine code is P0300 multiple misfires cylinders 1-6.
 

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Could be a bad pre-cat which is what caused my 04 to have multiple misfires and misfire codes. Assuming the upstream and downstream 02 sensors are good and operating correctly.
 

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Well since you changed injectors I'd start there. Put the old ones back

(Not shooting down your work but none of those changes are going to gain you much of anything)
 

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Discussion Starter · #4 ·
Could be a bad pre-cat which is what caused my 04 to have multiple misfires and misfire codes. Assuming the upstream and downstream 02 sensors are good and operating correctly.
Jeep was running good. Prior to these mods. The rear most cat didn't have any of sensors. We left the pre-cut as to connect to the NEW header.


*forgot to add this it's running at about 1000-1100rpm at idle. Sprayed wd40 trying to find any leaks but wasn't able to find any.
 

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Discussion Starter · #5 ·
Well since you changed injectors I'd start there. Put the old ones back

(Not shooting down your work but none of those changes are going to gain you much of anything)
Changed alot. It woke that jeep up it really truly is way quicker now. Night and day difference.
 

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If the idle is too high, check the voltage of the throttle position sensor. Are the injectors direct bolt in, or are they just ones to fit? If they aren't OE replacement and are an "upgrade" are they high or low impedance? I would start as the other user said; with putting the oem injectors back in it first. Did you put the old oxygen sensors in the new exhaust? If so, did you unplug the sensor before removing it, or remove the sensor end first (causing the wires to twist). You may have damaged the sensor or wires when removing.
 

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sometimes the old parts were so warn/clogged, you can get a large improvement with just placements.

not sure i would want any bosch product on my jeep though
X2 for the most part, Bosch's 02 sensors and spark plugs are notorious for not working well in our Wranglers. The main exception I am aware of is Bosch's fuel pump which is very good and is a good replacement for the Mopar fuel pump. Most of the other aftermarket fuel pumps like from Airtex and Spectra are little more than short-lived junk.
 

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Discussion Starter · #11 ·
If the idle is too high, check the voltage of the throttle position sensor. Are the injectors direct bolt in, or are they just ones to fit? If they aren't OE replacement and are an "upgrade" are they high or low impedance? I would start as the other user said; with putting the oem injectors back in it first. Did you put the old oxygen sensors in the new exhaust? If so, did you unplug the sensor before removing it, or remove the sensor end first (causing the wires to twist). You may have damaged the sensor or wires when removing.
unplugged before removal of the sensor. Have not swapped old OEM injectors out yet. These are direct replacement upgrades plug and play. Not sure of they are high or low. It's only one cylinder Cylinder 6 while the jeep is running I unplug the last injector and the miss goes away. It doesn't do it on any other cylinders.
 

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Discussion Starter · #12 ·
X2 for the most part, Bosch's 02 sensors and spark plugs are notorious for not working well in our Wranglers. The main exception I am aware of is Bosch's fuel pump which is very good and is a good replacement for the Mopar fuel pump. Most of the other aftermarket fuel pumps like from Airtex and Spectra are little more than short-lived junk.

It's the stock fuel pump the 03 rubicon only has 58k miles on it
 

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Discussion Starter · #13 ·
If the idle is too high, check the voltage of the throttle position sensor. Are the injectors direct bolt in, or are they just ones to fit? If they aren't OE replacement and are an "upgrade" are they high or low impedance? I would start as the other user said; with putting the oem injectors back in it first. Did you put the old oxygen sensors in the new exhaust? If so, did you unplug the sensor before removing it, or remove the sensor end first (causing the wires to twist). You may have damaged the sensor or wires when removing.
Oh the idle today was hit or miss but was about 800-800-900 before it was roughly 1000-1100ish the gauge sucks foe accuracy. And my diablo trinity tuner does not work for the 03 oldest it works for is the 2005 which makes me wonder wtf is the difference between the 03 and 05?
 

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So it runs better with an injector unplugged?

Most run better with all six injectors plugged in.

Perhaps that injector is leaking
 

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Discussion Starter · #17 ·
Ok so yesterday we did a major upgrade to a friend's 2003 Rubicon 4.0(62mm throttle body, Bosch 4 hole injectors, rear cat delete, flow master muffler, and banks torque tube header) after install noticed a misfire in the engine checked for vacuum leaks also checked didn't find any vacuum leaks but still has a slight miss to the engine. Also checked plug gaps and they were all set to .35(they were at .45). Please has anyone run into this issue? Engine code is P0300 multiple misfires cylinders 1-6.
Update checked plugs and they looked good nice tan coloration. Went thru all the on board diagnostics. Long term trims were negative because the battery had been reset so no stored data. And the ignition time wasn't advancing(feeling is sensing a "knock" someone suggested that the jeep would have to be dyno tyned. But really. Imo the throttle body header and muffler along with the rear most cat delete shouldn't need to be performance dyno tuned as this are SIGNIFICANT mods yes they have hp/torque gains but still. I don't consider them to be MAJOR. Please anyone had this issue or know wtf is going on?
 

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Update checked plugs and they looked good nice tan coloration. Went thru all the on board diagnostics. Long term trims were negative because the battery had been reset so no stored data. And the ignition time wasn't advancing(feeling is sensing a "knock" someone suggested that the jeep would have to be dyno tyned. But really. Imo the throttle body header and muffler along with the rear most cat delete shouldn't need to be performance dyno tuned as this are SIGNIFICANT mods yes they have hp/torque gains but still. I don't consider them to be MAJOR. Please anyone had this issue or know wtf is going on?
Unfortunately, we don't see many folks doing most of the upgrades/replacements you did(except the flowmaster) on their Jeeps so I doubt you are going to find many with this exact experience. I know you don't want to hear this but if I were in your shoes, I would start taking each upgrade off, replacing it with the original part until you have isolated the culpret. In the future, you may want to test each part after installation, otherwise if something goes wrong you don't have a clue where to start. I have learned this the hard way, especially doing electrical projects..
 

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Discussion Starter · #20 ·
Unfortunately, we don't see many folks doing most of the upgrades/replacements you did(except the flowmaster) on their Jeeps so I doubt you are going to find many with this exact experience. I know you don't want to hear this but if I were in your shoes, I would start taking each upgrade off, replacing it with the original part until you have isolated the culpret. In the future, you may want to test each part after installation, otherwise if something goes wrong you don't have a clue where to start. I have learned this the hard way, especially doing electrical projects..



Found the issue. Needless to say it wasn't any of the parts the gentleman helping with the install just didn't get the back of the intake manifold down all the way. With everything on the top of the intake)injectors hoses it was hard to see the intake sitting to hi on the rear. Thank you for all your input everyone. :)
 
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