2015 5.7 8 speed Hard to start very rough idle...please help if you can

Shortbus 50 · Oct 19, 2019

yes all injectors seem to be working correctly no leaks all the coils seem to be fine the truck run on 7 cylinders for 2 weeks and ran at least ran you know like now it won't stay idling it'll die

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Elevated 2013 · Oct 19, 2019

Hmmm...I would think it could be a clogged cat but that would give you more problems getting up to speed than idling. Wish I knew more about the codes.

Elevated 2013 · Oct 19, 2019

The odd part is that it’s running rich and dieing. Usually it’s lean conditions that cause it to die. You could try disconnecting 1 oxygen sensor at a time and see if it changes the codes or how the engine runs to see if maybe you have 1 bad oxygen sensor as that’s 1 of the few sensors that really controls the fuel mixture. Otherwise, the engine coolant temperature sensor, MAP sensor, intake air temperature sensor, and throttle position sensor are the other ones.

Shortbus 50 · Oct 19, 2019

I will continue testing O2 sensors and other ideas. I have a buddy that may let me swap his throttle body over to mine to see if that's the problem thank you guys for the help I'll be going offline for a little while while doing this I'll check back in later

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Elevated 2013 · Oct 19, 2019

Keep us updated. I’ll still be around for an hour otherwise I won’t be near my phone or computer until late tonight.

bhonshell37 · Oct 19, 2019

Keep the beer cold and in hand reach

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2DirtyKids · Oct 19, 2019

I am not any help but amazing how quickly so many have offered assistance and offer continued help. Great to see.

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Elevated 2013 · Oct 19, 2019

That’s why I love this forum despite some of the people that just want to argue and cause drama.

Shortbus 50 · Oct 19, 2019

It is a nice forum, first and only one I have ever been part of. I going to call it quits for today I now have another headache. LOL Thanks again guys, will keep you all posted.

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DodgeDude99 · Oct 21, 2019

bhonshell37 said:
If you own a multimeter, pull the fuses in question. Touch the leads from the meter to the fuse prongs to test continuity.

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You don’t have to pull the fuses to test continuity. You can put your probes where the metal prongs come out on the top of the fuse

DodgeDude99 · Oct 21, 2019

A clogged cat would start fine cold but won’t rev up like normal or to much past 2500 rpm, but once warm it would have starting issues. You can test for back pressure by taking out the pre & post O2 sensor and screwing it a bing that has a nipple on it to put a pressure gauge on. If it has more than 3-4 psi. the cat is clogged, post O2 port should read 0-1psi.
Don’t have the **** adapter?, drill a 1/4” hole before and after the cat sharpen a piece of 1/4” brake line & tap it in the hole to put the gauge hose on.

A TB is just an air valve, it either opens or it doesn’t.

Without a scan tool you don’t have a clue as to what is actually wrong.

Marshall · Oct 21, 2019

I am not much help with all the newer ones
Have you pulled the spark plugs and looked at them? Should be able to see if too rich. Thought, if it will keep dying , they could be all crappy anyway

BenWH · Oct 21, 2019

Try investigating the Evap purge sensor. My 2015 5.7 started rough and that ended up being the culprit. It was about $300 to replace at the dealer but I had a sketchy aftermarket warranty that actually covered it.

Elevated 2013 · Oct 21, 2019

BenWH said:
Try investigating the Evap purge sensor. My 2015 5.7 started rough and that ended up being the culprit. It was about $300 to replace at the dealer but I had a sketchy aftermarket warranty that actually covered it.

Ben, an easier way to test that would be to just take the gas cap off and try starting the truck. But that really only effects the truck just after filling it up with gas. Even given time, a lot of times the extra vapors escape on their own and you can start the truck. Plus, that generally sets a code if it has a problem. I’m not trying to correct you or say you’re wrong, but there are 2 other ways to check it.

Shortbus 50 · Oct 22, 2019

Have the scan tool, it has only thrown 2 codes. p0175 and p0506. One is low idle air control the other is too rich fuel. I replaced the purge, map, pcv already. Only got cyl.- 1,2,3,4 plugs out and 1-2 look really bad, 3-4 look ok but covered in fuel. Want to take the valve covers off to check springs and other crap just to make sure whatever is wrong isnt screwing up the cam swap from back in july. Those plugs only have 2000 miles. I will test the o2 just to cross it off and because I am running out of ideas besides letting it go back but I do not want to hurt my credit. Just sucks I have had it less than a year and I don't roast the tires or even chirp off the line.

Shortbus 50 · Oct 22, 2019

Someone give me a simple list of Most reasons truck would run too rich: please when you have time

Elevated 2013 · Oct 22, 2019

If 3-4 spark plugs are covers I don’t fuel them the coils aren’t firing. You said 1-2 look bad. What do you mean by “bad”?

Elevated 2013 · Oct 22, 2019

Off the top of my head: malfunctioning ignition coil, bad oxygen sensor reading too lean, engine coolant temperature sensor (the one for the engine not the gauge), leaking fuel injector, bad MAP sensor, bad intake air temperature sensor, and bad throttle position sensor. That’s all I can think of outside of a faulty PCM. There’s probably some that I’m not remembering though.

Shortbus 50 · Oct 22, 2019

I already swapped back to old pcm and had same effect,map is new, air intake charge temp is new, there isn't a throttle positioning sensor (thanks ram) guess it is built into the electronic throttle body, will test ignition coils, o2, engine coolant temp, and injectors next. But the coils and injectors are new. As in bad i meant black as hell, the othe ones where a little dirty but wet.

Dodge 1500 4X4 · Oct 22, 2019

Hay Guys, you may have a collapse hydraulic lifter, there's no valve lash adjustment on the rocker arm assembly but you will be able to see a dead rocker did you replace the push rods
how's your oil pressure you said you replaced the pump, did you do a compression test these are a few ideas from the old days, did you replace all of your COP's and boots, I came back to Ram, for a true muscle head V-8 and sound, sick and tired of the VCT's, cam phasers duel timing chains and tensioners had my share of problems I was a Ford owner for 15 yrs.

2015 5.7 8 speed Hard to start very rough idle...please help if you can

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