missfiring no codes - Dodge Ram SRT-10 Forum
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post #1 of 37 Old 01-20-2014, 12:50 PM Thread Starter
ogromnii
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missfiring no codes

hi everybody
this is my first post here, I'm car mechanic from bulgaria. english is not my first language so i would ask you to excuse my mistakes
now the problem:
i have ram srt10 truck in my garage that is missfiring at idle and low load, and the owner says it has no power like before.
the truck visited many garages and the local dealer(mercedes-benz dealer) and it came to me with following things changed:
coils, wires and spark plugs
fuel pump
crank sensor, nock sensor(s)
inlet manifold gaskets
and maybe something else i don't know
no one of the changes seem to affect the performance
what i did: cheked wires and plugs(fine) flow-checked injectors(perfect)
first oxygen sensors are cycling betw. 0.2-0.7v.
second are constantly at 0.9
tps o.k., map sensor o.k.
cam sensor not checked
no error codes
car is with manual transmission with 26k miles on clock
everything stock as I know but this is something i can not be sure at
cold started it runs well, but as it goes warmer starts missfiring, as warmer it gets missfiring gets bigger, when I load the engine at idle by shifting to 6-th gear and partitialy releasing clutch missfire ..let's say dissapears.
so I think the valves dont seal due to something like sticky tappets or something... but it looks so uncommon to engine with 26k properly serviced. I dont want to disassemble the engine without reason so i'm looking for advice what may be wrong that i'm missing.
thank you in advance
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post #2 of 37 Old 01-20-2014, 01:31 PM
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what year is the truck?
has it been sitting long? (bad gas)
are you sure a ceramic on the spark plugs isn't cracked? (i had a car do this one time and never noticed it but the car ran like **** until we finally found the problem was a cracked ceramic)

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post #3 of 37 Old 01-20-2014, 07:21 PM
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If you're sure crank sensor was done, change cam sensor. They often act up without codes. Cam sensor depth is detrimental as well so double check that.
Likely your problem.

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post #4 of 37 Old 01-20-2014, 09:04 PM Thread Starter
ogromnii
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it's 2006, the gas is new, inspected spark plugs carefully, they are brand new denso, anyway I re-gapped and changed to original champions but no difference.
all previously swapped parts are in a box, and there is a crank sensor there, the one on the engine looks new, so i'm pretty sure it's new.
today i will try to take the ecm out so i can reach connectors and check with oscilloscope crank and cam signals going in, power supply (for bad ground etc.) and signals going to coils and injectors to see if i find something wrong.
thank you for ideas, i'm open for more
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post #5 of 37 Old 01-20-2014, 10:34 PM
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Wire bundle on the passenger side down by the exhaust. There is the possibility you have some heat damage in that area. Another possibility is the case on the PCM might be cracked and moisture and corrosion may have occurred.

Just thinking out of the box. Both are known to have happened, just not sure it is the cause in your case

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post #6 of 37 Old 01-20-2014, 10:39 PM
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start with the basics, when it does start missing the one header pipe that is "not firing" will turn cold, since there is no "fire' there is no heat

so take a squirt bottle of water, and when it starts missing, shoot each header pipe with a light stream of water, the cylinder that is missing the water will not evaporate off

from there you know the bad cylinder

next check as you say the plugs make sure that cylinder is firing, if so the wire, coil so forth should be good. if not , you found the problem

if not tho , move an injector , that will tell you if the injector is bad

if its ok, then you need to remove the valve cover, visually check the valve spring and push rod, make sure the spring is not broken, or the rod not bent.

if all is ok, check the compression on that cylinder and do a leak down test

if all this is good I have seen the driver in the pcm go bad, that is not good there are no replacement pcms at the moment from dodge, it would have to be repaired

do these basic checks, and that will get you in the right direction, but throwing parts at it for the fun of it can get expensive, check things correctly


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post #7 of 37 Old 01-21-2014, 11:34 AM Thread Starter
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a little update
everything checks fine, good signal from all sensors and to all coils and injectors.
but ignition advance check with stroboscope light shows advance sometimes fine, sometimes jumping to .. let's say -30 degree more. I couldn't finish the check because my stroboscope died, purchased new one, tomorrow with fresh head.
some ideas what can cause advance jumps? cam and crank signal checked at pcm connectors, seem perfect, constant and ignition power supply ok, ground ok. maybe something wrong inside pcm? may loosed timing chain cause this without making noise? engine perfectly quiet, only sound injectors clicks. any ideas?

Last edited by ogromnii; 01-21-2014 at 10:03 PM.
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post #8 of 37 Old 01-21-2014, 11:45 AM
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Quote:
Originally Posted by ogromnii View Post
a little update
everything checks fine, good signal from all sensors and to all coils and injectors.
but ignition advance check with stroboscope light shows advance sometimes fine, sometimes jumping to .. let's say -30 degree more. I couldn't finish the check because my stroboscope died, purchased new one, tomorrow with fresh head.
some ideas what can cause advance jumps? cam and crank signal checked at pcm connectors, seem perfect, constant and ignition power supply ok, ground ok. maybe something wrong inside tcm? may loosed timing chain cause this without making noise? engine perfectly quiet, only sound injectors clicks. any ideas?
Cam sensor is an inexpensive repair. I've seen a few do this similar thing with no codes. It does affect your timing!
You try cycling the key 3 times and leaving on 3rd time? Sometimes dataloggers won't pick up all DTCs

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post #9 of 37 Old 01-21-2014, 10:01 PM Thread Starter
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Originally Posted by Venomous1 View Post
Cam sensor is an inexpensive repair. I've seen a few do this similar thing with no codes. It does affect your timing!
You try cycling the key 3 times and leaving on 3rd time? Sometimes dataloggers won't pick up all DTCs
yes, it's not expensive but sensor seems perfect, I watch signal with oscilloscope while engine idling and missfiring on pcm connector, is perfect square wave 0-5v without any interruption or interference.
Crank sensor makes 2 pulses-pause-2 pulses-pause 5 times at revolution, googled, but didn't found pictures of crankshaft, but sensor is located in the middle of the block wall, so I suppose there isn't separate tone wheel, but crank sensor teeth machined directly on crankshaft, am I right?
cycling the key is only way I check for codes, my readers don't support this truck, it isn't OBD-compliant.

i'm thinking if at any reason timing chain jumped a tooth? it seems impossible, pcm has error code for bad synchronisation, but is not giving it
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post #10 of 37 Old 01-21-2014, 10:38 PM
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DTC Codes
https://www.srt10forum.com/forums/showthread.php?t=10557

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