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need a hand on a 2004 8.1L spark knock

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Old 08-20-2018, 05:20 PM
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Default need a hand on a 2004 8.1L spark knock

this 1 is a hard 1 so hope some 1 can give me a hand as i am working on a big RV that i cant just drive into the shop

I have a 2ed gen 8.1L 2004 on a Allison 1000 MH reman motor with about 50Kmiles on it and 30k i have own it
So when under hard load and WOT i get just for a sec a tapping sound from my motor only when in drive with load on the system and only when at running temp of 195f
when driving at 55 to 45 mpr its tapping alot . not some thing i can over look
Sound is coming from top end only behind the throttle body on left side of motor but is very hard to track down.no sound from lower end . when it started i was on a trip and it still made it home from 400 miles like nothing was wrong
there is no loss of power

the only thing i did find wrong was the ground wire to fuel injector 2 was some times touching ground and in doing so would just dump fuel

no sounds coming from trans or back of motor / flywheel
for the last month i have been trying to find it . tried all kinds of things . stick to ear all over the motor . dropped drive belt to make sure its nothing on the front of motor . but when doing so sound is cut by 40%
pulled intake looked at all hydraulic lifters and pulled them all the way out to look at rollers on end and pulled valve covers too
pulled oil pan and pulled all caps and manes all looked good and looked at rod pins as good as i could from below and looked for piston slap and every thing looks good
no codes in ECM ...new spark plugs ...coils have a good jump of spark to them
wires tested and look good as there not that old but moved them around and tried a old set with no change
pulled both cam and crankshaft position sensor both looked good with nothing on them
both O2s run .8 to .1v and MAFs and knock sensors show ok on obd2 from what i can tell but not 100% sure what i am looking at
pulled all 8 fuel injectors and tested them under test stand and moved them around to see if tapping moves . same with coils .installed new fuel filter and fuel pressure regulator and showing 65 pis with only 2psi drop with wot . system call for 58psi i think
holds 175 to 180 psi compression test on all 8
i can not get mode 6 to come up on my obd2 so i cant see if there is any real time misfires
just tried seafoma and marvel mystery oil
ran it out of fuel and put 93 in it still no change

i really feel is some kind of timing / spark knock and i am not sure how fuel injector 2 could have hurt the system buy staying on but the fuel injector sounds and works as it should and no sounds from around it and
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Old 08-20-2018, 06:53 PM
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What part of the world does this happen in?

Where does this motorhome live normally?

Originally Posted by terry735001 View Post
I have a 2ed gen 8.1L 2004 on a Allison 1000 MH reman motor with about 50Kmiles on it and 30k i have own it
How many miles on the chassis?

Originally Posted by terry735001 View Post
So when under hard load and WOT i get just for a sec a tapping sound from my motor
WOT and what RPM?

WOT and what speed?

WOT at many speeds will trigger a kickdown in the transmission to a lower gear, is the knocking before or after a kickdown?

Originally Posted by terry735001 View Post
only when in drive
So, not in any of the other five available gear selections?

. . . or is this the only selection you've observed the problem in?

Originally Posted by terry735001 View Post
only when at running temp of 195f
So it does NOT have this issue at cooler and at warmer temperatures?

Originally Posted by terry735001 View Post
when driving at 55 to 45 mpr its tapping alot
What RPM?

Originally Posted by terry735001 View Post
Sound is coming from top end only behind the throttle body on left side of motor but is very hard to track down.no sound from lower end
What is the oil pressure when this is happening?

What kind of oil do you use in this engine brand and weight)?

Originally Posted by terry735001 View Post
the only thing i did find wrong was the ground wire to fuel injector 2 was some times touching ground and in doing so would just dump fuel
Probably not related, however: Any idea how long this was happening?

Originally Posted by terry735001 View Post
for the last month i have been trying to find it . tried all kinds of things . stick to ear all over the motor . dropped drive belt to make sure its nothing on the front of motor . but when doing so sound is cut by 40%
Without accessories the difference would be that voltage is lower. This points me toward thinking noisy injector.

Originally Posted by terry735001 View Post
pulled intake looked at all hydraulic lifters and pulled them all the way out to look at rollers on end and pulled valve covers too
pulled oil pan and pulled all caps and manes all looked good and looked at rod pins as good as i could from below and looked for piston slap and every thing looks good
no codes in ECM ...new spark plugs ...coils have a good jump of spark to them
wires tested and look good as there not that old but moved them around and tried a old set with no change
pulled both cam and crankshaft position sensor both looked good with nothing on them
both O2s run .8 to .1v
All good things to do.

Originally Posted by terry735001 View Post
MAFs and knock sensors show ok on obd2 from what i can tell
If you disconnect the MAF does the sympton change?

It could be a knock sensor that shows up fine to OBD2 scanner but isn't detecting knock properly.
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Old 08-20-2018, 08:09 PM
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Originally Posted by CathedralCub View Post
What part of the world does this happen in?

Where does this motorhome live normally?
out of FL but every trip is all most 5000 miles to CA and back


How many miles on the chassis?
this RV was in a fire so its 100% custom from 30K miles ago and has been running grate for the last 5 to 6 years



WOT and what RPM?
just at the start of 800 rpm up to 2000 .

WOT and what speed?
when in drive moving it does not take much wot to make it do it or when trying to hold speed at 45 to 55mpr . going slows does not do it . going light on gas does not do it

WOT at many speeds will trigger a kickdown in the transmission to a lower gear, is the knocking before or after a kickdown?
before and after. i am sure this is the motor . oil looks really good in trans no hard shifting all does it in R



So, not in any of the other five available gear selections?

. . . or is this the only selection you've observed the problem in?
not tested but its a 5 speed and does it in all 5



So it does NOT have this issue at cooler and at warmer temperatures?
yes it seems to be at running temp only and some times on the first 3 WOT to 4 it well not do it but well after the 4th and every time after like clock work



What RPM?




What is the oil pressure when this is happening?
at idle holding 9psi . min i think is 5psi for the 8.1l gose all the way into the 30pis . when driving with load on system it runs 20 psi and still makes the sound . new oil pump 20K miles ago . pulled it and had a good look at it when looking at the manes

What kind of oil do you use in this engine brand and weight)?
5/30 is what it calls for and tryed 10/40 still have sound . it takes 2 gallons of oil and i have had the motor opened up a few times trying to find this



Probably not related, however: Any idea how long this was happening?
the motor is fly by wire 35 feet away in the back of the RV and the sound was so low that i could never hear it .
on a trip to Yellowstone from FL and back . i had a exhaust pipe brake and not from age so i feel with the fuel injector adding to much fuel made every thing run more hotter
i think this was the start of what ever is going on if i had to really guess 1500 miles ago



Without accessories the difference would be that voltage is lower. This points me toward thinking noisy injector.
the RV has a 12vdc converter that keeps the 12v system up . when setting testing its plug in all the time . but this is something i well look into and see



All good things to do.



If you disconnect the MAF does the sympton change?
yes the motor wants to dead but does not . i used MAF cleaner on it

It could be a knock sensor that shows up fine to OBD2 scanner but isn't detecting knock properly.
the obd2 scanner i have is just a low cost cell phone app to help show codes and other small things
not 100% that the MAF nkock or o2 are good . i do know the 02 shows a good wave of .1 to .8 so both look ok

the 8.1l are known for when in higher gear but low RPMs making a diesel like sound when getting on the gas and it does not sheft . it sounds like that

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Old 08-20-2018, 08:11 PM
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sorry added info in quote . well not let me edit
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Old 08-20-2018, 09:21 PM
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Me: WOT at many speeds will trigger a kickdown in the transmission to a lower gear, is the knocking before or after a kickdown?
You: before and after. i am sure this is the motor . oil looks really good in trans no hard shifting all does it in R
For this one I'm not thinking the transmission has any problem at all. I'm thinking of my Buick big blocks that - if you get the timing just a little too advanced - on a hot day they will ping when shifting to the next gear at WOT.

Me: How many miles on the chassis?
You: this RV was in a fire so its 100% custom from 30K miles ago and has been running grate for the last 5 to 6 years
Ah, okay my eyes are opening . . .

Me: Probably not related, however: Any idea how long this was happening?
You: the motor is fly by wire 35 feet away in the back of the RV and the sound was so low that i could never hear it .
on a trip to Yellowstone from FL and back . i had a exhaust pipe brake and not from age so i feel with the fuel injector adding to much fuel made every thing run more hotter
i think this was the start of what ever is going on if i had to really guess 1500 miles ago
I'm a bit out of touch with the RV world, so I never knew of gas-pusher motorhomes until looking it up today. Good to know. Something that sounds like detonation heard through 35' of motorhome is pretty bad.

Exhaust pipe breaking from heat alone is really bad. I'm amazed that this is possible, and surprised the engine survived it.

Is this 2004 8.1L completely factory stock?

If not, what modifications does it have?

Me: Without accessories the difference would be that voltage is lower. This points me toward thinking noisy injector.
You: the RV has a 12vdc converter that keeps the 12v system up . when setting testing its plug in all the time . but this is something i well look into and see
Wait, back up a step: You mentioned that you took off the belt to see if the noise was an accessory. This means that the alternator was not spinning and the engine electrical system would then be at battery voltage and not 13.6-14.2 volts. This would possibly make an injector sound quieter. It'* a long shot. Now that I know the engine is in the back, there'* no way that injector noise is being heard in the driver'* seat unless the injector has a megaphone attached.

Last edited by Mike; 08-29-2018 at 04:00 PM.
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Old 08-20-2018, 09:42 PM
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hope it takes this video .. this is my motor
this is the sound its making
this was before i found the bad wire so its just dumping fuel
still making this sound but not as bad
this is not WOT its doing it at 30% or less

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Old 08-20-2018, 10:21 PM
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that is the wire the got me . as you can see i have been very deep into this thing and all parts are stock in and on the motor BUT the ecm has a HPtunes flash on stock ecm as i had to have it set for 4.7 rear ax
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Old 08-21-2018, 12:26 AM
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Good video!

Is the HPtunes changing anything besides the gear ratio? . . . like timing, spark advance, fuel maps, etc.?

That definitely sounds like detonation to me.

If HPtunes is only changing the gear ratio then I'd replace the knock sensors.

If HPtunes is changing other stuff too then I'd undo that and then I'd replace the knock sensors.
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Old 08-21-2018, 12:08 PM
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Originally Posted by CathedralCub View Post
Good video!

Is the HPtunes changing anything besides the gear ratio? . . . like timing, spark advance, fuel maps, etc.?

That definitely sounds like detonation to me.

If HPtunes is only changing the gear ratio then I'd replace the knock sensors.

If HPtunes is changing other stuff too then I'd undo that and then I'd replace the knock sensors.
sadly yes . when i order the ECM from a guy in NY and that this was a full custom install alot of things had to be change . there is no EGR system and all the stander stuff you do when doing a motor swap like this
but I DID let him install a towing / economy tune . but every thing else is set for stock in the ECM . so no funny over sized cam or any thing like that .. i still have the PDF file i set him on every thing and i all so had him send me the a copy of the files so if the ECM / TCM should ever go bad i would have a way to get back on the road / if any 1 has a copy od hptunes i can send the files to them to look at
but this has been a road block for me as i dont have a copy of HPtunes . and so i have no way of troubleshooting the ecm and my Torque app on my phone says mode 6 not supported so i dont know if this well happen on higher end scanners
i all so had to make the wiring from the ground up for this motor and trans but i used all gm stock parts pins plugs and this is why i did find the bad wire as i was thinking it would have been a err on my part or a pulled pin

i can test and make sure the knock sensor is seeing 5v and why running is pulled down like it should be to 1.5v i think it is
i have dumped so much money into this thing in parts all ready but i can just go into town today and get 2 new knock and map sensors
some times i feel this could be a coil dropping out as well
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Old 08-21-2018, 01:16 PM
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ok i went out there and made sure i seen 5vdc on the wires going in to the knock sensor and i could only see 4vdc but when i pulled the wire out of the driver side sensor the plug was moving really good inside the sensor so yes i think its bad
i have 2 on order and well be in latter today so tonight i well come on and say the out come
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