LT1Birds truck sounds bad need opinions

[68skylark455]

his truck seems to be making a slight knocking sound under light accell like an injector. the injectors are fairly new under warranty replacement and the data looked normal. he put in some 2 cycle no ash and it got quieter but still there. he said today it is getting worse. I attached 2 logs while driving and it does it in 3rd and 4th around 1700rpms and goes away in 5th?

 

[stacks04]

ever since my head gaskets i have had a terrible knock. i have determined it to be fueling related because while on the highway if i let off and the decel fuel cutoff turns on the noise goes away. as soon as i tap the throttle it returns. i have tried cutting each injector trying to find which one it is to no avail. the balance rates are all good. mine is around the same rpm also. if i didnt know better one would think and internal knock.

 

[68skylark455]

there is another thread in the tuning and logging section with an lly doing the same thing also-he describes it as pinging/knocking. Jimmy's LB7 is stock. He pulled out the hypertech it had in it and returned it to stock except for tire size. no other mods except mbrp exhaust. It sounds like an injector on a dodge that has gone bad but it runs fine.

 

[LT1BRD]

thanks for posting this Larry.

it used to do it only when the truck was warmed up, but this morning on my way to work, i noticed it before the truck was fully warmed up. i tried listening with a stethoscope and the fuel line going to #6 (assuming the numbering is the same as a small block chevy) is kinda noiser/pinging than the others. i don't know if that's the problem or not, just something i noticed.

Larry Jewell advised me to look for exhaust leaks, just to rule out the possibility. i haven't found any yet, but i haven't really gotten my hands dirty looking either. the MBRP is fairly new, but i remember hearing the noise slightly prior to installing the exhaust. nothing to the effect of what i'm hearing now.

it's pretty loud under load. inside the cab, you can't hear it at all if i just bring up the RPM's in park. crusing around 45-50 mph and accelerating, it sounds like a midget jackhammering under my hood. all balance rates are in check. all less than 2.00 and 5 of them less than 1.00 +/-

 

[stacks04]

there is another thread in the tuning and logging section with an lly doing the same thing also-he describes it as pinging/knocking. Jimmy's LB7 is stock. He pulled out the hypertech it had in it and returned it to stock except for tire size. no other mods except mbrp exhaust. It sounds like an injector on a dodge that has gone bad but it runs fine.

it is the same noise, just different injectors. his post above mine is exact. mine does it with stock tuning or any tuning. its freekin annoying.

 

[LT1BRD]

Larry,
i remember you saying the ECT was incorrect. i'm going to change it out anyway, but what should the voltage going into this sensor be? i know with my LT1, it's supposed to be 5v (key on, engine off). when my LT1 was running rich, it was because i was only getting 4.x volts at it's ECT sensor. i traced it to the ECM and got the same voltage there too. ended up having to get a new ECM and that fixed the rich condition.

i'm not saying it's the same thing here, but is it possible that a cooler temp being read would cause too much injection timing? it does it worse when the truck is warm...don't know if means anything.

is there only one coolant temp sensor? the computer reads one, but what does the gauge read? the computer?

 

[LT1BRD]

ok, i got 1.26V at the wires going to the ECT. not sure what it should be, but i believe the sensor is reading incorrectly.

the temp on the truck was around 175 before and after checking the resistance the sensor was reading. the resistance was 510 ohms...which should be around 150's or so.

i'm going to change out the sensor this evening. not saying it should fix the problem, but won't hurt anyway.

 

[68skylark455]

Every gm sensor I have ever tested had a 5v reference. Not sure on theses dmaxs but I would guess its the same.

 

[Mike]

ok, i got 1.26V at the wires going to the ECT. not sure what it should be, but i believe the sensor is reading incorrectly.

the temp on the truck was around 175 before and after checking the resistance the sensor was reading. the resistance was 510 ohms...which should be around 150's or so.

i'm going to change out the sensor this evening. not saying it should fix the problem, but won't hurt anyway.

Just curious where you got the resistance vs. temperature comparison? If this is the two wire sensor you are referring to, you would not see 5 volts.

See attached.

Also curious if you've ruled out a pilot injection event noise?

 

[LT1BRD]

yes, that's the sensor. i changed it last night. didn't take care of the noise

i haven't ruled anything out at this point.

 

[LT1BRD]

nobody? it gets really bad when the temp goes up. i turned to A/C on today and the temp got up to 195-200 range...the "clacking" is really noisy at any speed when the temp is up like that.

 

[S Phinney]

Injectors can be noisy like that without showing measurable diagnostic data. Some are definitely louder than others and higher temps seem to make them more noticeable.

 

[LT1BRD]

tonight, i took off the oil cap with the engine running. there's some light smoke coming out and a really loud whistle.

 

[wilsonck]

What was the outcome of your noisy injectors?