Truck idleing crappy

[White Elephant]

Hey yall, i got a problem thats really got me stumped. I got a 91 idi i swapped in my truck and i cant get it to idle down low without the knocking sound that makes it sound like it aint gettin enough fuel. It runs fine at higher rpm just knocks when idleing. Ive checked all the lines and stuff for leaks, replaced the fuel filter, the housing for the filter (cause i thought it looked wet), i just put in some injectors earlier today and it still does the same thing. All the injectors are firing cause i loosened them all while it was runnin and listened to em. And when i loosened them the knock might sometimes go away for a second or too but come right back. i put a fuel can right underneith the mechanical fuel pump and sucked fuel from there and elimated the lines runnin to the tank, so they cant be bad. And i did the same thing with the return lines. When i bought the motor the idle was turned up a little and i turned it down and it started doin the knocking. The ip pump on it is a reman pump but it was on there when i bought the engine and i assumed it was good. I did turn it up almost 2 flats. I dont know if that would affect it any tho. But heres the thing... i took the ip pump off the engine and the water pump and everything because it was way advanced when i bought it to make it run. So i took everthin off and made sure all the timing gears were lined up and i put it back together and set it where it was supposed to be and it wouldnt run. So i advanced it back to where it was before and it ran great. It idled and everything for a week or so. Then one day i drove it to the next town over and it did the knocking thing again. ( it started doin it when goin down a hill in neutral at idle) and i saw an o ring on the return lines was leakin. so i replaced it and now i got the knocking sound again. So i figured its either got to be taking air in somewheres between the mechanical fuel pump to the injectors( without leakin fuel) or its gotta be a bad ip pump. It did have a lot of junk in the filter when i changed it but i wanted to see what yall say before i start pricing ip pumps. cause maybe theres somethin i overlooked. thanks for any help yall.

 

[johnnyb1]

Could be an injector not popping at low rpm. I'm sure other guys can be specific on testing them. Just a thought.

 

[White Elephant]

i just got a set of injects and put em in there yesterday and it didnt change nuthin. I think im gettin air in the lines but it aint leakin fuel anywheres. can that happen?

 

[johnnyb1]

I'm usually on here early morning before work so I'm not fully awake ALOT. !! Sorry. I just saw the "new injectors" in your post. Don't know if it will suck air in the fuel system since it's under pressure BUT it can suck air in the intake manifold. Could be bad intake gasket,cracked fitting,ect. Do you have access to a vacuum gauge? I would do a vacuum test on it. Not sure what acceptable vacuum should be but I know someone here would know. {AGNEM,ICANFIXALL,OLDBULL8,ect.} If low,erratic vacuum you have a leak somewhere. Let us know.

 

[DeepRoots]

this isn't a gas engine. No throttle plates, no vacuum. It's irrelevant anyway, with an NA diesel

On another note, brand new injectors can pop weird too. Insist on them being tested. Try shorting out each injector to see if that is the cause... if so, swap that injector with another cylinder, if it follows, replace injector. You say you tested that, so there is that....

also get your timing set properly, you might be way off. I think you are dangerously advanced, but it's hard to tell from where I'm sitting.

 

[White Elephant]

yea i know its way advanced... or thats what is says by lookin at the marks anyways. but thats the only way it runs. i would get it timed but i aint found no place to do it or anythin. but heres just a side note..... and another thought. um... im pretty sure the dampener springs are bad in the clutch ( forgot to check em when i installed everythin) but you can hear the rattle goin down the road at certain times. ya know. and the more i listen to the "knock" sound it sounds like it coming from that area.. at first i thought it was the starter hangin up first time i started it but it aint that. lol But.. could it be the engine at a lower rpm be spinnin and making all that stuff rattle in the tranny ( in neutral) because the springs might be bad and make it sound like the way it sounds? or am i just thinkin crazy

 

[Fordsandguns]

Could be the dmf. They have been known to go bad.

 

[White Elephant]

I really dont know much about them... but i mean the truck drives fine and everythin( and tows whatever i got behind it no problem) . I mean would it even go anywheres if that was bad?

 

[White Elephant]

Are there springs in the dual mass that could be rattleing... i didnt even know there was such a thing as a dmf until i seen that comment. Im still learnin bout this stuff. lol

 

[Fordsandguns]

Yes there are springs in the dmf. (dual mass flywheel) The work like the springs in the clutch to dampen the vibration spikes from ignition. When a dmf starts going bad they rattle.
Mine rattles some. The springs can break and get spit out in pieces.
They make a aftermarket smf for these trucks too.
Or you can do the Lucky mod on yours by taking it apart and re-drilling it and bolting back together using quality grade 8 bolts. There have been a few members do this.
It gets it's name from the member that first did it.

 

[White Elephant]

Hmm.. that lucky mod thing sounds pretty cool. Might try it if i get some time on my hands. lol As long as it holds up and works and i dont get it out of balance i"ll be happy. haha

 

[Fordsandguns]

You said that your clutch has the springs in it right? You need them in the clutch if you turn the dmf into a smf.
There is a member that welded his, but I don't remember what he said about it afterward.
My father in law said they welded one also and didn't have any issues. But I would caution about welding it without checking the balance. I thing bolting it shouldn't be a problem with balance but welding it might. I don't want to recommend something that might cause damage to your truck.

 

[White Elephant]

yea i looked furthur into it last night and found out about all that bolting and weldin it. and i think i could do it. but im not too sure i wanna take the chance cause bein my luck it would be outa balance when i get done. so i think imma save up and get a single flywheel and a decent clutch to go wit it. just to be sure its done right. ya know lol