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My 93 having a mysterious tapping or knocking under acceleration that comes and goes

Wonder if I should just try retarding it a little and see what happens. iirc advancing is moving the top of the IP towards the passenger fender. this is what I did previously as you can see my blue mark is slightly off (IP turned counter clockwise) correct me if I have it backwards.
 
dbrannon79 said:
since driving the 95 around yesterday and today, I now realize just how much louder the clatter is from the 93 with the newly rebuilt injectors. figured I would look at timing to see if it needs to be adjusted.

took a gander at the IP timing mark and looked for the center timing mark on the timing cover. this engine has a timing cover for a newer block meant for a DS4. looking at this pic, what would be the center mark on the cover? I can see the center (base time) mark on the IP.

View attachment 93475
View attachment 93474

on the DS4 timing cover you can see that tiny "V" shape mark just to the right of the IP mark and my blue paint mark I made for my reference last time I moved the IP. also that weird looking dimple in front of the bolt sticking out. does anyone know what the center base timing mark is on this timing cover? @Will L. @ak diesel driver
Click to expand...
That little Vee mark looks like the left side of it is the straight line for a timing mark.
 
In a little while I can go take a measurement/ picture for you on mine.
There is a specific tool made to add the timing mark to new covers. But it’s basically a jig to hold a chisel part in the right place.

The V mark is something someone did as a diy- that isn’t the factory mark for timing a db ip.

Retarding it is the wrong way.
As pop pressure goes up - that retards it.
As the timing chain stretches that retards it. We learned 30,000 mile intervals were about the right time to do it. Iirc you have near 300,000 miles on it then the new pop pressure is above stock so you’re running about 10X retarded. (thats not a measurement just a joke). but seriously saying you need advanced compared to stock.

I’ll get you the pics but idk if I can before heading to church today.
 
I did mess with it some and moved the IP back to where my blue paint line lined up with each other. when I was messing with it I first tried to push in the advance piston on the lever. it went to missing and belching whitish grey smoke if I tried to move the IP to the passenger side more (advancing it) pulling it back to the drivers side (retarding) past my blue mark, it just quieted down on the clatter when I pushed on the lever.

I did that a couple of times till I finally landed on exactly where my marks lined up. pushing the lever it still pushed some white/grey smoke and stumbled some, but not as much. during the whole time me advancing it or retarding it the clatter from the injectors at idle never changed.

when I get the chance I will go back and look at where the top stud is and where the mark is on the IP.

also I did notice that the advance solenoid was connected. I thought I had left that disconnected. while it was idling, I manual applied power to it to see if and what happens. nothing!! only thing I could see was the fuel pressure gauge went down maybe 1psi when I applied power to it. no noise change or anything.

I know this IP has been messed with by the PO. both the fuel screw has been turned up as well as the pressure screw inside the inlet that changes the transfer pressure. on a hair brained idea, I grabbed my duckbill plyers and started pinching the clear return hose on the IP. not completely pinching it off but slowly squeezing it more and more. as I started squeezing it the clatter started to diminish more and more. at one point it started running smoother and got about as quiet as my 95, squeezed it more and it started to get less RPM and I know I would kill the engine if I went further.

I also tried momentarily pinching the inlet hose before the gauge to drop the fuel pressure some, it dropped to around 4-5psi but didn't effect anything when idling.

my fuel pressure stays at 9-10 psi unless I goose the throttle then it goes to about 5psi. gauge is mounted on the hose coming out of the FFM into the IP.

just a theory there. since the screw that lives inside the IP inlet has been messed with, I feel like the transfer case pressure is too high and when I restricted the return the housing pressure went up which caused it to change timing and run better. I feel like the advance solenoid is barely doing anything because of that adjustment has been moved.

I don't want to go messing with that adjustment and really screw it up, but also don't know if what I did and saw says anything.
 
In all the searching I did previously on what all had been done to this truck. I think I had found that the PO had given that transfer pump adjustment about a 1/4 turn, I also found a post where he wished he had left that adjustment alone! IDK if he tried to put it back.

Maybe @Rockabillyrat or someone that knows these DB2's can jump in here and tell us how critical that adjustment is for the operation. and if I were to attempt to back it off 1/4 turn lowering the transfer pressure, what would happen, also maybe even how much 1/4 turn would effect the pressure. Even if how I am describing what it's doing by restricting the return flow or how it does nothing other than a slight decrease in the inlet pressure when actuating the advance solenoid might point to the transfer pump out of adjustment.


I have another DB2 on that 6.2 engine. the engine did run off of it, but kept loping or had a slight surge at idle while puffing blackish smoke out of the exhaust manifolds while on the stand. this is why I don't trust it, idk if that is a sign it's on it's way out. engine revved up decent with that IP though and I had to screw in the idle screw quite a bit for it to idle and not just fire up and immediately die in the beginning when I was trying to get it to run on the stand.

I'd be willing to trade someone it for a known good used DB2 or even trade with the one that's on the 93 now needing to be re-adjusted. I'm sure they'd want some extra doe it would basically be a good core.
 
Thinking about it more, it might not even have anything to do with the transfer pump pressure and everything to do with the advance piston. I know it's happened in the past randomly getting a load of clatter, but it hasn't done that in quite a while. not sure if that is due to me using the stanadyne lube formula in the fuel.

but if it's the advance piston sticking where I pinched off the return forcing it back, wouldn't the lever on the side of the IP also not work properly?
 
dbrannon79 said:
it just quieted down on the clatter when I pushed on the lever
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The RETARD lever on the side of the pump driven off the throttle shaft is working. This means the advance system is operable on the pump. I don't believe it cares what the housing pressure is to work. I vaguely recall it's all mechanical to force the piston back or equalizes the pressure across the piston by a valve so the advance/retard spring moves it.

dbrannon79 said:
only thing I could see was the fuel pressure gauge went down maybe 1psi when I applied power to it. no noise change or anything
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The high idle solenoid appears bad. The internal to the IP cold advance solenoid appears working by the fuel pressure change. Engine off listen for a click when you apply 12V to it on the IP connector. Watch fuel flow in the clear line engine running: it's an insane amount at operating temp solenoid off. Cold advance solenoid(s) on the fuel flow slows way down. Last you should verify the switch for this in the t stat crossover is working. Should have 12V at the solenoids when the engine is cold. Offhand it's 600 RPM hot and 700 RPM cold, but check the sticker under the hood to verify. I sort of recall it kicks off at 140F.

Ar 45 MPH hold a steady throttle operating temp on engine. You should hear the IDI clatter. Roll some fuel into it and the clatter should quiet down as the precups get some heat in them. This is where the timing is correct done by ear. Now if you can't find this then try undoing the transfer pump 1/4 turn.

It's possible the transfer pressure change has pinned the advance piston at max advance.
 
WarWagon said:
The high idle solenoid appears bad. The internal to the IP cold advance solenoid appears working by the fuel pressure change. Engine off listen for a click when you apply 12V to it on the IP connector. Watch fuel flow in the clear line engine running: it's an insane amount at operating temp solenoid off. Cold advance solenoid(s) on the fuel flow slows way down. Last you should verify the switch for this in the t stat crossover is working. Should have 12V at the solenoids when the engine is cold. Offhand it's 600 RPM hot and 700 RPM cold, but check the sticker under the hood to verify. I sort of recall it kicks off at 140F.
Click to expand...

The high idle solenoid does work, but you have to tap the pedal for it to keep the throttle held up. The cold advance solenoid does click with the engine off. I cannot tell on the fuel flow with the clear hose when running since there is absolutely no air bubbles, so I can't see a change in the fuel flow. the switch on the crossover does work. I have it connected and when it's cool in the morning, the high idle will kick in for a few minutes and shut off. RPM is at 650 idle and bumps up to 750 with the high idle on. though I do have to tap the pedal for it to hold at the high idle. the solenoid won't bump up the RPM on it's own.

WarWagon said:
Ar 45 MPH hold a steady throttle operating temp on engine. You should hear the IDI clatter. Roll some fuel into it and the clatter should quiet down as the precups get some heat in them. This is where the timing is correct done by ear. Now if you can't find this then try undoing the transfer pump 1/4 turn.
Click to expand...

This does work at virtually any speed. I can tell when the engine goes under a slight load it quiets down and when I'm cruising or let off the pedal, clatter is more pronounced.

WarWagon said:
It's possible the transfer pressure change has pinned the advance piston at max advance.
Click to expand...
I had suspected this before when randomly while accelerating the engine would begin clattering very loudly from a stop. as well as on occasion would go into a loud clatter when cruising in town. a couple of times it was loud enough that my wife looked at me from the passenger seat asking what was that!! I would just let off the pedal and it would go away. it has not done this for quite a while, but again was random.

what harm would it do to attempt to undo and back off on the transfer pump screw 1/4 turn? since I am unable to see pressures.

I think I have the timing set pretty close now after retarding it slightly, IDK, but was going off from how it acted when I pushed the retard lever in, as it is now, when I press it in it has a slight stumble to the idle and will throw some light grey or white smoke. it just struck me as odd when I used my pliers to slowly restrict the return from the IP and as soon as I began pinching the hose, the clatter from the injectors got quieter and sounded more "normal", still clattered, but no near as loud. I'm guessing I had it pinched about half way. by doing this I was guessing I was forcing the advance piston back where it should be. iirc it just floats in the bore and is moved by fuel pressure on one side or the other.
 
dbrannon79 said:
the solenoid won't bump up the RPM on it's own.
Click to expand...

I believe that’s correct. Tap the throttle once to kick the idle up. I recall starting instructions on the sun visor backside on my 1993.

It’s a 1/4 turn stab in the dark. Expensive to have a shop calibrate it. IDK if the pressure gauge and adaptor you need to DIY is available.
 
Iirc I had seen one on eBay once before but I didn’t remember what it was called. Rockbillyrat showed pic where it goes and what it looks like I recall it’s should be somewhere around 200psi but don’t quote me on that. Maybe I should look around for one and research further on that

It seems to running decently now and the tapping noise it’s making is still there coming from a lifter or even the cam bearings. This engine has so much wear on the valve train parts it’s not funny!

Hopefully in the coming weeks I can focus on ether fixing up this old 6.2 to go in. If it will last a while it’ll give me time to figure out a plan for a better engine, weather that will be using the one in the 95 or finding another used one still in decent shape.
 
@WarWagon I found what was done to this IP. Check this out What would you recommend?

DB2: Increase Case Pressure-Turn Up Fuel: Questions...........

i have done both per these instructions: "Transfer pump: This increases case pressure. Looking at intake of pump inside inlet fitting, there's a 5/32 allen screw, turn clockwise looking at it, increasing case pressure and timing advance across board. Be careful, too much and it will blow seals...
www.thetruckstop.us
 
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