89 IDI NA, Clatter on occasion at start or coming off throttle?

Oldfrogdiving

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OK I know this is probably fuel related but here goes and I did search for this. I have been OCONUS for about 3 months (none use of any vehicles). Started the 89 IDI really no issue starting (2 GP cycles) but it had a "clatter", I bipped the throttle it settled down and chugged contentedly at initial higher idle to idle down (op temp), It has done this off n on since i have owned it more off then on and especially if your trying to demonstrate to some one the noise. Since driving the past few days it seems to be more consistent, usually at start, or coming off throttle downshifting for a light. Bipp the throttle and it goes away. Normal Acceleration no issues she pulls pretty good for an IDI, It has about 400 miles on an oil and fuel filter change. Runs and idles good except on the occasional "clatter" episode (69K miles) on original motor. Fuel filter/pump are stock, no leaks (im pretty sure its not air cuz she fires right up) am I correct in thinking the only fuel pump is the one mounted forward on engine? no pumps in fuel tanks?
 

ih8minimumwage

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Are we talking "clatter" like the RPMs jump around (like air intrusion/low fuel), or "clatter" like the cold idle is on at startup?
 

mblaney

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Mine does that too, usually on the highway when easing off the throttle at around 1200 rpm. Sounds / feels like a heavy resonance or harmonic coming from the top of the engine or behind the dash. When it does it (seems only after worked hard) I can increase and back off the throttle and have it repeat.

If I remember correctly I had this issue before the turbo install, and it still exists today (post turbo install). The noise reminds me of a muffle heat shield that is loose but my exhaust has been totally changed and customized with no difference.

E4OD if that matters.
 

CBRF3

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your issue is likely injector pop pressure related and a worn injection pump if the pop pressures fluctuate you will get iradic internal timing adjustment inside the injection pump also if your input pressures are to low or to high will throw this off also and around 2000rpm's is where the injection pump changes the timing internally but if you got odd injector pop pressures on your injectors say 3 are 1650psi and 1 is 1450psi then another 1750psi this will make you pump pulse timings uneven and will make the pump act odd and could hold it in and out of a pump advance or retard state coming down on RPM or when accelerating and usually pop pressure makes a huge difference on engine clatter on initial fire up.

the reason pop pressure is so important is higher pop pressure increases velocity of the fuel spray in the pre cup in the head which makes the fuel burn even a lower pop pressure will delay it making that cylinder iradic on how it burns the fuel and how evenly it starts the flame coming out of the pre cup into the ricardo bowl in the piston will determine how evenly it ignites if it only partially ignites this can cause piston to slap and rattle against cylinder wall due to incomplete burn.
 
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