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Replying to Thread:

3406 Rough Idle


Created On Tuesday 24, January, 2006 8:44 AM by DieselMech

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DieselMech
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Note Tuesday January 24, 2006 08:44 View thread in raw text format
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I recently did an out of frame overhaul on a Cat 3406 model A direct injection engine.

The engine runs great with plenty of power when running down the road but when it idles it will start to develop a slight "hicoup" where the rpms will jump up to 850 or so. This will continue for a while and gradually get worse to the point that the engine will start to miss, almost sounding like pre-ignition or an engine brake at idle.

When the engine is cold it idles just fine.... It has to be driven a few miles before this issue will develop..

When the engine was overhauled I had the injection pump rebuilt and used new injectors and fuel transfer pump.

So far I have tried re-setting the pump timing, checking the valve lash, disconnecting the Jake brake wires, replacing the fuel filter, replacing the suction line, trying different fuel, checking fuel pressure and bypassing the entire filterhead...

When you crack injection lines at idle when it's cold you can distinctly hear a difference in the rpms.

When you crack an injection line when it is warm (and missing) there doesn't seem to be much difference in rpm...

If it's idling warm (and missing) and you hit the thottle it accelerates immediately and runs fine until you allow it to return to idle again...

Any help would be GREATLY appreciated as I'm at my witt's end.......


Doug
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catmech
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Note Tuesday January 24, 2006 18:20 View thread in raw text format
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catmech
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Note Tuesday January 24, 2006 18:32 View thread in raw text format
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Did they replace the piston and vavle assembly in the governor. The guide that it rides in can wear on both inside and out. That valve and piston with cold oil that is thick will work differently than when warm. also look at the advance weights and springs, they can break and the springs get worn on the sides. This is an engine that has a long aluminum accessory drive tube between front plate and injection pump, and the transfer pump mounts under it.
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DieselMech
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Note Wednesday January 25, 2006 04:50 View thread in raw text format
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<< Did they replace the piston and vavle assembly in the governor. The guide that it rides in can wear on both inside and out. That valve and piston with cold oil that is thick will work differently than when warm. also look at the advance weights and springs, they can break and the springs get worn on the sides. This is an engine that has a long aluminum accessory drive tube between front plate and injection pump, and the transfer pump mounts under it. >>



I'm not sure if the piston and valve assembly has been replaced...I was charged $1500.00 for rebuilding the injection pump so I hope everything was done correctly, but I have another injection pump laying here that I just took off an engine that I'm going to try today..

I went through the advance unit and replaced the springs during the rebuild.

When it revs up a little when the problem first starts it isn't smooth at all and knocks a little ...Almost like spraying ether in a running engine, so yesterday I pulled the injectors and found that a few of them were loose on the holders which doesn't make much sense...They're supposed to only be hand tight on the holders and there's a hold down on top that forces the injector against the inside of the adapter so how could they come loose???

I drove it for about 20 miles and it seemed to be running fine...even at idle...I shut it off for about a half hour then went to go for another ride and it started idling bad again.


Thank you very much for your input.......I'll post my findings hopefully later today...


Doug

Edited: Wednesday January 25, 2006 at 06:05 by DieselMech
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catmech
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Note Wednesday January 25, 2006 20:24 View thread in raw text format
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You have a capsule type nozzle that has a green flat seal above it on the adapter. you should change that seal if you did not already, it keeps fuel from leaking into the oil. the capsule type nozzle spins on with a flick action, or snug. does yours have four small twelve point bolts, with two clamps and a spacer or one big nut?
Also the injection pump cam has a c spring from cam to the gear that it drives. if the dowels that it rides against are worn the engine can hunt.
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DieselMech
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Note Thursday January 26, 2006 06:05 View thread in raw text format
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<< You have a capsule type nozzle that has a green flat seal above it on the adapter. you should change that seal if you did not already, it keeps fuel from leaking into the oil. the capsule type nozzle spins on with a flick action, or snug. does yours have four small twelve point bolts, with two clamps and a spacer or one big nut?
Also the injection pump cam has a c spring from cam to the gear that it drives. if the dowels that it rides against are worn the engine can hunt.
>>



I did replace the seals on the holders.......My adapters have the four twelve point bolts that hold the injectors in... When I took the injectors out again I called my local Cat dealer to get the torque spec for the bolts since my book doesn't show this setup, and they had a hard time figuring out what I had... Since they're only 5/16" bolts I torqued them to 25 ft lbs...

I took the truck for another hard run yesterday and it ran EXCELLENT even at idle...I shut it off and re-started it after about a half hour and it would only misfire every once in a while and only on ONE cylinder. Once it warmed all the way back up it stopped misfiring, so I think that the injectors leaking may have been the issue. I still have no idea why they wouldn't seat properly in the adapters the first time, I didn't do anything different, just pulled them out, tightened the capsules again, and re-installed them but it does seem to run better so we're going to put some miles on it and see what happens............

Again, Thank you very much for your helpsmile


Doug
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catmech
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Note Thursday January 26, 2006 20:18 View thread in raw text format
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they torque at 22-23 lb. ft. but 25 is ok but wouldn't go any higher. torque all four bolts then torque them again, and again tell they stop moving. I have found that I can go around about 4 times, before they stop moving. the nozzle will be loose when you pull them out because of the thread to nut fit inside the nozzle, but only a little loose. when tighened back down after retighting them to the adapter, like you did they should do fine. biggest problem is people over tightening the nozzle and distrorting them, at the top, then they are no good.
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DieselMech
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Note Thursday April 27, 2006 07:18 View thread in raw text format
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Well, the problem came back againsad.....Even worse than before.......At cold start up it runs good....Going down the road it runs good......At hot idle it misses and runs terrible......


I pulled the injectors out AGAIN and also removed the adaptors from the head thinking one or more may be cracked and found nothing wrong... I put it all back together and the problem was still there....

I took off the newly "REBUILT" injection pump and replaced it with one that probably has over a million miles on it and it runs PERFECT!!!!!!!!!!


Doug

Edited: Thursday April 27, 2006 at 07:20 by DieselMech
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catmech
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Note Sunday May 14, 2006 18:16 View thread in raw text format
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the rebuilt pump could have a check valve on top of the injection pump that is bad, or not seating correctly. these check valves hold fuel in the line going to the nozzle, at low idle hot fuel is thinner and one may be letting the pressure drop off in that line. Is the pump still under warranty or its not been on longer take it back and tell the dealer your problem and how you solved it. Should fix it for you or at lest look at it, does not need to be taken all the way apart just the bonnets and barrel and plunger grps. They can see the check valves then. might even flow check the injection pump on the bench to see flow.
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hoss805
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Note Thursday June 01, 2006 00:04 View thread in raw text format
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hey buddy
i picked up a 82 Pete a few weeks ago and ran into the same problem
i first test drove it a few miles and it ran good ,
well before picking it up i warmed it up for about 20 minutes and when taking it it home i noticed the same exact problem
at idle it sounds and runs terrible but only after being on or being driven a few minutes
the mechanic checked it out and first said it was timing so he set the timing
the he ran the rack and told me it was all screwed up and not adjusted right.
now he tells me it can be a lifter and to run it a little like that and see if it gets better.
now i find this thread and it brightens up my day knowing i can atleast get an idea what s wrong .
can any proffesional here give me some advice on this and see what i can do to have a mechanic fix the problem
and Doug did the problem ever come back

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catmech
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Note Thursday June 01, 2006 18:49 View thread in raw text format
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You are saying it runs badly at low idle? look on your engine and get the serial, and arrangment number. It should be on the left side of engine, or on the valve cover. number sould be like 92u********.

Edited: Thursday June 01, 2006 at 18:49 by catmech
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hoss805
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Note Thursday June 01, 2006 19:20 View thread in raw text format
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its doing exactly what
DieselMech post says
at start up it sounds good and runs good
but about 10-15 minutes after start up it just has a bad miss
the miss is at lower rpm
at higher gear, rpm it runs good

i'll post serial number in a few
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hoss805
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Note Saturday June 03, 2006 22:28 View thread in raw text format
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the serial number is 92u53309
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catmech
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Note Thursday June 08, 2006 17:49 View thread in raw text format
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looks like you have a direct injection, not a B model. has the late injection pump for that serise. could be the bonnets to injection barrels is leaking, so your pressure is dropping off in the line to the cylinders at low idle it may be more noticable than at higher rpms. also what is the fuel pressure at idle.
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hoss805
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Note Friday August 11, 2006 12:16 View thread in raw text format
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well im still having problems
so far
replaced the head
took off the fuel injection pump and had it bench tested and they couldn't get it to fail
so mechanic replaced some worn out springs and seals put it back in and im still having the same problem

when its cold it sounds fine and runs fine.
seams the miss starts once the temp goes above 140 dergrees
and it sounds like cram
starts backfiring


can it be the rings failing
if it were what symptoms would we be getting
would it smoke

i really need some help,advice
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catmech
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Note Friday August 11, 2006 17:55 View thread in raw text format
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when you had the injection pump off did you look at the gear assembly that does the advance. the four bolts that hold it tight for timing take the bolts out, pull that gear assembly off, take the half circle wire out, pull the gear assembly apart, look at the slids and guides. see if they are broken. look at the springs, see if they are worn on the sides. I would replace those springs anyway while I was in there. re-time the injection pump. see if that helps.
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hoss805
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Note Saturday August 12, 2006 23:53 View thread in raw text format
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yes we replaced worn out parts and all springs
spent about $400 in parts for the injection pump
plus $318 for bench test they couldn't get it to fail
do you think it can be the injection pump
they did put it on the bench
but im not sure if they can get the oil hot enough on the bench machine to see if the pump fails at higher temperature




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catmech
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Note Sunday August 13, 2006 08:19 View thread in raw text format
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you say that you replace the head. did you get a bare head and tranfer the parts, or get and exchange with all the parts already installed. have seen where a head had the wrong adapters (chambers) that the nozzle assembly goes in. there is a vee chamber and a inline chamber. if the wrong one is in the head it changes were the tip deepth of the nozzle is in the cylinder. changing were the nozzle spray hits the piston. pull the valve cover and look at the top of the adapter, that is were it's marked.
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hoss805
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Note Sunday August 20, 2006 20:54 View thread in raw text format
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hoss805
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Note Sunday August 20, 2006 21:04 View thread in raw text format
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well catmech
thanks for your help
once i found this formum and read the first thread about the pump i knew it would be my FI pump
i guess my pump must of had the same problem as DieselMech's pump
i spent over 400 in parts and 300 for a bench test and they told me it was good
i found an olddddd pump locally for $90.00 and after more than $4000.00 of parts and labor, we finaly fixed it
all we did was switch it over and the problem is gone

i wish they would of listened to me when i told them it might be the pump
they though i was crazy and ignored me
the bad thing about it was that the person i bought the truck off of had a friend back east with a pump and was going to give it to him for free
he should of taken it when it was available
few months later he could'nt find that guy and were out of luck.
well its fixed

thanks
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