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Thread Title:

3406 Rough Idle

Created On Tuesday January 24, 2006 08:44

DieselMech

Posts: 6
Joined: Jan 2006

Tuesday January 24, 2006 08:44

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

Posts: 326
Joined: Nov 2005

Tuesday January 24, 2006 18:20

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catmech

Posts: 326
Joined: Nov 2005

Tuesday January 24, 2006 18:32

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

Posts: 6
Joined: Jan 2006

Wednesday January 25, 2006 04:50

<< 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

Posts: 326
Joined: Nov 2005

Wednesday January 25, 2006 20:24

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

Posts: 6
Joined: Jan 2006

Thursday January 26, 2006 06:05

<< 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 help

Doug

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catmech

Posts: 326
Joined: Nov 2005

Thursday January 26, 2006 20:18

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

Posts: 6
Joined: Jan 2006

Thursday April 27, 2006 07:18

Well, the problem came back again

.....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

Posts: 326
Joined: Nov 2005

Sunday May 14, 2006 18:16

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

Posts: 8
Joined: May 2006

Thursday June 01, 2006 00:04

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

Posts: 326
Joined: Nov 2005

Thursday June 01, 2006 18:49
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

Posts: 8
Joined: May 2006

Thursday June 01, 2006 19:20
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

Posts: 8
Joined: May 2006

Saturday June 03, 2006 22:28
the serial number is 92u53309

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catmech

Posts: 326
Joined: Nov 2005

Thursday June 08, 2006 17:49
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

Posts: 8
Joined: May 2006

Friday August 11, 2006 12:16

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

Posts: 326
Joined: Nov 2005

Friday August 11, 2006 17:55

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

Posts: 8
Joined: May 2006

Saturday August 12, 2006 23:53
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

Posts: 326
Joined: Nov 2005

Sunday August 13, 2006 08:19

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

Posts: 8
Joined: May 2006

Sunday August 20, 2006 20:54

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hoss805

Posts: 8
Joined: May 2006

Sunday August 20, 2006 21:04

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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catmech

Posts: 326
Joined: Nov 2005

Sunday August 20, 2006 21:15
glad you got it fixed! Do me a favor and look at the camshaft end of your old fuel system see if has the + looking plug in it. if it does take it out and look at it. it should be a screen assembly. see if the end is broke off. let me know please.

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hoss805

Posts: 8
Joined: May 2006

Sunday August 20, 2006 21:23
sure will give me a couple of days and i will let you know

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DieselMech

Posts: 6
Joined: Jan 2006

Friday August 25, 2006 04:24
<< Doug did the problem ever come back >> No, it's still running GREAT!!! The shop that "rebuilt" my pump still has not done a thing with it..... Pretty soon I'm going to go get my $1500.00 BACK from them. Doug

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fs1990

Posts: 1
Joined: Jun 2012

Saturday June 23, 2012 20:47

Man ive been having the exact same problem with my motor.starts fine get it warm n it misses n stutters like its misfiring n gonna die.anyone know exactly how to fix this or where I can get another pump.im reluctant to keep dumpin thousands to mechanics n its not fixed mines now low on power after pple messin with my pump.its literally put me under.i parked the truck.now im tryn to get started can anyone help please email me frnknvic@gmail

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CATMAD

Posts: 5
Joined: Aug 2015

Friday August 07, 2015 02:51
I know this is an old thread but, i have the exact same problem with my 3406A, I was wondering if anybody found out what the problem in the Fuel Injection pump was? Any help would be greatly appreciated Regards Chris

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catmech

Posts: 326
Joined: Nov 2005

Sunday August 09, 2015 16:01

ALL the above can be the problems for the injection pump, drive gear, nozzles, fuel transfer pump. Again serial numbers of engine and arrangement numbers make a big difference when setting up injection pumps and putting the right parts in them. I have seen a serial number one different have completely different parts and cam in them, that is why serial numbers and arrangement numbers a so critical!

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CATMAD

Posts: 5
Joined: Aug 2015

Wednesday August 26, 2015 14:28

Ok thanks, for your reply Catmech, i guess stripping the pump is my only option ( if i want to fix the issue.), I was hoping one of the guys that had the problem found the exact part in the pump that was playing up, Obviously it's an oil pressure related problem as it only does it at idle when the engine is warm, No one over here (that i have spoken to has heard of the problem), It was very interesting reading the thread, Atleast i know it's a pump issue, I was trying to get away from rebuilding the whole pump as parts over here are rare and very expensive.

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catmech

Posts: 326
Joined: Nov 2005

Wednesday August 26, 2015 21:17
were are you located? do you have a serial number and arrangement number off the tag? If so post please!

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CATMAD

Posts: 5
Joined: Aug 2015

Friday August 28, 2015 03:55
I'm from Australia, No prob give me a couple of days and i'll put it up

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bfbrennan

Posts: 40
Joined: Nov 2007

Friday August 28, 2015 07:54

If this is an actual 3406 truck engine and it's an "A" model it will have a serial number prefix of 92U. The FIP/GOV are all basically the same. One of the differences will be the governor spring. Your problem is most likely within the governor. The flyweights/race are bad, weak governor spring, spring guide,or piston assembly. Since the FIP was rebuilt i have to believe there are no problems with it {worn rack-bad pump assemblies}. That being said what does rebuilt mean to them and why then the problems? This is an easy problem to fix and should not be so confusing. Frank
I

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catmech

Posts: 326
Joined: Nov 2005

Friday August 28, 2015 19:36
I do agree that it is probably in the governor! There is also a c shaped spring under the plate at the end of the cam shaft. It wears the dowels that it locks against, the dowels and spring become worn and you can get a rough idle.

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CATMAD

Posts: 5
Joined: Aug 2015

Friday August 28, 2015 20:18

Ok engine number is 92U48159, Not sure what you mean by arrangement number,
Hi frank i've jumped in at the end of this Forum, My FIP hasn't been rebuilt like the other guys had i recently bought this truck and it had this problem, I just googled the problem and found this forum, It's strange because it only has the issue at idle and only after 10 - 15 minutes of the engine running, doesn't seem to have any issues driving just when you let it idle again.

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CATMAD

Posts: 5
Joined: Aug 2015

Friday August 28, 2015 22:35
OK i found out i can get the arrangement number on Monday when Cat open as the plate on the motor is missing, This / Spring camshaft problem you mentioned would that only happen with a warm engine?

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catmech

Posts: 326
Joined: Nov 2005

Saturday August 29, 2015 20:51
I believe that it would be more noticeable when the oil was warm. You would have the governor housing off any way to check the weights, main spring, piston and valve, their all in the same place and if I had the housing off would inspect all these parts while I was in there, not to much more time involved when your that far in.

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