Rough Idle on Caterpillar 3208 Suggestions?

[DumnMad]

Based on my old Ford experience, with no glo-plugs; there's nothing wrong with your engines, just that they're not getting up to temperature for long enough. My mechanics tell me to give it a good spell at high revs every now and then & not to worry about the smoke. Start up, put into gear, and push against mooring ropes until engine is warm, then you can idle the boat to where you are going.

[whatever]

Ok, here are the dreaded results on installation of a pony tank on port engine..installed with fresh diesel attached at the secondary(spin on) filter. Same thing! Will not idle below 900 rpms without fluctuation. For those that have questioned our pre-occupation of wanting to idle at lower rpms, we have owned this boat for 9 yrs this month, lived aboard for 8 yrs 11 mos of that time, EVERY time the motors have been cranked, this boat would start and idle at 500-600rpms without any movement of throttle lever at helm, while we did our 15mins. or so of warmup before getting underway, it concerns us when that is not the case now ..of particular notice when bleeding manual fuel relief valve on top, am getting a drip of fuel from bottom of engine, but drip stops when valve closed and does not drip while motor running. We assume now the only thing left now that could be the problem is the injector pump

[donradcliffe]

Just google Cat 3208 surging and you will know that you are not alone.

There's a lot of noise out there, but there are a few guys who know what they are doing.

11 Bravo 11 Bravo is offline
Cast Iron
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Feb 2008
Location
Gillette, Wyoming
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I suspect that some of the folks running the 3208 down really don't have all that much experience with them. I worked in field service for Cat dealers for 17 years and worked on my share of 3208s. They were most definitely not the best engine Cat made, and they had some problems that were not normal Cat problems, but they really weren't all that bad.

I had 3 service trucks with 3208s in them and got over 100,000 miles on all 3 without any serious problems. One of the trucks went to one of my helpers when I got rotated into a new one and that truck had almost 160,000 on it with the original engine. It still ran fine when we sent it to the auction. They didn't seem to do well with extended idle times, especially if it was cold. We had solenoids on our service trucks so that when we were running the PTO for the crane and air compressor it kicked the engine RPM up to about 1000. We never left the truck sitting around at low idle. They are like everything else, you have to take care of them and service them properly.

I did have more trouble with the 3126s in the newer trucks I got, but again, they really weren't terrible engines. The first truck I got with a 3126 I had to pull the engine at 135,000 ish because it was using oil. The bores were worn pretty badly and I put a re-man engine it. That was the only engine I ever replaced in all the service trucks I had.

To the OP.

If you have fuel running off the bell housing and you have had fuel lines open to bleed the system, you may very well just have fuel that is built up in the valley that is dribbling out around the back end of the engine. If it keeps dripping off the bell housing for an extended time, then you probably have a leak on one of the high pressure fuel lines. With the engine running, spray some brake clean or compressed air on the fuel lines where you broke then loose to bleed the engine. These will often leak ever so slightly after the lines have been loosened and re-tightened. It can be hard to spot the leaks unless everything is clean and dry at the fittings. It could have leaks other places on the pump too, but I would start by looking closely at the connections you had loose.

There are 3 plastic lines that come off the fuel injection pump and run around the front of the left (drivers side) head. One of those lines hooks to a bleed valve that is on the top cover of the fuel system. The valve has a T handle so you can open it to bleed the air out of the pump housing and the fuel will go out the line onto the ground. The other 2 lines are bleed lines, or "Puke Tubes" off the injection pump. One comes from the cavity between the 2 seals in the front of the pump. If fuel leaks past the inner seal it will run out this tube rather than making it's way into the crankcase. The other one comes off the governor housing and again is a way for the fuel to escape if the seals start leaking. Find those lines and watch them with the engine running. Sometimes I would put soapy water on the end of the lines to make it easier to see if there was any pressure at all there.

If any of them have fuel leaking out, you are loosing the prime in the injection pump and also very likely sucking some air in. If the one from the bleed valve is leaking you can fix that pretty easily. If one of the other ones is leaking it will probably be easier for you to get a re-main fuel injection pump and just replace it. They are not a hard pump to rebuild / reseal, but they take some special tooling.

Someone else suggested putting a sight glass in the fuel lines to look for air. This is a very good suggestion. Most of these engines had hard lines between the fuel filter housing and the injection pump. Even if you have to remove that line and make up a hose to install a sight glass it is worth doing. If you can do this and you see air bubbles getting to the pump, you know your problem is somewhere in the supply lines, the filter, or the water separator.

This could very well end up being a simple fix. I went out on a service call on an engine in a delivery truck once that had very similar symptoms to what you are describing. I ended up finding that a hose off the steering box was rubbing the fuel filter and had rubbed a paper thin spot and a pin hole in the filter can. The hose held enough pressure against it that it didn't leak much (the steering hose was just a little slimy), but the engine would pull air in when it was running.

Check simple stuff first.

[River Cruiser]

It sounds like you may need to check the lift pump pressure, I would do that check while you have the pony tank still set up. The problem may be a check valve in the lift pump or the lift pump itself that is not keeping the proper charge pressure on the system. I've replaced dozens of them on the 3306 series engines, typically when they go bad there is a loss of power or the engine won't start. I have a hard time believing both engines would have the same problem at the same time. Do they have the same rough idle once they are up to operating temp?


Sent from my iPad using Cruisers Sailing Forum

[whatever]

River Cruiser after running the boat from point a to point b, if the throttle is reduced to the lowest rpm the motor will die.

[HappyMdRSailor]

Originally Posted by donradcliffe

Just google Cat 3208 surging and you will know that you are not alone.

There's a lot of noise out there, but there are a few guys who know what they are doing.

11 Bravo 11 Bravo is offline
Cast Iron
Join Date
Feb 2008
Location
Gillette, Wyoming
Posts
431
Default
I suspect that some of the folks running the 3208 down really don't have all that much experience with them. I worked in field service for Cat dealers for 17 years and worked on my share of 3208s. They were most definitely not the best engine Cat made, and they had some problems that were not normal Cat problems, but they really weren't all that bad.

I had 3 service trucks with 3208s in them and got over 100,000 miles on all 3 without any serious problems. One of the trucks went to one of my helpers when I got rotated into a new one and that truck had almost 160,000 on it with the original engine. It still ran fine when we sent it to the auction. They didn't seem to do well with extended idle times, especially if it was cold. We had solenoids on our service trucks so that when we were running the PTO for the crane and air compressor it kicked the engine RPM up to about 1000. We never left the truck sitting around at low idle. They are like everything else, you have to take care of them and service them properly.

I did have more trouble with the 3126s in the newer trucks I got, but again, they really weren't terrible engines. The first truck I got with a 3126 I had to pull the engine at 135,000 ish because it was using oil. The bores were worn pretty badly and I put a re-man engine it. That was the only engine I ever replaced in all the service trucks I had.

To the OP.

If you have fuel running off the bell housing and you have had fuel lines open to bleed the system, you may very well just have fuel that is built up in the valley that is dribbling out around the back end of the engine. If it keeps dripping off the bell housing for an extended time, then you probably have a leak on one of the high pressure fuel lines. With the engine running, spray some brake clean or compressed air on the fuel lines where you broke then loose to bleed the engine. These will often leak ever so slightly after the lines have been loosened and re-tightened. It can be hard to spot the leaks unless everything is clean and dry at the fittings. It could have leaks other places on the pump too, but I would start by looking closely at the connections you had loose.

There are 3 plastic lines that come off the fuel injection pump and run around the front of the left (drivers side) head. One of those lines hooks to a bleed valve that is on the top cover of the fuel system. The valve has a T handle so you can open it to bleed the air out of the pump housing and the fuel will go out the line onto the ground. The other 2 lines are bleed lines, or "Puke Tubes" off the injection pump. One comes from the cavity between the 2 seals in the front of the pump. If fuel leaks past the inner seal it will run out this tube rather than making it's way into the crankcase. The other one comes off the governor housing and again is a way for the fuel to escape if the seals start leaking. Find those lines and watch them with the engine running. Sometimes I would put soapy water on the end of the lines to make it easier to see if there was any pressure at all there.

If any of them have fuel leaking out, you are loosing the prime in the injection pump and also very likely sucking some air in. If the one from the bleed valve is leaking you can fix that pretty easily. If one of the other ones is leaking it will probably be easier for you to get a re-main fuel injection pump and just replace it. They are not a hard pump to rebuild / reseal, but they take some special tooling.

Someone else suggested putting a sight glass in the fuel lines to look for air. This is a very good suggestion. Most of these engines had hard lines between the fuel filter housing and the injection pump. Even if you have to remove that line and make up a hose to install a sight glass it is worth doing. If you can do this and you see air bubbles getting to the pump, you know your problem is somewhere in the supply lines, the filter, or the water separator.

This could very well end up being a simple fix. I went out on a service call on an engine in a delivery truck once that had very similar symptoms to what you are describing. I ended up finding that a hose off the steering box was rubbing the fuel filter and had rubbed a paper thin spot and a pin hole in the filter can. The hose held enough pressure against it that it didn't leak much (the steering hose was just a little slimy), but the engine would pull air in when it was running.

Check simple stuff first.

GOOD INFO!

Originally Posted by whatever

Ok, here are the dreaded results on installation of a pony tank on port engine..installed with fresh diesel attached at the secondary(spin on) filter. Same thing! Will not idle below 900 rpms without fluctuation. For those that have questioned our pre-occupation of wanting to idle at lower rpms, we have owned this boat for 9 yrs this month, lived aboard for 8 yrs 11 mos of that time, EVERY time the motors have been cranked, this boat would start and idle at 500-600rpms without any movement of throttle lever at helm, while we did our 15mins. or so of warmup before getting underway, it concerns us when that is not the case now ..of particular notice when bleeding manual fuel relief valve on top, am getting a drip of fuel from bottom of engine, but drip stops when valve closed and does not drip while motor running. We assume now the only thing left now that could be the problem is the injector pump

Whatever...

Plumb the pony tank directly to the IP bypassing EVERYTHING... Also run a short RETURN line to your pony tank... One at a time though!

[EngNate]

I have a 3208 and it idles nicely at 700 after 2 min warm up at 1000 from cold start. This is as it should be, IMO, though yes some will start up and do 600 right from cold.

Nobody seems to have mentioned the injection pump case bleed, a needle valve on the top of the return line port. It has a length of tubing attached that goes down the right side of the engine (looking from the front of the engine). Pull that tube off, remove it and route it to a convenient place where you can put the end into a small container and see it.

Before moving on here - the other two tubes you will see are leak-off drains, one on the top of the pump is for the stop or run solenoid, and from the bottom the drive shaft seal. If either of these seals leak the fuel goes out these drains. In the case of the drive seal this prevents fuel from getting into the engine oil in this event, I'll revisit this one momentarily.

Place the end of the bleed tube in a container, open the needle valve several turns and operate the hand priming pump until fuel fills the container free of air bubbles, close the valve. This is the procedure that also has to be done after the secondary filter is replaced. (There should be no need to bleed injectors after filter change.)

For test purposes leave the container in place with fuel in it so that no air enters the tube. (You will later be able to tell if any air has entered the pump) If there was air in the pump there may also be air in one or more injection lines. Start the engine, give it a minute or two at 1000 rpm and check for normal idle. If not, crack each injector line, taking note of any that does not cause a rough response. Allow 3 or 4 squirts of fuel from each one to purge any air. If the engine is not idling normally at this point, you're probably looking at another issue. If any injector cracking didn't cause a response, replace it before looking further. Otherwise, check to see if any air entered the pump by bleeding again as above. If so, this has to be solved. If it is idling normal now, give it some running time with the bleed container still in place and then check to see if any air enters the pump.

If you've got air getting into the pump and can't seem to find the cause, the drive shaft seal is likely it. With the bleed valve closed operate the priming pump (just hold pressure on it) for a minute or so, then follow those other two black tubes down the side of the engine and look carefully for a drop of fuel at the end of one. Note which one and follow it back to either the top or bottom of the pump. The top one (solenoid cavity) should not be of consequence, but if a drop of fuel comes from the bottom drain tube the drive seal will have to be replaced and that is for an injection shop, it will have to be removed and sent in then reinstalled and timed.

A leaking drive seal can temporarily be worked around by running a fuel lift pump to supply the engine, and routing the drain hose to a container to collect the leak-off. The end of the tube should be submerged in fuel so it does not drain and allow air in. Do not treat this as a permanent solution or you may eventually be diluting your oil with fuel.

If we've ruled out air in the system then the next thing I'd look at is one or more valve clearances well out of spec or the possibility of a sticking or leaking valve.

....My 3208 broke a valve spring, the retainers came off and the valve dropped into the cylinder and it suffered no damage except the spring and a pushrod! There's luck for ya!

[whatever]

EngNate, HappyMdRSailor, donradcliffe and River Cruiser thanks so much for all these tips and suggestions. Still trying to figure it all out and muddling thru. Had a retired diesel mechanic suggest cleaning the governors and then the Captn pulled a tendon in his right hand, and yes he is right handed, so we are in the process of ordering the various gaskets and seals suggested to replace after that cleaning and as soon as the Captn can grip a screw driver or wrench, that will be a step on 1 motor to see if it changes our issue. I will update when we have gone any further thru. Again, THANK YOU for all that continue to try to assist us with your wonderful ideas and suggestions! All we want to do at this point is get 'er fixed to put her up for sale! Its time to jump ship!

[marlinmike]

All the best in finding your issue, at this juncture it might be prudent to find a good Cat mechanic to resolve this once and for all.

[whatever]

Easier said than done. Today we have determined, by virtue of port motor not starting, taking the fuel pressure pumps off and having the rebuild. No fuel coming out of one line thru the fuel pump....

[whatever]

Is there anyone out there that has knowledge to give us a step by step in removing the fuel pressure pump on our 3208 Caterpillars???and maybe some diagrams included??? Word of mouth is a great thing, but when you are the one actually doing the work and that person that diagnosed is not local, printed words and pictures would be so helpful! We have now got one motor that will not start. It did a month ago!!! So apparently from lack of use, the fuel pressure pumps have lacquered up significantly and we have made the decision to pull them and send in for a rebuild. If we do the taking off and reinstalling when they come back, that will save us several thousand dollars in labor costs of a mechanic. So Help!!!!!!!!!!!!!!!!!!!

[FlyingCloud1937]

You will likely save yourself, thousands of dollars by hiring a Mechanic that knows those engines.

If you don't know how to remove them, how will you ever reinstall them, and get the timing right?

Second, an onsite mechanic, may be able to diagnose that the pumps don't need to pulled.

Find a good mechanic.

Lloyd

Originally Posted by whatever

Is there anyone out there that has knowledge to give us a step by step in removing the fuel pressure pump on our 3208 Caterpillars???and maybe some diagrams included??? Word of mouth is a great thing, but when you are the one actually doing the work and that person that diagnosed is not local, printed words and pictures would be so helpful! We have now got one motor that will not start. It did a month ago!!! So apparently from lack of use, the fuel pressure pumps have lacquered up significantly and we have made the decision to pull them and send in for a rebuild. If we do the taking off and reinstalling when they come back, that will save us several thousand dollars in labor costs of a mechanic. So Help!!!!!!!!!!!!!!!!!!!

[marlinmike]

Not sure what you mean easier said then done, is it you can't find a CAT mechanic in Florida or you just rather not pay for one, notice on the CAT forum this has been an issue since the end of August for you. If you want help finding one I could do that, but not sure what you are looking for.

Originally Posted by whatever

Easier said than done. Today we have determined, by virtue of port motor not starting, taking the fuel pressure pumps off and having the rebuild. No fuel coming out of one line thru the fuel pump....

[whatever]

Lloyd, a retired diesel mechanic from another state gave us some of his time and we have determined the pumps are more than likely(more at this point) lacquered up and need rebuild. We know that we would spending thousands of dollars to have a mechanic do this work, IF and that it is a huge IF we could find someone to come to this little marina where we are. If we can pull them, send them off for rebuild and then have difficulties getting all ok when they are send back, then we can pay a little less and hopefully get someone to come from Jacksonville that knows Cat's! That is our dilemma!!! Thanks for your suggestion, believe me we have struggled thru this whole ordeal!!hoping that was not the case!!

[marlinmike]

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