Cummins 350 Troubleshooting

More truck problems... This one is a '85 International S2200 with a Cummins big cam 350.
Earlier this summer I was cruisin along and the motor was feeling sluggish, didn't really like pulling the excavator up a hill.
I was almost to the job so continued on. On my return trip it was still feeling sluggish with an empty trailer. I had just put
new fuel filters on it but figured this would be the easiest place to start. So I changed them, no change. It was slow to rev
up, very poor throttle response. So I had a guy come take a look at it. No turbo boost was the problem, so I took another one off
of my old 290 cummins with 1,100,000 miles on it...problem solved! weee.......no. It lasted for about 2 weeks then I am having the same
problem again, very sluggish, no power, naturally aspirated feeling. So that was an old turbo, probably on its last leg. So I took the original one in and had it
rebuilt, put it on...problem solved! weee....... no. This one lasted 3 weeks and its back to its same old game, this time I was quite suspicious of
its intentions. But I had to start with the turbo, off it went back for inspection. Nothing wrong with it. I then took the intercooler off and its clean
as a whistle, aircleaner is new. I am getting a vac until 1500 rpm then the turbo starts boosting and I will get 1lb at 2400 rpm with no load.
Looking for some ideas, thanks!

I'm sure you've already checked the obvious, like exhaust manifold leaking, gasket on turbo flange...etc.? How many miles on her?

What about the fuel strainer in the fuel pump? Assume this is a good old fashion PT pump.

Top of pump just in front of the fuel solenoid there should be a large slotted screw looking cap. There should be a screen type filter and a spring holding it down under this cap.

Trouble shooting for PT pump here:

http://oregonfuelinjection.com/pdf/cummins-pt-pump-diagnostic.pdf

Might give some ideas.

Another thing could be a suction leak in fuel line to pump from tank.
There is a special tool to check for this but with a little work with some fittings you can make one. just need to make up a short section of clear tubing with fittings to allow you to install in in the suction line to the pump. Run engine and watch for bubbles in the fuel. Install a various places on the suction side of pump, at pump, at each fuel filter and so on back to the tank.

Thanks for the ideas, I haven't had a chance to tear into it again. Very busy lately, what stumps me is that it would work for a few weeks after a different turbo. If it was fuel related I would think it would do it all the time. My mechanic is thinking it is the AFC diaphragm, but its on the back side of the injection pump.. fun fun

Have you done a tune up on the engine recently?

kshansen has the easiest solution to check for fuel/air problems though, before you dig too far.

A common problem among Cummins (855's) is just that; cracked pick-up tubes in tank, or even more common is a deteriorated inner rubber fuel line that develops a "flap" of rubber that when fuel is demanded, the flap acts like a check valve and closes/restricts flow.

Another is simple porous fuel lines. They act strange...not occuring when you expect, etc. I have taken lines off from tank to filter housing, plugged one end and submerged in a 5 gal. bucket of water...applied shop air and watched for bubbles in water, indicating porosity.

Heck, I had a shop rag down inside a tank once, that would find it's way over the pickup tube when it felt like messing with me, and just about shut the motor down. Change the pitch of the vehicle and it would flow away and act fine. That one drove me about out of my mind.

How about check air filter?

Turned out it was the Injection Pump, slapped a new one on there and problem solved.. Thanks for the ideas

The problem has returned!!!!! Its worked great untill now. The sluggish throttle response is no longer a issue. It revs quickly
As it should and drops off as it should. I just dont have any more than a lb or two of boost pressure and no power!?! I have checked all lines from airfilter (new) to turbo and from turbo to intercooler and from intercooler to PT Injection pump. All is clear, tight with no leaks... I have a full full tank of fuel so im assuming the pickup is fine.. Any ideas???? Thanks

I might start by removing the suction hose from the back of the fuel pump and make up a short 3-4 inch section of clear tubing to install betwee the pump and suction hose then run engine at high idle to see if there are air bubbles in the fuel. If you see bubble there move the sight gauge to the inlet to the fuel filter and again check for bubbles. If still has bubbles see if you can install it at the tank. This will help rule out a problem with the supply side.

Another thing would be to check fuel pressure to the injectors. Should be an 1/8 inch pipe plug in fitting in lines leading to the front heads. You will need to contact the pump shop to get the full load fuel pressure and you will need a hose long enough to reach cab so you can read the pressure while pulling a hill at full load. Also should get the full pressure by hard acceleration.

One more thing to try would be to put about 30psi to the aneroid if it is separate on this engine or to the fuel pump if it is internal. There should be a 1/4 line from the intake manifold to either the aneroid or fuel pump remove and plug the fitting at the manifold then us a small air regulator to supply the 30 psi. Now try driving the truck to see if you get good boost pressure and power. Report back on anything you find and I'm sure someone can offer more or better ideas.

Run a clear line on the return where you can see it going down the road (your looking for bubbles)

Could be compression or sucking air.

Also what is your rail pressure and boost going down the road.

I think you have aneroid prolems

If you dont mind a little smoke you can block it out need to learn how to feather foot the fuel though.

I must type slow as I see this is covered^^^

Thanks for the replies I really appreciate the help. Very frustrating spending the money on turbo's and Injection pumps, having it fixed only to return. So the aneroid is supplied from pressure coming out of the block, downstream of the intercooler. I dont believe I was getting enough pressure through the intercooler to tell the pump "more fuel". So I ran a jumper line from my intake manifold (where ether assist was)
strait to the injection pump, bypassing the intercooler restriction. I drove it around empty for a few miles and it seems to be working normally. I will try it loaded tomorrow.

alaskaforby4 said:

Thanks for the replies I really appreciate the help. Very frustrating spending the money on turbo's and Injection pumps, having it fixed only to return. So the aneroid is supplied from pressure coming out of the block, downstream of the intercooler. I dont believe I was getting enough pressure through the intercooler to tell the pump "more fuel". So I ran a jumper line from my intake manifold (where ether assist was)
strait to the injection pump, bypassing the intercooler restriction. I drove it around empty for a few miles and it seems to be working normally. I will try it loaded tomorrow.

Click to expand...

Not sure I understand but is the air pressure going to the aneroid coming from the outlet side of the intercooler? Can you check to see if there is a difference in boost pressure on the inlet to the outlet side? Could be intercooler is restricted?

kshansen said:

Not sure I understand but is the air pressure going to the aneroid coming from the outlet side of the intercooler? Can you check to see if there is a difference in boost pressure on the inlet to the outlet side? Could be intercooler is restricted?

Click to expand...

I have seen an aftercooler core on a 3406A nearly completely plugged with fine dust/oil mix. And another time I actually found an old teeshirt in a cummins after cooler inlet. Hmm. How would that get in there?

grandpa said:

Have you done a tune up on the engine recently?

Click to expand...

alaskaforby4 said:

The problem has returned!!!!! Its worked great untill now. The sluggish throttle response is no longer a issue. It revs quickly
As it should and drops off as it should. I just dont have any more than a lb or two of boost pressure and no power!?! I have checked all lines from airfilter (new) to turbo and from turbo to intercooler and from intercooler to PT Injection pump. All is clear, tight with no leaks... I have a full full tank of fuel so im assuming the pickup is fine.. Any ideas???? Thanks

Click to expand...

When's the last time it had a tune up and the valve lash adjusted? Also that old of a truck just replacing all of the fuel lines wouldn't hurt. If it can't get fuel it's not going to spool the turbo.

alaskaforby4 said:

Thanks for the replies I really appreciate the help. Very frustrating spending the money on turbo's and Injection pumps, having it fixed only to return. So the aneroid is supplied from pressure coming out of the block, downstream of the intercooler. I dont believe I was getting enough pressure through the intercooler to tell the pump "more fuel". So I ran a jumper line from my intake manifold (where ether assist was)
strait to the injection pump, bypassing the intercooler restriction. I drove it around empty for a few miles and it seems to be working normally. I will try it loaded tomorrow.

Click to expand...

kshansen said:

Not sure I understand but is the air pressure going to the aneroid coming from the outlet side of the intercooler? Can you check to see if there is a difference in boost pressure on the inlet to the outlet side? Could be intercooler is restricted?

Click to expand...

There was a psi difference of about 5 psi before/after depending on RPM

alaskaforby4 said:

There was a psi difference of about 5 psi before/after depending on RPM

Click to expand...

OK, anyone with more info on this. I have not worked on too many with intercoolers but a 5 psi drop in pressure sounds high, could be wrong though.

Did some looking on the subject and at least one company says:

>What ranges of pressure loss can be expected? And what is acceptable?
>For good solid performance, the pressure loss across the intercooler ought to be kept to less than 1.0 to 1.5 psi. If any pressure in excess of 4 psi is measured, then the intercooler is not suited for the job and certainly harming the performance.

I would be interested in knowing what Cummins thoughts are on this.

Drop in pressure could be from dirty core or leaks.

Yes there was enough of a restriction through the intercooler to affect the aneroid valve from operating correctly. So i by-passed the intercooler and connected directly to aneroid.. Problem seems to be solved so the problem is a plugged intercooler

When you take the after cooler apart you tend to break off several bolts so it is good to have a helicoil set handy before you start.

Air to water.

The problem returned again, We yanked the after cooler out and it was clean as a whistle. The psi differential I was see was a difference in gauges. The silicone boot that connects the turbo was looking a little suspect so we replaced that and it seemed to help....for awhile, then it returned. just gutless and no power after about 5 miles... I luckily have very short equipment moves so I just dealt with driving 10 - 30 mph places. very frustrating! I then dove into the fuel supply conspiracy and installed a auxiliary tank in the cab that is gravity fed. Made no change what so ever.

I finally gave up and bought a different truck. But I still had to get this one to my mechanic, about 20 miles away. I dropped to 5 mph going up this hill with a line of traffic behind me, very embarrassing, especially when your name is plastered all over the doors. I pulled over as soon as I could and shut it off to weigh my options... At this point I had 10 miles left. I said to heck with it and jumped back in for the "slow ride" Well it ran great for a couple miles then fell back into its old tricks. I found that if I shut it off for a minute or two it will start up and have normal power for a couple miles..:beatsme So I did this a few times, made it to the yard and parked it. This one really has us baffled