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JCTech, Diesel Mechanic
Category: Heavy Equipment
Satisfied Customers: 387
Experience:  31 years experience as a Diesel Mechanic, 14 years at Cummins, good with electronic control systems
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2000 ism cummins with caps fuel system in a KW concrete mixer

Customer Question

2000 ism cummins with caps fuel system in a KW concrete mixer chassis, no malfunction codes but the engine surges from idle through the rpm range. Installed a new transfer pump, pump shop diagnosed the injection pump bad, bought a new pump through cummins and still the same surging rpm issue. Shorted cylinders one by one, every cylinder firing, temp range measured with a point and shoot thermometer each cylinder on exhaust manifold measured 280F to 320F. Disconnected fuel pressure sensor on pump and engine smooths out but the malfunction code turns on and white smoke from stacks.Reconnected sensor,ran engine from a bucket of fresh fuel straight to the transfer pump, still no change in running condition, the fuel pressure sensor on the accumilator being disconnected is the only thing that makes the engine smooth out, I think I'm fighting a fuel pressure issue but I'm out of ideas and the local shop is at a stand still also.
Submitted: 7 years ago.
Category: Heavy Equipment
Expert:  JCTech replied 7 years ago.


Does your repair shop have Cummins Insite or another electronic tool to monitor the engine parameters.

I think you may have a pressure sensor "stuck in range". This means that the sensor is giving out a valid pressure signal, however it is incorrect.

The other thing that may have happened is a connector or wiring problem giving a bad reading.

When you disconnect the sensor, the engine goes into a default setting and ignores the inputs from the sensors.

I would want to monitor the inlet manifold pressure and temperature, fuel pressure and fuel pressure setpoint and fuel temperature and see if they change.

You could try disconnecting the inlet manifold pressure and temp sensors, one at a time.

The other thing to check is the delivery pressure from the pump, measured at the fitting on the side of the CAPS pump, this should be 150 PSI



Hope this helps


Customer: replied 7 years ago.
The shop has Cummins insite, watching the parameters the fuel pressure reads 4989 factory target is 5002 so I think I'm right there reading wise, voltage to the sensor at idle is 1.6 and at full goverensd rpm it't at 2.2. I followed the harness to the module, the wiring looks to be intact and every sensor disconnected either kills the engine or sets a malfunction code. The comcheck fuel port at the caps side of the pump was at 3psi when running with the old pump, I need to recheck fuel pressure at the new pump. The fuel pressure sensor and all sensors are new on the pump are new so this is why I'm leaning towards a mechanical problem. Lots of new parts and still runs the same.
Expert:  JCTech replied 7 years ago.

Hi trucks 113,

3 PSI of gear pump pressure is way too low, should be 150 PSI.

Check for a fuel restriction, lift pump has a valve behind it that opens under vacuum, once the lift pump stops running after 45 seconds, this may be sticking.

There is a relief valve in the gear pump, however very unlikely for this to fail in two pumps, like you say something on the chassis.

Check fuel tank breather and all pipework and fittings.




Edited by JCTech on 11/14/2009 at 3:19 PM EST
Customer: replied 7 years ago.
Hi John, This was the pressure before replacing the injection pump, I need to drive to the shop and get the pressure readings now. I'll email when i get the results. Thanks, JACK
Expert:  JCTech replied 7 years ago.

OK, let me know how you get on



Customer: replied 7 years ago.

checked fuel pressure at the pump with mechanical gauge, strong 160psi. printed out at idle monitered parameters accel interlock switch-locked

accumulator pressure 3779.3

accum pressure sensor voltage 1.3v

accum press setpoint 2000

ambient air pressure 28.9

battery voltage 13.8

calibration software phase 070402e5

clutch switch released

coolant temp112.0

coolant temp sensor voltage 2.2

cps state valid sync

cruise set/resume switch neutral

cruise/pto switch on

diagnostic switch on

engine brake switch level 0%

engine harness supply voltage 0.50v

engine oil pressure 70.6

engine oil pressure signal voltage 3.2v

engine speed 726

engine speed sensor supply voltage 5.0v

engine torque limit switch off

fan clutch status on

fuel economy 0.000mpg

fuel pressure deviation 90.8 psi

fuel temp 69.7

gear ratio 16.0

idle increment switch none

injection control valve circuit status fault

injector control valvedelay time 2.648ms

injector control valve open time0.058ms

intake air heater #1 off

intake heater#2 off

intake man pressure 0.8inhg

intake man pressure sensor signal voltage 0.5v

intake man temp 67.6

intake manifold temp signal voltage 3.5v

j1939 engine control source none

j1939 engine control status inactive

j1939 retarder control source none

j1939 retarder control status inactive

key offs 6943

key switch on

manual fan switch on

max expected vca 27.8 deg

oem harness supply voltage 5.0v

percent fuel 0.00%

percent throttle 0%

powertrain protection torque limit 0ft*lb

pto additional switch off

pto set/resume switch neutral

pto status inactive

rear axle ratio switch low

remote pto switch off

service brake switch released

throttle signal voltage 0.5v

throttle signal (idle validation) on idle

throttle supply voltage 4.2v

total ecmtime (key on time) 16987:39:56 hh:mm:ss

transmission gear ratio 16.00

user fueling state low speed gov state

vca 32.4 deg

vehicle speed 0

water in fuel no

Expert:  JCTech replied 7 years ago.


Two things stands out, accumulator pressure is 3779PSI, when accumulator pressure setpoint is 2000PSI,the maximum expected VCA, (valve close angle, how long your pumping control valves remain closed to produce the required fuel pressure) is 27.8 degrees, however your actual VCA is 32 degrees.

you would need to see a datalog to know if this was an issue, although it fits in with your problem.

Was a complete CAPS pump fitted, or was it a modular repair?

Was the engine surging when this snapshot was taken?

Engine speed is 726RPM, yet user fueling state is low speed governer, what is your normal idle speed?

Are you able to get a datalog done and post it here for me to check?

Has the workshop carried out the CAPS pump tests, the main one I am thinking of is the pumping control valve cutout test to ensure both pumping elements are functioning correctly.


Hope this helps



Customer: replied 7 years ago.
yes the engine was surging when this snapshot was printed, a new injection pump from cummins was installed, entire pump came with all new sensors, only a couple of fittings and mounting bolts reused from the old pump, we even checked for debris blocking inside fitting elbows reused from the old pump. Insite was used from the beginning of this whole diagnosing process and a local pump shop was also used to determin a no good pump. original fuel pressure testing at the test port under the accumulator was ony 3psi. we thought we had the issue resolved! Plenty of transfer pump volume (never checked transfer pump pressure, just cracked a line and it flows, pump was replaced before injection pump). Buzz testing on accumulator sensors, with front and rear sensor cut out testing, engine responds to testing and a noticable differance from all actuacting testing performed. all sensors click and buzz when actuated with engine off. One thing I noticed on the data sheet emailed yesterday was at the injector control status parameter reads FAULT, Insite never showed a active fault until we unplugged a sensor? This thing is driving me crazy and I don't have far to drive!!! I can't make it back to the shop today but I'll be all over this Monday morning. What would your next step be if this was in you shop besides lighting it on fire?!! Thanks, JACK
Expert:  JCTech replied 7 years ago.


Just checking, are the symptoms the same as before the pump was changed


One thing you mention, a noticeable difference from all actuating testing performed,

when doing the pumping control valve test, you should not have a noticeable difference, there will be a dip when changing from both to one, what you are looking for is the VCA, there should not be more than 13 degrees difference from front to rear.


Does the engine still surge when the tests are being carried out.


There is a J1939 cutout test, has this been tried to isolate the dashboard and ABS commands.


The first thing I would do was to run the engine from a container of clean fuel, straight into the gear pump inlet on the side of the pump, also the return back into the bucket, that will tell you if it is a pump/sensor issue or a fuel supply/return issue, the length of pipe used will need to be prefilled with fuel.


Hope this helps


Customer: replied 7 years ago.
yes, the engine runs the same since the new injection pump and transfer pump were installed, surge in rpm. I'll try the J1939 tests , run the engine from a bucket of clean fuel and monitor the vca on a pumping control test.
Expert:  JCTech replied 7 years ago.
Did the engine run like this before this pump was fitted?
Customer: replied 7 years ago.
yes, nothing has changed the original running (surging) condition, the truck went into the repair shop for this condition, alot of new parts and still the same result, truck is unusable running like this.
Expert:  JCTech replied 7 years ago.

OK thanks, XXXXX XXXXX keep on about it, just making sure in my own mind.

If you can get a datalog of the engine and fuel pump sensors as well would be good, a couple of minutes of surging would be enough.