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Cat Man
Cat Man, Cat Engine Expert
Category: Medium and Heavy Trucks
Satisfied Customers: 8412
Experience:  I am ASE Master Truck Certified.
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I am a diesel tech but don't see to many older Cat Engines.

Customer Question

Hello, I am a diesel tech but don't see to many older Cat Engines. I am working on a 1990 Pete 377 with a Cat 3406b. Customer has been restoring truck and just starting hauling with it recently. He started it one morning & the idle was surging so he parked it for day. Got in it next morning and as soon as it starts engine races up and bounces off limiter for as long as you let it. Its a non stop rev as if someone was in the cab flooring the fual pedal on and off to full rpm. Its equipped with PEEC and I have codes 22- Rack pos sens, 23- Timing pos sens, 24- oil press sens, 25- Boost press sens & 34 Loss of engine RPM signal. I am thinking that there might be a issue with the Transducer Module but would like to confirm. I utilize Mitchell Prodemand & followed most of there flow charts but at a dead end. Would hate to change transducer module and that not be the problem.
Submitted: 1 year ago.
Category: Medium and Heavy Trucks
Expert:  Cat Man replied 1 year ago.
Hi. Thanks for asking your question and requesting me. I will try and help you out.
There is a very good chance the transducer module is faukty. I see this a lot. The transducer carries both the rack position and rpm sensor signals to the ECM. Also, any time I have an active boost sensor fault. I often find the transducer bad. The reason is the boost sensor is in the transducer. However, it could be a wiring problem to the transducer. I would inspect the engine harness first and make sure it is OK.
Please reply back if you need more help or have more questions. I am happy to assist.
Customer: replied 1 year ago.
I took apart all connectors and visual inspected terminals & harnesses. I did not get as far as tracing individual circuit wiring due to the amount of codes I have. Have you ever seen engine race like this before? As soon as you crank it starts up and hits 2500 rpm limiter and continues to bounce off limiter from 2200 to 2500 rpm.
Expert:  Cat Man replied 1 year ago.
Thanks for the information.
Yes. I have seen them rev like this before. It's normally caused by a bad rack position signal or bad rpm signal. If course it could be the sensor or the transducer. Simply because the transducer carries both of these signals.
Please reply back if you need more help or have more questions. I am happy to assist.
Customer: replied 1 year ago.
Thanks for the quick response. Since wiring passes visual inspection do you recommend replacing transducer. If so can you recommend a supplier. Are there any particular wiring values I should be checking for at transducer for the rack postion or bad rpm signal that you believe is cause of eng race? Also like I stated I do not have much experience with PEEC 3406b engine but is it coincidental that all these sensors are bad in the transducer or does one code trigger the rest?
Expert:  Cat Man replied 1 year ago.
You are very welcome. I am happy to assist.
You will need to get the transducer from a Caterpillar dealer. They are the only people that sell it.
Unfortunately Cat does not give an voltage specs for the signal wires. Sorry.
Yes I would not suspect all four sensors are bad. I have seen transducers cause these codes many times.
Please reply back if you need more help or have more questions. I am happy to assist.
Customer: replied 1 year ago.
Would you recommend replacing transducer? If so can the pump assembly stay on engine and are there any timing issues to worry about during replacement?
Expert:  Cat Man replied 1 year ago.
Yes. The reason is nornally when you have both boost and oil pressure faults. The transducer is to blame.
The pump can stay on the engine. It does not need to be removed. However in order to replace the transducer. The entire back of the pump will need to come off. After installing the transducer, the rack position sensor and rpm sensor does need to be calibrated. There are special tools needed along with Cat ET software. It's a big job.
Please reply back if you need more help or have more questions. I am happy to assist.
Customer: replied 1 year ago.
Hello and thank you for assistance. We have installed the new transducer. We are at the point were we need to calibrate. How is this done? We do have access to Cat ET but I cant find a diagnostic connector anywhere on this vehicle. It is a 1990 Pete 377.
Expert:  Cat Man replied 1 year ago.
Thanks for the update.
To calibrate the boost sensor in the transducer. Either Cat ET or the old ECAP programmer is needed.
IF your serial number starts with 8TC, you must locate the 9 pin connector over the ECM. There are two of them. The one with the least amount of wires is the one the tool connects to. You will need a "Y" connector to do this. Basically, you will disconnect the 9 pin connector and insert the 9 pin Y connector between the two.
If you have 4CK, there should be a 9 pin plug with a cap on it to connect the tool .
Please reply back if you need more help or have more questions. I am happy to assist.
Customer: replied 1 year ago.
Thank you for the info. It is a 8TC engine and located the diagnostic connector at PCM. I have a Nexiq Prolink Grapiq with the Caterpillar Cartridge (model 202024) for electronic controlled engines including the 3406. I have 9 pin adapter but not a Y adapter to tap into between the 2. I have looked for the connector but can not find anywhere online. Any help will be appreciated. ty
Expert:  Cat Man replied 1 year ago.
You are very welcome my friend. I am happy I could help.
The Y adapter you need is Cat part number(###) ###-####
Please reply back if you need more help or have more questions. I am happy to assist.
Expert:  Cat Man replied 1 year ago.
Hey.
I just wanted to see how things were going. Please let me know if you need more help. I am happy to assist. If my information was helpful, please leave a good or higher rating so that I receive credit. You will still be able to view this link and ask more questions after leaving a positive rating if needed.
Thanks.
Customer: replied 1 year ago.
Sorry for the delay. Thanks allot for your assistance, you have been great. I just received the Y adapter this morning. Gonna give it a go today, I will keep you posted. Thank you
Expert:  Cat Man replied 1 year ago.
You are very welcome my friend. I am happy I could help.
Customer: replied 1 year ago.
The engine starts but wants to run away so I blocked intake with metal plate. I have same codes 34, 22, 23,24 & 25. I am purchasing CAT ET program as we speak to properly calibrate boost sensor. I am getting codes by counting CEL flashes. Should I still have these codes present?
Expert:  Cat Man replied 1 year ago.
Yes the codes will stay there as they are most likely logged. To get rid of them they would need to be cleared with Cat ET.
If the engine wants to run away. I would suspect the BTM May not be installed correctly. The small arm on the BTM must go into the rack actuator. When it does not. The engine will run away.
Customer: replied 1 year ago.
What is BTM? I can start and shut off engine with key its just RPM races. The transducer module seemed pretty straight forward on the install.
Expert:  Cat Man replied 1 year ago.
BTM is the brushless torque motor. It's that's big round motor on the side of the fuel system that has two wires connected to it.
Customer: replied 1 year ago.
Okay we noticed when we put that in it had to be in correct alignment. Another thing we noticed was during dis-assembly we took off a cover on the front of motor in front of pump and found that same rod with a linkage that was no in correct position. We installed that as well and were thinking maybe this was our problem all along. All wiring seams sound but engine still racing. As I stated earlier the engine starts and turns off, it just has a uncontrollable High Ide. I purchased CAT ET but not running yet. Cat states to calibrate Boost sensor but on a warm engine. I can warm up because Idle crazy high. Do you think codes not being cleared causing this?
Expert:  Cat Man replied 1 year ago.
Thanks for the information.
No the codes can not casue this. The engine is running away because of one of two things.
Either the arm of the BTM is not in the slot on the actuator. Or the rack position sensor is not connected to the rack. There a magnet on the rack that sticks to the sensor.
When you get et connected. You should remove the small cover held on by two bolts on the side of the pump and move the rack. Then go to the status screen and monitor rack position. If it is not moving when you move the rack, the sensor is not stuck to the rack magnet.
Please reply back if you need more help or have more questions. I am happy to assist.
Customer: replied 1 year ago.
I have round motor off at back of pump facing out. It has a small arm which fits in a slot on the rod. There is also a small cover on side of pump more towards the front. I can push the rod back and forth and has about a inch of play. Behind the small cover the rod is not connected to anything- is this correct? And on the front of the motor in front of front cover there's another round motor with 2 wires that connects to another rod. Very confused by this setup. If you can help me locate which components are what would be a great deal of help. Thank you.
Expert:  Cat Man replied 1 year ago.
Sure.
Yes the arm of the BTM fits in the slot. When it's out of the slot, the engine will overspeed or run away.
Yes the BTM on the front is the timing BTM. It moved the timing advance to advance and retard the timing.
Yes that is correct. The rod is not connected. That area is used for connecting a dial indicator for checking rack travel. This is mainly used on full mechanical engines.
Please reply back if you need more help or have more questions. I am happy to assist.
Customer: replied 1 year ago.
Great info. Now above the BTM on back of pump (closer to block) ther is a solenoid that has 2 wires going to it. It looks like it opens & closes to move a linkage bracket & spring which meets the backend of rod. What is this solenoid? Thank you
Expert:  Cat Man replied 1 year ago.
No problem. I am happy to help.
That is the shutoff solenoid. When the key is turned off. The solenoid pushes the rack to fuel off.
Customer: replied 1 year ago.
Okay good stuff. You been great & quick to response. Thank you for that. The "the magnet on the rack that sticks to sensor" you mentioned- is that rack sensor on the transducer module we replaced? So it seems there are 2 racks- a upper & lower and the timing BTM rack seems to be on plane with the transducer module that we replaced.
Expert:  Cat Man replied 1 year ago.
You are very welcome my friend. I am happy I could help.
Ther is only one rack. The rack sensor signal travels through the transducer.
Customer: replied 1 year ago.
The BTM on the front and the BTM on the rear seam to be connected to different rods. Where is the rack located? TY
Expert:  Cat Man replied 1 year ago.
Yes they are. The BTM on the rear is connected to the fuel rack. The timing BTM is connected to the spool that controls oil flow in the timing advance to change timing.
Customer: replied 1 year ago.
Okay thank u. Cat et will be ready in morning. I will hook up and move fuel rack like you mentioned while monitoring data.
Expert:  Cat Man replied 1 year ago.
Ok sounds good. Keep me posted.
Customer: replied 1 year ago.
Okay have a update for you. I purchased CAT ET yesterday and hooked up to truck today through my Prolink USB link connected to the y- adapter I purchased through cat as well. My USB link began smoking and I had no communication with Cat ET. Very confused. I used this USB link everyday with Cummins insite & International service maxx.
Expert:  Cat Man replied 1 year ago.
Thanks for the update. Sorry you are having trouble.
Unfortunately I have only used the Cat comm adapter. I have not used the Prolink adapter. Sorry. But it should work as good as the Cat adapter.
Expert:  Cat Man replied 1 year ago.
Hey. I just wanted to see how things were going. Please let me know if you need more help. I am happy to assist. If my information was helpful, please leave a good or higher rating so that I receive credit. Thanks.

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