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N14 celect plus intake manifold pressure

allen pardon

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Nov 27, 2021
Messages
20
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indiana
ok guys, im new here so take it easy on me lol. 3 years ago i bought a 99 fld 120 with a 98 n14 celcet plus in it over the first 2 1/2 years the truck ran fine but the ecm had 2 million miles on it and the person i bought it from did not know how many miles was on the first rebuild. i was starting to get alot of oil and water leaks on the engine so i had it rebuilt on my terms before it went on me. i pretty much done a major over haul including the cam without pulling the block. the truck was still running fine when i took to the shop. the day i picked it up from the shop, i started having back fire issues, 10 to 15 times a day, i took it back to the guy that done the rebuild and he changed the cam position sensor and that did not fix it so he sent me a bill for 200$. im not here to bash the guy but i basically told him what to do with that. well any way i started changing parts and have been unsuccessful so far but i do have an issue that i found and maybe one of you might can help.
i have my own diagnostic laptop and was driving down the road and watching the parameters and noticed that my manifold boost pressue was staying on 6 inh20 but my mechanical boost gauge would go from 0 to 40 depending on the load. i replaced the manifold sensor and no changes on ecm, it just stays at 6. i checked the continuity of all 3 wires on the harness and all tested fine, i checked the voltage and 5v is what its supposed to be and was so my question is, could my ecm be bad or going bad? any help would be greatly appreciated
 

Truck Shop

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Dec 7, 2015
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I have a Cummins Celect and Celect plus troubleshooting and repair manual. It does not really have a tree
for backfire only misfire. As far as a boost sensor issue it has a short tree but all related in troubleshooting
section for connections and harness. The ECM section is actually brief, probably on purpose. But with that said
the fact that this engine was disassembled that far still setting in the rails tells me a very close inspection
of engine/injector harness needs to be done. Plus every ground connection and or grounds period.
There could be tons of fault codes logged, have you pulled all codes? And yes Those ECMs can and will go
bad, but the fact as you say it ran ok before rebuild then issues after tells me connections and or harness,
Check the harness leading to cam position sensor. In most cases on those old Cummins harnesses you will
need to remove the black loom and inspect all of it. I have found many injector harnesses on Celect engines
where the insulation covering the wire is full of cracks.
 

allen pardon

Member
Joined
Nov 27, 2021
Messages
20
Location
indiana
Thanks for the reply, if it was a ground issue, wouldn’t I have other things not acting correctly? I do not have any active codes unless I initiate it by unplugging something. I have done a cylinder test and I get the same results from each cylinder. I did video it but I’m not sure the file will upload. It like the fuel shuts off and back on instantly and cause the back fire. Is some cases it violent enough to kick cruise control off. The picture that is shown was at high idle and each cylinder responded the same way.
 

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Truck Shop

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Intermittent ground possibly. Beyond that It's hard to figure-Much easier if it just went dead-Intermittent
electrical issues with equipment especially a engine baked harness are problematic all on it's own. Truthfully
you need to hook up with OEM diagnostic equipment.
 

Truck Shop

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What was the boost psi before overhaul? One thing to check is the fuel shutoff solenoid. Plus what brand of
cam position sensor was installed.
 
Last edited:

allen pardon

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Nov 27, 2021
Messages
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Location
indiana
What was the boost psi before overhaul? One thing to check is the fuel shutoff solenoid. Plus what brand of
cam position sensor was installed.
Boost was 0 to 35 before overhaul. I had new turbo put on and now 0 to 40 and have only put Cummins parts on truck before the rebuild and after
 

allen pardon

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Joined
Nov 27, 2021
Messages
20
Location
indiana
Intermittent ground possibly. Beyond that It's hard to figure-Much easier if it just went dead-Intermittent
electrical issues with equipment especially a engine baked harness are problematic all on it's own. Truthfully
you need to hook up with OEM diagnostic equipment.
All of the harness was replaced 2 years ago along with the injectors
 

Truck Shop

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Ok-more info learned a shred at a time. You have new harnesses and injectors, all cummins parts including turbo.
Plus a new cam position sensor. Not much left.
Either-fuel shutoff solenoid {which won't leave a code} or ECM.

My shot at your dart board.
 

allen pardon

Member
Joined
Nov 27, 2021
Messages
20
Location
indiana
Ok-more info learned a shred at a time. You have new harnesses and injectors, all cummins parts including turbo.
Plus a new cam position sensor. Not much left.
Either-fuel shutoff solenoid {which won't leave a code} or ECM.

My shot at your dart board.
Thanks for the info. A dartboard it is, I have a buddy that has an 97 celect plus. Trying to get in touch with him and see if I can swap them out and see if I have the same problem,
 

westerner

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Sep 30, 2020
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Northern Arizona
We had 6 Celect II engines in our fleet for years. We lost some crank seals, a pantload of radiators (an International problem, not Cummins) and other than that, ALL other failures were ECM related.
Our best mechanic moonlighted hauling fuel for an outfit that ran dozens of these engines. Their parts room had a reman ECM on the shelf. YMMV
 

allen pardon

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Nov 27, 2021
Messages
20
Location
indiana
well guys i do believe that i have found my problem i hope, i pulled the manifold pressure sensor and hooked it back to the wiring harness and blew air into the end of the sensor and watched for a change in pressure on the laptop and nothing happened. since the continuity is fine on all three wires, i do believe that the ecm is the root cause of my problem. i want to thank all for your help and my last question is are there any recommendations on where to get the ecm repaired or to buy another one?
 

56wrench

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Dec 4, 2016
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alberta
No but just another point about potential corrosion between the fuel cooler plate behind the ecm. I've removed my ecm and cleaned this off a couple times over the years. I put some dielectric grease all over the plate last time to try to keep the moisture from getting in there but i haven't had it apart since. TRUCK SHOP, what's your solution for the corrosion or is this only more common in my area? I assume too much corrosion may cause the ecm to overheat?
 

Truck Shop

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Kind of a funny thread, the company I work for had 16 Celects-never lost a ECM and some
of those were well over 800,000.
I haven't found a decent aftermarket for ECM's personally. I have been told corrosion can cause a problem
but have never seen it myself.
 

mekanik

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Aug 20, 2015
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Canada's Northwest
It seems odd to me your getting 40 PSI boost on the manual gauge.
The ECM should cut the fuel way back if the boost sensor does not
see enough boost pressure. Are you sure you have the right sensor?
 

allen pardon

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Nov 27, 2021
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Location
indiana
Yes it is the correct sensor, I changed the sensor thinking the old one was bad. Everything worked correctly before the rebuild. The ecm was removed along with the cooling plate to paint the block. I know things can just go bad and maybe it did. The truck has over 2 million miles on it and I believe it is the original ecm so it might be warning me lol. I will take it out around Christmas and have it tested and fixed if needed. I believe the fuel is being miss calculated ant that’s why im getting the back fire and miss at times. You are correct that the boost sensor should read the same as the gauge but it is stuck on 6. When I unplug the sensor I do get a code thrown for low voltage to the sensor and when I plug it back in it goes to stored memory but I clear it any way
 

John C.

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My concern about the boost pressure is that it seems way high. 40 PSI converts to around 80 inches of mercury which is about twenty more than I've ever seen in any engine. The hottest engines I've worked on were the twin turbo K Cummins running at about 60 inches or or 30 PSI at full load. Those were in 50 ton Haulpak rock trucks and pulling around 750 horsepower. I can see 40 inches in a highway truck fixed up hot to pull the mountains out west here. No way could I understand 80 inches on any 855 Cummins pulling freight.
 
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terex herder

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Nov 10, 2017
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Kansas
Can you backprobe the wires on the boost sensor to see if the sensor readings actually change? I would confirm that before condemning the ecm.

The spark ignition side of my brain says either a intake valve isn't sealing or the spark plug wires are on wrong. Is it possible the wiring harness was put on the injectors wrong?
 

allen pardon

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Joined
Nov 27, 2021
Messages
20
Location
indiana
My concern about the boost pressure is that it seems way high. 40 PSI converts to around 80 inches of mercury which is about twenty more than I've ever seen in any engine. The hottest engines I've worked on were the twin turbo K Cummins running at about 60 inches or or 30 PSI at full load. Those were in 50 ton Haulpak rock trucks and pulling around 750 horsepower. I can see 40 inches in a highway truck fixed up hot to pull the mountains out west here. No way could I understand 80 inches on any 855 Cummins pulling freight.
When I had the engine rebuilt, I had them put the largest turbo made for the n14 on and the boost before the rebuild was 35. Not sure why you haven’t seen a higher boost, I’ve seen 50 on a highway truck so 40 is not really that much but back to the sensor. This problem started the day I took it from the shop, before a load was ever put on it. The man that rebuilt it said bring it back when a check engine light comes on. Well that hasn’t happened yet
 

allen pardon

Member
Joined
Nov 27, 2021
Messages
20
Location
indiana
Can you backprobe the wires on the boost sensor to see if the sensor readings actually change? I would confirm that before condemning the ecm.

The spark ignition side of my brain says either a intake valve isn't sealing or the spark plug wires are on wrong. Is it possible the wiring harness was put on the injectors wrong?
I done a continuity test on all three wires and they tested fine. I get power to the sensor but apparently the signal doesn’t return or it does return but the sensor signal doesn’t transmit, either way something is not clicking to make this ecm compute the correct boost pressure, I put air to the sensor but no changes were made to the ecm
 
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