Journey with Confidence RV GPS App RV Trip Planner RV LIFE Campground Reviews RV Maintenance Take a Speed Test Free 7 Day Trial ×
RV Trip Planning Discussions

Go Back   iRV2 Forums > THE CHASSIS CLUB FORUMS > Freightliner Motorhome Chassis Forum
Click Here to Login
Join iRV2 Today

Mission Statement: Supporting thoughtful exchange of knowledge, values and experience among RV enthusiasts.
Reply
  This discussion is proudly sponsored by:
Please support our sponsors and let them know you heard about their products on iRV2
 
Thread Tools Search this Thread Display Modes
 
Old 09-14-2017, 05:20 PM   #1
Senior Member
 
Join Date: Feb 2016
Posts: 309
3126E No Start RESOLVED

Hello Folks,
Getting our FL chassis Discovery ready for a trip to find it started but kicked, bucked and idle was ruff. Hit the accelerator pedal and it ran smooth at 1,500 rpm. So, a definite fuel supply issue, I thought! prefilled a new fuel filter installed and same issue. Attempted to start her back up a third time to not even fire this time. Wonderful!!!!

Noting, this engine has had pampered life, 44,000 miles, having oil changes at 7,500 miles along with fuel filter. Stored inside, washed and waxed annually. My heart sunk.

Being an engineer I put my experience to work searching the internet, calling FCC, calling local CAT dealer to find one answer: "Tow it in". What? seriously, I was a little put back that these "support" resources wouldn't take a moment to listen. I should clarify, FCC did listen to my pain but really had no experience with a 3126 to help. CAT, I couldn't get past the "gate keeper" to speak with a guy that probably has some insight.

SOLVED!! I researched the fuel handling system on the internet and how the system functions regarding several sensors feeding back to the ECM.
Not having a code reader to pull any codes, I studied how the system functions and what could cause this condition. (Let me say that this engine has never even farted. It has run like a dream from day one) That said, it may not be your specific issue but well worth testing without spending a dollar.

Cat uses a IAP sensor (injection activation pressure) to monitor the high pressure oil that opens the injectors. The HEUI pump takes engine oil at 60-65 psi and amplifies it to 1,200 psi at starting to 4,000 psi relative to the engine demand/load. The IAP sensor feeds back to the ECM indicating that the pressure is at desired pressure called by the ECM. The IAP is supplied with 5 vdc and feedbacks a linear voltage to the ECM. The IAP is a fancy name for a pressure transducer. IF and when the IAP fails to feedback to the ECM, Fuel is shut off to the injector supply port.

So, I unplugged the IAP. This "fooled" the ECM to think pressure was low. She started up and idled perfect. (((NOTE: I would NOT advise extended running/driving because the ECM will not provide proportioning fuel to the system under high load conditions))) However, this proved the sensor was defective. Went to my local cat dealer, picked up a new IAP sensor and oring.
Took ten minutes to install. Our baby is back to purring. $165.00 w/tax.

Location: The IAP is located on the front left side of the engine and screws into the head just to the right of the HEUI pump. Has a 10" wire harness with a triangular 3 pin connector. Google "3126 sensor locations" for some clear pictures if in doubt.

I hope this helps many that may some day experience this issue.

Travel Safe.
__________________
George and Diane, 2004 Discovery 39S pushed by our Keywest CC w/115 Johnson
discovery39s is offline   Reply With Quote
Join the #1 RV Forum Today - It's Totally Free!

iRV2.com RV Community - Are you about to start a new improvement on your RV or need some help with some maintenance? Do you need advice on what products to buy? Or maybe you can give others some advice? No matter where you fit in you'll find that iRV2 is a great community to join. Best of all it's totally FREE!

You are currently viewing our boards as a guest so you have limited access to our community. Please take the time to register and you will gain a lot of great new features including; the ability to participate in discussions, network with other RV owners, see fewer ads, upload photographs, create an RV blog, send private messages and so much, much more!

Old 09-14-2017, 05:33 PM   #2
Senior Member
 
Rook's Avatar
 
National RV Owners Club
Solo Rvers Club
Freightliner Owners Club
Join Date: Mar 2011
Location: FT for 6 years, NW in the summer, S in winter.
Posts: 1,173
GREAT informative post! Thank you George. Rook
__________________
When you get a chance to dance, or sit this one out......I hope you DANCE!

98 National Tradewinds 7370, powered by a 3126B 300HP CAT Turbo, Freightliner XC chassis
Rook is offline   Reply With Quote
Old 09-14-2017, 05:43 PM   #3
Senior Member
 
les.warden's Avatar
 
Tiffin Owners Club
Join Date: Nov 2011
Location: Foley, AL
Posts: 1,093
3126E No Start RESOLVED

I don't have a Cat, but am the Engineering type (Electronics, WAN, LAN). While some probably glazed over at your detailed explanation, I found it quite an interesting read. Good details, troubleshooting, diagnosis, and solution. Good job! [emoji106]
__________________
Les & Pam Warden
(Tiffin) 2017 Phaeton 40QBH; 2023 Wayfarer 25RW (coming soon)
2016 Jeep JKUS with Ready Brute Elite towbar
les.warden is offline   Reply With Quote
Old 09-14-2017, 05:57 PM   #4
Senior Member
 
Unplanned Tourist's Avatar
 
Winnebago Owners Club
Workhorse Chassis Owner
Join Date: May 2016
Location: Kamloops, BC, 60 miles from the Center of the Universe according to the Rinpoche, of the SF monks.
Posts: 7,321
Good job on the trouble shooting and repair! You wouldn't believe how many "techs" dive in and just start changing out parts when a rig comes into the shop! I used to just about pull my hair out at times. I would check the logged codes and tell them where to start looking and the next thing I knew, they were coming back from the parts counter with compleatly wrong parts.
Sorry about the rant, am I ever glad to be retired!
Happy Glamping.
__________________
Happy Glamping, Norman & Elna. 2008 Winnebago Adventurer 38J, W24, dozens of small thirsty ponies. Retired after 40 years wrenching on trucks! 2010 Ford Ranger toad with bicycles or KLR 650 in the back. Easy to spot an RVer, they always walk around with a screwdriver or wrench in one hand!
Unplanned Tourist is online now   Reply With Quote
Old 09-14-2017, 06:50 PM   #5
Senior Member
 
Skip426's Avatar


 
Join Date: Apr 2011
Location: Powell River, B.C.
Posts: 31,311
If you posted your problem originally ; I'm sorry I missed it .
Because I have on file these pdfs that although for a 3126B , probably would have helped you with your problem.
I hope every one reading that has either version B or E , downloads them and has them handy ; JUST in CASE, they are faced with the same problem.
Attached Thumbnails
Click image for larger version

Name:	IAP%20Location (640x530).jpg
Views:	2168
Size:	190.5 KB
ID:	176620  
Attached Files
File Type: pdf 3126B Heui Engines.pdf (168.7 KB, 682 views)
File Type: pdf 3126B no start.pdf (130.3 KB, 665 views)
__________________
99DSDP 3884, Freightliner, XC, CAT 3126B, 300 HP /ALLISON 3060
2000 Caravan toad, Remco & Blue Ox.
Skip426 is offline   Reply With Quote
Old 09-14-2017, 08:09 PM   #6
Senior Member
 
Join Date: Feb 2016
Posts: 309
Thanks Skip. Nice graphics.
I always thought these engines used high pressure fuel to the injectors. I learn something new every day!!!!
__________________
George and Diane, 2004 Discovery 39S pushed by our Keywest CC w/115 Johnson
discovery39s is offline   Reply With Quote
Old 09-14-2017, 09:24 PM   #7
Senior Member
 
Skip426's Avatar


 
Join Date: Apr 2011
Location: Powell River, B.C.
Posts: 31,311
Quote:
Originally Posted by discovery39s View Post
Thanks Skip. Nice graphics.
I always thought these engines used high pressure fuel to the injectors. I learn something new every day!!!!
I spent 14 years before retirement , doing Dodge/Cummins repairs .
When I bought the coach with the Cat ; I thought " It can't be that different ". Epic wrong!
Over the past 8 years , I've collected a lot of info on this Cat.

BTW: If your coach has the hydraulic pump mounted to the back of the air compressor , the oil pressure sensor is is re-located with a hose "T'd" off the side of the engine at the location shown and mounted up on the intake manifold.
__________________
99DSDP 3884, Freightliner, XC, CAT 3126B, 300 HP /ALLISON 3060
2000 Caravan toad, Remco & Blue Ox.
Skip426 is offline   Reply With Quote
Old 10-09-2019, 02:39 PM   #8
Junior Member
 
Join Date: Jul 2013
Posts: 3
Not at all too techie! After trying everything I could think of or find elsewhere on the web, disconnecting the IAP allowed the 3126 to start immediately, but run just a little ragged.

Reconnecting the IAP afterwards, while running, the engine smoothed out and continued to operate normally. Allowing it to run for 20 minutes, it started right back up. 2 hours, $0. Lucky me. Problem Solved.

BIG THANKS out to discovery39s for the solution, and to skip426 for the critical diagram!

Karl
HKHeidemann is offline   Reply With Quote
Old 10-10-2019, 06:33 AM   #9
Senior Member
 
gatorcq's Avatar
 
Freightliner Owners Club
Join Date: Apr 2004
Location: Show Low Az
Posts: 1,321
When removing the IAP sensor, it goes into LIMP MODE.. You can drive a long way in Limp Mode. RPM is limited to 1700 RPM.
__________________
Dale&Susan, 08 Alfa Gold, DaGirlsRv Blog
2015 F-150XLT_2000W Solar_800 AmpHr Lithium
Magnum_MSH 3012 & PT100
gatorcq is offline   Reply With Quote
Old 10-13-2021, 03:55 PM   #10
Junior Member
 
Join Date: Nov 2020
Posts: 3
IAP Sensor: Years later and still very helpful post!

Almost identical situation and the replacement of the IAP solved our issue. GREAT POST AND VERY THANKFUL it was here.

Couple of items to add...I do have the ScanGauge and the code ID 164, FM 03, CNT 36 appeared. Code 164 03 relates to IAP (Injection Actuation Pressure) sensor. Maybe helpful tidbit, I understand this is also a reference to the ICP (Injector Control Pressure) sensor. For Caterpillar, it is called IAP.
Now, there was another code of engine RPM (ID34), but I know now was thrown due to the engine not starting with the defective IAP.

So update on the price was around $187, and get the $6 "O" ring! After taxes was around the $211 mark. Fairly easy to replace, once you get to the engine from the bedroom!

Most important....we are thankful for the original post. Saved us a tow bill and shop bill!!
Grogu is offline   Reply With Quote
Old 10-13-2021, 06:30 PM   #11
Senior Member
 
Skip426's Avatar


 
Join Date: Apr 2011
Location: Powell River, B.C.
Posts: 31,311
Quote:
Originally Posted by Grogu View Post
Almost identical situation and the replacement of the IAP solved our issue. GREAT POST AND VERY THANKFUL it was here.

Couple of items to add...I do have the ScanGauge and the code ID 164, FM 03, CNT 36 appeared. Code 164 03 relates to IAP (Injection Actuation Pressure) sensor. Maybe helpful tidbit, I understand this is also a reference to the ICP (Injector Control Pressure) sensor. For Caterpillar, it is called IAP.
Now, there was another code of engine RPM (ID34), but I know now was thrown due to the engine not starting with the defective IAP.

So update on the price was around $187, and get the $6 "O" ring! After taxes was around the $211 mark. Fairly easy to replace, once you get to the engine from the bedroom!

Most important....we are thankful for the original post. Saved us a tow bill and shop bill!!
Glad these old posts are coming up in the search feature , one thing to add , after another member went through 3 , " O " rings , do not over torque the sensor . Spec for tightening is in this page from the manual . If you think you may have over torqued the sensor , grab another O ring just in case .

Yes the spec is " in lbs " so easy to over tighten and split the O ring .
Attached Thumbnails
Click image for larger version

Name:	Sensor torque.JPG
Views:	229
Size:	185.1 KB
ID:	346034  
__________________
99DSDP 3884, Freightliner, XC, CAT 3126B, 300 HP /ALLISON 3060
2000 Caravan toad, Remco & Blue Ox.
Skip426 is offline   Reply With Quote
Old 10-13-2021, 09:17 PM   #12
Senior Member
 
astrnmrtom's Avatar
 
Join Date: Sep 2013
Location: Pacific Northwest and Arizona
Posts: 2,043
Another thing that can be tried is to remove the sensor and flush it out with carburetor cleaner and re-install. This can be a side of the road repair to get you going again in a pinch. The sensor can get clogged and flushing it can clean out the gunk and get it working again.

It's important to remember that if you ever get it towed to a shop and they tell you it's a failed HEUI pump, make sure they've checked the IAP sensor FIRST before paying to have the pump replaced.
__________________
Tom and Pris M. along with Buddy the 18 year old Siamese cat
1998 Safari Serengeti 3706, 300HP Cat 3126 Allison 3060, 900 watts of Solar.
Dragging four telescopes around the US in search of dark skies.
astrnmrtom is offline   Reply With Quote
Old 09-12-2022, 12:34 PM   #13
Junior Member
 
Jbull's Avatar
 
Join Date: Feb 2016
Location: League City, Texas
Posts: 9
I know this is an old post but I owe you a big thank you. I just went through the same situation with my IAP sensor. Thank you for taking the time to document and to share your experience. No telling how much time and money you saved me. I’m back on the road and all is well. Thanks again.
__________________
2004 Coachmen 40' Sportscoach Elite 401TS Cat 330HP 3126
Jbull is offline   Reply With Quote
Old 09-12-2022, 08:58 PM   #14
Senior Member
 
Skip426's Avatar


 
Join Date: Apr 2011
Location: Powell River, B.C.
Posts: 31,311
Quote:
Originally Posted by Jbull View Post
I know this is an old post but I owe you a big thank you. I just went through the same situation with my IAP sensor. Thank you for taking the time to document and to share your experience. No telling how much time and money you saved me. I’m back on the road and all is well. Thanks again.
Jbull ; your signature line shows Cummins engine , have you traded coaches and not updated your signature line ??
__________________
99DSDP 3884, Freightliner, XC, CAT 3126B, 300 HP /ALLISON 3060
2000 Caravan toad, Remco & Blue Ox.
Skip426 is offline   Reply With Quote
Reply

Tags
no start



Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
wont start hot may be resolved Dupdyke Monaco Owner's Forum 2 05-04-2016 04:15 PM
A cold start/running issue on a Cat. 3126E RCtime Caterpillar Engine Forum 18 11-02-2011 01:25 PM
Cat 3126E Won't Start Leon G Class A Motorhome Discussions 3 08-24-2011 11:20 AM
3126E Hard start hot Vintage Caterpillar Engine Forum 5 06-20-2011 05:36 PM
Finally got air filter water ingestion issue resolved KTYSTR Newmar Owner's Forum 4 01-01-2007 12:20 PM

» Featured Campgrounds

Reviews provided by


All times are GMT -6. The time now is 11:25 AM.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2024, vBulletin Solutions, Inc.