Community Forums

olsbergma · 02-06-2022, 03:44 PM

I am having an issue with my RV that causes the coach to not be able to maintain speed on any incline and falls to about 40 mph. If I push on accelerator i am usually limited to around 2000 rpm and experience what i call chattering or shuddering until i let off the accelerator. This usually starts happening after driving about 30 or 40 miles. Any suggestions as to what could be wrong. This is a freightliner chassis with 300hp CAT 3126b and Allison 6 speed transmission.

Thanks!

grldst · 02-06-2022, 05:36 PM

Fuel filters, air filter???? What gear are you in at 40 mph? Do you have a guage that reads turbo boost?

You should be able to climb a 5-6% grades at 55mph..

olsbergma · 02-06-2022, 08:22 PM

Quote:

Originally Posted by olsbergma

I am having an issue with my RV that causes the coach to not be able to maintain speed on any incline and falls to about 40 mph. If I push on accelerator i am usually limited to around 2000 rpm and experience what i call chattering or shuddering until i let off the accelerator. This usually starts happening after driving about 30 or 40 miles. Any suggestions as to what could be wrong. This is a freightliner chassis with 300hp CAT 3126b and Allison 6 speed transmission.

Thanks!

Correction this is a 98 not a 89,

olsbergma · 02-06-2022, 08:32 PM

Gridst, Can fuel filter cause this? Air filter was replaced about a year ago and very little use since then. I experience slow acceleration from stop light and can maintain 55 if no hills. The travels include rolling hills and typically start shuddering after i have driven about 30 or 40 miles. As for gauge, on the dash i do not have turbo boost. Besides standard gauges, i have a Scan-D gauge that i can look at if there is a setting to monitor.

hex nut · 02-07-2022, 10:44 AM

Your issue is most likely fuel related. Change fuel filters first (you may have two, one on the engine and a water separator mounted somewhere in the fuel supply). Considering the age of your coach, I would suspect you have leaking fuel lines or connections. Your fuel pump is on the engine and it "sucks" fuel from the up front tank. If any of your fuel lines or connections have small leaks, they will allow air into the system. The harder you accelerate, the more air is sucked into the system. You will not see any fuel on the outside since there is no pressure to expel fuel. HEUI systems like the CAT 3126 really do not like air in the system, so you really need to find and repair the leaks. A thorough inspection of your fuel lines is in order. Your fuel lines are probably "push to seal" plastic connectors. I would recommend replacing them with brass compression fittings. Good luck.
Richard

Jon_C · 02-07-2022, 11:14 AM

The scan gauge should be able to show turbo boost, mine does on my 98 but its Cummins. If your having a fuel issue it wont make much boost and will be down on power. Air Leaks in the charge air cooler or associated piping can also cause low boost. Im not sure how much your cat should make but id think at least 20psi under load while driving

grldst · 02-09-2022, 09:18 PM

I have a ScanGuage D on my Cat 3126b. It will show turbo boost but you have to select it. Pulling a grade you should show 20-25 lb pressure.

Yes a bad/dirty fuel filter will cause your issue.

RileyRRC · 04-21-2022, 12:29 PM

My C7 is doing the same thing. Replaced the fuel filters and still in some limited mode. There are no check engine lights or codes. Starts fine, just a very limited performance from a stoplight and shuddering at a speed of 50 mph. Did you figure out what the issue was with yours?

Jim_HiTek · 04-21-2022, 12:41 PM

After checking the other things mentioned: You might check the ECM and TCM device connections on the engine and tranni. Remove the big multi-wire connectors, spray with contact cleaner, slather with dielectric grease and replace.

Skip426 · 04-21-2022, 12:41 PM

Quote:

Originally Posted by RileyRRC

My C7 is doing the same thing. Replaced the fuel filters and still in some limited mode. There are no check engine lights or codes. Starts fine, just a very limited performance from a stoplight and shuddering at a speed of 50 mph. Did you figure out what the issue was with yours?

Riley ; Welcome to iRV2

Can you complete the " About me " section of your profile , or add a " Signature Line " so members will know what year and chassis your coach is built on .

Your problem could be related to a turbo waste gate being stuck open or your exhaust brake not completely opening , after use ; or other more serious turbo problems.

ftodaro · 04-25-2022, 06:39 PM

Quote:

Originally Posted by Jim_HiTek

After checking the other things mentioned: You might check the ECM and TCM device connections on the engine and tranni. Remove the big multi-wire connectors, spray with contact cleaner, slather with dielectric grease and replace.

Just make sure you use the dielectric grease as in insulator of your connections not a conductor or you will create more problems than you have now. It should not be used between the contacts.

rallain · 05-12-2022, 02:21 PM

Pick up bad fuel I poured Howes injector cleaner runs like a rocket now dirty injectors would not shift to 5 or 6 gears felt like I was running out of fuel

olsbergma · 05-14-2022, 11:17 AM

Quote:

Originally Posted by grldst

I have a ScanGuage D on my Cat 3126b. It will show turbo boost but you have to select it. Pulling a grade you should show 20-25 lb pressure.

Yes a bad/dirty fuel filter will cause your issue.

I changed the fuel filter and water separator and runs like a champ now. Thanks!

Skip426 · 05-14-2022, 11:40 AM

Quote:

Originally Posted by olsbergma

I changed the fuel filter and water separator and runs like a champ now. Thanks!

Great to hear that you've got things fixed ; just thought I'd post something that I'd forgotten earlier .
All diesel pushers will have a fuel filter ; most will have two ; some will have three , as I'm sure mine did and a PO ( Previous Owner ) removed .
The fuel system strainer , is hidden in the wiring harness above the passenger side rear air suspension bag and is detailed in this diagram ( from Freightliner) and picture ( first picture from another member showing the strainer ) and second of my chassis showing fittings in the same location , that lead me to believe one of the two POs had removed the strainer .
Next time your under the coach have a look for this strainer , if it's not there , your good , if it is there change or remove it . My chassis has 12+ years without the strainer and is doing fine .

The light brown plastic lines in the first photo are the fuel supply and return lines , in the second , my supply and return lines are blue.