Help needed with my 5 cylinder CAT C-7

The friendliest place on the web for anyone with an RV or an interest in RVing!
If you have answers, please help by responding to the unanswered posts.
See posts with no answers
gmsboss1

gmsboss1

Well-known member
Joined
Mar 23, 2007
Posts
892
Location
Cary, NC
For the last year, my 2007 (mfg'd in 2006) C-7 has intermittently decided to run on only 5 cylinders. It sounds and shakes just like a 6 cylinder gasser with one spark plug wire removed.

Now for the strange/frustrating part.  While this is going on, I get no "Check Engine" light (or in my case a message in the Freightliner dash information panel) and when the CAT techs hook up their computers, there are no "codes" stored.  The condition is readily corrected by turning off the engine and restarting it.

Once restarted, the engine runs like it should.  The time periods between incidences has varied from one day to 8 months.  Lately, the occurrences have become more frequent, so I took the moho to Peterson CAT in Medford, OR, ever hopeful that somehow they could find a condition that could be fixed.

Unfortunately, everything checked out as absolutely normal.  We even took a test ride around town and up and down the interstate with the computer attached to the data port and nothing unusual appeared.

The current suggested approach is to, if possible, on the next occurrence take the coach to the nearest CAT authorized facility and get them to hook up the computer to see what is revealed while the 5 cylinder problem is "live".

It is hard to believe that the engine could run like this without "throwing a code" and that coach performs pretty well on 5 cylinders!

Anyone have a similar experience? Solution?

Don

 
I'm no diesel wizard, but it sounds to me like an injector for one cylinder is failing from time to time. Apparently re-starting the engine resets it for a time.  I don't think the ECM has any way of knowing is an injector does not "inject" when commanded to do so - there is no feedback mechanism that I know of. So, no code stored.
 
We had an injector fail and it did store a code, but there may be more than one failure mode.  It's almost certainly an injector, however.  Without a code, the hard part is determining which one.
 
It can also be an intermittent blockage in one injector or fuel supply line, I would think that would be an obvious "code" condition.>>>Dan
 
You may need to run it for a time before an injector will cause a code and it meay not be the code you expect when it does. I too suspect fule delivery but don't know the C-7 well enough to have any sugestions.

wayne
 
This whole thing gets curiouser and curiouser.

I made a similar post on the CATRVCLUB Yahoo forum and received the following:

Don,
>
> My C-7 did the same thing about a year. Everything was checked by Cat and
found no problem. I changed the fuel filters, check the ground wires on the
engine and chassis. All was tight.
>
> Finally found that the cable that went to the tow car had a loose ground wire.
Tighten it and have had not problem since. Hope this helps.
>

Here's what I wrote back after today's experiences:

I've got to admit I couldn't see anyway that your loose ground on
the cable to the toad could possibly affect the running of your engine --- until
today.

We have a problem with the cable to the toad in that the circuit for the right
turn signal is hard to make work. It will work when you jiggle it enough to
find the "hot spot".

Today we had 2 experiences with the 5 cylinder operation. The first was
crawling up a long grade on I-5 north of Grants Pass with the flashers on. Lots
of shaking, some loss of power, etc. We were approaching a rest area so I
turned on the right turn signal and went into the rest area.

I was contemplating unhooking the toad and returning the coach to Peterson CAT
in Medford so they could diagnose it in action when I realized that the engine
had stopped shaking. With the engine running smoothly, we decided to continue
our trip.

A couple of hours later as were driving about 30 mph through a small town, the
shakes started again. Again I turned on the right turn signal and again the
engine returned to normal operation instantly!

So, tomorrow I'll tackle the entire cabling between the coach and the toad.
Hopefully, I'll find something loose, tighten it and live happily ever after.

Will keep you posted.

Don

Can anyone explain why a loose ground on the toad cabling would cause this problem?

Thanks, Don
 
You have not been making proper offerings to the RV gods. ::)
 
    Don, it's all in how you hold your tongue.  8)  Hopefully that's the problem.  We've all had unexplained electrical problems and fixes, as you may recall my speedometer/odometer problems heading into Quartzsite last winter.  Several hours of fiddling, no loose wires found, but has worked fine since, for the 7,000 miles we put on since leaving AZ.  Go figure.  Hope you're as lucky.

Ed
 
I have worked with a lot of Cat marine engines and have found them to be very sensitive to electrical grounding issues.  A good possibility could be that with the loose ground on the toad cable and the proximity to the engine the power is finding a ground and it interferes with the engine.
 
For what it is worth it sounds like a 'hot bit', this is a term your Cat mechanic will never of heard of, it means a switch inside a IC (computer chip) in the control module for the engine (ECM) hangs up from time to time, or switches when it is not supposed to, this is typically caused by electrical noise in the power system of the vehicle. A loose ground could cause it as well as any electrical switch activation could cause it, such as a light switch or pump switch, they all cause noise in the system, the only fix is to replace the chip which typically means replace the ECM, you may find a bad ground that causes the problem  such as the trailer connection mentioned, but the ECM should be robust enough to handle any noise in system. The computer will not see this as a fail because it can not happen by design so no fail is assigned, another words it does not know it happened. If the monitoring system is smart enough a fail would probably occur sooner or later, such as cylinder misfire, any modern system can detect low power output from a cylinder and identify that cylinder as the problem, no feedback from injector is needed . The typical symptom of this problem is, it happens but no fail occurs on computer, works perfect most of the time, an example would be my wife turned on her fan and the engine started running rough or the transmission down shifted for no reason. Good luck
 
I am not up on the C series Cats in trucks and RVs but on the marine engines the battery ground cable went to a stud on the starter.  Our local Cat master tech had us run a ground cable from the ground stud on the starter to the bolt that had the ground wire from the ECM on it.  That cleared up the majority of the issues we were having.  I believe we ran a 6 ga cable. 
 
Thanks for all the useful suggestions.

Tonight I took the cable from the coach to the Tahoe apart and cleaned everything, including the sockets and pins on the male and female plugs -- including spreading the split pins a little.  When I plugged it together and Mary Ann turned on the turn signals, brake lights, and flashers, they all worked as they should with no wiggling and jiggling of the plug needed.

I ran out of time so the treatment of the grounds will wait until tomorrow.

We won't be driving anywhere until next Tuesday.  Will let you know how that turns out.

Thanks again.

Don
 
Bad grounding can cause weird problems.  Do not know if the TOAD issue would impact the ECM.  Since this is an intermittent problem it makes it difficult to trouble shoot.  But the intermittent does suggest a electrical problem.  If you know how do a volt drop test on the ground circuit's for the ECM/TOAD do it.

A point about CODES.  Not all mechanical issues will set a CODE.  So you can have a problem with out the CEL coming on or setting a code.
 
UPDATE

After all my work on the toad wiring and the grounds, I have succeeded in eliminating the "tight turn signal" cure. It now has no effect on the "5 cylinder mode".

OTOH, I'm now finding that the "5 cylinder mode" will self correct after a variable period. Also, the problem occurs less frequently.  Only once in the 150 mile trip from Lincoln City, OR to Salem, OR, once on the Salem to Walla Walla, WA leg and not at all on today's 320+ miles from Walla Walla to Missoula, MT.  Sigh.  Maybe I need to massage the grounds again, or something......

Don
 
You must log in or register to reply here.

Latest posts

Members online

Total: 923 (members: 40, guests: 883)

Forum statistics

Threads
131,960
Posts
1,388,212
Members
137,711
Latest member
crazymom
Back
Top Bottom