Community Forums

jmcgarvie · 11-15-2019, 10:17 AM

On our last couple of trips we noticed a very occasional, momentary, hesitation in our Cummins 5.9 ISB. It only lasts about a second or less, but it can be felt and heard. On our most recent trip, about 400 miles, it occurred maybe four times, twice within a couple minutes of each other.

Seems like a fuel issue, but I can’t be sure. It happens too fast for me to see any change in the boost.

Any ideas about what I should look for? I don’t want to have it quit altogether and strand us somewhere.

Thanks.

Jim M.
2002 Monaco Knight 30PBD

vito.a · 11-15-2019, 11:08 AM

You are probably right about it being fuel. First thing is to change fuel filters.

jmcgarvie · 11-15-2019, 11:11 AM

Quote:

Originally Posted by vito.a

You are probably right about it being fuel. First thing is to change fuel filters.

Thanks.

Milford 47 · 11-15-2019, 01:21 PM

If you have canister type filters dissect them and see what you have there, same on paper, look for abnormal material

If the filters appear to be very clean then you may have a fuel or lift pump issue

jmcgarvie · 11-15-2019, 01:33 PM

Quote:

Originally Posted by Milford 47

If you have canister type filters dissect them and see what you have there, same on paper, look for abnormal material

If the filters appear to be very clean then you may have a fuel or lift pump issue

Great suggestion, thanks.

imnprsd · 11-17-2019, 05:38 AM

You might read this thread:

http://www.irv2.com/forums/f123/cumm...cm-469287.html

And you will find my comments about tightening your lift pump bolts.

Then you will find a link to upgrading to a FASS TS Fuel pump if you decide to go that route.

These links speak to many other symptoms you may or may not be heading towards. TBD. Also, I only have experience with Cummins-ISC-8.3L engines, but I think your Injection Pump is very similar to my CAPS pump. Do you have a V44 or CAPS or other?

Anyway, you probably have a lift pump and thus you may find you can fix your engine hesitation by just tightening 3-lift pump bolts. ...And all you need to do is access the top of your engine on the passenger side.

jmcgarvie · 11-17-2019, 06:45 AM

Quote:

Originally Posted by imnprsd

You might read this thread:

http://www.irv2.com/forums/f123/cumm...cm-469287.html

And you will find my comments about tightening your lift pump bolts.
...
Anyway, you probably have a lift pump and thus you may find you can fix your engine hesitation by just tightening 3-lift pump bolts. ...And all you need to do is access the top of your engine on the passenger side.

Thanks for that excellent information! I don't know what kind of injection pump I have, but I do know I have a lift pump similar to yours. I will try tightening those bolts, although my symptoms are not like yours or the OP of that thread... at least not yet!

imnprsd · 11-17-2019, 10:35 PM

Right... these symptoms progress over time. However, if you ever see your engine light come on and then go off, these "soft codes" are logged in you ECM and you can look at your code history... So the next time you get a engine hesitation, note the date and time and then compare this to the engine soft code and you may find the part you need to replace... before you get a hard failure and need a tow.

If you don't have fuel deliver concerns (vacuum falling below minimum -5 PSI to your injection pump) then you might have electrical problems... an "open" or loose connection; or a ground problem.

Electrical "spikes" can cause momentary engine hesitation too. This is what your ECM Suppressor Diode is supposed to protect against. But what is causing the electrical spike is Low Fuel Pressure to your Injector pump... and that maybe due to a vacuum leak... because you have 3 loose lift pump bolts!!!

...And/or you need to also read this thread about changing your key ignition switch.

One symptom of a bad ingnition switch that is supposed to send a clean +12V to your ECM... is a "sloppy" key cylinder, but this is not always the case. My key cylinder was solid, but the key switch was rotating. So eventually, I decided to replace it; about the same time I was trying to figure out my engine stall condition.

(Preventative maintenance is hard to do sometimes, but there are a number of inexpensive parts you can replace to void a hard failure and tow for another 75,000 miles.)

http://www.irv2.com/forums/f123/why-...ch-421913.html

==>>> BE SURE TO CHECK YOUR ENGINE GROUND CABLE TOO! ...And your story reminds me to add additional ground cables to 3 different spots in my engine to be sure I always have a "good ground." How to ensure you have a "good ground You run 3 different ground wires as follows.

1) Battery negative to chassis ground. (4 gauge or bigger)
2) Alternator Housing to Chassis Ground. (4 Gauge)
3) Engine Block to Chassis Ground. (4 gauge)

Good luck to you and keep us posted if you find the problem.

jmcgarvie · 11-18-2019, 08:00 AM

Quote:

Originally Posted by imnprsd

Right... these symptoms progress over time. However, if you ever see your engine light come on and then go off, these "soft codes" are logged in you ECM and you can look at your code history... So the next time you get a engine hesitation, note the date and time and then compare this to the engine soft code and you may find the part you need to replace... before you get a hard failure and need a tow.
....

Thanks for all the good suggestions! And I checked out your message about ignition switch replacement. Who knew?? That seems like a good thing to do if for no other reason than mine is 18 years old!

imnprsd · 01-21-2020, 04:36 PM

This is an interesting video on a weak/bad electrical connection to your CAPS fuel solenoid that causes the engine to hesitate for a second.

My guess is that temperature can also cause a similar result.

https://www.youtube.com/watch?v=8QJHQ0B7294

trampsrv · 01-21-2020, 04:47 PM

do you notice if it takes longer to start after sitting?

jmcgarvie · 01-22-2020, 07:13 AM

Quote:

Originally Posted by imnprsd

This is an interesting video on a weak/bad electrical connection to your CAPS fuel solenoid that causes the engine to hesitate for a second.

My guess is that temperature can also cause a similar result.

https://www.youtube.com/watch?v=8QJHQ0B7294

Thanks. Very interesting; I will save for future reference. But in our particular situation we were fortunate in that the problem went away when I replaced the fuel filters.

Jim M.
2002 Monaco Knight

jmcgarvie · 01-22-2020, 07:20 AM

Quote:

Originally Posted by trampsrv

do you notice if it takes longer to start after sitting?

Not in this case.

Ljwt330 · 01-22-2020, 08:53 AM

Just a "heads up."

I don't know what chassis you have, buy your vintage ISB was sometimes equipped with an in-line "filter" which was buried in the hoses and wire looms above the right rear wheel, along the frame. This filter is really more of a screen, but not only is it well hidden, it is often not even known by those who service the coach, specifically the shop mechanics. Some of these filters are never changed since leaving the factory so they often clog and begin starving the lift pump for fuel. There are threads in which over $3k was spent trying to solve a problem like yours, and it turned out to be that clogged in-line filter. My previous coach, a 2007 on a Freghtliner chassis with the ISB, had that filter.

If you think your coach may have that filter buried in the mess of lines along the frame, let us know and I'll try to link the thread where this is described, in detail.