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jeb · 04-16-2021, 05:39 AM

Our RV lost power coming home from a trip. Still ran smooth, but boost pressure was way down. It ended up being a bad transient suppressor. But after getting it home from the local Cummins shop, a 30 minute drive, the idle was rough, which was an issue we'd never seen before.

Took it back to Cummins and they are now telling me that they think it has a bad fuel pressure sensor. I'm really having a hard time believing them. It did not have an idle issue before they replaced the suppressor, but they're saying "It's just one of those things". I'm very mechanically inclined and their explanation just does not make sense to me.

A little history on it. We had a surging issue at full throttle on this motor years ago. Diesel shop (not the same one) said high pressure fuel pump. I argued with them too, but am not a diesel mechanic so agreed to the $6K fix. Which did not fix it. Turned out to be a $200 lift pump, which I'd suggested to them before approving the high pressure pump. We got some of our money back, but really got burned on that. So I'm not anxious to pay the Cummins shop $1700 to replace my fuel pressure sensor when everything I feel like I know says it's not going to fix the issue.

The motor has been reliable overall. The above are the only issues with it. 75K miles, of which we've owned it for 70K of. No mods, all stock.

I'm thinking of going elsewhere, but the two shops I've used so far are some of the best known shops in the area. Just looking for advice here, I guess. Or experience with a bad fuel pressure sensor and/or suppressor.

Xmcdog · 04-16-2021, 05:58 AM

I like simple fixes.
I change fuel filters as my first go to fix.

In your case I would be looking for another shop. They have already taken several thousand of your cash. Why give them a chance to take more?

jeb · 04-16-2021, 06:03 AM

Thanks for the reply. I should have mentioned both fuel filters are new, less than 500 miles on them. The first shop that ripped me off for $6K years ago installed a 2nd fuel filter, before the lift pump.

swampdog2 · 04-16-2021, 06:08 AM

Ask them if they put the relay on and it does not fix it will they put your old one back on and just charge you the labor ?

Wild Card · 04-16-2021, 07:39 AM

$1700 to replace the fuel rail pressure sensor? Holly Crap.

It's a $200 part and 5 minute repair.

Do it yourself.

Invest the rest of that money you would have wasted into a diag laptop and software of some sort so you can work on your own rig.

jeb · 04-16-2021, 07:58 AM

Yeah, I was wondering about that too. From what I've seen, that sensor does not seem hard to replace. I'll look into that more. I still think it would be a waste of time and money, though.

It's not throwing any codes. I have a code reader for it.

vito.a · 04-16-2021, 10:22 AM

I'd recommend you find a private diesel repair shop that will work on motor homes. The Cummins corporate shops are short on experienced techs and labor rates are sky high.

jeb · 04-19-2021, 12:01 PM

Quote:

Originally Posted by Wild Card

$1700 to replace the fuel rail pressure sensor? Holly Crap.

It's a $200 part and 5 minute repair.

Do it yourself.

It's not a common rail fuel system with a rail pressure sensor. It's CAPS.

Ray,IN · 04-19-2021, 05:30 PM

Quote:

Originally Posted by jeb

It's not a common rail fuel system with a rail pressure sensor. It's CAPS.

Yup; If the transient suppressor fails it usually causes the lift pump to fail and injector pump fuel distributor module to fail. Been there paid for that.
Cummins Great Plains Rock Island ILL diagnosed and replaced defective parts.

Ray,IN · 04-19-2021, 07:58 PM

At the beginning of this Cummins video you are looking at the 12VDC fuel distrubutor module.

https://www.youtube.com/watch?v=xp-YuZ5uQYY

Here are many more associated Cummins videos.

jeb · 04-20-2021, 02:25 PM

I appreciate everyone's input. Ray's experience helped me understand that a bad suppressor can take other systems out. Still kind of odd that the problem didn't start until after the suppressor was replaced, IMO. But I let the Cummins shop do the work and it seems to be running like a top again. Hopefully that is the last of it.

geordi · 04-20-2021, 02:36 PM

I replaced my fuel pressure sensor in a parking lot after seeing the pressure bouncing from low to high in rapid succession and getting codes for that. Wasn't hard and DEFINITELY was not worth $1700.

Glad your CAPS is working again, but I think they are playing "parts cannon" at your RV with your wallet as the gunpowder.

jeb · 04-20-2021, 03:27 PM

Quote:

Originally Posted by geordi

I replaced my fuel pressure sensor in a parking lot after seeing the pressure bouncing from low to high in rapid succession and getting codes for that. Wasn't hard and DEFINITELY was not worth $1700.

You did that on a CAPS system? I need to get more familiar with working on diesels. I rebuild and tune gas motors, but have never messed much with diesel. BTW, the bill ended up at $1400, so a little easier to take.

Quote:

Glad your CAPS is working again, but I think they are playing "parts cannon" at your RV with your wallet as the gunpowder.

Yeah, I hear you. But I have to say both things they replaced did fix the problem at hand. The question is, was the 2nd repair something they caused? I'm not a big believer in coincidence on this kind of thing. My experience says that if immediately after working on something it develops another problem, the work you just did is suspect. But Ray's experience does shed some light on it too. And I read in other places that you don't want to run very far on a bad suppressor.

geordi · 04-20-2021, 04:42 PM

Quote:

Originally Posted by jeb

You did that on a CAPS system? I need to get more familiar with working on diesels. I rebuild and tune gas motors, but have never messed much with diesel. BTW, the bill ended up at $1400, so a little easier to take.

Still $1100 in labor for something I did in about 2 hours, and that was with some farting around on the work b/c I wasn't 100% on where it was located. If I knew right where I was going and had the right wrench at hand like a shop tech should, it would have easily been faster.

The sensor is on the top of the pump between two hard lines and needed a special socket (sensor socket) to access.... BUT clearly was designed with a special special socket in mind b/c my regular sensor tool still didn't fit over the plastic connector. The new one had to get the plastic connector shaved a bit to make the tool work properly - that was some of the farting around.

But other than that - the access wasn't hard at all if you have access to the top of the motor.

Now I'm a bit dubious about this "transient suppressor" as a device, but clearly it does something on the engine. I'm not a diesel tech by training, but they aren't much different than working on a gas engine - simpler in a lot of ways though. The older they are, the less computer controls to mess with, but these CAPS systems STILL have a decent set of internal diagnostics that can speed you along to a solution WAY faster than you'd be without them. A good code scanner is essential for every owner to have. I use the Xtool HD900 which works well with our engines.