Pacar MX Engine fuel mileage

Still didn't check whether it's a davco filter or not but engine responds the same with or without filter.

I've been testdriving with the computer hooked on today. It seems that fuel pressure fluctuates way too much. It goes up and down, even when idling. Mecanic is going to check tomorrow if other Paccar engines work the same as mine. Probably not, why else would there be a low fuel pressure code in the system.

While driving nothing showed in the computer when the red stop engine light came on and engine got derated. It just happens without leaving any traces in the computer. That Davies system is really great... NOT..!!

Hope to know more tomorrow afternoon...

 

fland, I'm sorry but that is not possible for the truck to show a stop engine light derating the motor and there be no history on it. Everytime there is any type of light or code come on in that engine, there is a logged event in the ECM hands down. Now, it is possible to have an electrical issue showing that you have an engine light coming on and off, but it would not derate and affect the performance of the truck as you are stating. It's also very possible for the mechanic to have told you that there was no trace of a code or event as there are some unscrupulous ones out there, but it probably due more to the fact that he doesn't know exactly how to fix the problem. Good luck, and maybe ask for a different technician to look at the truck if you don't feel good about the one on the truck now.

 

Hi Sako,

At my dealer there are two mechanics that work on the MX. I have full confidence in both of them, they know what they're doing. It's an oldfashioned shop, the driver can stay with his truck, talk to the mecanics and it's no problem when I'm reading the computer results over there shoulder and discuss it with them...

My truck shows two problems. When driving on a flat road, engine idling along, not having to work at all, the yellow check engine light comes on. It doesn't effect the driving, it's just there. It shows up in the history of inactive fault codes when they read out the computer. It was there for about 15 - 20 times. It reads out as low fuel pressure, but that's all the information it's giving.

The second problem occurs when the engine has to work. Driving with a loaded trailer and the road is going up a bit, turboboost comes up and the red stop engine light comes on (most of the time there's no yellow check engine light on). Light comes on, buzzer comes on, boost drops down 10 - 15 psi. Truck slows down and lots of times has to shift back. Same happens going up hill. Shift back, engine speed exceeds 1300 rpm and red light and buzzer come on, boost drops... There's no code showing on the dash, just the red light. There's nothing to be found in the history of the truck between active and inactive codes.

We've been testdriving, with the computer hooked on. First thing that surprised the mechanic was the fuel pressure jumping up and down, something he had never seen before. A little fluctuation is okay but not the way it worked in my truck. We didn't get the yellow light on while driving with a loaded trailer but several times the stop engine light came on, engine got derated. Nothing was showing in the computer, also it wasn't on a moment that there was no pressure at all.

Probablytoday the other mechnic will work on my truck on his day off. He is the one who has been working on my truck since the day I got it. My truck has never worked good, not enough power, slow respond to the throttle, bad fuel mileage. He has been working close with Paccar engineers to get the problem solved but they never could find anything wrong with the engine. Now, since two weeks the truck is working fine. Pulls better, more turboboost, quicker respond to the throttle and most important of all, 10 - 20 % better fuel mileage. Nothing has been changed to the truck, it just happened. Only at the same time this yellow and red light problem showed up.

BTW, both mechanics would agree with you for 100%. There should be something in the computer but there isn't...

Thanks for the respond..!!

 

About the Davies tool, my mechanics tell me the same. They don't both agree on the ISX having less problems though.

 

I had an issue with on of our DAF trucks a few years back.
It had the older 12,6l motor.
Quite similar problem but it would actually die at times.
Davie tool also did not pin point the problem.
If we put an external fuel pump at the pick up it would run fine.
Checked everything.
Changed all pipes , sealed everything.
In the end while servicing another truck with the same motor the mechanic noticed that there was a tube that came up internally through the cartage in the fuel filter.
He said he didn't see one in the problem truck.
We checked and sure enough this tube was not there.
If you did not know is should be there you would not miss it.
We got one and turned it in to where there were threads for it and the problem was cured.

Would a Fass not perhaps help.

 

fland, Im sure from your confidence in them that your tech's are smart guy's and maybe they have already checked this, but could they have missed something as minor as a lose fuel line sucking air or possibly a faulty fuel filter or transfer pump, maybe???? Hope you get it figured out soon. Am curios what they find as the final issue cause I have given this engine some thought. Be sure to let us know when they find the bugger causing the issue.

 

I will keep you posted, for sure..!!

Today they have been doing all kinds of tests with mechanic gauges, as far as I understood by phone. Mechanic showed up on his day off to do the tests, that is something i really do appreciate.

Everything has been sent to the Paccar service place, now it's waiting on them to come up with a way to solve the problem. Don't think these guys work on Sundays so don't expect to hear anything till Monday.

Better try to enjoy the weekend i guess...

 

http://www.fassride.com/

Had to figure out what a FASS is... Will keep it in mind king Q, thanks..!!

 

Hay fland, did they find the problem?????

 

Nope..!!

Mechanic working with Paccar engine support noticed some similarities in the data log after test driving. Seemed that bthe fuel lift pump had some difficulties in the 1300 - 1400 rpm area, same area where red light comes on and engine gets derated. After adjusting or changing things fuel pressure was good on all rpms. No lights during test drive so i picked up my truck yesterday evening.

Today i did a testrun with a loaded trailer and nothing seemed to have changed. I do realize though that the truck is driveable if grossweight is 80,000 lbs. You can drive it without going over 1300 rpm. That's hardly possible in my regular triaxle 100,000 gross work. I might need to jump to tandemwork for a while, cannot afford to have my truck in the shop for a couple of weeks.

I'll be in the shop again tomorrow, hope they can come up with something to solve the problem...

Thanks..!! more info in the weekend I hope...