Well, if you have followed my recent posts, I've been noting a marked drop in power/economy, coupled with the fact that the truck will no longer build EGT's above 1100 or so no matter what. So, I take it to the dealership for an evaluation. Well guess what, according to their whip-zammy computer, there is nothing wrong. "Rail pressures are exactly where they need to be" is what the tech tells me. He says if rail pressure is good, the lift pump is fine...

Here's my question: Does the fuel system operate differently under load than during a test like this? He suggests taking it out with a trailer hooked up, all the while using his scan tool to see what might be happening. I think this is a good idea, but does it really stand a chance of showing anything different?

 

Yes.

More technicians should use this approach.



phox

 

I have question regarding the "Rail pressures are exactly where they need to be" is what the tech tells me. He says if rail pressure is good, the lift pump is fine..." quote.

The lift pump is what pulls fuel from the tank and supplies the CP3 with fuel. If it was weak how would that effect the pressure on the Pressure side of the CP3? I could see a issue if the truck was at WOT or underload where the lift pump might not be able to supply enough fuel to "keep up" with the fuel demand of the engine. Even than I wonder if you would see a pressur drop? I think you would be more likely to starve the engine of fuel. This is my first deisel so I am probley just missing something here or do not understand the complete workings of the fuel system.

 

They are just saying what they've been told to say,
because research shows the customer accepts it and moves on.

(kinda like the salesmen back in mid 2002 talking up the new "Hemi Diesel" coming out in the 2003 trucks)

A large number of dealer techs know less about these engines than we, the laymen, know.
If their scanning equipment doesn't detect a problem, then the problem cannot exist,
it must be all in the customers head.

This tech sounds a couple steps above most though, as he is willing to have his scanner hooked up under real world conditions, not just revving it in the garage.
Still, he is too reliant on the computer.

There are some quite competent dealer techs out there, a couple of them on this board even.


phox

 

Well, went for the test flogging with the tech this morning. The truck did exactly what it has been doing, i.e. meager pulling power and EGT's that would not go over 1150. I was pulling my 7500lb (verified many times at a local DOT scale) toy hauler behind me, attempting to maintain 65mph up a short 5% grade. Immediately had to grab 5th, and it would maintain about 62 or so but nothing more. EGT's wouldn't go over 1150, and that was straight to the wood. The tech was plugged into the diagnostic port with the scanner, and was reading the variables off as we drove. It seems the truck was putting out "100% power", 22000psi of fuel rail pressure, and 26psi of boost, all read straight off the scan tool. All other sensor readings were within target as well. It seems the scanner produces and displays target values, and then it's up to the tech to monitor the actual values produced and compare to these target values. My truck was right on the target values, variable for variable, time after time (we were gone for over an hour...). Basic diagnosis, 7500lbs is too much for a 305/555 Cummins

Guess I'll have to buy a Hemi...

 

I'm no expert, but I agree that something is not right. My '99 would do better then that when it was bone stock.

 

Toby,
Only thing I can think of is the lift pump is getting weak.
Can the dealer test the fuel pressure going into the CP3?

MikeyB

 

Thats not rite. You should have no problem driving whatever speed you want with 7500 pounds back there. I have had just short of 12000 pounds back there and can tow that around in 6th at any speed I want without any problem. Granted its flat as a bord here but I even passed a few times without down shifting so 7500 should be absolutely no prob. Be persistant and make them understand something is wrong. If it comes down to it ask to use a used one off the lot to tow your trailer and repeat the test to compare differences. If they wont let ya find a freind or make one with someone that has a cummins you can borrow to repeat the test.

 

I agree with bkrukow. I towed a 6700lb TT accross country at normal highway speeds and above without any problems or slow downs and I was driving a stock 235hp (Cali) CTD. If your 305hp Handshaker could not handle the load you put behind it @7500lbs then I guess I got the better deal with the 235hp engine

 

tobyw,

I'm assuming that you have no engine mods and 3.73 gears with the 315's. Here 's my experience. 3.73 geared dually, stock tires, stock fueling, and an 9000 lb empty ENCLOSED gooseneck (brick wall). On 5% and 6% grades I'll slowly lose speed until I drop to 5th and then I can accelerate until an upshift is needed. I don't because I know that even with stock tire sizes I will just lose speed again in 6th. I can duplicate this with both the '03 and the '04 at work. We also have a dmax and a powerstroke. Same results with them but you have to hold both of them at redline to maintain the speed that the cummins will hold in 5th. I think that there is a LOT of hype and exaggeration when it come to the stock towing ability of these trucks, just like fuel mileage claims. You guys can flame me all you want. I spend most of my time on the road and towing heavy. Way more time than most normal people do and I'm constantly passing stock trucks with big 5vr's going between 45 and 55 mph up grades. Don't tell me that they're going 45 mph because they want to. In stock form these trucks aren't as impressive as some would like them to be. On the other hand 20 years ago you didn't see 1/10 the number of trucks on the road trying to tow 10k to 15k like it was nothing. The hp to weight ratio just isn't there without mods and the larger tires are hurting your overall gearing even more. In the last year I can count on two hands the number of trucks that were truly towing heavy that could stay with me running up a grade at even 65 mph. They were all bombed and so am I.

JMHO

Richard

 

I believe his statement was probably in reference to the actual rail psi was meeting the target psi that the ecm was commanding. If you have a weak lift pump, or a pressure limiting valve that is leaking slightly it can cause the rail psi NOT to reach target and that may cause some drivability issues. If I were the tech testing your truck I would have rounded up a set of stock size tires.

 

I can certainly attest to how well these trucks can pull, and no, 7500lbs shouldn't be slowing me up like it is. I've personally had over twice that behind me for several extended trips through the moutains of Oregon, Idaho, Montana, Utah, and Colorado and never expereinced what I am now... But I agree 100% with Gypsyman, there are a lot of "fishin' stories" being tossed around out there about the capabilities of these trucks in stock form. All I know is that it will no longer do what it used to do...

Which brings me back to what in the world could be wrong? The tech says the CP3 will build rail pressure with whatever fuel it's getting, but if the transfer pump is failing and not supplying enough volume, you would see some smoke. I've got no smoke, so that combined with the "good" rail pressures leads him to believe the transfer pump is fine. How can I argue with that? Seems logical, but I don't know if his reasoning is accurate. He also says that volume supplied by the transfer pump is more important than pressure, so Chrysler recommends a volume check rather than a pressure check. So, that's next. Had to schedule for next Tuesday. Anyone got any other ideas I can throw at him?

J Body - What would stock size tires have changed for the test flogging?

 

can you have the correct pressure in the rail but not the the correct volume of fuel?

currently deployed on Enduring Freedom and missing my truck more than my wife

 

Stew130,

I am in the USAF and have been deployed many times and on 1 year remotes so I understand what you are saying but....... I just hope the better half does not check this site (for your sake).

 

I hope this helps....
I have the exact same truck in an 04 with the exception of an Auto instead of the 6-banger. I too, pull a toy box full of gear. I average about 64mph up a 5% sustained for about 3 miles (long sucker!). When I had my Edge EZ it was better, but level 4 required that I pay attention to the EGT's. Level 3 didn't require that I even look at the pyro. Would't go over 1200.

The big difference between our trucks is the tires size. I purchased a brand new set of take-offs (Hummer Wheels and tires), and towed ONCE with them. My milage dropped about 2.5mpg over the exact same trip, and the performance was HORRIBLE!. I have my Take-offs in the garage and await gearing options (hopefully soon). Obviously, the 6-banger changes things abit and you probably wouldn't have noticed the huge result right away. But let me tell you, the performance drop for me was signifigant!!!!!!!! I believe that the 4:10/4:11 in combination with the 315's put you just a hair over what stock tires are with the 3:73's. That is an option that you have now, although I think that you can only get the gears from the dealer. Good luck and keep us posted.