Engine/Transmission (1998.5 - 2002) 99 dodge ram feels like pulling 6k# when empty

[JHyneman]

Well I have been hanging around here surfing threads for a while trying to get answers but am still lost. I am not new to diesels. I have owned 5 cummins (2 with VE pumps, 1 97 ram and a 06 common rail) and they all got in the 17 city to 22 hwy. This is my first 24 valve and am very frustrated. I get 14 around town and 17 on the interstate.



Now the specs 99 ram, 4x4, all stock, no power adders, only 102k miles, 2" lift kit and 35" AT's. 4. 10 rear, Fass 95/95 fuel system and has boost, pyro, trans, and fuel pressure guages.



the truck feels sluggish. like when you stomp on it the boost goes up, rpm goes up but it dosen't take off. AT 70mph, 2000rpm step on it WOT to pass boost at 25psi, fuel pressure @14, and trans temp @ 160, EGT @ 800 it almost feels like transmission is slipping.



The truck feels like I am hooked up to a load of 5000#'s all the time.

There are no codes.



Can any one enlighten me.

 

[JLandry]

JH,



Does it feel this way when accelerating from any speed, or mostly from a stop?



Have you calculated the fuel economy yet?



John L.

 

[JHyneman]

When the truck is cold it accelerates fine, but once the truck is warmed up everything starts getting sluggish. I am conserned b/c All of my other trucks were peppy even with 35's and 3. 55/3. 73 gears but this one has 4. 10 and I would think it should be even more responsive.



I have kept a detailed mpg list since I bought the truck last november. my usual city mileage is 14. 6-15. 1 and my hwy is 16. 1-17. 1. And this is with a light foot.



I have also added a 4" exhaust and a k&n airfilter. Still the same.

 

[JLandry]

How are you measuring boost and fuel pressured? Is it safe to assume you have a set of aftermarket gauges?



Without doing diagnostic testing during actual operation, I'm going to go out on a limb and suggest there may be a faulty sensor or two involved in this. The IAT (Intake Air Temp) sensor or the MAP (Manifold Air Pressure) sensor would be the primary suspects. If one or both of these sensors were supplying bogus information to the ECM, the engine wouldn't get proper fuel delivery for a given rpm and load.



John L.

 

[JHyneman]

Well I do have a set of aftermarket guages. If my IAT and or MAP sensors were supplying bogus info wouldn't I throw a Check Engine light and some sort of codes? Could it be the transmission slipping. I typically feel it when the Trans meausres 150 degrees and up. I have the sensor in the test port.

 

[JLandry]

If my IAT and or MAP sensors were supplying bogus info wouldn't I throw a Check Engine light and some sort of codes?

No...

If the sensor is still providing information within parameters that the ECM is expecting, then the check engine light wouldn't be illuminated. For example, let's say the MAP sensor was stuck telling the ECM the manifold is at a low boost pressure even though your mechanical gauge says it's at 25 psi, then injector fueling and timing generated by the ECM would be delivered at an appropriate level for that low boost condition. The result could be sluggish performance just as described.

The same goes for the AIT sensor.

Could it be the transmission slipping.

It could be, but the engine rpm's you metioned at 70 mph don't sound too high with 4. 10 gearing. If anything they sound low.

From a stop, you should be able to see the rpm changes and feel whether the transmission is shifting through all 4 gears and the torque convertor is locking up and staying locked in 4th gear.

John L.

 

[JHyneman]

Well rpm's are low because of the 35's I have on. 35 + 4. 10 gears = 3. 58 so at 69mph I am turning 2000 rpm. But with WOT should my rpms be at 2400 at 70 to pass?



I now understand the sensor thing. Will that affect the mileage? I am told that my mileage is normal for this truck I just have a hard time believing it. The only time I have mileage this low on a cummins is when something was wrong, like slipping clutch or trans, or leaking boost lines, or failing injector pump. My 93 (I know different Injection pump/ heads) averages 23mpg city and 26hwy. I just don't have the passenger space for my lil one.

 

[JLandry]

Well rpm's are low because of the 35's I have on. 35 + 4. 10 gears = 3. 58 so at 69mph I am turning 2000 rpm. But with WOT should my rpms be at 2400 at 70 to pass?

If everything's working and adjusted correctly, then going to WOT will result in the transmission downshifting from 4th to 3rd. Based on my calculations, at 70mph the engine would go from about ~1900 rpm to ~2750 rpm.

Based on a 4:10 axle ratio and the 47RE transmission ratios of:

1st = 2. 45:1
2nd = 1. 45:1
3rd = 1. 00:1
4th = 0. 69:1

I calculate:

At 60 mph, 4th = 1901 rpm and 3rd = 2755 rpm
At 60 mph, 4th = 1630 rpm and 3rd = 2362 rpm
At 50 mph, 4th = 1358 rpm and 3rd = 1968 rpm

You can test for proper rpm on a 4th to 3rd downshift by holding a steady speed (say 50 mph) let up slightly on the accelerator, push the OD button on the end of the gear selector lever, then reapply the accelerator after the downshift. The torque convertor should naturally be locked prior to the downshift, will unlock during the downshift, then re-lock after the downshift. You should be able to see the rpm drop as it locks up again after the downshift from 4th to 3rd.

I now understand the sensor thing. Will that affect the mileage?

Sure!

While I don't have the exact same configuration as your truck, your fuel ecomony does sound on the low side to me.

My 4x2 truck has a 4. 10:1 axle, a canopy, usually a full tank of fuel (or more with the aux tank), a few hundred pounds of permanent stuff in the bed, and it averages a solid 20 mpg of combined city highway driving. Most of that is highway crusing at 60 mph. Fuel economy drops noticeably at 70 mph. I also drive for best fuel economy (gradual acceleration and braking, no hot rodding).

I hope that helps,

John L.

 

[Bob4x4]

Don't rule out a bad torque converter,they can suck up power

 

[cerberusiam]

Bad TC like Bob says can really make them a dog. VP-44 failing will also do the same thing and generally feel worse when they get warm, and no, you got to work at it to get a code that indicates that.



Assuming you have changed the filters lately, air and fuel, trying cleaning the IAT and MAP sensor with Electronics Parts cleaner to see if it makes a difference.

 

[JHyneman]

I will check rpm ranges on my way home tonight.

How do I check to see if my TC isn't working properly?



My filters are about 3 months old when I installed the fass fuel system. I installed it to prevent issues. The truck still had the stock engine mounted lift pump when I bought it that is one of the first things I changed that and a vulcan draw straw, and added guages. How do I check the pump to see if it is working properly?



I will clean the MAP sensor. it looks a little more involved to clean the IAT so that will have to wait till the weekend.

 

[cerberusiam]

There is no way to check the TC for operation, unless it quits working completely. Mostly its just by feel to see if it is transferring power.



The pump can be a bugger ot diagnose also. About the best way is drive the snot out of it heaviest load conditions you can find, lots of throttle operation up and down.

 

[JHyneman]

If everything's working and adjusted correctly, then going to WOT will result in the transmission downshifting from 4th to 3rd. Based on my calculations, at 70mph the engine would go from about ~1900 rpm to ~2750 rpm.



Based on a 4:10 axle ratio and the 47RE transmission ratios of:



1st = 2. 45:1

2nd = 1. 45:1

3rd = 1. 00:1

4th = 0. 69:1



I calculate:



At 60 mph, 4th = 1901 rpm and 3rd = 2755 rpm

At 60 mph, 4th = 1630 rpm and 3rd = 2362 rpm

At 50 mph, 4th = 1358 rpm and 3rd = 1968 rpm



You can test for proper rpm on a 4th to 3rd downshift by holding a steady speed (say 50 mph) let up slightly on the accelerator, push the OD button on the end of the gear selector lever, then reapply the accelerator after the downshift. The torque convertor should naturally be locked prior to the downshift, will unlock during the downshift, then re-lock after the downshift. You should be able to see the rpm drop as it locks up again after the downshift from 4th to 3rd.



Sure!



While I don't have the exact same configuration as your truck, your fuel ecomony does sound on the low side to me.



My 4x2 truck has a 4. 10:1 axle, a canopy, usually a full tank of fuel (or more with the aux tank), a few hundred pounds of permanent stuff in the bed, and it averages a solid 20 mpg of combined city highway driving. Most of that is highway crusing at 60 mph. Fuel economy drops noticeably at 70 mph. I also drive for best fuel economy (gradual acceleration and braking, no hot rodding).



I hope that helps,



John L.

Well I checked my rpm at 60 and at 50 and your calculations are spot on or at least within 50rpms. Everything locked and unlocked like you told me to test. I really can't find anything wrong with the truck from all that I am told to check out. On the Dodge Cummins diesel Forum they are all telling me that my mileage is normal and that these 24v are just dogs. All I can say is I miss my 12V.

 

[JLandry]

On the Dodge Cummins diesel Forum they are all telling me that my mileage is normal and that these 24v are just dogs.

Well I have to respectfully disagree with that last part. While the fuel economy can be highly variable due to many factors, most notably driving style, once the turbo spools up it shouldn't feel like a dog.



Because you said the acceleration feels normal when the engine is cold but not after it's warmed up, I still think you should look seriously at outright replacing the IAT and MAP sensors. Worst case if that does nothing, at least you'll have positively ruled them out and you'll have spares for your emergency parts box.



Regards,



John L.

 

[cerberusiam]

The 4. 10's and 35" tires are going to hurt the mileage, there is no way around that. The mpg you see is within the normal range for a stock truck and those gears\tires.



Trying to compare your current truck to a tweaked 12V is not going to work either. Too much difference in the fueling curves. The 24V is managed and purposely held back in the lower rpms, TC is also extremely loose because the lockup was relied upon to handle the power.



I have extensive miles on both combinations and it is noticeable.



If you feel a noticeable difference warm to cold engine, something is wrong somewhere. Either the sensors are giving false info or the electronics on the VP are starting to fail warm. Have seen both situations cause driveability\mpg problems.

 

[Vaughn MacKenzie]

Yes the power curve of a 24v is much different and a stock one will not give you the low RPM pulling grunt of a 12V. If you want power rev it up, my 98 24v doesn't really come alive til above 2000 RPM and pulls best at about 2800. When towing up a hill I take OD off and run it at 2500. Complaints of low RPM power were common when the 24V came out and Cummins stated the engine was designed for a wider and higher RPM operating range.

 

[Wyomingcowboy]

Pulls best at 2800? I'm not doubting you but I rarely have enough guts to rev that high... . motor sounds like it's going to fly apart on me!

 

[JHyneman]

Yes the power curve of a 24v is much different and a stock one will not give you the low RPM pulling grunt of a 12V. If you want power rev it up, my 98 24v doesn't really come alive til above 2000 RPM and pulls best at about 2800. When towing up a hill I take OD off and run it at 2500. Complaints of low RPM power were common when the 24V came out and Cummins stated the engine was designed for a wider and higher RPM operating range.

Yeah I have never driven my truck with rpms that high. It gets to loud I can't think. My usual is around 18-2200 rpm interstate. So if this is the case, What can be done to get the rpm into the lower opperating range like my old 12v was?

 

[cerberusiam]

So if this is the case, What can be done to get the rpm into the lower opperating range like my old 12v was?

If your not winding it up to to around 2500-2800 then your missing out on a lot of the power band. They make a little noise but thats the way you have to drive them to get them to run.



Its electronically controlled and managed to keep from trashing the transmission, you need a programmer or box that will allow returning the power down low. Smarty is a good choice for doing that, and, I beleieve the TST allows prgramming TQ levels also.



Once you remove the TQ management though, then transmission is the weakest link.

 

[JHyneman]

I bought a superchips tuner a while back and tried it out but the truck actually felt more sluggish with it installed than with out it so I removed it. I guess it is possible that if my trans was slipping it was amplifying the situation giving it a more gutless feeling. I also have the edge tuner but didn't use it b/c I was afraid of tapping the injection harness.