Volvo gutless at take off

[colson04]

I've shared a bit about this truck before.

1998 Volvo WG64, 7.3L Volvo D7 engine @ 275hp, Allison MD3060P automatic trans. Truck is built heavy. 18k front, 46k rears, full length double frame. 22ft silage/grain box, all steel. Came from Southern California in 2017. Truck grosses 55,000+ lbs, tare weight is 25,000 lbs with driver.

When taking off from a stop, whether you ease the throttle down or mash it, it revs up to 1500rpm slowly, then around 1550/1600 rpm, you can hear and feel the turbo kick in and it launches forward. Then it always seems to have power, has no issues running 65mph while loaded, pulls hills as well as a small engine can at those weights. The acceleration is slow when loaded, as expected. But the issue at takeoff is a problem that affects the truck empty or loaded, soft ground or hard, cold or hot. When empty, the truck still lags, but takes off faster. When loaded, it can be several seconds before the turbo comes in. These seconds make a difference in whether I can safely make a turn in an intersection, or wait for an obscenely huge gap before making a turn.

The issue is compounded on soft ground like loading out of fields. Our other two trucks have no issues getting loaded, and then taking off from a dead stop, but I had to get pulled out after getting loaded because truck wouldn't build boost. I was parked in field beside other trucks. Got loaded, sank in a bit. I put truck in gear and it felt like it stalled against the torque convertor. Full throttle it would only get up to 1450 rpm and slightly rock the truck. I tried rocking it back and forth to get started, but it would only rock just a tiny bit in either direction. I don't have a boost gauge on this truck, but I dont think turbo was building any boost, or enough boost). Just a low diesel drone, no turbo whine from exhaust sound. Would not even try to spin tires. We pulled it out with tractor to where I was pointed downhill. It would move under its own power, but still would not build engine speed past 1450 rpm until I got onto the hard gravel road. Then it suddenly took off like nothing was wrong. Also, I had manually shifted all the way to first to make sure truck wasn't trying to take off in 2nd with no affect.

This can't be normal, can it? Truck has been like this since we got it. As I am learning about the MD3060P and its programming options, I'm starting to wonder if this truck was programmed for a specific type of conditions for its past life in SoCal that doesn't work for our normal conditions. I know it has a very low PTO cutout speed programmed as it cuts out at 1000rpm. Also, in neutral, full throttle only goes to 1600rpm, but truck will run full range (2300rpm ish) when driving.

I don't know if I'm facing a programming related situation, a normal operating situation, or something not functioning as it should situation.

I know our other 3 trucks (2 autos, 1 manual trans) will break traction and build full rpm in the same situation that I wouldn't even build rpm.

 

[cfherrman]

Definitely need a boost guage (even temporary) and check the cac system foeal leaks and if that turbo has a wastegate check it out moves or is sealing correctly.

Might check the pre turbo exhaust system as well.

 

[crane operator]

Being just a 7.3 with that kind of weight, I'd guess its just having a hard time having enough power, to get things rolling through the torque converter. Then once it finally gets it all flowing, it either locks the torque converter up, or is finally up in the power and you just hear the turbo when it finally gets over the hump and starts to spool up. In the lower rpms when its struggling getting moving, I don't think you will hear much turbo.

Have you ever tried manually bumping it down into 1 when you are in the field trying to get rolling?. One of my allisons doesn't start in 1 unless you manually put it down there, and then instead of shifting down into 1- almost stalls out in 2, and just sits there. Try it sometime loaded up and see what it does.

my smaller grove is only a 7.7 cat and its up there at 55,000+. Its will climb pretty good if you set it down in 1, but its no speed demon.

 

[colson04]

Being just a 7.3 with that kind of weight, I'd guess its just having a hard time having enough power, to get things rolling through the torque converter. Then once it finally gets it all flowing, it either locks the torque converter up, or is finally up in the power and you just hear the turbo when it finally gets over the hump and starts to spool up. In the lower rpms when its struggling getting moving, I don't think you will hear much turbo.

Have you ever tried manually bumping it down into 1 when you are in the field trying to get rolling?. One of my allisons doesn't start in 1 unless you manually put it down there, and then instead of shifting down into 1- almost stalls out in 2, and just sits there. Try it sometime loaded up and see what it does.

my smaller grove is only a 7.7 cat and its up there at 55,000+. Its will climb pretty good if you set it down in 1, but its no speed demon.

Yes, I did manually shift it down into 1 when loaded trying to leave the field. Didn't change anything. This is the first harvest that I drove this truck daily to realize what its quirks where. I've got a list of stuff to putter with during the off season, including looking into this sluggish take off issue. If we are just maxed out on what the D7 can do, then so be it. I just hate accepting that without first knowing whether everything is functioning properly.

 

[Spud_Monkey]

My opinion which may be worthless is a 7.XX litre engine is just too small for 55k pounds, I was having fun with 8.3 Cummins at 50k lbs then again I have hills and it's only rated at 237 HP. As the saying goes, there's no replacement for displacement since I don't know how much torque you have as horsepower is useless without it.

Edit: I can go into low range for all my gears too even though I have an automatic.

 

[colson04]

I wouldn't expect the torque rating to be over 600 lb-ft, but I don't know what it is either. The data sticker on valve cover just says 275 hp @ 2200rpm

 

[cfherrman]

775 ft lbs, and the HP is listed at 2200 rpm, which is very high.

I am very surprised that's in a tandem rear truck, that's basically a pickup engine. I did a little looking and that's a class 8 truck, has that engine been swapped in?

 

[colson04]

775 ft lbs, and the HP is listed at 2200 rpm, which is very high.

I am very surprised that's in a tandem rear truck, that's basically a pickup engine. I did a little looking and that's a class 8 truck, has that engine been swapped in?

No, its factory. The build sticker on the drivers door frame confirms this.

For a small displacement diesel, 2200rpm isn't out of line. My old 466 international was 250hp @2100rpm. Not great for a large truck, but capable for a smaller rig.

The more I ponder this, the more I think this was specced for delivery work in an urban setting. This truck did have a manual for a laddervator in it when we got it, but was a cab n chassis configuration at that time. Also, an intercity delivery truck wouldn't need a big engine for short delivery run with no time at highway speeds.

 

[cfherrman]

The high HP rpm means not a lot of power where you need it.

 

[thepumpguysc]

Does it have a mechanical injection pump.??
If so, I can tell u what to adjust to get the boost u need..

 

[Truck Shop]

^^^^^^------------can't make boost without lots of fuel.

How is it if starting out on a slight down hill?

 

[Truck Shop]

Just what is the final drive ratio?

 

[colson04]

^^^^^^------------can't make boost without lots of fuel.

How is it if starting out on a slight down hill?

Just what is the final drive ratio?

4.88 rear end ratio.

Downhill it does the same, but it gets ground speed faster and thus builds rpms quicker. It still has a sort of delay. I saw @thepumpguysc post this morning, took this picture of the injection pump. It has multiple electronic connections to it. I'll try to snap a couple more pics after I get back to the field.

 

[Truck Shop]

The IH's I took care of some years back had 210 hp 466's with a 6613 deep reduction
and 488's-18k fronts. 46K was about all those could handle.

 

[thepumpguysc]

Dam.. the 2green pipes are blocking the boost device..
Get a better shot of it & I’ll tell u how to get the fuel u need for take off..

 

[thepumpguysc]

Never mind.. I just blew it up and saw it was an “H” pump..
There’s no adj u can make..sorry.
It has a red cap on it.. did u have the pump off.?? THATS a service cap..that the fuel shops use.

 

[colson04]

Never mind.. I just blew it up and saw it was an “H” pump..
There’s no adj u can make..sorry.
It has a red cap on it.. did u have the pump off.?? THATS a service cap..that the fuel shops use.

We've never touched this truck mechanically. It is as it came from the broker we bought it from. We drove it to a truck shop, they swapped dump body off our old truck onto this one and we put it in the field. All we've done is regular PM work. Truck starts well, even this morning at 32°F, it lit off fairly quick.

 

[Spud_Monkey]

Small displacement and inline 6, it should easily light off quick at only 32° F, when you start hitting in the teens and lower is when it has hesitation. My 8.3 lights off fairly quick in low 20's/

 

[Delmer]

I was hoping Thepumpguy had a good solution. Sounds like it's not giving fuel till it gets some boost, so it doesn't roll coal as much. 98 was one of the first steps in emissions so they may have cranked down the limits farther to meet the new regs, then worked out the kinks later. If Thepumpguy doesn't have a way to adjust your boost control on the pump, then I won't guess. At least you can make sure the tube is hooked up and clear, make sure if you blow into the injection pump through the boost tube, it holds pressure.

Is that soot on the fuel filters? 4.88 is the high ratio on two speed rear axles that medium duty trucks with small diesels like that had, low was 6 something. The torque converter makes some difference, but that's already factored into the auto gearing which is much higher than granny low manual. If the torque converter was somehow acting up, it could make it feel like that, I'm not a transmission guy anymore than a injection guy though, can't say if it's possible for a torque converter to fail that way. Though I drove a gas baby dump that drove just like that, zero starting torque, but engine had plenty of power once rolling. Never looked into it, too much wrong to even start.

 

[cfherrman]

If there were a problem with the auto you could probably rev past 1500 with it not moving. It's trying to move it sounds like. Don't think that has mechanical modulator, probably tied into the ecm so that's out