Trans Problems when Towing

[Aepozzi]

Hello Everyone,

I am new to this site. I just joined today. I have a 2003 GMC 1 ton.

I installed the "Powerup Diesel" 80 hp program about 10 months ago. 2 weeks ago was the first time towing the trailer.

The trailer is a 36' Newmar and weighs 13,200 empty and 17,450 +/- when traveling. We departed CA and drove to Seattle, WA. The trip going up went flawless.

Coming home on Interstate 205 near Portland we were climbing a long grade. I had it tow mode, however, I did not take it out of overdrive. I could tell the truck had a load and was working hard. We hit a little bump and it seemed to drop into 3rd gear. The tach read 2,800 rpms at 50 mph. I pulled off the side of the road and received a msg "Shift Inhibited". I shut the key off and re-started. It seamed to run fine until the next hill which it did it again.

I pulled off and shut the key off, but this time on re-start it didn't clear itself. I shut it off again and waited a while. I restarted and it seemed to be fine.

Went down the road some more, this time when I hit a grade I would press the button to take it out of OD. I went a lon way with no problems.

We pull in to stay the night. I crawled under and checked all the connections. They all seemed to be tight.

Next morn. I took-off down the road, in tow mode, with OD on, and it did it again. I had beed watching the Instant Fuel Eco. It seems when the Instant Fuel Eco drops to 4 mpg the trans acts up, defaulting into 3rd gear.

I tried this 3 times with the same results. I finished the trip home pressing the OD button to off when going up a grade. When the instant MPG got to 6 MPG I pressed the OD button.

I called Powerup diesel and tey did have any answers. They did say to install the 70 hp in-place of the 80 hp program. I have. I have not had the chance to take the trailer out. I will at the end of the month.

I did look at all the problem codes. There were many. I guess over 40. I wrote about 30 of them down. I finally deleted the rest.

Does anyone have any suggestions?

I would appreciate it,

Respectfully Submitted,
Andy

[Kennedy]

I did look at all the problem codes. There were many. I guess over 40. I wrote about 30 of them down. I finally deleted the rest.

Does anyone have any suggestions?

I would appreciate it,

Respectfully Submitted,
Andy

And the codes were? DTC list is critical.

I mean I can state teh obvious and that is your power is likely higher than the trans can handle and/or poorly written. This could well be tuning related, but could also be fluid related. Assuming you have done al of your maintenance are you running any special super duper synthetic fluid?

Simplest test is to run at stock power level and see how it does.

[Aepozzi]

The stock power level ran fine, however, at the stock level it would not pull the trailer, and the fuel eco was down to 9 mpg.

When we first purchased the truck it pulled the trailer good. Going to destination 10.5 mpg, and the home trip was 11.0 mpg. It was like this for3 years in a row. Then the injectors went out and we had them replaced. From that point on the power was down as well as fuel economy.

I think I spoke to you regarding a chip and you only re-configure the ECU. With the new CA smog test I could not take the chance. I know I could purchase another ECU,but that is more than I wanted to do.

I don't race. All I wanted is what I had.

Just prior to taking this trip the batteries went completely dead. Some have said that could be the problem. Could be the problem.

Some of the codes that came up are as follows: 0735, 0843, 484D, 5258, 5E64, 6A70, 767C, 8288, 8E94, 9AA0, A6AC, B2B8, BEC4, CAD0, D6DC, E2E8, EEF4, FA00, 060C, 1218, 1E24, 2A30, 363C, 4248, 4E54, 5A60, 666C, 7278, 7E84, 8A90, 969C, A2A8, AEB4, BAC0, C6CC, D2D8, DEE4.

There were more I just deleted them.

The power level I installed was the 80 hp / aprox 150 ft lbs extra tq. I just reinstalled and put the 70 hp level in.

Thank You,
Andy

[Kennedy]

The code list is kind of suspect. Clear then and see what comes back. P0735 is 5th gear incorrect ratio which means slip.

[Aepozzi]

0735. That makes sense. The truck was pulling hard in OD (5th gear). I think when hitting a hill one should take it out of 5th (OD). For me I am towing quite o lot of weight. OD is just to much.

I installed the 70hp program. I wonder if I should put it back to 80hp?

Did you ever come up with a plug-in reprogramer?

With the CA smog law I would think that would be a must.

Andy

[DmaxMaverick]

Don't worry about CA smog, for now anyway. If it doesn't smoke (no load), all the parts are in place, and the SES isn't on, no worries. The inspections are only "visual", in that, no smoke, no codes, with all the smog parts installed (working or not), is a pass. The computer program doesn't mean anything, as long as the VIN matches. If you want the best of both worlds, get a spare PCM and switch in the OEM for testing. Get one on Ebay for less than $100 and have John stick in his best econ/tow program.

[Mark Rinker]

Agreed with above...any LB7 will benefit greatly from JKs switchable tow/haul A$$ tune, and the boost valve to bring up boost to match.

Better power, better unloaded mileage, etc.

Q: Do you use the tow/haul setting anytime your trailer is on the truck? If not, I would recommend it. Couldn't tell from your descriptions....

[Kennedy]

0735.
Did you ever come up with a plug-in reprogramer?

With the CA smog law I would think that would be a must.

Andy

With the ECM swap you have the ability to simply swap back the stock ECM into place and do your thing. I have not embraced the hand held stuff. I have it available, BUT the tuning becomes a free for all. I consider my tuning work to be sacred and I won't let it out without control. I could release something less special to run with the competitive offerings, but then my capabilities would undoubtedly be measured by my "B" work.

That said, you may well see a handheld offered for LBZ and LMM Dmax trucks as I can control copyright with those platforms.

[Aepozzi]

I always use the Tow/Haul mode. It's the OD I leave on, and it was on when the trouble started. I was in OD, pulling a grade, went over a bump in the road, and thats when it happened. This 0735 code makes sense. Upon going over the bump, and it was a good bump, it might of slightly broke a little traction. When it happened again I think I went over another bump, under a good load.

Has anyone had any experience with "Power up diesel"?

Thanks,
Andy

[DmaxMaverick]

Agreed with above...any LB7 will benefit greatly from JKs switchable tow/haul A$$ tune, and the boost valve to bring up boost to match.

Better power, better unloaded mileage, etc.

Q: Do you use the tow/haul setting anytime your trailer is on the truck? If not, I would recommend it. Couldn't tell from your descriptions....

Yeah, the boost valve. I forgot about that. It's the best bang for the buck, bar none! Don't accept substitutes, they are NOT the same.

[Kennedy]

What fluid are you running in the trans?

My only experience with the company that you mention is getting fallout from issues when people realize that they should have done it right the first time.

[Aepozzi]

Whatever is at the GM dealership; I'm not sure what they use.

Andy

[More Power]

Hello Everyone,

I am new to this site. I just joined today. I have a 2003 GMC 1 ton.

I'm curious about the history of this 9 year old truck. Have you owned it since new? How has it been used since new? Does it have a history of performance mods? History of trans replacement? How fast do you tow?

Jim

[SoTxPollock]

Aepozzi, you might get better results if you list what truck you have and what is on it, especially any add on's. These guys have given you some good advice, but I'm thinking it's base on a lot of assumptions of things we don't know about your truck. I tow a 36' 5er that weighs in a little lighter than yours with Kennedy's boost valve and edge set on 2, I think that's something like 60 addidtional hp and 140 additional ft. lbs of torque. The only anomoly I experieced so far is if it's on cruse control and pulling a really steep grade if it ever downshifts it will overslip the clutches in the trans. trying to lock them up after the shift. I've learned to just tap the brake real quick and nail the accelerator at the same time to keep the power on and then just back off until I can feel it lock up then put the power on and it will hold it after that.
I really should not have been in cruse in the first place, just got lazy and relaxed and forgot about how hard the truck was working once. After that happened I checked my gauge memory and it had hit 27 lbs of boost and exh. temp of 1457 F.
You really need to monitor those things closely if your truck is a diesel.
I think JK is on the right track about trans slippage. I'd watch that real close, it probably wouldn't take too long to glaze over the clutches and then it won't want to lock up and the problem will just escelate to more of a problem. What kind of trans temp's are you seeing?

[Aepozzi]

The truck is a 2003 GMC dually. It is bone stock right down to the wheels. Tires are 245/75R 16.

I purchased the truck used with 60k miles on it. It ran well and pulled the trailer well.

I had the injectors replaced about 3 years ago. That cost a pretty penny, after I found it should have been covered under warrenty.

When I got the truck back from the dealer, who is now long gone, the truck never had the power it had prior to the injector replacement. The tech/mechanic went for several rides with me with the GM scanner. According to him the truckwas fine.

I was told the truck was "flashed" after the injectors. I do not know for sure. The dealer went out of business before I could ask.

Last year I went on vacation and was pulling about a 4-5% grade. I was down to 40 mph. That was enough.

While on vacation I spoke with anyone who would talk to me about diesels.

Most that pulled large trailers had some sort of chip in their truck. Some had switchable on the dash others just flashed the existing computer.

I went with the re=flash the computer route. I went with Power up Diesel. I installed the 80 hp and everything worked fine. Until my last trip.

I just spoke with a GM diesel gearhead. He told me the 2003 GM Allision transmissions were light in the torque converter, and if the converter had any slippage it would trip off the 0735 code, and go into "limp" mode.

That makes sense.

He suggested installing a new H.D. converter, and future problems would be gone.

He also suggested that I downshift sooner and not let the trans downshift on its own.

I always tow in the "tow" mode. On level ground I do tow in O.D. with the RPM's at around 2,000 at 60 mph.

When I hit a hill and the truck starts to load I will take it out of OD by pushing the button.

I appreciate the help and advise.

Andy

[Kennedy]

P0735 is a slip in the 5th gear clutches and not the converter. I don't buy the 2003's being light in the converter. We had a customer that beat the hell out of one truck pulling with the stock trans for quite some time.

A properly written tune wil not limp the trans, BUT I have had cases where synthetic (super fluids) tend to decrease holding capacity. Must be friction modifiers.

[Aepozzi]

Not sure I understand. Are you saying the trans fluid needs modifiers, and if so what type?

I know very little about automatic transmissions. For that matter I know little about diesels.


Thanks,
Andy

[Kennedy]

Allison Transynd (not knockoffs either) is my recommended fluid. That or good old Dex III. Back when we were stretching the limits of the stock trans and before the good mods were out I had experience with customers who changed their fluid to wiz-bang synthetics. Immediate transmission limp at the same power levels. Switch back to Dex III or Transynd and worked fine again.

[Aepozzi]

I will go back to the dealer and ask what they are using.

The dealer (Chevy) onlyflushed the system. Acording to my bill they did not replace any of the filters, which I thought was strange. I doubt the 2 filters would cost that much.

I asked for the trans fluid to be flushed and that's what I got.

Some say do not flush the fluid, just replace it without flushing. I don't know what is right. Mayby someone can shed some light on this.

Thank you,
Andy

[DmaxMaverick]

They should have replaced the external spin-on filter with any type of service. The internal filter is recommended for replacement only at overhaul, not during a routine service, absent a specific reason.

The Allison tranny is somewhat unique, when it comes to the "flush". Allison states a power flush machine will damage the tranny. However, a passive "machine" can be used, or the home/driveway method (repeated on this forum numerous times) can be used. Ask the dealer which method was used. If you get the deer-in-the-headlights-look from them, they either didn't do a flush, or did it wrong. I recommend a flush (home/driveway method) if you are changing fluid types (dino to synthetic, for example), or the old fluid is burned or worn out. Only a drain/fill/filter is necessary for a routine service.