Towing uphill and going into a limp mode

[rclippard]

This past weekend I was towing my buggy up to do some crawling. There are three big hills to tow and usually I can just go to 3/4 throttle and hit 1100 on the pyrometer. The setup will go right on up at 45mph. This time the check engine light came on and the truck fell flat on its face. It had trouble holding 35 mph up the hill and it didn't matter what I did with the throttle the engine wouldn't work any harder. Checked the codes at the top of the hill and had a 73 and 78. 73 is some AC code and I couldn't find the 78. It did this on every hill.

The truck already has a PMD, 4 inch exhaust, and a manual wastegate to keep the boost around 12-13 pounds. It tows well but with the check engine light I am scared to make any more trips until I get a new truck. Hopefully this is something simple that I can fix.

Does anyone know what could be causing this?

[JohnC]

Your manual boost control is set to high. The PCM wants to reduce the boost, but can't, so it cuts the fuel rate. Reduce the boost a little bit at a time until the light stops coming on, or install a "boost fooler," available from John Kennedy and maybe others, or revert to the vacuum controlled wastegate.

[rclippard]

Thanks, I am going to do a boost fooler. I had the vacuum system and this was the second one I put in. After the second one failed during a long road trip with some serious hills I decided to go manual. This truck has never towed the way I would like so it might be time to change to a different make. I have another pull coming up so I will probably install the boost fooler and bump my optical sensor to see if that helps. It is pretty misrable watching my roommate blow by me in his gas 1/2 ton on the hills though pulling a similar load.

[DennisG01]

It is pretty misrable watching my roommate blow by me in his gas 1/2 ton on the hills though pulling a similar load.

Maybe, but wait until you put some real weight behind your trucks - then you'll be smiling :D Plus, what do you think his average MPG is? It's sure as heck not anywhere close to yours - especially when towing. Towing my boat (10,000lbs), wife, children, Yellow Lab and a ton of food and gear inside and a bunch of junk on top of the Burb for a vacation I still broke double digits. That's not too shabby (The same situation with a 6,000lb boat I was getting almost 14). If I had a 454 gasser, I'd probably be lucky to get 6. Forget about a 350 1/2 ton hooked up to a 4L60 - it wouldn't of even survived the first hill. Now, I'm not saying that you're going to be able to make power equivalent to a DMax, especially one that's on juice, but this 6.5 ain't gonna cost you anywhere near what a DMax will cost, either - to buy it or to fix it.

Take a look around on this site - look at threads, do some searches, look at people's signatures. You'll see that you can make some more power (reliably) and it's relatively inexpensive.

But, in the end you gotta do what's right for you. If that means another truck better suits your needs, that's cool too. All I'm saying is don't give up - the 6.5 is very capable of giving good performance coupled with a long life. Yes, it's got it's quirks, but what engine doesn't? Besides, that's what this forum is here for - to help!

Good luck in whatever you decide! :)

[Robyn]

As you already have the 4 inch exhaust, don't waste the time with a fooler.
Get a chip or a reprogramed ECM (depending on the year) JK and Heath both sell fine products.

This will change the fuel rates, timing, and a whole lot of other things as well as stop that anoying "Defueling" and the codes (SES LIGHT)

My DaHooooley had the spring waste gate control but did not have a good chip and would defuel every time I got into it for any length of time.

A NEW prom (94-95) and woo hooo what a difference.

You will see some significant reductions in EGT with the chip too as the timing and fueling curves are a lot different than stock.

Good luck

Robyn

[rclippard]

A chip is in the future, but is way out of the budget right now. Currently I have added a simple fooler and bumped the optical sensor to try and squeeze a little more power for the hills. Towing 7k through the mountains I need all I can get. It sucks getting passed by a grand cherokee and a 1/2 ton truck both pulling similar weight. It is still setting the SES light, but I have not had time to see what code is there. I will be towing this weekend so hopefully it won't defuel.

I did get to ride in a newer Duramax truck, and I am pretty sure that one day I will upgrade to a new truck so I can start pulling upwards of 18k. Of course that is after I finish up school. Thanks for the help.

[rclippard]

Towed great! Over 400 miles with no problems. It held 65 on the hills although none were big. The EGTs only broke over 1000 once and that was when I was really in the throttle trying to pass someone up a hill. Typically the boost was around 10-12 just cruising with a little throttle. Went down there running 65-75 depending on the road and came back at 65. Fuel consumption was way better at 65.

Thanks for the help. Hopefully a chip is in the future but right now the engine studders under heavy acceleration and so does the trans. Gotta sort those out first.