Loss of power when towing

[arveetek]

My electronic 6.5L does not like to tow trailers!

Currently I have a stock 6.5L, missing CAT, and wired-shut wastegate. I drive by the boost gauge and never let it get over 11 psi. It runs and drives great when empty, but as soon as I put any kind of trailer on behind, even an empty 16', the engine loses power and I loose boost. I might be driving along just fine, and then when I pull away from a stop light, I don't have any power and the boost drops down to a max of 9 psi at full throttle. I can shut the engine off and restart and the power comes back and boost runs back up to 12 pretty easily. I'm suspecting the engine is defueling due to unacceptable boost pressures, but I can't understand why when I don't let the boost get that high.

I was towing my Jeep this weekend, and it would run and pull great until I got to a stop light, and then the power would disappear, as if I only had 1/2 throttle. Anything past 1/2 throttle made no difference. Restarting the engine would fix the problem for a while.

I know, I know, I need to fix the wastegate control or get a Turbomaster. But I drive by the boost gauge! And my SES doesn't work, and I haven't tried to pull any codes. I'm just trying to get an idea what might be happening.

I can sure see why the 6.5L's have such a bad reputation. Either the boost doesn't work at all, or else the computer doesn't like the readings and pulls the fuel back, or the PMD quits altogether and leaves you stranded. My 6.2L has never given me any of these problems! ;)

Casey

[DmaxMaverick]

With your wastegate wired shut, it's no wonder. It will pull fuel at max boost. With the WG operating normally, it will continue fueling, somewhat more, but EGT's increase with more fuel and less boost. When unloaded, it rarely reaches the PCM max boost (sustained), so power seems better. The PCM calculates cylinder temp via the boost level and throttle position, which is very different from unloaded to loaded. You'll need an aftermarket PCM program (chip) to get around it, but the results may not be desirable with a defunct wastegate.

[arveetek]

That makes sense. I couldn't figure out why it would only defuel when loaded. I can romp the throttle and hold it to the floor, and only one time did it defuel when the boost ran over 13 psi. But driving carefully with a load and not letting the boost get over 10 psi, it constantly defuels. If I leave the factory boost control in place, it drops boost completely when under load and I lose power anyway.

It's quite annoying.

Casey

[JohnC]

Your factory setup is not working correctly either. When things are working correctly the PCM will NEVER defuel or dump the wastegate.

When the boost exceeds the desired amount for some length of time (30 seconds?) the PCM will reduce fuel and open the wastegate. Wit the wastegate wired shut you bypass the second symptom, but to no benefit. In addition, your exhaust backpressure under load must be through the roof.

[rustyk]

Also check your air filter...

[arveetek]

Your factory setup is not working correctly either.

In addition, your exhaust backpressure under load must be through the roof.

Agreed, the factory setup is not working. It's a rather cheesy and unreliable system at that.

How is it that my exhaust backpressure is through the roof when I won't let the boost get above 11 psi? I don't give it that much "throttle" when towing..... I know to keep it easy because of my temporary "fix."

Casey

[arveetek]

Also check your air filter...

Ah yes, I do need to check that....it's been a while.

Casey

[Robyn]

When I bought my DaHoooooley it had a Banks exhaust (still does) a turbo master and a B-D chip in the Puter.

The boost would hit about 12 PSI under a hard load and it would defuel after about 8-10 seconds on the skinny pedal and do it regularly.

I changed the chip to a Late Heath unit and the sucker screams. I can hold the pedal on the floor and it will hit about 12 PSI and hold and the EGT will run about 900 (Post turbo) while under max power on a hard pull.

The defuel is the ECM doing what it is supposed to do.

Get the exhaust flowing freely along with a good boost control and a chip that allows things to work with the added fuel and boost and you will do fine.

Just remember and stay out of the "Crispy Zone"

Robyn

[JohnC]

Agreed, the factory setup is not working. It's a rather cheesy and unreliable system at that.

I disagree with your assessment of the system's qualities. Mine worked fine for 100K miles, once I figured out the solenoid. Much more precise than a spring sensing backpressure.


How is it that my exhaust backpressure is through the roof when I won't let the boost get above 11 psi?

Because you're forcing it to make 11 psi when the situation probably only warrants 4 or 5 psi at the most.

[arveetek]

I disagree with your assessment of the system's qualities. Mine worked fine for 100K miles, once I figured out the solenoid. Much more precise than a spring sensing backpressure.


I made my previous statements based on the experiences I've had with my non-wastegated turbo 6.2L mechanical engine. I prefer a non-wastegated turbo....I like the fact that the harder the engine works, the higher the boost pressure. Very simple. I agree that the factory 6.5L turbo system, when working properly, will give a better control of boost and less turbo lag. Problem is, it doesn't seem to work properly very often.

I dream of ditching the DS4 system and going back to a mechanical pump and no wastegate. I like the idea of turning the key and having the engine start every time! :D

I've actually been contemplating replacing the 6.5L with a 4 cylinder diesel to gain fuel economy. I'm just not convinced that the numbers make it justifiable....yet.

I guess I'm a guy with a dilemma....I love the newer body style trucks for their comfort and style but love the older trucks for their simplicity and reliability!

Casey

[rustyk]

I guess I'm a guy with a dilemma....I love the newer body style trucks for their comfort and style but love the older trucks for their simplicity and reliability!

Casey

I agree - I have several friends with computer-controlled everything in their coaches - one, with a $350K coach has been back to the factory 4 times in 18 months, and everything's STILL not fixed. I'll admit the chairs are comfy, and the entertainment system is spiffy...

[DmaxMaverick]

I made my previous statements based on the experiences I've had with my non-wastegated turbo 6.2L mechanical engine. I prefer a non-wastegated turbo....I like the fact that the harder the engine works, the higher the boost pressure. Very simple. I agree that the factory 6.5L turbo system, when working properly, will give a better control of boost and less turbo lag. Problem is, it doesn't seem to work properly very often.

I dream of ditching the DS4 system and going back to a mechanical pump and no wastegate. I like the idea of turning the key and having the engine start every time! :D

I've actually been contemplating replacing the 6.5L with a 4 cylinder diesel to gain fuel economy. I'm just not convinced that the numbers make it justifiable....yet.

I guess I'm a guy with a dilemma....I love the newer body style trucks for their comfort and style but love the older trucks for their simplicity and reliability!

Casey

I don't disagree with your reasoning. Turbo lag or long legged power. A choice, of sorts. But, wiring the wastegate closed will not give you the best of both worlds. The WG turbo (GM-X) is too small for the displacement and fueling involved to operate w/o a WG. You will run out of turbo under load, but it'll look good 'til things get cooking. You can get and install a non-wastegate turbo, if that's your preference. Lots to choose from.

[JohnC]

Yeah, I assumed you were comparing different wastegate control strategies.

Non-wastegated turbos are great for engines that run at a steady load most of the time, but not good for driving around town. The turbo that builds boost quickly from a standing start is not going to be able to provide boost under high power applications as it will choke the exhaust first. Hence the wastegate...

Pick your poison.

[daustin]

Interesting conversation, in a nutshell i love my '93 with the mechanical IP and home-made turbo master. Simple and works every time like the old 6.2 mechanical setup. Instead of wiring the wase-gate shut, get or fab a turbo master and control that boost. Maybe look at HP4 software flash and use the extra boost reliably without de-fueling or cooking the engine.
Don

[Turbine Doc]

Not necessarily John C.

A properly sized non WG turbo as TDO7-22 Mitsubishi does very well for all round driving and towing, better yet is Chinese variant of TDO-7 I have on mine now which has nearly same offline performance as the GM-8 mine came with, some lag which mite matter if racing, but not enough lag to be an issue in tow mode. Due to low backpressure mpg is up, as much as 4 mpg on for 22 on a couple of conservative runs @ 68 mph rolling empty truck. Me n Slim Shady have been comparing notes/sharing turbo his being stick, mine being auto trans for comparative notes/observations.

I just did 2200 miles with it to Iowa & back pulling 7' tall-7' wide-16' long tandem axle trailer loaded to estimated 5000# trailer weight, 2 "healthy sized" occupants in cab, luggage and 60 gal fuel in bed, max EGT 1100F on long grades in OD shifting to 3rd as trans dictated, 212F max water temp, 96F outside temp, 82mm fuel, 158 max IAT, 370#' indicated Tq on scanner, 80 mph in passing if need be cruise at 73 mph most times with EGT 950-1000 56-65mm fuel requested, turbo back pressure no more than 2x boost, boost 3-5 psi cruise up to to 8-10 psi on hard pulls.

Casey have a look at the fuel filter, I had similar scenario on mine early on partially blocked filter "just changed" within last 5K miles, truck ran like a banshee unloaded, hooked up to my 5600# g/n trailer and it would barely make 45 mph up a hill.

Have you checked your lift output at WOT, a lift just starting to go south may not show until you have big load demand on it, I have permanent gauge to mine now at IP inlet, but you can do same by putting test gauge to you filter mgr drain and snaking rubber vac hose into cab (be careful to not pinch the line & dead head it) and read lift output at WOT you should sustain 1 psi min, short dips to less than that but should quickly recover & maintain 2-3 psi when at cruise speed setting.

Another one that bit me on a dyno event was bad boost sensor, boost kept clipping but only showed 9 psi boost on gauge; but boost sensor went bad high, PCM thought I was making 35psi boost.

As far as IP goes once I got the driver off of it and remote mounted out of bay; I have yet to have a IP issue in nearly 4 years. As for under fueling DS-4 supported Ian's 303 Hp dyno run last month with some pane & Nitrous assist, my own rig with latest heath tune is running 200+ rwhp, I don't know how much as I haven't dynoed since 2005 where I saw 197 rwhp, & have had done some more mods since then.

[arveetek]

I do plan on getting a turbomaster. Wiring the wastegate shut was just a temporary fix because the stock controls would dump boost altogether when loaded or at speeds above 65 mph.

The turbo on my 6.2L is actually quite responsive around town. I think it's a pretty good fit for the 6.2L. I do think it starts to choke the exhaust around the upper RPM limit, but there's so much power down low, I don't ever get the engine revved that high anyway.

I know that I have a defueling problem, and not a filter or lift pump problem, because shutting the engine off and restarting immediately solves the problem. I'll have low power and a max of 9 psi, so I shut the engine off and restart, and then power returns and the boost climbs until I let off the go pedal.

It just disappoints me that the computer is so sensitive. I'm not asking for full throttle or max power, but it still shuts me down.

I tried unplugging the boost sensor (I think!). Isn't the boost sensor the one on top of the intake hat? When I unplugged it, the glow plug cycle doubled in length of time and kept cycling long after the engine started, so I plugged it back in. Why would the boost sensor affect that? :confused:

Casey

[JohnC]

... turbo back pressure no more than 2x boost, ...


OK, we're talking different languages. For a non-wastegated turbo in a fixed speed application (think generator, pump, etc.) this is outrageously high backpressure. In the absense of a wastegate, or better still, variable vanes, you'll either have turbo lag or choking at heavy loads. Asking an unwastegated turbo to produce boost efficiently from 1400 RPM through 3400 RPM and from moderate load through full load is futile. Like I said, pick your poison. you have chosen slightly reduced throttle responsiveness and fairly high backpressure. Better than stock, maybe, but far from optimal.

Arvee: Replace the wire with a spring and you're home free. You're hitting the boost cutoff way before you get any significant fuel flowing.

Or, purchase my Turbo Bastard patent pending wastegate controller (http://www.thedieselpageforums.com/photopost/data/500/turbo_bastard.jpg), the only one worth buying, guaranteed to fix everything that ever has or will go wrong with your truck.

;)

[arveetek]

Arvee: Replace the wire with a spring and you're home free. You're hitting the boost cutoff way before you get any significant fuel flowing.

Or, purchase my Turbo Bastard patent pending wastegate controller (http://www.thedieselpageforums.com/photopost/data/500/turbo_bastard.jpg), the only one worth buying, guaranteed to fix everything that ever has or will go wrong with your truck.

;)

I was thinking of doing something like that! Since the patent is pending, I can copy your design and not break any patent laws, eh? ;) I'll call mine the Turbo Faster!

Casey