Welcome to Top Tech Questions. Oftentimes, readers contact us with questions about articles, or to praise us on what a good job we are doing. But our favorite form of reader communication is tech questions. Our Top Tech section is a place where you ask what’s on your mind, and we answer it. Got a trouble code? Wondering how to get your engine to make more power? Send us an email at jason.sands@sorc.com and we’ll do our best to answer it.
Limp Mode Code Question: I have an ’05 Chevy Silverado 2500HD with what I believe is an Allison transmission issue. When I push the throttle down hard to pass someone (or try to run the quarter-mile), the transmission drops out of Overdrive and the truck’s check engine light comes on. I used a handheld code scanner to find that the vehicle’s diagnostic system is recording a P0700 trouble code. The only modifications I currently have on the truck are an Edge Evolution programmer and MBRP 4-inch downpipe-back exhaust.
Tyler Kirk Gene Autry, Oklahoma
| With just a lift pump, tuner, intake, and exhaust, Duramax diesels can break the 500-rwhp mark. However, putting that power to the ground reliably definitely involves some transmission work.
Answer: The P0700 code is a generic transmission control system malfunction code from the transmission control module (TCM), which tells the engine control module (ECM) to activate the check engine light. The fact that your truck is throwing the code in higher gears during passing and dropping down a gear probably means it’s time to start saving for a transmission upgrade. Even though the Edge Evolution only adds 100 hp (we’re assuming you have it cranked all the way up), that can still be enough power to slip the stock transmission—especially in the higher gears.
The amount of power you’re looking to eventually add will determine the type of modifications to your transmission. Most Duramaxes will survive somewhere between 550 rwhp and 650 rwhp before they will start bending the stock connecting rods, so that’s where we’d draw the line for transmission upgrades. As Allison expert Mike Lovrich from Inglewood Transmission said, “Buy the best transmission you can afford at the time. If you have to go into it again, you’ll spend way more than if you just did it right the first time.” He also added that driving style comes into play, because the Allisons are learning transmissions. “Nothing is harder on Allisons than those DSP5 switches,” Lovrich explained. “The transmission has learned to deal with a certain power within certain parameters, and then suddenly, everything changes.” When the Allison doesn’t know what to do with a power change, it can flare shifts, hang shifts, or slip the transmission—all of which are detrimental to transmission life.
If it were us, we’d get a good triple-disc converter and Stage IV transmission kit from the likes of Sun Coast or PPE, which will hold about 600 rwhp and retail for about $2,500. By the time transmission disassembly, inspection, reassembly, and shop labor is involved, the price is usually in the $4,000 to $6,000 range. It will be money well spent, however, as the transmission will now be able to deal with the extra horsepower while drag racing, sled pulling, or towing.
Mini-Diesel
Question: Even though fuel prices seem stable for now, I’m betting they will go up, up, up, in the next few years. I like the diesel trucks, but I don’t need to tow a 20,000-pound boat with one. I hear about old 6.2L GMs and Dodges getting good fuel economy, but what about the diesel mini-trucks that were around in the ’80s? I know Nissan, Toyota, and Ford all used to make them. Are they any good? And what kind of fuel economy do they get?
Robert Shoup
Tempe, Arizona
| Diesel Power reader Joe Carr sent us photos of this cool Toyota powered by a Mercedes OM617 engine. The lesson here is that with enough time and ingenuity, you don’t need to buy a diesel mini-truck—you can build your own.
Answer: These aging diesel mini-trucks are holding their value quite well, mainly because there’s nothing else like them out there right now. Expect to pay anywhere from $2,000 to $5,000 for one, depending on condition. The most commonly found mini-diesels are Isuzu PUP/Chevy Luv trucks, and Ford Ranger diesels. Toyota and Nissan diesel trucks are out there, but they’re a lot harder to find.
If you live in a county or state with easygoing smog laws, another option is to make your own diesel. Cummins 4BT engines out of GM P-30 step vans (commonly used by bread delivery companies) can make for good swap candidates, but don’t forget the numerous diesel industrial engines and old 240- or 300-series Mercedes car engines, which can be had for dirt cheap and run on nearly anything. Whether you make your own small diesel truck or buy one that was made from the factory, expect about 30 to 40 mpg, depending on driving style and conditions. Oh, and with the naturally aspirated versions, your top speed will most likely be headwind-dependent, so keep that in mind.
| Diesel Power reader Joe Carr sent us photos of this cool Toyota powered by a Mercedes OM617 engine. The lesson here is that with enough time and ingenuity, you don’t need to buy a diesel mini-truck—you can build your own.
7.3L Power Stroke Questions
Question: My name is John Chamberlain and I’m in the United States Army Infantry in Afghanistan right now. I have a ’97 F-350 Power Stroke with a five-speed transmission, AFE intake, AFE turbo-back exhaust, and Edge programmer. I want to add an Adrenaline high-pressure oil pump (HPOP). Do I need to add a Dieselsite high-volume low-pressure oil pump to a keep the HPOP supplied with oil? What does the exhaust backpressure valve (EBPV) in the turbo pedestal do? Is there any benefit in deleting it with an EBPV delete pedestal?
John Chamberlin
-via email
| This hydraulically activated, electronically controlled exhaust backpressure chamber sits between the turbine side of the turbo and the downpipe on 7.3L Power Strokes. In cold weather, a rod and spring assembly (activated by oil flowing through the turbo pedestal) keeps the butterfly near closed and restricts exhaust flow until the engine oil is up to operating temperature.
Answer: Unless you are experiencing low oil pressure supply, you shouldn’t need to upgrade your low-pressure oil pump. While the LPOP’s gears can wear out over time and with high miles, you probably don’t need to worry about that. As long as you’re seeing normal oil supply pressure from the LPOP (the dummy gauge in the cab will suffice), the Adrenaline high-pressure oil pump will be supplied with plenty of oil.
The exhaust backpressure valve is actually located post turbo, right before the downpipe. It is actuated by oil pressure (fed through the pedestal) and according to oil temperature. In cold weather (when engine oil temp is very low), it acts as a choke to warm the engine, where a butterfly valve in the exhaust stream will stay closed until operating temperature is reached. According to enthusiasts, deleting the EBV opens up exhaust flow, reduces EGT, and provides one less failure point (the actuator itself can start to leak oil over time). You can delete the EBV yourself, and on the cheap. All you need to do is put a ¾-inch freeze plug in the butterfly shaft hole once the butterfly is removed and then tap the oil inlet for the actuator to accept a ¼-inch pipe plug (which stops oil flow to the area).
