OBD-II and DB2 pump

[Andy Chesek]

Has anyone converted their OBD-II truck from electronic fuel injection to mechanical?


I was curious what others have done in converting from a DS4 to a DB2, so I picked up the 2002 Feature Articles and the 6.5L Turbo Diesel book looking for stories (and of course for all the other good stuff in those books). Seems like those who went mechanical had '94 or '95 trucks. And from others' input on this site it appears the big hurdle is getting automatic transmissions to function properly, so I'd bet the conversion would be more popular if it weren't so difficult (or expensive) to do so with an automatic. The third item I noticed is the issue of throttle cables and the dual thermostat housing, which More Power provided lots of insight in dealing with that in the 6.5L book.

My truck is a '99 with a 5-speed manual. I'm trying to plan my attack to get more power, one way (mechanically) or the other (electronically). Let's hear some input.

[mklein]

I changed from a TBI 454 to a mechanical 6.5. I used a t32 TCM and eprom from a hmmwv. All of the real estate electrically was already in the cab at the pcm, I just had to make a wiring diagram to convert from the old PCM, cut the trans wires I needed, and plug them into the connectors for the TCM. All in all, it went pretty well. There were, of course, some electrical gremlins, but it works pretty well.

[DA BIG ONE]

I have a 99 and will convert as soon as my elect IP fails. I will beusing a standalone tranny controller $800.+.

As I have AutoTrac I need to dump the auto feature, fabricate a manual shifter (3 position) for the t-case and use the PosiLoc to engage front axles. With my ARB front locker this will be a killer setup!

I consider the mech IP and mods I have planned to be well worth the effort, and I can sell off my electronic aftermarket mods to recoup some $$$.

[Andy Chesek]

TBI 454's were last used in '95, which means they were controlled by an OBD-I computer. I'm trying to find out if there would be a problem with the newer OBD-II computers and a mechanical fuel injection setup, still haven't heard from anyone or read anywhere that someone has successfully done this.

[DA BIG ONE]

Originally posted by 93_Burrito:
TBI 454's were last used in '95, which means they were controlled by an OBD-I computer. I'm trying to find out if there would be a problem with the newer OBD-II computers and a mechanical fuel injection setup, still haven't heard from anyone or read anywhere that someone has successfully done this. Surely, there are more problems like electronic A/C, heat control, cruse control and on, and on.
Perhaps, my idea of a conversion needs rethinking too.

[Bobbie Martin]

You shouldn't have any trouble converting a 5 speed. There is not any good info on a DB2 conversion anywhere - yet! Hope to change that soon, but it takes much more time than I thought. Anyway, I really don't see a problem for you. Biggest challenge will be the thermostat housing and the throttle cable, but if you have basic fabrication skills its no problem.
You are right about it being more popular if it were easier. With automatics, its not too bad if 2WD, 4WDs have additional problems that at present don't have an easy solution. Trans computers are cheap if you know where to look. For all cruise is cheap & easy to get back. After having a DB2 for 2 years now, I can't recommend it enough.

[mklein]

There really is not an OBD1 vs OBD2 problem, there is only the issue of connecting the new trans controller to your existing hardware. My truck is a 4wd, so I had to add the extra speed sensor and wire it into the TCM. I still use the old style OBD1 diagnostic connector, I just select a 1993 ck truck as my vehicle when I use the Tech2 for diagnostic work.

[jjgmc96]

since my other truck is an SS I have been on there website also and been thinking that since our computor is programable why can't we just program out the injection pump part of the program. with heath and kennady and i think wester's, who else understands our needs and program enough to pull something like this off?

[Andy Chesek]

mklein,

If I understand what you just said, then I wouldn't have any problems because my truck has a manual transmission... right?

[Bobbie Martin]

Originally posted by jjgmc96:
why can't we just program out the injection pump part of the program. The PCM is not your problem, its the APP inputs. IF you could get the PCM to work with one throttle control input, this would be easy. I burned numerous chips for my PCM using a program Westers use to sell when I did my pump conversion. He didn't seem real interested in doing much more for the 6.5s. I can understand that as the market is small compared to the newer Diesel stuff and I'm sure this is time consuming. I did talk to a guy who is reasonably certain he could make a box that would take a DB2 TPS and convert it to the 3 APP inputs. This would allow you to keep your PCM and convert to a DB2 fairly cheap & easily. It would probably take a couple thousand dollars for his time and for me it just wasn't worth it. However, if you were going to market one......

[Bobbie Martin]

Originally posted by mklein:
My truck is a 4wd, so I had to add the extra speed sensor and wire it into the TCM.I'm guessing from this you installed an additional speed sensor in the rear of the 4L80E for the trans computer? This is the only method I know of to make a standalone computer work on a 4X4. Not to bad if the reluctor ring is there but from what I'm told most 4X4 4L80Es don't have a factory installed reluctor ring. Did you keep the transfer case speed sensor for the speedo?

[mklein]

yes, I connected an extra sensor - but it is the one at the back of the transmission. Since my truck was already a 4WD, I already was using the sensor in the Tcase, but with the 7.4L PCM, there was no need for the trans output speed sensor. The hole was filled, from the factory, with a sensor, just nothing connected to it. Switching to a TCM required wiring in the unused sensor to pins B11 and B12 on the TCM. 93_Burrito, yes, you shouldn't have much of a problem going mechanical if you are using a manual trans.

[DickWells]

Hi Burrito: I don't think you have a problem with your unit, since you have a manual transmission.
I've read a lot of articles on the conversions, and the problem always seems to be with the mechanical throttle cable to APP sensor interfacing. Well, I've put 15 thousand on my settup now, and I'm really happy with the shifting. Jim's articles in the how-to manuals touch on this, but my settup is quite different. Too detailed to explain here, but not complicated in the actual doing. If it comes down to it, just drop me an e-mail at dwells@pshift.com, and let me know where to send some diagrams, etc. Be glad to show you, or anyone.
The other thing, with dual crossover cooling (which I have) seems to be the bracket for the throttle cable and after market cruise. Not to worry! I just cut off a piece of 2X2X.125 angle and bent it, cut reliefs in it, and cut rectangular openings for the cable clamps to pull against. It's bolted right to the two top T-stat housing bolts. Again, will be happy to mail you a hen-scratched picture, or two. Mine is so simple and neat, I should get a patent!
You'll have,an SES light glowing 100% of the time, of course. Unless you remove the bulb. Used to bother me, but I seldom notice it now.
Some things about it, I don't understand. Like, the VSS letting me do all of this without messing up my L80E's shifting. My settup allows me to adjust the progression of my TPS opening in relation to the throttle cable. But, the kicker here is that my original assumption of which way to go with the TPS advance was the opposite to my thinking. Still don't know why it works in the direction that it does, but it works, so I'm not fighting it. Feel free to jump in here anywhere RJ, or GMCTD.
As of this date, I can only say that the old Sub. runs like I wanted my truck to run back in 98 when I bought it. Fifteen thousand, without a skip! Who woulda thunk it?
I'm a worry wart, so I fret over the extra rattle. I worry that the 21+ pistons won't like the extra fuel, etc, etc. But. I run cool, with great boost control (up to 15 psi. Got way more power. Didn't lose any fuel mileage. Get instant starts. I still worry, but I'n the guy who thinks that Murphy was an optimist!
BTW, my pump is a marine DB2 configuration, but I understand that you could run well with one set up for a factory 6.5, or even a 6.2.
Let me know if you want some snail mail info. Good luck.
Dick Wells