Thank you for letting me join this group. I have read the posts listed and feel that there are many folks here that know what they are talking about. I bought my 98 6.5 1/2 ton(100,000mi) in Oct. It hasn't been going too good. I thought I researched the subject on pmd to the fullest. And my problem seemed to be the same. Poor fuel milage 15mpg, ecessive smoking at times, but still had good power. So i looked around and saw all the pmd located on the intake when relocated. That really didn't make too much sense to me, its still pretty hot up there. So I purchased one to go on the fender wall, plus it had boost and fuel controls. You have probably already guessed, A1. I am not here to bash or anything. I just found that the install wasn't very clean for that kind of money. And the power increases from the boost/fuel controls is not there. maybe less power. It did clean up the smoking, bucking. It will smoke when I turn upp my fuel too much. The boost control setts off 236 code, turning off my waste gate. Is there anything anyone can add?

Black smoke, poor mileage can be dirty air filter.


Bucking can be fuel filter.


Boost should be set to ~7psi for stock '98 PCM flash.


And, check Turbine Doc's 6.5 upgrades post for power and reliablilty improvements.


Your '98 already has the most important upgrade - HD hiflow water pump, dual t-stat coolant manifold.

I replaced:lift pump, fuel filter, air filter, used fuel conditioner, and tried different fuel stations. Also, not related, had to replace 4 glow plugs. All within 5000 miles.

A1 was your biggest mistake.

Hopefully John Kennedy will chime in. He knows this stuff quite well ahem.... along with a lot of guys around here.Edited by: hoot

Ok - good start with filters.


May need replacement down-pipe - usually pretty mis-shapen from factory, doesn't really look like much of a pipe at all.


The oxidizing convertor, soot trap, may be plugged - a trip at hiway speeds will usually incinerate the junk out of it.


Or, a better exhaust system, 3 - 4" with free flow muffler.


And, of course none of us guys have been victimized by this, but the right foot tends to get more active after the first surge of power from the turbo-fied Diesel.http://www.dieselplace.com/forum/smileys/Cool.gif


'Smileage' increase usually results in mileage decrease, as it were.


Nothing much can be done about that - except put more money into it in an addictive quest for more power.http://www.dieselplace.com/forum/smileys/Wink.gif


And, as Hoot sez, product hype is seldom helpful.

I will look into a down pipe, mine's pretty rough. Is there any kits that will replace my current down pipe and cat converter? funds are as always short. and of course it is easier on mpg with less happy peddel, at 65 w/ 3.73 the best is 15.5 when nice

Check Kennedy Diesel, Heath Diesel, Banks and other websites ('cept maybe B2, if you can ascertain my meaning http://www.dieselplace.com/forum/smileys/Cool.gif) for replacement exhaust systems.


Some trucks were worse than others in the exhaust system, and replacement is definite improvement for those.


Almost fergot - PCM cuts fuel at over-boost condition, generally 10psi, for more than 20 seconds. The electrical boost control was meant to 'fool' the PCM into allowing vacuum or mechanically controlled 10 ~ 12psi boost without DTC.


Stock PCM control is 7~8psi.


Edited by: gmctd

sweetner,


I get 15.5 avg with my four ton cc k3500 with a load of rock in the back.


When I see black smoke it is an indication to me that I'm not getting full boost. Generally, these trucks can accelerate loaded upto freeway speeds without a dark cloud hanging behind them.


In the stock configuration, you have a vacuum pump, plumbed through a wastegate solenoid, that closes the wg flapper based on the ECM triggering the solenoid. If any leaks develop in the vacuum lines, if the solenoid hangs up (as they do) or if the wg flapper jams open you will burn extra fuel trying to make the same power.








The back-up in the soot trap is tragic. I couldn't see through mine to daylight. If you order a downpipe for a '93 there's no flange bolt for the trap.


I almost got the 4", but the 3" was such a hudge improvement I'm happy.


I think the 42" wiring harness I made for my trucks added resistance to the FSD circuit, because both trucks had an immediate throttle response improvement. If I "hotrod" (especially hard acceleration up hills)my truck it can burn enough fuel to give me 13-14mpg despite how I drive the rest of the time.





http://www.dieselplace.com/forum/uploads/F6F_exhausts.jpg

I am seeing very light smoke on acceleration prior to changes. Now I am jsut trying to dial this setup in for a little more power or at least the power I had before.

quantum mechanic: are you saying that the 42" wiring harness has hurt your fuel mileage?


sweetner: heathdiesel.com sells a bigger downpipe and crossover pipe. I have also found that diesel concepts sells a 4" downpipe.Edited by: steiner43511

The 42" harness and all the work I have into making my engine go give me the ability to burn alot of fuel at once.

made the best improvement yet. I removed the A1 pmd, and controls. My old pmd was "hooking" (the way a fishing line feels when you get a bite) It wasn't what I would consider "bucking". We will see if it starts again. I also was hoping that the pmd was part of the poor fuel milage.

The downpipe and else can be made by any good muffler shop.


The smooth mandrel bend look is nice, but not all that necessary unless you're running normally aspirated - Baro in, Baro out.


Smooth curves and bends, with no diameter reduction, kinks, flat spots, or distorted pipe is more important.


Compare QM's original with the replacement.


I'll say it again, QM - show and tell rules!