92 auto and poor mpg's

[dpuckett]

My mom bought my 92 D350 Club cab two years ago (against my advice, but she can be hard headed). Anyway, 220K on the original transmission, and last time I drove it, it didnt seem as crisp and quick to take off as when I owned it, and towed with it. I think it is part of the reason she only gets 17 mpg (I AVERAGED 19 in town at 5000ft when I had it. Last time she got the fluid changed, the shop said it just showed "normal wear. " THis is in southeast Missouri, where if it runs, it aint broke, dont fix it. ANd no one knows about diesels, because they are all loud, smoky, and smelly. What are some signs of transmission failure? Or going south at least? It seems to take more pedal to get going, and hold speed, not to mention it works harder than before. Pump and injectors were done about 15K ago, so I doubt that is the problem. She refuses to get guages, so I cant give those figures (yet she can spend $1500 on a horse she doesnt ride) I am about ready to give up on the whole thing, and tell her I told ya so, but I am not normally that kind of guy. It really bugs her I get 5 mpg better than her, with a heavier truck and right foot. I want to help her, but it takes money to get stuff right, sometimes, and that is hard to come by.



Daniel

 

[BushWakr - RIP]

Well... . with my mods as listed, I run a strong 18 Mpg US.

That is pretty well all around town, stoplight to stoplight stuff. Only 10% or so is highway speeds, over 55 MPH.



Even on my winter settings it's still running rich at low boost.

The pump probably needs a bit of a tweak if it was "just done".

I'd bet that the shop has no idea about modest tweaking that can really perk these things up, and have very little negative impact on mileage.



The transmission will do things like be slow to engage in the mornings, or after sitting a few days. That is TC drainback.

You are quite likely seeing/having the effects of normal wear, some pressure losses in the transmission which affects how well it "hooks up" in any particular gear. This will leave you feeling like it's 'slipping' a bit.

Shifts won't be quite as crisp, and it won't feel like its 'holding' after you pickup each gear.

You can do a stall test on the TC. Warm up the truck/transmission, plant the breaks HARD and step on the accelerator... . max WOT time = 5-6 seconds. If you can get a tach hooked up for this you want to see it stay in the 1750-1950 RPM range. If you go over 2000RPM you got a TC that is out of DC spec and slipping too much.

After the test, let it idle in "N" for a couple minutes to bring the temps down cause she can get pretty toasty doing this.



Last thing to do is a proper series of pressure tests. A decent transmission shop should be equipped to do this. Check your transmission line pressure at idle and WOT. Set toward the high end of DC spec.



Does that help at all ????



bob.

 

[dpuckett]

Yes, that does help

Now I just have to convince her of it. I am going back there next weekend, and may do a few tweaks on it while she isnt looking, and blame it on the Stanadyne. I will also try the stall test when I get a tach. Getting a shop in that area that can do more than change fluid and filters is a bit of a chore. There is little to no smoke during a WOT acceleration. I may turn a bit on the full power screw, and recompensate via the AFC. I just dont want it to crap out halfway across Kansas. Murphy's Law says that is where it will happen. SHe is also accustomed to older transmissions that slip (73&75 C6), and thus not as watchful as I am when it comes to problems.



THanks a lot.



Daniel

 

[BushWakr - RIP]

Personally if I were going to tweak it, I'd use the AFC/cone adjustment before the full fuel screw. The main reason is that will allow fueling to happen a bit sooner if she gets on it but won't send a lot of extra fuel to the low end like the full fuel screw will.

But, that's just me... .

You can go 1/4 to 1/2 turn on the full fuel if that is your decision.

Of the total increase that makes to fueling a larger portion always seems to be sent to the low/low~mid range with the balance to mid/high range.

Thing is the AFC is a bit more work and harder to sneak it past someone when you don't wanna be too obvious... .



Bob.