Three parter question on trans and Diesel eng.

[smokinpipes]

Hello all, long time reader, first time writer... and this seemed to be the place I should ask upon fellow Ford fans (or knowlegable ones aswell )

I have an '85 F250 with the 6.9L diesel, I just changed my air filter, replaced the injectors, the o-rings, the caps, and lines, checked everything for fuel leaks, but I'm only getting 12.5 mpg on average. Sometimes 13!!! Now being my third 6.9l diesel truck, it seems low compared to my other two. It does have an automatic, but so did one of my other ones. My first truck was an extrended cab 2wd, with a 6.9l, and auto and that got 15-17mpg, then my second was a 250 2wd, manual, standard cab, and that got 15-20 mpg,
Now my latest one is only getting this? Any ideas? It does have a subtle miss when it's cold (all glow plugs work) and blows out the occasional blue smoke puff right after it misses. It has only 97,000 on it.

Next question...same truck, but it shifts hard going into second gear, the harder I press the throttle, the longer the engine revvs and then just slams into gear, if I'm light on the throttle, it shift smoothly. I adjusted the throttle vacuum valve, and made sure the kickdown rod wasn't misaligned... Again, ideas?

Then the last one, I did a head job on my 85 with the manual trans, got it put back together, started it up, and ran for about 10 seconds, just long enough to start to build oil pressure, (changed the oil too) and then something broke on the #1 cylinder and bent the exhaust valve pushrod, and stopped the engine dead flat. took the glow plugs out, and cranked the engine over with a ratchet and found no air moving in or out of the glow plug hole. Now I suspect I broke a writst pin, or a connecting rod, but why? It has only 160,*** miles on it. The head gasket was leaking antifreeze from the front of the block, but I wasn't burning any coolant, and when I looked at the original solid steel gasket, it showed no signes of compressioin loss, and the hone marks were still very visable on the cylinder walls, so the piston wasn't scraping... do you think is might be possible to salvage something out of the eninge/block or am I screwed. Yet once again, any ideas?


Thanks to you all for your thoughts and advice
-Don

BTW, I photographed my cylinders with my camera to "document" the job if itmay help.

 

[highest_vision]

1- I've always gotten 12mpg and it seems to be on the low end of every one, but I had head issues. Drive it for awhile and see what you use re fluids and when.
2 - There is a vacuum diaphragm/modulator on the trans also, could be bad but if you pull the vacuum line and don't see ATF, probably ok. The VRV you adj may be bad or adj inproperly.
Here is the procedure for the VRV adjustment.
You don't have the engine running for the test, you need to apply 20" vacuum to upper VRV port and attach vacuum gauge to lower VRV port. The lower port is the one that goes to tranny, the upper to vacuum pump.
You have to maintain 20" througout this test. If it drops off you need to pump it back up.
Remove throttle return spring, cycle throttle lever 5 times from idle to WOT. Make sure 20" vacuum is maintained on upper port side.
Move throttle so it is 0.515" (33/64") from wide open (they make a tool for this). Vacuum gauge should read from 6-8" of vacuum. If incorrect adjust VRV to 7".
Again apply 20" vacuum, cycle throttle from idle to WOT 5 times. Return to idle. Gauge should read at least 13".

If you can't get the 7" or the 13" replace the VRV. If VRV checks out maybe the diaphragm (modulator), line from VRV goes to the vacuum diaphragm. Can't find any adjustment for the diaphragm but I think there is a little.
Couldn't find the part number for VRV, but the diaphragm is D70Z-7A377-A, the guage (if you want it) is T83T-7B200-AH.
Basically all you need for the test is a vacuum pump (handheld type), vacuum gauge and a ruler to measure 1/2" or a 33/64" drill bit in lieu of the .515" tool. And a screwdriver for any adjustment needed. I have found that maintaining 20" while cycling throttle is impossible, I generally skip this. Cycling the throttle dumps vacuum.
3 - probably need to pull the head or pan.
James

 

[Diesel JD]

In a related vein...the vaccum pump itself could be in poor condition...they don't last forever. As far as fuel mileage, 12.5-13mpg could be right depending on your gear ratio and what kind of driving you do. If you have the 4.10s and the C6 its a great combination for towing, but bad for fuel mileage on a daily driver. If it helps, on B100 biodiesel I have been getting 13-14 in town empty and over 14 loaded on the highway cruisng with my 3.55s. When I had 4.10sit was closer to 11-12 around town and 12 on the road with the bio, a little more with D2. As far as your old 6.9, sounds to me like you spun a bearing or dropped a valve. i guess a broken wristpin would do the same thing. First thought is that you got unlucky and a valve dropped or something was in between the head and piston, so something had to give, and it did. Looks like you're to at least pulling that head and seeing what broke, maybe more...but its highly likely you'll find a lot in there to salvage. Almost for sure the block and crank. Who worked over those heads for you and did they stand behind their work in any warranty?

 

[LUCKY_LARUE60]

Last December I had to go to Kansas, 680 miles one way, had tail gate down, ran between 60 to 65MPH got 17.5MPG. I have a 7.3 nonturbo, ZF5, 4:10's rpm's around 2200. On the way back, same distance, I was running 70 to 75MPH around 2400RPM's tailgate up got 17MPG, go figure.

Jim

 

[Agnem]

I'd say welcome to the site, but since you confess to having been here all along, I'll say instead, Congratulations! For posting that is. And also, Congratulations for obviously READING and being a good student, having now done many of the things that most folks come in here looking for info when it's too late, having already tried it and broken something, which is a good sequay to your last comment, but let's take them in order.

On the 85' 6.9 C6 truck, what gear ratio? You say the IP has less than 100K on it, but have you timed it, especially since your injector change? If not, I guarantee you it is several degrees retarded, which will hurt your fuel economy. As for the miss, it is possible that if you did not have your replacement injectors tested, a marginal one may have been installed.

On the shift problem, I concur with what the others have said. Definitely get the vacuum system completely checked out and adjusted. It probably would not hurt to also adjust the band to compensate for wear. Change your fluid too, because there is some slipping going on in there right now.

As for the last problem, THAT ROTS! I assume the engine was cranked a fair amount before it actually started and then broke. Definitely sounds like the valve and piston colided. Obviously that head will have to come off again to assess the damage. Two comments on this one. First, I've come to adopt a policy of starting the engine with no coolant in it when doing a head gasket job. No belts, no accessories, and no water. Just long enough, like you said to build oil presure and listen to it. Just a minute of running at idle will get things warm and help seat everything without the chance of water interfering in the process. That, and then of course if you have a problem, you've saved a few hours by not having to take all that crap off again. Since you say you had a water leak near the same cylinder that jamed up on you, that makes me go "hmmmm" but of course we won't know anything until you get it apart. It's possible the exhaust valve is the reason your not feeling any air, but once again, disassembly will be required before we can stop guessing. Tough break. Keep us posted.

 

[sle2115]

What work was done on the cylinder heads while they were off? Were the valves reground? I wonder if a keeper was not installed properly or was disturbed in the process of removal/reinstallation allowing a valve to come loose. Hard to tell after the fact because if there was contact, there is a good chance they are off the valve now and the question becomes which came first, the chicken or the egg (contact or faulty installation by a machine shop or knocked loose during R&R).

 

[GenLightening]

Mythbusters did a test on the tailgate up or down theory and found that the manufacturers designed them to be more aerodynamic with them up. With the gate down it creates a, for lack of a better term, "suction bubble" that adds drag.
End of hijack.
Doug