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6.5 still having problems

F

frostedapp

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Hudson Valley
:mad2: Well... I just can't seem to get this truck running right. She idles fine and cruises good, but when I get up to about 50 or 55 mph and 2000 rpm the tach needle starts going nuts like someone is feathering the pedal, then the tach drops to nothing like I took my foot off the pedal, but didn't. if any of you remember I changed a a few parts, starting with new fuel lines from tank to lift pump, changed the whole sock assembly in the tank, changed the lift pump twice, changed the ops, changed the vac pump, and changed and relocated the pmd to the top of the manifold:. Is there some kind of solenoid ?
 
I know it sounds like a broken record. but how about the grounds???? Or your alternator could be on its way out. The tach in these 6.5's reads from the alternator. Check the plugs and connections on the alt, and see if this helps.
 
X2 If the engine RPM is steady but the tach moves it is the alternator or related wiring back to and including the tach. Check the gauges fuse for corrosion. Check the charge wire on the Alt and positive battery cables as well.

Be careful that the new alternator has the same size pulley as your old one! They love to sneak a gasser pulley on them at the rebuild depots. Your RPM readings will never be the same after that...

If the engine is cutting out then you have a different issue. PMD on the intake manifold is like an oven... Is it a new PMD or one off the pump?

Air in the system will cause any 6.5 to jump RPM and stall.
 
Maybe a dumb question, but how many tanks of fuel have you put through it since this started happening? Could it be old fuel from a mom and pop fuel station? I went through this, I also answered a thread like this on the other site, guy having similar problems and that is exactly what it was. Old fuel and no conditioner will cause your truck to buck like a mofo around that 1200-2000 rpm range. Toss in a bottle of Diesel 911 or pump the tank out.

FWIW I also was crappin my pants thinking all the bad things like PMD, IP, etc etc too.
 
Next time your all wamed up (heat SOAKED) At Idle revv it up to 2500 slowly, and then slowly bring it back to idle.

Do this about 5 times or so, and see if you loose smoothness at any rpm range(s).

Good IP generic health test.
 
The tach signal comes from the alternator. I did not realize that when my alternator went bad. In other words, I did not realize that my alternator was bad.
I would check the alternator first since that is cheaper than IP. Eliminate that possibility.
 
when it's all warmed up at idle she runs fine, when I raise the rps to about 2500 or so she starts spitting and sputtering like crazy, when I let off the accelerator she's fine. took her out today and she acted up, especially going up a small incline, started sputtering and choking, and blowing a little blue smoke out of the exhaust. also lost alot of power. Have put several tanks of fuel in since all this started, all from Hess or Mobil. Alternator grounds and connections seem fine.
 
Sounds like you are getting air in the fuel, have you made sure there is lift pump pressure? Just changing the parts doesnt really tell you that. Even if you have pressure youre more likely to get air in there under load with a air hole between the tank and the LP. I see you changed all those lines and pickup, was it because of this exact same issue?

You may actually have an IP on its way out. If you have pressure and youve watched for air in the return or supply at the IP and none there must be an IP issue.

Try unplugging the optical sensor on top of the IP and driving it that way and if it works any smoother. You will still lose some power at RPMs but not as much.
 
X100 on the alt. I just went through that two weeks ago. I had it tested and it had a bad diode, it was putting out 10 volts, enough to make the tach needle bounce or even go to zero intermittantly. Heck for the last 40 miles on my way back from a trip it finally turned the battery light on and my volt gauge went to ten.

The next morning I started it and it was charging for a little while and started all over again. That's when I took it off and brought it in to have it tested, and that alt. was only two weeks old. Needless to say the replacement that I now have is fine so far. BTW the one before the the last replacement was doing the same thing..


My vote is your alt is on it's way out.
 
subclatter said:
X100 on the alt. I just went through that two weeks ago. I had it tested and it had a bad diode, it was putting out 10 volts, enough to make the tach needle bounce or even go to zero intermittently. Heck for the last 40 miles on my way back from a trip it finally turned the battery light on and my volt gauge went to ten.

The next morning I started it and it was charging for a little while and started all over again. That's when I took it off and brought it in to have it tested, and that alt. was only two weeks old. Needless to say the replacement that I now have is fine so far. BTW the one before the the last replacement was doing the same thing..


My vote is your alt is on it's way out.
Click to expand...

Don't ya just love these Quality replacement parts!
 
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