Mid rpm miss under load

[1989idi350]

Ill keep it simple. 1989 f350 7.3 idi unknown condition of injectors and injection pump. Replaced seals under injectors. Smoke only on startup for a few seconds. My problem is that under load I have what feels to be a miss under partial throttle and wot. I don't see any leaking fuel. Some help would be more than appreciated.

 

[DrCharles]

What is your fuel pressure doing? You may need to tape a gauge to the windshield and watch it when you put a load on the engine. First suspect (besides a dirty fuel filter) is a weak lift pump.

 

[Macrobb]

If you end up with good fuel pressure under load, it's timing(from a worn IP). At part throttle, the light-load advance goes away, meaning you are relying on the internal pressure-based advance mechanism. Low input pressure(clogged fuel filter etc) will cause retarded timing. Also, pump wear will do the same thing - you can advance the pump mechanically(just rotate it to the passenger side), which can help... but if it is a worn IP timing advance, it won't end up "right" throughout the RPM range. You can make it work until you get a new IP, though.

 

[1989idi350]

After double checking my work, I do have a few leaks between the injection lines and the injectors. Im going to try to tighten them down. Hopefully this is my issue.

 

[1989idi350]

I was only able to get one injection line a little tighter and still have fuel past that injector. That same injector when the line is loosened it sounds different. Went around the rest and loosened the lines individually and only one seemed to not change when loosened. I'm going to try seafoam and replace the return lines and the injector o rings.

 

[1989idi350]

The misfire seemed to be below 2200 rmps. If it is in the upper rpm range it isnt noticeable. Hope it's not the pump.

 

[Shadetreemechanic]

You still haven't said whether you replaced your filter or checked you fuel pressure. Those would be first in my mind.

 

[1989idi350]

No I haven't. Is pressure checked at the Schrader valve? I've owned this truck for about a week now. I am reading many posts on many different forums to get up to speed here. I appreciate the suggestions. Thank you.

 

[Vern]

May be it's a good idea for me to do the same i.e. 'T ' in a pressure gauge between the filter and the ip to watch what's happening with fuel delivery to the transfer pump given my situation. I've a blue smoke issue at offload times like coasting with a small amount of pedal, more or less exactly as this guy describes with his 94 idi "no load smoke".

"At idle smoke a little, under no load, such as coming down a hill half throttle, smoke is terrible. Blue in color and burns nose and eyes. Under a load smoke clears up, has plenty of power..."

Also, during shifts as I let off, a "puff". And, it will roll coal if I push too hard.

I do know that I have a cylinder that is slow to warm up. I get puffs from it at idle and at low load until warmed up. I'm not certain but I think it's cylinder no. 1. Also I have a smoke at idle even when warm.

I brought the truck back from the dead... put in a inline pump, by-passed filter with in-line filter, had the pump cap off, tightened up a loose injector body, rerouted return lines, eventually got dirty diesel to the injectors. took the CDR off. I sprayed some water in the intake with a hot engine. The latter seemed to help some.

Now I'm wondering about timing and the 'light load advance (retard?). The cam seems to engage just past idle as some has described as the proper adjustment. I'm inclined to advance the timing a nudge and see what happens. Any thoughts?

 

[hesutton]

Doubt it's the return lines. Typically, you'll have hard starts with some air intrusion there.... not a miss like your describing. Fuel pressure/supply, worn IP/injectors would be my initial thoughts.

Easy place to check fuel pressure is the filter head where the fuel light switch is plumbed in. Pull the switch and plumb in a sender or mechanical gauge.

Heath

 

[Vern]

Guys, what is good fuel pressure? I realize the e pump I installed may be under delivering. its the facet 1-2psi 15gph.

Also, I wonder if I have killed my mechanical lift pump running it dry for a good while now. There's risk of dumping fuel into the oil I understand. It was not known to be bad when put in the e pump. If it weren't ruined I would see if it made a difference in the smoking I'm experiencing.

 

[DrCharles]

1-2 psi is way below the spec (5 psi?) and 15 gph probably isn't enough either.

As has been said at least twice above, check your pressure at the filter head already!
Although if the pump is only rated for 1-2 psi that is the first thing to replace. Most people use a Facet 40285 or the slightly higher-pressure model (don't recall the number.

 

[Vern]

Reinstated the mechanical lift pump as it was testing no leaks with the vacuum pump plugged on the inlet. I now have the inline e pump and the mechanical pump working together, and through the original filter instead of my bypass inline filter. no change in smoke symptoms. Next idea is to advance the timing and perhaps turn down the fuel.

 

[snicklas]

DO NOT HAVE THE E-PUMP PUSHING FUEL THROUGH THE MECHANICAL PUMP!!!!!!!

That is an excellent way to fill you crankcase with diesel! Either get an E-Pump that is the proper specification, or run the mechanical, NOT BOTH!!!!

I strongly recommend not running the truck again until one of the pumps are removed from the circuit. Diesel isn’t a good engine lubricant.....

 

[riphip]

Plus check your oil for rising level, diesel fuel smell, & dipstick & see if it will 'light-up' from diesel in oil.