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'99 7.3L loping on startup and miss until warm

19K views 23 replies 6 participants last post by  caboose 
#1 ·
Hi all.

Hoping I can get some pointers here. I have a 99 F250 (I think it's an early 99) and recently it's been acting a little odd.

It will lope a pit on start up. Warm or cold, doesn't seem to matter. If I shut it off and start it right back up it won't do it but after siting for a an hour or so it will do it. It seems a bit sluggish and I feel a vibration at lower rpm that makes me think an injector isn't firing.

On my way to work today it cleared up and ran fine after about 10 mins of driving.

I plan to drain the fuel bowl, get a new filter, and get some fuel with lots of dieselkleen added. Any suggestions if that doesn't yield any positive results?
 
#2 ·
How many miles on it? The injectors may be worn to the point where some won't fire when the engine is cold due to reduced clearance between the armature plate and injector body. The cold thicker oil keeps the armature stuck to the body, and the solenoid doesn't have enough power to lift it free. If you've ever messed with machinist's gage blocks, which are so smooth they can stick together with nothing in between them, you'll have an idea what I'm talking about.There are shim kits sold that can provide a temporary fix, but ultimately the injectors would need replacement if that's the problem.

If your oil is "old" that may also cause problems. The 7.3L is oil-sensitive as the engine oil is used to drive the injectors, so an oil change may help.
 
#5 ·
AAAGH! Why? Trying to kill your motor? Do NOT do that. First, ATF has friction additives. Second, HUEI engines are VERY sensitive about what you put in the oil. I had a friend who was "conned" into buying a can of Rislone additive by the highly qualified, greasy haired, pimple faced teenager at the parts store. He poured it in, started his truck and it was dead by the time he got out of his driveway. Oil had foamed and wouldn't build high pressure. Had to drain the oil, suck out the HPOP and start over. Nothing goes in the engine oil but engine oil.

I agree with Kevin - I suspect your injectors are worn out. You could plug the block heater in for a few hours and see if it runs better from the start. That would almost confirm the injector problem. Getting out a feeler gauge would be the ultimate test. Read this article to see why:

View attachment PoppetValve.pdf
 
#7 ·
Do you feel the same about Archoil and/or REVX?
The only thing they do is suck money out of your wallet. The 7.3L doesn't NEED oil additives.
 
#9 ·
Update:

Drove home from work and the behaviour was the same. Chugged a few times on start up but smoothed out a little.

Still had the sluggishness at lower rpm and a bit of vibration. After about 10km of driving it started running normally again.

All signs point towards a sticking injector. So my plan is to:
- remove the valve covers
- inspect UVCH
- check injectors with feeler gauge as described above
- unplug injectors one at a time to ID the sticking injector

Does that seem reasonable?
 
#10 ·
Yes - as a quick test before you do that - unplug the ICP sensor and take it for a quick run. Could be a biased sensor giving you issues.
 
#11 ·
Ya less than .002 thousands will cause running issues. They usually clear up when warm.

A lighter weight 5w/40 will usually help if armature clearances are tight.
 
#14 ·
I wouldn't buy parts store injectors.

Look into rosewood, full force, PIS,
 
#15 ·
I agree - a set of Full Force injectors is the way to go.
 
#17 ·
You never mentioned you were a puckhead. Maybe we can go ahead and make Canada the 51st state so you guys can get a better deal on parts!
 
#18 ·
Could be stiction every so often I run a stiction eliminater. I had the same issue at 277,000 miles. Once I ran cleaner through It she cleared up. Now I use it every other oil change.
 
#19 ·
Truck seems to be running normally today.....




Do you remember what specific product you're using?

You never mentioned you were a puckhead. Maybe we can go ahead and make Canada the 51st state so you guys can get a better deal on parts!

I'm not much of a hockey fan to be honest. Didn't even know that the Stanley Cup was over until today. Motorcycle racing occupies a lot of my time!
 
#22 ·
You should be able to identify a fuel contaminant by draining the fuel filter housing into a clear jar and letting the contents settle out overnight.

Are you familiar with the procedure?
 
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