7.3 runs rough at start then smooths out warm - PowerStrokeNation : Ford Powerstroke Diesel Forum
 
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post #1 of 2 (permalink) Old 08-20-2018, 01:03 PM Thread Starter
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7.3 runs rough at start then smooths out warm

I have a 97 F350 7.3 PSD that i bought in Texas. It started well and ran great cold, then ran rough at idle with a miss after warmed up. I tracked it down to worn injector tips. I reasoned that the viscosity of the fuel got thinner after the injector warmed up and it essentially leaked into the cylinder instead of spraying after it got hot. I confirmed this by running the tank very low and having it running warmed up with the miss, poured a gallon of 15w40 into the fuel tank. As soon as the fuel hit the injectors, it smoothed right out.

So, bad injectors. I purchased a set of used injectors from a guy who had them in a truck for a very short time, he said they were rebuilt and only had a few hundred miles on them before the truck got wrecked. He pulled them and scrapped the truck and they sat on a shelf in his unheated garage for a few years.

I installed them into my truck and after getting it started, worked on getting all the air out of the rails. That took quite a while. Couple hundred miles easy. After all that, it ran pretty decent warm, much smoother than it had with the previous injectors.

Then on every cold start, i have an extended crank, up to 5-10 seconds where it doesn't fire, then stumbles a bit and very rough idle. I then rev it up to about 2-3000 rpm and i can hear injectors coming online one by one. After a couple minutes, i can drive the truck on the road and as the engine warms up it returns to the nice smooth idle.

I thought perhaps there was a stiction issue with the injectors, so i tried hotshot stiction eliminator, and that did not help after 75 miles. It did run even smoother at idle than before but only when hot.

Since the only thing that changed was injectors i think it must be the injectors, but the symptoms are a bit puzzling to me.

Why does it have an extended crank before firing after all the oil is out?
Could the anti drainback valve be leaking suddenly? It started fast before the injector swap out.

Has anyone seen this type of problem before? Ideas?

1997 F350 CCLB Dually XLT
1986 Bronco 6.9 Turbo XLT
Powertrain engineer by trade have worked for three OEM's.
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post #2 of 2 (permalink) Old 08-20-2018, 08:58 PM Thread Starter
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Join Date: Jun 2009
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Re: 7.3 runs rough at start then smooths out warm

Quote:
Originally Posted by 86turbodsl View Post
Why does it have an extended crank before firing after all the oil is out?
Ideas?
Should be after all the *AIR* is out above. Edit post doesn't seem to work.

1997 F350 CCLB Dually XLT
1986 Bronco 6.9 Turbo XLT
Powertrain engineer by trade have worked for three OEM's.
86turbodsl is offline  
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