Strange engine behavior. knocking. sluggish
Thread Starter
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Laughing Gas
Joined: Nov 2004
Posts: 790
Likes: 35
From: Austin
Strange engine behavior. knocking. sluggish
After a 30 mile highway drive, pulled into town and immediately noticed a loud 'knocking' sound. Engine was sluggish.
Knew I was low on fuel, so pulled in to fillup. Noticed that fillup took 28.6 gallons, usually takes around 26.
Started engine, still heard knocking. Truck ran, but again low power and noticed that I was not getting any turbo boost on the gauge.
Checked oil, was at the "add" line on the stick, so added 2 quarts.
Still knocking, still sluggish.
After about 10 more minutes of driving, truck started operating normally, no knock, no sluggishness, and turbo gauge showing boost again.
Been a couple of days now, and truck has been running as normal ever since.
Any ideas what happened?
Knew I was low on fuel, so pulled in to fillup. Noticed that fillup took 28.6 gallons, usually takes around 26.
Started engine, still heard knocking. Truck ran, but again low power and noticed that I was not getting any turbo boost on the gauge.
Checked oil, was at the "add" line on the stick, so added 2 quarts.
Still knocking, still sluggish.
After about 10 more minutes of driving, truck started operating normally, no knock, no sluggishness, and turbo gauge showing boost again.
Been a couple of days now, and truck has been running as normal ever since.
Any ideas what happened?
Fleet Mechanic
Joined: Jan 2006
Posts: 1,510
Likes: 7
From: Anchorage, AK
Being a newb I will take a stab at this but I am sure the big dogs will chip in soon.
Since you were low on oil, the engine may have stopped firing on all injectors and this then caused the lack of power and extra knocking. Im guessing that based on the simple fact that your adding oil solved the problem.
Did your check engine light come on?
Since you were low on oil, the engine may have stopped firing on all injectors and this then caused the lack of power and extra knocking. Im guessing that based on the simple fact that your adding oil solved the problem.
Did your check engine light come on?
Hotshot
Joined: Jan 2008
Posts: 13,144
Likes: 11
From: Rochdale MA
If you were that low on fuel you were probably sucking in some water mixed fuel from the bottom of the fuel tank, after you filled up it took the 10 minutes to "purge" it from the lines with the fresh fuel. I would consider changing your fuel filter.
Fleet Owner
Joined: Jun 2004
Posts: 25,090
Likes: 1,111
From: Rio Rico, AZ.
Air and/or water is not fuel, will not burn, so no smoke.
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Laughing Gas
Joined: Nov 2004
Posts: 790
Likes: 35
From: Austin
no smoke
Thanks for the replies. I ordered a new fuel filter on ebay, and just went out and drained the fuel out of the existing fuel bowl/filter.
I noticed no smoke out the pipe during the strange behavior.
I noticed no smoke out the pipe during the strange behavior.
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Fleet Mechanic
Joined: Jan 2006
Posts: 1,510
Likes: 7
From: Anchorage, AK
I decided to re-read my 7.3 owner manual and it states that I run low on fuel air could get into the fuel system. It also warns that if this happens the truck might produce white smoke while the air is purged.
What gives?
What gives?
Fleet Owner
Joined: Jun 2004
Posts: 25,090
Likes: 1,111
From: Rio Rico, AZ.
Then the injection pressure drops way off because air is compressable.
Low injection pressure causes the fuel to not atomize very well and it doesn't burn.
Engine power drops off and the ECU increases pulse width to compensate.
Basically you have a bunch of unburned fuel coming out in the exhaust because of this cascading "failure" just because of air in the fuel.
.
Does this explain why I moved my fuel pump to the tank?
