Air in fuel system
02-16-2017, 11:08 PM
#1
Air in fuel system
Howdy guys,
I had time today to do some more diagnosis of my misfire/detonation issue I've been fighting for over a year now. Long story short, I hooked up a fuel pressure gauge to the fuel rail test port and bled fuel into a bottle to check the flow rate. I discovered that while my fuel pressure is within spec (38psi), I was getting just as much air as fuel coming out of the line. That being the case, I suspect the detonation I'm having under partial load is due to a lean condition. I spoke with one of my professors who has 30+ years of automotive shop experience and is knowledgeable about these older Fords, and he thinks that this lean condition may be also causing my ICM's to burn up. His thought is that since it is more difficult to fire a spark plug in a lean cylinder, this higher resistance when firing the plugs causes a voltage spike within the coil which may be backfeeding, resulting in ICM damage and ultimately failure. While his theory makes sense to me, I'm a little skeptical. However at this point my main concern is finding where my fuel system is sucking in air.
My truck is a 1992 with the 5.0L with dual tanks. The truck has detonation and misses regardless of what tank is selected. That tells me that the fuel system is sucking in air somewhere that is not affected by which tank is supplying the fuel. Is anyone aware of a fitting/wear point along the fuel lines that are known to suck in air? I haven't had a chance to do a visual inspection of the fuel lines yet.
As always, thanks for any input!
I had time today to do some more diagnosis of my misfire/detonation issue I've been fighting for over a year now. Long story short, I hooked up a fuel pressure gauge to the fuel rail test port and bled fuel into a bottle to check the flow rate. I discovered that while my fuel pressure is within spec (38psi), I was getting just as much air as fuel coming out of the line. That being the case, I suspect the detonation I'm having under partial load is due to a lean condition. I spoke with one of my professors who has 30+ years of automotive shop experience and is knowledgeable about these older Fords, and he thinks that this lean condition may be also causing my ICM's to burn up. His thought is that since it is more difficult to fire a spark plug in a lean cylinder, this higher resistance when firing the plugs causes a voltage spike within the coil which may be backfeeding, resulting in ICM damage and ultimately failure. While his theory makes sense to me, I'm a little skeptical. However at this point my main concern is finding where my fuel system is sucking in air.
My truck is a 1992 with the 5.0L with dual tanks. The truck has detonation and misses regardless of what tank is selected. That tells me that the fuel system is sucking in air somewhere that is not affected by which tank is supplying the fuel. Is anyone aware of a fitting/wear point along the fuel lines that are known to suck in air? I haven't had a chance to do a visual inspection of the fuel lines yet.
As always, thanks for any input!
02-17-2017, 08:39 AM
#3
That is a high pressure system that pushes fuel right from the pump in the tank to the fuel rail. Any openings that could suck air would blow fuel instead. I don't see how it could suck air in anywhere but right at the pump ?
Could air be getting in at the gauge and misleading you ?
There's 2 different colours of ICM - basically seems to be for auto or manual trans. Just make sure you have the correct one.
Could air be getting in at the gauge and misleading you ?
There's 2 different colours of ICM - basically seems to be for auto or manual trans. Just make sure you have the correct one.
02-17-2017, 10:18 AM
#4
I'm using the correct ICMs.
I thought I was getting air in through the gauge but my professor looked at it and insisted that the connection is tight and air is coming from elsewhere.
I thought I was getting air in through the gauge but my professor looked at it and insisted that the connection is tight and air is coming from elsewhere.
02-17-2017, 10:48 AM
#5
Senior Member
X2 on what Chris said would be leaking fuel not sucking air . Odds of both pumps sucking air in tanks is slim . Maybe your professor should research the system to understand it ,
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02-18-2017, 01:13 PM
#10
I see. Well I'll check it again to verify if there's air or not.
Yes, the entire ignition system has been replaced. All new parts. Timing is 10* BTC with SPOUT connector out. Ran some carbon cleaner through the motor and it made no difference. No DTCs
I had the fuel pressure gauge hose connected to the test port on the fuel rail and with the fuel pump running, fuel and air was coming out of the hose, you know, all sputtery and whatnot. I don't know how to explain this any clearer.
Yes, the entire ignition system has been replaced. All new parts. Timing is 10* BTC with SPOUT connector out. Ran some carbon cleaner through the motor and it made no difference. No DTCs
I had the fuel pressure gauge hose connected to the test port on the fuel rail and with the fuel pump running, fuel and air was coming out of the hose, you know, all sputtery and whatnot. I don't know how to explain this any clearer.