No idea whats going on with my engine... IT HARDLY STARTS!
1994 trucks had a different fuel system and fuel injectors. Just some weird first model year stuff that is normal with every car line.
So with that in mind, if the spec for the fuel pump output is spec'd out at 39 psi ± 5 psi, that means the min psi rating per spec would be 34 psi.
Now, the question is: what is the fuel pressure output. I noted two readings: one at 33 and one at 30 psi so, which one is the accurate reading or, is there variation? This is what we want to find out.
In order to measure this, one would measure pressure in two ways:
Test Method 1. using a good, fairly accurate pressure gage, tap into the Schrader valve (providing the 04s have one) and turn the key to <ON> one time. NOTE PRESSURE. The pressure should be within the proper range with one turn of the key providing there's no leaky injectors or failing check valve / gross leaks etc.
If the pressure is not within spec, turn the key to <ON> one more time and note pressure. IF it's not within spec, repeat the process one last time and note pressure.
Monitor the pressure gage and watch closely for a drop in psi. It should at a minimum hold pressure for a min of 15 minutes. If it fails to hold a minimum of 20 psi for 15 minutes, there's an issue.
That's when we proceed to Test Method No 2.
Test Method 2 isolates the fuel pump and supply feed.
For now, start with Test Method No 1 and, if it holds pressure, no need to proceed with Test Method 2.
Test Method 2:
Remove the fuel supply line from the rail. The objective here is to connect a gage to this line directly. In doing this, this tests the pump and supply lines only. What this will tell you is whether or not it's the pump and / or supply feed.
If no drop in pressure is witnessed using Method 2, you now know the problem is rooted at the EFI components.
Let's just start first and see what we've got. In addition to this, I would strongly recommend you to also look at your IAC and determine if it's functioning as far as movement is concerned. I described how to do this in a previous post.
CM
Now, the question is: what is the fuel pressure output. I noted two readings: one at 33 and one at 30 psi so, which one is the accurate reading or, is there variation? This is what we want to find out.
In order to measure this, one would measure pressure in two ways:
Test Method 1. using a good, fairly accurate pressure gage, tap into the Schrader valve (providing the 04s have one) and turn the key to <ON> one time. NOTE PRESSURE. The pressure should be within the proper range with one turn of the key providing there's no leaky injectors or failing check valve / gross leaks etc.
If the pressure is not within spec, turn the key to <ON> one more time and note pressure. IF it's not within spec, repeat the process one last time and note pressure.
Monitor the pressure gage and watch closely for a drop in psi. It should at a minimum hold pressure for a min of 15 minutes. If it fails to hold a minimum of 20 psi for 15 minutes, there's an issue.
That's when we proceed to Test Method No 2.
Test Method 2 isolates the fuel pump and supply feed.
For now, start with Test Method No 1 and, if it holds pressure, no need to proceed with Test Method 2.
Test Method 2:
Remove the fuel supply line from the rail. The objective here is to connect a gage to this line directly. In doing this, this tests the pump and supply lines only. What this will tell you is whether or not it's the pump and / or supply feed.
If no drop in pressure is witnessed using Method 2, you now know the problem is rooted at the EFI components.
Let's just start first and see what we've got. In addition to this, I would strongly recommend you to also look at your IAC and determine if it's functioning as far as movement is concerned. I described how to do this in a previous post.
CM
Professional
Joined: Feb 2008
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From: manassas va
Olsen is right.You need to check for volume.Everybody gets wound up on pressure while ignoring volume.Pump can deliver lots of pressure but little volume.Your sock may be clogged.If you smell fuel thats what called a clue.Check injector bosses,fuel rails,fuel lines for source.Try starting truck on propane.If it starts easier you know your on point.
Professional
Joined: Feb 2008
Posts: 141
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From: manassas va
Im snowed in now but I will gladly look it up on alldata when I get in.You know alldata right?Sorry thats a professional tool.Most factory manuals have a flow minimum....you really should have known.
NO, I don't have a manual that covers his year so, I was hoping that you had answer. Once he knows what the flow rate is, can verify what it is and note whether it's to spec or not.
Without knowing what the flow rate is, there's no way to verify if it's correct or not.
CM
Without knowing what the flow rate is, there's no way to verify if it's correct or not.
CM
you really should have known
Professional
Joined: Feb 2008
Posts: 141
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From: manassas va
Didnt say I didnt know,just didnt have the exact right now.You sure are testy!Anyway,the general rule of thumb is a quart in thirty seconds,but like I said,I dont have an exact.You can also block the return line and see if you get a pressure increase.If not chances are pump is worn or voltage is low.I have seen the electrical connectors at the fuel tank develop some corrosion,causing low voltage to the pump itself.Last,I have seen pinholes develop in the return line stand tube that cause a loss of pressure and fuel smell.Hey just so you know,dont do the volume test while running.You just have to energize the pump,not crank it.Its also a good idea to clean the tank out while you have everything apart.I dont know about the fuel in your part of the country,but we get lots of ethanol on east coast,which leads to phase separation.Essentially the ethanol combines with water and drops out of suspension.It smells like paint thinner.You will see this when doing the volume test.It plays hell on pumps and regulators.I have a GMC in the shop now that has a transfer pump problem and the inside of the tank and components look poo-poo.