Fuel pump question
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Fuel pump question
I've got a 1990 F350 with the 7.5L EFI engine and it used to run sort of ok at idle but bogged down horribly when you put it in drive though you could still drive it on flat ground ok. Now it won't start at all and am trying to diagnose the problem.
Here is what I've found so far.
Most all of the cylinders are at 150 psi except for the #8 cylinder which is at 75 psi but jumps up to 150 on a wet compression test. Obviously it has an issue with the rings or cylinder wall or both on that piston.
I tested for spark and all of the cylinders have spark that I can visibly see and look like good spark
I changed out the rear tank fuel pump and then checked both front and rear pressure at the rail and when you turn the key on the pressure reads at 44 psi and then settles down to 40 psi in the key on position. When you turn the key off then it settles down to 39 psi and both front and rear pumps act the exact same even though I put in a new one in the rear tank.
What is the correct fuel pump PSI that these things run at and what other tests should I run? I would assume that the truck should still run fine even with poor compression in only one cylinder.
Here is what I've found so far.
Most all of the cylinders are at 150 psi except for the #8 cylinder which is at 75 psi but jumps up to 150 on a wet compression test. Obviously it has an issue with the rings or cylinder wall or both on that piston.
I tested for spark and all of the cylinders have spark that I can visibly see and look like good spark
I changed out the rear tank fuel pump and then checked both front and rear pressure at the rail and when you turn the key on the pressure reads at 44 psi and then settles down to 40 psi in the key on position. When you turn the key off then it settles down to 39 psi and both front and rear pumps act the exact same even though I put in a new one in the rear tank.
What is the correct fuel pump PSI that these things run at and what other tests should I run? I would assume that the truck should still run fine even with poor compression in only one cylinder.
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I got a code 34 and the fuel pump I bought was only $14.99 off Ebay and I figured it was worth the try. I removed the EGR valve and cleaned it as I noticed that it was stuck but was able to get it moving properly
Fleet Owner
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From: Kentucky
KOEO fuel pressure should be in the 40-45 PSI range. KOER @idle ~30-35 PSI, KOER vacuum line off: 40-45 PSI. KOER under load the fuel pressure should rise from 30-35PSI to 40-45 PSI as the vacuum decreases. At no time should the fuel pressure drop below ~30 PSI.
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Thanks, so from what you are saying the numbers I'm getting look like I'm getting the correct fuel pressure.
Fleet Owner
Joined: Oct 2005
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From: Kentucky
Static KOEO pressures look good. Now you need to see if the injectors are getting pulses to allow fuel to enter the cylinder. Pull a plug to see if it is wet to begin with.
If the distributor has been R&R verify it is in time and not 180 degrees out.
Try spraying a little ether in the intake to see if the truck starts momentarily. If so, you are back to verifying the injectors are being commanded on.
If the distributor has been R&R verify it is in time and not 180 degrees out.
Try spraying a little ether in the intake to see if the truck starts momentarily. If so, you are back to verifying the injectors are being commanded on.
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Static KOEO pressures look good. Now you need to see if the injectors are getting pulses to allow fuel to enter the cylinder. Pull a plug to see if it is wet to begin with.
If the distributor has been R&R verify it is in time and not 180 degrees out.
Try spraying a little ether in the intake to see if the truck starts momentarily. If so, you are back to verifying the injectors are being commanded on.
If the distributor has been R&R verify it is in time and not 180 degrees out.
Try spraying a little ether in the intake to see if the truck starts momentarily. If so, you are back to verifying the injectors are being commanded on.
Ok, I pulled one of the plugs and the plug is wet with fuel.
The distributor hasn't been disturbed ever since the problems started showing up and I doubt that it's ever been touched.
I wonder if the issue might be a weak or intermittent spark. I ordered a new cap and rotor and coil since I'm sure that the ones the truck currently has are original.
Ok, I'll try spraying some starting fluid in the intake.
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Sprayed starter fluid in the intake and it didn't help start so I'm thinking there is a spark issue like either a weak or intermittent spark
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Ok, replaced the coil and the rotor. Still no change. I see that there is a little condenser also mounted next to the coil. Would something like this wear out and cause a no run condition?
Basically the truck fires up for about 3 seconds and then dies. Still waiting for the new distributor cap to show up in the mail.
Basically the truck fires up for about 3 seconds and then dies. Still waiting for the new distributor cap to show up in the mail.
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