Crazy hunting / surging after fuel pump replacment

[DavidInMi]

Hello forum!

I am new to the forum. I did search the forum prior to posting this but I couldn't find an answer.

I have a 2001 Sport Trac 4.0, it's my wife's vehicle. We have owned it since new. ~175K on it. Two years ago we started to have issues with two of the tires losing pressure. Turned out to be corrosion on the inner lips of the rims. I had the tires broken down, rims sand blasted and power coated and installed new tires. While that was going on I decided to do some rust repair on the running boards. Got started on that and my father passed away in another state. So, past two years have been busy selling houses, moving Mom back to Michigan, getting her in a condo, etc. I started the truck every two to three months just to keep it lubed up. I go to start it in January and it won't start. It would turn over but not fire. I shot some starting fluid into it and it fired. That, in combination with not hearing the fuel pump running led me to believe it was the fuel pump. I was also concerned given how old the gas was getting from sitting. So, dropped the tank, drained the old gas, installed a new pump, complete assembly from Rock Auto. Installed a new fuel filter. Also have been doing some other maintenance while it was up in the air. New cat back stock exhaust system, new rear shocks, new pinion seal.

Anyway, the problem. I get it all done and go to start it up yesterday. Turn the key, here the new pump fire up. Runs a short time to build pressure then stops, I start the engine. It fires and immediately starts to surge all over the place, up to 3K, down to almost stalling, back up, back down. I tied this half a dozen times leaving a few minutes between attempts. Everything I've read on this forum (and others) says it could be a vacuum leak, bad fuel pressure sensor, or perhaps a bad ground. Maybe even the pump assembly I got was bad.

So, I plan to get a fuel pressure gauge from the local auto zone to check the pressure. Not sure how that's going to work since I can't get the RPM's stable at all. I'm also going to check for vacuum leaks. Pull the vacuum line off the fuel pressure sensor and see if there is any fuel in the line. Check the Oil for fuel. Clean the MAP sensor.

Any other suggestions? Is it possible since I had the system open that it needs to be purged? It being a 2001 I understand it was an interim system. It's the one line fuel filter system.

Any thoughts would be appreciated.

 

[ptf18]

Fuel pressure should indicate within spec regardless if the engine is running...or not.

I would "assume"....

As for your question of purging... I would think that it would be not be different than when the Filter is changed. I turn of the key of a second or two prior to cranking.

 

[koda2000]

A 2001 return-less fuel system should show around 65 PSI with the engine running. It might show something less with with the engine off, IDK but if you don't see around 65 PSI when running something is wrong.

As far as purging, after installing a new pump I turn the ign key ON/OFF a few times before starting the engine, but this is just done to prime the system so the engine gets fuel. Nothing else is required. Once running the engine should idle/run normally almost immediately.

In my experience, when an engine surges it's usually due to it not getting enough fuel (or too much air) and it's running lean. I suspect that there is something not right with your new fuel pump or its pressure regulator. Checking the fuel pressure at the rail should verify this.

Edit:
As @david4451 says in post #5 below, check for vacuum leaks. A vac leak wouldn't effect fuel pressure, but it would also cause surging and high idle (lean running).

 

[DavidInMi]

Thanks! I work full time so I won't get around to checking it till the weekend. I'll report back on what I found.

I sure hope it's not the pump assembly. What a pain. Of course, it's all been apart now so....should be easier.

 

[david4451]

Your problem sure sounds like a vacuum leak, check pcv valve connections.

 

[DavidInMi]

I feel like an a@@hat!

Got home from work today and took a look at the engine while wife was getting dinner ready. I don't ever remember pulling the pvc tube out of the elbow! One thing I didn't think I did was work on the engine. There was nothing wrong with it. ANYWAY, I plug the tube into the elbow, turned the key and it instantly fires up and purrs like a kitten.

Best case scenario!

Thank you for the help!