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Changed fuel pump and now it wont start

I just changed the fuel pump on my 98 Isuzu Rodeo and now it wont start. The pump is getting power because i can hear it humming. Fuel is getting to the fuel rail, I checked the the shrader valve. I tested the battery and its fully charged but it wont start. Im stumpped, can anyone help?

What happens when you try to start it? Does the starter turn the crankshaft with good strength?
Have you checked for spark?

Did you change the fuel pump because it wasn’t starting, if so, how did you diagnose a bad fuel pump?
Spray some starting fluid into the air intake. If it cranks well but doesn’t start, your problem is not fuel related.
That would leave ignition, compression and timing , in that order.
Have you checked for a broken timing belt?

The starter turns the engine fine. I used some quick start and it started and died so I know it’s getting spark. I just hooked up a fuel pressure tester and it jumps to 45 and drops down fairly quickly to 10 psi and holds there. I checked th belt and thats in good order too.

Bad replacement fuel pump? is there a gas filter that might need attention?

The way the pressure goes to 45 then drops to ten might indicate a forward leak in the fuel pressure regulator. Could also be a bad check valve in the fuel pump but you’ve already changed that.

I dont think the pump is bad and the filter was changed recently. Ill have to check the pressure before the filter to see if the pressure stays To eliminate the regulator. Ill have to check the valve too, I only changed the pump not the whole assembly to due to the fact that for the 98’s the3 ecm has to be re flashed to read the new assembly

Can you check to see if the injectors are getting juice to fire?

Did it start before you changed the fuel pump?

Why did you change the fuel pump?

I had to change the pump because it had failed, no pressure or electrical humming.

Make sure the fuel injectors are pulsing as oldtimer mentions.

Even if the injectors are pulsing it won’t run with only 10 psi fuel pressure.

Just curious, do you have a check engine light? If so it can help figure out the problem. I think AutoZone has a reader you can rent

No I havent checked for a CEL but ill check that and the injectors

I checked and the injectors are pulsing

10 psi isn’t enough to run most fuel injection systems. So you got to resolve that issue as first order of business. Are you certain of that reading? Did you bleed the fuel pressure sensor as recommended in the instructions?

If the reading is correct, either the pump is faulty, the fuel filter is plugged up, or the fuel pressure regulator is on the fritz. Of those, the easiest thing to check is to see if there is any gasoline in the vacuum line going to the fuel pressure regulator. If there’s any at all in that line, it means the diaphragm has sprung a leak and the fuel pressure regulator needs to be replaced.

I checked the regulator and theres no sign of gas leaking. I put a gauge before the filter amd still not holding pressure and now it drops to zero relatively fast. So im guessing the problem is either the pump or check valve correct?

Also, make sure the connections on the white nylon accordian tube on the fuel pump assembly are securely attached and that there are no cracks on the tube.

I checked no leaks and everything is tight

I put a new fuel pump on a Buick Century a few years ago and had the same problem. The check valve in the fuel pump was bad right out of the box. It happens.