Strange fuel pressure behavior

sevynos · Jul 27, 2009

Hi,

I have a ford ranger '90 2.9L EFI.

I'm suspecting a fuel pressure regulator (FPR) problem so I made a pressure test. The result is bugging me!

With the key to ON, on the first fuel pump activation I have a reading of 0 (Zero) PSI. To get the needed 40 PSI I had to activate the pump 5 times. And that's not all! If I don't touch anything, the pressure start going down until it reach zero.

Then I started the engine and got a constant reading of about 78 PSI.

With these results, should I consider that my FPR is faulty or a vacuum problem?

Area 52 · Jul 28, 2009

It would be safe to say that the regulator is shot. You are getting full pump pressure. As for the pressure dropping after shutting engine off, the injectors are leaking. Pressure should hold for at least an hour before you start to see any pressure drop off. Time to get some rebuilt injectors. Don't drive it until after you get the regulator changed out...will cause engine damage. After the regulator swap, change oil/filter. The oil will be diluted from the excess gas.

RustedRanger · Jul 28, 2009

sevynos mine acted very similar when my FPR was shot. It would jump up to almost 80 then slowly drop down. I ran fuel injector cleaner in it several times and replaced the FPR and now the pressure reads good and doesn't drop off anymore.

bobbywalter · Jul 28, 2009

sounds more like a pump issue to me. or rather a cobination of it...as in the pump check valve failed..but an open injector would do that...the 70 psi though dont jive that..that or the return line is plugged and caused the c/v failure in the pump or something.

without pulling the return line to check for volume i cant really say. i would do that before buying parts.

be very careful when working with the fuel lines, dont want to burn yourself down.

sevynos · Jul 29, 2009

Thanks to all for your replies.

According to your oppinions, some on another forum and people i've talked to, i will replace the FPR since I found an affordable one at CarQuest. Anyway, it won't hurt to get a new one!

bobbywalter: I'm no expert but if it is a pump issue, I think I shouldn't get a 78PSI pressure instantly after startup. Am I wrong?

Again, thanks to all!

Sasquatch_Ryda · Jul 29, 2009

Yes but it sounds like the pump is leaking down, and not holding the fuel pressure which is why you would have to cycle the key 5 times like you say you do. All the fuel has drained back out the lines and into the tank.

sevynos · Jul 30, 2009

Thanks all again!

I've got my new FPR. I will install it on next Monday or Tuesday depending on weather conditions. I will post a follow up of the results.

gw33gp · Jul 31, 2009

I had a similar problem with an 89 2.9L Ranger and recently with my 02. Replacing the fuel pump solved the problem. The check valve was not working properly and I would have to cycle the ignition key 4 to 5 times to get the engine to start. The pressure would not build to full pressure when turning on the ignition switch because not enough volume would pump before the pump automatically shut off.

The check valve is not the only thing that causes this problem but if the new FPR does not solve the problem you should take a hard look at the fuel pump. I find the quickest way to check that is; disconnect the fuel filter and connect a pressure gauge to the line coming from the tank. Cycle the ignition switch and if the pressure drops off when you shut of the ignition switch, the check valve is not functioning properly.

warrior24 · Jul 31, 2009

Where do you connect the fuel pressure gauge to?

Psychopete · Jul 31, 2009

warrior24 said:
Where do you connect the fuel pressure gauge to?

The schrader valve on the fuel rail.

Pete

gw33gp · Jul 31, 2009

warrior24 said:
Where do you connect the fuel pressure gauge to?

I connect it to the end of the fuel line. It might take some ingenuity to come up with a good connection with some fuel pressure gauges. I have one that has a tapered fitting that fits inside the line and requires holding them together. That requires a helper to cycle the ignition switch.

sevynos · Aug 4, 2009

Finally I installed my new FPR yesterday.

Truck runs well and startup are much more easier!

Now my pressure reads 37-38 on key ON position. There's seem to have a small leak, in about 5 minutes engine off, I lost 10 PSI. When the engine is running, the pressure climbs to 40 and stay there. It's the opposite of specifications. Anybody have an idea?

And there's now another little issue about the gas! When I hit accelerator, the pressure and engine RPM drops a little to go back up after 1-2 seconds. I've seen this before but I don't remember what it was. Anybody knows?

Cyberbeer · Aug 4, 2009

Check the little black canister under the drivers door. Should be 4 lines connected to it. Make sure that isnt leaking. Its a left over from the days Ford used canister fuel filters, instead of in line, there is no longer a filter in it.

Strange fuel pressure behavior

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