2.9 fuel system

[deadbeat]

Ok, Ive got a 90 x-cab ranger 2.9 5 speed, and it runs really rough at low rpms. I checked codes and it doesn't have any. The fuel pressure at idle is 34 pounds and if you rev it up it goes up to 37 and back to 34. Do I have a problem here, the book says it should be 35-45 but mine never even reaches 40?

 

[vrruumm]

Your fuel pressure is great, The regulator changes the fuel pressue slightly with engine load, this is normal. Put your gauge somewhere you can see it while driving and put your foot to the floor up a hill, you will see 40+.

If your engine runs good everywhere else but idle, you may have a vacuum leak, injector issues or a mechanical engine problem. This symtom rules out fuel delivery to the injectors, fuel filter, air filter etc... Usually plugs wires etc.. wont just have a problem at idle either. A compression test will probaly reveal your problem. You will be looking for un-even compression cyl to cyl. Dont wory to much about what the pressure is, just uniformity.

My guess is you will find one or two cyls with low compression.

Good luck.

 

[deadbeat]

Did a compression test the other day, all cylinders were between 130 to 150. Took a stethoscope and put to each injector and they all sounded the same. Put a vaccum gauge on it and the vaccum was right where it should be. About 19 pounds.

 

[vrruumm]

Compression should be good enough, your vacuum seems a little low. The low vacuum is not a sign of anything, just a symptom of running poorly. Still could be a vacuum leak. Just because you have vacuum does not mean you dont have a vacuum leak. If you dont find an air leak, try narrowing it down to a certain cylinder.

Try a power balance test. Get some small pieces of metal wire and tuck them under each plug wire connection to the distributor cap. The wire should be contacting the metal plug wire ends and protruding out of the boot enough to touch with a grounded test light.

We are not looking for the test light to light up, the test light is just a handy object to ground the spark from the dist. Start your engine, using a tachometer, whatch the rpm's carefully. Ground one wire at a time (touch with tip of grounded test light) and see how much the rpm's drop when each wire is grounded with the test light. The cylinder(s) that drop the least are the one(s) that are running the poorest.

Still stumped? Gunna have to get it on a gas analyzer.