1992 ford ranger

I have a 1992 ford ranger 4.0 liter with 136,000 miles. I was told the motor needs to be replaced but I dont think it does.Hope someone can help,here is the problem.The truck has a little miss at idle and some vibration around 45mph.A diagnostic check revealed #5 cylinder had 5 psi of compression. The truck does not smoke and the only problems are what I already said. I do not want the expense of replacing the moter if somebody knowes of another fix.

With that litle compression you certainly need an overhaul at least. Years ago, a mechanic would tally up all the items, and often the shop would repair the engine, if only a valve was casuing the low compression, for instance. Nowadays, a complete overhaul, if shops still do that or a rebuilt or a good used engine from a low mileage wreck would be you choice.

But you can’t keep driving like that. Who told you you needed to replace the motor and what was his evaluation of the rest of the cylinders?

Have the mechanic do a leak test of cylinder #5 and find out where the air is going. If the air is going into the intake or exhaust, a valve job on that head is called for. If the air is leaking into the cooling system, replacing the head gasket and checking for a cracked head is in order. If the air is going into the crankcase, something is wrong with the piston, rings, or cylinder wall meriting a replacement engine.

Let us know what the leak down test shows.

Thanks for the information it was real helpful. I am going to replace the engine. I found one at search parts.com. It is a 4.0 out of a ford ranger. Acording to the sales rep.the motors are run thru several tests before they are sold. I got a complete drop in motor for 875.00 dollars. Again thank you for the help.

On the compression check: valves which are stuck open, or warped, won’t allow compression to hold. That’s why a cylinder leakdown test is advised. This test will show where the leak is occurring. Too bad, some mechanics don’t have the cylinder leakdown tester, and air compressor, and don’t know how to do it.