hard starting and not running on all cylinders part time
 

I have a 1991 ranger with a 4.0 liter. I have replaced throttle position sensor, crank position sensor, oil sending unit, coil pack, baromic pressure sensor and ignition module. when my truck gets hot it runs on 4 or 5 cylinders and is always hard startingany help out there?

I'll take a shot at your hard starting issue. There are numerous things that could be the problem. First, check your oil. Is it at the proper level and is it the proper viscosity? When oil gets cold, it gets thick. Using the wrong viscosity oil can make it too difficult for the starter to do it's job and get the crank spinning. Also, if the level is too high, the crank might actually be trying to spin through the oil, which is difficult.

Second, check your battery. What's the CCA rating? When it gets cold out, it becomes more difficult for the battery to send a good amount of amperage to the starter. Your battery may just not have enough CCAs to turn over your starter quicly. Is it fully charged? Get out your DMM (or borrow/buy one if you don't have one), set it to DC volts, and put the red lead to positive and the black lead to negative. What's the reading? Here's a rundown of the reading/charge level:

12.6 - 100%
12.4 - 75%
12.2 - 50%
12.0 - 25%
11.8 and below - 0%

Third, check your starter. This one is a little difficult to test without a VAT-40. But, this could be a possible cause of your problem.

Fourth, check the wiring. Are your connections good and tight? Is there any corrosion? Are the wires frayed? Is the insulation cracked? Replace and/or clean as necessary.

Hope this helps,

Joe, aka SuperKid

how is your coolant?

what about yyour plug wires?