Computer problems? Low RPM reading.

Stubby3 · 06-23-2009, 03:26 PM

I have a 1994. About 1 1/2 years ago the truck would just start running rough. The RPM gauge would read low, the check engine light would come on. I would have no throttle response. It was like I was starting from a dead stop in 4th gear. Then it would stop, and the truck would run fine. Well, I took it to a buddy who replced the computer with a used one. Truck ran fine for about 8 months, then the same thing. Replaced the computer with a brand new one. Truck ran fine for about 9 months. Now it is starting again. I noticed the temp. gauge is not always working. It will not read the temp. It did it the other day for about 3 miles. Then stopped. It has not messed up in 4 days. HELP

oldtimer35 · 06-26-2009, 03:03 PM

I would guess that it is a 94 4.0L Ranger. I would check to see if there are any codes in memory in the PCM. This is an EEC IV system and most Auto Zones and the like cannot read the codes in it. I would look at the idle air control motor to see if it is contaminated and needs to be cleaned. This can be cleaned with a good choke cleaner. The passages need to be sprayed until you remove most of the carbon. Check to see if you have blown a vacuum cap off the intake vacuum tree. Listen to see if you can hear a vacuum leak with the engine running. And bring back some more info on what you are driving.

Stubby3 · 07-02-2009, 05:58 AM

It is a 4.0 1994. I am going to have the codes checked this weekend. I cleaned the idle motor. Nothing. Yesterday I drove to work, no check engine light on, ran good. Then on the way home the check engine light was on, and the RPM gauge read 0. But the truck ran fine. I changed the engine coolant sensor on Monday. Still the same. No vaccum leaks that I can hear.

Stubby3 · 07-06-2009, 02:00 PM

Scanned the comput. It was the mass airflow sensor.

BroncoJoe19 · 07-06-2009, 02:22 PM

and the RPM gauge read 0. But the truck ran fine
You have another issue going on there.

I noticed the temp. gauge is not always working. It will not read the temp. It did it the other day for about 3 miles. Then stopped

I'll bet you have a bad ground.
Since changing the PCM twice gave you a temporary fix, I would check the ground that goes to it. It is usually near the firewall.

Check your battery connections, the big fat ones, and the little ones to both sides of the radiator support, and the fenders, firewall, etc.

Stubby3 · 07-08-2009, 02:27 PM

ok, thanks, I'll look.

Stubby3 · 07-22-2009, 05:41 AM

Cant find any vacuum leak or ground wire problem. I am about to put on a new Mass Airflow sensor. Truck runs fine in cooler air temps, does this sound like a faulty air flow sensor?

BroncoJoe19 · 07-22-2009, 06:23 AM

A new MAF is a bit on the expensive side. I don't think there is a code that says the MAF is BAD, but rather the reading is above or below some range. Often it is a crapy connection, or a dirty MAF, which can be cleaned with Spray on MAF cleaner (alot cheaper than a new MAF) if that fails not much is lost, but if it works, you are way ahead of the game.

MAF gives air temp, and volume info to the PCM so it can adjust fuel air mixtures by modulating the IAC, and the pulse width of the fuel injectors. A faulty MAF can cause a variety of problems, so the short answer to your question is: yes.