2.3L ('83-'97) Intermittent Misfire

[RangerRick1994]

I have 1991 Ford Ranger XLT 2.3L. 5-speed manual. I bought it for $1,000 and it seemed fine on the ride home, which was about a two hour drive. Then when I was a few miles from home, it’s like the engine lost all of it’s power and when I accelerated it was very difficult to get up to speed. It only did this for a minute and then the truck “woke up” and it’s like nothing ever happened. Fast forward a couple weeks later and I’m driving to work and it does it as soon as I get on the highway. So the whole drive to work it’s like the engine was misfiring. At a stop light, the engine would idle really hard and almost try to die when accelerating. I’ve replaced all spark plugs, spark plug wires, and both coil packs. After doing so I fired it up, drove it around for a little while and everything seemed fine. Then I parked it and about a hour later I went to go somewhere and it started misfiring immediately. I’ve read it could be the ICM. I just don’t understand why sometimes is runs fine and then all of the sudden it starts to misfire, shake, and act like it may die. Also, there’s a missing hose from my vacuum tree. My vacuum hose diagram doesn’t show that there is supposed to be a hose in that spot, but when I put my finger on it, the engine dies. Finally, could this be because of a bad EGR? Long post, but I had to get it all out there! Thanks!

 

[RonD]

Welcome to TRS

Yes, the 1989 to 1994 2.3l ICMs did wear out and cause issues, they would get heat sensitive or just cause misfires, and yes could be intermittent

There should be no open vacuum port on the intake, plug it and see if engine will start
Is the PCV Valve hooked up?
Its a controlled "vacuum leak"

EGR is not used at idle, you can pull the vacuum hose off the EGR valve and plug the hose, then drive it for a few days and see if problem still happens
The EGR system can cause running issues IF the valve is opening too much or opening when it shouldn't open

 

[RangerRick1994]

Welcome to TRS

Yes, the 1989 to 1994 2.3l ICMs did wear out and cause issues, they would get heat sensitive or just cause misfires, and yes could be intermittent

There should be no open vacuum port on the intake, plug it and see if engine will start
Is the PCV Valve hooked up?
Its a controlled "vacuum leak"

EGR is not used at idle, you can pull the vacuum hose off the EGR valve and plug the hose, then drive it for a few days and see if problem still happens
The EGR system can cause running issues IF the valve is opening too much or opening when it shouldn't open

Welcome to TRS

Yes, the 1989 to 1994 2.3l ICMs did wear out and cause issues, they would get heat sensitive or just cause misfires, and yes could be intermittent

There should be no open vacuum port on the intake, plug it and see if engine will start
Is the PCV Valve hooked up?
Its a controlled "vacuum leak"

EGR is not used at idle, you can pull the vacuum hose off the EGR valve and plug the hose, then drive it for a few days and see if problem still happens
The EGR system can cause running issues IF the valve is opening too much or opening when it shouldn't open

Thank you for the quick response!

So I plugged the vacuum port and it seemed to run more smoothly, but when I started driving, the engine began to vibrate heavily and stutter. The PCV is hooked up and doesn’t seem to have any issues. I pulled the EGR and it seems to be working fine and has a good vacuum seal. The ICM is still my biggest concern. Could it be a head gasket problem? Attached is a diagram of my vacuum hose. The red writing represent a hose that was there, but it broke and I have no idea where it leads to. It’s not in my diagram. That is the port that I plugged.

 

[RonD]

You are missing the Vacuum reservoir(VRES) on that drawing, it was for the Vents in the cab, i.e. defrost, panel, floor air direction

But as long as the port is plugged it wouldn't cause a running issue, but you would just have Defrost in the cab, no panel or floor air direction

No probably not head gasket as that causes overheating as the first sign

Sure, ICM was a known issue and has many failure modes, not just heat
Wiring on ICM can also get brittle

 

[RangerRick1994]

You are missing the Vacuum reservoir(VRES) on that drawing, it was for the Vents in the cab, i.e. defrost, panel, floor air direction

But as long as the port is plugged it wouldn't cause a running issue, but you would just have Defrost in the cab, no panel or floor air direction

No probably not head gasket as that causes overheating as the first sign

Sure, ICM was a known issue and has many failure modes, not just heat
Wiring on ICM can also get brittle

Based off of the symptoms to include intermittent misfiring/rough idle do you think it may be the ICM or the ICM wiring?

 

[RonD]

I think some auto parts stores have ICM testers, this can't tell you if its 100% good, but can tell you if its bad

You could also pull out the PCM(engine computer) and open it up, there are 3 blue capacitors that can leak and cause odd issues
And its free to have a look, and also see that the PCM connector is OK, no corrosion

 

[RangerRick1994]

I think some auto parts stores have ICM testers, this can't tell you if its 100% good, but can tell you if its bad

You could also pull out the PCM(engine computer) and open it up, there are 3 blue capacitors that can leak and cause odd issues
And its free to have a look, and also see that the PCM connector is OK, no corrosion

Do you happen to know where the PCM is located? I’m by no means a mechanic, but I wasn’t aware that my model had a PCM.