My poor Ranger!

[Planetpluto718]

Hello everyone!

I've of course got a problem with my Ranger, and can't seem to figure it out!

First off I am not getting a MIL, and am sure the lamp functions properly. When I start the truck, it runs just fine, if not for a slight idle issue. At idle the engine seems to rev up and down, but not much, maybe at a range of 100rpm difference. I can put the truck in gear and take off down the road and it drives perfectly. But within a short period of time, one to five minutes, it starts running very rough! Engine acts like it wants to stall, almost like it's starving for fuel, and pressing the gas pedal does absolutely nothing, but the engine doesn't cut off. It just lopes along erratically for a short bit, and then seems to "jump" back into running correctly. This will occur randomly and does not seem to be affected by engine temp, outside temp, or any other variables that I can think of. It also will do the same thing at idle. If I start truck and just let it idle it runs great for a few minutes, then exhibits same symptoms for a short bit, and then jumps back to running normally. I was getting a MIL and decided to do a tune up and replace some things, after that I don't get the lamp on any longer, but truck still runs terrible. Here's what I've done so far, and thanks for any input on this issue!

1994 Ranger 4.0 2WD Extended Cab

New parts include -
Mass Air Flow Sensor
Plugs
Wires
Electronic Coil Pack
Fuel Pressure Regulator
Idle Air Control
Both O2 Sensors
Vacuum lines replaced
Brake Booster / Master Cylinder

Also I should mention I have tested fuel pressure and it falls within spec. Thanks again!

 

[97RangerXLT]

check to make sure all of your vacuum lines are in good condition, and check your intake hoses/ pipes and fittings to make sure there are no rips or leaks. check the hose to the PCV valve, make sure it fits snug and is not cracked.

Use some carburetor cleaner and spray it in short bursts all around the intake. if the engine revs after you sprayed it, you have a vacuum leak in that area.

AJ

 

[Planetpluto718]

Will do!

Thanks for the quick reply!

I failed to mention the PCV valve and hose were replaced as well.

I'm going to do an inspection of all the vacuum lines today, and also check for an exhaust restriction. I will try the carb cleaner trick and post results later.

Thanks again!

 

[RonD]

Normal cold start should have RPMs jump to 1,500+ then drop down to about 1,000, that's the computer opening IAC valve all the way(1,500+ RPMs), then computer reads ECT(coolant temp) sensor and sets idle based on engine temperature by closing IAC valve, colder temp = higher RPMs, so idle RPM cold could be 1,200 in winter depending on where you live.
At this time computer is in Open Loop, it isn't using O2 sensors at all, it is running higher idle and richer fuel mix based on tables in its memory, so basically a Choke Mode.

As engine warms up computer closes IAC valve a bit more to set "target idle", 700 for manual and 800 for automatic trans.
Computer is now in Closed Loop and is using the O2 sensors to get feedback on exhausts oxygen content, too much oxygen is lean, too little rich, and adjusting injectors accordingly.

Ir reads like your computer is failing in Closed Loop.
And if MIL/CEL is not coming on with the key to do its test you may have a computer issue, I assume you have checked fuses.
I would check the computers connector and remove the cover of the computer and give the circuit board a look.
Good info here on your computer model(EEC-IV): http://www.auto-diagnostics.info/ford_eec_iv

I would also get a volt/ohm meter to test sensors, outside of the O2 sensors, pretty much any sensors or controls on an engine can be tested with a meter, saves you lots of money.

TPS(throttle position sensor) would be a good one to test with a meter.

 

[85_Ranger4x4]

Use some carburetor cleaner and spray it in short bursts all around the intake. if the engine revs after you sprayed it, you have a vacuum leak in that area.

AJ

Brake cleaner will work too and isn't as nasty of stuff.

 

[Planetpluto718]

Thanks for the replies!

I inspected vacuum system and everything seems to be fine. I also get no change in idle when spraying brake / carb cleaner around air intake. I also sprayed it around throttle body, IAC, and the other intake vacuum ports with no change in idle.

According to your numbers, the engine is idling exactly like it's supposed to. Truck starts at about 1000rpm depending on outside temp and withing a minute or two idles down to 800rpm.

The computer is a good idea and one I have not looked into yet. I will give that a good look.

The throttle position sensor is new as well. The old one had failed, or at least it was throwing a code for it so I replaced it along with the other sensors listed above and code went away.

I have checked fuses and relays, and the check engine light will come on when you turn the ignition. I just meant it never comes on when engine exhibits it's erratic behavior.

Thanks again!