At my wits end here....

[Twizzler09]

and I'm about to go on a week long vacation 500 miles from home.

Same story as usual, idle miss, runs smoother under a load/higher rpm. Smells like its running rich, plugs come out white (lean?), good cranking compression (180-185lbs all cylinders), etc etc

Heres the thing though...its slowly starting to get worse. Used to be the same no matter what temp it was at, but now it runs best cold, and starts missing more as it warms up. Stumbles occasionally if it sits for a minute, but not always, and the newest development is an occasional stumble while accelerating...but rarely.

Good example was just a little bit ago. Was on my way home from work, just got up to the speed limit after stopping at an intersection, then out of nowhere the engine stumbled, bad. Felt the truck vibrate and drag a bit as the motor was stumbling, kinda felt like it just quit firing altogether for a second

I've checked for vac leaks, good fuel pressure, O2 sensors read properly, etc.

I'd appreciate any other ideas anyone has, I'm completely lost!

 

[4x4fun]

bad or no spark all together. idk if you have a dist or no. or if you all ready check that. but make sure your not arching out some were, is your rotor is good (dist) and clean. an easy way to check for arcing out is run it at night with the hood open and look at all the wire as best as you can in the dark. if something is jumping youll see the blue arc

 

[Twizzler09]

the '96 4.0L is EDIS (distributorless)

Checked for arcing, didnt find anything though

 

[4x4fun]

check the maf bad reading, wrong amount of fuel, shuddering or missing

i dont really know just trying to cover all the basics.

 

[fireguy12117]

wiggle tests on as much engine wiring harness you can get at. i actually had an engine wiring harness on a 93 85% rotted through and before ultimatly pulling the motor, i remember bumping the section of harness that crosses between the firewall and engine block and getting big engine idle changes.

i assume no check engine lights?

engine coolant sensor has a lot to do with drivability and could possibly be giving bad data, but not be 'bad' by the PCM's estimations to throw a CEL. had a 94 with that exact problem.

right now i am looking at a bad PCM altogether as a culprit for your same symptoms on my 93, and im waiting on getting the correct replacement, but i threw in a spare 91 explorer PCM and the truck runs almost at 100%.

it was suggested to me one time to take the truck into a stealership and pay the $80 or so to get the truck hooked up to thier computer and get a print out for whats actually going in and coming out of the PCM. play dumb about your real reasons for being in case they try to say sensor XYZ is bad, we can replace it for you blah blah...

 

[Twizzler09]

No engine light, it does throw a catalyst efficiency code, but I assumed it was because it was dumping raw fuel into the exhaust due to the misfire. Could be wrong on that one *shrug*

I'm gonna clean the MAF and as suggested, wiggle test as much of the harness as I can get my hands on.

Is there any good way to test the coolant temp sensor or the PCM?

 

[fireguy12117]

the PCM is pretty hard to test on its own. im not aware of any specific procedure for that. what ive seen is process of elimination leading to deducing its a bad PCM for whatever reason, as in my case. nothing ran right, swapped controlers and presto, stupid truck ran great...

its a pain in the butt, but if you can get at it, you can test the resistance readings of the sensor as it sits in the intake. take a cold reading before you start the engine, and a warm one after its been running. just googled around ('ford ranger engine coolant temp sensor readings') for the readings, but it looks like it should be high when cold, lowering as it warms.

 

[Twizzler09]

Fireguy, I think you had the right idea when you mentioned the Coolant temp sensor.

After I got back from my vacation, it started loping extremely bad at idle, and now it kicks a Bank 1 Lean code and an Excessive EGR flow code (replaced the DPFE this morning, seems to have taken care of that one). But it *only* lopes when the motor reaches the point where its supposed to kick out of "warmup mode", and enrich the fuel mixture. Picked up a new Coolant temp sensor for $15 after I got out of work, gonna install it tomorrow and pray like hell that it works, haha.

 

[Twizzler09]

Updated:

FIXED!!!!

upper EGR seal was leaking big time. Two hours later its running like its new! woot!

thanks for the input everyone.