Engine control system problems

[macx]

I think this applies to all the EEC-IV systems rather than just to any one specific engine type, so here goes.

93 Ranger with 5 speed and about 80k miles. Previous owner neglected it horribly. Symptoms are irregular frequent miss or stumble under load in 4th & esp in 5th, at moderate engine speeds in lower gears it acts like I turn the switch off then back on a few seconds later and jerks pretty severely when trying to maintain a steady road speed, altho the engine doesn't die.

When I start it at all warm, it goes to nearly 3k rpm for 20 seconds or so, then settles down.

Engine starts fine, idles fine (other than the warm start hi rpm).

Mileage is about 20% lower than it should be, and it seems down on power.
Vacuum (I installed a gauge) is steady altho maybe 3 to 4 lbs lower than my small block vehicles (maybe just because smaller engine?)

Even with a new 192 T-stat is has a problem staying over 160F on the highway, but warms up to 180 around town and creeps up from there when driving slow or at a stoplite. I've installed a numbered gauge and insulated and wrapped the line from the T-stat housing to beyond the ECT. Fan is removed for cooler winter weather as most of my driving is highway.

I've done lots of testing and replaced the ECT, ACT and TPS and main coil. The ECT and ACT had ohm tested bad. The coil ohm tested OK but was starting to leak a little oil. The new sensors and coil each made an incremental improvement, but the basic problems are still there. Ignition wires ohm out fine. The VREF to all sensors is fine at 5.16, but the signal to the ecu is high from all of them, as well as on the EVP. The main problem has to have something to do with that. I consistently get codes that the ECT, TPS, ACT and EVP signals or circuits are too high voltage, incl after clearing the ecu. Backprobing them with the engine off or on confirms that. Voltage signals to the ecu are way high and erratic, altho the VREF is fine at 5.15. Feeding back from the ecu thru the signal return or even the input circuit? The CEL continues to stay on. I've checked the system grounds and even cleaned the ecu pins and plug and crimped the plug sockets a little tighter to make sure they're making contact.

I've got the actual Ford shop oem electrical trouble shooting manual with all the circuit diagrams, the oem Ford complete wiring diagrams, and the shop manual, and have traced and checked wires till I'm tired of it. I've got a fair amount of experience with EEC-IV on my warmed up 351 Lightning powered Lincoln Mark VII LSC converted to mass air and using a Mustang ecu with other components enhanced from stock, but I'm stuck on this simple little pickup!

I've about come to the conclusion it's time for a reman ecu. The only other thing I can think of is that there may be a short in the wiring someplace I can't find. I'm in the process of replacing the injectors and fp regulator and 02 sensor just because of the miles.
Fuel pressure is acceptable altho right on the bottom of the acceptable range. Compression checked out OK and reasonably even.

Any experiences with this kind of problem or suggestions most welcome!

Also, I've got to get this solved in time for the annual smog check in July.

 

[adsm08]

I didn't read the whole post, there is a rabbit crawling all over me.

I have found symptoms like yours to be related to bad ignition coils in the past. I have no idea why, but the truck I'm thinking of would misfire randomly, only at 55 in 5th gear with light throttle. It had a bad coil. Have you tried an ignition overhaul?

 

[macx]

Yes, thought along those lines becaue it would exhibit the miss most strongly in 5th on the freeway. At 65+ I had to keep the footfeed pretty much on the floor, esp when pulling any kind of grade, and the vacuum was predictably 0 to less than 5, so was under pretty good load.

I ohm'd the plug cables, & new plugs of course. Then got a new Motorcraft coil and it did help but didn't cure the problem. Everything I've read suggests that the ICM either works or it doesn't like in no-start or REAL rough running, and being it runs without really missing at moderate throttle around town the crank sensor must be OK. Does that sound reasonable?

I've about convinced myself it's the ecu - with proper 5.15 VREF going to the ECT, IAT, TPS (those 3 all new and ohm out correctly unplugged) and EVP but with high voltage on the output side of all those sensors (input to the ecu) that voltage has to be coming from someplace, only place I can figure is backfeed from a bad circuit in the internal voltage regulator in the ecu. If one or two sensors, I can see a bare / shorted wire in the harness, but all 5 of them? I've backprobed and measured voltages with engine off/key on, and engine running. All measure 5+ volts higher than they're supposed to. And then the 3,000 rpm for ~20 seconds on a warm start (at least the IAC works!).

With 80+k on the odo, I'm replacing injectors, fp reg (it's acceptable but at the bottom of "OK") and 02 sensor as long as I've already got new ECT, IAT, and tps and coil. Then should be pretty much up to like new specs. I've gotta pass smog next July anyway, and all that should also make it run better and with better mpg (400 mi / week to work when it's too cold for the bike).

I wasn't going to keep this truck past this current job I'm on in Vegas (retiring afterwards WOO HOO!) but now I might as well keep it "forever" being so much new on it (incl rebuilt trans, new clutch & t/o bearing, new front hubs/bearings/rotors/calipers and a host of smaller items). Bought most of the parts at good prices from Rock Auto and did all the work myself, so have more sweat equity in it than actual $, but still would never sell it for anywhere near what I've got in it all together, so - - . Had originally bought it just to get me by for this job after my nearly new car got stolen /-( Have fun with your bunny!

 

[macx]

A small update. New injectors and FP regulator, just got back from another test drive.

Another significant improvement. Idles and runs smoother at lower rpm, doesn't jerk as bad with the on-off problem in 2nd thru 4th, definitely has more power on the road in 4th & 5th. First time it's been able to accelerate in 5th, altho slowly, up my test grade. Holds a couple inches better vacuum on average, runs just about 10 degrees warmer except at 65 mph (numbered gauge). So I think the few pounds extra fuel pressure and the new injectors definitely helped. Probly had at least 1 injector that wasn't delivering a full load. Still gonna do a reman ecu and new 02 sensor, though. Want to lick this thing all the way! CEL still stays on and still revs to 3k on warm starts, so probly still have the hi voltage in the tps/ect/act/evp circuits.