It's been a year now and many new parts have gone in and the problem has morphed slightly but still rearing it's weird head.
1994 Ranger 4.0 V6 5 speed. When it goes from open loop to closed loop there is something that will "cut out" and send the engine to idle. It's VERY abrupt when it does this, to the point that if I'm driving along at say 3,500 rpm the cut is hard enough to chirp the tires and throw me forward. It used to "reset" if I feathered the throttle but now does not.
IF I drive the truck with the MAF unplugged then it stays in open loop "limp" mode and never does this. But when I plug it in the problem returns. The problem is that driving in limp mode kinda sucks, it gets E36 M3 mileage and drivability isn't particularly smooth. So I'd like to fix it.
New parts include Ford genuine MAF, pigtail plug for same (soldered wires), intake charge temp sensor, coolant temp sensor, TPS, plugs, wires, thermostat.
Something is wrong, please help me diagnose the beast.
Bad O2 sensor maybe? That could cause it do do weird E36 M3 in closed loop.
maybe a cam/crank position sensor is going bad/loosing signal intermittently? that would cause timing to jump back to base timing with i think with the EDIS igitions is 5 degrees? coil could be going out too maybe.
If you are chasing symptoms and they keep moving around the motor, check and log the voltage over time. If you have a flat spot or a load condition that dumps you under the threshold voltage of the electronic sensors all sorts of pandemonium will occur in the ECU's thinker and it will come to the wrong conclusions... shut E36 M3 down to save stuff, run about screaming, etc.
If you see a voltage drop, it's time to check the grounds, the regulator... the alternator (flat spots at certain RPM), shorts in the harness, etc.
rslifkin wrote:
Bad O2 sensor maybe? That could cause it do do weird E36 M3 in closed loop.
Oh yeah, new O2 sensors as well. And fuel filter.
edizzle89 wrote:
maybe a cam/crank position sensor is going bad/loosing signal intermittently? that would cause timing to jump back to base timing with i think with the EDIS igitions is 5 degrees? coil could be going out too maybe.
Only if it's tied to the MAF plug. When that's disconnected the problem doesn't occur.
Does this have throttle by wire?
HappyAndy wrote:
Does this have throttle by wire?
Yes. It's a '94 so pretty old school. OBD 1 so very little information from that either.
KyAllroad wrote:
HappyAndy wrote:
Does this have throttle by wire?
Yes. It's a '94 so pretty old school. OBD 1 so very little information from that either.
You sure on that? I'd be amazed if anything OBDI doesn't have a throttle cable.
Umm, sorry. I misunderstood the throttle by wire. It's an actual throttle linkage (a wire), not the modern electric doohickey.
Ranger50: Megasquirt? Are you suggesting I install one on my old beater truck?
KyAllroad wrote:
edizzle89 wrote:
maybe a cam/crank position sensor is going bad/loosing signal intermittently? that would cause timing to jump back to base timing with i think with the EDIS igitions is 5 degrees? coil could be going out too maybe.
Only if it's tied to the MAF plug. When that's disconnected the problem doesn't occur.
well it may just go off a a 'dumb' timing table when in limp mode, which i guess could rule out the coil but may still be a crank/cam sensor?
How do you know that it's a closed/open loop transition?
Sounds to me you have a MAF problem. Which could be a leak, too.
The fueling is close when it's running TP/engine speed back up. It sounds like it's not when the MAF is running.
BTW, since you have a real throttle, it's not trying to go into idle- the idle control valve doesn't have that kind of ability. It's just doing some other things wrong.
Try doing a KOEO and KOER test. That helps find problems. And check codes.
KOEO codes: 54, 56, 62, 85, 66
KOER codes: 52, 36, 53, 85
Of course one of those is saying that the automatic transmission has a problem......and it's a 5 speed 
tester
New Reader
9/9/16 4:35 p.m.
In reply to KyAllroad:
I would suggest checking the voltage on the throttle position sensor. You stated that the problem goes away if you feather the throttle. Seems like a good place to start. Take a good look at the connection and wiring.
Never mind, I see you already threw a TPS on it. It still might be worth checking the voltage and wiring to the sensor.
alfadriver wrote:
How do you know that it's a closed/open loop transition?
Sounds to me you have a MAF problem. Which could be a leak, too.
The fueling is close when it's running TP/engine speed back up. It sounds like it's not when the MAF is running.
BTW, since you have a real throttle, it's not trying to go into idle- the idle control valve doesn't have that kind of ability. It's just doing some other things wrong.
Try doing a KOEO and KOER test. That helps find problems. And check codes.
The reason I (suspect) the problem is open loop/closed loop related is that with the issue doesn't seem to happen until the engine is warmed up (closed loop).
MAF plugged in last night for my commute and I drove gently, shifting at 2,500/light throttle and nothing unpleasant happened. Which was a nice surprise since the last time I tried it "died" (idle, no throttle/power) in an intersection during rush hour. Forcing me to jump out and unplug the MAF sensor in order to stop being a nuisance to other motorists.
Have you tried cleaning the maf? Lots of instructions on ford webpages.
In reply to KyAllroad:
Actually, I agree that it's related to closed loop fuel, but it's not the cause- just a symptom. The O2 sensor will try to change the mixture to it's best ability- but with a MAF error, that ability could easily be well outside of where it works.
In reply to Fueled by Caffeine: it's new
