Low to No idle - can start with throttle - Here I go again...

[motopsycho650]

Last night I let off the gas and the engine died. Since, it will not start or run without throttle. Once warmed up, (holding the throttle to keep it alive) it will idle at around 300 rpm's, which it very low and rough.

Parts I have swapped with used, known working parts I had:
1. Idle air control valve
2. Mass Air flow sensor
3. Throttle position sonsor

Just for fun, I tried starting it with the IAC un-plugged, there was no change. There is no check engine light coming on, and that was known to be working a month ago when I replaced the cam sensor, upper and lower intake gaskets, and valve cover gaskets.

Any ideas what to try next?

 

[MrShorty]

When you replaced the IAC, did you verify that any air passages leading to the IAC were clear? Your symptoms sure do sound like something wrong with the air flow with the throttle closed.

 

[motopsycho650]

When you replaced the IAC, did you verify that any air passages leading to the IAC were clear? Your symptoms sure do sound like something wrong with the air flow with the throttle closed.

Yes I did. I looked in each hole with a flashlight, and stuck a piece of wire up in there to see if anything felt clogged. Also, while the IAC was removed, I started the engine and it jumps right up to 3000 rpm's, then it surges between 1000-3000 RPM's. I didn't let it run too long that way. Seems like there is plenty of air available.

I have no more ideas at the moment...

 

[motopsycho650]

I managed to get it up into the garage this morning. I'm planning to remove the throttle body off the upper intake and checking all the ports going into the IAC.

Another point worth mentioning is this. I can get it to start with throttle. While I'm holding the throttle, the engine does NOT sound like it's missing. It sounds like all 6 cylinders are firing, however I have little power compared to normal.

I'm starting to regret buying this explorer. My older '92 was a POS, and this '94 does not seem much better even though it's only got 115K on it, and is in much better visual condition than my older one was. I've already got over 1500 bucks in it and only 200 of that was the vehicle it's self. 1300+ in parts, and it just keeps wanting more...

 

[motopsycho650]

Can anyone tell me if this makes sense? Being the engine will not run on it's own, I did a Key On Engine Off code test. I am getting both a 116 code and a 114 code. The 116 is the Engine Coolant Temp Sensor, and the 114 code is the Intake Air Temp Sensor. Both of those codes say "voltage is high or lower than expected." There were no memory codes, and the check engine light does not turn on when I get the engine running.

Would either of these sensors cause severe running/idling issues? It seems like the intake temp sensor could cause the PCM to adjust the fuel trim.

P.S. It is about 30-35 degrees F out in the garage today.

 

[motopsycho650]

I might be getting somewhere... Or Not...

Okay, forget the 2 temp sensor codes. I hadn't warmed up the engine before the KOEO test, duh...

Then, when I did try to start it, it started, idled, and ran as smooth as could be. For 2 days now, I've been disconnecting the battery, messing with stuff, and re-trying without any progress. This morning I barely drove it up the driveway. A few hours later it is fine...

So, I start driving around with the code scanner. Eventually, it acts up again. I quickly pull over as it's dying and I do a KOEO test again. Finally, I get a code that makes a little sense... 542 - Fuel pump circuit is open - PCM to motor.

I cleared the code and waited a few minutes as I'm looking at wiring. Again, the things starts without a problem, drives back home, and has nothing but 111 - system normal codes during both KOEO & KOER tests.

I am thinking I have a bad wire connection somewhere. Any ideas where to look first?

 

[MrShorty]

I'm not sure where I'd start first. As commonly as relay's seem to go bad, I might start at the relay to see if the relay is failing open intermittently.

Or maybe check the fuse. It's rare, but I have seen fuses fail where they make intermittent contact.

Another place I might start would be to hook up a test light/voltmeter at the inertia switch (because it's in the cabin where I can easily get to it and monitor it while driving), and see if I could see if that point in the circuit is losing power when it stalls/won't start. That would likely tell me if the fault seems upstream or downstream of the inertia switch.

In the end, the fuel pump circuit is really a pretty basic DC circuit. Do you have a wiring diagram? I'd almost certainly get a wiring diagram.

 

[scas]

whats you max speed on the road with holding the throttle open?
If its really sluggish, pull your air filter and try it without the filter

 

[motopsycho650]

Well, so far so good. My Exp has not had any issues starting since. I'm thinking I'll replace both the fuel pump relay and the EEC relay.

However, after talking to my cousin, who is a very skilled tech. He told me he had seen a 1st gen explorer at his shop recently having a very similar issue. He said that one started having weird, intermittent running problems and had gotten worse to become a constant problem. He told me that one had a bad computer. They replaced it with a used one, and it runs fine ever since.

If the relay's don't solve the problem, I may go to pull & save and try to find a used computer.

 

[motopsycho650]

Well, it did it's acting up again last night and will not start this morning without throttle. I did get a CEL to turn on and back off a few times while it was acting up. I have yet to check the memory codes to see what it was. I am willing to bet that I'll get some sort of oxygen sensor code.

 

[motopsycho650]

I pulled the memory codes at lunch. I got a 543 - Fuel Pump circut open battery to PCM.

I looked on ShopKey this afternoon here at work, and it says it is either a short in the Left O2 sensor, or it's a bad PCM.

Being that I previously saw the 542 - Fuel pump circut open PCM to engine, I'm leaning towards it has a bad PCM.

I'm planning on doing a resistance test on the O2 Sensor tomorrow morning. If it passes, I'll be off to the junk yard for a PCM. We'll see...

 

[Tony H]

Keep us up to date. I'm am curious what the fix will be

 

[MrShorty]

I looked on ShopKey this afternoon here at work, and it says it is either a short in the Left O2 sensor, or it's a bad PCM.

Really? They didn't want to consider a possible loose connection in the fuel pump wiring or anything like that? Personally, I'd inspect the wiring until I was reasonably sure there wasn't a loose connection somewhere before I went shopping for a PCM. Several years ago, I was getting an intermittent 542 or 543. Then one morning when it wouldn't start, I was able to put a voltmeter on it and discovered that there was a loose connection between the fuse and the relay.

 

[motopsycho650]

Really? They didn't want to consider a possible loose connection in the fuel pump wiring or anything like that? Personally, I'd inspect the wiring until I was reasonably sure there wasn't a loose connection somewhere before I went shopping for a PCM. Several years ago, I was getting an intermittent 542 or 543. Then one morning when it wouldn't start, I was able to put a voltmeter on it and discovered that there was a loose connection between the fuse and the relay.

The fuel pump has power and does not ever shut off during these episodes. When turning the key to on, I can hear both the fuel pump relay click, and I can hear the fuel pump power up. I swapped a few relays in the power box since they are the same part number, so it's not a relay issue. The fuel rail pressure is correct during these episodes, and the exhaust smells rich too, so lack of fuel is not the problem.

The main question Shop Key asked was if it ran or not, and if there was a 556 code in memory too. There is no 556 code, and I can get the engine to start. It then told me to do the wire shake tests, which I found nothing. The second step is said was to check the left side O2 sensor's resistance. If it passes, step 3 in the list is to replace the PCM. For vehicles that only have one O2 sensor, it said to go straight into replacing the PCM.

I have unplugged, and replugged all the wiring harnesses in the engine compartment, wiggled and bent wires, and nothing seems to fix this issue. If this failure stays in it's current repeating pattern, it should fix it's self any time now. I just don't see how it will work perfectly, getting 17mpg, for 2 weeks at a time. It will die for about 2 days, then be perfectly fine again for another two weeks. This pattern has been very consistent for months now.

Thursday night when it died most recently, I had already drove around 100 miles that day, made it back home, and it acted up as I was leaving a friends house. It had been sitting for about 20 minutes.

I'm not trying to shoot down your ideas, they help me think of other possibilities. This is the single most baffling problem I have ever had with a ford. This pattern has been happening since I bought it. I have solved every other problem in this vehicle except for this "ghost" problem.

 

[motopsycho650]

Okay, this morning I disconnected the battery, tested the resistance of both O2 sensors for a short as described by ShopKey. Both tested okay. I disconnected the PCM, and tested the resistance of all 3 ground wires against a frame ground. All the wires tested with 0 ohms, so good contact to ground. I then wiggled all the wires, looked for burn, worn wires and found nothing.

I reconnected everything, then reconnected the battery. I tried starting, but still the same problem. With a little throttle I started it, and kept it around 1000 RPM's until the engine was warm. I could easily hear the fuel pump running steadily, and could easily hit 3000+ RPM's with throttle. I kept the engine alive for approx 10 minutes until it was warmed up. Still, as soon as I let off the throttle, instant death. Never once did the CEL come on in that 10 minutes. I hooked the scanner back up and did a KOEO test. Got a system normal code from the first set, then I got a 157 and 542 code from the memory. 157 is "MAF voltage is below minimum" and the 542 is back to "Fuel Pump Circuit Open PCM to engine". In reading, the PCM to Engine is the ground side of the fuel pump circuit, all 3 of those wires tested good at the PCM wire connector.

I am going to go buy a used PCM. I'm getting weird 542 & 543 codes that change back and forth, I know the MAF is working because of the quick throttle response I have when I manually keep the engine running. And, I know the grounds on the PCM wire harness are good.

 

[motopsycho650]

So, went to pull n' save auto parts and pulled a used PCM from a '94. The key numbers all matched. The truck started right up and seemed fine until I hit the highway back. I started feeling slight hesitation followed by the CEL coming on. I pulled into a parking spot with the code reader, and it does not work with this PCM. Neither the KOEO or the KOER tests activate the self test cycle. My code flasher does not respond at all. Being that my new issues are totally different than the old issues, I'm going to say that it's still the PCM. I'm thinking I'll get a remanufactured from Napa for 135.00. I have 30 days to take the used PCM back.

 

[MrShorty]

When you said that shopkey was leading you to consider either the O2 sensor or PCM, I somehow missed that you had already been through the wiring.

If you feel you've adequately followed the diagnostic tree up to the point of replacing the PCM, then that sounds like the best next step.

 

[motopsycho650]

When you said that shopkey was leading you to consider either the O2 sensor or PCM, I somehow missed that you had already been through the wiring.

Yeah, I did forget to mention that in the first post yesterday.

However, I am still not fixed. I replaced the PCM with a matching numbered PCM from a junk yard. Now I get an entirely different set of running issues. The CEL comes on & goes off. The engine runs much better, but stumbles during acceleration. My code flasher will not respond to this PCM. On either KOEO or KOER tests, I flip my code flasher to test, and nothing happens. The PCM does not do it's self-test cycle, and the flasher does nothing.

So, wasting the second half of my day, I went to Napa and bought a remanufactured PCM. It produced the exact same running issues as the junk yard PCM. The napa one will do the KOEO self test with my flasher, but will not respond to a KOER test. I have also gotten a code 512 - Keep Alive memory failure from the Napa PCM. The interesting thing is, I see the KOEO codes, but then it will not display memory codes. I'll see the string of KOEO codes, the the separator flash should happen followed by memory codes. I never get the separator flash. Instead, the code flasher shuts off as if I had flipped the switch back to hold.

Today I'll be returning the Napa PCM because of the 512 code. I can't go return the used PCM from the junk yard until next weekend, but I do have a 30 day guarantee.

I am back a square one, not having any idea what is really wrong, or how to fix it. The only real facts I have are: With the stock PCM hooked up, it runs perfectly for around 2 weeks at a time, then dies. With either the used PCM, or the NAPA PCM, it runs but lopes at idle, hessitates during acceleration, and will not do the self test cycle with my code flasher. Where do I go from here? Besides the used car lot...

I am so sick of this vehicle. Half the miles of my '92 and so far, twice the problems. Right now I'd really like to stick a burning rag in the fuel tank. Anyone want to buy a '94 charcoal briquette?

 

[motopsycho650]

What would you guys do if this was your vehicle? Continue trying to fix it, or abandon the idea in search of a different vehicle?

Here is my history with it: I bought it around June '09 for 200 bucks with a blown transmission. It ran really well, but gave a Neutral Safety Switch code and a Delta Pressure Flow Valve code. I used a 20K mile, re-built transmission from my '92 Exp as a donor. While doing the transmission, I installed a new DPFV. Both the codes were fixed, but the CEL was still on. This time it gave me a CID Circuit Failure code. Testing revealed the Cam Position Sensor was not sending a signal. It still ran pretty well, so I didn't do anything about that right away.

About a month later, it began doing the current problem of cutting out and dying intermittently, then would mysteriously fix it's self. I began by cleaning the IAC valve, and it didn't change anything. I decided to replace it, and for around two weeks I thought it was fixed and it seemed to improve the engine response. The cutting out problem returned. Next I went after the Fuel Pump. I had a 1 year old OEM fuel pump from the '92 that I had saved. I swapped them out just as an elimination method. It did not improve anything.

I'm finally convinced that the CID code is the cause of my problems. I replaced the cam sensor and all the needed gaskets and the CEL finally went away. For a few more weeks, I thought I had fixed it. It ran like it was brand new. But, again I would have intermittent problems where it would simply die, and not idle. Mysteriously fixing it's self, and never turning on a CEL. Last Thursdays failure was this first time it turned back on the CEL, which is when I started this thread.

I am beginning to think that this truck will be a never ending nightmare. I currently have over 1500 bucks into it, not including the original 200, and I feel like I haven't fixed anything yet.

 

[motopsycho650]

I returned the Napa PCM, got my original back, tried it. It started right up, idled perfectly for 5 minutes, then died. I'm back to the original problem with the stock PCM, or I have a different problem with the used PCM and no way to flash it's codes. Someone shoot me...