Hi guys,

Let me start off by saying that I have searched the forums and web alot and still haven't come up with anything.

My truck ('94 Ranger/4.0L) started lighting the CEL whenever the engine was under moderate to heavy loads (going up a hill, >2500-3000 RPM shifts). It doesn't light any other time.

I pulled a code 117 for the ECT voltage being low.

Replaced the ECT (the two wire one for the PCM) and reset the computer.

Code came back, so I cleaned the connector and sensor. No change.

I had a bit of galvanic charge in the coolant, so I had the system flushed (needed to be done anyway), No change, still got the code.

Then I tested the voltage from the PCM to the ECT connector, KOEO: 4.74 V

Tested the voltage to the IAT connector, KOEO: 4.74 V

Tested the voltage to the TPS connector, KOEO: 5.1 V

Tested the voltage to the IAC connector, KOEO: 11.xx V

Tested the continuity of the VREF wire between IAC & TPS: good

Tested the continuity of the VREF between thw TPS & ECT: good

Then I noticed that when I replaced the ECT, I left the old seal in the connector. So there was 2 seals. Thought that was the problem as the contacts weren't seated all the way. Still get the code 117

Truck fires right up in the morning and then dies. Restarts are VERY hard. Even after the engine has fully warmed up, in the first mile or so of driving, the engine will just shut off, but it will restart right away.

The other morning when I started the truck (engine still cold), every time I shut the door (fairly hard) it would kill the engine.

Are there any other things I can test? I am completely lost at this point with it. Any other thoughts to this issue? I need to get this fixed with colder weather setting in, the truck doesn't want to stay running in the morning.

Thanks

 

My you've been busy on this one!!!!!

Sounds like you have more than one problem.

Have you back probed the ECT return signal level at the computers firewall connector????

Seeing as how the computer is unhappy with the ECT's return signal input being low, maybe there is a problem at the computers firewall connector, or with the ECT return wire to the connector.

Seeing as how your also having some engine stalling problems that can be had by slamming the drivers side door, maybe while your there trouble shooting the ECT problem, also consider pulling the computers connector on the firewall & checking it & the pins/sockets out for bent pins or sockets, tightness of the connectors fit & connector corrosion.

If that proves naught, on the engine stall, maybe try a ignition switch wiggle test & thumping around the ignition switch & the in dash & underhood power distribution/fuse boxes, to see if you can cause the engine to shut off.

If so, suspect a ignition switch problem, or a faulty relay or wire, or fuse in the power distrbution/fuse box's.

Also check the battery cables, they should be clean, bright & tight!!!!

Edit: I'd also check the in cabin fuel pump inerita switch & it's electrical connector on the engine stall problem.

A bunch more trouble shooting thoughts for consideration, let us know what you find.

 

Thanks pawpaw for the reply.

After I had tested all of those sensors and wrapped everything up, I realized that there were two more tests I could do.

One you have already mentioned which is to check the return signal back to the PCM. Would I do this by back probing the ECT signal wire with one probe and grounding the other? Or would I have to back probe the ECT wire and the VRef wire? I'm pretty good and mechanics, but not electrical work.

The other test is to check the continuity between the PCM connector and the ECT connector. I'll check out the PCM connector.

The battery connectors are good and tight. I also checked the various grounds (4 or 5 I think) for looseness and all seemed good.

Also, I noticed that the engine will only stall by shutting the door when it is still cold. The other day when I got to work, I slammed the door and the truck stayed running (truck was warm by then). Perhaps there is just a bad connection or corrosion at the PCM connector?

Lately I have been leaving home in the dark and returning in the dark. Plus I've been working on my FIL house for the past few weekends. So working on my truck when it is still light out has been a bit of chore.

Thanks again!

 

Ok good feedback.

Yup, with a high impedance digitial voltmeter, back probe the ECT wire at the fire wall computer connector, to ground & see if the signal return voltage going into the computer is making it that far.

If not, then pull the connector & check it's pin/socket connections & the sig return leads continuity back to the ECT connector.

You've already checked the ECT's VRef at the sensor & found it's ok, so the Sig Return lead is still suspect at this point.

The fact that it only acts up when cold is a clue & sure sounds like a contact problem, so check those connectors pins & sockets carefully.

Flex their leads while measuring the Sig & Sig Rtn lead at the ECT & Computer end, when doing the continuity test.

Even though you had a good Sig voltage at the ECT when you tested it, check it's leads continuity anyway, beause if it's intermittent, it will cause a low Sig Rtn voltage to the computer.

It's possible, though not likely, that the new ECT is faulty, as I've seen bad new parts right out of the box, so keep that in mind if all else fails.

Will be interesting to hear what you find is the cause.

 

pawpaw,

Today I checked the continuity between the ECT signal pin at the PCM connector and the ECT sensor connector. I got a good continuity check, but did this test with the ECT connector still connected (oops). Hopefully the continuity test is still accurate.

I cleaned the PCM connector and PCM pins with some brake cleaner and used a can of compressed air to blow it out.

Reconnected the PCM connector, back probed the ECT signal wire and set the DMM to volts. The truck wasn't completely cold, but had been setting for ~3 hours or so in ~40° to 45° weather.

As the engine warmed up, the voltage started decreasing by 0.001 to 0.002 volts at a clip. It started at ~3.xxV. It had decreased to ~0.58V and would fluctuate between 0.58V and 0.62V. The ohms were also fluctuating with the voltage. If I understand the system right, the voltage would fluctuate with the changing coolant temp, correct? Also, it should show that the T-stat is working too, correct?

I then checked the voltage/ohms being sent by the ECT sensor. It was pretty much the same reading at the PCM.

When checking the ohms, they were fluctuating at ~8.7M to 10M ohms.
A print out on ECT values shows that for the voltage i was getting, the ohms should be ~2.07K to 2.80K ohms.

The DMM was showing a little capital M next to the ohms instead of a K. Is there something I'm missing here? Do I need to convert or is this telling me that the resistance is to high?

I also disconnected the battery before pulling the plug on the PCM. The bolt holding the connector to the PCM may have been a little loose, I'm not sure though. I made sure it was tight when I put it back on.

Any thoughts?

Thanks

 

Well lets see, on the DMM scale, the "M" = Meg ohms (millions of ohms & the "K" = Kilo (thousands of ohms), a big difference.

So it seems you were reading 8.7 to 10 Meg ohms at some temperature & should have been reading around 2.07-2.80 K ohms.

If the ect sensor is the wrong resistance range or profile (higher resistance) than specified for a given temperature, it'll cause the ECT's return signal voltage to the computer to be lower than spec & confuse the computer.

Here is a link to a good temp/resistance profile for the ECT sensor.
Ford Fuel Injection Engine Coolant Temperature Sensor (ECT)

Yup you needed to do a end-to-end lead continuity & resistance check with both the ECT sensor & computer connectors disconnected.

Then, if the wires being tested have low ohms resistance numbers, their good. Be sure to flex them some when doing the measurement.

Then with the ECT's connector removed, do a resistance check of the ECT at cold & hot temps & see how it's temp/resistance profile checks out with the chart.

If it's ok, then hook everything up & with the engine operating, back probe the ECT signal return voltage at the computers firewall connector & compare it to the charts value for the engines temp when tested. Flex the leads on both ends when doing this.

If it reads ok, then maybe suspect a compuer circuit board problem.

More thoughts for pondering, keep us posted.

 

pawpaw,

I thought that the 'M' meant mega ohms which is FAR more than the specified value.

By back probing both the PCM connector and the ECT connector, I got a very low ohm reading, maybe .006ohms or something like that.

When I reconnected the battery, I checked for codes and got none. Then I ran an errand for work. I only went a few miles, but the truck had fully warmed by then. On the way back the truck stalled once (not driver error ) and almost stalled 2 or 3 more times when hitting large bumps (railroad xing, parking lot entrance curb).

When, I got back to work I rechecked for codes. I got a system pass for both 'on-demand and 'continous memory'. So it would appear that the code hasn't come back for now at least.

But the truck wanting to die when hitting a bump is not good. Looks like I need to recheck some grounds again.

Also, would putting the PCM connector on too tight also cause this?

Thanks.

 

I have a 91 that had a ghost problem, I would be driving along (sometimes slow maneuver clutch work ) and it would stall. Being a stick it would promptly bomb start itself immediately ( MY TEETH ) , my problem was a flaky pcm relay that would act up whenever it felt like it. You may want to check/change your pcm relay as it might be a contributing problem.

 

Update,

With the truck running, I smacked the power distribution box. Everytime I hit it, the engine would start to die, drop RPM's. I didn't have to hit it very hard either.

Would this be a relay going bad or something else. I must admit, I never opened one up, other than to replace a relay. Also, after the engine would cut out (by hitting it a few times in sucession), the key would have to be turned off before the engine would restart.

Any ideas?

 

R031Kona,

I just got your reply as I was typing. I'm starting to believe that it is a PCM or Fuel Pump relay going bad.

After I hit the box and the engine died, I swapped the PCM relay with the Fog light relay and it still did the same thing. The fog light relay is only about 7 mos. old. Maybe I should try the fuel pump relay?

 

Update:

Went to the parts store across the street and bought two relays. Replaced both relays for the fuel pump and the PCM. The fuel pump had the original relay still in it. I didn't know which one was bad, so I just replace both ($10 ea.)

Hopefully the ECT code doesn't come back. It hasn't so far. All I really did was clean the PCM connector contacts with some brake cleaner and used compressed ait to blow them out. Also made sure the connector was good and tight. It seemed the bolt was a little loose.

I'll post back if the problems persist.

Thanks!!

 

Yup we're saying the same thing, (Meg & Mega ohms) & they are a thousand times more than "K" ohms.

So you need to be careful when making the resistance reading, DON'T have the ignition switch on, as the DMM doesn't like to have voltage on the circuit when making a ohms reading, you could smoke your meter.

When you do the lead, end-to-end resistance check, be sure the connectors are removed from ends, so your meauring only the wire under test, resistance.

I don't think snugging the PCM connector down is the problem.

 

Dang your trouble shooting & fixing things faster than I can type.

Good find, fix & feedback on the relays.

 

See, I told you I'm not very good at electrical stuff. When I was testing the signal return voltage to the PCM, the engine was running. One probe on a paper clip that was back probed into the PCM connector and the other end on the neg. side of the battery. Then I got the idea 'Hey, maybe I should check the ohms and see if their in spec', with the engine still running! Hopefully I didn't fry the DMM. Nah, it seems fine. Luckily the voltage was quite small, < 1V

Also, you verified what the 'M' stood for. I asked because I wasn't sure.

 

yeah I tried swapping my relays too , I could not get the pcm to self test unless I disconnected the battery. My swapping did nothing $40 part and $160 diagnosis fixed it good.