I have to wait for materials to make up jumper wires to reach from the ECM connector to the EDIS connector. So, while waiting I found a tutorial on how to check the injector pulse with a test light. I didn't read anything abouot this situation that I ran into. With the key off, the test light connected to the positive lead of the battery, and probing the wire for the pulse signal the light comes on. When I turn the key to the on position and before cranking, the light goes out. While cranking I get no flashing of the light, it stays off. Is it supposed to be on with the key off and go out when the key is turned on? I realize the light should flash when cranking which tells me I have no signal at this time. I do have power to the injector with the key on through the other wire to the injector. I am starting to think that either the ecm is not getting the PIP signal form the edis or the ECM is bad. Is there a way to check the PIP signal is getting to the ECM without a scope?

 

The injectors each have a RED wire, that's 12volts with key on, it just daisy chains from one injector to the next

The OTHER COLOR wire is the ground controlled by the computer, this is the one that will pulse when computer is opening up the injectors while cranking
But the pulse is only a few milliseconds long, so very very hard to see with a test light, much much faster pulse than "Coil Ground pulse"
With an old analog volt meter(has a needle) you could sometimes see a pulse on the needle

There are NOID lights, made for doing this, they have a circuit that shows when there is a fast ground pulse

If test light was hooked to battery positive then pretty much any lower voltage would cause it to light up
So if you shut off the 12volts(key off) then yes it would probably light up

 

Yeah, I have a test light that is supposedly safe for electronics. I verified that the one lead does hae 12 volts to it. With the light hooked up to the positive terminal of the battery though the other injector lead does not light up while crnaking. The light will come on in the key off postion though. Also, is there any way to trace the PIP signal to insure it is getting to the ECM without using a scope? Also all noid lights I am seeing for fords are for TBI. Is that the system my truck has?

 

You don't really ever need a NOID light unless you are testing for pulse on each injector
Just test for fuel pressure, if you have any, then crank engine
Pull a spark plug
If is WET pulse is there
If its DRY no pulse

I remember finding a bad injector by removing all spark plugs and cranking engine over, could see no "mist"(fuel) coming from #5, bad injector on #5

The ground pulse is so short the test light doesn't have enough time to light up, key off that wire is a ground or pretty close to it, if engine was running it would probably glow enough to see since injector wire would be grounded longer, but at cranking speed(150-200rpm) just don't think so

I have never tested PIP with EDIS system
But I have read it is a 12volt ON/OFF pulse, so with grounded test light, pulse "may" be long enough to light it up when cranking

 

ok, thanks Ron. Stranded out in the boonies so it will be a few days before I can get to a store to buy the correct socket to fit the screws of the ECM case. I'll come back when I have been able to inspect it and the wiring. The plugs that I pulled to check compression were all dry. I had cranked the engine a few times prior to pulling them.

 

Then computer is not pulsing injectors, assuming there is fuel pressure

 

I don't have a fuel pressure guage but I can hear the pump prime up when I turn the key on and pressing the schrader valve get a good stream of fuel all over the place.

 

Then you have pressure

 

I was able to see pulse signal for PIP at both the EDIS and the ECM connector using a test light. So the EDIS seems to be working fine. I checked the four grounds of the ECM connector for voltage drop and the worst one was .183v. is that too much? I am lucky enough to have a shop near me which can check my ECM and repair if necessary. I plan to give it to them Monday. Does it sound like the ECM went bad? It is only about 3 months old.

 

Also have a nagging question in the back of my mind. With test light hooked to the positive terminal of the batter and probing the wire which supplies the injector pulse at the injector, The light comes on with the key off, but but goes out when the key is placed in the on position. No flash when cranking, just wondering why the light is on with the key off. is that normal? I think this is a circuit like the switching circuit for the coil where the ground is supplied and then broken by the ECM to operate the injector. Is the ground always present with the key off? Just wondering for my own knowledge is all. I'm sure it shows that I don't know a lot about electrical but I am trying to learn.

 

Light is ON with key off because that wire is now a "ground" sort of
When key is on the computer powers up and "lifts" the ground or injectors would open because they have 12volts with key on

Simple diagram of transistor used to pulse an injector ground: https://i.ytimg.com/vi/JTCgUY51g0s/hqdefault.jpg

 

Finally, after 3 weeks the shop tells me that they can't test my computer because they can't work on anything "that old". That's fine with me but why couldn't they have told me that right up front? Anyway, I took a chance because everything was pointing that way to me and I purchased a remanufactured computer. Put it in and I read somewhere that I should turn the key to on and leave it there for 5 minutes, then turn it back to off before attempting to start the truck. I did that and then the truck started right up. let it run for about 5 minutes and it seems to be fine. Ron, I want to thank you so much for hanging in there with me and sharing all of your knowledge. Whether you realize it or not you taught me a great deal and even more than that, you gave me the confidence I lacked to try this myself.

 

Well, that was a nice evening of thinking all is well. CEL came back on and was able to retrieve 2 codes. 16 again, and now 22. not sure about code 16, it came up before on the old computer. 22 is new. best I can come up with is the BARO sensor but I know nothing about that sensor nor even where it is located. Is it harmful to the truck to drive it with this fault? Any help is greatly appreciated.

 

16 again, does CEL go off when cranking engine over?

22 is MAP sensor, unplugged its 4 wire connector and have a look inside for any corrosion, plug it back in a clear the codes to see if it comes back

Its odd that everything worked OK with "new" computer, then didn't
Almost makes me think the connector for computer might be the issue
When you unplug and plug back in a connector, it "cleans" the pins and slot a bit, but if connection on one or two pins are still "dirty" then problem comes back

 

Thanks Ron. The CEL does go off when cranking. comes back on after engine has started and ran for 10 - 15 seconds.
My truck is a California emissions and I hav no "MAP" sensor so I have heard. Mine is a BARO sensor or BMAP I saw it called also. Finally found a picture of it and its location but I can't test it as I have no way to change pressure. I will definitely try connecting and disconnecting the computer a few times. I am supposed to disconnect the battery prior to taking the connector off, correct?

 

Sorry MAF sensor, its on the air filter box, 4 wire connector
I didn't think any of the Ranger 4.0l V6's used a MAP sensor so its an odd code come to think of it
Computer used MAF sensor data and throttle position + RPM to calculate manifold pressure(engine load) on the fly

But 1990 4.0l in Calif may be a one off year and have a BMAP

 

Tried connecting and disconnecting the ecm and sprayed connector with electronics cleaner but still have the same situation. I ordered the BMAP sensor and it will come on Tuesday. the code 16 is now what I am wondering about. Is that code telling me that the circuit between the EDIS module and the ECM is open? The tan/yellow wire from the edis to the ecm is marked as the3 IDM. Is that what this code is telling me is bad? Does anyone know of a way to check this?

 

Found this here:
https://www.fordforumsonline.com/thr...-systems.3764/

"HDR EDIS Ignition Diagnostic Monitor (IDM)
The IDM line is a signal line used to convey EDIS operating status to the PCM. In previous, conventional ignition systems, the IDM signal was generated by the back EMF created when the coil turned off. This voltage was called the flyback voltage. Since the flyback voltage could be as high as 400 volts, the signal was filtered by an external resistor or by internal circuitry in the ICM. The PCM uses this signal (via the IDM line) as feedback, to verify that a spark event occurred. For the EDIS ICM, the IDM pulse is also triggered by coil flyback voltage. The EDIS module uses this to trigger a pulsewidth-encoded signal on the IDM output. During normal operation, the IDM signal is 52 microseconds. During Key-on, Engine Off mode, the EDIS outputs a 64 microsecond pulse at 262.144 millisecond time intervals to verify normal EDIS operational status.
The IDM line is also used to drive the "Tach" output. Note that 4-cylinder applications, this signal is brought out on 2 pins. These applications also have a "Clean Tach Out" CTO output from the EDIS."

Am I correct that I should be able to get a pulse in this wire at the edis module when the truck is running? Would checking for a pulse at the ECM connector be useful also?

 

The CEL should go off when cranking engine over if PCM(ECM) is getting a pulse from EDIS(spark module) on that wire

Tan/yellow wire is also the "tachometer wire", so if you have a tach then it should move up when cranking engine ovver

 

Ok, so this is where I am today. Took voltage readings at the EDIS module and the ecm connector for the IDM wire with key in the on position. Both readings matched at 66.4 MV so I believe that the wire has good continuity. Nearly ashamed to admit it but at this point I am grabbing at any straw with in reach so I used the "justanswer" web site and asked about this. The "expert" said to replace both the ecm and the EDIS. This sounded kind of like easter egging to me as both are less than 6 months old. His reasoning is that by not replacing both at the same time one could be giving the other one fits. From what I gathered, one component may be screwing up the newer component and by only replacing one component at a time I may be keeping the original problem going. Does that even sound plausible?

To answer you Ron, the tach does function and seems to be accurate. The CEL does go out when cranking, then comes back on about 10-15 seconds after the engine starts. The guy from justanswer said that he believes the new ecm is bad because the tach seems to work fine.

From what I have been able to read about the IDM wire, it is something akin to a confirmation from the EDIS to the ECM that the coil did actually fire. Is that correct? Also, there is a capacitor for radio/ignition interference attached to the hot wire of the coil. I know it is for keeping radio interference down, but does it also have anything to do with reducing voltage spikes? I think mine is shot as I have incredibly loud whining on AM stations and some FM stations with the motor running. I don't care about radio interference as I never use the radio but am not sure if this could cause other problems with electronics.

 

Yes, thats exactly what the Noise capacitor is for, absorbs voltage spikes and drops as computer grounds and ungrounds the coils
No, shouldn't effect EDIS or PCM systems

The IDM confirms RPMs which means coils are working, not really a 'test" that coil fired

Had a thought and easy to test, and your question about the noise capacitor triggered it
Alternators can leak AC voltage which will cause issue in PCM and even EDIS, especially timing circuit
Unplug the 3 wire connector on the back of alternator, this will prevent alternator from starting up
Clear codes
Start engine and see if the CEL comes back on after start up
Engine should run fine on battery voltage only for 10+ minutes

You can test for AC Voltage with alternator hooked up and engine running

Google: automotive AC ripple voltage

This is a long shot but not a no shot, lol, just another straw to try and grab

Yes, professional mechanics have the luxury of not having to "pay the bill" when doing repairs, so their "best method" can be a wholesale swap of parts to fix a problem
The "why" of the problem is not their concern, just the results of no more problem
A DIYer approaches a problem differently, they want more of the "why" so they don't have to pay alot to replace parts

In example
The problem: You have a dirty ashtray or an empty cup in the cup holder
You could just trade the vehicle in and buy a NEW vehicle with clean ashtray and no cup in the cup holder, the "problem" is solved
OR
You could clean the ashtray or throw out the cup, "problem" solved

Both result in "problem" solved, neither is WRONG but one is pretty silly, I won't say which one, in case a professional mechanic reads this

 

Thanks for the tip Ron. I will test the alternator Wednesday after replacing the BMAP sensor. Gonna rain hard tomorrow so I'll get to it Wednesday.

 

Tried clearing codes and disconnecting alternator. Codes stil came back. Tested the alternator for ripple affect and got no AC voltage so at least I know the alternator isn't it. Appreciate the try Ron, I did learn something about alternators that I didn't know before. I am going to bite the bullet once more and replace both the ecm and the EDIS at the same time. Figure I can always box the ones I have now as spares in case I get stranded, they will at least start the truck and run it for a short ways. Personally, I am starting to believe it is the EDIS as both computers gave me the code 16, but the tach still works which puzzles me as I am thinking if the EDIS wasn't giving out the proper signal then I shouldn't have a working tach. I just don't know and at this point am willing to try investing a little more to see this thing go away. I'll let you know how it turns out once the parts arrive. Again, thank you for all your help RonD.

 

New developments. replaced the BMAP sensor after clearing all codes from the computer. Did a KOEO test and still getting the codes 16 & 22. now also getting new code 86. took the truck for a short run (7-8 miles) and it now won't shift into 4th gear. I know that is what the code 86 is about. IS there a way to test the 3/4 shift solenoid with just basic tools (test light and digital multimeter? This happened with the old computer but after driving a day or so it began to shift again. I'm not sure if the problem is the computer or the solenoid. I had read somewhere that a bad solenoid can cause a failure of the computer so I wouild like to test the solenoid before I put a new computer in the truck.

 

There will be a 3 wire connector on drivers side of transmission just in front of shifter
Unplug connector
Center wire feeds 12volts to the 2 solenoids inside
Test that center wire(red) has 12volts key on, this red wire doesn't have its own fuse, same red wire powers computer and other solenoids, like fuel injectors, 12v comes from EEC relay and its 30amp fuse

You can test if solenoids are connected inside trans using OHM meter
Put 1 probe on center pin and other probe on either side pin, should see 20-40 ohms, then test other side pin
OHMs is the resistance in a wire, 0 ohms would be a short or a good wire it testing 2 ends of the same wire
A solenoid is a coil of wire so has a little bit of resistance but not much, if OHM meter doesn't change at all when testing that means there is no connection, so broken wire

You can also test at computer end, trans connector plugged in, key on
Pins 52 and 53 are the two solenoid wires from transmission, a pink/yellow and orange/yellow
With key on each of those wires should show 12volts

A solenoid is just a coil of wire inside, so 12v in = 12volt out, might read 0.1 less than battery voltage
The computer would Ground each of these wires internally to activate each solenoid
If no 12v then wire or solenoid is broken