Ignition Timing and Power Ground

lilfordrunner · Feb 24, 2013

Recap: 87 ford ranger 5 speed-removed the 2.9-replaced with 93 4.0 that had an auto trans-stuck with original 5 speed

Truck idles very high

Question 1. It appears we don't have much control of the ignition timing. What would cause that, what are some things we can do to fix that.

Question 2. Pins 40 and 60 on the Explorer ECM are Power Ground. What IS Power Ground. I know what Power is and I know what Ground is…. But Power Ground??

adsm08 · Feb 24, 2013

The lack of control over timing is design intent. To "fix" that you would have to swap the engine to something with a distributor.

"Power ground", from my research, is the pin that grounds the unit's operating circuits. The PCM has many ground points so it can provide grounds to things like the fuel injectors, so it has a lot of grounds, but the "power ground" is the one for the power that comes in to run the computer.

lilfordrunner · Feb 24, 2013

So, what am I supposed to do about the timing in this case…? If the computer is supposed to "learn" where the timing is supposed to be, and its not…what would cause that?

PanamaExpat · Feb 24, 2013

Sure it is timing and not a high idle caused by a vacuum issue? After all you said you have just completed the swap.

lilfordrunner · Feb 24, 2013

There doesn't appear to be any vacuum leaks/issues anywhere…We did a lot of vac tests, including a smoke test…Everything is tight.

lilfordrunner · Feb 24, 2013

I guess what my real question is when it comes to power ground is, If I pin it out at the PCM what am I supposed to read? Ohms, voltage? How much ? Perfect ground?

adsm08 · Feb 24, 2013

Ok, don't worry about the power ground pin. If it doesn't have a good ground, the engine won't run. It is the ground for the computer. If it isn't going where it's supposed to lots of things that work won't work. It isn't your problem, stop worrying about it.

To give you a good analogy for this, get out some pliers and pull one of the prongs out of the plug of your old floor fan, the one that only has a 2-prong plug. Now go plug it into the wall and turn it on. Same idea as having this "power ground" pin hooked up incorrectly. It should read perfect ground.

Do you know that you have a timing issue? Excessive advance can raise the idle, but it is doubtful that is your issue. I have yet to see an EDIS system get that far out of time without something being noticeably broken. You might not be able to set the timing, but you should still be able to check it just like any other engine. Pop the spout jumper out and bust out the timing light. It should dwell at about 10*.

I don't think a 93 has a cam sensor. I know the 94 engine in my garage doesn't. That means that only 3 things can affect timing, the PCM, the EDIS module, and the crank sensor.

I want you to try something else for me before going any further with this ignition timing train of thought. It's just a little diagnostic step to help eliminate things.

Go out, remove the IAC. Put some masking tape over the ports on the intake and put the valve back on. Try to start the engine and tell me what happens. Does it fire up and idle high, idle normally, or not run at all? Those are your 3 options, if it does anything not in that list it has been possessed by an evil spirit.

One last thought on this for tonight. Have you checked out your MAF sensor? Not "looked at and cleaned" but actually tested it. MAF sensors are very fragile and sensitive. I've seen more than one be damaged during an engine swap and a bad sensor giving bad readings to the computer can cause a high idle. That is a much more likely scenario than and EDIS system getting itself out of time.

lilfordrunner · Feb 25, 2013

What is the best way to test the MAF and for the matter how would you test the EDIS?

a31ford · Feb 25, 2013

Here, I'll explain "Power Ground"

Power ground is as ADSM says, the ground that operates the actual electronics package in the ECM, there are also "Floating grounds" for other things, ex: the O2 Sensor is on a floating ground, as well as the TPS, the ECT and ATS all are on a floating ground.

What is a floating ground you ask ?? Well, back in the days of tube radio and tube amplifiers (Guitar amp is a good example) they found that if the placed grounds directly on to the steel chassis just where-ever, the amp tended to be very "Hummy" (had a background hum to it), It turns out that the electronics where so sensitive, that the "eddie currents" that flowed along the steel chassis would cause "ground loops" between certain parts, but NOT with other parts. SO, the answer was to ground EVERY wire at one common point on the chassis, there by eliminating these bothersome eddie currents.

This procedure of having one common ground is even MORE IMPORTANT with these new electronics, SO, what they do is what is known as a floating ground that tails back to the electronics package (ECM) all the sensors have this "Floating ground" that in effect is like the single chassis ground. IN TURN, this makes the external sensors more reliable, because things like eddie currents in the frame and body of the truck (or car) are eliminated. (these can cause false or high or low readings).

Example..... car coming at you with one really dim headlight, (bad ground) THIS, will casue an eddie current back feed into the ground of the other headlight.

another example, trailer lights with a bad ground.... turning left, the left lamp goes off, BUT, the right lamp blinks dimly.......

I know.... "clear as mud"

Greg

adsm08 · Feb 25, 2013

lilfordrunner said:
What is the best way to test the MAF and for the matter how would you test the EDIS?

MAF test is just testing resistances.

The EDIS module is pretty much like the PCM. It's there or it isn't. If you suspect a problem with the EDIS module, go check your timing.

All of my arguments and instructions for tests go back to one thing. You are fixated on a timing issue that should not exist, but in all the threads I have seen you post on this matter I do not remember seeing where you actually verified the timing is incorrect. GO CHECK THE TIMING!!

Ignition Timing and Power Ground

lilfordrunner

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adsm08

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lilfordrunner

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PanamaExpat

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lilfordrunner

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lilfordrunner

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adsm08

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lilfordrunner

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a31ford

Electronics GURU

adsm08

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