'01 5.0: Spark only on cylinders 1 & 6

[monkeyfist]

This is a bit of long story but here it is: I've swapped a 2001 Explorer 5.0 into a '68 Bronco. It's in and, to the best of my knowledge, wired up correctly. I'm using an EQE5 EEC-V PCM. After months of trying, I've not been able to get it to start.

I'm getting good fuel pressure, which means that the failure is likely to be with spark... When I check with a timing light, I only see spark on cylinders 1 & 6 so I pull all of the plugs and confirm that this is indeed the case - none of the other plugs are firing.

Next step: swap the coils to see if the problem follows the coil but no change - still firing 1 & 6 only. One by one, I swap each plug wire and plug to either cylinder 1 or 6. Each plug is firing so I know that the plugs and plug wires are working.

So then I pull out the oscilloscope to check the coil driver lines to the coils. When I look at the coil driver signal going to the coil for 1 & 6, I see a big swing when it sparks. When I check any of the other coil driver lines, I see a much smaller swing, definitely doesn't appear to be getting to ground. I've checked all of the ground points from the 104-pin PCM connector and I'm seeing, on average, 0.5 ohms to ground, which is in within the accuracy of the ohmmeter I'm using.

Looking at the coil driver line for 2 & 8, I start wondering if the small swing I see in the signal is induced noise from the spark on 1 & 6 so I unplug the connector to the right coil pack (cylinders 3 & 5, 1 & 6). When I check the coil driver signal on 2 & 8 now, I see the same swing, however, I noticed that I'm now getting spark on cylinders 4 & 7!!!

This is a big clue but I'm not entirely certain how to interpret it. Anyone have any thoughts or experiences with something like this?

Thanks!

 

[2000StreetRod]

PCM configuration?

I'm not familiar with your PCM but I assume that it can be configured for number of cylinders and firing order. Maybe its not set up correctly for a V8 with a waste spark ignition system.

 

[monkeyfist]

Sorry - I should have been more clear. I'm using a Ford EEC-V PCM, catch code EQE5. I should hope that it's setup to work with this engine, as it was designed to work with this engine!

 

[2000StreetRod]

Ground points?

. . .
So then I pull out the oscilloscope to check the coil driver lines to the coils. When I look at the coil driver signal going to the coil for 1 & 6, I see a big swing when it sparks. When I check any of the other coil driver lines, I see a much smaller swing, definitely doesn't appear to be getting to ground. I've checked all of the ground points from the 104-pin PCM connector and I'm seeing, on average, 0.5 ohms to ground, which is in within the accuracy of the ohmmeter I'm using.

Looking at the coil driver line for 2 & 8, I start wondering if the small swing I see in the signal is induced noise from the spark on 1 & 6 so I unplug the connector to the right coil pack (cylinders 3 & 5, 1 & 6). When I check the coil driver signal on 2 & 8 now, I see the same swing, however, I noticed that I'm now getting spark on cylinders 4 & 7!!! . . .
Thanks!

I don't have the wiring diagram for a 2001 but it is probably similar to the 2000 for ignition. Have you verified that PCM pin 26 goes to Coil #1, PCM pin 52 goes to Coil #2, PCM pin 78 goes to Coil #3 and PCM pin 104 goes to Coil #4?

What did you mean by checking the PCM ground points? Are you referring to PCM pins 24, 25, 51, 76, 77 and 103?

Is the crankshaft position sensor wired to PCM pins 21 and 22?

Have you tried disconnecting the radio noise suppression capacitor connected to the ignition coil power side? Sometimes they short out.

Have you checked the supply voltage to the coil packs? It should be battery voltage in Start or Run.

What did you do to keep PATS from disabling your start capability?

 

[monkeyfist]

I don't have the wiring diagram for a 2001 but it is probably similar to the 2000 for ignition. Have you verified that PCM pin 26 goes to Coil #1, PCM pin 52 goes to Coil #2, PCM pin 78 goes to Coil #3 and PCM pin 104 goes to Coil #4?

Yes, I have verified that those connections all go to the correct coils - they are what I was referring to as the "coil driver signals".

What did you mean by checking the PCM ground points? Are you referring to PCM pins 24, 25, 51, 76, 77 and 103?

Yes, I have checked PCM pins 24, 25, 51, 76, 77 and 103 and each has a resistance to ground of no more than 0.5 ohms.

Is the crankshaft position sensor wired to PCM pins 21 and 22?

Yes.

Have you tried disconnecting the radio noise suppression capacitor connected to the ignition coil power side? Sometimes they short out.

I have not tried this - I'll have to give it a try and see if that changes the behavior.

Have you checked the supply voltage to the coil packs? It should be battery voltage in Start or Run.

Yes, the supply voltage to the coil packs is within 0.5v of the supply voltage, so there's no meaningful voltage drop from the battery to the coils.

What did you do to keep PATS from disabling your start capability?

This is where I've been a bit surprised. I hadn't expected to get any spark from the 2001 PCM until I disable PATS (using a X3 tuner), however, I was seeing spark without any changes. I've been under the assumption that if PATS disables the engine start capability, it will cut *all* spark and will disable the fuel pump, but with this PCM I'm getting spark on some cylinders and the fuel pump is operating without problem!

Just to satisfy my curiosity, I hooked up an older 1997 (pre-PATS) PCM, swapped the camshaft sensor to the older style to match the expected PCM input for that signal, and I was still only getting spark on cylinders 1 & 6. Once I saw this, I have been thinking that I've got some other non-PATS problem.

I been having trouble getting the X3 to talk to my PCM, so I haven't disabled PATS yet... May be on my list of things to do before I go much further.

 

[2000StreetRod]

PATS & fuel injectors

When I first bought my 2000 Sport last year I pulled it into the garage and the next day it wouldn't start. I spent most of the day troubleshooting and finally got it to start and run for a few seconds by spraying starting fluid into the intake manifold. I finally realized I was using the other ignition key. When I tried the other key the engine started immediately. That was my introduction to PATS. For my vehicle PATS only disables the fuel injectors. Do you have a noid light to check the injectors?

 

[monkeyfist]

I don't have a noid light, but I may be able to find something that will work... If nothing else, I'll go out and get one to test. It'll certainly come in handy once I get to trying to test with fuel.

I wasn't aware of that form of PATS (no fuel injectors), but if my PCM is the kind that only disables fuel injectors, I would imagine that I'd see spark on all 8 cylinders. Only seeing it on two, and the cylinders that are sparking changes depending on whether I have the driver's side coil pack plugged in tells me that I probably have some other problem. I'm starting to wonder if I'm not able to get enough current to the coils to charge them up between sparks. Guess I'll have to keep testing!

 

[2000StreetRod]

coil supply

Normally power for the coils comes from a 25 amp fuse. Unless your wiring size is extremely small the coils will draw the amount of current they need. If they needed more than your fuse can supply, the fuse would blow.

Is the PCM you're using from the same doner vehicle as the engine? Do you know if the combination ran before they were pulled from the vehicle? Do you have power wired to the PCM KAM?

 

[monkeyfist]

Normally power for the coils comes from a 25 amp fuse. Unless your wiring size is extremely small the coils will draw the amount of current they need. If they needed more than your fuse can supply, the fuse would blow.

Yes, but this isn't stock wiring (it's in a '68 bronco), so there's the possibility that due to some other wiring issue, I'm not able to get enough current to the coils. If some of the current is being routed elsewhere instead of the coils, I'll still see the proper voltage at the coils but I may not be able to get enough current to the coils. This is the avenue I'm currently investigating.

Is the PCM you're using from the same doner vehicle as the engine? Do you know if the combination ran before they were pulled from the vehicle? Do you have power wired to the PCM KAM?

Unfortunately, the engine that I bought didn't have the original PCM available with it so I don't have it as a reference. Bit of a bummer but it's what I've got to work with. And, yes, I have KAM wired correctly (although I'm not entirely certain what this would have to do with incorrect / missing spark - perhaps you could provide a bit more detail?)...

Thanks for all of your help and suggestions so far!

 

[2000StreetRod]

Not the supply

Yes, but this isn't stock wiring (it's in a '68 bronco), so there's the possibility that due to some other wiring issue, I'm not able to get enough current to the coils. If some of the current is being routed elsewhere instead of the coils, I'll still see the proper voltage at the coils but I may not be able to get enough current to the coils. This is the avenue I'm currently investigating..

The coils don't require a surge of power on the supply side. Energy builds up and is stored in the electromagnetic field and then is rapidly discharged when triggered by the PCM. I suspect 18 gauge wire or larger would be adequate for the primary side. I think your problem is elsewhere.

Unfortunately, the engine that I bought didn't have the original PCM available with it so I don't have it as a reference. Bit of a bummer but it's what I've got to work with. And, yes, I have KAM wired correctly (although I'm not entirely certain what this would have to do with incorrect / missing spark - perhaps you could provide a bit more detail?).. .

Although the PCM does not need KAM values to start, the PCM does know when there is no KAM power. I was mainly looking ahead to when you get the engine started.

You may have a PCM problem. Have you tried to store a copy of the strategy tune on your X3?

On my 2000 the PATS is connected to the OBD-II bus lines. Since you probably did not wire in PATS the PCM may be detecting that it is not present on the bus. The PCM could be preventing the engine from starting until PATS is disabled.

 

[monkeyfist]

The coils don't require a surge of power on the supply side. Energy builds up and is stored in the electromagnetic field and then is rapidly discharged when triggered by the PCM. I suspect 18 gauge wire or larger would be adequate for the primary side. I think your problem is elsewhere.

I agree that it's like that the problem is elsewhere, I won't rule it out until I have definitive proof that it's not the problem. A coil can't charge up instantaneously - it will charge at an exponential rate over time (see http://www.tpub.com/neets/book9/0315.GIF) and there's only a finite amount of time between sparks on a given coil. At 1200rpm, it's roughly 50ms between successive discharges for a given coil - that should be plenty of time to charge up, provided the current isn't being sunk elsewhere.

Although, now that I think more about it, there's 4 separate coils (2 in each coil pack, each with outputs for 2 cylinders), so even as one is charging, the others should already be charged. I can put the oscilloscope on the voltage line to one of the coil packs - if I have enough current, the signal should stay level around 12-14v, but if I'm unable to source enough current I'll see "droops" in the input voltage to the coil packs. That should give me a pretty definitive answer as to whether this could be the problem or not.

Although the PCM does not need KAM values to start, the PCM does know when there is no KAM power. I was mainly looking ahead to when you get the engine started.

Gotcha - that's where I thought you were going with that question but just wanted to make sure.

You may have a PCM problem. Have you tried to store a copy of the strategy tune on your X3?

I have not been able to get the X3 to talk to the PCM so I haven't touched any of the strategy settings. While I am not ruling the PCM out yet, I don't think that it's likely - I see the exact same behavior with three different PCMs, two of which are pre-PATS PCMs.

On my 2000 the PATS is connected to the OBD-II bus lines. Since you probably did not wire in PATS the PCM may be detecting that it is not present on the bus. The PCM could be preventing the engine from starting until PATS is disabled.

I agree wholeheartedly - I don't expect to be able to get the engine started until I disable PATS, however, if my PCM is like yours and only disables the fuel injectors, I should still get spark on all 8 cylinders and right now I'm not seeing that.