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Jul 10, 2019 | 02:27 PM

Kalando82

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need some opinions

My grandfather owns a 2003 ford expedition with the 4.6, it started with a misfire on the number 8 cylinder its not backfiring. so naturally i replaced the coil, well all of them (and the spark plugs with the correct gap aswell). it ran good for about 200 miles then it came back, same cylinder. so next i ran a compression test and it was at 155 or so, and the other cylinders where about the same. so i moved onto the injector, we bought a brand new oem injector and still same issue. i replaced the intake gaskets, same thing, this whole time its still pulling a code for the number 8 cylinder. a few days ago we took it down the road and it made it there, we went to go and turn it on, and no start. we had it towed back home, and the next day, the thing fired up. i'm thinking the fuel pump or the fuel filter? what do y'all think? it still fires up and runs with the 8 missing. i checked that bleeder valve under the hood and good strong pressure of fuel shot out, im gonna get a fuel pressure tester and see. just trying to get some other thoughts. i might be over thinking this.

Jul 10, 2019 | 06:03 PM

pdqford

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From: Central NYS

How could the fuel pump or fuel filter only effect cylinder #8 ?

When you changed the COPs did you also replace the COP boots?

Do you have full battery voltage available at the COP #8 connector?

What shape are the connector pins in the COP #8 connector and in the ECM connection?

Jul 10, 2019 | 06:37 PM

Kalando82

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I replaced the coils and the boots, brand new. I don't know about battery voltage, I could check. I haven't checked the ECM connectors but the connectors at the #8 coil is good, I cleaned all of them when i changed them with some electronic and connector cleaner. the reason for the fuel pump at the time was because it didn't want to start the other day, it wanted to fire but didn't quite get there almost like a fuel issue. we were on a slight incline, so this morning I put the front end up on ramps to see if it'll start after letting it sit like the day it didn't fire up, and just a min ago it fired up. so I don't think its really a fuel issue but I'm gonna get a fuel pressure tester anyways just to check. I don't know what the misfire on #8 (and thats the only code that keeps popping up all the time before and after I replaced all these parts) has anything to do with it not starting up that's why I need some opinions. I'll check the voltage at the coil connector and check the plug at the ECM. what should the voltage be at the coil?

Jul 11, 2019 | 12:34 AM

R&T Babich

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From: Thousand Oaks, CA

Quote:

Originally Posted by Kalando82

.... . I'll check the voltage at the coil connector and check the plug at the ECM. what should the voltage be at the coil?

With the key in RUN or START voltage will be sent to the coil connectors and the injector connectors and should be around 12.5v (battery voltage).
The 12v goes thru the coils and injectors to the PCM.
The PCM will ground individual circuits at the appropriate times to fire the coils or open the injectors.
Checking for 12v at the PCM connector for #8 coil (probably WH/RD) and injector (LB) would show the wiring is good thru them.

You may have 2 problems.
Did you have fuel pressure when it didn't start?
The fuel pump could be sticking or the fuel pump relay contacts may be pitted.
Check the voltage at the Inertia Switch which is between the relay and the pump.

Jul 13, 2019 | 02:33 PM

alloro

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It could be a failing output driver for #8 inside the ECM. I've seen that happen a few times now.

Jul 19, 2019 | 06:26 PM

Kalando82

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I don't know if I had fuel pressure. I just went in there the next day after we had it towed and it fired up then I drove it on the ramps to test it further. Its still missing pretty bad but it passed inspection the other day with no check engine lights but I don't think we driven it enough for the CEL to come back on. (I disconnected the battery) As for the output driver, what exactly is that? I'm used to the older engine terms but when it comes to fuel injected engines I'm still learning all the terms.

Jul 19, 2019 | 11:05 PM

R&T Babich

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From: Thousand Oaks, CA

Quote:

Originally Posted by Kalando82

.... As for the output driver, what exactly is that? ....

The Wiring Diagram shows for the coils/fuel injectors that 12v is connected to them when the ignition switch is turned to RUN or START.
The voltage goes thru the coils/injectors, out the 2nd wires in the coil/injector connectors to the PCM on individual wires.
In the PCM each circuit has a solid state chip controlled by the PCM that will connect the circuits to Ground.
At the appropriate times the PCM will enable/disable the chips completing/opening the circuits to ground, thus firing the coils/injectors.
The grounding chips can fail in the PCM and the coil/s or injector/s will not function.
The PCM would need to be replaced as the chips are normally not serviceable.
There are a few things to test before saying the PCM is bad.

Last edited by R&T Babich; Jul 20, 2019 at 01:35 PM. Reason: Clarification