[ttammag]

My son has a 2008 4.0L. Recently, it has developed a misfire during hard acceleration. It is difficult to reproduce, but it seems the most common occurrence is during a hill climb and merging onto the highway. So it is during a hard acceleration, mostly uphill. During the misfire, it briefly flashes two dash lights, hesitates, and continues to accelerate. The dash lights flash so fast that I'm not 100% sure which ones they are.

One time, it did set the following codes:

P0300 Random Misfire
P0302 Cylinder 2 Misfire
P0306 Cylinder 6 Misfire
P0607 Control Module Performance

I cleared the codes and was able get to misfire again, but it hasn't set the codes again.

He has only put about 4000 miles on car since we bought it. When we first got it, it had a stalling issue at idle. At that time, we changed the fuel filter, spark plugs, and crank position sensor, which resolved the idle stalling problem. I also replaced the thermostat housing and cleaned the throttle body and MAF sensor at that time. This misfire issue seems to have started within the last 500 miles.

I haven't been able to catch anything significant with the live data on my cheaper scan tool.

I will appreciate any and all suggestions you may have.

Thank you,
Matt

 

[Beechkid]

IMHO I would replace the fuel filter (IIRR that one is not permanent).

 

[ttammag]

IMHO I would replace the fuel filter (IIRR that one is not permanent).

Thanks for the reply. Fuel filter is the first thing I thought about too, but we changed it less than 4000 miles ago. Forgive me for this question, but what do you mean by IIRR?

 

[Yadkin]

You probably have a worn out coil pack. Replace all three as a set, along with the wires and plugs. Rock Auto sells a kit - my son just did his 04 Explorer and it fixed a similar issue.

 

[Kraig1957]

Thanks for the reply. Fuel filter is the first thing I thought about too, but we changed it less than 4000 miles ago. Forgive me for this question, but what do you mean by IIRR?

I'm pretty sure IIRR means 'If I Remember Right,' kind of like IIRC for 'If I Remember Correctly.'

 

[ttammag]

I'm pretty sure IIRR means 'If I Remember Right,' kind of like IIRC for 'If I Remember Correctly.'

Thanks. That makes sense to me now.

 

[Cobrajet67]

My son has a 2008 4.0L. Recently, it has developed a misfire during hard acceleration. It is difficult to reproduce, but it seems the most common occurrence is during a hill climb and merging onto the highway. So it is during a hard acceleration, mostly uphill. During the misfire, it briefly flashes two dash lights, hesitates, and continues to accelerate. The dash lights flash so fast that I'm not 100% sure which ones they are.

One time, it did set the following codes:

P0300 Random Misfire
P0302 Cylinder 2 Misfire
P0306 Cylinder 6 Misfire
P0607 Control Module Performance

I cleared the codes and was able get to misfire again, but it hasn't set the codes again.

He has only put about 4000 miles on car since we bought it. When we first got it, it had a stalling issue at idle. At that time, we changed the fuel filter, spark plugs, and crank position sensor, which resolved the idle stalling problem. I also replaced the thermostat housing and cleaned the throttle body and MAF sensor at that time. This misfire issue seems to have started within the last 500 miles.

I haven't been able to catch anything significant with the live data on my cheaper scan tool.

I will appreciate any and all suggestions you may have.

Thank you,
Matt

The P0607 code is a computer programming issue. There is some sort of fault in the PCM. This might not be a physical problem or a problem with the software however since it can be caused by weak voltage or a poor ground. The misfires are probably coming from this. Since you said that your dash lights flicker I'm betting that you have either a weak battery, bad alternator, poor cable connections, bad cable, a poor main or secondary ground, or a bad ground to the PCM.
You should test the battery for voltage after it's sat for a day and make sure that it has at least 12.6v. Then do a load test on it. You should also test the alternator output on the charging post on the back of it to make sure that it's putting out a consistent 13.5-14.5v when the car is running.
I watched a video once of a 2005-2010 Mustang 4.0 like yours that had a bad ground on the back of the engine block. In that particular case it kept the car from starting though.
P0607 causes are:
-Loose ground terminal on PCM/ECM
-Dead or defective (12V main) battery
-Open or short in the power or ground circuit
-Loose or corroded battery terminals
-Failed PCM/ECM
-Aftermarket electronics causing a voltage or programming issue(bad aftermarket tune)
Sometimes the PCM needs to be reset or reprogrammed. The reset you can do yourself by disconnecting the battery and then connecting the power and ground cables together for a few minutes to drain any voltage left in the system.
Reprogramming can only be done at the Ford dealer. There are apparently some TSBs out there for Ford vehicles with this code. I would look up all the TSBs for a 2008 Mustang.
If it turns out to be the PCM itself is failed then you can have it repaired by any module repair service. Ford probably can't get you a new PCM now anyway with the parts/chip shortages.

 

[Beechkid]

Thanks for the reply. Fuel filter is the first thing I thought about too, but we changed it less than 4000 miles ago. Forgive me for this question, but what do you mean by IIRR?

it wasn't long after they went to permanent filters....ya get to change the fuel filter & pump as one unit

 

[ttammag]

UPDATE: I took the 4.0 to the local shop. They were able to reproduce the problem and determined that it was a ground issue and the battery ground to the block was missing. So they installed a #2 copper ground wire from the strut tower (where the existing battery ground runs) to the passenger side of the block. They stated that they tested the vehicle again in the same location and the issue was resolved.

I drove it home hard and in a location where I previously replicated the issue, was pleased that it ran great. However later this evening, I took the car to buy gas and tested it again on a highway ramp, when it happened again. This time, I noticed the security light (car with the padlock symbol) on the dash came on briefly, while the car bucked for a split second. The car instantly recovered and I drove home. I checked and found no error codes.

I also checked the voltage in the driveway. I read about 14 V, running. With the engine off, the battery read about 12.6 V.

 

[Cobrajet67]

UPDATE: I took the 4.0 to the local shop. They were able to reproduce the problem and determined that it was a ground issue and the battery ground to the block was missing. So they installed a #2 copper ground wire from the strut tower (where the existing battery ground runs) to the passenger side of the block. They stated that they tested the vehicle again in the same location and the issue was resolved.

I drove it home hard and in a location where I previously replicated the issue, was pleased that it ran great. However later this evening, I took the car to buy gas and tested it again on a highway ramp, when it happened again. This time, I noticed the security light (car with the padlock symbol) on the dash came on briefly, while the car bucked for a split second. The car instantly recovered and I drove home. I checked and found no error codes.

I also checked the voltage in the driveway. I read about 14 V, running. With the engine off, the battery read about 12.6 V.

I would look at the ground to the PCM.
The PATS(antitheft) system is routed thru the SJB. The SJB is known to be a problem in the 2005-14 Mustangs if the cowl gets clogged up with dirt/debris and then water fills it up and eventually overflows thru the firewall and onto the SJB. It's a very common issue on these years. If this has ever happened in the past it would slowly corrode the connections to the SJB.

 

[ttammag]

I would look at the ground to the PCM.
The PATS(antitheft) system is routed thru the SJB. The SJB is known to be a problem in the 2005-14 Mustangs if the cowl gets clogged up with dirt/debris and then water fills it up and eventually overflows thru the firewall and onto the SJB. It's a very common issue on these years. If this has ever happened in the past it would slowly corrode the connections to the SJB.

I believe that the PCM is under the hood, on the passenger side. Is that correct? For the SJB (passenger kick panel), should I try and disconnect each of the cable connectors and look for corrosion? Would spraying the connection pins with electronic cleaner be a bad idea?

Thanks.

 

[Yadkin]

Do you have a corrosion issue with the car? You might have to go through and clean all of the chassis grounds as well. You can always add more.

 

[Cobrajet67]

Yes, those are the locations. How to Replace PCM on 2005-2009 Mustangs - YouTube
It can't hurt to look. Contact cleaner can only help. Sometimes cleaning any detectable corrosion will help with an SJB but not as often as you'd think. The only reason I mentioned the SJB is because you mentioned the PATS light briefly lighting up. As I recall no powertrain circuits go thru the SJB but the PATS does. I know that a bad SJB can keep the car from starting at all so I'm thinking perhaps it may be able to interrupt the antitheft while it's operating if that's possible that is. Idk if that's actually possible though as the PATS may only be used to prove out on initial startup and not come into play at all once the car is running.
Unfixable misfires are sometimes attributed to a bad PCM. Seeing how adding the missing ground cable helped the problem I still think it might just be a grounding issue somewhere. That doesn't rule out the PCM itself though. These kinds of problems are often hard to diagnose but you have to go thru all the motions first before blaming the actual PCM.

 

[ttammag]

UPDATE: I checked the resistance at all the grounds I can find. I read 0.5 ohms from the grounds on the passenger side of the radiator support, near the PCM, to the negative battery cable. I even added a separate #12 AWG ground wire to that point on the radiator support and it still read 0.5 ohms. I also bought a voltmeter that plugs into the cigarette lighter, so I can monitor the voltage while driving. During a test drive, I noticed during the fault, the voltage briefly dips from 14.2 volts to 13.0 volts. The fault goes away after a split second, and the voltage is back to a steady 14 volts. I also noticed that the fault always happens between 3000-4000 RPMs. I don't believe it is a bad alternator now, but something is pulling down the voltage during the fault.

No codes have been triggered since I cleared them. However, I did notice a U1900 - Controller Area Network Comm Malfunction code. Some internet searches led me to believe that the code is related to the ABS system. I also read that the 4.0L typically has a rev limiter at 3000 RPMs, when in park or neutral. So after a recent test run, I decided to turn off the Traction Control button. After this, I couldn't replicate the fault again for the rest of the evening. We tried four different times, with the TCS button on and off.

I haven't trying cleaning the SJB yet. I took off the trim panel and looked at all the connections and thought I might break something and possibility make the situation worse.

 

[Cobrajet67]

Did you hook up the scanner to it while it was running? This is important to know because if you did that will often trigger this U1900 code.
If not, then I suppose in theory if the ABS module were malfunctioning then it could trigger this code and somehow momentarily trip the rev limiter if it's a short of some kind but I would imagine that you would get another code that would be more specific to the ABS module as well. I would think this would imply that the PCM would be more involved with this fault since the rev limiter at idle shouldn't kick in while in gear. You also had specific cylinder misfires and a P0607 code before which is more PCM specific. It is interesting that the TC(traction control) being off so far has kept the problem away. I would continue to drive the car with the TC off to make sure that it doesn't come back before blaming it on the ABS module.
The popular things that seem to trigger this U1900 code are the PATS system, instrument cluster, ABS control module, PCM, or a wiring/connector issue in the high speed CAN bus network. A bad connection somewhere in the ignition switch is also possible since basic power could be momentarily interrupted to the network. Any short or open in the high speed network or one of the modules in it anywhere can cause a fault when the car is running. A high end scan tool can run diagnostics on individual modules so you might want to pay a Ford dealer or other shop to run a complete diagnostic.
If the fault ever comes back with the TC off then if it were me I would probably pull the PCM and send it out to check/fix at a PCM/module repair service. Otherwise, if it never comes back with the TC off then I would suspect the ABS module. You should be able to get that fixed too.

 

[ttammag]

Did you hook up the scanner to it while it was running? This is important to know because if you did that will often trigger this U1900 code.
If not, then I suppose in theory if the ABS module were malfunctioning then it could trigger this code and somehow momentarily trip the rev limiter if it's a short of some kind but I would imagine that you would get another code that would be more specific to the ABS module as well. I would think this would imply that the PCM would be more involved with this fault since the rev limiter at idle shouldn't kick in while in gear. You also had specific cylinder misfires and a P0607 code before which is more PCM specific. It is interesting that the TC(traction control) being off so far has kept the problem away. I would continue to drive the car with the TC off to make sure that it doesn't come back before blaming it on the ABS module.
The popular things that seem to trigger this U1900 code are the PATS system, instrument cluster, ABS control module, PCM, or a wiring/connector issue in the high speed CAN bus network. A bad connection somewhere in the ignition switch is also possible since basic power could be momentarily interrupted to the network. Any short or open in the high speed network or one of the modules in it anywhere can cause a fault when the car is running. A high end scan tool can run diagnostics on individual modules so you might want to pay a Ford dealer or other shop to run a complete diagnostic.
If the fault ever comes back with the TC off then if it were me I would probably pull the PCM and send it out to check/fix at a PCM/module repair service. Otherwise, if it never comes back with the TC off then I would suspect the ABS module. You should be able to get that fixed too.

I was using my cheap scanner to try and capture live data, while it was happening. Unfortunately, the sample rate wasn't high enough to catch any data at the exact moment. The TC was just a hunch. I'll have my son drive around with the TC off, and report back. It is important to note that it only happens between 3000 - 4000 RPMs. Thanks for all the helpful suggestions.

 

[Cobrajet67]

Then in that case the U1900 was likely from the scanner being hooked up while the car was running. Fall back on the previous codes that you were getting. I would suspect the PCM but if it were me I would have a full diagnostic run on the modules before dropping the $ on a PCM repair. A Ford dealer or capable shop with a modern real high end scan tool can perform this for about $140 which seems to be the standard 1 hour rate price these days.

 

[Deadmeat101]

Did you figure out what the problem was? Mine is doing the same thing...