Wits End Multiple Misfire Codes

[NoNothing]

2002 GT: Receiving misfire on startup, random, cylinder 3 and cylinder 5 (earlier 2 and 4). Stored for 6 months with Stabil added to fuel, but I had one misfire code last fall on heavy acceleration. Changed plugs x8, Coil-on-plugs x8, checked vacuum (22lbs constant), replaced PCV valve and hose. Ran STP and K100 system/injector cleaner through to dry up any water in gas.

Continues to display codes and MIL. The misfires are real (feel them while driving), however not constant instead always under load (uphill and WOT) so I doubt it's a computer problem.

Next step is to check fuel pressure, replace injectors, and depending on pressure test, filter and pump.

My main question is; am I overlooking something obvious? It's getting a little expensive and very annoying.

 

[wmburns]

I always suggest staring EVERY possible electrical trouble shooting session with a through review of the charging system. A bad alternator diode will cause excessive AC ripple which can cause false CAM DTC's. Today's cars simply will not run right without a strong battery and alternator.

Howto perform charging system voltage drop test
https://www.stangnet.com/mustang-fo...perform-charging-system-voltage-drop-test.56/

Did the new misfires start after you replaced the spark plugs and COP's?

When the COP's were replaced was there any moisture or other debris in the spark plug well or on the boots?

Did you save the old COP's? If so, consider getting new COP insulator boots. Refurbish a couple and use the old COP with new boot insulators to swap through the misfiring cylinders.

Double check the spark plug gap. Misfires under load can be a sign of:

• Excessive spark plug gap
• Something bleeding off the spark energy (arching) such as moisture or high resistance connection.
• Combustion problem such as a lean fuel charge (clogged injector).

If you are willing to replace the fuel injectors as a trouble shooting step then consider sending the whole set out to InjectorRX.com. Once cleaned and flow tested they are as good as new. Cheaper than new. I have had great luck with their service and use them for every motor project I have done.

Consider renting a compression tester from your local auto parts store and perform a compression test so that the over all health of the motor is known.

I don't think this is a fuel pressure problem. Fuel pressure low enough to CAUSE a misfire would show up across all cylinders. Same for the fuel pump.

How many miles on this motor? If over 150,000 consider the possibility of worn timing chains or broken chain guides. Do the chains make noise on start up? If yes at the minimum the chains have been stretched.

Consider getting yourself an oil filter cutter. Cut the oil filter open and inspect for debris. I do this on EVERY filter change of all the cars/trucks my family own. So far it has saved two motors. Here's the one I own but there are others slightly cheaper.

https://www.summitracing.com/parts/lng-77750/overview/

Finally consider getting yourself an ODB2 scanner. The ability to monitor operational PID's can be a trouble shooting game changer. Here's some information on an affordable Windows based unit.

ForScan ODB2 scanner w ELM327 USB
https://www.stangnet.com/mustang-forums/resources/forscan-odb2-scanner-w-elm327-usb.57/

One of the biggest advantages that having an ODB2 scanner will give is the ability to test more and perhaps replace fewer parts without a "fix".

 

[NoNothing]

WMburns,

Wow! Thank you for the detailed response.
Howto perform charging system voltage drop test
I will do this today.

Did the new misfires start after you replaced the spark plugs and COP's?
Yes and no. I replaced the spark plugs as a preventative measure. The first misfire showed up 5 months later. The COPs were done in response to the misfires which gradually became more frequent and migrated to all cylinders (mostly 3 and 5).

When the COP's were replaced was there any moisture or other debris in the spark plug well or on the boots?
Yes, the wells were very dirty. I blew them out with compressed air. Cylinder 7 had some oil deposits but it did not appear to originate from underneath. Looked like a previous spill.

Did you save the old COP's? If so, consider getting new COP insulator boots. Refurbish a couple and use the old COP with new boot insulators to swap through the misfiring cylinders.
I do have the old ones still. I replaced all of them at the same time with Pertronix Flamethrowers COPs.

Double check the spark plug gap. Misfires under load can be a sign of:
I spot checked 3 of 8 plugs for gap. All were .054 so I did not go any further.

If you are willing to replace the fuel injectors as a trouble shooting step then consider sending the whole set out to InjectorRX.com. Once cleaned and flow tested they are as good as new. Cheaper than new. I have had great luck with their service and use them for every motor project I have done.
I removed all injectors and cleaned them in an ultrasonic cleaner in a bath of injector cleaner, then blew them out with compressed air in the reverse flow direction. Reinstalled them. Definitely made a difference in the smooth running (I had fuel pressure loss prior to this).

Consider renting a compression tester from your local auto parts store and perform a compression test so that the over all health of the motor is known.
I have a compression test scheduled for tomorrow with my local mechanic.

I don't think this is a fuel pressure problem. Fuel pressure low enough to CAUSE a misfire would show up across all cylinders. Same for the fuel pump.
Constant read prior to cleaning was 33PSI, now it's stable at 41.

How many miles on this motor? If over 150,000 consider the possibility of worn timing chains or broken chain guides. Do the chains make noise on start up? If yes at the minimum the chains have been stretched.
127,000

Consider getting yourself an oil filter cutter. Cut the oil filter open and inspect for debris. I do this on EVERY filter change of all the cars/trucks my family own. So far it has saved two motors. Here's the one I own but there are others slightly cheaper.
Will do this.

Finally consider getting yourself an ODB2 scanner. The ability to monitor operational PID's can be a trouble shooting game changer. Here's some information on an affordable Windows based unit.
I have a DiabloSport Predator that I'm using to read the codes. Came with the car. I've backed the tune down to stock (modified for 4:10 gears and raised my engine idle from 680 to 800).

My mechanic thinks it make be a blown gasket between cylinders. Due to the required surgery to repair, he suggested I consider an engine swap. I'm not competent to perform this action on my own nor willing to pay to have it done. Based on the test results, I may be looking at calling this car a loss.

 

[Noobz347]

There is no way on God's earth that I would swap a motor because of a gasket.

I would start looking for another mechanic.

How many miles on the car?

 

[running11s]

I second that.

There is no way on God's earth that I would swap a motor because of a gasket.

I would start looking for another mechanic.

How many miles on the car?

I second that. That's crazy. I'd only swap the engine if the miles were super high and the engine was neglected or something.

 

[Neuron]

OP said 127K Miles.

 

[wmburns]

Well.......

A blown head gasket would certainly explain the chronic misfires.

 

[NoNothing]

Follow-up:

Compression tested on all cylinders. Between 151-160 on all according to the shop. Looks like it's not a compression issue.

Mechanic recommends replacing all the plugs with Motorcraft. They're on order. I'm going to try the new plugs with the current (new) COPs and if no-go I'll install the old stock ones.

I unplugged the MAF sensor and drove it a while. Misfires still occurred with or without.

The Diablosport Predator tune was reverted to the stock program. Still happens.

One armchair expert said I should disable the traction control.

Any other ideas?

 

[wmburns]

FWIIW, 160 PSI seems on the low side of normal to be. But the numbers are close to each other. So that means that likely the head gasket is good.

If you truly are at your "wits end" to solve the misfire problem then it would seem to me that you are running out of the "usual" fixes.

Perhaps it's time to consider going to a mechanic with an ignition scope. One that can actually look at the primary and secondary ignition wave forms and trouble shoot it in a direct fashion.

 

[running11s]

I would do what NoNothing says and try the plugs first. I would try all of the easy solutions to get them out of the way. Sometimes an arcing plug wire can cause a misfire. I had that happen before.